US2101857A - Manufacture of motor fuels - Google Patents

Description

Patented Dec. 14, 1937 UNITED STATES PATENT OFFICE MANUFACTURE or" MOTOR FUELS No Drawing. Application April 23, 1936, Serial No. 76,078

16 Claims.

This application is a continuation-in-part of my co-pending application, Serial No. 30,932, filed July 11, 1935.

This invention relates particularly to the treat-'- ment of hydrocarbons of an unsaturated character, such as the mono-olefins. p

In a more specific sense, the invention is concerned with the selective treatmentof the monoolefins, which are normally gaseous, to produce particular compounds which are of a superior value as antiknock blending fluids for gasolines inferior in this respect.

Oil cracking processes which are in use as a means ofv supplementing thesupply of gasoline obtainable by straight run distillation from crudes, and also for producing higher antiknock value material than the so-called "naturaP gasolines 1-. e. gasolines which are produced by straight 0 distillation of crude oils, are also productive of considerable quantities of fixed gases and heavy residual products, both liquid and solid, which are in a sense waste products of the process in that very little utilization of them has been made other than.as fuels. The fixed gases produced, for example, in cracking a topped crude with the primary objectof producing gasoline may run as high as 10% by weight of the charging oil under intensive cracking conditions. The composition of these gases will vary with the severity of the cracking operation, the nature of the charging stock, the. phase prevalent during the operation, and other factors. The following table shows a list of the hydrocarbon compounds which have been found in the fixed gases from oil cracking plants:

Hydrogen Hz Methane CH4 Ethane "a; C2Hs Ethylene C2H4 Propane CaHs Propylene CaHs Butanesv (normal and iso) C4H1o Butenes (normal and iso) C4Ha The above tabulation omits mention of minor constituents such as hydrogen sulphide, low boiling mercaptans, and more highly unsaturated hydrocarbons than the mono-olefins, such as butadienes, but it will serve to indicate the general character of some of the gas mixtures which may be treated by the present process.

Intensive researches have been conducted to find a practical method for augmenting the supply of cracked gasoline by forming liquid polymers from the gaseous olefins present in cracked hydrocarbon gas mixtures; Fortunately, all of the dimers and manyv of the trimers and mixed polymers of the normally gaseous mono-olefins boil within the range of commercial motor fuel 10 and are characterized by a satisfactory stability and particularly by a good antiknock value, which generally exceeds that of any of the components of cracked gasoline. For purposes of reference the following table is introduced to show the boiling ranges of the dimers of the lower boiling mono-olefins:

Boiling points of olefin dimers The tendency of the gaseous mono-olefins to polymerize varies considerably when using different catalysts and also with the same catalyst. The present process is an adaptation of a particular type of catalyst to selectively polymerize normally gaseous olefins, and particularly those present in the gases from oil cracking operations.

In one specific embodiment, the present invention comprises treatment of hydrocarbon gas mixtures, comprising principally paraflins and mono-olefins of 3 and 4-carbon atoms, in the presence of solid phosphoric acid catalysts in stages for the selective and successive polymerization of the olefins in order of their reactivity, characterized by the use of substantially liquid phase conditions for the polymerization of the butenes and vapor phase conditions for the polymerization of residual propene, while using definite combinations of temperature and pressure best suited for the selective polymerization of each individual olefin.

In a further embodiment, the process is directed to the treatment of the hydrocarbon gas mixtures produced incidental to oil cracking operations, particularly those containing relatively high percentages of 3 and 4 carbon atom hydrocarbons such as stabilizer refluxes, and in one very specific embodiment it is applied to the treatment of close out hydrocarbon fractions comprising principally butanes and butenes and known tothe trade as 3-3 fractions.

The following table shows in greater detail the structural formulas and boiling points of the normal and iso-olefins which may be treated as such In the case of stabilizer refluxes produced by only moderately accurate fractionation there will be vapors of some amylenes present, but these generally constitute an inconsiderable portion of the total gaseous hydrocarbon mixture and their various isomers need not be listed.

