CA1155600A - Process for preparing polyolefins - Google Patents
Process for preparing polyolefinsInfo
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- CA1155600A CA1155600A CA000365442A CA365442A CA1155600A CA 1155600 A CA1155600 A CA 1155600A CA 000365442 A CA000365442 A CA 000365442A CA 365442 A CA365442 A CA 365442A CA 1155600 A CA1155600 A CA 1155600A
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- olefin
- hydrogen
- signal
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Abstract
ABSTRACT
The invention is to provide an improved process for preparing polyolefins having predetermined properties, in particular, melt index and/or density by polymerizing olefin in the presence of a Ziegler catalyst and hydrogen.
The parameters corresponding to the concentrations of olefin and hydrogen, participating in the properties, in the gas phase of reactor are detected by high-speed gaschromatography. The detected signals are applied to a computer.
The feed volumes of olefin and hydrogen into the reactor are controlled by means of an operation control output, and the respective concentrations in the reactor are controlled. Consequently, the resulting polyolefins possess extremely stable and uniform properties.
The invention is to provide an improved process for preparing polyolefins having predetermined properties, in particular, melt index and/or density by polymerizing olefin in the presence of a Ziegler catalyst and hydrogen.
The parameters corresponding to the concentrations of olefin and hydrogen, participating in the properties, in the gas phase of reactor are detected by high-speed gaschromatography. The detected signals are applied to a computer.
The feed volumes of olefin and hydrogen into the reactor are controlled by means of an operation control output, and the respective concentrations in the reactor are controlled. Consequently, the resulting polyolefins possess extremely stable and uniform properties.
Description
1 1556~0 DESCRIPTION
PROCESS ~OR PREPARING ROLYOLEFINS
. .
TECHNICAL FIELD
The present invention relates to a process for preparing polyolefins having predetermined properties in the presence of a Ziegler catalyst. More particularly, it relates to a process for preparing polyolefins having predetermined properties by detecting parameters in~olved in the properties by a gaschromatography, then by operating and controlling the detected signals with a computer.
BACKGROUND ART
In industrial preparation of polyolefins, it is generally desiarable to perform the reaction in a reactor kept at a determined temperature and at a constant production rate by way of a continuous process in order to obtain polyolefins having predetermined standard or properties.
In the preparation of polyolefins that is performed in the presence of a Ziegler catalyst, there are lots of properties for the produced polyolefins to be controlled. Of these properties, the melt index and the density are most important factors. The melt index and the density of polyolefins take part in the guidance for the average molecular weight and are optionally set up, depending on the purpose to be used. These indexes enable consumers to choose brands of polyolefins properly.
The melt index is usually measured at 190C for polyethylenes and at 230C for polypropylenes, according to the method ASTM D1238. The polymerization rate of polyolefins - is proportional to each of concentrations of catalyst and monomer, independently, once the polymerization temperature ,3~
1 155~0~
and the catalyst are determined. In the polymerization in which a Ziegler catalyst is used, the melt index of resultinq polyolefin is controlled by hydrogen as a chain transfer agent. Thus, the melt index of resulting polyolefin is S determined by the concentration ratio or hydrogen to olefin (other factors, including species of catalyst, temperature, volume and shape of the reactor give influence upon the melt index). In the meantime, the density of polyolefin is measured according to the method ASTM D1505~67. The density of polyolefin is usually determined by factors, including species of catalyst, temperature, volume of the reactor, amount of comonomer, and the like. Control of the density is usually performed by controlling the molar ratio of olefin and comonomer. Increase in the amount of comonomer generally results in decrease of the density. For the reasons mentioned above, preparation of polyolefins is generally carried out in a continuous process by feeding predetermined amounts of catalyst, olefin and hydrogen to a reactor kept at a predetermined temperature to produce a polyolefin having predetermined properties or standard.
Although it is required to feed predetermined amounts of catalyst, olefin and hydrogen to the reactor in order to maintain the reaction system under predetermined conditions, it is difficult to maintain the conditions only by keeping the feed of the reactants at the predetermined amounts.
For example, subtle variation or decrease in the activity of catalyst in the polymerization reaction brings about increase in the olefin concentration in the reactor, thus resulting in decrease of the melt index of the produced polyolefin. There are many indefinable factors that give ~ tS5~00 influence upon the properties of product, as described above. Variation of the melt index of resulting polyolefin is sensitive to variation of concentration ratio of olefin to hydrogen. In industrial processes for preparing poly-ethylenes, for example, the relationship between the changein the melt index (M I.) and the change in the partial pressure ratio of gas phase is approximately as shown below, always depending on polymerization conditions such as species of Ziegler catalyst, temperature, and the like.
h MI
MI
_ = 3 -,~ (H~/C2) (H2/C2 In the case of polyethylene, a polyethylene pro-duced will be discarded for the reason of below standard, if it has the melt index of above +10~ range out of the predetermined value. Therefore, ~ (H2/C2) needs to be maintained within +3% in order to avoid the loss of product-ion. In prior art processes, the control of the melt index has been carried out by the method in which volumes of ethylene and hydrogen are controlled by means of an operat-ion of respective feed valves in response to the melt index measured. However, this method involves such a grave difficulty as delay in the response due to the fact that it takes approximately an hour to accomplish the measure-ment of the melt index. Therefore, a solution to this problem is proposed by a method to monitor the inside of the reactor directly, that is, to determine the concent-rations of olefin and hydrogen of the liquid phase in the reactor. However, the method is not preferable for the following reasons:
1. The liquid phase to be measured must be separated from the reaction mixture or slurry composed of liquid and solid.
Under such measurement conditions, it is difficult to obtain the absolute values of olefin and hydrogen con-centrations because splash of the components to be measured tends to happen from the liquid phase.
PROCESS ~OR PREPARING ROLYOLEFINS
. .
TECHNICAL FIELD
The present invention relates to a process for preparing polyolefins having predetermined properties in the presence of a Ziegler catalyst. More particularly, it relates to a process for preparing polyolefins having predetermined properties by detecting parameters in~olved in the properties by a gaschromatography, then by operating and controlling the detected signals with a computer.
BACKGROUND ART
In industrial preparation of polyolefins, it is generally desiarable to perform the reaction in a reactor kept at a determined temperature and at a constant production rate by way of a continuous process in order to obtain polyolefins having predetermined standard or properties.
In the preparation of polyolefins that is performed in the presence of a Ziegler catalyst, there are lots of properties for the produced polyolefins to be controlled. Of these properties, the melt index and the density are most important factors. The melt index and the density of polyolefins take part in the guidance for the average molecular weight and are optionally set up, depending on the purpose to be used. These indexes enable consumers to choose brands of polyolefins properly.
The melt index is usually measured at 190C for polyethylenes and at 230C for polypropylenes, according to the method ASTM D1238. The polymerization rate of polyolefins - is proportional to each of concentrations of catalyst and monomer, independently, once the polymerization temperature ,3~
1 155~0~
and the catalyst are determined. In the polymerization in which a Ziegler catalyst is used, the melt index of resultinq polyolefin is controlled by hydrogen as a chain transfer agent. Thus, the melt index of resulting polyolefin is S determined by the concentration ratio or hydrogen to olefin (other factors, including species of catalyst, temperature, volume and shape of the reactor give influence upon the melt index). In the meantime, the density of polyolefin is measured according to the method ASTM D1505~67. The density of polyolefin is usually determined by factors, including species of catalyst, temperature, volume of the reactor, amount of comonomer, and the like. Control of the density is usually performed by controlling the molar ratio of olefin and comonomer. Increase in the amount of comonomer generally results in decrease of the density. For the reasons mentioned above, preparation of polyolefins is generally carried out in a continuous process by feeding predetermined amounts of catalyst, olefin and hydrogen to a reactor kept at a predetermined temperature to produce a polyolefin having predetermined properties or standard.
Although it is required to feed predetermined amounts of catalyst, olefin and hydrogen to the reactor in order to maintain the reaction system under predetermined conditions, it is difficult to maintain the conditions only by keeping the feed of the reactants at the predetermined amounts.
For example, subtle variation or decrease in the activity of catalyst in the polymerization reaction brings about increase in the olefin concentration in the reactor, thus resulting in decrease of the melt index of the produced polyolefin. There are many indefinable factors that give ~ tS5~00 influence upon the properties of product, as described above. Variation of the melt index of resulting polyolefin is sensitive to variation of concentration ratio of olefin to hydrogen. In industrial processes for preparing poly-ethylenes, for example, the relationship between the changein the melt index (M I.) and the change in the partial pressure ratio of gas phase is approximately as shown below, always depending on polymerization conditions such as species of Ziegler catalyst, temperature, and the like.
h MI
MI
_ = 3 -,~ (H~/C2) (H2/C2 In the case of polyethylene, a polyethylene pro-duced will be discarded for the reason of below standard, if it has the melt index of above +10~ range out of the predetermined value. Therefore, ~ (H2/C2) needs to be maintained within +3% in order to avoid the loss of product-ion. In prior art processes, the control of the melt index has been carried out by the method in which volumes of ethylene and hydrogen are controlled by means of an operat-ion of respective feed valves in response to the melt index measured. However, this method involves such a grave difficulty as delay in the response due to the fact that it takes approximately an hour to accomplish the measure-ment of the melt index. Therefore, a solution to this problem is proposed by a method to monitor the inside of the reactor directly, that is, to determine the concent-rations of olefin and hydrogen of the liquid phase in the reactor. However, the method is not preferable for the following reasons:
1. The liquid phase to be measured must be separated from the reaction mixture or slurry composed of liquid and solid.
Under such measurement conditions, it is difficult to obtain the absolute values of olefin and hydrogen con-centrations because splash of the components to be measured tends to happen from the liquid phase.
2. A sampling line must be provided with to collect samples from the reactor. Under such sampling conditions, it is difficult to know the exact reaction conditions in the reactor because poly~erization occurs before sampling is accomplished ~USP 3,835,106).
In prior art processes for preparing polyethylenes, control of the density has been also carried out by the method in which the feed volumes of ethylene and comonomer are controlled by means of an operation of respective valves in response to the density measured of the formed polyethylene. However, the method also involves such a grave difficulty as delay in the response due to the fact that it takes approximately an hour to accomplish the measurement of the density. For the solution of this problem, a method to monitor the inside of the reactor directly is also proposed. The method, however, is not preferable for same reasons as described above in the case of the melt index. Another prior art discloses monitoring inside of the reactor and measuring the pressure in the reactor in order to control the properties of the final product or the ethylene copolymer having a uniform quality (USP 3,691,142). However, there has not yet been known .
any preferable art to produce polyolefins having desired properties, in particular, the desired melt index and/or density.
