CA1131657A - Recovery of methacrylic acid and alcohol in methacrylate production process - Google Patents
Recovery of methacrylic acid and alcohol in methacrylate production processInfo
- Publication number
- CA1131657A CA1131657A CA321,785A CA321785A CA1131657A CA 1131657 A CA1131657 A CA 1131657A CA 321785 A CA321785 A CA 321785A CA 1131657 A CA1131657 A CA 1131657A
- Authority
- CA
- Canada
- Prior art keywords
- methacrylic acid
- organic solvent
- zone
- alcohol
- solution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
- C07C51/48—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/08—Preparation of carboxylic acid esters by reacting carboxylic acids or symmetrical anhydrides with the hydroxy or O-metal group of organic compounds
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Methacrylic acid esters are effectively obtained from a feedstock dilute aqueous solution of methacrylic acid containing by-produced acetic acid and others, obtained by gas phase catalytic oxidation of at least one member of isobutylene, tert.butyl alcohol and methacrolein, by (1) subjecting said feedstock to extraction in a methacrylic acid extracting zone (a) using an extracting solvent prepared by adding to a water-insoluble, inert organic solvent having a boiling point above 120°C, 15 - 50% by weight of a methacrylic acid ester, (2) separating the resulting extract solution into a mixed solvent of the methacrylic acid ester and most of the organic solvent and a methacrylic acid solution on the remaining organic solvent by distillation in an extracting solvent-separating zone (b), (3) subject-in the resulting organic solvent solution containing methacrylic acid to esterification reaction in the presence of an acid catalyst together with an excess amount of an alcohol having a boiling point below 100°C
in an esterification reaction zone (c), while removing water formed by the esterification reaction by azeotropic boiling with the organic solvent together with a part of the formed methacrylic acid ester as a distillate solution, thereby making an acid catalyst concentration of the remaining reaction solution constant, (4) separating the reaction solution discharged from the bottom of the esterification reaction zone (c) into an organic solvent layer containing the methacrylic acid ester and an aqueous layer containing the acid catalyst in a decanting zone (d), (5) recycling the aqueous layer at the constant acid catalyst concentration to the esterification reaction zone (c) after separating by-produced polymerization products therefrom, (6) Joining the organic solvent layer with the distillate solution in step (3), (7) subjecting the resulting mixture alcohol extraction using an aqueous solution of an inorganic salt in an alcohol extraction zone (e) to recover unreacted alcohol, (8) recycling the recovered alcohol to the esterification reaction zone (c), (9) separating low boiling materials from a raffinate organic solvent phase leaving the top Or the alcohol extraction zone (e) by distillation, (10) separating the raffinate organic solvent phase freed from the low boiling materials into a high purity methacrylic acid ester product and the organic solvent containing unreacted methacrylic acid, and (11) recycling the organic solvent containing methacrylic acid to an appropriate position Or the methacrylic acid-extracting zone (a) in step (1) or to a feedstock to be separated in step (2).
Methacrylic acid esters are effectively obtained from a feedstock dilute aqueous solution of methacrylic acid containing by-produced acetic acid and others, obtained by gas phase catalytic oxidation of at least one member of isobutylene, tert.butyl alcohol and methacrolein, by (1) subjecting said feedstock to extraction in a methacrylic acid extracting zone (a) using an extracting solvent prepared by adding to a water-insoluble, inert organic solvent having a boiling point above 120°C, 15 - 50% by weight of a methacrylic acid ester, (2) separating the resulting extract solution into a mixed solvent of the methacrylic acid ester and most of the organic solvent and a methacrylic acid solution on the remaining organic solvent by distillation in an extracting solvent-separating zone (b), (3) subject-in the resulting organic solvent solution containing methacrylic acid to esterification reaction in the presence of an acid catalyst together with an excess amount of an alcohol having a boiling point below 100°C
in an esterification reaction zone (c), while removing water formed by the esterification reaction by azeotropic boiling with the organic solvent together with a part of the formed methacrylic acid ester as a distillate solution, thereby making an acid catalyst concentration of the remaining reaction solution constant, (4) separating the reaction solution discharged from the bottom of the esterification reaction zone (c) into an organic solvent layer containing the methacrylic acid ester and an aqueous layer containing the acid catalyst in a decanting zone (d), (5) recycling the aqueous layer at the constant acid catalyst concentration to the esterification reaction zone (c) after separating by-produced polymerization products therefrom, (6) Joining the organic solvent layer with the distillate solution in step (3), (7) subjecting the resulting mixture alcohol extraction using an aqueous solution of an inorganic salt in an alcohol extraction zone (e) to recover unreacted alcohol, (8) recycling the recovered alcohol to the esterification reaction zone (c), (9) separating low boiling materials from a raffinate organic solvent phase leaving the top Or the alcohol extraction zone (e) by distillation, (10) separating the raffinate organic solvent phase freed from the low boiling materials into a high purity methacrylic acid ester product and the organic solvent containing unreacted methacrylic acid, and (11) recycling the organic solvent containing methacrylic acid to an appropriate position Or the methacrylic acid-extracting zone (a) in step (1) or to a feedstock to be separated in step (2).
Description
~31~5~
1 This invention relates to an improved process for continuously synthesizlng methyl methacrylate or ethyl methacry]ate, and a process for recovering unreacted methacrylic acid and unreacted alcohol.
To avoid a complicated description, description will be made below only of a process for methylesterifi-cation of methacrylic acid, but quite the same thing can be applied to a process for ethylesterification of methacrylie acid unless otherwise speeifically mentioned.
Heretofore, methyl methacrylate has been ~a . c~r~c~h4~1~;n produced according to acetone~ t~ process using acetone and hydrogen cyanide as starting materials, but the process has not been satisfactory as an industrial process for producing methyl methacrylate owing to the use of highly toxic hydrogen cyanide, and production of a large amount of ammonium sulfate as a by-product, ete. Recently, another process for producing methyl methacrylate by obtaining methaerylic aeid through a gas phase catalytic oxidation of isobutylene, etc., and then by esterifying the resulting methacrylie acid by methanol has been proposed as a substitute for the acetone cyanhydrin process. The methacrylic aeid produet that ean be obtained through the oxidation reaetion of at least one member of isobutylene, tert.butanol and methacrolein is in a form of 10 - 50wt.% aqueous solution \~s ~3~L~;S~
1 containing by-produced acetic acid and a small amount of other substances. It is known that the methacrylic acid is extracted into an organic solvent from the aqueous solution and methacrylic acid is then recovered from the solvent by distillation. In selecting an extractlng solvent, a distribution coefficient of methacrylic acid is especially important. The distributlon coefficient is defined as follows: -Concentration of methacrylic acid Distribution = in solvent (wt.%) coefficient Concentration of methacryllc acid in aqueous layer (wt.%) A large distribution coefficient means that methacrylic acid can be correspondingly efficiently extracted. On the other hand, acetic acid by-produced in the oxidation step is an organic acid similar to methacrylic acid, and often has a similar extraction property for an organic solvent to that of methacrylic acid. Thus, when a solvent is selected only in view of the distribution coefficient, acetic acid is also extracted together with methacrylic acid, and acetic acid reacts with methanol in the esterification step succeeding the extraction step, so that methyl acetate is formed. That is, methanol is lost, and thus acetic acid must be removed to less than some concentration by separation before the esterification step.
Usually, methacrylic acid and acetic acid are separated from each other by distillation, but such ~13~57 1 usual process is disadvantageous in the heat econo~y and the simplification of steps. Thus, it is advantageous to properly se].ect an extracting solvent for methacrylic acid, and selectively separate methacrylic acid into the extracting solvent, while separating most of acetic acid into a raffinate aqueous phase in the methacrylic acid extraction step. It is known that the solvent having a high distribution coefficient of methacrylic acid and a lower distribution coefficient of acetic acid than 1.0 and being capable of separating acetic acid and methacrylic acid from each other in the methacrylic acid extraction step is a solvent system . of ethylbenzene and/or xylene (Japanese Patent Publication l~ 3 ~3-~
No. ~ ). On the other hand, it is also known that 15 hydrocarbons such as heptane, toluene and xylene have a low extraction efficiency for an aqueous methacrylic acid solution of low concentration (Japanese Patent Publication No. 41413/74).
As a result of extensive studies on the solvent 20 system of ethylbenzene and/or xylene, the present J
inventors have confirmed that said solvent system has a fatal defect in an extracting solvent for methacrylic acid such that their methacrylic acid extraction ratio never exceeds some limit, and thus cannot be applied 25 industrially, and have found that such defect can be overcome and an industrially applicable extraction can be attained by the use of an extracting solvent prepared by adding 15 to 50% by we~ght of a methacrylic ~3~5'7 1 acid ester to a water-insoluble, inert organic solvent having a boiling point of higher than 120C, such as ethylbenzene, xylene, cumene, cymene, etc. (which will be hereinafter referred to as a first component of extracting agent), and further that unreacted alcohol and methacrylic acid ln the esterification step can be efficiently recovered by using such extracting solvent and improving each step in the production process of the methacrylic acid ester.
The present invention provides a process for preparing a methacrylic acid ester from a feedstock dilute aqueous solution of methacrylic acid containing by-produced acetic acid and others, obtained by gas phase catalytic oxidation of at least one member of isobutylene, tert.butyl alcohol and methacrolein, which comprises (1) subjecting said feedstock to extraction in a rnethacrylic acid extracting zone (a) using an extracting solvent prepared by adding to a water-insoluble, inert organic solvent having a boiling 2Q point above 120C, 15 - 50% by weight of a methacrylic acid ester, (2) separatin~ the resulting extract solution into a mixed solvent of the methacrylic acid ester and most of the organic solvent and a methacrylic acid solution in the remaining organic solvent by distillation in an extracting solvent-separating zone (b), (3) subjec~-ing the resulting organic solvent solution containing methacrylic acid to esterification reaction in the presence of an acid catalyst together with an excess ~3~S7 1 amount of an alcohol having a boiling point below 100C
ln an esterification reaction zone (c), while removing water formed by the esterification reaction by azeotropic boiling wi.th the organic solvent together with a part of the forrned methacrylic acid ester as a distillate solution, thereby making an acid catalyst concentration of the remaining reaction solution constant, (4) separating the reaction solution discharged from the bottom of the esterification reaction zone (c) into an organic solvent layer containing the methacrylic acid ester and an aqueous layer containing the acid catalyst in a decanting zone (d), (5) recycling the aqueous layer at the constant acid catalyst concentration to the esterification reaction zone (c) after separating by-produced polymerization 15 products therefrom, (6) ~oining the organic solvent i~
layer with the distillate solution in step (3), (7) subject-ing the resulting mixture to alcohol extraction using an aqueous solution of àn inorganic salt in an alcohol extraction zone (e) to recover unreacted alcohol, (8) recycling the recovered alcohol to the esterification reaction zone (c), (9) separating low boiling materials from a raffinate organic solvent phase leaving the top of the alcohol extraction zone (e) by distillation, (10) separating the raffinate organic solvent phase freed from the low boiling materials into a high purity methacrylic acid ester product and the organic solvent containing unreacted methacrylic acid, and (11) recycling the organic solvent containing methacrylic acid to ~3~i57 1 an appropriate position of the methacrylic acid-extracting zone (a) in step (1) or to a feedstock to be separated in step (2).
