US2389984A - Production of motor fuel - Google Patents

Description

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Nov. 27, 1945. J p JONES 2,389,984 PRODUCTION OF MOTOR FUEL Filed 001;. 21, 1940 ALKYL AT ION CATALYST RIZATION MEANS SEPARAT ING 27 POL ISOMERIZAT ION DEHYDROGENAT ION NORMAL BUTANE CATALYST ISOBUTANE ISOMERIZATION INVENTOR J EAN P. JONES BY mm, M

m'TORNEY l atented Nov. 27, 1945 Search Roam PRODUCTION OF MOTOR FUEL Jean P. Jones, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application October 21, 1940, Serial No. 362,145

2 Claims.

This invention relates to the production of higher molecular weight hydrocarbons from hydrocarbons of lower molecular weight. More particularly, this invention relates to the production of a motor fuel or motor fuel blending stock containing aliphatic hydrocarbons which are highly branched, and have a molecular weight of 112 or more, from low boiling hydrocarbon materials comprising predominantly normal paraflins. This application is a continuation-in-part of my copending application Serial No. 300,462 filed October 20, 1939.

The production of large quantities of motor fuels in the motor fuel boiling range and with high antidetonating characteristics is of increasing importance. The antidetonating qualities or characteristics of a motor fuel are ordinarily expressed by the well known octane number, a fuel having good antldetonating characteristics having a high octane number. More gasoline is consumed by automobile motors than by motors used for any other purpose, and the average octane number of regular grades of automotive gasoline is now about '73, whereas during 1932 it was only about 62 and during 1935 it was about 68. Although considerably less fuel is used in aeroplane motors, the recent increase in the amounts used and in the average octane numbers is quite marked, as evidenced by the following table.

Military aviation gasoline (United States) Average octane number 1 Estimated.

number of aviation gasoline was only 87, refiners were allowed to include in the gasoline up to 6 cc. of tetraethyl lead per gallon of gasoline, in order to produce a fuel with this octane number. However, in 1939 considerable quantities of aviation gasoline with an octane number of 100 are being used, and in producing this gasoline refiners are generally allowed to use only 3 cc. of tetraethyl lead per gallon of gasoline. Thus, not only is the amount of aviation gasoline required increasing rapidly, and the quality of this gasoline as represented by its octane number increasing rapidly, but the requirements and restrictions with respect to the actual hydrocarbons used for aviation gasoline are becoming restricted even more rapidly. In addition to octane number requirements, aviation gasoline must have a high stability as to gum and color formation. Requirements along this line make the production of paraffin hydrocarbons having high octane numbers of major importance because these hydrocarbons also are quite stable as to gum and color formation.

One of the most desirable of these hydrocarbons is the well known iso-octane (2,2,4-trimethylpentane). One of the principal sources of supply of this hydrocarbon is in the isobutylene content of the so-called cracked gases" produced by oil cracking. When this isobutylene ls polymerized to form di-isobutylene, and this product is saturated with hydrogen by nondestructive hydrogenation, 2,2,4-trimethylpentane results. This hydrocarbon can also be formed from isobutane present in natural gas by first dehydrogenating the lsobutane to isobutylene. In either case the amount of valuable hydrocarbons which can be produced in this manner is limited to the actual amount of isobutylene, or lsobutane, available.

However, it has been found possible to treat a refinery butane-butene fraction, which contains both isobutylene and normal butylenes, in such a manner that isobutylene will react with normal butylenes to produce co-polymers. These co polymers can be hydrogenated to produce octanes somewhat similar to the well known 2,2,l-tri methylpentane, but of slightly inferior octane numbers. However, the octane numbers of the products from this operation are well above and those products show a good response to the addition of agents such as tetraethyl lead. Such a method therefore increases considerably the amount of aviation gasoline with an octane number of about which can be produced from the isobutylene present in a refinery butane-butene fraction. It has also been found possible to p mrtance. In 1933, although the average octane duce uch highly branched paraflln hydrocarbons by direct union of isoparafllns and olefins in alkylation processes.