It is, therefore, an object of the invention to provide a process for preparing polyolefins having extre-mely uniform predetermined properties in the presence of a ziegler catalyst and hydro~en by polymerizing olefin, which comprises measuring the gas phase components set up in the reactor by which to exclude completely the disadvan-tages involved in the measurements of the liquid phase asmentioned above.
It is another object of the invention to provide a process for preparing polyolefins having extremely uniform predetermined melt index in the presence of a Ziegler catalyst and hydrogen by polymerizing olefin, which comprises measuring the gas phase components set up in the reactor.
It is still another object of the invention to provide a process for preparing polyolefins having extre-mely uniform predetermined density in the presence of aZiegler catalyst and hydrogen by polymerizing olefin, which comprises measuring the gas phase components set up in the reactor.
DISCLOSURE OF INVENTION
Accordingly, the invention provides a process for preparing polyolefins having predetermined properties by polymerizing olefin in the presence of a Ziegler catalyst and hydrogen. At least two parameters relating to the concentrations of one or more olefin monomers and of hydrogen in the reac~or are detected by gaschromatography.
7 155~00 The signals responsive to the parameters detected by gaschromatography are applied to a computer which - compares the signals with the preset values and emits new signals as the function of the deviation from the preset values to control hydrogen and olefin feed volumes and/or the amount of catalyst into the reactor and the pressure inside the reactor, thereby controlling the amounts of the olefin and/or hydrogen, thus resulting in the preparation of polyolefins having the predetermined properties. In this manner, when prompt response is made to the data of olefin and hydrogen concentration measure-ments i~ gas phase of the reactor detected by high-speed gaschromatography, for example, at intervals of one minute, no huntings of the properties are substantially brought about in the resulting polyolefin. It is diffi-cult, however, to control olefin and hydrogen feed volumes into the reactor and pressure in the reactor by means of manual operation according to the measurement data detected by high-speed gaschromatography (even if the measurement is performed by high-speed gaschromatography at intervals of one minute, the slow response caused by the manual operation results in the huntings of properties of the resulting polymer). Therefore~ in the method of the present invention; control of the feed volumes into the reactor and the pressure in it is achieved by means of an automatic control through employment of a computer.
In the process for the preparation of polyolefins having predetermined melt index in the presence of a Ziegler catalyst and hydrogen, the parameters relating to the concentrations of olefin and hydrogen in the reactor are .
1 1556~Q
also detected by gaschromatography. The signals responsive to the parameters detected by gaschromatography are applied to the computer which compares the signals with the preset values relating to the predetermined melt index in the s computer and emits new signals as the function of the deviation from the present values to control the hydrogen feed volume into the reactor, the pressure in the reactor, and optionally the amount of catalyst feed, thereby cont-rolling the concentrations of olefin and hydrogen, thus resulting in the preparation of polyolefin having the predetermined melt index.
Further, in the process for preparing polyolefins, according to the invention, having the predetermined den-sity, by polymerizing not less than two olefin monomers in the presence of a Ziegler catalyst and hydrogen, the parameters relating to the concentrations of the olefin monomers are detected by gaschromatography. The signals responsive to the parameters detected by gaschromatography are applied to the computer which compares the signals with the preset values relating to the predetermined density and emits new signals as the function of the deviation from the preset values to control the olefin feed volumes into the reactor, thereby controlling the concentrations of olefins, thus resulting in the preparation of poly-olefins having the predetermined density.
In the method of the invention, the concentrationsof olefin and hydrogen are detected by gaschromatography in the gas phase set up in the reactor. The reactor tem-perature is kept constant and the concentra~ions of olefin and/or hydrogen are controlled to produce, at the temperature, _ - ` ~r~7'--.
.4 1 1S5~;00 polyolefins having predetermined properties, such as melt index and/or density. A gaschromatography to be used'is so regulated that the time required to detect the olefin is 10 minutes or below, preferably from five seconds to S one minute. In the present invention, olefins mean ~-olefins such as ethylene, propylene, l-butene or 4-methyl-l-pentene, preferably those having from 2 to 6 carbon atoms. In the present invention, polyolefins mean homo-polymers, copolymers of the above-mentioned ~-olefins or copolymers of at least one olefin mentioned above and a diolefin. In the present invention, monomers mean olefins of major fxaction of all olefins in the polymerization system, whereas comonomers mean olefins of minor fraction '~ except for the above-defined monomers and/or diol~fins.
In the process of copolymerization of monomer with comonomer for the preparation of a polyolefin, the ratio of comonomer - to the monomer should be not more than 30 mole %, preferably not more than 10 mole %.
Examples of diolefins are conjugated diolefins such as ~utadiene, or isoprene and non-coniugated diolefins such as dicyclopentadiene or ethylidenenorbornene.
'Especially preferred olefins are ethylene, and '`' mixtures of ehtylene and not more than 30 mole ~, preferably not more than io mole % of other olefin or diolefin to ethylene.
; The Ziegler catalysts to be used in the preparat-ion of polyolefins according to the invention comprise generally two major components: ~a) a compound of a transi~
tion metal belonging to Group IV to VI in the Mendeiejeff's periodic table, and (b) an organometallic compound or :
~ 155600 g hydride of a metal belonging to Group I to III in the periodic table. Especially preEerred are those that comprise as the major constituent a titanium or vanadium halide, and an organoaluminum compound. The components (a) and (b) may be supported on a carrier or may be dena-tured with a denaturing agent such as electron donor. As the Ziegler catalysts in the present invention, there may be employed those disclosed, for example, in U.S. Patents Nos. 3,257,332; 3,826,792; 3,113,115; 3,546,133; 4,125,698;
4,071,672; 4,071,674; 3,642,746; 3,051,690 and 3,058,963, and British Patent No. 1,140,649.
In the polymerization of olefin, the quantities of (a) and (b) components in the catalyst to be used will be determined as follows: the quantity of (a~ component being 0.001 to 100 m mole per liter of solvent, based on the titanium,~and the quantity of (b) component composed of an organometallic compound or hydride o~ a metal belong-ing to Group I to III being 0.1 to 1,000 molar times, preferably 0.2 to 100 molar time% of (a) component.
; 20 The polymerization reaction according to the invention with the catalyst may be performed in a similar manner as in the conventional polymerization of olefins with a Ziegler catalyst. Thus, polymerization reaction is performed substantially in the absence of oxygen and water.
The polymerization reaction is performed in an inert solvent, such as aliphatic hydrocarbons, e.g. hexane, heptane or kerosene, into which a catalyst, an olefin and, if necessary, a diolefin are fed to effect the polymerization. The poly-merization reaction is normally performed at a temperature of from 20 to 200C, preferably at 50 to 180C. The polyme-rization reaction is preferably performed under application 1 1$560~
of pressure, generally at pressure of from 2 to 100 kg/cm2.
BRIEF DESCRIPTION OF DRAWI~GS
.
Fiqure 1 illustrates a block diagram of an embodiment of the present invention. Figure 2 illustrates the relationship between the polymerization period and the melt index of the resulting polyolefin. Figures 3a and 3b illustrate a block diagram of an embodiment of the control system in the present invention. Figure 4 illust-rates responses of the detector of gaschromatography in the controller. Figure 5 illustrates a controlling system of hydxogen feed valve and vent valve (pressure release valve) in the controller. Figure 6 illustrates the rela-tionaship between the polymerization period and the density of the resulting polyolefin.
BEST MODE FOR CARRYING OUT THE INVENTION
.
Figure 1 illustrates a block diagram of an embo-diment of the present invention to prepare polyolefins, wherein the reactor 1 kept at a constant temperature is equipped with a liquid phase part la and a gas phase part lb. The reactor 1 is equipped with the lines 2, 3, 4 and 5 for feeding hydrogen, olefin, catalyst and solvent into the reactor, respectively, as well as the line 6 for releasing pressure in the reactor and the line 7 for taking out the resulting polyolefin from the reactor, respectively. Further, the feed lines 2, 3, 4 and 5 are equipped with control valves 2aS, 3a, 4a and 5a to control the feed volumes, respectively~ Also, the vent line 6 and the outlet line 7 are equipped with the vent valve 6a and the switch valve 7a, respectively. Among these valves, the degree of opening of thse valves 2a, 3a, 6a and, in some ~ 1551~00 cases 4a too, is controlled in response to the control signals from the computer which will be described hereunder in order to control the concentrations of hydrogen and olefin to produce polyolefins having the predetermined melt index. The gas phase part lb of the reactor 1 is equipped with the sampling line 8. The hydrogen and olefin in lb are introduced through the switch valve 8a into the gaschromatography 9 to measure their concentrations.
The gaschromatography to be used should be a high-speed gaschromatography that suffices conditions under which the time required for the detection of olefin ~i.e. retent-ion time) is shorter than the residence time of the produ~t in the reactor (the retention time whould be not more than 10 minutes, preferably from five seconds to one minute).
The electric signals responsive to the concent-rations of hydrogen and olefin detected by the gaschroma-tography 9 are applied to the computer 11. The computer 11 comprises a program to determine the polymerization - conditions under which polyolefins having the predetermined melt index are produced. The computer 11 carrys out operat-ion according to the changes in the signals and emits new signals to control the hydrogen feed valve 2a, vent valve 6a, olefin feed valve 3a and, in some case catalyst feed valve 4a too, whereby the concentrations of olefin and hydrogen are controlled so as to produce polyolefins having the predetermined melt index.
In this case, the data from gaschromatography 9 and the control signals emitted from the computer 11 are recorded on the recorders 10 and 12, respectively.
~igures 3a-3b illustrate preferred embodiments ~ 155600 of the control system in order to perform the process according to the invention. Sorne elements in Figures 3a-3b that are identical with those in Figure 1 are represented by the corresponding referential signs.
In summary, the present invention is to provide a process for preparing polyolefins having the predetermined proper-ties, wherein hydrogen and olefin are sarnpled through the sample line 8 from the gas phase lb in the reactor 1;
the sampled gases are detected by the process gaschromato-graphy 9; the signals responsive to the concentrations areapplied to the computer 11; the hydrogen feed valve 2a, vent valve 6a and the olefin eed valve 3a are manipulated by the operation control output of the computer 11 finally to control the concentrations of hydrogen and olefin in the reactor.