The present invention will be described in detail, referring to the accompanying drawings.
Figure 1 is a diagram showing relations between a methacrylic acid concentration in a feedstock aqueous solution and a methacrylic acid distribution coefficiént by the first component of extracting agent alone or the present extracting solvent comprising the first component of extracting agent and methacrylic acid ester.
Figure 2 is a flow diagram showing one embodiment of the present process.
The present inventors have made a detailed study of how the distribution coefficient of methacrylic acid is changed against the methacrylic acid concentration of feedstock aqueous solution when methacrylic acid ester is added or not to the solvent system of ethyl-benzene and/or xylene, and the results are shown in Figure 1. It is seen from Figure 1 that in the case of the solvent system comprising ethylbenzene and/or xylene alone, the distribution coefficient of methacrylic acid is extremely lowered, if the methacrylic acid concentration of the feedstock aqueous solution is below 3% by weight, and particularly the distribution coefficient approaches 1.0, if the methacrylic acid concentration of the feedstock aqueous solution is below 2% by weight, so that the extracting capacity for methacrylic acid ~3~
1 is almost lost and a function as the extracting agent is not fulfilled. This means that, so far as the extraction operation is continued, there are always locations, at whlch the methacryllc acid concentration is lowered in the aqueous solution, in an extractor, irrespective of the methacrylic acid concentration of a feedstock aqueous solution, and thus there is ultimately a limit to the methacrylic acid extraction ratio, when the solvent system comprising ethylbenzene and/or xylene alone is used for extracting methacrylic acid. For example, when the methacrylic acid concentration of the feedstock ;
aqueous solution is 20% by weight and an equal amount of an extracting agent is used to that of the feedstock aqueous solution, about 2% by weight of methacrylic acid remains in the raffinate aqueous layer, and thus an upper limit of the extraction ratio will be about 90%.
That is, the methacrylic acid loss is industrially so large that an industrial significance is lost, even if the successive steps could efficiently be carried out.
On the other hand, it is seen from Fig. 1 that the extracting solvent of- the present invention attains a satisfactory extraction capacity even in a low concentration range of methacrylic acid in the ~eedstock aqueous solution.
An extracting solvent comprising a combination of a methacrylic acid ester and the solvent system of ethylbenzene and/or xylene has been already disclosed in Japanese Patent Publication No. 41413/74, where it is ~3~
l disclosed that single methyl methacrylate itself is excellent in a static extraction capacity for methacrylic acid, but shows various troubles in a dynamic state in the actual operation. The inventors of said Japanese Patent Publication No. 41413/74 attempted to improve such problems by combining a methacrylic acid ester with xylene, ethylbenzene, or xylene isomers in mixture thereof, thereby obtaining a dynamic stability of the extracting solvent. Thus, a mixing proportion of the xylene isomers is restricted to less than 50% by weight in said prior art. However, such an extracting agent of binary mixture containing the methacrylic acid ester as a main component has such a disadvantage that the distribution coefficient of acetic acid, a by-product in the oxidation step, becomes larger, and it is difficult to efficiently separate methacrylic acid and acetic acid from each other in the extraction step, as described above.
The above disadvantage due to the poor selectivity of the binary mixed extracting agent containing methacrylic acid ester as a main component for the acetic acid separation can also be overcome by the extracting solvent of the present invention, in other words by inverting the mixing proportion of the binary mixed extracting agent, that is, by adding 15 to 50%
by weight, preferably 20 to 45% by weight of methacrylic acid ester to the first component of extracting agent.
Furthermore, it seems preferable in the process steps but actually not so simple to directly use the extract ~L31~
- l solution obtained from said extracting operation as a feed for the esterification step without separating methacrylic acid from the extracting solvent, as disclosed in Japanese Patent Publications Nos. 38535/77 and 41ll13/l4.
The aqueous methacrylic acld solution obtained from the oxidation of at least one member of isobutylene, tert.butanol and methacrolein is generally dilute, that is, at a concentration of not more than 20% by weight. In order to recover methacrylic acid from such a dilute aqueous solution in a high extraction ratio, it is usual to use the extracting agent in an amount equal to or down to about two-fifths of the amount of the feedstock aqueous methacrylic acid solution.
The use of such a large amount of the extracting agent makes the methacrylic acid concentration of the extract solution as low as 15 - 50% by weight, in the most cases, 15 - 30% by weight. When such a dilute extract solution is used directly as the esterification feedstock together with an alcohol and an acid catalyst 3 a mixed phase state consisting of two phases, that is, an organic solvent phase and an aqueous phase containing the acid catalyst, in which aqueous phase most of esterification reaction proceeds, prevails in the esterification reaction zone owing to the presence of a large amount of the organic solvent. Even if the methacrylic acid ester, a reaction product, is effectively transferred into the organic phasé~ and moreover by-produced water is ~3~5~
1 distilled and removed by azeotropic boiling with the organic solvent, the methacrylic acid concentration and the alcohol concentration of the aqueous phase, in which most of the acid catalyst exists and the esterification reaction mainly proceeds, become lower because a large amount of the organic solvent properly having a high affinity toward the methacrylic acid is contained in the mixed phase~ and consequently the rate of ester formation reaction is considerably decreased.
To obtain a conversion of such a high degree as to make the recovery of unreacted methacrylic acid negligible, a very long residence time is required~ Since a large amount of the organic solvent is used as the feedstock, an extremely large reactor volume is necessary for the esterification also owing to a large amount of the feedstocks to be charged. Furthermore, a strong stirring power is required, and also special devices must be provided by using a multi-vessel type reactor. Without such devices, realization is almost impossible, and if realized, the operation would be very uneconomical.
According to the process of the present invention, a reactor volume can be reduced considerably, while effectively utilizing the effect of adding the organic solvent, by effectively recovering unreacted methacrylic acid. That is, a mixture of methacrylic acid ester and most of the first component of extracting agent used as the extracting solvent of the pre~ent invention is recovered from a methacrylic acid extract ~31fi5~
1 solution obtained in a methacrylic acid extracting æone by distillation, and recycled to the methacrylic acid extracting zone to be used for extracting methacryllc acid, and a highly concentrated me~hacrylic acid solution in the remaining first component of extracting agent is withdrawn from the bottom of the extract solution-distilling zone and used as a feedstock for the esterifica-tion. As the distillation process, any of the ordinary distillation, azeotropic distillation using an entrainer, etc. can be employed. The methacrylic acid concentration of the methacrylic acid solution in the first component of extracting agent used as the feedstoc~ for the esterification reaction is 20 to 80% by weight, preferably 30 to 60% by weight.
The reaction residence time can be considerably shortened in the esterification process of the present invention by controlling a conversion of esterification to as low as 50 - 90%, desirably 70 - 90%.
Esterification reaction of the methacrylic acid solution in the first component of extracting agent in accordance with the present invention is carried out in the presence of methanol and an acid catalyst. The acid catalyst employed includes~ for example, phosphoric acld, sulfuric acid, benzenesulfonic acid, p-toluenesulfonic acid etc., and further a cation exchange resin. Water formed during the esterification reaction is distilled off as an azeotropic mixture with a part of methyl methacrylate simultaneously formed, and the first component ~33L~i57 1 of extracting agent contained in the feedstock, whereby the acid catalyst concentration of the aqueous phase can be kept constant in the esterification zone. More specifically, such can be carried out by controlling the degree of heating or a pressure for conducting the esterification reaction. The pressure for conducting the esterification reaction is mostly the normal pressure, but can be a subatmospheric or superatmospheric pressure.
Thus, the reaction mixture can be readily separated into two liquid phases (an oil phase containing methyl methacrylate and an aqueous phase containing the acid catalyst) at the outlet of esterification zone by decantation. Since the acid catalyst concentration of the separated aqueous phase is kept constant, the aqueous phase can be reused for the esterification reaction while making up the acid catalyst loss in a very small amount after separating polymers formed during the reaction by filtràtion, etc. ~hat is, the esterification reaction can be very effectively carried out without discharging the acid catalyst to the outside of reaction system, in other words, without causing a serious environmental pollution.
It is economical to carry out the esterification reaction in a single vessel, but of course the reaction can be carried out in a plurality of vessels.
Distilled vapor from the esterification reaction is condensed in a condenser, joined with the oil phase separated by decantation at the outlet of the esterirication 6~
1 zone, and led to the successive methanol extraction step.
In a methanol extraction zone, unreacted methanol in the Joined mixture solution is separated by extraction using an aqueous solution of an inorganic salt such as ammonium sulfate, sodium chloride, etc. The raffinate oil phase containing the first component of extracting agent, methyl methacrylate and unreacted methacrylic acid, freed from most of unreacted methanol excessively added for the esterification reaction in the methanol extracting zone is further freed from low boiling materials and the methyl methacrylate by distillation, whereby a solution of unreacted methacrylic aci-d in the first component of extracting solution is recovered.
Separation of the low boiling materials and the methyl methacrylate is generally carried out in two rectification columns arranged in series, but is not restricted by an arrangement of a distillation system or its operating conditions, such as a utilization of compound columns, etc.
It may be possible to recycle the solution of unreacted methacrylic acid in the first component of extracting agent freed from low boiling materials and methyl methacrylate directly to the esterification reaction zone, but the methacrylic acid concentration of the solution is too low.
According to the process of the present invention, the solution of unreacted methacrylic acid in the first component of extracting agent is recycled to a middle ~L~IL3~L6~'7 1 stage position of the methacrylic acid extracting zone, at which the methacrylic acid concentration of the solution of unreacted methacrylic acid corresponds to the meth-acrylic acid concentration of the extract solution, and therefore extraction of methacrylic acid can be carried out at the higher methacrylic acid concentration side having a large methacrylic acid distribution coefficient, thereby decreasing an extracting agent ratio (= amount of extracting agnet/amount of feedstock aqueous solution).
This is thermally advantageous also in the successive distillation carried out for separating the extracting agent.
