US2348815A - Manufacture of motor fuel - Google Patents

Description

May 16, 1944. F. HoRToN .Er AL MANUFACTUREHOF MOTOR FUEL Filed June 20, 1939 Patented May 16, 1944 l I MANUFAOTURE or Moron FUEL Francis Horton, Riverdale, N. Y., Lebbens C. Kemp, Port Arthur, Tex., and Richard E. Nagle, New York, and Loren P. Scoville,'` White PlainaN. Y., assignors, by-mesne assignments, to The Texas Company,'New York, N. Y.,`a corporation of Delaware Application June 20, 1939, Serial No. 280,064

' 12 claims. (ci. esca-683.4)

This invention relates to the manufacture of motor fuel and has to do particularly with the alkylation of isoparains with olens to produce high antiknock branch chain parailln` hydrocarbons of gasoline boiling range. The invention is concerned with the conversion of normally gaseous hydrocarbons into high antiknock gasoline hydrocarbons by the alkylation of low-boiling y isoparafins,such as isobutane or isopentane', with oleflns in the presence of an alkylation catalyst.

The invention contemplates a process for the commercial production of high antiknock motor fuel, for example aviation gasoline, from refinery gases including cracking still gases.

In the alkylation of isobutane with olens, it.

is desirable to treat an unsaturated hydrocarbon mixture containing isobutane in excess of the oleiins. Renery gases such as cracking still gases generally contain an excess of oleiins and special methods for obtaining a, suitable charge for alkylation are necessary. A phase of the invention includes the preparation of a suitable charge to the alkylation operation. n

In the preparation o f the charging stock, cracking still gases or other refinery gases or mixtures thereof, are fractionated to obtain a charge suitable for alkylation with or Without the addition of additional low boiling isoparafins from another source. For example, gases derived from a cracking still may be--fractionated to remove lighter and heavier constituents and the remains intermediate cut used as the charge. Thus, by removing propaneon the low side and normal butane and heavier on the high side, a middle cut may be obtained of the desired characteristics. Such -an intermediate cut may comprise 'a fractionator or stabilizer side stream which on fractionation or debutanization lproduces a satisfactory charge for alkylation. In case the side stream has a fairLy wide boiling range, showing only rough fractionation, then the side stream may be fractionated to obtain a, rather sharply' fractionated cut, and thisv cut used as such, or after debutanization to separate a portion of the normal butane.

It is desirable when using a stabilizer side stream to enrich suchv stream, preferably after extraneous light condensate may be anvoverhead fraction from a fractionator or stabilizer, gases from an accumulator drum of va cracking still, or

an absorption condensate obtained by absorption extraction of various cracking-still gases.

'I'he light condensate is preferably depropanized prior to mixingthereof with the side stream.

The mixture of side stream and light condensate is preferably debutanized, prior to charging the mixture tothe alkylation operation. The debutanizing operation removes al1- or a portion of the normal butane and thereby increases the ratio of isobutane to loleflns. By regulating the respective 'proportions of the side stream and the light condensate, .a product containing the `de sired ratio of isobutane to oleflns for alkylation is readily secured. It is preferable that the charge contain a ratio of isobutane to oleiins of at least 1:1 and preferably a considerable excess of isobutane, for example a, ratio of isobutane to oleiins within the range of about 2:1 and 7:1, or higher.

Another feature of the invention is an improved type of alkylation operation. In lthe alkylation operation a stream of isobutane and catalyst may be circulated through a mixer, a chiller, a reaction zone, and back to the mixer. The

vhydrocarbon charge containing the isobutane'and oleiins is injected into this stream. Fresh catalyst may be added to the stream and spent catalyst withdrawn. In the reaction zone the isobutane is alkylated by the oleflnsin an exothermic increase the volume of available charge. Such reaction,. and the exothermic heat of reaction is removed in the chiller by refrigeration with a suitable refrigerant, such as propane.

IA further feature of the invention is the treatment or distillation lof the hydrocarbon alkylation products. The crude alkylate is fractionated to remove excess or residualnormally gaseous hydrocarbons which are recycled, at least in part. to the charge fractionation operation. It ispreferable to' debutanize the crude alkylate and'fractionate at least a portion of theoverheadcut to separate a fraction rich in isobutane which may be recycled to the alkylation operation. The remainder containingsnormal butane may be returned to the fractionation operation in which the charge is fractionated for depropanization. A preferred method of operation is to split the overhead from/the debutanizer, returning one4 portion to the charge fractionator and further fractionatin'g the other portion to concentrate the isobutane for recycling to the alkylation operation. The normal butane which is separated in the fractionation of the latter portion may be discharged from the system andthe normal butane so discharged may be so regulated as tobe approximately equal to thenormal butane entering thesystem in the fresh feed. In this way a balanced operation is obtained whereby an ex- I cessivevolun'ie of butane will not build up in the system.

The invention will be more fully understood from the following description read in connection with the accompanying drawing which shows a diagrammatic sketch oi' one form of apparatus for carrying out the process of the invention.

l Referring to the drawing, a cracked naphtha, for example from an accumulator drum of an adjacent cracking still, is passed through a line I to a stabilizer 2. In this stabilizer a stabilized naphtha is'produced which is withdrawn from the bottom thereof' through the line 3. A light hydrocarbon fractionA containing all or a portion of the C3 hydrocarbons, including propane, is

taken overhead through the line 5; A side stream` containing C4y hydrocarbons, with or without any portion of the Cs hydrocarbons, is with' drawn through the line G. Such a side stream may be relatively high in isobutane content .and contain isobutane in considerable excess of the oleiins. The side stream is forced by the pump 1 through the line 8 to a fractionator I0. In the.

fractionator the lighter hydrocarbons, such as all or; a portion of the Ca hydrocarbons are re` moved overhead through the line II. The light fractions taken overhead from the stabilizer 2 through the line 5 and from the Iractionator @il through the line l i, are joined and passed through ythe line I2 and a condenser ill, wherein the hy- Edrooarbons are at least partially condensed, and the' resulting condensate collected in receiver i5. The uncondensed hydrocarbons are removed from the top of the accumulator through the line It. The condensate inthe accumulator w, including propane, 'is withdrawn from the bottom thereof through the line I and pumped by the pump is through the line i@ to the upper portion of the fractionator Iii, and through the line Y 2l to ythe upper portion of the stabilizer 2. as a refiuiemediurn.. The liquid fraction in the fractionator It, preferably a C4 fraction, is withdrawn from the bottom of the fractionator I@ through the line 22 and pumped 'by the pump 23 or sent under fractionator pressure without a pump through the line 2@ to a debutanzer 2%, o; may be used direct as alkylation charge by naming it through branch line 26.

A light condensate, such as the lower boiling fractions of a debutanized cracked naphtha, or

y debutanized absorption condensate, preferably containing C4 hydrocarbons and a considerable amount of hydrocarbons boiling somewhat above C4 and containing isobutane and butylenes in which the butyienes are ordinarily Ain excess oi the isobutane, may be charged through the line 27 and commingled' in the line 22 with the Cr cut withdrawn from the bottom of the fractionator It. This light condensate in mixture with the C4 cut is passed to a debutanizer 2b. In the debutanizer ze, a debutamzed iight: napmha,

preferably containing at least a portion of the normal butano, is withdrawn from the bottom of the debutanizer through the line 2E. A C4 fraction 'containing isobutane in excess of the olens is removed overhead from the debutanizer through the line 2s and condenser Ill. In the condenser the hydrocarbons are liquefied and the condensate forced by the pump 3i tothe manifold line 32, continunicisttirigA with branch lines 33. 34 and "85 whreby'the. hydrocarbon charge may be split and passed in multiple injectioninto alkyiation stages I. 2l and 3 respectively. A portion of the condensate in line 32 may be returned to the upper portion of debutanizer 25 as a reux.

The alkylation stages I, 2 and 3 are multiple units and while three stages are shown, it is to be understood that any number may be used. The details of only stage I are shown.

The hydrocarbon charge is passed through branch line 33 to the stage number I and is introduced into the line 35 through which is circulated, by the pump 36, a stream of alkylation catalyst, alkylate and isobutane. The mixture is passed through a mixer 31 which may be of any well knownl or preferred type whereby the hydrocarbons are intimately contacted with the catalyst. The mixture is then passed through the line 3B to a chiller 39 wherein the exothermic .heat of reaction is removed by a refrigerating medium passing in indirect contact with the hydrocarbons.-

The refrigerating medium is preferably propane which is introduced through the line to a tank 4i. The liquid propane is passed from the bottom of the tank 4I through the line 42 into the chiller 39 wherein the propane is vaporized thereby eiecting cooling by indirect heat exchange., The vapors passfrom the chiller through the vapor line 43 back to the tank 4I. The vapors of propane are removed through the line it to a compression unit to be oompressed, cooled and .condensed to form liquid propane which may be recharged to the system through the line il?.

The mixture of catalyst and hydrocarbons the settler 5&3 the catalyst is separated from the hydrocarbons and is withdrawn through the line so and'rnay be recycled through the line 55. The

hydrocarbons are passed from the settler through the line 56 to the stage 2 of the process which is substantially identical with stage I and is shown diagrammatically. The hydrocarbons from stage 2 are passed through the line 51 totage 3. From stage s thehydrocarbons are passed through the line 5t to a neutralizer tu, referred to hereinafter.

Fresh catalyst may be introduced into the alhylation stages through the line 61 connecting with branch lines $8, Si! and III whereby the fresh catalyst may be introduced into stages I, il and t respectiveb, preferably into the circulating stream'of hydrocarbons and catalyst. The spent catalyst may be withdrawn from stages I, 2 and 3 respectively through the lines 1I, 12 and lo, which communicate with a draw-oir line 1I. for discharging the spent catalyst from the systeni for recovery or other disposal.

In the amlation units just described, the circulating streams oi' hydrocarbon and catalyst contain a ratio ofcatalyst to hydrocarbon oi about 1:1 by volume. The catalyst is preferably sulfuric acid 0i' about 9o to 100% strength, al-

though other suitable liquid catalysts are co'ntemplated. such as hydrated boron trliiuoride. A

very high ratio of circulated hydrocarbon to fresh .hydrocarbon is maintained. The ratio may range between about 5:1 and 100:1 and preferably between about` 10:1 and 30:1.

In the neutralizar $9,v the hydrocarbons are bons are pumped from the neutralizer 60 through.

the line. by the pump to a debutanizer 85. The overhead from the debuntanizer 85. containing isobutane and all or a portion ofthev normal butane, is passed through line 18 to a.

condenser Il wherein the hydrocarbons are substantially condensed. 'I'he condensate from the condenser 88 is passed all or in part through the line 8| and recycled by the pump 82 through the line 83 to the fractionator l0. In this way the recycled hydrocarbons are refractioated along with the fresh charge so that the isobutane content thereof eventually reaches the alkylation system for further reactionwith olens and for increasing the ratio of isoparaiilns to oleiins.

It is evident that this recycle portion of the ovel'rlld Yfrom debutanizerv85-isrthereby sub1 jected to the depropanizing operationin fractionator Il, thereby preventing propane buildup in the system. v y

It is preferable to withdraw at least a portion of the condensate from the condenser 8l through the branch line 84 and -pump 88 to a fractionator 88. In the fractionator 88 separation is made between the isobutane and normal butane. The normal butane fraction iswithdrawn as a condensate from the lower portion ofthe fractionator 88 through the line 98 and discharged from the system or used, if desired, for increasing the volatility of stabilized naphthas, for example the stabilized naphtha withdrawn from the bottom of stabilizer 2. A fraction rich in isobutane is passed from the top of the fractionator 88 through the vapor line 9| to a condenser 92 wherein the hydrocarbons are substantially condensed. l'I'he condensate is passed through the line 94 to a. pump 95 which recycles the isobutane fraction through the line 96 to the line 3,3. for charging along with the fresh olenic charge to the iirst stage of the alkylation system. 'I'he isobutane so recycled increases the amount of available isobutane for alkylation and also aids in creating a considerably higher ratio of isobutane to olens in the reaction mixture thanv in the fresh feed to the alkylation system. The Lamount of hydrocarbons charged through the branch line 84 to the fractionator 88 is preferably regof an excess normal butane n-the system is avoided.

The alkylate is withdrawn from the bottom of .the debutanizer 85 ariel passed through the line 98 to a iractionator |00, wherein the alkylate is separated into the desired fractions. An aviation gasoline of approximately 311 F. end lpoint is taken overhead through the vapor line lill and condenser |02. A side stream of `naphtha is withdrawn f rom an intermediate point of the iractionator |00 through the line |03 'to a strinper |04 from which vapors may be returned to the fractionator through vapor line |05. A naphtha of about 300 to 400 F. is withdrawn from the bottom of the stripper through the line |06.. The latter naphtha may be used in the manufacture of a heavy aviationor safety fuel. A fraction heavier than gasoline and boiling isobutane, 13.6 parts isobutylene, 9.9,parts butylabove about 400?. is withdrawn from the bottom of the fractionator through the line |08.

An example will now be given of the operation of the invention although it is to be understood that the invention is not limited to the specific example.

l An unstabilized naphtha from a cracking still is charged to a stabilizer from which a stabilized naphtha. an overhead vapor fraction containing C3 hydrocarbons, "and a side stream relatively. rich in isobutane, comprising mainly `C4 hydrocarbons with some lighter hydrocarbons, are

withdrawn. 'Iheside 'stream contains about 20 parts isobutane, 5.3 parts isobutylene, 3.8 parts butylene-l, 12 parts n-butane. 4.1 parts butylene-2 and the remainder lighter yand heavier hydrocarbons. The side stream is passed to al fractionator wherein the lighter hydrocarbons are fractionated out in order to obtain a more concentratedY C4 fractionfrhe bottoms from the fractionator` containing the C4 fraction are mixedy "n-butane, 17.5 parts butylene-2 and the remainder heavier hydrocarbons. The depropanized absorption condensate contains about 9.6 parts isobutane, 7.3 parts isobutylene, 5.4 parts butylene-l.

'- 22.4parts n-butane and 10 parts butylene-2 and the remainder heavier hydrocarbons.

The resulting mixture containing about 46 parts' offractionated stabilizer side stream. about 174 parts of depropanized debutanizer overhead` and'about 122 parts of depropanized absorption condensate. are charged to a debutanizer. 'I'hc mixture charged to the debutanizer analyzes about 47.6 parts isobutane. 25.5 parts isobntylene, 18.7 parts butylene-l, 70.9 parts n-butane, 31.6 parts butylene-Z and the remainder mainly heavier hydrocarbons. In the debutanizer a fraction consisting essentially of Ca hydrocarbons. amounting to about 23% of the charge to the debutanizer, are separated as overhead,`and a light naphthacontaining a-portion of the normal butane is withdrawn as bottoms. The debutanizer overhead contains'about 45.2 parts of ene-l, 7.1 parts n-butane and 3.2 partsbutylene-2. The overhead fraction is condensed and the condensate split into approximately equal portions between three allqylation units connected in series. A recycle stream of isobutane is also charged to the irst stage, whereby a v ratio of isobutane toolens in the feeds to each stage is at least 5:'1 by volume. I

In each alkylation unit the fresh feed is mixed with a stream of recycle hydrocarbons, principally isobutane, alkylate and sulfuric acid catalyst and the mixture passed through a mixer to obtain intimate contact. then through a chiller wherein the heat of reaction is removed by propane refrigeration. The mixture is passed from the chiller to a reaction tank from which the hydrocarbons and catalyst are withdrawn. "The stream so withdrawn is split. a portion recycled andthe remainder passed to settler. The ratio of acid to hydrocarbon in the circulating stream is about 1:1 by volume. The ratio ot strength; sumcient fresh acid is added to maintain the strength of the acid catalyst at the desired point and an amount of spent acid is withdrawn approximately equal to the amount of the fresh acid added. In the settler the remainder of the acid is separated from the hydrocarbons and may be recycled to the system o r sent to the next mixing stage.

The crude alkylate withdrawn from the nal settler is neutralizedwith dilute,caustic soda solution and the neutralized hydrocarbons are passed to a debutanizer. An overhead cut from the debutanizer is split into two streams, a portion being returned to the side cut fractionator,4

referred to heretofore, and the balance going to a butane fractionator. The net normal butane content of the fresh feed is separated in the fractionator and discharged from the system. A recycle stream rich in isobutane taken overhead from the butane fractionator is recycled to the first stage of the alkylation system. The bottoms from the debutanizer are charged to a nal fractionator where they are separated by conventional atmospheric distillation into a 311 F. end point overhead, a 311 to 400 F. side cut and bottoms boiling above 400 F. An aviation gasoline of 311 F. end point amounting to approximately 90%, 311 F. to 400 F. naphtha, amounting to about 8%, and bottoms boiling above 400 F. amounting to about 2%, are obtained. The aviation gasoline shows an octane number of about 90, the intermediate naphtha fraction an octane number of about 80.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicatedin the appended claims.

We claim:

1. A process for the manufacture of antiknock gasoline, which comprises stabilizing an unstalbilized cracked naphtha, separating an overhead stream from the stabilizer containing mainly C3 and lighter hydrocarbons, separating a side stream from the stabilizer containing C4 oleflns vand paraffns and some Ca hydrocarbons, fracbutane therefrom to. provide a fraction concentrated in isobutane and C4 oleflns, Vsubjecting said concentrated isobutane and C4 olen fraction to an alkylation operation in an alkylation reaction zone wherein isobutane is alkylated by said olens, separating an unstabilized alkylate from the reaction products, stabilizing said separated alkylate to separate normally liquid alkylate from an overhead fraction consisting. essentially of isobutane and normal butane, together with any C3 hydrocarbons remaining in the system, recycling a portion of said overhead fraction to the said side stream fractionating operation to prevent buildup of C3 hydrocarbons in the system, fractionating another portion yof said overhead to separate an isobutane fraction from a normal butane fraction, and recycling the said isobutane fraction directly to i'zing the said fractionated C4 stream to separate at least a portion of the normal butane, thereby increasing the concentration of the isobutane and butylenes therein, subjecting the debutanized product to alkylation in the presence of an alkylation catalyst whereby isobutane is alkylated by the butylenes to produce gasoline hydrocarbons of high anti-knock value, separating unstabilized alkylate from the reaction prodducts, stabilizing said separated alkylate to remove therefrom a light fraction consisting essentially of isobutane and normal butane together with any C3 hydrocarbons remaining in the system, and recycling at least a'portlon of said light fraction to the stabilizer C4 stream fractionating operation to thereby prevent bulldup of C3 hydrocarbons in the system while maintaining excess isobutane therein.

3. A process for the manufacture of anti-knock gasoline, which comprises stabilizing an unstabilized cracked naphtha, separating a C4 hydrocarbon stream from the stabilizer containing butylenes, normal butane, isobutane and some C: hydrocarbons, fractionating said stream to separate C3 hydrocarbons therefrom, debutanizing the 'said fractionated C4 stream to separate at least a portion of the normal butane thereby increasing the concentration of the isobutane and butylenes therein, subjecting the debutanlzed product to alkylation in the presence of an alkylation catalyst whereby isobutane is alkylated by the butylenes to produce gasoline hydrocarbons of high anti-knock value, separating normally liquid alkylate from the reaction products, also separatingfrom the reaction products a residual gaseous fraction consisting essentially, of isobutane, normal butane and any C; hydrocarbons retained in the system, recycling a' portion of said residual gaseous fraction to the stabilizer C4 stream fractionating operation to prevent buildup of C3 hydrocarbons in the system while returning isobutane, thereto, fractionating another portion of said residual gaseous fraction to separate a fraction rich in isobutane from a fraction rich in normal butane, and recycling said fraction rich in isobutane to the alkylation operation to maintain excess isobutane therein while preventing buildup of normal butane in said system.

4. A process for the manufacture of anti-knock gasoline, which comprises stabilizing an unstabilized cracked naphtha, separating a C4 hydrocarbon stream from the stabilizer containing bu-` tylenes, normal butane, isobutane and some C: hydrocarbons, fractionatingsaid stream to separate Cs hydrocarbons therefrom, debutanizlng the said fractionated C4 stream to separate at least a portion of the normal butane thereby lncreasing theconcentration or the isobutane and butylenes therein, subjecting the debutanized product to alkylation in the presence cf an alkylation catalyst whereby isobutane is alkylated by the butylenes to produce gasoline hydrocarbonsof high anti-knock value, separating normally liquid alkylate from the reaction products, also separating from the reaction products unreacted normally gaseous hydrocarbons consisting essentially of isobutane. and normal butane and any ,Ca hydrocarbons retained in the system, dividing said unreacted normally gaseous hydrocarbons into separate streams, recycling one stream to the stabilizer C4 fractionating operatlonto prevent buildup f C: hydrocarbons in the system while returning isobutane thereto, subjecting another stream containing normal butane in an amount .approximating that in the said debutanized'product fed to the alkylation operation to fractionation to separate an isobutane-rich fraction from a normal butane fraction. and recycling the isobutane-rich fraction to the alkylation operation to thereby maintain .excess isobutane in the system while preventing buildup vof normal butane therein.

5. A process for the manufacture of anti-knock `gasoline which comprises stabilizing an unstabilized cracked naphtha,separating a C4 hydrocarbon stream from the stabilizer containing butylenes, normal butane, isobutane and some Ca hydrocarbons, fractionating said stream to separate Cs hydrocarbons therefrom, debutanizing the said fractionatedstream to separate at least a portion of the normal butane thereby increasing the concentration of isobutane and butylenes therein, continuously injecting said debutanized product in a circulating stream oi emulsion of hydrocarbons and liquid alkylation catalyst in a closed circuit in an alkylation `zone wherein isobutane is alkylated by the olens with the production of gasoline hydrocarbons of high antiknock value, withdrawing reaction products from the alkylation zone and separating unstabilized alkylate therefrom; stabilizing said separated a1- kylate to remove a light fraction consisting essentially of isobutane, normal butaneand any Cs hydrocarbons retained in the system, recycling a portion of said light fraction' to the aforesaid stabilizer C4 fractionating operation to preleasta portion -of the isobutane-richl fraction still gases to remove C3 and lighterhydrocarbons vent buildup of Ca hydrocarbons in the system while retaining the excess isobutane therein, fractionating another'portion of said light fraction carbon. stream from the stabilizer containing lbutylenes, normal butane, yisobutane and some C: hydrocarbons, fractionating said stream to remove Cs hydrocarbons therefrom, debutanizing the said fractionated stream to separate at least a portion of the normal butane thereby increasing the concentration of isobutane and butylenes therein, splitting said debutanized product into a plurality of streams, separately and simultaneously passing each stream to separate stages of a multi-stage alkylation system comprising a plurality of serially connected alkylation zones through which the hydrocarbons undergoing treatment ow in series,.and in each of which the hydrocarbons are subjected to contact-with a liquid alkylation catalyst under conditions such that isobutane is alkylated by the butylenes to produce vgasoline hydrocarbons of high antiknock value, withdrawing reaction products from the final stage of the system and separating unstabiiized alkylate therefrom, stabilizing said separated alkylate to remove a light iractionconsisting essentially of isobutane, normal butane and any Ca hydrocarbons retained in the system, recycling a portion of .said light fraction to the aforesaid stabilizer C4 fractionatlng operation to prevent buildup of C3 hydrocarbons in the system lwhile retaining the excess isobutane therein, separately fractionating another portion of said light fraction to remove an isobutane-rich fraction from a normal butane fraction, and recycling at directly to the rst stage of said alkylation system, whereby an excess of isobutane is maintained in said system and flows serially therethrough while buildup of normal butane in the system is prevented.

7. In the alkylation of isobutane with butylenes vof a normally gaseous hydrocarbon fraction of cracking still gases in the presence of an alkylation catalyst for the production of gasoline hydrocarbons of high anti-knock value, the method which comprises fractionati'ng the said cracking therefrom, and also to remove at least a portion of the normal butane to providea Cr'fraction concentrated in isobutane and butylenes, subljecting the-said C4 fraction to alkylation with excess isobutane 1in the presence of an alkylation catalyst under conditions such that isobutane is alkylated by the butylenes to producegasoline hydrocarbons of high anti-knock value, separating unstablized alkylate from the reaction products, stabilizing said separated alkylate` to remove a normally gaseous fraction consisting essentially of isobutane and normal butane with any C3 hydrocarbons retained in the system, and recycling at least a portion of said normally gaseous fraction to the mst-mentioned fractionating operation of the cracking still gases to thereby prevent buildup of C3 hydrocarbons and normal butane in the system while maintaining excess isobutane therein.

8. The method according to claim 7, wherein the said normally gaseous fraction removed in the stabilization of the alkylate is divided into streams, one stream being recycled to the said fractionating operation of the cracking still gases, and another stream being separately fractionated to remove an isobutane-rich fraction from a normal butane fraction, and the said isobutanerich fraction is recycled directly to the alkylation operation.

9. In the alkylation of isobutane with butylenes of a normally gaseous hydrocarbon fraction of cracking still gases containing C3 and C4 hydrocarbons including propane, isobutane, normal butane and butylenes in the presence of an alkylation catalyst for the production of gasoline hydrocarbons of high anti-knock value, the method of handling the said fraction of cracking still gases without the addition oi extraneous large amounts of isobutane which comprises fractionating the said cracking still gases to separate Ca hydrocarbons and alsoto 'separate a substantial proportion of the normal butane therefromto thereby obtain a C4V hydrocarbon fraction concentrated in isobutane and butylenes and containing only a relatively small proportion of normal butane, the isobutane content of said fraction being in molar excess of the total olen content thereof, subjecting the said C4 fraction to alkylation in the presence of an alkylation catalyst under conditions such that isobutane is alkylated by the .butylenes to produce gasoline hydrocarbons of high anti-knock value, separating an unstabilized alkylate from. the reaction products, stabilizing said separated alkylate to remove a normally gaseous fraction consisting essentially of normal butane and the excess isobutane together with any C3 hydrocarbons retained in the system, and recycling at least a portion of the said normally gaseous fraction t0 the ilrst-mentioned. fractionating operation of the cracking still gases to thereby prevent buildup of C3 hydrocarbons and normal butane in the system while maintaining excess isobutane there- 10. The method according to claim 9, wherein the said normally gaseous fraction separated in the stabilization of the alkylate is divided into streams, one streambeing recycled to the said cracking still gas ractionating operation, and another stream being separately fractionated to remove an isobutane-rich fraction from a normal lontane fraction, with the said isobutane-rich fraction being recycled directly to the alkylation operation.

11. In the allrylation of isobutane with butylenes in the presence of an alkylation catalyst in a multi-stage system involving serial ilow through a plurality of alkylation zones for the production of gasoline hydrocarbons of high anti-knock value, and wherein a Ca-Ci hydrocarbon fraction of cracking still gases containing propane, isobutane, butylenes and normal butane is ernployed as a charge stock, the method which comprises fractionating the said Cs-C4 hydrocarbon fraction to remove C3 hydrocarbons and also to remove a substantial proportion of the normal butane therefrom to provide a C4 hydrocarbon fraction concentrated in isobutane and butylenes, with the isobutane in molar excess of the butylenes, separately and simultaneously introducing portions of the said C4 fraction into at least two stages of the said multi-stage alkylatio'n system whereby isobutane is alkylated by butylenes in each of said stages to produce gasoline hydrocarbons of high anti-knock value and gasoline hydrocarbons together with excess isobutane ow serially from a preceding stage to a succeeding stage of said system, separating an unstabilized alwlate from the reaction products of a final stage of said system, stabilizing said separated alkylate to remove a normally gaseous fraction consisting essentially of normal butane and excess isobutane, fractionating at least a portion of said normally gaseous fraction to separate an isobutane-rich fraction from a normal butane fraction, returning another portionof `said normal gaseous fraction to the said Ca-C4 hydrocarbon fractlonating step, recycling the isobutane-rich fraction directly tothe rst stage of the alkylation-system to thereby provide a substantial excess of isobutane which ows serially through the multiple stages of said system, -and discharging the normal butane fraction to remove normal butane from the system in an amount comparable to the amount of normal butane introduced with the C4 hydrocarbon feed into the alkylation system.

l2. A continuous multi-stage process foralkylating a low-boiling isoparailln with an oleiln in the presence of an immlscible liquid alkylation catalyst to produce gasoline hydrocarbons of high anti-knock value, which comprises maintaining in' each stage of said multi-stage systeml a recirculating liquid emulsion stream of catalyst, hydrocarbon reaction products and excess isoparamn in a closed circuit including a restricted now passage and an enlarged reaction zone, splitting the olefin feed between at least two of said stages by simultaneously introducing the olen in liquid phase and in controlled amounts into the restricted flow passage of each of said stages under conditions such that the isoparailln is maintained in substantial molarexcess in each of said stages and isoparamn is alkylated with the oleiln to produce gasoline hydrocarbons of high anti-knock value as the emulsion stream circulates through the restricted ow passage and enlarged reaction zone, continuously removing a small portion of the recirculating emulsion stream from each stage, 'passing hydrocarbon reaction products and excess isoparafiin of the removed stream from a prior stage and introducing the same linto the recirculating emulsion stream of a subsequent stage whereby the hydrocarbon reaction products ',and excess isoparailln ow serially through said stages, continuously separating excess isoparan from hydrocarbon reaction products removed from the final stage, dividing said excess isoparailln separatedfrom hydrocarbon reaction products, recycling one portion of `said excess-isoparain to the recirculating emulsion stream of the first-mentioned stage to thereby 'assist in maintaining the said substantial molar excess of isoparaflin in said stages, and adding another portion of said separated excess isoparaiiln'to the oleiin feed which is then iractionated to remove propane and ultimately split between said stages.

FRANCIS HORTON.

LEBBEUS C. KEMP. RICHARD E. NAGLE. LOREN P. SCOVILLE.

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