At first, the sampling line 8 will be explained as follows.
As illustrated in Figure 3a, the sampling line 8 is equipped with the dual sampling lines 8a' and 8a".
The sampling line 8a' is basically used to measure directly the gases in the gas phase lb of the reactor. In the line 8a', the sample gas is passed through the block valve 13 which is used for shifting the sampling line to the sampling line 8a", flushed by means of the pressure control valve 14 which reduces the sample gas pressure to the predetermined value, and then vaporized completely with the sample vaporizer 15. The sign 16 illustrated in Figure 3a is PID controller to control the control valve 14 by means of PID (proportional-plus-integral-plus-derivative) control, responsive to the sample pressure detected by 1 155~00 the transmitter 17. The flow amount of sample gas in the line is observed by means of the flow amount indicator 19 through the flow amount transmitter 18 like orificemeter, if the flow amount is maintained within the standardized range or not. Then, the sample gas is pretreated by means of the sample pretreatment unit 22 which is composed of the vent valves 20 and 20a, and the filters 21 and 21a, in two steps, and regulated so as to fit for the operation conditions of the process gaschromatography 9. The sample pretreatment unit 22 is placed in the thermostat 23 to prevent condensation of the sample gas and the thermostat 23 is kept at a certain temperature between 40 and 150C
by means of the thermocontroller 24. Thus, by using the sample line 8a', dry sample gas may always be injected into the detector 25 of the process gaschromatography 9, even in the operation in which a monomer having a boiling -. point comparable with that of a solvent is used. In some cases, monomers having significant difference in boiling point compared with that of solvent are solely used to produce polyolefins of certain standard or brand.
In such cases, certain and stable measurement of the sample gas by the process gaschromatography may be constantly carried out by operating the sample line 8a"
equipped prior to the pressure control valve 14. Thus, in the sample line 8a", the solvent in the sample gas sampled from the gas.phase lb in the reactor 1 is condensed and separated by means of the sample condenser 26 and the sample receiver 27. The sample temperature at the outlet of the sample condenser 26 is automatically controlled by the thexmocontroller 28 at a certain temperature between - 14 ~ 1155600 -15 and 10C. Thus, the sample gas from the sample receiver 27 may be completely vaporized by heating it with the vapo-rizer 15 after flushing it through the pressure control valve 14O In this case, the separated solvent is returned into the reactor 1 through the line 8b. Further, selection of the sampling lines, either 8a' or 8a", may be undertaken by operating the block valve 13a equipped prlor to the sampling line 8a' in conjunction with the block valve 13.
Employment of the sampling system brings about an advantage that normal operation of the process gaschromatography is maintained without paying much attention to the sampling conditions. In this case, the component of gas phase in the reactor is, however, defferent from that of the sample gas. In the embodiment of the present invention wherein the temperatures of the reactor and of the outlet of the sample condenser 26 are controlled independently, the gas component in the reactor may readily be estimated from the data of the sample gas by means of a simple precalcu-lation of the gas-liquid equilibrium. Thus, in the embodi-ment of the present invention, the sample gas is completelyvaporized before it is introduced into the process gaschro-matography; Therefore, the sampling system of the present invention may exclude completely such troubles involved in conventional systems that liquid flow of components having high boiling point into sampling line or condensation thereof therein, which brings about involvement of liquid particles of sample gas in gaschromatography, results in the variation of indication of gaschromatography or in-operation thereof due to packing in the line. The fact also means the improvement in the stability of operating gaschromatography and consequently enablement of accurate measurement of gas concentrations of gas phase in the reactor. In addition, in the embodiment of the present invention, conversion between the sampling lines 8a' and 8a" according to the standard of olefins to be prepared enables wide varieties of operations using different monomers, depending on the standard.
In summary, the sampling system used in the embodiment of the present invention suffices the both requirements for the gaschromatography to detect the gas concentrations and for the preparation process to produce polyolefins according to the predetermined standard, at the same time.
Next, the detector 25 of the process gaschromato-graphy 9 will be explained taking polymerization ofethylene as an example. The sample gas adjusted to detectable conditions with the gaschromatography through employment of the sample pretreatment unit 22 is introduced into a separation column of the detector 25. Then, each component of the sample gas is detected by a thermal contact detector composed of a resistance bridge. Each output signal generated from the detector shows a response as shown in Figure 4. In the case where ethylene is used as the monomer, the normal order in the response time is inherently hydrogen (H2), methane (CH4), ethane (C2H6~
and ethylene (C2H4). However, in the detection system of the present invention, the response time of ethane and ethylene may be put between hydrogen and methane, as shown in Figure 4, by having ethane and ethylene bypassed into columns of shorter response time, using three columns I 1 ~560.~
connected in series and parallel. By doing so, the detection time may be shortened.
The output signals generated from the detector are applied to the controller 28. Since each output sig-nal, for ex~mple, that corresponding to hydrogen (H2) orethylene (C2H4) as shown in Figure 4, is genera-ted from the detector at intervals of a certain fixed period depending on the inherent character of the detector 25, : the peak value of each signal corresponding to each gas component may be measured at the respective response time in the controller 28 and taken out as the d.c. voltage signal. The peak value of each component represents the parameter of each gas concentration. The d.c. voltage signals are converted into the d.c. voltage within 1-5 V
according to the magnitude of the peak value, and taken at as signals Yl' and Y2', respectively.
In a continuous process for the preparation of polyolefins, measurement of the components in the reactor - by gaschromatography 9 should be carried out in short periodic time, as described above. It is desirable that the periodic time is within 10 minutes, preferably from five seconds to three minutes.
In the embodiment of the present invention, YAMATAKE-~ONEWELL H-lOOOTE by Yamatake-Honewell Co., Tokyo, Japan is employed for the gaschromatography.
The Model H-lOOOTE used in the present invention can be operated in periodic time within two minutes and, in practice, can be automatically operated at intervals of 60 seconds, as shown in Figure 4.
Consequently, the signals generated from the detector 25 at intervals of measurement time as shown in Figure 4 are transmitted to the controller 28, wherein the received signals are separated into each component to measure each peak value and converted into each d.c.
voltage signal within 1-5 V according to the magnitude ; of each peak value.
The signals are held at intervals of measurement time and output successively. When the Model ~-lOOOTE
is used, hydrogen ~H2), monomer-A, monomer-B and monomer-C, for instance, in a certain sample gas may be measured and the resulting d.c. voltage signals may be represented successively as Yl', Y2', Y3' and Y4'. As described above, by separating the signals generated from the detector 25 into those of respective components and taking out new signals successively after the holding thereof, complex treatment in the computex of the signals generated from the detector need not be carried out and, consequently, the simplicity of system, cost down and improvement in the whole reliability may be attained. The signals separated into those of respective components in the controller 28 are recorded on the recorder 29. The d.c.
voltage signals Yl' - Y4' are applied to the computer 11 (Figure 3b) and, simultaneously, recorded on the multipoint recorder 10. The process computer controller system will be explained hereinafter by referring to Figure 3b.
The successive d.c. voltage signals Yl', Y2', Y3' and Y4' teach 1-5 V) corresponding ~ ~2~ monomer-A, monomer-B and monomex-C respectively taken out from the gaschromatography 9 and the voltage signal (l-S V~ generated from the pressure transmitter 30 of the reactor 1 are connected to the input terminal 32 of the computer 11.
The computer 11 comprises the scanning plot (not illust-rated) for scanning five kinds of the signals noted above automatically and periodically, the A/D (analog/degital) converting plot 34, the linearizing plots 35, 36 and 37 for linearizing the signals generated from the converter, the opèrating plots 38, 39 and 40 for operating the signals, and the controlling plots 41, 42 and 43 for controlling the signals generated from the operating plots in compari-son with the standard values preestablished. In the embodiment, YAMATAKE-HONEWELL TDCS-2000 by Yamatake-Honewell Co., Tokyo, Japan is used as the computer 11.
The method for controlling of properties of polyolefins by using the process computer control system will be explained concretely hereinafter.
First, the control loop for controlling the melt index (M.I.) of polyolefins will be explained in detail regarding, for example, polymerization of ethylene.
As mentioned above, the M.I. value of polymers is funda-mentally a function of molar ratio of hydrogen to monomer-A
in the gas phase lb of the reactor 1. In the process for preparing polyethylene from hydrogen (H2) and ethylene as monomer-A, the control loop for controlling the molar ratio of hydrogen ~H2) to ethylene ~C2H4) ~represented as H2/C2 in hereinafter description) for preparing polyethy-lene having the predetermined M.I. i5 described below.
The signals Yl' and Y2' A/D converted by the converter 34, representing H2 mole % and C2 mole %, respectively, are applied to the linearizing plots 35 and 36, respectively.
As output signals generated from the gaschromatography 9 ~r~ -- r 1 15S60~
correspond to each peak height shown in Figure 4, they are calibrated into respective correct mole % concentrat-ions by means of linearization in the linearizing plots 35 and 36, respectively.
When the integration of the signals is carried out in the controller 28 of the gaschromatography 9, the mole ~ concentration may be measured accurately. In such a case, it is unnecessary to linearize the signals in the computer.
The linearization of signals in the linearizing plots 35 and 36 may be carried out by way of folded-line approximated operation. The output signals Yl and Y2 generated from the linearizing plots 35 and 36 indicate exactly the mole % concentrations of hydrogen (~2) and ethylene (C2H4), respectively. The signals Yl and Y2 are again converted into the analog signals by the D/A
converter 34, and the resulting voltage signals (1-5 V) are recorded on the multipoint recorder 12 and simultaneously applied to the operating plot 38.
In the operating plot 38, Yl/Y2 operation is performed and the resultiny Yl/Y2 output is recorded on the multipoint recorder 12 as the H2/C2 value through the D/A converter 34 and simultaneously applied to the PID
controller 41 as the process variable. In the PID controller 41, the preestablished value _~corresponding to the pre-determined melt index has been previously set up by means of the operation of the data entry panel 44 by an operator.
In the PID controller 41, the input signal (H2/C2 value3 is compared with the preestablished value m, and the both are PID controlled automatically for coincidence or agreement.
~15.560~
In accordance with the difference between the both values, 4-20 mA current signal is taken out. The current signal is converted into the air pressure signal within 0.2-1.0 kg/cm2G with the current/air pressure converter 46 accord-ing to the magnitude of the value, and the resultingpressure signal is supplied to the positioners of the hydrogen feed valve 2a and the vent valve 6a. Control of the positioners of the valves 2a and ~a is carried out by means of a so-called split range method.