We have found that, by utilizing certain types of solid phosphoric acid catalysts, whose preparation and properties will be later described in detail, the olefins present in hydrocarbon gas mixtures can be selectively and successively polymerized and have particularly determined that this separation is best effected while varying the temperatures at which the olefins are contacted with the solid catalysts over definite ranges, and furthermore, by applying sufllcient pressure to maintain a substantial proportion of the butenes in liquid phase in the first stages of the treatment. We have further determined that, when using the preferred catalyst, isobutylene, which is one of the heavier constituents of olefin-containing gas mixtures, is rapidly and selectively polymerized at temperatures from as low as 70 F. to temperatures of 150 F. so that, within this approximate temperature range, it may be removed from mix tures without afiecting propylene at all, while the normal butenes are affected to a minor extent depending upon the actual temperature employed, which may vary somewhat with the composition of the gas mixture treated and particularly the relative proportions of the diiferent olefins therein contained. The formation of polymers of isobutene to the practical exclusion of polymers from n-butenes and propene is further assisted according to the present process by the maintenance of suflicient pressure within the temperature range mentioned so that the 4-carbon atom hydrocarbons are in liquid phase, pressures of from about 50 to 150 pounds per square inch being sufficient for this purpose at temperatures between 70 and 150 F. In the case of the B-B mixtures, which contain substantially only 4-carbon atom hydrocarbons, the necessary temperature can be definitely predicted from the known vapor pressures of the hydrocarbons in the mixture. The following table is introduced to show the approximate pressures necessary for maintaining 4-carbon atom hydrocarbons in liquid phase at moderately elevated temperatures including those within the preferred treating range. When'there are relatively high percentages of lower molecular W ght compounds present these pressures will necessarily be higher than those shown.

Temperature-pressure table for (-carbon atom r The figures in the above table are only approximate since the actual pressure necessary will depend upon the composition of the hydrocarbon mixture undergoing treatment.

According to the present process, n-butenes are polymerized, after the primary removal of the isobutenes, at temperatures within the approximate range of 150-250 F., still maintainihg sufliclent pressure to insure at least a major portion of the hydrocarbons in liquid phase. Within the temperature range mentioned. a substantial liquid phase of n-butenes can be maintained with pressure of from about 150 to 350 pounds per square inch. This operation may involve an intermediate fractionating step to remove the primary isobutene polymers and the use of such a step is comprised within the scope of the invention. As a rule, the actual temperatures employed for isobutenes and n-butenes respectively will show a definite spread of possibly 50-i00 F. While the object of the invention is to successively polymerize the 4 and 3-carbon atom olei'lnic hydrocarbons, there may at times be some mixed polymerization between the iso and n-butenes, though it is the purpose of the present process to keep this reaction at a minimum.

We have found that it is possible and practical by utilizing temperatures within the approximate range of IO-150 F. to first cause the polymerization of the isobutylene present in olefin-containing mixtures so that the polymer di-isobuty- .lene which hydrogenates to 2,2,4-trimethyl pentane is formed and further that, at temperatures above 150 F. and below 250 F. and after the removal of a considerable portion of the isobutylene by polymerization, the next stage in the polymerization reactions at slightly increased temperatures is represented by the condensation of residual isobutylene molecules with molecules of normal butenes, themixed polymers formed in this manner yielding 2,2,3-trimethylpentane on hydrogenation. However, by employing primarily a minimum temperature for the polymerization of isobutene when considering the throughput of a given apparatus and then raising the temperature considerably in the second stage directed to the polymerization-of n-butenes, the intermediate range of temperature which might foster mixed polymerization may be avoided so that this occurs only to a minimum extent.