On the other hand, it is necessary to separate and recover methanol from the aqueous solution of inorganic salt containing the unreacted methanol, which has been excessively added in the esterification reaction.
According to the conventional process for recovering methanol, for example, as disclosed in Japanese Patent Publication No. 38535/77, methanol is extracted by an aqueous solution of inorganic salt such as sodium chloride or ammonium sulfate, the resulting extract solution is led to a middle stage of a distillation column to distill off methanol from the column top and separate from the column bottom the water in an amount corresponding to that formed by the esterification reaction in the form of an aqueous solution of the inorganic salt, and the remaining portion of the aqueous solution of the inorganic salt is recycled and used as -1~33 ~
1 the methanol-extracting solvent while supplementing it with the inorganic salt in such an amount as thrown away together with the water formed by the esterification reactlon. However, in such conventional process ror recovering methanol, a large amount of the inorganic salt must be thrown away to the outside of the system, rendering the process uneconomical and very disadvantageous in the prevention of environmental pollution.
In the methacrylic acid esterification reaction which is conducted by adding an organic solvent to the reactîon system, methacrylic acid is much distributed into the organic solvent phase, and the volume of an esterification reactor must be increased by a volume of the added organic solvent. However, an available volume of a reactor is limited, and thus it is impossible to elevate the conversion of esterification as high as possible~ and sometimes unreacted methacrylic acid remains in the reaction solution. In such a case, the unreacted methacrylic acid is recovered together with the organic solvent in the rnethyl methacrylate purification step, and is recycled to the step preceding the esterifica-tion step and used therein, as described before. Ho~ever, in the alcohol extraction step succeeding the esterifica-tion step, most of the unreacted methacrylic acid leaves the alcohol extractor together with the organic solvent and methyl methacrylate as a raffinate, but the methacrylic acid distributed into the aqueous solution of the inorganic salt as the methanol-extracting solvent ~31~S~
1 and brought together therewith is discharged from the bottom of the distillation column for recovering methanol, and a considerable amount of methacrylic acid is thrown away as a loss to the outside of the system at the same tlme when khe water formed by the esterif`ication is thrown away.
The process of the present invention can improve the above defects. That is, the aqueous solution of the inorganic salt containing extracted methanol, withdrawn from the bottom of the alcohol-extracting zone is supplied to a middle stage of a methanol distillation zone to recover methanol in the form of vapor or condensate at a high methanol concentration from the top of the distillation zone, and an aqueous solution of the inorganic salt freed from water in the amount correspond-ing to that formed by the esterification and from the bottom of the distillation zone. The aqueous solution of the inorganic salt is cooled as such and directly recycled to the methanol-extracting step and used therein.
Separation of the water formed by the esterifica-tion in question is carried out by withdrawing a portion of vapor from the distillation zone at an appropriate level, most preferably the evaporated vapor in a reboiler of the distillation zone or ascending vapor from the bottom of the distillatlon zone as a side cut, and condensing the withdrawn vapor in a condensing zone, thereby separating the water formed by the esterlfication from the aqueous solution of the inorganic salt. While, ~13~5~
1 the methacrylic acid brought at a low concentration, sueh as a few percents by welght in the aqueous solution of the inorganic acid can azeotropically boil with water in such a low concentration range, and thus is contained still at a low concentrat:lon such as a few percents by weight in water separated as a side cut.
In this respect, the process of the present invention comprises supplying the separated water containing a few percents by weight of methacrylie aeid to the aqueous phase side of the extraeting zone for extracting methacrylie aeid from the dilute aqueous solution of methacrylic acid obtained by gas phase eatalytie oxidation reaction of at least one member of isobutylene, tert.butanol and methaerolein, that is, to a position of the extraeting zone at whieh the methaerylie aeid eoneentration of the aqueous phase is almost equal to the methaerylie acid concentration of the separated water, thereby extracting and recovering the methacrylie acid contained in the separated water and throwing away the separated water together with the raffinate water of the dilute aqueous solution o~ the oxidation to the outside of the system, as described above.
The alcohol distillation can be carried out under a superatmospheric pressure to a subatmospherie pressure, and usually is carried out under the normal pressure or a little superatmospheric pressure.
When the separation of the aeid eatalyst is ineomplete, so that a very small amount of the aeid ~13~5~
1 catalyst leaks into the organic solvent phase separated at the outlet of the esterification zone, the acid catalyst can be neutralized by an alkali before the alcohol-extraction, but it is preferable to neutralize the aqueous solution of the inorganic salt as the alcohol extract solution before the alcohol distillation. When the salts formed by the neutralization or water-soluble high boiling materials extracted in the alcohol-extraction zone are accumulated in the aqueous solution of the inorganic salt as the methanol-extracting agent during the recyclic use, an appropriate amount thereof can be withdrawn from the solution from the alcohol distillation column at an appropriate time to prevent accumulation' of the undesired materials in the aqueous solution of the inorganic salt as the extracting agent.
The present process for recovering unreacted ' alcohol as described above can be obviously applied to e7~ rY // c an esterification reaction of ~P~ acid.
The present invention will be described in detail, referring to the flow diagram of Figure 2 showing one embodiment of carrying out the present invention.
The present invention is, however, not restricted thereto.
An aqueous solution of crude methacrylic acid obtained by oxidation of at least one member of isobutylene, tert.butanol and methacrolein is supplied to a column top of a,methacrylic acid extractor 2 through a line 1, and a mixed extracting agent comprising methyl methacrylate and the first component of extracting agent is supplied i5~
l thereto through a line 35. A methacryllc acid extract solution is withdrawn therefrom through a line 5 and supplied to a mi.ddle stage of an extracting agent-separating column 7. On the other hand, raffinate water is withdrawn therefrom through a line 6, and a very small amount of the extracting agent component dissolved in the raffinate water is separated into the extracting agent component and waste water in a recovery system 32.
The waste water is discharged from the system through a line 34 and the extracting agent component is recovered therefrom through a line 33.
An extracting agent comprising methyl methacrylate and the first component of extracting agent is recovered from the top of the extracting agent-separating column 7, and recycled to the methacrylic acid extractor 2 through a line 3. A solution of methacrylic acid in the first component of extracting agent from the bottom of the extracting agent-separating column 7 is supplied to an esterification reactor 18 through a line 8. Make-up sulfuric acid and methanol are added to the esterification reactor through a line 9 and a line 12, respectively.
Distillate vapor comprising methacrylic acidj water and the first component of extracting agent from the esterification reactor 18 is condensed in a condenser 17, and withdrawn through a line 13.
; ~ Bottoms from the esterification reactor ~
is withdrawn through a line 14 and separated into two li~uid phases, that is, an oil phase and an aqueous phase, 1~3~65~
1 in a decantor 15, and the aqueous phase is withdra~n therefrom through a line 16 and passed through a filter 17' to remove polymerization products, etc. from the aqueous phase, and recycled to the esterlfication reactor through a line 10 and a line 11 together with recovered methanol and the make-up sulfuric acid coming through a line 24 and the line 2, respectively.
The oil phase separated in the decantor 15 is supplied to the bottom of an alcohol extractor 21 through a line 19 together with the distillate 13 from the esterification reactor, and unreacted methanol is extracted and separated from the oil phase ~y an aqueous solution of inorganic salt circulated to the top of the alcohol extractor 21 through a line 20. The aqueous solution of the inorganic salt containing extracted unreacted methanol and also a few percents by weight of methacrylic acid is supplied to a middle stage of an alcohol distillation column 23 through a line 22 from the bottom of the alcohol extractor 21 as an extract solution. Alcohol is withdrawn from the top of the alcohol distillation column through a line 24 and reoycled to the esterification reactor. The aqueous solution of the inorganic salt freed from alcohol is recovered from the bottom of the alcohol distillation column 23 through the line 20 and recycled to the top of the alcohol extractor 21. Of course a most of the methacrylic acid brought in the feedstock supply line 22 of the alcohol distillation column 23 is '7 l recovered into the aqueous solution of the inorganic acid withdrawn from the bottom of the alcohol distillation ~3 mn/through the line 20.
Water formed by the esterification reaction entering into the line 22 through the line 19 is withdrawn in the form of vapor from a side cut line 25 at an appropriate level in the recovery section of the alcohol distillation column 23 at which the methanol entrainment is the least, condensed in a condenser 36, withdrawn therefrom through a line 37, and is supplied to a position of the methacrylic acid extractor 2, at which the methacrylic acid concentration of the raffinate aqueous phase is almost equal to the methacrylic acid concentration of the line 37, if the amount of methacrylic acid entrained in the line 37 is not negligible in view of the entire system. If the amount of methacrylic acid entrained in the line 37 is negligible in view of the entire system, the water can be directly discharged from the line 37 to the outside of the system. If too large an amount of water is withdrawn through the line 3~, the amount of water excessively withdrawn can be returned to the line 20 to adjust the concentration of the aqueous solution of the inorganic salt to a desired value.
On the other hand, the raffinate oil phase æ~
of the alcohol extractor/is withdrawn from the top of the extractor through a line 26 and supplied to a middle stage of a low boiling material-separating column 27 ~13~ 7 1 and low boiling materials such as water, methyl acetate, methanol, etc. are separated from the top of the column 27 through a line 28, and bottoms comprising methyl methacrylate, the first component of extracting agent and unreacted methacrylic acid are withdrawn from the bottom of the column 27 through a line 29. Then, the bottoms are supplled to a middle stage of a product column 30, and product methyl methacrylate is separated from the top of the column 30 through a line 31, and a solution of unreacted methacrylic acid in the first component of extracting agent is recovered from the bottom of the column 30, and recycled to a middle stage of the meth-acrylic acid extractor column 2 through a line 4 or the line 5.
There is a risk of accurnulating high boiling materials in the recycle system during the recyclic use, but such high boiling materials can be appropriately withdrawn from the lines 4, 8, etc. if necessary.
Any type of the methacrylic acid extractor column, the extracting agent-separating column, the alcohol extractor, the alcohol distillation column, the low boiling material-separating column and the product column, for example, various types usually used, can be employed in the present`invention, and the present invention is independent upon types of the extractor columns and the distillation columns.
The present invention will be described, referring to Examples, but the present invention is never ~3~5~
1 limited thereto.
Example 1 Methyl esterification reaction of methacrylic acid was carried out according to the flow diagram of Figure 2 by connecting the line 4 to a middle stage of the extractor column 2 without any supply of sulfuric acid from the line 9. The esterification reactor 18 was a cylindrical glass flask, and other apparatuses were operated according to conditions of Table 1.
Compositions and flow rates at each point in the flow diagram of Figure 2 were as given in Table 2.