Namely, as illustrated in Figure 5, the valve positioner of the vent valve 6a is regulated in such manner that it is completely opened at the input air signal pressure of 0.2 kg/cm2G or below, and completely closed at the pressure of 0.6 kg/cm2G or above, and further the hydrogen feed valve 2a is regulatedin such manner that it is completely closed at the pressure of 0.6 kg/cm2G
or below and completely opened at 1.0 kg/cm2G or above.
Thus, control of the two valves may be carried out by the single control signal pressure.
The input of the standard H2/C2 value preestab-lished into the computer 11 may be carried out by using the data entry panel 44. Alternatively, it may be carried out by using the H2/C2 analog indicator 49 of the analog display apparatus 48. The indicator 49 also indicates the agreement or difference of the H2/C2 value determined by the gaschromatography and operated by the computer, compared with the preestablished H2/C2 value in the form of analog display.
In this manner, by using the H2/C2 control loop, the H2/C2concentrations in the gas phase lb of the reactor 1 may be automatically controlled to the preestablished value, and in consequence, polyethylene having the predetermined M.I. may be continuously prepared. Therefore, the H2/C2 control loop is called the M.I. control loop S since the H2/C2 control is substantially equal to the M.I. control.
In the introduction of the desired volume of monomer (ethylene) into the reactor 1 equipped with the gas phase part lb, if there occurs an outer turbulance, for example, change in the activity of Ziegler catalyst introduced into the reactor 1 through the catalyst feed line 5, the partial pressure of the monomer (C2) in the reactor 1 varies; the dissolved volume of the monomer in the solvent also varies, correlated to the variation of the partial pressure; and the dissolved monomer flows out of the system as the unreacted monomer together with the solvent. In other words, the polymerization rate varies even when the monomer feed volume is kept constant.
Heretofore, if such outer turbulance occurs, the partial pressure of monomer tC2) alone varies and this results in the variation of the H2/C2 value and of M.I.
value. However, in the present invention, as the H2/C2 value is controlled automatically with the hydrogen feed valve 2a and the vent valve 6a as described above, the M.I. may be kept constant even when such outer turbulence occurs. However, if such polymerization conditions as mentioned above is maintained, the polymerization rate will deviate from the preestablished rate. Thus, in the present invention, the polymerization rate may be restored to the preestablished rate by controlling the catalyst ~ -~r--~p~q~ r~ r r r,~r.-~-~ .-r~ --.n~ -r~-rr~r~
1 1556~
feed volume to compensate the variation of catalyst activity, thereby returning the partial pressure of monomer lC2) to the original value.
The control loop for C2 partial pressure will be explained hereinafter. The output voltage signal (1-5 V) generated from the pressure transmitter 30 at the pressure Po of the reactor 1 and the output signal Y2 representing the ethylene mole % generated from the linearizing plot 36 are applied to the operating plot 40 and the operation of (Po -~ 1.03)Y2 is performed. In the equation, the part in the parentheses needs the conversion to absolute pressure, wherein 1.03 represents atomospheric pressure. In case an absolute-pressure gauge in the pressure transmitter 30 of the reactor 1 is used, the value 1.03 in the parentheses of the equation becomes unnecessary. The output signal gene-rated from the operating plot 40 is recorded on the multipoint recorder 12 through the D/A converter 34 and used as the running indicator for the C2 partial pressure. On the other hand, the C2 partial pressure signal is applied to the PID
controller 43 in the same way as in the H2/C2 control loop mentioned above, and PID controlled so as to coincide with the preestablished standard value for the C2 partial pressure p in the reactor given by an operator with the data entry panel 44 or with the partial pressure analog indicator 50 of ; 25 the analog display apparatus 48. The output signal therefor (4-20 mA) is applied to the current/air pressure converter 52 through the D/A converter 34 and converted to the operation signal for the stroke control unit 4a' of the catalyst feed pump 4a" in the form of air signal. In this manner, control of the H2/C2 concentrations at the predetermined value and the regulation of the C2 partial pressure at the predetermined 1 1 ~iS600 value when an outer turbulence like variation of catalyst activity occurs may be attained at the same time. Further, properties of polyolefins when prepared with other olefins may be controlled by the similar operations as mentioned above.
Lastly, as mentioned in hereinbefore description, it is sometimes required to produce polyolefins having predetermined properties, in particular, the predetermined density by performing the polymerization, maintaining the ratio of monomer-A (for example, ethylene) and comono-mer-B (for example, propylene), or the ratio o~ monomer-A
and comonomer-C (for example, l-butene) constantly, depend-ing on the properties or brands of polyolefins to be prepared. Control of the comonomer ratio may be achieved by using the same line-up as in the H2/C2 value control loop. Each signal corresponding to monomer-A, monomer-B, and monomer C, generated from the gaschromatography 9 is represented~ say, by Y2', Y3' and Y4', respectively. The signals Y3' and Y4' are applied to the D/A converter 34 by an change-over switch (not illustrated) in an alternative way. An example in which the signal Y3' is chosen will be explained hereinafter.
The signals Y2' and Y3' of monomers A and B are applied to the linearizing plots 36 and 37, and linearized therein. The output signals Y2 and Y3 are recorded on the recorder 12 through the D/A converter 34 and simultaneously applied to the operating plot 39. Operation of Y2/Y3 is performed in the operating plot 39 and the output therefrom is recorded on the recorder 12 through the D/A converter 34 and simultaneously applied to the controller 42.
In the controller 42, the input signal is PID-controlled so as to coincide with the predetermined standard value d for the comonomer ratio given by an operator with the data entry panel 44 or with the comonomer ratio analog S indicator Sl of the analog display apparatus. The output signal therefor (4-20 mA) is controlled with the cascade type controller 54 through the D/A converter 34, and the feed volume of the comonomer is regulated by operating the comonomer feed valve 3a'.
In this manner, by controlling the concentrat-ions of monomer and comonomer, the continuous process for preparation of polyolefins having the predetermined density may be performed.
In the embodiments described above, the feed volumes of olefin as monomer and of solvent are controlled automatically with the flow rate indication controllers 56 and 58 through the olefin feed valve 3a and the solvent feed valve Sa, respectively. As was the case in the process computer control mentioned above, the control may be per-formed either with the output from the computer 11 alone,or with combination of output control from the computer 11 and the flow rate indication controllers 56 and 58.
As explained above, the process for preparation of polyolefins according to the invention employes a technique to determine the components in the gas phase of the reactor, whereby the situation of the reacti.on system may be made clear, exactly. By measuring the gas phase and making response, for example, at 1 minute intervals with high speed gaschromatography (Figure 4), almost no huntings of the properties such as melt index and/or 1 ~55600 density are observed. Further, since the process of the present invention employs a computer control system, any unstability due to manual control depending on operator's intuition may be excluded, whereby, in combination with the measurement of the gas phase in the reactor and the use of a high speed gaschromatography, polyolefins having the uniform properties such as predetermined melt index and/or density may be obtained.
In Figure 2, the solid line A illustrates the relationship between the melt index and the polymerization period for the continuous preparation of polyethylene according to the invention; whereas the dotted line B
illustrates the relationship between the melt index and the polymerization period when the control of the melt index is carried out by manual operation of the hydrogen feed valve, the ethylene feed valve or the like according to the melt index measured at every 4 hour intervals.
The polymerization period as abscissa in Figure 2 is reckoned not from the initial time of the polymeri-zation but from an arbitrary time at the steady state in the process.
As shown in Figure 2, the process of the present invention makes it possible to produce quite steadily polyolefins having uniform melt index.
In Figure 6, the solid line C illustrates the relationship between the density and the polymerization period for the continuous preparation of polyethylene - according to the invention; whereas the dotted line D
illustrates the relationship between the density and the polymerization period when the control of the density is 1 15r~6(~O
carried out by manual operation of the ethylene feed valve as a monomer and the propylene feed valve as a comonomer or the like according to the density measured at every 12 hour intervals. The polymerization period as abscissa in Figure 6 is reckoned not from the initial time of the polymerization but from an arbitrary time at the steady state in the process. As shown in Figure 6, the process of the present invention makes it possible to produce quite steadily polyolefins having uniform density.
INDUSTRIAL APPLICABILITY
, As will be clear from the foregoing embodiments, the present invention provides a useful art to produce polyolefins having predetermined properties, in particular predetermined melt index and/or density, and are suitable, therefore, to produce quite steadily polyolefins having uniform properties, inter alia, predetermined melt index and/or density in the process for preparing polyolefins by polymerizing an olefin in the presence of a Ziegler catalyst and hydrogen.
In prior art processes for preparing polyethylenes, control of the density has been also carried out by the method in which the feed volumes of ethylene and comonomer are controlled by means of an operation of respective valves in response to the density measured of the formed polyethylene. However, the method also involves such a grave difficulty as delay in the response due to the fact that it takes approximately an hour to accomplish the measurement of the density. For the solution of this problem, a method to monitor the inside of the reactor directly is also proposed. The method, however, is not preferable for same reasons as described above in the case of the melt index. Another prior art discloses monitoring inside of the reactor and measuring the pressure in the reactor in order to control the properties of the final product or the ethylene copolymer having a uniform quality (USP 3,691,142). However, there has not yet been known .
any preferable art to produce polyolefins having desired properties, in particular, the desired melt index and/or density.
It is, therefore, an object of the invention to provide a process for preparing polyolefins having extre-mely uniform predetermined properties in the presence of a ziegler catalyst and hydro~en by polymerizing olefin, which comprises measuring the gas phase components set up in the reactor by which to exclude completely the disadvan-tages involved in the measurements of the liquid phase asmentioned above.
It is another object of the invention to provide a process for preparing polyolefins having extremely uniform predetermined melt index in the presence of a Ziegler catalyst and hydrogen by polymerizing olefin, which comprises measuring the gas phase components set up in the reactor.
It is still another object of the invention to provide a process for preparing polyolefins having extre-mely uniform predetermined density in the presence of aZiegler catalyst and hydrogen by polymerizing olefin, which comprises measuring the gas phase components set up in the reactor.
DISCLOSURE OF INVENTION
Accordingly, the invention provides a process for preparing polyolefins having predetermined properties by polymerizing olefin in the presence of a Ziegler catalyst and hydrogen. At least two parameters relating to the concentrations of one or more olefin monomers and of hydrogen in the reac~or are detected by gaschromatography.
7 155~00 The signals responsive to the parameters detected by gaschromatography are applied to a computer which - compares the signals with the preset values and emits new signals as the function of the deviation from the preset values to control hydrogen and olefin feed volumes and/or the amount of catalyst into the reactor and the pressure inside the reactor, thereby controlling the amounts of the olefin and/or hydrogen, thus resulting in the preparation of polyolefins having the predetermined properties. In this manner, when prompt response is made to the data of olefin and hydrogen concentration measure-ments i~ gas phase of the reactor detected by high-speed gaschromatography, for example, at intervals of one minute, no huntings of the properties are substantially brought about in the resulting polyolefin. It is diffi-cult, however, to control olefin and hydrogen feed volumes into the reactor and pressure in the reactor by means of manual operation according to the measurement data detected by high-speed gaschromatography (even if the measurement is performed by high-speed gaschromatography at intervals of one minute, the slow response caused by the manual operation results in the huntings of properties of the resulting polymer). Therefore~ in the method of the present invention; control of the feed volumes into the reactor and the pressure in it is achieved by means of an automatic control through employment of a computer.
In the process for the preparation of polyolefins having predetermined melt index in the presence of a Ziegler catalyst and hydrogen, the parameters relating to the concentrations of olefin and hydrogen in the reactor are .
1 1556~Q
also detected by gaschromatography. The signals responsive to the parameters detected by gaschromatography are applied to the computer which compares the signals with the preset values relating to the predetermined melt index in the s computer and emits new signals as the function of the deviation from the present values to control the hydrogen feed volume into the reactor, the pressure in the reactor, and optionally the amount of catalyst feed, thereby cont-rolling the concentrations of olefin and hydrogen, thus resulting in the preparation of polyolefin having the predetermined melt index.
Further, in the process for preparing polyolefins, according to the invention, having the predetermined den-sity, by polymerizing not less than two olefin monomers in the presence of a Ziegler catalyst and hydrogen, the parameters relating to the concentrations of the olefin monomers are detected by gaschromatography. The signals responsive to the parameters detected by gaschromatography are applied to the computer which compares the signals with the preset values relating to the predetermined density and emits new signals as the function of the deviation from the preset values to control the olefin feed volumes into the reactor, thereby controlling the concentrations of olefins, thus resulting in the preparation of poly-olefins having the predetermined density.
In the method of the invention, the concentrationsof olefin and hydrogen are detected by gaschromatography in the gas phase set up in the reactor. The reactor tem-perature is kept constant and the concentra~ions of olefin and/or hydrogen are controlled to produce, at the temperature, _ - ` ~r~7'--.
.4 1 1S5~;00 polyolefins having predetermined properties, such as melt index and/or density. A gaschromatography to be used'is so regulated that the time required to detect the olefin is 10 minutes or below, preferably from five seconds to S one minute. In the present invention, olefins mean ~-olefins such as ethylene, propylene, l-butene or 4-methyl-l-pentene, preferably those having from 2 to 6 carbon atoms. In the present invention, polyolefins mean homo-polymers, copolymers of the above-mentioned ~-olefins or copolymers of at least one olefin mentioned above and a diolefin. In the present invention, monomers mean olefins of major fxaction of all olefins in the polymerization system, whereas comonomers mean olefins of minor fraction '~ except for the above-defined monomers and/or diol~fins.
In the process of copolymerization of monomer with comonomer for the preparation of a polyolefin, the ratio of comonomer - to the monomer should be not more than 30 mole %, preferably not more than 10 mole %.
Examples of diolefins are conjugated diolefins such as ~utadiene, or isoprene and non-coniugated diolefins such as dicyclopentadiene or ethylidenenorbornene.
'Especially preferred olefins are ethylene, and '`' mixtures of ehtylene and not more than 30 mole ~, preferably not more than io mole % of other olefin or diolefin to ethylene.
; The Ziegler catalysts to be used in the preparat-ion of polyolefins according to the invention comprise generally two major components: ~a) a compound of a transi~
tion metal belonging to Group IV to VI in the Mendeiejeff's periodic table, and (b) an organometallic compound or :
~ 155600 g hydride of a metal belonging to Group I to III in the periodic table. Especially preEerred are those that comprise as the major constituent a titanium or vanadium halide, and an organoaluminum compound. The components (a) and (b) may be supported on a carrier or may be dena-tured with a denaturing agent such as electron donor. As the Ziegler catalysts in the present invention, there may be employed those disclosed, for example, in U.S. Patents Nos. 3,257,332; 3,826,792; 3,113,115; 3,546,133; 4,125,698;
4,071,672; 4,071,674; 3,642,746; 3,051,690 and 3,058,963, and British Patent No. 1,140,649.
In the polymerization of olefin, the quantities of (a) and (b) components in the catalyst to be used will be determined as follows: the quantity of (a~ component being 0.001 to 100 m mole per liter of solvent, based on the titanium,~and the quantity of (b) component composed of an organometallic compound or hydride o~ a metal belong-ing to Group I to III being 0.1 to 1,000 molar times, preferably 0.2 to 100 molar time% of (a) component.
; 20 The polymerization reaction according to the invention with the catalyst may be performed in a similar manner as in the conventional polymerization of olefins with a Ziegler catalyst. Thus, polymerization reaction is performed substantially in the absence of oxygen and water.
The polymerization reaction is performed in an inert solvent, such as aliphatic hydrocarbons, e.g. hexane, heptane or kerosene, into which a catalyst, an olefin and, if necessary, a diolefin are fed to effect the polymerization. The poly-merization reaction is normally performed at a temperature of from 20 to 200C, preferably at 50 to 180C. The polyme-rization reaction is preferably performed under application 1 1$560~
of pressure, generally at pressure of from 2 to 100 kg/cm2.
BRIEF DESCRIPTION OF DRAWI~GS
.
Fiqure 1 illustrates a block diagram of an embodiment of the present invention. Figure 2 illustrates the relationship between the polymerization period and the melt index of the resulting polyolefin. Figures 3a and 3b illustrate a block diagram of an embodiment of the control system in the present invention. Figure 4 illust-rates responses of the detector of gaschromatography in the controller. Figure 5 illustrates a controlling system of hydxogen feed valve and vent valve (pressure release valve) in the controller. Figure 6 illustrates the rela-tionaship between the polymerization period and the density of the resulting polyolefin.
BEST MODE FOR CARRYING OUT THE INVENTION
.
Figure 1 illustrates a block diagram of an embo-diment of the present invention to prepare polyolefins, wherein the reactor 1 kept at a constant temperature is equipped with a liquid phase part la and a gas phase part lb. The reactor 1 is equipped with the lines 2, 3, 4 and 5 for feeding hydrogen, olefin, catalyst and solvent into the reactor, respectively, as well as the line 6 for releasing pressure in the reactor and the line 7 for taking out the resulting polyolefin from the reactor, respectively. Further, the feed lines 2, 3, 4 and 5 are equipped with control valves 2aS, 3a, 4a and 5a to control the feed volumes, respectively~ Also, the vent line 6 and the outlet line 7 are equipped with the vent valve 6a and the switch valve 7a, respectively. Among these valves, the degree of opening of thse valves 2a, 3a, 6a and, in some ~ 1551~00 cases 4a too, is controlled in response to the control signals from the computer which will be described hereunder in order to control the concentrations of hydrogen and olefin to produce polyolefins having the predetermined melt index. The gas phase part lb of the reactor 1 is equipped with the sampling line 8. The hydrogen and olefin in lb are introduced through the switch valve 8a into the gaschromatography 9 to measure their concentrations.
The gaschromatography to be used should be a high-speed gaschromatography that suffices conditions under which the time required for the detection of olefin ~i.e. retent-ion time) is shorter than the residence time of the produ~t in the reactor (the retention time whould be not more than 10 minutes, preferably from five seconds to one minute).
The electric signals responsive to the concent-rations of hydrogen and olefin detected by the gaschroma-tography 9 are applied to the computer 11. The computer 11 comprises a program to determine the polymerization - conditions under which polyolefins having the predetermined melt index are produced. The computer 11 carrys out operat-ion according to the changes in the signals and emits new signals to control the hydrogen feed valve 2a, vent valve 6a, olefin feed valve 3a and, in some case catalyst feed valve 4a too, whereby the concentrations of olefin and hydrogen are controlled so as to produce polyolefins having the predetermined melt index.
In this case, the data from gaschromatography 9 and the control signals emitted from the computer 11 are recorded on the recorders 10 and 12, respectively.
~igures 3a-3b illustrate preferred embodiments ~ 155600 of the control system in order to perform the process according to the invention. Sorne elements in Figures 3a-3b that are identical with those in Figure 1 are represented by the corresponding referential signs.
In summary, the present invention is to provide a process for preparing polyolefins having the predetermined proper-ties, wherein hydrogen and olefin are sarnpled through the sample line 8 from the gas phase lb in the reactor 1;
the sampled gases are detected by the process gaschromato-graphy 9; the signals responsive to the concentrations areapplied to the computer 11; the hydrogen feed valve 2a, vent valve 6a and the olefin eed valve 3a are manipulated by the operation control output of the computer 11 finally to control the concentrations of hydrogen and olefin in the reactor.
At first, the sampling line 8 will be explained as follows.
As illustrated in Figure 3a, the sampling line 8 is equipped with the dual sampling lines 8a' and 8a".
The sampling line 8a' is basically used to measure directly the gases in the gas phase lb of the reactor. In the line 8a', the sample gas is passed through the block valve 13 which is used for shifting the sampling line to the sampling line 8a", flushed by means of the pressure control valve 14 which reduces the sample gas pressure to the predetermined value, and then vaporized completely with the sample vaporizer 15. The sign 16 illustrated in Figure 3a is PID controller to control the control valve 14 by means of PID (proportional-plus-integral-plus-derivative) control, responsive to the sample pressure detected by 1 155~00 the transmitter 17. The flow amount of sample gas in the line is observed by means of the flow amount indicator 19 through the flow amount transmitter 18 like orificemeter, if the flow amount is maintained within the standardized range or not. Then, the sample gas is pretreated by means of the sample pretreatment unit 22 which is composed of the vent valves 20 and 20a, and the filters 21 and 21a, in two steps, and regulated so as to fit for the operation conditions of the process gaschromatography 9. The sample pretreatment unit 22 is placed in the thermostat 23 to prevent condensation of the sample gas and the thermostat 23 is kept at a certain temperature between 40 and 150C
by means of the thermocontroller 24. Thus, by using the sample line 8a', dry sample gas may always be injected into the detector 25 of the process gaschromatography 9, even in the operation in which a monomer having a boiling -. point comparable with that of a solvent is used. In some cases, monomers having significant difference in boiling point compared with that of solvent are solely used to produce polyolefins of certain standard or brand.