I have now invented a process whereby large quantities of premium motor fuel, or premium blending stocks for such motor fuels, can be produced from natural gas, or other mixtures of low molecular weight hydrocarbons consisting essentially of paraffin hydrocarbons of at least four carbon atoms per molecule, comprising predominantly normal paraflins, especially normal butane, normal pentane, and the like. In one modification of my process I subject such a mixture to a fractional distillation, or a series of fractional distillations, and separate from said mixture 9. fraction comprising essentially a low boiling isoparamn and another fraction comprising essentially the corresponding normal paraflin. A portion of this second fraction is then subjected to dehydrogenation to form low boiling olefins, which are then reacted either with the isoparaflin or with olefins produced from at least a portion of the isoparamns by dehydrogenation. A further portion of the normal paraflin fraction is subjected to an isomerization treatment to convert at least a part thereof into the corresponding isoparafiln. and a hydrocarbon material containing isoparaflins so formed is passed along with fresh hydrocarbons, to the aforesaid fractional distillation. The reaction of clefins produced d rectly from a portion of the normal paraflins with the isoparaflflns may be effected either directly with isoparafllns, with or without the presence of catalysts, or may be effected with iso-olefins resulting from dehydrogenation of the isoparaflln. While all the conversion steps may be carried out in the absence of catalytic materials, it i preferable to employ appropriate catalysts throughout for the dehydrogenations, isomerization, alkylation or reaction of olefins and isoparaflln directly, and/or polymerization or reaction of normal oleflns and iso-oleflns. The invention is particu larly applicable to butane or pentane fractions from natural gas or other natural accumulations of hydrocarbons. since these fractions in nearly all cases contain considerably more normal paraflins than the corresponding isoparaflins. By a practice of the invention it is possible to produce highly branched l quid hydrocarbons in amounts considerably greater than twice the weight of the isoparafllns in the original charge stock.

It is an obiect of my invention to produce a premium motor fuel in high yields from low molecular weight paraflln hydrocarbons.

It is a further object of this invention to produce large quantities of highly branched aliphatic hydrocarbons in the motor fuel range from low boiling para-flin hydrocarbons predominating in normal paraflins.

Another object of my invention is to produce motor fuel stocks of high antidetonating qualities and low vapor pressures.

A further object of this invention is to produce a paramnic motor fuel of premium quality from a hydrocarbon material comprising predominantly or consisting essentially of normal butane.

A further object of this invention is to produce a parafilnic motor fuel of premium quality from a hydrocarbon material comprising predominantly or consisting essentially of normal pentane.

Further objects and advantages of my invention will become a parent from the accompanyins disclosure and discussion.

A particular modification of the present invention will now be described in connection with the accompanying drawing which forms a part of this specification, and which shows diagrammatically an arrangement of apparatus for practicing my invention. This description will also serve as an illustrative example of my invention.

Referring now to the drawing, a butane fraction comprising predominantly normal butane,

such as a butane fraction from a natural gas containing 20 to 25 per cent isobutane and 80 to 75 per cent normal butane, is introduced to the process through pipe l0 and valve H to fractional distillation means illustrated by fractional distillation column i2. Such a fractionating column is of the usual bubble tray type, with liquid reflux, suitable heating means for the bottom illustrated by coil l3, and suitable cooling and reflux means for the top, illustrated by coil M. In this distillation means the hydrocarbon material is separated into an isobutane fraction and a normal butane fraction, each in a substantially pure state and preferably consisting of 95 per cent or more of the respective hydrocarbon. Any undesirable lower boiling material is removed from the system through pip l5 and valve l6, and any undesirable higher boiling material is removed through pipe I! and valve Hi. If substantially only butanes are charged to the fractional distillation, a single distillation column may be used, operating with about 60 bubble plates under a pressure of about 85 pounds per square inch gauge with a bottom temperature of about 150 F., a top temperature of about 115 F., and a reflux ratio of about 30: 1.