5~
~ _ _ _ _ ,c~ tn W c~ ~ O
t~> C. (U Ei ~d ~n c~ ,~
~i X ~h t~J c~-rl ~U o ~ o o ot~
:~ t~) r-l td r-l O X Ei E~ t~l ~O O
O r~ td O~ bO X t~ ~; td r-l O I
h O ~ t) rl td rl r~
~ t~) __ ~ _ __ bO I ~ .
S~ 1 ~0 ~C ~ tl) r~ td-r7 t~,¦rcl ,~u~ td (U O
~-r~ ~U ~~ u~
O ~ td ~ ~~ tl~ td R tU h E~c) r~td r-l c~ ~ ~1 ~ ~_ O ~1 ~ td ~ td O~ ~0O to ~ r-l O
3 td P~ r~P~ c~ X E~O r~
~0 ~ ~ tO~ ~-CJ r~ ~ _ __ __ I ~ ~
t~ t~J tn ~ o ,~,~ ~ c~tnbO c~ ~U
Orl~ ~ X :~ ~ cd O-r~ O O O O O O t~J
O ~-rl :~ tO r-ltd r~l XX ~ ~3 1:~ r-l ~ c~
~ r-l td O~ b0rl O ~; cd r~ ~ O P~ O ~ cd rl 'C ~J O ~,tr)~ _ _ ~ C~ ~ ~R ~a r~ O _ O cn .
O ~ rl ~ O l cd S O ~ O ,c~r-l O ~ C~
O cd r-l¦ cd cd ~~ ,~ tH tl~ ~ o LS~ ~ o I, o ~ c~l Iu~ ~ ~,~ a) h ~ td ~ cr r-l ~ r-l ~ r~cd 5) ~U Cd ~ C-- o X ~ C O ~1~ ~ ~\. t~J
~U P~ ~ o u~ ~ _ _ r~ _ _ ~ ~ t~ __ _ (u ~, ,7 ~ ~ td tU O
.~1 ~ ~ ~U ~ ~ ~
Cd o_, cd E~ ~ ::~ ~ cd C~J
E-l cd a~ ~ ~ O r-l ~ ~d S: ^-rl ~ t-- O O Ll~
c~O Cd r~ cd Ocd ,~ o cn ~d c~ 1S~
cd Q~ O P~ o ~C ~0 ~o _ ~.,7.'~
cd r-l . O tU .
o o ~a P ~:, ,~ h c~ O cn ~U cd O ~ ~ ~ cd ~q ?~
c~ r l ~ O l~ ~1 td ~ 1 O
o o cd cd ~ ~ r-l O u~ ~D ~rl cd ~ Ll~
cd cd ~ rl ~U ~H :., ~ ~1 ~U ~ ~U
,5~ r~ 1 cd ~U h cd ~ r r~
X O ~ ~ ' ~ t I ~ cr~
X ~ ~U o u~ ~ __ ~ -- E E E
::~ ~ o . tH O ~U
O ~ ~ l ~ bD . cd ,~ o ~a C ~u ~ ~
~ h cd ~ bO ~rl h cd ~ c~
~ ~ ~
h S:: ~ ~ ~ h ~ O ~U O 5 ~ X
h ~ rl ~d u O a~ ~U ~ ~ ~ ~ tD ::; O
~U ~U ca ~: h u~ ~ ~ o C~ ~ O ~ ~ ~ ,-1 _ o ~u tu ~ E3 _ o o o t) ,~ cd tH ~
cd O cd Q~ h O ~U O rl ~U ~U ~ O ~ :~ Cd E~ ~: o~ o ~ m ~ c~ ~ cq ~ ~ c~ ~ ~: h _ _ _ ___ _ U~ . . . l . . l , l CO
~ ~ _~ =r ___ ~ _ u~
~r o . . l . l l l l ~r ~ U~ ~ ~ ~
. _ ____ __ _ ~o l . . o . . . l l U~
U~ ~ o o o o _ _ o u~ =r U~ l . l l l . .
o U~
a~
_ . _ m ~ ~D co ~r ~r ~ l . l . . . l l c~
_ _ o o _ o . l l . l l . l . l o~
_ __ U~ ~D L~ ~r C;~ l . o o . . .
~ ~ ~1 . ) ~ ~ ~o a)' __ ~ o u~ ~ _ ~
. L- ~ ~D ~O O O
~D l l . . . . . l . J
r-l ~1 ~1 O N ~rl O
E~ ~ ~r ~ . ~
.~ __ l l 1~ _ _ O l l ~ : .
_ u~ ~r oo ~ In-o~ O . . l . l l l l O
. ~O O ~I ~1 'O ~, . ~ __ ~
~ ~ O ~ ~ L
Ir~. . . l . . . l l l L~
O rl ~ ~C) O ~1 ~ l O O ~ l ,0. _ ~ __ ___ l 0 I_ N . O
L~ O LS~ O~
~1 . . l l .
_ _ ~ _ _~ _ ~J ~1 ~ ' C~^ _ _ _ _ . C) ~_ ~1 O
;Z td ~ h i: ~ ~ ~) ~ t~ ,_ O ~ ~ ~ rl S
c~ ~ c~ _r~ ~d ~1~ O ~ . 1:: ~ ' ~ ~_ h--a~ ~ ~d:~, I ~1 ~ ~ ~ S:: ~ ~ ~ td ~ ~ ~ ~ :S
~_ ~: ~ ~ ~ ~ ~ J~ S ~ o 3: ~ ~ o ~ :~ ~ ~ ~
_ ~ ~ _, ~ ~ ~ ~ ~ ~_ ~ ~ ~ O
c~ ~ c~a) a) c~ a) s~:~ ~ ~ ~ ~ ~ c~
¢ ~: ~ ~ ~ ~ ~ ~ X _ :~: ¢ ~ u~ ~d ~4 .
~13~L~S7 1 ~xample 2 Methyl esterification reaction of methacrylic acid was carried out in the same manner as in Example 1 except that cumene was used in place of xylene and the pressure of the alcohol distillation column 23 was changed to 50 rnmHg and that of the low boiling material-separating column 27 to 60 mmHg to make the temperatures of the respective distillation columns equal to those in Example 1. Compositions at each point were sub-stantially identical with those of Example 1.
Example 3 Methyl esterification reaction of methacrylicacid was carried out in the same manner as in Example 1, except that a mixed organic solvent consisting of 57%
by weight of xylene and 43% by weight of ethylbenzene was used in place of xylene. Compositions at each point were substantially identical with those of Example 2.
Example 4 esterification reaction of methacrylic acid was carried out in the same manner as in Example 1, except that ethanol was used in place of methanol and a mixed solvent of methyl methacrylate and xylene was used as the extracting solvent for methacrylic acid.
Compositions at each point in the flow diagram are shown in Table 3.
~3~
~o _ 0 _ __ _ L~ . . . l . . l l l ~o ~ ~ __ N _. __ _ ~O
~ l . . l . l l l l O
N C~ O O
__. , ___ _ _ ~O O~ ~ ~ Ln ~ O
~O ~ . . . . . . l l ~
N _ ~ N O _ . O O ~1 _ l _ ~ N ~ cr~
N l N l l l ~ O l l 3 _ __ _~
O \~ O 3 .~1 3N ll 3 l O r~ 3 l l 3 _ ,~ a~ o o O l . l l l . l . l O
N N N lr~ L~
~ _ __ 0 ~ ~
Q~ ~ ~ oO ~ ~ o~ ~
~1 ~ ~ . . l . . . ~ l N
,D~1 O ~ ~1 ~1 ~D ~Y) ~
N =~ N ~1 E' __ __ o ~D l l . . . . . l .
_ ~1 W O ~ N O
rl 1 3 ~ /_ 1 l O I_ l O
00 . . l ., . l l l l ~fl O ~ O ~o ~1 U~ ~ W ~ ~ C~
. . . l . .
O o~ O ~c) O ~ ~1 t~ O ~r7 ~1 3 l . . l . l l l l 0 r-l ~1 _ CI:) t-~1 Ir~ O l l l N l l I . ~1 .
^ C~^ I ,_ _~ ~ ,_ _~ ,_ .
. o ~ ~ . . . . . . . a~ ~
o ~ ~ :>,~ a~ a) ~ ~ ~ ~ ~ E~ ~ c) ~ ~ 5:
Z:3: ~ 3: ~ Q~ ~: 3: 3: ~ 3: ~ ~ 3 ~ ~
c) ~ c)~ td`-- ~ ~ a~ ~-- ~_ o ~-- ~ ~ ~ ~_ ~ ~o td ~ ~1 ~ ~ ~ ~ ~ ~ ~ ~ _~
~:: ~ ~ ~ ~ , ~ J~ ~ a) ~ o ~ c~ ~o :~
a) ~ rl ~ ~ ~ a~ ~ ~ ~ ~ ,~ ~1 rl O
c) ~ c) ~ c) ~ c) :>, ~ ~ ~ ~ ~ c) ~
:~ ~d ~ ~ ~ ~C 3 ~,3 ~: ~ c~
1 This invention relates to an improved process for continuously synthesizlng methyl methacrylate or ethyl methacry]ate, and a process for recovering unreacted methacrylic acid and unreacted alcohol.
To avoid a complicated description, description will be made below only of a process for methylesterifi-cation of methacrylic acid, but quite the same thing can be applied to a process for ethylesterification of methacrylie acid unless otherwise speeifically mentioned.
Heretofore, methyl methacrylate has been ~a . c~r~c~h4~1~;n produced according to acetone~ t~ process using acetone and hydrogen cyanide as starting materials, but the process has not been satisfactory as an industrial process for producing methyl methacrylate owing to the use of highly toxic hydrogen cyanide, and production of a large amount of ammonium sulfate as a by-product, ete. Recently, another process for producing methyl methacrylate by obtaining methaerylic aeid through a gas phase catalytic oxidation of isobutylene, etc., and then by esterifying the resulting methacrylie acid by methanol has been proposed as a substitute for the acetone cyanhydrin process. The methacrylic aeid produet that ean be obtained through the oxidation reaetion of at least one member of isobutylene, tert.butanol and methacrolein is in a form of 10 - 50wt.% aqueous solution \~s ~3~L~;S~
1 containing by-produced acetic acid and a small amount of other substances. It is known that the methacrylic acid is extracted into an organic solvent from the aqueous solution and methacrylic acid is then recovered from the solvent by distillation. In selecting an extractlng solvent, a distribution coefficient of methacrylic acid is especially important. The distributlon coefficient is defined as follows: -Concentration of methacrylic acid Distribution = in solvent (wt.%) coefficient Concentration of methacryllc acid in aqueous layer (wt.%) A large distribution coefficient means that methacrylic acid can be correspondingly efficiently extracted. On the other hand, acetic acid by-produced in the oxidation step is an organic acid similar to methacrylic acid, and often has a similar extraction property for an organic solvent to that of methacrylic acid. Thus, when a solvent is selected only in view of the distribution coefficient, acetic acid is also extracted together with methacrylic acid, and acetic acid reacts with methanol in the esterification step succeeding the extraction step, so that methyl acetate is formed. That is, methanol is lost, and thus acetic acid must be removed to less than some concentration by separation before the esterification step.