In accordance with the present invention, after substantially all of the 4-carbon atom olefins have been polymerized the pressure may be reduced and the temperature increased so that propylene in the gases is polymerized in vapor phase by contact with fresh portions of solid phosphoric acid catalysts. If the butylenes have been practically all removed the propylene may then be polymerized to form low boiling dimers at temperatures above 250 F., and temperatures as high a 500 F. may safely be employed without danger of overpolymerization with the formation of high boiling polymers. As a rule in dealing with most gas mixtures from hydrocarbon cracking plants the optimum temperature range for polymerizing propene is from 400-500 F. when considering the rate of polymerization and the quality of the polymer product in respect to percentage of gasoline boiling range constituents. The usual range of pressures employed in the propylene polymerizing stage is from 100 to 300 lbs. per square inch. I

As already stated, the present process is particularly applicable to intermediate hydrocarbon fractions generally designated as stabilizer reflux and in such mixtures the amount of five carbon atom hydrocarbons is small and not a considerable item either in the matter of direct recovery by absorption processes or indirect recovery by The catalysts which are used in the present connection are of a special and unique character and warrant detailed description, as they are evidently peculiar in their action. They are made generally by mixing an acid of phosphorus, preferably a phosphoric acid such as the ortho and/or the pyro acid, with a substantially unreactive and generally siliceous adsorbent until a paste is obtained, this paste being then calcined to produce a solid cake, which is ground and sized to produce catalyst granules. It has been found in the case of highly adsorbent materials, such as kieselguhr, that primary composites may be made in which the acid of phosphorus is the major constituent by weight. Thus a stiff paste is produced when parts of commercial orthophosphoric acid is mixed at ordinary temperatures with 20 parts of kieselguhr. Conversely,

relatively dry mixes result when about 30 parts of By controlling the proportions of adsorbent and acid and also the temperature employed in the drying or calcining step. granular catalyst composites may be produced which vary both in the percentage of the acidic component and in the strength of said component. Thus for the polymerization of such readily polymerizable compounds as isobutylene catalysts may be utilized which have been produced by merely mixing commercial ortho phosphoric acid of approximately concentration. with a siliceous and finely divided adsorbent material and drying at temperatures of approximately 250 F. to 300 F., with operation if conducted for periods of time which vary somewhat with the amount of acid present in the mix, ultimately yields solid catalysts which contain ortho phosphoric acid as their essential constituent. To produce catalysts useful for selectively polymerizing alpha and beta butenes after isobutylene has been selectively removed it is preferable to employ conditions which ultimately produce an acid somewhere between 100% ortho and 100% pyro acid in composition, and in this operation the temperatures of calcining in the preparation of the catalyst will vary from approximately, 300 F.

to 400 F'., depending again upon the exact amount of acid by weight'of the mixture and the type of the' adsorbent.

When utilizing the temperature and pressure ranges and the phases already designated, a solid catalyst comprising an acid approximating the pyro acid in composition as the essential active ingredient is preferable, and if the ortho acid has been used in the primary mixtures, the most'efiective catalysts are produced when the pasty mixtures are heated at temperatures from approximately 400 to 600 F. for a considerable period of time, usually from 40 to 60 hours. During this heating water is evolved and analysis shows that v the remaining acid has a composition closely approaching that of the pyro acid. Advantages are frequently gained in utilizing the higher temperat-ures and also in starting with the pyro acid.

When using this acid in primary mixes temperatures of from approximately 310 to 360 F. are used to insure proper fluidity. With efficient mixing devices the time required for producing uniform distribution is lowered considerably, frequently only 5 minutes being required. If dehydration is found to have taken place to too great an extent so that the polymerizing efiectiveness is Y400 to 600 F. to produce the catalytic acid of optimum composition;

A feature of the present invention resides in the employment of ordinarily liquid phosphoric acids as polymerizing catalysts in substantially solid form, this being accomplished by the alternative use of a number of different adsorbent carrying materials which vary somewhat in their adsorptive capacity and also in their chemical and physical properties and their influence upon the catalytic efiect of the mixtures. The materails which may be employed aredivisible roughly into two classes. The first class comprises materials of a predominately siliceous character and includes diatomaceous earth, kieselguhr and artifically prepared porous silica such as, for example, Sil-O-Cel. In the case of naturally occurring diatoms it is believed that they sometimes contain minor amounts of highly active aluminum oxide which in some instances seems to contribute to the total catalytic effect of the solid catalyst. the artifically prepared forms of silica.