The normal butane fraction is passed from a low point of the fractionating column through pipe 20, and a portion is passed through valve 2| to dehydrogenator 22. If desired a normal butane fraction from an outside source may be passed to the system through pipe 33 and valve 34 to pip 20, if such is available. In some instances such a normal butane fraction may constitute the entire charge to the process, with no material being added directly through pipe H2. The dehydrogenation carried out in dehydrogenator 22 is preferably carried out in the presence of a suitable catalyst such as unglowed chromium oxide, bauxite, mixtures of chromium oxide and other oxides, and the like, under low pressures and dehydrogenating temperature about 900 to 1200 F. to form essentially butenes and free hydrogen. The eflluent of the dehydrogenation is passed through pipe 23 to separating means 24, with suitable intermediate cooling and compression by means not shown. The temperature and pressure of the material entering the separator means 24 is such that substantially all the C4. and any Ca, and higher boiling hydrocarbons are in a liquid state. Gases containing free hydrogen and any low boiling hydrocarbons such as methane are removed through pipe 25 and valve 26. Liquefied hydrocarbons comprising essentially normal butane and butenes, pass from separator 24 through pipe 21. If desired, a portion of this material may be returned to the dehydrogenation step by being passed from pipe 21 through pipe 28 and valve 29 to pipe 20, as shown. In this manner the olefin content of the hydrocarbon stream discharged from separator 24 for subsequent treatment, to be described, will be increased beyond that which would be possible from a simple single-pass operation after the system has attained a steady state of operation.

A further portion of the normal butane fraction passing through pipe 20 is removed there- 76 from through pipe 30 and valve 3| and passed to an isomerizer 32. In isomerizer 32 the normal butane traction is contacted with a suitable isomerization catalyst, such as aluminum chloride or bromide, alone or on a suitable support, and at a temperature preferably between about 100 and 400 F. The i-somerization reaction is preferably carried out in the presence of a small amount of a hydrogen halide, such as hydrogen fluoride, chloride, or bromide. Such a material may be added, as desired or necessary, through pipe 35 and valve 36 to pipe 30. When a fluid isomerization catalyst is used, it may also be added through pipe 35, but in most cases a solid catalyst will be used, as will be hereinafter discussed in more detail. Under essentially equilibrium conditions the maximum amount of isobutane in the butane fraction of the hydrocarbon eflluent from such an isomerization is generally of the order of 65 to 85 per cent. However, in connection with the present invention it products produced by undesirable side reactions.

is restricted. Since my process includes a cooperative combination of fractionation, isomerization, and conversion such a limitation is not unduly restrictive from the point of view of net yield, and is one of the advantages of the present invention.

The eflluent of the isomerizer 32 is passed through pipe 31 and valve 38 to separating means 40. Separating means 40 will consist of various filters, washers, fractionators and the like suitable for the particular modification of operation used. Thus, when a solid isomerization catalyst such as alum num chloride sup orted on pumice. silica gel, or charcoal is used, with a small amount of added hydrochloric acid, the eflluent may be treated by fractional distillation to remove the hydrogen chloride, or by an alkali wash or the like. Low boiling undesired material may be removed through pipe II and valve 42, and high boiling material such as high boiling hydrocarbons, tar, or spent isomerization catalyst may be removed, as through pipe 43 and valve 44. A

butane fraction comprising both isobutane and normal butane is passed from separating means 40 through pipe 45 and valve 46 and may be introduced to the fractional distillation means l2 through valve 41.

An isobutane fraction is passed from a high point of the iractionating means I! through pipe 50. When the polymerization step, to be described, is a part or the process, at least a. portion oi the isobutane fraction is passed through valve to dehydrogenator 52 for conversion b dehydrogenation to low boiling olefins. As will be more fully discussed hereinafter, a. portion or all of the isobutane fraction may be passed from pipe 50 through pipe 53 and valve 54 to the alkylation step in alkylation unit 90. The dehydrogenation eilected in dehydrogenator 52 is preferably also carried out in the presence of a dehydrogenation catalyst such as unglowed chromium oxide, bauxite, or the like, at temperature of about 900 to 1200" F. and low pressures to form Search Room mainly i'ree hydrogen and isobutene. The eilluent of the dehydrogenation is passed through pipe I! to separating means 53, with suitable intermediate cooling and compression by means not shown. The temperature and pressure of the material entering the separating means 53 is such that substantially all C4, and any C3, and higher boiling' hydrocarbons are in a liquid state. Gases containing free hydrogen and any low boiling hydrocarbons such as methane are removed through pipe 51 and valve 58. Liquefied hydrocarbons, consisting essentially of isobutane and isobutene, and at times along with some propene if the dehydrogenation operation in unit 52 is carried out with a large extent of conversion or carried out at least in part in the absence of a catalyst, are passed from separating means 58 through pipe 60. If desired a portion of the material may be returned to the dehydrogenation step by being passed from pipe 60 through pipe 32 and valve 63 to pipe at the inlet of dehydrogenator 32, as shown.