Usually, methacrylic acid and acetic acid are separated from each other by distillation, but such ~13~57 1 usual process is disadvantageous in the heat econo~y and the simplification of steps. Thus, it is advantageous to properly se].ect an extracting solvent for methacrylic acid, and selectively separate methacrylic acid into the extracting solvent, while separating most of acetic acid into a raffinate aqueous phase in the methacrylic acid extraction step. It is known that the solvent having a high distribution coefficient of methacrylic acid and a lower distribution coefficient of acetic acid than 1.0 and being capable of separating acetic acid and methacrylic acid from each other in the methacrylic acid extraction step is a solvent system . of ethylbenzene and/or xylene (Japanese Patent Publication l~ 3 ~3-~
No. ~ ). On the other hand, it is also known that 15 hydrocarbons such as heptane, toluene and xylene have a low extraction efficiency for an aqueous methacrylic acid solution of low concentration (Japanese Patent Publication No. 41413/74).
As a result of extensive studies on the solvent 20 system of ethylbenzene and/or xylene, the present J
inventors have confirmed that said solvent system has a fatal defect in an extracting solvent for methacrylic acid such that their methacrylic acid extraction ratio never exceeds some limit, and thus cannot be applied 25 industrially, and have found that such defect can be overcome and an industrially applicable extraction can be attained by the use of an extracting solvent prepared by adding 15 to 50% by we~ght of a methacrylic ~3~5'7 1 acid ester to a water-insoluble, inert organic solvent having a boiling point of higher than 120C, such as ethylbenzene, xylene, cumene, cymene, etc. (which will be hereinafter referred to as a first component of extracting agent), and further that unreacted alcohol and methacrylic acid ln the esterification step can be efficiently recovered by using such extracting solvent and improving each step in the production process of the methacrylic acid ester.
The present invention provides a process for preparing a methacrylic acid ester from a feedstock dilute aqueous solution of methacrylic acid containing by-produced acetic acid and others, obtained by gas phase catalytic oxidation of at least one member of isobutylene, tert.butyl alcohol and methacrolein, which comprises (1) subjecting said feedstock to extraction in a rnethacrylic acid extracting zone (a) using an extracting solvent prepared by adding to a water-insoluble, inert organic solvent having a boiling 2Q point above 120C, 15 - 50% by weight of a methacrylic acid ester, (2) separatin~ the resulting extract solution into a mixed solvent of the methacrylic acid ester and most of the organic solvent and a methacrylic acid solution in the remaining organic solvent by distillation in an extracting solvent-separating zone (b), (3) subjec~-ing the resulting organic solvent solution containing methacrylic acid to esterification reaction in the presence of an acid catalyst together with an excess ~3~S7 1 amount of an alcohol having a boiling point below 100C
ln an esterification reaction zone (c), while removing water formed by the esterification reaction by azeotropic boiling wi.th the organic solvent together with a part of the forrned methacrylic acid ester as a distillate solution, thereby making an acid catalyst concentration of the remaining reaction solution constant, (4) separating the reaction solution discharged from the bottom of the esterification reaction zone (c) into an organic solvent layer containing the methacrylic acid ester and an aqueous layer containing the acid catalyst in a decanting zone (d), (5) recycling the aqueous layer at the constant acid catalyst concentration to the esterification reaction zone (c) after separating by-produced polymerization 15 products therefrom, (6) ~oining the organic solvent i~
layer with the distillate solution in step (3), (7) subject-ing the resulting mixture to alcohol extraction using an aqueous solution of àn inorganic salt in an alcohol extraction zone (e) to recover unreacted alcohol, (8) recycling the recovered alcohol to the esterification reaction zone (c), (9) separating low boiling materials from a raffinate organic solvent phase leaving the top of the alcohol extraction zone (e) by distillation, (10) separating the raffinate organic solvent phase freed from the low boiling materials into a high purity methacrylic acid ester product and the organic solvent containing unreacted methacrylic acid, and (11) recycling the organic solvent containing methacrylic acid to ~3~i57 1 an appropriate position of the methacrylic acid-extracting zone (a) in step (1) or to a feedstock to be separated in step (2).
The present invention will be described in detail, referring to the accompanying drawings.
Figure 1 is a diagram showing relations between a methacrylic acid concentration in a feedstock aqueous solution and a methacrylic acid distribution coefficiént by the first component of extracting agent alone or the present extracting solvent comprising the first component of extracting agent and methacrylic acid ester.
Figure 2 is a flow diagram showing one embodiment of the present process.
The present inventors have made a detailed study of how the distribution coefficient of methacrylic acid is changed against the methacrylic acid concentration of feedstock aqueous solution when methacrylic acid ester is added or not to the solvent system of ethyl-benzene and/or xylene, and the results are shown in Figure 1. It is seen from Figure 1 that in the case of the solvent system comprising ethylbenzene and/or xylene alone, the distribution coefficient of methacrylic acid is extremely lowered, if the methacrylic acid concentration of the feedstock aqueous solution is below 3% by weight, and particularly the distribution coefficient approaches 1.0, if the methacrylic acid concentration of the feedstock aqueous solution is below 2% by weight, so that the extracting capacity for methacrylic acid ~3~
1 is almost lost and a function as the extracting agent is not fulfilled. This means that, so far as the extraction operation is continued, there are always locations, at whlch the methacryllc acid concentration is lowered in the aqueous solution, in an extractor, irrespective of the methacrylic acid concentration of a feedstock aqueous solution, and thus there is ultimately a limit to the methacrylic acid extraction ratio, when the solvent system comprising ethylbenzene and/or xylene alone is used for extracting methacrylic acid. For example, when the methacrylic acid concentration of the feedstock ;
aqueous solution is 20% by weight and an equal amount of an extracting agent is used to that of the feedstock aqueous solution, about 2% by weight of methacrylic acid remains in the raffinate aqueous layer, and thus an upper limit of the extraction ratio will be about 90%.
That is, the methacrylic acid loss is industrially so large that an industrial significance is lost, even if the successive steps could efficiently be carried out.
On the other hand, it is seen from Fig. 1 that the extracting solvent of- the present invention attains a satisfactory extraction capacity even in a low concentration range of methacrylic acid in the ~eedstock aqueous solution.
An extracting solvent comprising a combination of a methacrylic acid ester and the solvent system of ethylbenzene and/or xylene has been already disclosed in Japanese Patent Publication No. 41413/74, where it is ~3~
l disclosed that single methyl methacrylate itself is excellent in a static extraction capacity for methacrylic acid, but shows various troubles in a dynamic state in the actual operation. The inventors of said Japanese Patent Publication No. 41413/74 attempted to improve such problems by combining a methacrylic acid ester with xylene, ethylbenzene, or xylene isomers in mixture thereof, thereby obtaining a dynamic stability of the extracting solvent. Thus, a mixing proportion of the xylene isomers is restricted to less than 50% by weight in said prior art. However, such an extracting agent of binary mixture containing the methacrylic acid ester as a main component has such a disadvantage that the distribution coefficient of acetic acid, a by-product in the oxidation step, becomes larger, and it is difficult to efficiently separate methacrylic acid and acetic acid from each other in the extraction step, as described above.
The above disadvantage due to the poor selectivity of the binary mixed extracting agent containing methacrylic acid ester as a main component for the acetic acid separation can also be overcome by the extracting solvent of the present invention, in other words by inverting the mixing proportion of the binary mixed extracting agent, that is, by adding 15 to 50%
by weight, preferably 20 to 45% by weight of methacrylic acid ester to the first component of extracting agent.
Furthermore, it seems preferable in the process steps but actually not so simple to directly use the extract ~L31~
- l solution obtained from said extracting operation as a feed for the esterification step without separating methacrylic acid from the extracting solvent, as disclosed in Japanese Patent Publications Nos. 38535/77 and 41ll13/l4.
The aqueous methacrylic acld solution obtained from the oxidation of at least one member of isobutylene, tert.butanol and methacrolein is generally dilute, that is, at a concentration of not more than 20% by weight. In order to recover methacrylic acid from such a dilute aqueous solution in a high extraction ratio, it is usual to use the extracting agent in an amount equal to or down to about two-fifths of the amount of the feedstock aqueous methacrylic acid solution.
The use of such a large amount of the extracting agent makes the methacrylic acid concentration of the extract solution as low as 15 - 50% by weight, in the most cases, 15 - 30% by weight. When such a dilute extract solution is used directly as the esterification feedstock together with an alcohol and an acid catalyst 3 a mixed phase state consisting of two phases, that is, an organic solvent phase and an aqueous phase containing the acid catalyst, in which aqueous phase most of esterification reaction proceeds, prevails in the esterification reaction zone owing to the presence of a large amount of the organic solvent. Even if the methacrylic acid ester, a reaction product, is effectively transferred into the organic phasé~ and moreover by-produced water is ~3~5~
1 distilled and removed by azeotropic boiling with the organic solvent, the methacrylic acid concentration and the alcohol concentration of the aqueous phase, in which most of the acid catalyst exists and the esterification reaction mainly proceeds, become lower because a large amount of the organic solvent properly having a high affinity toward the methacrylic acid is contained in the mixed phase~ and consequently the rate of ester formation reaction is considerably decreased.
To obtain a conversion of such a high degree as to make the recovery of unreacted methacrylic acid negligible, a very long residence time is required~ Since a large amount of the organic solvent is used as the feedstock, an extremely large reactor volume is necessary for the esterification also owing to a large amount of the feedstocks to be charged. Furthermore, a strong stirring power is required, and also special devices must be provided by using a multi-vessel type reactor. Without such devices, realization is almost impossible, and if realized, the operation would be very uneconomical.