In such cases, certain and stable measurement of the sample gas by the process gaschromatography may be constantly carried out by operating the sample line 8a"
equipped prior to the pressure control valve 14. Thus, in the sample line 8a", the solvent in the sample gas sampled from the gas.phase lb in the reactor 1 is condensed and separated by means of the sample condenser 26 and the sample receiver 27. The sample temperature at the outlet of the sample condenser 26 is automatically controlled by the thexmocontroller 28 at a certain temperature between - 14 ~ 1155600 -15 and 10C. Thus, the sample gas from the sample receiver 27 may be completely vaporized by heating it with the vapo-rizer 15 after flushing it through the pressure control valve 14O In this case, the separated solvent is returned into the reactor 1 through the line 8b. Further, selection of the sampling lines, either 8a' or 8a", may be undertaken by operating the block valve 13a equipped prlor to the sampling line 8a' in conjunction with the block valve 13.
Employment of the sampling system brings about an advantage that normal operation of the process gaschromatography is maintained without paying much attention to the sampling conditions. In this case, the component of gas phase in the reactor is, however, defferent from that of the sample gas. In the embodiment of the present invention wherein the temperatures of the reactor and of the outlet of the sample condenser 26 are controlled independently, the gas component in the reactor may readily be estimated from the data of the sample gas by means of a simple precalcu-lation of the gas-liquid equilibrium. Thus, in the embodi-ment of the present invention, the sample gas is completelyvaporized before it is introduced into the process gaschro-matography; Therefore, the sampling system of the present invention may exclude completely such troubles involved in conventional systems that liquid flow of components having high boiling point into sampling line or condensation thereof therein, which brings about involvement of liquid particles of sample gas in gaschromatography, results in the variation of indication of gaschromatography or in-operation thereof due to packing in the line. The fact also means the improvement in the stability of operating gaschromatography and consequently enablement of accurate measurement of gas concentrations of gas phase in the reactor. In addition, in the embodiment of the present invention, conversion between the sampling lines 8a' and 8a" according to the standard of olefins to be prepared enables wide varieties of operations using different monomers, depending on the standard.
In summary, the sampling system used in the embodiment of the present invention suffices the both requirements for the gaschromatography to detect the gas concentrations and for the preparation process to produce polyolefins according to the predetermined standard, at the same time.
Next, the detector 25 of the process gaschromato-graphy 9 will be explained taking polymerization ofethylene as an example. The sample gas adjusted to detectable conditions with the gaschromatography through employment of the sample pretreatment unit 22 is introduced into a separation column of the detector 25. Then, each component of the sample gas is detected by a thermal contact detector composed of a resistance bridge. Each output signal generated from the detector shows a response as shown in Figure 4. In the case where ethylene is used as the monomer, the normal order in the response time is inherently hydrogen (H2), methane (CH4), ethane (C2H6~
and ethylene (C2H4). However, in the detection system of the present invention, the response time of ethane and ethylene may be put between hydrogen and methane, as shown in Figure 4, by having ethane and ethylene bypassed into columns of shorter response time, using three columns I 1 ~560.~
connected in series and parallel. By doing so, the detection time may be shortened.
The output signals generated from the detector are applied to the controller 28. Since each output sig-nal, for ex~mple, that corresponding to hydrogen (H2) orethylene (C2H4) as shown in Figure 4, is genera-ted from the detector at intervals of a certain fixed period depending on the inherent character of the detector 25, : the peak value of each signal corresponding to each gas component may be measured at the respective response time in the controller 28 and taken out as the d.c. voltage signal. The peak value of each component represents the parameter of each gas concentration. The d.c. voltage signals are converted into the d.c. voltage within 1-5 V
according to the magnitude of the peak value, and taken at as signals Yl' and Y2', respectively.
In a continuous process for the preparation of polyolefins, measurement of the components in the reactor - by gaschromatography 9 should be carried out in short periodic time, as described above. It is desirable that the periodic time is within 10 minutes, preferably from five seconds to three minutes.
In the embodiment of the present invention, YAMATAKE-~ONEWELL H-lOOOTE by Yamatake-Honewell Co., Tokyo, Japan is employed for the gaschromatography.
The Model H-lOOOTE used in the present invention can be operated in periodic time within two minutes and, in practice, can be automatically operated at intervals of 60 seconds, as shown in Figure 4.
Consequently, the signals generated from the detector 25 at intervals of measurement time as shown in Figure 4 are transmitted to the controller 28, wherein the received signals are separated into each component to measure each peak value and converted into each d.c.
voltage signal within 1-5 V according to the magnitude ; of each peak value.
The signals are held at intervals of measurement time and output successively. When the Model ~-lOOOTE
is used, hydrogen ~H2), monomer-A, monomer-B and monomer-C, for instance, in a certain sample gas may be measured and the resulting d.c. voltage signals may be represented successively as Yl', Y2', Y3' and Y4'. As described above, by separating the signals generated from the detector 25 into those of respective components and taking out new signals successively after the holding thereof, complex treatment in the computex of the signals generated from the detector need not be carried out and, consequently, the simplicity of system, cost down and improvement in the whole reliability may be attained. The signals separated into those of respective components in the controller 28 are recorded on the recorder 29. The d.c.
voltage signals Yl' - Y4' are applied to the computer 11 (Figure 3b) and, simultaneously, recorded on the multipoint recorder 10. The process computer controller system will be explained hereinafter by referring to Figure 3b.
The successive d.c. voltage signals Yl', Y2', Y3' and Y4' teach 1-5 V) corresponding ~ ~2~ monomer-A, monomer-B and monomex-C respectively taken out from the gaschromatography 9 and the voltage signal (l-S V~ generated from the pressure transmitter 30 of the reactor 1 are connected to the input terminal 32 of the computer 11.
The computer 11 comprises the scanning plot (not illust-rated) for scanning five kinds of the signals noted above automatically and periodically, the A/D (analog/degital) converting plot 34, the linearizing plots 35, 36 and 37 for linearizing the signals generated from the converter, the opèrating plots 38, 39 and 40 for operating the signals, and the controlling plots 41, 42 and 43 for controlling the signals generated from the operating plots in compari-son with the standard values preestablished. In the embodiment, YAMATAKE-HONEWELL TDCS-2000 by Yamatake-Honewell Co., Tokyo, Japan is used as the computer 11.
The method for controlling of properties of polyolefins by using the process computer control system will be explained concretely hereinafter.
First, the control loop for controlling the melt index (M.I.) of polyolefins will be explained in detail regarding, for example, polymerization of ethylene.
As mentioned above, the M.I. value of polymers is funda-mentally a function of molar ratio of hydrogen to monomer-A
in the gas phase lb of the reactor 1. In the process for preparing polyethylene from hydrogen (H2) and ethylene as monomer-A, the control loop for controlling the molar ratio of hydrogen ~H2) to ethylene ~C2H4) ~represented as H2/C2 in hereinafter description) for preparing polyethy-lene having the predetermined M.I. i5 described below.
The signals Yl' and Y2' A/D converted by the converter 34, representing H2 mole % and C2 mole %, respectively, are applied to the linearizing plots 35 and 36, respectively.
As output signals generated from the gaschromatography 9 ~r~ -- r 1 15S60~
correspond to each peak height shown in Figure 4, they are calibrated into respective correct mole % concentrat-ions by means of linearization in the linearizing plots 35 and 36, respectively.
When the integration of the signals is carried out in the controller 28 of the gaschromatography 9, the mole ~ concentration may be measured accurately. In such a case, it is unnecessary to linearize the signals in the computer.
The linearization of signals in the linearizing plots 35 and 36 may be carried out by way of folded-line approximated operation. The output signals Yl and Y2 generated from the linearizing plots 35 and 36 indicate exactly the mole % concentrations of hydrogen (~2) and ethylene (C2H4), respectively. The signals Yl and Y2 are again converted into the analog signals by the D/A
converter 34, and the resulting voltage signals (1-5 V) are recorded on the multipoint recorder 12 and simultaneously applied to the operating plot 38.
In the operating plot 38, Yl/Y2 operation is performed and the resultiny Yl/Y2 output is recorded on the multipoint recorder 12 as the H2/C2 value through the D/A converter 34 and simultaneously applied to the PID
controller 41 as the process variable. In the PID controller 41, the preestablished value _~corresponding to the pre-determined melt index has been previously set up by means of the operation of the data entry panel 44 by an operator.
In the PID controller 41, the input signal (H2/C2 value3 is compared with the preestablished value m, and the both are PID controlled automatically for coincidence or agreement.
~15.560~
In accordance with the difference between the both values, 4-20 mA current signal is taken out. The current signal is converted into the air pressure signal within 0.2-1.0 kg/cm2G with the current/air pressure converter 46 accord-ing to the magnitude of the value, and the resultingpressure signal is supplied to the positioners of the hydrogen feed valve 2a and the vent valve 6a. Control of the positioners of the valves 2a and ~a is carried out by means of a so-called split range method.
Namely, as illustrated in Figure 5, the valve positioner of the vent valve 6a is regulated in such manner that it is completely opened at the input air signal pressure of 0.2 kg/cm2G or below, and completely closed at the pressure of 0.6 kg/cm2G or above, and further the hydrogen feed valve 2a is regulatedin such manner that it is completely closed at the pressure of 0.6 kg/cm2G
or below and completely opened at 1.0 kg/cm2G or above.
Thus, control of the two valves may be carried out by the single control signal pressure.
The input of the standard H2/C2 value preestab-lished into the computer 11 may be carried out by using the data entry panel 44. Alternatively, it may be carried out by using the H2/C2 analog indicator 49 of the analog display apparatus 48. The indicator 49 also indicates the agreement or difference of the H2/C2 value determined by the gaschromatography and operated by the computer, compared with the preestablished H2/C2 value in the form of analog display.
In this manner, by using the H2/C2 control loop, the H2/C2concentrations in the gas phase lb of the reactor 1 may be automatically controlled to the preestablished value, and in consequence, polyethylene having the predetermined M.I. may be continuously prepared. Therefore, the H2/C2 control loop is called the M.I. control loop S since the H2/C2 control is substantially equal to the M.I. control.
In the introduction of the desired volume of monomer (ethylene) into the reactor 1 equipped with the gas phase part lb, if there occurs an outer turbulance, for example, change in the activity of Ziegler catalyst introduced into the reactor 1 through the catalyst feed line 5, the partial pressure of the monomer (C2) in the reactor 1 varies; the dissolved volume of the monomer in the solvent also varies, correlated to the variation of the partial pressure; and the dissolved monomer flows out of the system as the unreacted monomer together with the solvent. In other words, the polymerization rate varies even when the monomer feed volume is kept constant.
Heretofore, if such outer turbulance occurs, the partial pressure of monomer tC2) alone varies and this results in the variation of the H2/C2 value and of M.I.
value. However, in the present invention, as the H2/C2 value is controlled automatically with the hydrogen feed valve 2a and the vent valve 6a as described above, the M.I. may be kept constant even when such outer turbulence occurs. However, if such polymerization conditions as mentioned above is maintained, the polymerization rate will deviate from the preestablished rate. Thus, in the present invention, the polymerization rate may be restored to the preestablished rate by controlling the catalyst ~ -~r--~p~q~ r~ r r r,~r.-~-~ .-r~ --.n~ -r~-rr~r~
1 1556~
feed volume to compensate the variation of catalyst activity, thereby returning the partial pressure of monomer lC2) to the original value.
The control loop for C2 partial pressure will be explained hereinafter. The output voltage signal (1-5 V) generated from the pressure transmitter 30 at the pressure Po of the reactor 1 and the output signal Y2 representing the ethylene mole % generated from the linearizing plot 36 are applied to the operating plot 40 and the operation of (Po -~ 1.03)Y2 is performed. In the equation, the part in the parentheses needs the conversion to absolute pressure, wherein 1.03 represents atomospheric pressure. In case an absolute-pressure gauge in the pressure transmitter 30 of the reactor 1 is used, the value 1.03 in the parentheses of the equation becomes unnecessary. The output signal gene-rated from the operating plot 40 is recorded on the multipoint recorder 12 through the D/A converter 34 and used as the running indicator for the C2 partial pressure. On the other hand, the C2 partial pressure signal is applied to the PID
controller 43 in the same way as in the H2/C2 control loop mentioned above, and PID controlled so as to coincide with the preestablished standard value for the C2 partial pressure p in the reactor given by an operator with the data entry panel 44 or with the partial pressure analog indicator 50 of ; 25 the analog display apparatus 48. The output signal therefor (4-20 mA) is applied to the current/air pressure converter 52 through the D/A converter 34 and converted to the operation signal for the stroke control unit 4a' of the catalyst feed pump 4a" in the form of air signal. In this manner, control of the H2/C2 concentrations at the predetermined value and the regulation of the C2 partial pressure at the predetermined 1 1 ~iS600 value when an outer turbulence like variation of catalyst activity occurs may be attained at the same time. Further, properties of polyolefins when prepared with other olefins may be controlled by the similar operations as mentioned above.
Lastly, as mentioned in hereinbefore description, it is sometimes required to produce polyolefins having predetermined properties, in particular, the predetermined density by performing the polymerization, maintaining the ratio of monomer-A (for example, ethylene) and comono-mer-B (for example, propylene), or the ratio o~ monomer-A
and comonomer-C (for example, l-butene) constantly, depend-ing on the properties or brands of polyolefins to be prepared. Control of the comonomer ratio may be achieved by using the same line-up as in the H2/C2 value control loop. Each signal corresponding to monomer-A, monomer-B, and monomer C, generated from the gaschromatography 9 is represented~ say, by Y2', Y3' and Y4', respectively. The signals Y3' and Y4' are applied to the D/A converter 34 by an change-over switch (not illustrated) in an alternative way. An example in which the signal Y3' is chosen will be explained hereinafter.
The signals Y2' and Y3' of monomers A and B are applied to the linearizing plots 36 and 37, and linearized therein. The output signals Y2 and Y3 are recorded on the recorder 12 through the D/A converter 34 and simultaneously applied to the operating plot 39. Operation of Y2/Y3 is performed in the operating plot 39 and the output therefrom is recorded on the recorder 12 through the D/A converter 34 and simultaneously applied to the controller 42.
In the controller 42, the input signal is PID-controlled so as to coincide with the predetermined standard value d for the comonomer ratio given by an operator with the data entry panel 44 or with the comonomer ratio analog S indicator Sl of the analog display apparatus. The output signal therefor (4-20 mA) is controlled with the cascade type controller 54 through the D/A converter 34, and the feed volume of the comonomer is regulated by operating the comonomer feed valve 3a'.
In this manner, by controlling the concentrat-ions of monomer and comonomer, the continuous process for preparation of polyolefins having the predetermined density may be performed.
In the embodiments described above, the feed volumes of olefin as monomer and of solvent are controlled automatically with the flow rate indication controllers 56 and 58 through the olefin feed valve 3a and the solvent feed valve Sa, respectively. As was the case in the process computer control mentioned above, the control may be per-formed either with the output from the computer 11 alone,or with combination of output control from the computer 11 and the flow rate indication controllers 56 and 58.
As explained above, the process for preparation of polyolefins according to the invention employes a technique to determine the components in the gas phase of the reactor, whereby the situation of the reacti.on system may be made clear, exactly. By measuring the gas phase and making response, for example, at 1 minute intervals with high speed gaschromatography (Figure 4), almost no huntings of the properties such as melt index and/or 1 ~55600 density are observed. Further, since the process of the present invention employs a computer control system, any unstability due to manual control depending on operator's intuition may be excluded, whereby, in combination with the measurement of the gas phase in the reactor and the use of a high speed gaschromatography, polyolefins having the uniform properties such as predetermined melt index and/or density may be obtained.
In Figure 2, the solid line A illustrates the relationship between the melt index and the polymerization period for the continuous preparation of polyethylene according to the invention; whereas the dotted line B
illustrates the relationship between the melt index and the polymerization period when the control of the melt index is carried out by manual operation of the hydrogen feed valve, the ethylene feed valve or the like according to the melt index measured at every 4 hour intervals.
The polymerization period as abscissa in Figure 2 is reckoned not from the initial time of the polymeri-zation but from an arbitrary time at the steady state in the process.
As shown in Figure 2, the process of the present invention makes it possible to produce quite steadily polyolefins having uniform melt index.
In Figure 6, the solid line C illustrates the relationship between the density and the polymerization period for the continuous preparation of polyethylene - according to the invention; whereas the dotted line D
illustrates the relationship between the density and the polymerization period when the control of the density is 1 15r~6(~O
carried out by manual operation of the ethylene feed valve as a monomer and the propylene feed valve as a comonomer or the like according to the density measured at every 12 hour intervals. The polymerization period as abscissa in Figure 6 is reckoned not from the initial time of the polymerization but from an arbitrary time at the steady state in the process. As shown in Figure 6, the process of the present invention makes it possible to produce quite steadily polyolefins having uniform density.
INDUSTRIAL APPLICABILITY
, As will be clear from the foregoing embodiments, the present invention provides a useful art to produce polyolefins having predetermined properties, in particular predetermined melt index and/or density, and are suitable, therefore, to produce quite steadily polyolefins having uniform properties, inter alia, predetermined melt index and/or density in the process for preparing polyolefins by polymerizing an olefin in the presence of a Ziegler catalyst and hydrogen.
Claims (22)
1. A process for preparing a polyolefin having predetermined properties by polymerizing at least one olefin in the presence of a Ziegler catalyst and hydrogen, said process comprising:
introducing the catalyst, olefin and hydrogen into a gas/liquid phase reactor and establishing a continuous gas phase space above the liquid phase in the reactor;
analyzing the concentrations of the one olefin and hydrogen in the gas space within the reactor by gas chromatography;
generating input signals representative of said detected concentrations;
comparing said input signals with preset values corresponding to said predetermined properties;
generating control signals as a function of deviations between said input signals and said preset values; and, controlling the feed rates of said hydrogen and said one olefin responsive to said control signals.
introducing the catalyst, olefin and hydrogen into a gas/liquid phase reactor and establishing a continuous gas phase space above the liquid phase in the reactor;
analyzing the concentrations of the one olefin and hydrogen in the gas space within the reactor by gas chromatography;
generating input signals representative of said detected concentrations;
comparing said input signals with preset values corresponding to said predetermined properties;
generating control signals as a function of deviations between said input signals and said preset values; and, controlling the feed rates of said hydrogen and said one olefin responsive to said control signals.
2. A process for preparing an polyolefin as claimed in claim 1, wherein the polymerization of said olefin is conducted in a continuous manner.
3. A process in accordance with claim 1, wherein said input signals are fed to a computer, said computer comparing said input signals with preset values and generating said control signals.
4. The process of claim 1 wherein the temperature in said reactor is kept constant and the feed rates of said hydrogen and said one olefin are controlled to produce an olefin having a predetermined melt index.
5. The process of claim 1 wherein samples of the reactor gas phase are analyzed at intervals not more than 10 minutes apart.
6. The process of claim 1 wherein the olefin feed to the reactor is ethylene or a monomer mixture containing at least 70 mole % ethylene and 30 mole % or less of an .alpha.-olefin and/or a diolefin.
7. A process for preparing a polyolefin having a predetermined melt index by polymerizing at least one olefin in the presence of a Ziegler catalyst and hydrogen, said process comprising:
a) introducing the catalyst, olefin and hydrogen into a gas/liquid phase reactor and establishing a continuous gas phase space above the liquid phase in the reactor;
b) analyzing the concentration of the one olefin (C2) and the concentration of hydrogen (H2) in the gas space within the reactor by gas chromatography;
c) generating an input signal Y1 representative of said hydrogen concentration and an input Y2 representative of said concentration of the one olefin;
d) comparing said input signals with preset values corresponding to said melt index;
e) generating control signals as a function of deviations between said input signals and said preset values; and, f) controlling the feed rate of said hydrogen, responsive to said control signals, to prepare a poly-olefin having the predetermined melt index.
a) introducing the catalyst, olefin and hydrogen into a gas/liquid phase reactor and establishing a continuous gas phase space above the liquid phase in the reactor;
b) analyzing the concentration of the one olefin (C2) and the concentration of hydrogen (H2) in the gas space within the reactor by gas chromatography;
c) generating an input signal Y1 representative of said hydrogen concentration and an input Y2 representative of said concentration of the one olefin;
d) comparing said input signals with preset values corresponding to said melt index;
e) generating control signals as a function of deviations between said input signals and said preset values; and, f) controlling the feed rate of said hydrogen, responsive to said control signals, to prepare a poly-olefin having the predetermined melt index.
80 The process of claim 7 wherein signals Y1 and Y2 are converted into a single input signal Y1/Y2 and said single input signal is compared with a predetermined value for H2/C2 corresponding to the predetermined melt index and wherein control signals for said hydrogen feed rate and said venting are generated as a function of deviation between said input signal Y1/Y2 and the predetermined value for H2/C2.
9. A process for preparing a polyolefin having a predetermined melt index by polymerizing at least one olefin in the presence of a Ziegler catalyst and hydrogen in a reactor, characterized by:
a) introducing the catalyst, olefin and hydrogen into a gas/liquid phase reactor and establishing a con-tinuous gaseous phase space above the liquid phase in the reactor;
b) analyzing the concentrations of the one olefin and hydrogen in the gas space within the reactor by gas chromatography;
c) generating a hydrogen concentration signal (H2) and an olefin concentration signal (C2) representative of the values obtained by said analysis;
d) converting said hydrogen concentration signal and said olefin concentration signal into a single signal representative of H2/C2;
e) comparing said single C2/C2 signal with a preset value for H2/C2 corresponding to the predeter-mined melt index;
f) generating control signals as a function of deviations between said input H2/C2 signal and said preset value for H2/C2;
g) controlling the feed rate of said hydrogen and venting said gas space to control pressure responsive to said control signals;
h) detecting the pressure within the reactor and generating a pressure signal representative of said detected pressure;
i) converting said pressure signal to a signal representative of the partial pressure of said one olefin by multiplying said pressure signal by said olefin concentration signal;
j) comparing said partial pressure signal to a pre-established value and generating a catalyst supply control signal as a function of deviation between said partial pressure signal and said preestablished value; and controlling the rate at which the catalyst is fed to the reactor, responsive to said catalyst supply control signal, to provide a polyolefin of the predetermined melt index.
a) introducing the catalyst, olefin and hydrogen into a gas/liquid phase reactor and establishing a con-tinuous gaseous phase space above the liquid phase in the reactor;
b) analyzing the concentrations of the one olefin and hydrogen in the gas space within the reactor by gas chromatography;
c) generating a hydrogen concentration signal (H2) and an olefin concentration signal (C2) representative of the values obtained by said analysis;
d) converting said hydrogen concentration signal and said olefin concentration signal into a single signal representative of H2/C2;
e) comparing said single C2/C2 signal with a preset value for H2/C2 corresponding to the predeter-mined melt index;
f) generating control signals as a function of deviations between said input H2/C2 signal and said preset value for H2/C2;
g) controlling the feed rate of said hydrogen and venting said gas space to control pressure responsive to said control signals;
h) detecting the pressure within the reactor and generating a pressure signal representative of said detected pressure;
i) converting said pressure signal to a signal representative of the partial pressure of said one olefin by multiplying said pressure signal by said olefin concentration signal;
j) comparing said partial pressure signal to a pre-established value and generating a catalyst supply control signal as a function of deviation between said partial pressure signal and said preestablished value; and controlling the rate at which the catalyst is fed to the reactor, responsive to said catalyst supply control signal, to provide a polyolefin of the predetermined melt index.
10. The process of claim 9 wherein said pressure signal is converted to a value representative of absolute pressure prior to said multiplication.
11. A process for preparing a polyolefin as claimed in claim 7, 8 or 9 wherein the polymerization of said olefin is carried out by a continuous process.
12. A process in accordance with claim 7, 8 or 9 wherein said input signals are fed to a computer, said computer comparing said input signals with preset values and generating said control signals.
13. A process for preparing a polyolefin as claimed in claim 7, 8 or 9, wherein the temperature in said reactor is kept constant.
14. A process for preparing a polyolefin as claimed in claim 7, 8 or 9 wherein samples of the reactor gas phase are analyzed in not more than 10 minutes.
15. A process for preparing a polyolefin as claimed in claim 7, 8 or 9, wherein said olefin is ethylene or a mixture containing at least 70 mol % of ethylene and 30 mole % or less of an .alpha.-olefin and/or a diolefin.
16. A process for preparing a polyolefin having prede-termined density by polymerizing at least two different olefins in the presence of a Ziegler catalyst and hydrogen, which is characterized by:
introducing the catalyst, olefins and hydrogen into a reactor and establishing a gas phase space above the liquid phase in the reactor;
analyzing the concentrations of said olefins in the gas phase space within the reactor by gas chromatography;
generating input signals representative of said detected concentrations;
comparing said input signals with preset values corresponding to the desired density;
generating control signals as a function of devia-tions between said input signals and said preset values;
and, controlling the feed rates of said olefins respon-sive to said control signals to prepare a polyolefin having said density.
introducing the catalyst, olefins and hydrogen into a reactor and establishing a gas phase space above the liquid phase in the reactor;
analyzing the concentrations of said olefins in the gas phase space within the reactor by gas chromatography;
generating input signals representative of said detected concentrations;
comparing said input signals with preset values corresponding to the desired density;
generating control signals as a function of devia-tions between said input signals and said preset values;
and, controlling the feed rates of said olefins respon-sive to said control signals to prepare a polyolefin having said density.
17. A process for preparing a polyolefin having prede-termined density by polymerizing at least two different olefins in the presence of a Ziegler catalyst and hydrogen, which is characterized by:
introducing the catalyst, olefins and hydrogen into a reactor and establishing a gas phase space above the liquid phase in the reactor;
analyzing the concentrations of said olefins in the gas space within the reactor by gas chromatography;
generating input signals representative of said detected concentrations;
converting said concentration input signals into a ratio signal representative of the ratio of said detected concentrations;
comparing said ratio signal with a preset value corresponding to the desired density;
generating control signals as a function of devia-tions between said ratio signal and said preset value; and, controlling the feed rates of said olefins respon-sive to said control signals to prepare a polyolefin having said density.
introducing the catalyst, olefins and hydrogen into a reactor and establishing a gas phase space above the liquid phase in the reactor;
analyzing the concentrations of said olefins in the gas space within the reactor by gas chromatography;
generating input signals representative of said detected concentrations;
converting said concentration input signals into a ratio signal representative of the ratio of said detected concentrations;
comparing said ratio signal with a preset value corresponding to the desired density;
generating control signals as a function of devia-tions between said ratio signal and said preset value; and, controlling the feed rates of said olefins respon-sive to said control signals to prepare a polyolefin having said density.
18. A process in accordance with claim 16 or 17 wherein said input signals are fed to a computer, said computer comparing said input signals with preset values and generating said control signals.
19. A process for preparing a polyolefin as claimed in claim 16 or 17, wherein the temperature in said reactor is kept constant.
20. A process for preparing a polyolefin as claimed in claim 16 or 17, wherein the reactor gas phase is analyzed at intervals not more than 10 minutes apart.
21. A process for preparing a polyolefin as claimed in claim 16 or 17, wherein said olefin is a mixture of at least 70 mole % ethylene and 30 mole % or less of an .alpha.-olefin and/or a diolefin.
22. The process of claim 1 or 7 additionally comprising controlling the pressure in said reactor by venting said gas phase space responsive to said control signals.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JPPCT/JP80/00085 | 1980-04-23 | ||
| PCT/GB1980/000085 WO1980002578A1 (en) | 1979-05-15 | 1980-05-09 | Prefabricated laboratory unit and octane analyser |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1155600A true CA1155600A (en) | 1983-10-18 |
Family
ID=10510404
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000365442A Expired CA1155600A (en) | 1980-04-23 | 1980-11-25 | Process for preparing polyolefins |
Country Status (2)
| Country | Link |
|---|---|
| JP (2) | JPS6028285B2 (en) |
| CA (1) | CA1155600A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2097520T3 (en) * | 1992-05-29 | 1997-04-01 | Amoco Corp | ALPHA-OLEPHINE POLYMERIZATION. |
| WO2002046738A2 (en) * | 2000-12-07 | 2002-06-13 | Bp Chemicals Limited | Methode d'analyse par chromatographie en ligne pour la polymerisation d'olefines |
| JP2017519084A (en) * | 2014-06-25 | 2017-07-13 | バーゼル・ポリオレフィン・ゲーエムベーハー | Method for controlling the ethylene polymerization process |
| US10400046B2 (en) * | 2015-06-25 | 2019-09-03 | Joseph J. Matsko | Portable powered paint system |
| JP6772103B2 (en) * | 2017-04-12 | 2020-10-21 | 横河電機株式会社 | Polymerization suppression system and polymerization suppression method |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3146223A (en) * | 1959-08-21 | 1964-08-25 | Shell Oil Co | Polymerization in the presence of controlled amounts of hydrogen |
| US3356667A (en) * | 1963-10-22 | 1967-12-05 | Phillips Petroleum Co | Process control |
| BE786683A (en) * | 1971-09-17 | 1973-01-25 | Polymer Corp | PROCESS FOR CHECKING THE QUALITY OF |
| US3817962A (en) * | 1971-10-26 | 1974-06-18 | Phillips Petroleum Co | Controlled polymerization process and apparatus |
| JPS4912589A (en) * | 1972-05-16 | 1974-02-04 | ||
| GB1430073A (en) * | 1972-07-13 | 1976-03-31 | Ici Ltd | Polymerisation proces |
| JPS5511826B2 (en) * | 1973-07-27 | 1980-03-27 | ||
| JPS5137112A (en) * | 1974-09-26 | 1976-03-29 | Asahi Glass Co Ltd | Garasuita no ketsutensenbetsuhoho |
| JPS5811448B2 (en) * | 1978-02-27 | 1983-03-03 | 株式会社トクヤマ | Manufacturing method of block copolymer |
| DK156279A (en) * | 1978-04-18 | 1979-10-19 | Union Carbide Corp | EXOTERM LOW PRESSURE GAS PHASE POLYMERIZATION IN FLUIDIZED RENTAL APPLIANCE FOR EXERCISE |
-
1980
- 1980-10-01 JP JP55137547A patent/JPS6028285B2/en not_active Expired
- 1980-11-25 CA CA000365442A patent/CA1155600A/en not_active Expired
-
1986
- 1986-05-09 JP JP10648586A patent/JPS6270404A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6270404A (en) | 1987-03-31 |
| JPS6340802B2 (en) | 1988-08-12 |
| JPS6028285B2 (en) | 1985-07-04 |
| JPS56151706A (en) | 1981-11-24 |
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