The polymerization of isobutene is preferably conducted in the presence of a catalyst and in the presence of normal butenes produced in dehydrogenator 22, previously discussed. In this manner high yields of highly branched iso-octenes and/0r isododecenes are produced. The hydrocarbon stream containing normal butane and normal butenes is passed from separating means 24 through pipe 21 and valve 63 to the polymerization unit 61. Polymerization unit 61 will comprise suitable pumps, heating and cooling units, polymerization catalyst chambers, and the like, knownto the art. All or a part of the stream containing isobutane and isobutene is passed to the polymerization unit 61 from separating means 53 through pipe 30 and valve 3| to pipe 21. The polymerization conditions in the unit 61 are. preferably such that normal butenes and isobutene undergo a union with each other, or copolymerization. This is preferably best accomplished by maintaining a polymerization temperature such that normal butenes polymerize with themselves only slowly while in contact with the catalyst used and by maintaining a relatively low concentration of isobutene. This may be accomplished by adding isobutene through a number of pipes, represented by pipe 34 and valve 65 leading from pipe to an intermediate point of polymerization unit 31, as described in more detail in the copending application of Frederick E. Frey, Serial No. 294,377, filed September 11, 1939. The olefin concentration of the streams passing through pipe 21 and/or pipe 60 may be increasedif desired by suitable separation of parafllns and olefins in apparatus not shown, but the increased operating expense is not warranted in most operations.

The polymerization eiiiuent, containing olefin polymers along with unreacted hydrocarbons which will be predominantly lutanes, is passed through pipe 10 and valve 1| to suitable separating means represented by iractionator 12, with a heating means 13 for the kettle and a cooling and condensing means 14 for the top, and which in actual practice will generallycomprise at least two conventional distillation columns, with their regular equipment. A polymer fraction in the motor fuel boiling range is removed through pipe 15 and valve II. This fraction may be subjected to further fractionation, as may be desired, and also be treated chemically, as by nondestructive hydrogenation using hydrogen produced in theprocessand discharged through pipe 25 and/or pipe 51. A butane fraction, comprising both normal butane and isobutane, is removed through pipe 11, and may be passed through valve I8 to the fractional distillation means I2. In some instances, however, it is preferable not to mix this butane fraction with a butane fraction charged to the system. The isomerization catalysts used in isomerizer 32 generally react quite readily with unsaturated hydrocarbons, and these latter tend to act as undesirable contaminants in the charge to the isomerization step. Since the unreacted butane fraction from the polymerization step generally contains a small amount of butenes, it is better that these butenes do not find their way to the isomerizer 32. I prefer to pass the butane fraction from separating means I2 through pipe I1 and through pipe I and valve IOI to a separating means represented by fractional distillation column I02, provided with suitable heating means I03 for the bottom and suitable cooling and condensing means I04 for the top. A normal butane fraction, containing a small amount of unreacted butenes, is then passed from a low point of the distillation column I02 through pipe I05 and valve I06 to the butane stream entering the dehydrogenator 22 through the latter part of pipe 20. An isobutane fraction, which will also contain a small amount of olefins, is passed from the top of the column I02 through pipe I01 and valve I08 to be mixed with the isobutane fraction passing from separating means I2 through pipe 50. That portion of the normal butane fraction passed to isomerizer 32 is thereby not contaminated by unreacted olefins produced in the process, and at the same time efllcient separation and recycling of specific hydrocarbon fractions is realized.

Lower boiling hydrocarbons, or any undesired low boiling material, may be discharged from the separating means 12 and from the process through pipe 80 and valve 8|, and if desired a part or all of the butane and 1ighter fraction may be so discharged. If this later procedure is followed, the butane fraction may be subjected to any desirable further treatment, and returned to the process through pipe I0. Olefin polymers boiling above the range of the material discharged through pipe 15 may be separated from higher boiling material and passed through pipe 83 and valve 84 to pipe 9| and the alkylation step, to be described. Higher boiling material, which may on occasion include a substantial part or all of any material higher boiling than the motor fuel fraction removed through pipe 15, is discharged from the system through pipe 85 and valve 86. It is, of course, understood that the characteristics of various particular products removed will be dependent on the desired characteristics of the motor fuel stock being produced and on the material charged, and the fractionating equipment used and its conditions of operation will be such as best adapted to the particular needs of the specific requirements at hand, as may be readily determined by one skilled in the art.

The charge to the alkylation step will consist of isobutane along with olefins produced from the normal butane fraction, either directly by simple dehydrogenation or somewhat indirectly by the use of heavier olefin polymers which are passed through pipe 83 as just discussed. A portion or all of the isobutane fraction passing from fractionating means I2 through pipe 50, along with that passed through pipe I01 from fractionator I02, is passed through pipe 53 and valve 54 to the alkylation unit 90. A portion or all of the normal butenes produced in dehydrogenator 22 may be passed directly from separating means 24 through pipe 21 and through pipe 9|, and valves 92 and 93 to be mixed with the isobutane fraction entering the alkylation unit 90. Alternatively, or concomitantly, the aforementioned heavier olefin polymers may be introduced through pipe 83 to pipe 9| and passed to the alkylation step.

As will be discussed more fully hereinafter, either a solid stationary alkylation catalyst or a fluid alkylation catalyst such as concentrated sulfuric acid, or the like, or concentrated hydrofiuoric acid, may be used. Fresh portions of such a fluid alkylation catalyst are introduced through pipe 96 and valve 91 to the alkylation unit 90. While it may be passed more directly to the alkylation step, it is more preferably mixed with the hydrocarbon material passing through pipe 53. In general it is desirable to keep the olefin concentration low during the alkylation process, as disclosed in Freys Patent 2,002,394, and the olefin-containing stream may be added at a number of points along a reaction zone through a number of pipes, represented by pipe 94 and valve 95, through which is passed a portion of the olefin-containing stream from pipe 9| to an intermediate point of alkylation unit 90. The effluent of the alkylation is passed through pipe 98 to a catalyst separator IIO. When a liquid catalyst such as concentrated sulfuric acid or concentrated hydrofluoric acid is used, the catalyst separator will generally include a. settling and separating tank, or the like, for the separation of the main part of the catalyst from the hydrocarbon part of the eflluent. The catalyst is then withdrawn through pipe III and valve II2 for further concentration, purification and other treatment, and if desired a part or portion of it may be recycled directly to the alkylation step through pipe H3 and valve II4 to pipe 96. In such a case the catalyst separator will also generally include some means for removing traces of acidic material from the hydrocarbon material, such as an alkali wash, or the like. The hydrocarbon material is then passed through pipe H5 and valve I I6 to fractionating means represented by the distillation column I20, provided with suitable heating means I2I and cooling and condensing means I22.

An alkylate fraction, containing normally liquid hydrocarbons produced in the alkylation step, is removed through pipe I23 and valve I24. This fraction may contain some definite controlled amount of normal butane, to furnish a desired volatility and vapor pressure, and this alkylate fraction may serve directly as a motor fuel, or as a motor fuel blending stock, and may be further treated and fractionated as desired. Any undesirable low boiling products may be separated from the fractionating means I20 and from the proces through pipe I25 and valve I26. A butane fraction is removed through pipe I30 and may be returned in part to the alkylation step through valve I3I to pipe 53. At least a part of this butane fraction will generally be subjected to fractionation to separate isobutane and normal butane. In many instances this is preferably done by passing the fraction to fractionating means I02 from pipe I30 through pipe I32 and valve I33 to pipe I00. Any portion of this butane fraction, if desired, may be fractionated in fractionating means I2 by being passed from pipe I32 through pipe I34 and valve I35 to pipe 11, especially when this stream is substantially olefinfree, as is often true for this part of the eilluent of a catalytic alkylation step.

The introduction of the hydrocarbon str passing through pipes I 0, 45, and 11 has been described as being made at different points to fractionating column I2. This is especially to be preferred when the charge stock to the process contains only a small amount of isoparaflins and the isomerization is conducted to produce isoparaflins in the higher part of the range discussed. However, in many cases it will be satisfactory to introduce any two or all three of the streams at a single point, with suitable control of valves MI and I42 in pipe I40 and of valve I in pipe I43, When both the polymerization and the alkylation steps are used, a portion or all of the unreacted butane efliuent from the polymerization may be passed from pipe Tl through pipe I45 and valve I46 to pipe 53 and the alkylation step, with suitable control of valves IDI and 19.

I also contemplate as a part of my invention, the treatment of a mixture of pentanes in substantiaily the same manner as has just been described for a mixture of butanes. When treatin a mixture of pentanes, the isopentane will pass overhead from the fractionating column I2 as did the isobutane as described. Likewise normal pentane will pass from the bottom of the column and may be treated in accordance with the treatment or normal butane described. Although a third pentane, neopentane or tetramethyl methane is known, its presence in naturally-occurring hydrocarbon materials has not been observed in any great amount. 11 such neopentane should be present, it can readily be separated from the isopentane-normal pentane mixture before this mixture is introduced to my process, or may be removed through pipe I5 and valve I6. Somewhat difierent temperatures of dehydrogenation, isomerization, polymerization, and/or alkylation may need to be used when using isopentane instead of isobutane and when using normal pentane instead of normal butane, but these conditions will not be widely different from corresponding conditions for the butanes and may be readily ascertained by one skilled in the art, for any particular case. The isopentenes produced by the dehydrogenation of isopentane will be predominantly tertiary-bas oleflns and will react with normal pentenes produced from normal pentane in a manner analogous to that herein described for the oopolymerization of isobutene with normal butenes. Normal pentenes will react with isopentane in the alkylation step under only slightly more drastic conditions than those used when a butane is being treated by the invention. Under some conditions of isomerization of normal pentane, especially with an extended conversion of normal pentane, appreciable amounts of isobutane are produced as well as isopentane. This isobutene may be retained in the isopentane fraction passed through pipe 50 and will undergo concomitant conversion into motor fuel in a subse quent step.

It is a feature of my invention that the process is quite flexible, and readily adapted to handle charge stocks of various proportions of normal and lsoparamns, and to produce large quantities of either parafllnic or olefinic, highly branched liquid hydrocarbons. If desired, either the polymerization or the alkylation steps may be practiced alone to the exclusion of the other. In one case an olefin produced from normal butane is reacted with an olefin produced from isobutane and in the other case an olefin produced from 7 Search Room normal butane reacts directly with lsobutane. In both cases, all the normal butane charged to the process eventually appears in the highly branched liquid hydrocarbon product, either directly through a normal olefin reaction step or indirectly through isomerization to isobutane, except of course for the material lost through unavoidable side reactions. In many instances a completely paraillnic product is desired, and in such a case the alkylation step produces this product directly while similar parafiin hydrocarbons may be produced in the process through polymerization and subsequent saturation of the polymers with hydrogen previously produced within the process by dehydrogenation. When an olefin-containing motor fuel stock can be used, a product with a high unleaded octane number (that is, before the addition of an antidetonating agent such as tetraethyl lead) can be produced by blending the olefin polymers produced in the polymerization step with the paraflinic product produced by the alkylation step. The product from the polymerization step has an octane number of about 82 and from the alkylation step of about to 96. While the polymer product, wnen saturated with hydrogen, also has an octane number within the range of 90 to 96, without such saturation it has a blending octane number of about when blended directly with a parariinic fuel and in amounts not greater than about 30 per cent by volume. I therefore prefer to operate my process to produce a single product with both the polymerization and alkylation steps, the product containing about 5 to 30 per cent, preferably 15 to 25 per cent, of olefin polymers and the remainder paraflinic material comprising paraflins produced by the alkylation step. The two steps can be made to cooperate further by passing any polymers too heavy for the desired motor fuel stock :to the alkylation step under conditions adapted to react isobutene, or isopentane, with these heavy polymers to produce liquid parafilns in the desired motor fuel range.

In most cases any known isomerization process may be used in connection with isomerizer 32, although of course such processes are not to be considered complete equivalents of each other either as to operating conditions or yields. However, any such process can-be operated by one skilled in the art to produce an efliuent, the predominant part of which is a hydrocarbon frac- :tion of the same. number of carbon atoms as the normal paraflln charged and containing appreciable quantities of the desired isoparaflin; and

. an advantage of the invention is that the process disclosed herein will adequately handle any such product. A highly desirable operation can be secured by using aluminum chloride or aluminum bromide, preferably deposited on a highly porous support such as activated charcoal or dried silica gel, or the like. The temperature is preferably in the lower part of the range of 163 to 400 F., and while the process may be opera ed with the reactants substantially in the gaseous phase, I prefer to operate with sufficient pressure to maintain the reactants in liquid phase and with the time of reaction so limited that the amount of isoparaffln in the eflluent is not greater than about 80 per cent of what it would become if the time were sufllcient for an equilibrium between the normal paramn and the isoparafiin. As previously indicated, the fraction of the product corresponding to the normal paraflln charged will preferably contain 30 to 60 per cent of isoparaflln. As mentioned, it is desirable that the charge to the isomerizer should be substantially free of unsaturated hydrocarbons, and a second butane, or pentane, fractionation means I02 has been described to accomplish this result. In some instances it may be desirable to submit the material passing through pipe 30 to isomerizer 32 to further treatment, as with concentrated sulfuric acid in means not shown, to remove small amounts of unsaturated material, or other contaminants, which may be present.

While any of a number of dehydrogenation catalysts may be employed in the dehydrogenation chamber 22 and in dehydrogenation chamber 52, I prefer to use a chromium oxide-containing catalyst such as described by Huppke and Frey in U. S. Patent 1,905,383, or in U. S. Patent 2,098,959, bauxite with deposited chromium oxide, certain hard bauxites alone, or the like. When dehydrogenating isobutane, I prefer to operate at a temperature within the range of 750 to 1150" F. and when dehydrogenating normal butane, I prefer to operate at a slightly higher temperature such as one within the range 800 to 1250 F. If my process is used to treat a mixture of isopentane and normal pentane I prefer to dehydrogenate isopentane, using such a catalyst. at a temperature between 700 and 1100 F. The normal pentane should be dehydrogenated at a temperature between about 725 and 1150 F. In all such dehydrogenation operations I prefer to operate at a pressure at or near atmospheric. If the pressure is above atmospheric, it should not, be more than 50 or 100 pounds per square inch pressure above atmospheric.

I prefer to use a solid polymerization catalyst in polymerizer 61 for the polymerization of the oleflns although this is not always necessary. Such a solid catalyst may be one prepared from hydrous silica intimately associated with hydrous alumina such as the silica-alumina catalysts described by McKinney in Patent 2,142,324 or 2,147,985, and in the copending application of Frey, Serial Number 329,195, filed April 1 1940 or one of the well known solid phosphoric acid catalysts, or may be zinc halide orsimilar halide deposited upon an inert support such as silica, pumice stone and the like.

While I prefer an operation in connection with a solid catalyst, nevertheless I do not desire necessarily to be restricted to the use of a solid catalyst. Operations are known in which liquid catalysts are quite suitable for the polymerization of olefins, such as sulfuric acid of about 75 per cent concentration in aqueous solution, strong phosphoric acid, various sulphonic acids and the like. While I may use any such catalyst in my process, I do not consider that one catalyst is the equivalent of another catalyst either as to preferable operating conditions or as to the products produced, but there will be minor variations between each catalyst when at their optimum operating conditions.

The polymers produced when using pentanes as a charge stock to my process will consist principally of decenes which will be highly branched and which, upon hydrogenation, will have high octane numbers and will be quite suitable for use in relatively nonvolatile aviation fuels and the like. With the exception of slight obvious changes in operating conditions to compensate for the difference in reactivities of pentanes and the corresponding butanes and pentenes and the corresponding butenes, such a process to which is charged a mixture of isopentane and normal pentane can be operated in substantially the man- 50 the art for any particular installation.

ner I have described for operating with a mixture of isobutane and normal butane.

The alkylation step is preferably conducted in the presence of an alkylation catalyst. Any one 5 of a number of known alkylation catalysts may be used, although not under completely equivalent conditions nor with completely equivalent results. Catalysts which may be used in my alkylation stepTnclude aluminum chloride and bronum chloride or bromide with metal halides, especially halides of the alkali metals. I prefer to use concentrated sulfuric acid or concentrated hydrofluoric acid, with the acid and reactants in liquid phase and with the reaction conducted at a temperature between about 0 and 100 F. The ratio of liquid acid to liquid hydrocarbon material should be between about 1:10 and 1:1, with intimate mixing and emulsification of the acid and reactants and with suitable means for removal of heat of reaction. As one means of accomplishing this, the reaction mixture may be rapidly passed through a tube coil of restricted cross sectional area immersed in a cooling bath. The olefin concentration in the reacting mixture in any case is preferably kept at a low value, and rather than initially mixing a large portion of oleflns and isoparaflins and passing the resultant mixture through the alkylation zone I prefer to add olefin during a reaction period of about 15 minutes to 2 hours. The rate of addition will be somewhat dependent on other operating conditions, and can be readily determined by trial for any particular case. Preferably the olefin containing material is added to the paraflinic stream in contact with the catalyst at a plurality of intermediate points, as discussed.

4o Numerous adaptations and variations of this invention may obviously be used and applied by one skilled in the art without departing from the spirit of the disclosure. It will be understood that the flow diagram is illustrative and that many additional conventional pieces of equipment, such I claim:

1. An improved process for converting butanes to an aliphatic motor fuel stock, hich comprises wggmaflrst -u- 1 man isobutane fraction and a norm bu fractiq l, subjecting a first ortion of said normal ntane frac on misgmmgatign to fogn a butane mixture and passing same to s d first utane rac onating means, de hydrogenating a second portion of said normal butane fraction to form a norma1 butenes fraction, dehydrogenating at least a portion of said isobutene fraction to form in a first portion or said normal butenes fraction and in said isobutene fraction to form copolymers boiling in the motor fuel range, separating from emuents of said copolymerization a copolymer fraction so produced and a C4 fraction containing unreacted butenes, passing at least a portion of said C4 fraction to a second butane fractionating means, removing from said second means an iso C4 fraction and a normal C4 fraction, admixing said normal C4 fraction with said second portion of said normal butane fraction, passing said iso C4 fraction to alkylating means, passing also to said alkylating means a second portion of the aforesaid normal butenes fraction and reacting normal butenes contained therein with isobutane in said iso C4 fraction to form isoparafllns boiling in the motor fuel range, separating from effluents of said alkylation a C4 fraction and passing same to the aforesaid second fractionating means, separating also from said alkylation efliuents an isoparaflinic fraction so produced, and blending said copolymer fraction and said isoparaffinic fraction to form an allphatic motor fuel stock containing between 5 and 30 per cent of olefins.

2. An improved process for converting isoparafiins and normal paramns of the class consisting of butanes and pentanes to an aliphatic motor fuel stock, which comprises isoparafiins and passing same to said first hydro- $22233 from a firsthydrogarhgn fractionating me n i arafin rrtctien of pfd cma'ggal carbon fractionating means, dehydrogenatin i wmof said normal param fraction to form a normal olefin fraction, dehydrogenating at least a portion of said isoparafiln fraction to Search Room form an iso-olefin fraction, wing-Qingdafins in a first portion of said norma olefin fraction and in said iso-olefin fraction t9 0- polymers boiling in the motor fuel range, separating from efliuents of said copolymerization a copolymer fraction so produced and a hydrocarbon fraction containing unreacted paraifins and olefins, passing at least n of sai reacted hydr'oEarBon fraction to a second hydrocarbon fractionating means, removing from said second means an isoparafiin fraction and a normal paraifin fraction each containing a small amount of olefins, admixing said normal paraflln fraction with said second portion of the first said normal parainn fraction, passing the last said isoparaflin fraction to w passing also to said alkylating means a second portion of the aforesaid normal olefin fraction and reacting normal olefins contained therein with isoparafllns in said isoparafiln fraction to form isoparafllns boiling in the motor fuel range, separating from efliuents of said alkylation a low-boiling paramn fraction and passing same to the aforesaid second hydrocarbon fractionating means, separating also from said alkylation efliuents a motor fuel range isoparaffinic fraction so produced, d blending said copolymer fractig ngnd the last $8 i opara 'c r c ion toform an aliphatic motor Tffiel' stockcontaining' between 5 and 30 per cent df'hl'fii''f JEAN P. JONES.

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