According to the process of the present invention, a reactor volume can be reduced considerably, while effectively utilizing the effect of adding the organic solvent, by effectively recovering unreacted methacrylic acid. That is, a mixture of methacrylic acid ester and most of the first component of extracting agent used as the extracting solvent of the pre~ent invention is recovered from a methacrylic acid extract ~31fi5~
1 solution obtained in a methacrylic acid extracting æone by distillation, and recycled to the methacrylic acid extracting zone to be used for extracting methacryllc acid, and a highly concentrated me~hacrylic acid solution in the remaining first component of extracting agent is withdrawn from the bottom of the extract solution-distilling zone and used as a feedstock for the esterifica-tion. As the distillation process, any of the ordinary distillation, azeotropic distillation using an entrainer, etc. can be employed. The methacrylic acid concentration of the methacrylic acid solution in the first component of extracting agent used as the feedstoc~ for the esterification reaction is 20 to 80% by weight, preferably 30 to 60% by weight.
The reaction residence time can be considerably shortened in the esterification process of the present invention by controlling a conversion of esterification to as low as 50 - 90%, desirably 70 - 90%.
Esterification reaction of the methacrylic acid solution in the first component of extracting agent in accordance with the present invention is carried out in the presence of methanol and an acid catalyst. The acid catalyst employed includes~ for example, phosphoric acld, sulfuric acid, benzenesulfonic acid, p-toluenesulfonic acid etc., and further a cation exchange resin. Water formed during the esterification reaction is distilled off as an azeotropic mixture with a part of methyl methacrylate simultaneously formed, and the first component ~33L~i57 1 of extracting agent contained in the feedstock, whereby the acid catalyst concentration of the aqueous phase can be kept constant in the esterification zone. More specifically, such can be carried out by controlling the degree of heating or a pressure for conducting the esterification reaction. The pressure for conducting the esterification reaction is mostly the normal pressure, but can be a subatmospheric or superatmospheric pressure.
Thus, the reaction mixture can be readily separated into two liquid phases (an oil phase containing methyl methacrylate and an aqueous phase containing the acid catalyst) at the outlet of esterification zone by decantation. Since the acid catalyst concentration of the separated aqueous phase is kept constant, the aqueous phase can be reused for the esterification reaction while making up the acid catalyst loss in a very small amount after separating polymers formed during the reaction by filtràtion, etc. ~hat is, the esterification reaction can be very effectively carried out without discharging the acid catalyst to the outside of reaction system, in other words, without causing a serious environmental pollution.
It is economical to carry out the esterification reaction in a single vessel, but of course the reaction can be carried out in a plurality of vessels.
Distilled vapor from the esterification reaction is condensed in a condenser, joined with the oil phase separated by decantation at the outlet of the esterirication 6~
1 zone, and led to the successive methanol extraction step.
In a methanol extraction zone, unreacted methanol in the Joined mixture solution is separated by extraction using an aqueous solution of an inorganic salt such as ammonium sulfate, sodium chloride, etc. The raffinate oil phase containing the first component of extracting agent, methyl methacrylate and unreacted methacrylic acid, freed from most of unreacted methanol excessively added for the esterification reaction in the methanol extracting zone is further freed from low boiling materials and the methyl methacrylate by distillation, whereby a solution of unreacted methacrylic aci-d in the first component of extracting solution is recovered.
Separation of the low boiling materials and the methyl methacrylate is generally carried out in two rectification columns arranged in series, but is not restricted by an arrangement of a distillation system or its operating conditions, such as a utilization of compound columns, etc.
It may be possible to recycle the solution of unreacted methacrylic acid in the first component of extracting agent freed from low boiling materials and methyl methacrylate directly to the esterification reaction zone, but the methacrylic acid concentration of the solution is too low.
According to the process of the present invention, the solution of unreacted methacrylic acid in the first component of extracting agent is recycled to a middle ~L~IL3~L6~'7 1 stage position of the methacrylic acid extracting zone, at which the methacrylic acid concentration of the solution of unreacted methacrylic acid corresponds to the meth-acrylic acid concentration of the extract solution, and therefore extraction of methacrylic acid can be carried out at the higher methacrylic acid concentration side having a large methacrylic acid distribution coefficient, thereby decreasing an extracting agent ratio (= amount of extracting agnet/amount of feedstock aqueous solution).
This is thermally advantageous also in the successive distillation carried out for separating the extracting agent.
On the other hand, it is necessary to separate and recover methanol from the aqueous solution of inorganic salt containing the unreacted methanol, which has been excessively added in the esterification reaction.
According to the conventional process for recovering methanol, for example, as disclosed in Japanese Patent Publication No. 38535/77, methanol is extracted by an aqueous solution of inorganic salt such as sodium chloride or ammonium sulfate, the resulting extract solution is led to a middle stage of a distillation column to distill off methanol from the column top and separate from the column bottom the water in an amount corresponding to that formed by the esterification reaction in the form of an aqueous solution of the inorganic salt, and the remaining portion of the aqueous solution of the inorganic salt is recycled and used as -1~33 ~
1 the methanol-extracting solvent while supplementing it with the inorganic salt in such an amount as thrown away together with the water formed by the esterification reactlon. However, in such conventional process ror recovering methanol, a large amount of the inorganic salt must be thrown away to the outside of the system, rendering the process uneconomical and very disadvantageous in the prevention of environmental pollution.
In the methacrylic acid esterification reaction which is conducted by adding an organic solvent to the reactîon system, methacrylic acid is much distributed into the organic solvent phase, and the volume of an esterification reactor must be increased by a volume of the added organic solvent. However, an available volume of a reactor is limited, and thus it is impossible to elevate the conversion of esterification as high as possible~ and sometimes unreacted methacrylic acid remains in the reaction solution. In such a case, the unreacted methacrylic acid is recovered together with the organic solvent in the rnethyl methacrylate purification step, and is recycled to the step preceding the esterifica-tion step and used therein, as described before. Ho~ever, in the alcohol extraction step succeeding the esterifica-tion step, most of the unreacted methacrylic acid leaves the alcohol extractor together with the organic solvent and methyl methacrylate as a raffinate, but the methacrylic acid distributed into the aqueous solution of the inorganic salt as the methanol-extracting solvent ~31~S~
1 and brought together therewith is discharged from the bottom of the distillation column for recovering methanol, and a considerable amount of methacrylic acid is thrown away as a loss to the outside of the system at the same tlme when khe water formed by the esterif`ication is thrown away.
The process of the present invention can improve the above defects. That is, the aqueous solution of the inorganic salt containing extracted methanol, withdrawn from the bottom of the alcohol-extracting zone is supplied to a middle stage of a methanol distillation zone to recover methanol in the form of vapor or condensate at a high methanol concentration from the top of the distillation zone, and an aqueous solution of the inorganic salt freed from water in the amount correspond-ing to that formed by the esterification and from the bottom of the distillation zone. The aqueous solution of the inorganic salt is cooled as such and directly recycled to the methanol-extracting step and used therein.
Separation of the water formed by the esterifica-tion in question is carried out by withdrawing a portion of vapor from the distillation zone at an appropriate level, most preferably the evaporated vapor in a reboiler of the distillation zone or ascending vapor from the bottom of the distillatlon zone as a side cut, and condensing the withdrawn vapor in a condensing zone, thereby separating the water formed by the esterlfication from the aqueous solution of the inorganic salt. While, ~13~5~
1 the methacrylic acid brought at a low concentration, sueh as a few percents by welght in the aqueous solution of the inorganic acid can azeotropically boil with water in such a low concentration range, and thus is contained still at a low concentrat:lon such as a few percents by weight in water separated as a side cut.
In this respect, the process of the present invention comprises supplying the separated water containing a few percents by weight of methacrylie aeid to the aqueous phase side of the extraeting zone for extracting methacrylie aeid from the dilute aqueous solution of methacrylic acid obtained by gas phase eatalytie oxidation reaction of at least one member of isobutylene, tert.butanol and methaerolein, that is, to a position of the extraeting zone at whieh the methaerylie aeid eoneentration of the aqueous phase is almost equal to the methaerylie acid concentration of the separated water, thereby extracting and recovering the methacrylie acid contained in the separated water and throwing away the separated water together with the raffinate water of the dilute aqueous solution o~ the oxidation to the outside of the system, as described above.
The alcohol distillation can be carried out under a superatmospheric pressure to a subatmospherie pressure, and usually is carried out under the normal pressure or a little superatmospheric pressure.
When the separation of the aeid eatalyst is ineomplete, so that a very small amount of the aeid ~13~5~
1 catalyst leaks into the organic solvent phase separated at the outlet of the esterification zone, the acid catalyst can be neutralized by an alkali before the alcohol-extraction, but it is preferable to neutralize the aqueous solution of the inorganic salt as the alcohol extract solution before the alcohol distillation. When the salts formed by the neutralization or water-soluble high boiling materials extracted in the alcohol-extraction zone are accumulated in the aqueous solution of the inorganic salt as the methanol-extracting agent during the recyclic use, an appropriate amount thereof can be withdrawn from the solution from the alcohol distillation column at an appropriate time to prevent accumulation' of the undesired materials in the aqueous solution of the inorganic salt as the extracting agent.
The present process for recovering unreacted ' alcohol as described above can be obviously applied to e7~ rY // c an esterification reaction of ~P~ acid.
The present invention will be described in detail, referring to the flow diagram of Figure 2 showing one embodiment of carrying out the present invention.
The present invention is, however, not restricted thereto.
An aqueous solution of crude methacrylic acid obtained by oxidation of at least one member of isobutylene, tert.butanol and methacrolein is supplied to a column top of a,methacrylic acid extractor 2 through a line 1, and a mixed extracting agent comprising methyl methacrylate and the first component of extracting agent is supplied i5~
l thereto through a line 35. A methacryllc acid extract solution is withdrawn therefrom through a line 5 and supplied to a mi.ddle stage of an extracting agent-separating column 7. On the other hand, raffinate water is withdrawn therefrom through a line 6, and a very small amount of the extracting agent component dissolved in the raffinate water is separated into the extracting agent component and waste water in a recovery system 32.
The waste water is discharged from the system through a line 34 and the extracting agent component is recovered therefrom through a line 33.
An extracting agent comprising methyl methacrylate and the first component of extracting agent is recovered from the top of the extracting agent-separating column 7, and recycled to the methacrylic acid extractor 2 through a line 3. A solution of methacrylic acid in the first component of extracting agent from the bottom of the extracting agent-separating column 7 is supplied to an esterification reactor 18 through a line 8. Make-up sulfuric acid and methanol are added to the esterification reactor through a line 9 and a line 12, respectively.
Distillate vapor comprising methacrylic acidj water and the first component of extracting agent from the esterification reactor 18 is condensed in a condenser 17, and withdrawn through a line 13.