The second class of materials which may be employed either alone or in conjunction with the first class (and with certain other optional ingredients to be later described) comprises generally certain members of the class of aluminum silicates and includes such naturally occurring substances as the various fullers earths and clays such as Bentonite, Monfmorillonite, etc. This class also includes certain artificially prepared aluminum silicates of which the product known as Tonsil" is representative, this substance being in a sense a purified aluminum silicate made by treating certain selected clays with hydrochloric or other mineral acid and washing out the solu This active material is not present'in capacity which is particularly in evidence in making up the present type of phosphoric acidcatalysts, and they may also contain traces of active ingredients which assist in producing the desired polymerizing effects. Again each substance which may be used alternatively will exert itsown specific influence which will not necessarily be identical with that of the other members of the class.

The invention may employ as a preliminary treatment on hydrocarbon mixtures any suitable method for the removal of hydrogen sulphide, low boiling mercaptans, dienes and other gases which may interfere with the normal functioning of the catalysts, the liquefaction of a substantial portion of the reactive olefins, or the production of polymers of sufficient purity for ready incorporation with refined gasolines. Subsequently, the liquid polymer products may be subjected to any of the ordinary chemical treatments commonly employed on cracked distillates, such as a limited amount of sulphuric acid, caustic soda, sweetening reagents and the addition of small amounts of inhibitors.

After some period of use which will vary with the material treated and the conditions of operation, any given catalyst mass will show a decrease in activity due to the gradual accumulation of heavy tarry materials and its regenerationwill be imperative. The regeneration steps commonly comprise: (1) removal of distillable materials by the use of superheated steam at temperatures of approximately 600 to '700'F.; (2) the use of oxodizlng gas mixtures of graded oxygen content to burn out the carbonaceous material; and (3)- the rehydration of the acid by steam at temperatures of 400 to 600 F. In the burning step it is most advantageous in commercial units to employ primarily instead of air a flue gas mixture produced by using only a very slight excess of air in the combustion of the fuel, so that the total oxygen content is below 1%. If air is used at first too high temperatures are likely to develop and portions of the catalysts will be over-burned, causing a loss of the volatile meta acid, which is formed as a result of too extensive dehydration. In the burning step the temperature of 950 F. generally should not be exceeded.

The reactions of polymerization of olefins are exothermic and consequently the temperature of a mixture on passage through a bed of the preferred catalysts tends to rise in proportion to the percentage of olefins present, the strength of the catalyst and the rate of passage of the hydrocarbon, and advantages are sometimes gained by intermediate cooling between towers connected in series. This may be extendedto the removal of the initially formed liquid polymers by intermediate fractionation.

In lieu of catalysts of varying acid content in successive towers, catalysts which are either fresh or partially spent may be employed to arrive at the desired selective polymerizing effects.

Solid phosphoric acid catalysts are characterized' by their ability to polymerize olefins to produce relatively low boiling hydrocarbon polymers rather than heavy tars ,or pitches and by their long life due to the absence of such highly carbonaceous reaction products and also due to lack of oxidizing tendency in the phosphoric acid which constitutes a substantial portion thereof. In contrast to this it is notable that when employing sulphuric acid as a polymerizing agent, caution is necessary to prevent oxidation and undesirable side reactions such as ester formation and that, when employing metal halides such as aluminum chloride or zinc chloride, the tendency toward the formation of heavy polymers is very pronounced, so that it is not possible to proface carbon deposits after long periods of service by merely burning oi! the deposits with air or other oxidizing gas at moderate temperatures.

' A still further advantage resides in the fact that they are substantially of a non-corrosive character as compared with the decided corrosive action of liquid phosphoric acid and other liquid polymerizing agents. The peculiar structural strength of catalyst masses of the solid phosphoric acid type should be noted in connection with the general advantages which they possess, this being of special commercial value.

