US2276171A - Production of motor fuels - Google Patents

Description

,March 10, 1942. R, B, EwELL PRODUCTION OF MOTOR FUELS Filed April 30, 1940 Patented Mar. 10, 1942 PRODUCTION VOl." MOTOR FUELS Robert Bartlett Ewell, Chicago, Ill., assigner to Universal Oil Products Company, Chicago,

Ill.,

a corporation of Delaware Appneatmnaprii so, 1940,'ser2a1 No. 332,428

6 Claims.

This invention relates to a process wherein volatile gasolines are converted by a number of treatment steps to substantial yields of high octane gasoline with increased boiling point and containing principally isoparaiiins and derivatives of aromatic hydrocarbons.

The purpose of this invention is to convert highly volatile gasoline such as natural gasoline, containing comparatively large proportions of butanes and pentanes, into more useful products boiling in the gasoline range. Simultaneously, it is desired to improve the antiknock properties of the gasoline.

This invention comprises a combination of the treatment steps of isomerization, dehydrogenation, alkylation of isoparains, alkylation of aromatic hydrocarbons and aromatization.

More specifically, this invention comprises fractionation of the gasoline to be treated into: (1)

heavy fraction containing principally Cs or higher hydrocarbons; (2) a fraction containing substantially all the normal pentane; (3) a fraction containing all the isopentane; (4) a normal butane fraction and (5) a fraction consisting principally of isobutane. The normal pentane fraction is passed through the isomerization step, the hydrocarbon products from which are returned tol the original separating zone. Employing a recycling operation, all original pentane is converted into isopentane. This isopentane may be (a) charged to an alkylation step, (b) blended with the nished gasoline or (c) stored for further blending with gasolines from other sources.

The normal butane fraction is entirely or in part contacted with a dehydrogenating catalyst and after removing ethane and lighter products, is used in alkylating isoparafiins and aromatics. If the quantity of aromatic hydrocarbons and isoparafns to be alkylated is relatively large, all

. of the normal butane obtained from the original charging stock may be dehydrogenated. In some cases, however, where the charging stock contains a large quantity of normal butane it may be found desirable to subject a portion of the normal butane to an isomerizing step to form isobutane. The isobutane present in the charging stock together with that which may be formed in the isomerizing process is alkylated with olens obtained principally in the dehydrogenation of normal butane. The Ce and higher hydrocarbons obtained from fractionation of the charge are contacted with an aromatization catalyst after which ethane and lighter products are removed. The unconverted paraftins and the olefins formed A in the dehydrocyclization step .are separated from the aromatic hydrocarbons by fractional distillation, by solvent extraction or by a combination of the twomethods. The unreacted parains and the olens formed in the .aromatization process are recycled to the aromatization catalyst. The

aromatic hydrocarbons obtained by the methods mentioned above are alkylated by the propylene and butenes obtained in the catalytic dehydrogenation step already referred to. It is a feature of this process that any propane formed in the mal butane, isopentane, normal pentane and higher boiling hydrocarbons, commingling said higher boiling hydrocarbons with a recycle stock of paraiiins and olens obtained in a manner to be subsequently described and subjecting said mixture to a catalytic aromatization process, separating the conversion productsfrom said aromatization process into a fraction composed of hydrogen, methane and Cz hydrocarbons, a fraction comprised essentially of aromatic hydrocarbons, a fraction consisting essentially of paraflins and olens containing three or four carbon atoms per molecule and a fraction consisting principally of unreacted parains and olens with Cs and higher boilinghydrocarbons separated from the charging stock to form the combined feed for the aromatization step as hereinbefore set forth, commingling the aforesaid aromatic hydrocarbons separated from the products of the aromatization step with C3 and C4 hydrocarbons obtained' from the butane dehydrogenation step to be subsequently described, directing said mixture of aromatics and olefin-containing hydrocarbons to an alkylation zone for catalytic alkylation of the aromatic hydrocarbons with propene and butenes to form alkylated aromatic hydrocarbons of the motor fuel boiling range, separating said alkylated aromatic hydrocarbons from the unreacted propane and butane, simultaneously catalytically isomerizing normal pentane separated from the charging stock into isopentane, catalyticallydehydrogenating a portion of the normal butane obtained from the charging stock, isomerizing the remainder of said normal butane into visobutane, commingling said-isobutane with the isobutane separated from the charging stock and catalytically alkylating the combined isobutane fractions with propylene and butenes vobtained in -the butane dehydrogenation step to forma saturated product substantially of motor fuel boiling range, separating from the products of the a1- kylation step alkymer and reacted lpropane and normal butane, commingling said unreacted propane and normal butane into propane and normal butaneseparated from the' aromatic Y. al-

kylation process with the normal butane 'obtained from the charging stock and directing said mixture to the butane dehydrogenation step as here-- vwhich may comprise a volatile gasoline such as a natural gasoline, is introduced by way of line I to separation zone 2. Separation zone 2 comprises a series of fractionating columns wherein the charging stock is fractionated jointly with the hydrocarbon conversion products of the isomerization steps. The normal butane obtained in separation zone 2v is removed by way of line 3 from which a portion or all may be directed through line 4 to dehydrogenation zone 5.

The dehydrogenation is accomplished in the presence of a catalyst which consists in general of pellets or granules of alumina or inert siliceous or refractory materials composited with compounds, and preferably the oxides, selected from the elements of the left-hand columns of groups IV, V and VI of the periodic table. Although the dehydrogenation catalysts disclosed above are the preferred catalysts, they are not to be considered as a limiting feature, for other catalysts capable of effecting dehydrogenation known to those skilled in the art may be employed in the broad scope of the invention. Dehydrogenating temperatures are ordinarily in the range from 900- l200 F., While employing a pressure ranging-from substantially atmospheric to a hundred or more pounds per square inch superatmospheric.

The products of the dehydrogenation treatment in zone 5 are directed through line 6 into separation zone 'I wherein hydrogen and light gases such as methane and the C2 hydrocarbons are substantially separated from the dehydrogenated products and withdrawn through line 8.

If so desired, a portion of the normal butane may be removed from line 3 by-way of line 9 and directed to isomerization stage I0 for conversion into isobutane. As there may be changes in the composition of the charging stock there will necessarily be corresponding modifications in the proportions of materials directed to the various steps in the process. Catalysts used in the isomerization process normally include anhydrous aluminum chloride with or without an inert support. In some cases it may be found advantageous to use mixtures of anhydrous chlorides of other elements in conjunction with the aluminumv chloride. Chlorides that have been found effective rin such combination include those of zinc, zirconium, iron and copper. It has also been found advantageous in the isomerization process to introduce anhydrous hydrogen chloride as well as elementary hydrogen along with the charging stock. The amount of hydrogen chloride introduced usually lies within the approximate range of 0.5 to by volume of the normal butane. It has been found that saturating the normal butane fraction with hydrogen gas at room temperature and under a pressure within the approximate range of 25 to 100 atmospheres produces beneficial results. The normal butane is contacted with a catalyst at a temperature within the approximate range of 50-350 C. and pressures varying from substantially atmospheric to approximately 200atmospheres may be used. The reaction of the isomerization of normal butane to `isobutane is never complete under the conditions of operation and the mixturev of normal butane and isobutane obtained is directed by way of line II to line I6 from which it is returned to separation zone 2 "wherein thegisobutane is fractionated from the normal butane. The hydrogen and hydrogen chloride used in the isomerization process may be recovered by methods Well known and reused in the process. These recovery steps are not `shown in the flow diagram. The isomerization of normal butane is always accompanied by the formation of both lighter and heavier products such as propane and pentane. Any 'propane formed in the isomerization step may be cominingled with the charging stock for the dehydrogenation zone 5.

gases in line I8 is directed to the alkylation zone The isobutane separated from the stock together with that formed in isomerizationis removed from separation zone 2 by Way of line I2 from which it is directed by way of line I1 to line I8 for commingling with the propyleneand butylene-containing gases obtained from the separation zone I followingthe dehydrogenation process.

The mixture of isobuta'ne and olefin-containing I9 for alkylation of isobutane to higher molecular weight isoparaflins. The normal pentane separated from the charging stock in zone 2 is removed by way of line I4 and directed to the pentane isomerization zone I5. Catalysts used for isomerizing normal pentane are substantially the same as those used in isomerizing normal butane. In some cases, it may be desired to isomerize normal pentane and normal butane in the same zone, although in general separate zones will give more selective results. The temperatures used'in the isomerization of normal pentane usually lie within the approximate range of -250 C. Pressures Within the range of 100-200 atmospheres may be used. The addition of hydrogen and anhydrous hydrogen chloride in approximately the same quantities as used in the butane isomerization step may be used here. A small amount of propane and butanes are formed in the pentane isomerization step. The propane separated from the pentane isomerization step may be added to the I5 by Way of line I6 and is separated in separation zone 2.

The isopentane separated from the charging stock aswell as that formed in the isomerization stepis removed from separation zone 2 by way of line I3 from which it is directed to line I8 for commingling with the dehydrogenation products obtained from separation zone 1. The mixture of isopentane and olens is directed from line I8 to alkylation zone I9. The catalysts used in the alkylation of isoparafllns with oleflns may comprise concentrated sulfuric acid, hydrogen fluoride, aluminum chloride with hydrogen chlorideand phosphoric acid either in liquid form or in the form of a solid composite with a siliceous adsorbent. When using sulfuric acid, temperatures within the range of l5-l00 F. are com' paraiins to olefins in the alkylation reaction zone. Ratios of isoparain to olefin lying between 80:1 and 20:1 give satisfactory results.l

According to the flow diagram isobutane and isoy pentane are alkylated in the same zone. If desired, separate alkylation zones may be used for isobutane and isopentane, although such procedure is not necessary. The products of the alkylation zone are removed by way of line 20 and directed to a fractionation step 2l. Since propane and normal butane are practically inert under the conditions of alkylation used, they are removed by way of line 22 and directed to line 3 for subsequent dehydrogenation to the corresponding olei'lns. The excess isobutane and/or isopentane separated in zone 2| is removed by way of line 23 and recycled to the alkylation zone. cipally of isoparaflins of the motor fuel boiling range is removed from the alkylation zone by way of line 24 and directed to storage 25. It may be subsequently redistilled to remove the small proportion of material boiling above the gasoline boiling range. In some cases it may not be desired to alkylate all the isopentane and a portion may be removed by way of line I3 to line 26 and directed to storage 25. Isopentane has a high antiknock value and may be disposed of as such of may be blended with gasolines to produce the desired vapor pressure and antiknock requirements.

The higher boiling paralins separated from the charging stock in zone 2 consist principally of hexane, heptane and octanes and are directed by way'of line 26 and after commingling the recycled charge of parains and olens directed to aromatization zone 21.

The alkymer product which consists prinv Catalysts used in the aromatization process table. Temperatures used in the aromatizationv process lie within the approximate range of 850- 1200 F. and pressures varying in the approximate range of atmospheric to 100 or more pounds are used. The conversion products of the aromatization process consist of aromatic hydrocarbons, unreacted parains, their corresponding olens, hydrogen and small quantities of light hydrocarbons. These conversion products are directed by way of line 28 to separation zone 29. The hydrogen, methane and C2 hydrocarbons separated in zone 29 are removed from the system by way of line 30. Separation zone 29 may comprise a series of fractionating columns for separation of aromatic hydrocarbons from paralins and olens. The boiling points of parafns such as normal hexane are usually 1012 C. below that of the corresponding aromatic hydrocarbon such as benzene. Such differencesin boiling point are suiicient to obtain necessary separation by distillation methods. It

may be preferred, however, to use such selective are removed from separation zone 29 by Way of line 32 and are commingled with propyleneand butene-containing gases separated from dehy-v drogenation zone 5 in zone 'I from which they are removed by. way of line 33. The mixture of aromatic hydrocarbons and olen-containlng gases is directed to alkylation zone 34.

The aromatic hydrocarbons are alkylated with the yoleflns in the presence of suitable catalysts such as sulfuric or phosphoric acid, solic phosphoric acid, metal'halides such as aluminum chloride, hydrogen fluoride, boron trifluoride or mixtures ofvhydrogen lfluoride and boron trifluoride. When using sulfuric acid, concentrations of about 84 to 100% are employed. The

so-called solid phosphoric acid catalysts consist of a composite ofl liquid phosphoric acid with kieselguhr or s imilar suitable siliceous materials. Metal halides employed should be substantially but not completely anhydrous. The temperatures used in the alkylation step depend upon the catalyst, its concentration, etc., and cover a range of approximately 35 to 200 F., but are usually Within therange of 50-150" F. The pressures may extend up tc 500 pounds per square inch or higher and are normally suilicient to maintain the gaseous olens used in substantially liquid phase.

The reaction products from alkylation zone 34 are passed through line 35-to separation step 36. The C3 and C4 parains present in the olefincontaining gases for the alkylation process are removed from separation zone 36 by Way o'fline 31 from which they are directed to linev3 for recycling to the butane dehydrogenation zone. The alkylated aromatic hydrocarbons, together with small amounts of unreacted aromatics are removed from separation zone 36 by Way of line 38 andsent to storage 25. These alkylated aro- .matic hydrocarbons lie within the gasoline boil- TABLE I Y East Texas natural gasoline- 1000 'pounds Octane number: 83 Reid vapor pressure: 2li

Volume Pounds percent l-Butane 18 2. 0 n-Butane 298 3l. 9 i-Pentane. 219 21.9 n-Pentane... 203 20. 0 Hexane 171 16.1 Heptane. 56 5. l Octane 34 3,0

TABLE II Summary of yields Volume Rcld Variation prrcent Octane vapor gglino number pressurey 73. 0 83 7 74. 2 B5 6 75. 6 S6 6 7G. 7 88 l1 The four examples cited differ partially in the proportion `of isopentane alkylated and the proportion of normal butane lsomerized to the iso derivative, The particular proportions directed to the various streams will depend in part upon the volatility desired in the final product.

. I claim as my invention:

1.A A process for producing more valuable products from volatile saturated gasoline which comprises fractionating the gasoline to form a, light fraction containing normal butane and a. heavier fraction containing hexane and higher boiling', hydrocarbons, subjectingsaid lightA fraction to dehydrogenation to produce oleiins'therefrom, subjecting said heavier fraction to aromatization to form aromatics, commingling the latter with at least a portion of saidolefins, subjecting the resultant mixture to alkylation to react olefins with aromatics, and recovering the alkylated aromatics thus formed.

2. The process as defined in claim 1 further characterized in that there is additionally separated from said gasoline an iso-paraiiln fraction of lower boiling point than said heavier fraction, said iso-parailin fraction being commingled another portion of said olens from the dehydrogenating step, the mixture subjected to alkylation and resultant alkymer` blended with said alkylated aromatics. Y.

3. The process as dened in claim 1 further characterized in that there is additionally separated from said gasoline an iso-butane fraction which is commingled with another portion of `said olens from the dehydrogenating step, the mixture subjected to alkylation and resultant alkymer mixture subjected to alkylation and resultant alkymer blended with said alkylated aromatics.

5. The process as deiined in claim 1 further characterized in that there is additionally separated from said gasoline a normal pentane iraction which is subjected to isomerization and resultant iso-pentane blended with said alkylated aromatics.

6. The process as defined in claimV 1 further characterized in that there is additionally separated from said gasoline a normal pentane fraction which is subjected to isomerization and the resultant isopentane commingled with another portion oi said`olens from the dehydration step, the mixture subjected to alkylation and-the resultant alkymer blended with said alkylated

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