; ~ Bottoms from the esterification reactor ~
is withdrawn through a line 14 and separated into two li~uid phases, that is, an oil phase and an aqueous phase, 1~3~65~
1 in a decantor 15, and the aqueous phase is withdra~n therefrom through a line 16 and passed through a filter 17' to remove polymerization products, etc. from the aqueous phase, and recycled to the esterlfication reactor through a line 10 and a line 11 together with recovered methanol and the make-up sulfuric acid coming through a line 24 and the line 2, respectively.
The oil phase separated in the decantor 15 is supplied to the bottom of an alcohol extractor 21 through a line 19 together with the distillate 13 from the esterification reactor, and unreacted methanol is extracted and separated from the oil phase ~y an aqueous solution of inorganic salt circulated to the top of the alcohol extractor 21 through a line 20. The aqueous solution of the inorganic salt containing extracted unreacted methanol and also a few percents by weight of methacrylic acid is supplied to a middle stage of an alcohol distillation column 23 through a line 22 from the bottom of the alcohol extractor 21 as an extract solution. Alcohol is withdrawn from the top of the alcohol distillation column through a line 24 and reoycled to the esterification reactor. The aqueous solution of the inorganic salt freed from alcohol is recovered from the bottom of the alcohol distillation column 23 through the line 20 and recycled to the top of the alcohol extractor 21. Of course a most of the methacrylic acid brought in the feedstock supply line 22 of the alcohol distillation column 23 is '7 l recovered into the aqueous solution of the inorganic acid withdrawn from the bottom of the alcohol distillation ~3 mn/through the line 20.
Water formed by the esterification reaction entering into the line 22 through the line 19 is withdrawn in the form of vapor from a side cut line 25 at an appropriate level in the recovery section of the alcohol distillation column 23 at which the methanol entrainment is the least, condensed in a condenser 36, withdrawn therefrom through a line 37, and is supplied to a position of the methacrylic acid extractor 2, at which the methacrylic acid concentration of the raffinate aqueous phase is almost equal to the methacrylic acid concentration of the line 37, if the amount of methacrylic acid entrained in the line 37 is not negligible in view of the entire system. If the amount of methacrylic acid entrained in the line 37 is negligible in view of the entire system, the water can be directly discharged from the line 37 to the outside of the system. If too large an amount of water is withdrawn through the line 3~, the amount of water excessively withdrawn can be returned to the line 20 to adjust the concentration of the aqueous solution of the inorganic salt to a desired value.
On the other hand, the raffinate oil phase æ~
of the alcohol extractor/is withdrawn from the top of the extractor through a line 26 and supplied to a middle stage of a low boiling material-separating column 27 ~13~ 7 1 and low boiling materials such as water, methyl acetate, methanol, etc. are separated from the top of the column 27 through a line 28, and bottoms comprising methyl methacrylate, the first component of extracting agent and unreacted methacrylic acid are withdrawn from the bottom of the column 27 through a line 29. Then, the bottoms are supplled to a middle stage of a product column 30, and product methyl methacrylate is separated from the top of the column 30 through a line 31, and a solution of unreacted methacrylic acid in the first component of extracting agent is recovered from the bottom of the column 30, and recycled to a middle stage of the meth-acrylic acid extractor column 2 through a line 4 or the line 5.
There is a risk of accurnulating high boiling materials in the recycle system during the recyclic use, but such high boiling materials can be appropriately withdrawn from the lines 4, 8, etc. if necessary.
Any type of the methacrylic acid extractor column, the extracting agent-separating column, the alcohol extractor, the alcohol distillation column, the low boiling material-separating column and the product column, for example, various types usually used, can be employed in the present`invention, and the present invention is independent upon types of the extractor columns and the distillation columns.
The present invention will be described, referring to Examples, but the present invention is never ~3~5~
1 limited thereto.
Example 1 Methyl esterification reaction of methacrylic acid was carried out according to the flow diagram of Figure 2 by connecting the line 4 to a middle stage of the extractor column 2 without any supply of sulfuric acid from the line 9. The esterification reactor 18 was a cylindrical glass flask, and other apparatuses were operated according to conditions of Table 1.
Compositions and flow rates at each point in the flow diagram of Figure 2 were as given in Table 2.
5~
~ _ _ _ _ ,c~ tn W c~ ~ O
t~> C. (U Ei ~d ~n c~ ,~
~i X ~h t~J c~-rl ~U o ~ o o ot~
:~ t~) r-l td r-l O X Ei E~ t~l ~O O
O r~ td O~ bO X t~ ~; td r-l O I
h O ~ t) rl td rl r~
~ t~) __ ~ _ __ bO I ~ .
S~ 1 ~0 ~C ~ tl) r~ td-r7 t~,¦rcl ,~u~ td (U O
~-r~ ~U ~~ u~
O ~ td ~ ~~ tl~ td R tU h E~c) r~td r-l c~ ~ ~1 ~ ~_ O ~1 ~ td ~ td O~ ~0O to ~ r-l O
3 td P~ r~P~ c~ X E~O r~
~0 ~ ~ tO~ ~-CJ r~ ~ _ __ __ I ~ ~
t~ t~J tn ~ o ,~,~ ~ c~tnbO c~ ~U
Orl~ ~ X :~ ~ cd O-r~ O O O O O O t~J
O ~-rl :~ tO r-ltd r~l XX ~ ~3 1:~ r-l ~ c~
~ r-l td O~ b0rl O ~; cd r~ ~ O P~ O ~ cd rl 'C ~J O ~,tr)~ _ _ ~ C~ ~ ~R ~a r~ O _ O cn .
O ~ rl ~ O l cd S O ~ O ,c~r-l O ~ C~
O cd r-l¦ cd cd ~~ ,~ tH tl~ ~ o LS~ ~ o I, o ~ c~l Iu~ ~ ~,~ a) h ~ td ~ cr r-l ~ r-l ~ r~cd 5) ~U Cd ~ C-- o X ~ C O ~1~ ~ ~\. t~J
~U P~ ~ o u~ ~ _ _ r~ _ _ ~ ~ t~ __ _ (u ~, ,7 ~ ~ td tU O
.~1 ~ ~ ~U ~ ~ ~
Cd o_, cd E~ ~ ::~ ~ cd C~J
E-l cd a~ ~ ~ O r-l ~ ~d S: ^-rl ~ t-- O O Ll~
c~O Cd r~ cd Ocd ,~ o cn ~d c~ 1S~
cd Q~ O P~ o ~C ~0 ~o _ ~.,7.'~
cd r-l . O tU .
o o ~a P ~:, ,~ h c~ O cn ~U cd O ~ ~ ~ cd ~q ?~
c~ r l ~ O l~ ~1 td ~ 1 O
o o cd cd ~ ~ r-l O u~ ~D ~rl cd ~ Ll~
cd cd ~ rl ~U ~H :., ~ ~1 ~U ~ ~U
,5~ r~ 1 cd ~U h cd ~ r r~
X O ~ ~ ' ~ t I ~ cr~
X ~ ~U o u~ ~ __ ~ -- E E E
::~ ~ o . tH O ~U
O ~ ~ l ~ bD . cd ,~ o ~a C ~u ~ ~
~ h cd ~ bO ~rl h cd ~ c~
~ ~ ~
h S:: ~ ~ ~ h ~ O ~U O 5 ~ X
h ~ rl ~d u O a~ ~U ~ ~ ~ ~ tD ::; O
~U ~U ca ~: h u~ ~ ~ o C~ ~ O ~ ~ ~ ,-1 _ o ~u tu ~ E3 _ o o o t) ,~ cd tH ~
cd O cd Q~ h O ~U O rl ~U ~U ~ O ~ :~ Cd E~ ~: o~ o ~ m ~ c~ ~ cq ~ ~ c~ ~ ~: h _ _ _ ___ _ U~ . . . l . . l , l CO
~ ~ _~ =r ___ ~ _ u~
~r o . . l . l l l l ~r ~ U~ ~ ~ ~
. _ ____ __ _ ~o l . . o . . . l l U~
U~ ~ o o o o _ _ o u~ =r U~ l . l l l . .
o U~
a~
_ . _ m ~ ~D co ~r ~r ~ l . l . . . l l c~
_ _ o o _ o . l l . l l . l . l o~
_ __ U~ ~D L~ ~r C;~ l . o o . . .
~ ~ ~1 . ) ~ ~ ~o a)' __ ~ o u~ ~ _ ~
. L- ~ ~D ~O O O
~D l l . . . . . l . J
r-l ~1 ~1 O N ~rl O
E~ ~ ~r ~ . ~
.~ __ l l 1~ _ _ O l l ~ : .
_ u~ ~r oo ~ In-o~ O . . l . l l l l O
. ~O O ~I ~1 'O ~, . ~ __ ~
~ ~ O ~ ~ L
Ir~. . . l . . . l l l L~
O rl ~ ~C) O ~1 ~ l O O ~ l ,0. _ ~ __ ___ l 0 I_ N . O
L~ O LS~ O~
~1 . . l l .
_ _ ~ _ _~ _ ~J ~1 ~ ' C~^ _ _ _ _ . C) ~_ ~1 O
;Z td ~ h i: ~ ~ ~) ~ t~ ,_ O ~ ~ ~ rl S
c~ ~ c~ _r~ ~d ~1~ O ~ . 1:: ~ ' ~ ~_ h--a~ ~ ~d:~, I ~1 ~ ~ ~ S:: ~ ~ ~ td ~ ~ ~ ~ :S
~_ ~: ~ ~ ~ ~ ~ J~ S ~ o 3: ~ ~ o ~ :~ ~ ~ ~
_ ~ ~ _, ~ ~ ~ ~ ~ ~_ ~ ~ ~ O
c~ ~ c~a) a) c~ a) s~:~ ~ ~ ~ ~ ~ c~
¢ ~: ~ ~ ~ ~ ~ ~ X _ :~: ¢ ~ u~ ~d ~4 .
~13~L~S7 1 ~xample 2 Methyl esterification reaction of methacrylic acid was carried out in the same manner as in Example 1 except that cumene was used in place of xylene and the pressure of the alcohol distillation column 23 was changed to 50 rnmHg and that of the low boiling material-separating column 27 to 60 mmHg to make the temperatures of the respective distillation columns equal to those in Example 1. Compositions at each point were sub-stantially identical with those of Example 1.
Example 3 Methyl esterification reaction of methacrylicacid was carried out in the same manner as in Example 1, except that a mixed organic solvent consisting of 57%
by weight of xylene and 43% by weight of ethylbenzene was used in place of xylene. Compositions at each point were substantially identical with those of Example 2.
Example 4 esterification reaction of methacrylic acid was carried out in the same manner as in Example 1, except that ethanol was used in place of methanol and a mixed solvent of methyl methacrylate and xylene was used as the extracting solvent for methacrylic acid.