As an important application of the present process, it is possible to produce from the olefincontaining gas mixtures from oil cracking operations maximum yields of iso-octene, which is readily hydrogenated to produce iso-octane, which is used at present asa standard of antiknock value but not as a rule as an actual blending agent because of its scarcity and the cost attending its preparation. The hydrogenation of iso-octene is a relatively simple matter, requiring the use of well known processes of a continuous and cobalt and the oxides and sulphides of the metals in the left-hand column of the sixth group of the periodic table, including chromium, molyb-.

denum and tungsten. When the iso-octene polymer is substantially free from sulphur compounds active metallic catalysts such as reduced nickel A mixture of hydrocarbons was treated which had the following composition by weight:

Per cent Isobutylene 16.8

n-Butylenes 36.0 n-Butane 47.2

The liquid cut was passed through a bed of solid catalytic material comprising 72% by weight of a phosphoric acid approximating the pyro acid in composition and 28% of kieselguhr. The average temperature throughout the catalyst mass was 100 F. The pressure was 100 pounds per square inch and the liquid hydrocarbon mixture was passed through the catalysts bed at the rate of 4 cubic feet'of equivalent gas under standard conditions per hour per pound of catalyst. An analysis of the liquid product indicated that, in this single once through operation, 64% of the isobutylene and 10% of .the n-butylenes were polymerized, which indicates a definite degree of selectivity under these conditions. The liquid polymer corresponded to 2.6 gallons per 1000 cubic feet of equivalent gas mixture, and 1.9 gallons or 72% oi the stabilized liquid polymers were found to be an octene which was readily hydrogenated to produce iso-octane.

After removal of the isobutene polymers the residual gas mixture was heated to a temperature of about 200 F. under a pressure of 250 lbs. per square inch and further contacted with the solid catalysts to polymerize the n-butenes. The liquid polymers produced corresponded to approximately 4 gallons per 1000 cubic feet of equivalent gas mixture and these polymers were found to consist of approximately 80% of a mixture of octenes which could be hydrogenated to produce a mixture of octanes having an octane number of approximately 85 referred to the standard 2,2,4-trimethylpentane.

Example If Percent Isobutylene 5 n-Butylenes z Propylene An efficient polymerizing catalyst was employed which had been manufactured by adding approximately 65% by weight of pyrophosphoric acid to kieselguhr followed by thorough mixing at a temperature of 160 C. to produce a cake and grinding and sizing to produce catalyst granules of approximately 6-20 mesh. A mass of these granules was used as a filler in vertical treating towers which were employed in series to remove first the major portion of the isobutylene, then the butenes and lastly the propylene.

For the selective polymerization of the isobutylene content the stabilizer reflux which was substantially in liquid phase was passed downwardly through the first treating tower at normal atmospheric temperatures of approximately 70 F. at a pressure of about 200 pounds per square inch. The liquid resulting was stabilized by heating to approximately 150 F. which vaporized substantially all of the residual unpolymerized three and four-carbon atom olefins and left principally di-isobutylene polymer. The liquid condensed from the vapors was passed through a second treater at a temperature of approximately 200 F. and a pressure of 250 lbs. per square inch and this second catalyst contact polymerized substantially all of the residual fourcarbon atom olefins to make a mixture of octenes. v

Following the second stage the liquid polymers were separated and the gas mixture which then contained substantially only propylene as its olefinic constituent was heated to a temperature of 450 F. under a pressure 01100 lbs. per square inch and passed through a third bed of catalyst to polymerize the propylene to dimeric meric forms.

The character of the present invention and its commercial aspects are clearly evident from the foregoing specification and the limited examples given though neither is intended to be undul limiting upon its generally broad scope.

and. tri- We claim as our invention:

1. A process for producing normally liquid hydrocarbons from a. hydrocarbon mixture containing three and four carbon atom olefins, which comprises subjecting the mixture to three successive stages of polymerization in the presence of solid phosphoric acid catalyst, the first stage being at a temperature of from about 70 to Y 150 F. to polymerize isobutene, the second stage at a temperature of from about 150 to 250 F. to polymerize n-butenes, and the third stage at a temperature of from about 250 to 500 F. to polymerize propylene.

2. A process for producing normally liquid hydrocarbons from a hydrocarbon mixture containing butenes and propylene, which comprises subjecting the mixture to polymerization in the presence of solid phosphoric acid catalyst, first at temperatures within the range of about 70 to 250 F. to polymerize the butenes and then at temperatures within the range of about 250 to 500 F. to polymerize the propylene.

3. A process for producing octene from a normally gaseous mixture containing 3 and 4 carbon atom olefins which comprises subjecting the mixture to the action of a solid phosphoric acid catalyst at between 70 and 250 F. and under a pressure sufllcient to maintain a substantial portion of the 4 carbon atom olefins in liquid phase to selectively polymerize 4 carbon atom olefins contained in the mixture.

4. A process for producing di-isobutene from a normally gaseous mixture containing isobutene and normal butenes which comprises subjecting the mixture to the action of a solid phosphoric acid catalyst at a temperature of from about 70 to 150 F. and under a pressure sufficient to maintain a substantial portion of the isobutene in liquid phase to selectively polymerize iso-butenes contained in the mixture.

5. The process as defined in claim 1 further characterized in that the first and second stages are under sufficient pressure to maintain a substantial portion of the butenes in liquid phase.

6. The process as defined in claim 1 further characterized in that the first stage is under a pressure of from to 150 pounds per square inch and the second stage under a pressure of. from 150 to 350 pounds per square inch.

7. The process as defined in claim 2 further characterized in that the butenes are polymerized under sufilcient pressure to maintain a substantial portion thereof in liquid phase.

8. The process as defined in claim 2 further characterized in that the butenes are polymerized under a pressure of from about 50 to 350 pounds per square inch.

9. A processfor producing normally liquid hydrocarbons from a hydrocarbon mixture containing butenes and propylene, which comprises subjecting the mixture to polymerization in the presence of solid phosphoric acid catalyst in a plurality of stages, the first stage being at a butene polymerizing temperature and under suflicient pressure to maintain a. substantial portion of the butenes in liquid phase, and a subsequent stage being at a propylene polymerizing temperature higher than that in the first stage and under a pressure such as to maintain the propylene in vapor phase.

10. A process for producing normally liquid hydrocarbons from a hydrocarbon mixture containing butenes and propylene, which comprises subjecting the mixture, in the presence of solid phostemperature under sui'ilcient pressure to maintain a substantial portion of the butenes in liquid phase, separating resultant butene polymers from unpolymerized propylene, and polymerizing the latter, in the presence of additional phosphoric acid catalyst and in the vapor phase, at higher temperature and under lower pressure than are maintained in the first-mentioned polymerizing step.

11. The process as defined in claim 3 further characterized in that said pressure-is within the range 01' from to 350 lbs. per square inch.

12. The process as defined in claim 4 further characterized in that said pressure is within the range of from 50 to 150 lbs. per square inch.

13. A. process for producing iso-octanes from a normally gaseous mixture containing 3 and 4 carbon atom oleilns which comprises subjecting the mixture to the action of a solid phosphoric acid catalyst at between and 250 F. and under suilicient pressure to maintain a substantial portion of the 4 carbon atom oleflns in liquid phase to selectively polymerize 4 carbon atom oleflns contained in the mixture, separating resultant polymers from the unpolymerized gases and saturating the former by hydrogenation.

14. A process for producing 2,2,4-trimethylpentane from a normally gaseous mixture containing isobutene and normal butenes, which comprises subjecting the mixture to the action of a solid phosphoric acid catalyst at a temperature of from about 70 to F. and under sufiicient pressure to maintain a substantial portion of the butenes in liquid phase to selectively polymerize isobutene contained in the mixture, separating resultant polymers from the unpolymerized gases and saturating the former by hydrogenation.

15. The process as defined in claim 13 further characterized in that said pressure is within the range of from 50 to 350 lbs. per square inch.

16. The process as defined in claim 14 further characterized in that said pressure is within the range of from 50 to 150 lbs. per square inch.

VLADHHIR IPA'I'IEFF. RAYMOND E. SCI-IAAD.