Compositions at each point in the flow diagram are shown in Table 3.
~3~
~o _ 0 _ __ _ L~ . . . l . . l l l ~o ~ ~ __ N _. __ _ ~O
~ l . . l . l l l l O
N C~ O O
__. , ___ _ _ ~O O~ ~ ~ Ln ~ O
~O ~ . . . . . . l l ~
N _ ~ N O _ . O O ~1 _ l _ ~ N ~ cr~
N l N l l l ~ O l l 3 _ __ _~
O \~ O 3 .~1 3N ll 3 l O r~ 3 l l 3 _ ,~ a~ o o O l . l l l . l . l O
N N N lr~ L~
~ _ __ 0 ~ ~
Q~ ~ ~ oO ~ ~ o~ ~
~1 ~ ~ . . l . . . ~ l N
,D~1 O ~ ~1 ~1 ~D ~Y) ~
N =~ N ~1 E' __ __ o ~D l l . . . . . l .
_ ~1 W O ~ N O
rl 1 3 ~ /_ 1 l O I_ l O
00 . . l ., . l l l l ~fl O ~ O ~o ~1 U~ ~ W ~ ~ C~
. . . l . .
O o~ O ~c) O ~ ~1 t~ O ~r7 ~1 3 l . . l . l l l l 0 r-l ~1 _ CI:) t-~1 Ir~ O l l l N l l I . ~1 .
^ C~^ I ,_ _~ ~ ,_ _~ ,_ .
. o ~ ~ . . . . . . . a~ ~
o ~ ~ :>,~ a~ a) ~ ~ ~ ~ ~ E~ ~ c) ~ ~ 5:
Z:3: ~ 3: ~ Q~ ~: 3: 3: ~ 3: ~ ~ 3 ~ ~
c) ~ c)~ td`-- ~ ~ a~ ~-- ~_ o ~-- ~ ~ ~ ~_ ~ ~o td ~ ~1 ~ ~ ~ ~ ~ ~ ~ ~ _~
~:: ~ ~ ~ ~ , ~ J~ ~ a) ~ o ~ c~ ~o :~
a) ~ rl ~ ~ ~ a~ ~ ~ ~ ~ ,~ ~1 rl O
c) ~ c) ~ c) ~ c) :>, ~ ~ ~ ~ ~ c) ~
:~ ~d ~ ~ ~ ~C 3 ~,3 ~: ~ c~
Claims (4)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for preparing a methacrylic acid ester from a feedstock dilute aqueous solution of methacrylic acid containing by-produced acetic acid and others, obtained by gas phase catalytic oxidation of at least one member of isobutylene, tert.butyl alcohol and methacrolein, which comprises (1) subjecting said feedstock to extraction in a methacrylic acid extracting zone (a) using an extracting solvent prepared by adding to a water-insoluble, inert organic solvent having a boiling point above 120°C, 15 - 50% by weight of a methacrylic acid ester, (2) separating the resulting extract solution into a mixed solvent of the methacrylic acid ester and most of the organic solvent and a meth-acrylic acid solution in the remaining organic solvent by distillation in an extracting solvent-separating zone (b), (3) subjecting the resulting organic solvent solution containing methacrylic acid to esterification reaction in the presence of an acid catalyst together with an excess amount of an alcohol having a boiling point below 100°C in an esterification reaction zone (c), while removing water formed by the esterification reaction by azeotropic boiling with the organic solvent together with a part of the formed methacrylic acid ester as a distillate solution, thereby making an acid catalyst concentration of the remaining reaction solution constant, (4) separating the reaction solution discharged from the bottom of the esterification reaction zone (c) into an organic solvent layer containing the methacrylic acid ester and an aqueous layer containing the acid catalyst in a decanting gone (d), (5) recycling the aqueous layer at the constant acid catalyst concentration to the esterification reaction zone (c) after separating by-produced polymerization products therefrom, (6) joining the organic solvent layer with the distillate solution in step (3), (7) subjecting the resulting mixture alcohol extraction using an aqueous solution of an inorganic salt in an alcohol extraction zone (e) to recover unreacted alcohol, (8) recycling the recovered alcohol to the esterification reaction zone (c), (9) separating low boiling materials from a raffinate organic solvent phase leaving the top of the alcohol extraction zone (e) by distillation, (10) separating the raffinate organic solvent phase freed from the low boiling materials into a high purity methacrylic acid ester product and the organic solvent containing unreacted methacrylic acid, and (11) recycling the organic solvent containing methacrylic acid to an appropriate position of the methacrylic acid-extracting zone (a) in step (1) or to a feedstock to be separated in step (2).
2. A process according to Claim 1, wherein the unreacted alcohol in the form of a solution in the aqueous solution of inorganic salt recovered in step (7) is supplied to a middle stage of an alcohol distillation zone (f), the alcohol is recovered from the top of the distillation zone (f) while the aqueous solution of inorganic salt is recovered from the bottom of the distillation zone (f), the recovered aqueous solution of inorganic salt is reused for the alcohol extraction in step (7), further the unreacted methacrylic acid having been contained in the aqueous solution inorganic salt in step (7) is withdrawn azeotropically with water vapor in the form of vapor from an appropriate position in the alcohol distillation zone (f), condensed and recycled to an appropriate position of the methacrylic acid extracting zone (a) to be extracted and recovered as the mixed solvent in step (2).
3. A process according to Claim 1, wherein a methacrylic acid concentration in the organic solvent solution to be subjected to esterification reaction in step (3) is 20 - 80% by weight.
4. A process according to Claim 1, wherein an esterification conversion in step (3) is controlled to 50 - 90%.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23029/78 | 1978-02-28 | ||
| JP2302978A JPS54115318A (en) | 1978-02-28 | 1978-02-28 | Recovery of methacrylic acid |
| JP3034178A JPS54122209A (en) | 1978-03-15 | 1978-03-15 | Recovery of unsaturated aliphatic acid and alcohol |
| JP30341/78 | 1978-03-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1131657A true CA1131657A (en) | 1982-09-14 |
Family
ID=26360319
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA321,785A Expired CA1131657A (en) | 1978-02-28 | 1979-02-19 | Recovery of methacrylic acid and alcohol in methacrylate production process |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1131657A (en) |
| DE (1) | DE2907602A1 (en) |
| FR (1) | FR2418216B1 (en) |
| GB (1) | GB2015509B (en) |
| IT (1) | IT1114704B (en) |
| NL (1) | NL7901502A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5826843A (en) * | 1981-08-11 | 1983-02-17 | Sumitomo Chem Co Ltd | Preparation of acrylic or methacrylic ester |
| US8212062B2 (en) | 2007-04-02 | 2012-07-03 | Inventure Chemical, Inc. | Production of biodiesel, cellulosic sugars, and peptides from the simultaneous esterification and alcoholysis/hydrolysis of oil-containing materials with cellulosic and peptidic content |
| US7943792B2 (en) | 2007-04-02 | 2011-05-17 | Inventure Chemical Inc. | Production of biodiesel, cellulosic sugars, and peptides from the simultaneous esterification and alcoholysis/hydrolysis of materials with oil-containing substituents including phospholipids and peptidic content |
| US7777085B2 (en) | 2008-10-01 | 2010-08-17 | Inventure Chemical, Inc. | Method for conversion of oil-containing algae to 1,3-propanediol |
| CN111807960B (en) * | 2020-08-01 | 2022-04-22 | 浙江亦龙新材料有限公司 | Preparation process of isooctyl acrylate |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1393173A (en) * | 1963-05-16 | 1965-03-19 | Distillers Co Yeast Ltd | Ethyl acrylate production process |
| GB1257399A (en) * | 1970-07-04 | 1971-12-15 |
-
1979
- 1979-02-19 CA CA321,785A patent/CA1131657A/en not_active Expired
- 1979-02-26 NL NL7901502A patent/NL7901502A/en not_active Application Discontinuation
- 1979-02-26 GB GB7906677A patent/GB2015509B/en not_active Expired
- 1979-02-27 DE DE19792907602 patent/DE2907602A1/en not_active Withdrawn
- 1979-02-27 IT IT48149/79A patent/IT1114704B/en active
- 1979-02-28 FR FR7905153A patent/FR2418216B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2015509B (en) | 1982-08-25 |
| GB2015509A (en) | 1979-09-12 |
| IT1114704B (en) | 1986-01-27 |
| DE2907602A1 (en) | 1979-09-06 |
| IT7948149A0 (en) | 1979-02-27 |
| FR2418216B1 (en) | 1986-02-14 |
| NL7901502A (en) | 1979-08-30 |
| FR2418216A1 (en) | 1979-09-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP0695736B1 (en) | Purification of acrylic acid by azeotropic distillation | |
| JP3346822B2 (en) | Method for producing acrylate or methacrylate | |
| US4250330A (en) | Process for the recovery of the solvent and of the by-produced methylacetate in the synthesis of terephthalic acid | |
| JP2001505199A (en) | Method for producing acetic acid | |
| US4956493A (en) | Process for producing methacrylic ester | |
| TWI627161B (en) | Process for preparation of methacrylic acid and methacrylic acid esters | |
| US3875212A (en) | Process for continuously synthesizing acrylic acid esters | |
| CZ214196A3 (en) | Purification process of acrylic acid obtained by catalytic oxidation of propylene | |
| US4329492A (en) | Process for production of methacrylic acid esters | |
| JP2002509905A (en) | Method for producing acrylic acid and acrylic acid ester | |
| CN103391914B (en) | A kind of (methyl) acrylic acid continuous collection method and collection device | |
| EP0102642A1 (en) | Process for purifying methacrylic acid | |
| CA1131657A (en) | Recovery of methacrylic acid and alcohol in methacrylate production process | |
| JP3568209B2 (en) | Method for purifying acrylic acid obtained by catalytic oxidation of propylene | |
| US4733004A (en) | Continuous esterification of methacrylic acid and product recovery | |
| JPH0239496B2 (en) | ||
| US5154803A (en) | Purification of contaminated propylene oxide by extractive distillation | |
| JP4104232B2 (en) | Acetic acid recovery from acetic acid containing wastewater | |
| EP0465853B1 (en) | Method for producing 4-hydroxybutyl (meth)acrylate | |
| US5116466A (en) | Propylene oxide purification by extractive distillation | |
| JP3918528B2 (en) | (Meth) acrylic acid purification method | |
| US6494996B2 (en) | Process for removing water from aqueous methanol | |
| JP3832868B2 (en) | Acrylic acid purification method | |
| JP2000281617A (en) | Purification of acrylic acid | |
| JPS6310691B2 (en) |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |