US2382067A - Alkylation - Google Patents

Description

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Patented Aug. 14, 1945 s PATENT OFFICE n ALxrLATToN l Ludwig ma, Jackson Heights, N. Y., mimo: to

The Lummus Compay 4poration of Delaware y, AN, ew York, N."-.Y., a cor- Application April 29, 1942, Serial N o. 440,930

6 Claims.

The present invention relates to improvements in the alkylation otisoparafllnic hydrocarlbons with olefinic hydrocarbons rto form hydrocarbons boiling within the range of gasoline and particularly suitable for use as a high antiknock aviation grade motor fuel.

In the alkylation of an isoparaiiln with an olefin in the presence of a suitable `alkylation catalyst to form high antiknock predominantly isoparafliniefgasoline hydrocarbons, a considerable problem is generally presented in fthe elimination of hydrocarbons lower boiling than the isoparaflinic reactant from the allwlation system, particularlyA inthe separation of the hydrocarbon mixture discharged from the alkylation zone for the recovery of the desired alkylate. This problem primarily involves fractionation difficulties in the handling of relatively large amounts of reactants and unreactive materials utilized in the formationof a relatively small amount of desired alkylate with the consequent large equipment required to accomplish the necessary fractionation.

Since it is necessary to have the isoparaflinic reactant, e. g., isobutane, present in an amount in substantial excess of that required to react with the olefinic reactant, e. g., abutene in the alkylation zone in order 'to' obtain a substantial degree of alkylation, it becomes desirable from an economic viewpoint to recycle the excess isoparafnic reactant separated from the` alkylate alkylation system along with the C4 fraction containing the isobutane and/or the butene, is to be avoided as much as possible since, for optimum operation, it is necessary to maintain a substantially low concentration of propane in the alkylation zone.

Accordingly, it is4 an object of my invention to provide an improved method of fractionating the hydrocarbon mixture discharged from the alkylation zone in an isoparafiln-olefin alkylation system whereby a material saving in equipment and operating costs can be effected.

It is a further object of my invention to provide an improved method of separating the isob'utane and the propane from the 4hydrocarbon mixture discharged from the alkylation zone in an isobutane-butene alkylation system for recycling of the isobutane to the alkylation zone and elimination of the propane from the alkylation system. n

Another object of my invention isto provide equipment and with substantially no loss of isobutane.

Further objects andadvantages of my invention will be apparent from the following'description of 'a preferred form of embodiment thereof taken in connection with the accompanying drawing, which represents a typical flow sheet of a. process embodying my invention.

For convenience only, my invention will bedescribed-in connection with the alkylation of iso- 'kylation catalyst to form predominantly isoparafllnic hydrocarbons suitable for use as a antiknock motor fuel.

According to my invention, al bu'tane-butene feed containing isobutane andl .butenesy and also containing propane unavoidably admixed therewith is; passed to an alkylation zone wherein the isobutane, maintained in excess of that required to react with the butenes, is alkylated with the :butenes in the presence of concentrated sulfuric acid to form high antiknock hydrocarbons boiling within the range of gasoline. 'I'he resulting alkylate product is separated from the acid and is neutralized, and the excess isobutane and lower boiling hydrocarbons including propane are separated asv overhead from 'the allwlate,

high

from which the desired jgasoline fraction is recondensate containing propane in a greater con-4 centration than the isobutane overhead whereby the propane is concentrated in a stream of rela.- tively small volume at a point in the alkylation system where it can be most readily eliminated therefrom by fractionation. The'isobuta'ne contained'in the nal condensate is recovered and is lrecycled to the alkylation zone.

In the operation of my invention,v a butane-butenefeed is supplied through line I to an alkylation reactor or chamber I wherein alkylation of lthe isobutane with the butenes is en'ected in the a relatively simple procedure forthe elimination of propane from an isobutane-'butene alkylation system without the use of excessive fractionating presence of concentrated sulfuric acid. Ihe butane-butene feed comprises C4 gaseous vhydrocarbons primarily and may b ederived from any suitable source, e. g., the overhead from the stabilization of natural gasoline, lcracked naphtha. or'the like. Preferably, this C4 fraction has been subjected to a prior depropanizing step to eliminate the greaterproportion of the C: hydrocarbons present in the overhead.

` ennuyer-abonnes to 98%.

Y actor.

` charged from the system through line I2, and

p line I9.

The molal ratio of the isobutane to the butenes introduced into reactor .3 should be at leas'tl:1 and preferably Within the range of 2:1 to 10:1 since it is necessary to `maintain an excess kof isobutane over that required to reactl with the .butenes during the alkylation reaction in order to accomplish a substantial' degree of alkylation.

Ordinarily. the butane-butene feed charged to f the alkylation system will not contain sufficient isobutane to provide the desired excess as well as that necessary for the alkylation reaction. This 1 deciency can be made up by introducing further isobutane from an extraneous source as through line 4 and/or by recycling the excess isobutane in the system. y

y In reactor 3, the isobutane and the butenes are e brought into intimate contact with each other and with the sulfuric acid to effect the desired alkylation. 'Ihis sulfuric acid, which acts as a catalyst for the alkylatlon reaction, should have j a concentration of .between 90 to 100% and pref- 3 The acid is sup'` plied to reactor3 through line i. .The pressure within the reactor should be sulllcient to maintain the isobutane and the butenes in liquid condition at the particular reaction temperature. which should be in the range of to 100 F. and

preferablywithin the range of 40 to 60 F. The ratio of acidto hydrocarbons is desirably maini tainedgwithin the range of V2 to 1%/2 volumes of acid per volume of hydrocarbon feed, tothe renecessary intimacy nf mixing. lAny mixing device which providesv a sufficient degree of agitation is suitable. The isobutane-butene mixture is maintained in reactor 3 for suilicient time to eiect substantial alkylation of the isobutane with the butenes. Substantiallycomplete `consumption of the butenes can be effected under. the proper falkylatingv conditions, which are well knowntotheart.

The acid-hydrocarbon mixture is continuously i withdrawn from reactor 3 through line 1 and is passedinto settling chamber 9, wherein it separates into an upper hydrocarbon layer and a lower acid layer.' This lower layencomprising used acid is withdrawn from the settler through line I0, and a major portion thereof is preferably recycled through lines II and 5 to reac'ztorv 3 to be: used` in the alkylation of additionalisobutane with butenes. A portion ofthe .used sulfuric acid from settler' 9 is desirably continuously 4dis-- fresh make-up sulfuric acid is continuously introduced into, the system through line I3.

The upper. hydrocarbon layer is withdrawn I from settler '9 through line I4 and is passed into neutralizer I5, wherein the hydrocarbon mixture is treated with a neutralizing. agent to neutralize i the acidity of the hydrocarbons resulting from the contact thereof with ythe acid in reactor 3. A suitable neutralizing agent comprises an alkaline solution such as a diluteaqueous caustic soda solution, ywhich may be introduced into the neutralizer through line I1. The alkaline. solution separates out in thebottom of neutralizer I5 and is continuously withdrawntherefrom through According to my l3 is desirably provided with an agiinvention, the neutralized hythe excess isobutane, the normal butane intro- I duced into the system along with the `isobuta'ne e and the butenes, and any propane unavoidably admixed therewith.v In tower- 23- the, hydrocarbon mixture is fractionated to separate the normal butane, the isobutane, and the lowerv boiling hydrocarbons including the propane from the alkylate, which is removed as a bottoms stream through line 25. The fractionating conditions in tower 23 may be sc adjusted that a sufficient amount of normal butane is retained in the vbottoms alkylate stream to give the resulting high antiknock gasoline product the particular volatility desired. i

This bottoms stream is passed through line 25 into alkylate fractionator 21, wherein the gasoline boiling range constituents are separated from the heavier alkylate, which is removed from the systemthrough bottoms line 29 for disposal as desired. The alkylate gasoline fraction is ,removed overhead in line '3l' for condensation in condenser 33. A portion. of lthe resulting condensate is returned through line 35 to vtower 21 to serve as reflux. The remainder of the con. densate lswithdrawn from the system through line 31 and comprises thehigh antiknock' aviation grade gasoline product. l n

Further. in accordance with my invention, the normal butane, the isobutane, andvthe propane separated in debutanizer 23 are removed therefrom askan overhead stream through line 38. The primary. feature of myA invention comprises subjecting this overhead ,to a progressive partial condensationrto form a plurality of partial condensates which contain the major portion of the isobutane to be recycled as well ras the normal butane and lsome propane and a nalcondensate which contains the majorportionrof the propane to be eliminated from the system as wellas some isobutane. The purpose ofthis progressive condensation operationvis to concentrate the propane in a stream of relatively small volume at a point in the alkylation system where it can be mostreadily eliminated therefrom by fractionation.

condensate in. accumulator 40, is passed through line 41 for condensation in condenser-49,` wherein it is subjected to a final condensation which substantially completely c'ondenses the remaining vapors. The'resulting condensate is desirably lcollected inya surge tank or accumulator 50, from which it is passed `to depropanizer tower 5I through line 53.

It will be appreciated that any number of partialcondensation stages maybe employed to ac complish the object of concentrating the undesirable propane in astream of relatively small vol- ,.fume so that it can "be more readily eliminated from the alkylation system. A(glnly two condensation stages have been shown here for purposes of simplicity in order to bring out thisgprimary `10,300 lbs. per day or debutanizer 23 as well as some yisobutane and a small amount of normal butane. In depropanizerA the propane isseparated from the isobutane, which is removed as a bottoms stream through line 55 and is passed throughline I3 to deisobutanizer 45 for separation andelimination of any normal butane admixed therewith. If desired, a part of the propane condensate from surge tank 5l may be passed directly to line 43 through line 55 according to the amount of propane to be eliminated from the system. n

v The overhead from depropanizer 5I comprises substantially only propane and is removed through line 51 Vfor condensation in condenser 5l. The resulting condensate is passed Aby line Il to accumulator 63, from which it is passed through line 65 to depropanizer 5i as redux. Condenser 55 is operated underlconditions `whereby only the necessary reiluxcondensate for tower 5i is condensed. Accordingly, the uncondensed propane is eliminated lfrom the system as through the valved vent line I1. Any loss of isobutane carried of! with the eliminated propaneis reduced to a substantially negligible minimum through .produced by condenser 39 is removed through line 1I for condensation -`in condenser 13. 'I'he resulting condensate is collected in accumulator l 15, from which a `suiiilcient portion of the condensate is returned through line 19 to tower 45 as reflux. The remainder of the condensate comhydrocarbon eiiluent. 'I'his uncondensedportion was substantially complet/ely condensed in`con tained 300 lbs. per day of isobutane. Thisrepprlsing the excess isobutane required in the reactor 3 is recycled through line 8| for use in the alkylation of further 'isobutane -v with butenes.

It is generally desirable to maintain the p'ercentage of propane in the' alkylation zone below 3% by weight because the propane is inert as far as the alkylation reaction is concerned andl because it also adversely aiects the yield of alkylate if it is present in too great a proportion during alkylation. Accordingly, unless ,the propane is continuously vented or eliminated from the alkylation system in some fashion, it will continuously be recycled along with the excess isobutane and will gradually accumulate in the system and thereby adversely affect the aikylation reaction.

It should be noted that the amount of propane that must be vented from the system controls all of the fractionating operations prior to this point.

In a particular application of my invention, the hydrocarbon efliuent from reactor l was 345,500 lbs. per day, of which propane comprised 3% by weight. This eilluent was debutanized in tower 23, the overhead from which was 240,000 lbs. per day and contained all of the propane as well as substantiall hydlolloric acid, and the like.

ly all of the isobutane and normal butane in the hydrocarbon eilluent. 'I'he concentration of propane in this overhead stream was thus increased to 4.3% by weight by removal of the alkylate. The partial condensate from condenser 39 contained 450% of the propane, of the isobutane, and of the normal butane in the debutanizer overhead. The uncondensed portion of this overhead was 82,100 lbs. per day, of which propane comprised 5,300 lbs. per day or 6.45% by weight. By means of this partial condensation procedure, the propane to be eliminated from the system was concentrated in a stream of considerably smaller quantity than that of the resents approximately 0.1% by weight of the isobutane content of the hydrocarbon emuent ami-Y constitutes practically a. negligible daily loss of isobutane. n Y

Several advantages flow from this procedure of increasing the propane concentration in the stream from which propane is to be eliminated. Concentration of propane reduces the charge to the depropanizer tower whereby a tower of smaller diameter and height can be employed: the charge contains a greater concentration of propane, and, hence, the amount of charge is less. Concentration of propane also reduces the reflux ratio required in the depropanizer with a corresponding reduction in the amount of cooling required and inthe tower size because of the smaller amount of material being treated whereby less reflux is needed. yConcentration of propane further effects a reduction in the number It will be'appreciated that my invention is not necessarily limitedv to the use of concentrated surfuric acid as the alkylation catalyst. Other Asuitable substances for effecting this alkylation comprise aluminum chloride, phosphoric acid,

Although I have described a preferred form of embodiment of my invention, I am aware that modications kmay be made thereto; therefore, only such limitations as appear in the claims appended hereinafter should be made.

I claim:

1. 'I'he vprocess of alkylating an isoparafhn with an olen to formhigh antiknock motor fuel, said isoparailln containing lower boiling unreactive hydrocarbons unavoidably admixed therewith, which comprises contacting the isoparaln and the oleiin in an alkylation zone with an alkylation catalyst to eiect alkylation of the isoparaiiln with the olen, maintaining an excess of isoparaflln over that required to react with the olefin during alkylation, separating the resultinghydrocarbon mixture from the alkylation catalyst, fractionating the hydrocarbon mixture to separate the unreacted hydrocarbons as overhead from the alkylate, partially condensing said overhead to produce a condensate containing primarily unreacted isoparamn and to concentrate the major portion of the lower boiling unreactive hydrocarbons in the uncondensed portion of the overhead, separating the uncondensed portion of said overhead and subjecting it to further fractionation within a zone independent of thezone of said first fractionation for control of fraction- 1 and 'condensate ma said bottoms fraction and recycling it to the alkylation zone to maintain said excess of isoparamn therein. and fractionating the alkylateto recover `a. high antiknock motor fuel.

2. In the process of alkylating an isoparamn with an olenn to form highantilmock motor fuel in the presence of an alkylation catalyst wherein reactive hydrocarbons both higher boiling and lower boiling than the isoparailin are also presboiling hydrocarbons lincluding Propane admixed therewith, which comprises'contacting the isobutane and the butene with concentrated sulfuric acid in an alkylation zone to eiect alkylation of the isobutane with the butene, maintaining an excess of isobutane over that requiredto react with the butene during alkylation, separating the resulting hydrocarbon mixture from the sulfuric acid, fractionating the hydrocarbon mixture to separate unreacted hydrocarbons as overhead from the alkylate, partially condensing said overent, the improvement which vcomprises fractionl ating thehydrocarbon eiliuent from the lalkylation zone consisting of"alkylate and unreacted hydrocarbons to separate the unreacted hydrocarbons as overhead from the alkylate, progressively condensing said overhead ina series ofpartial condensation stages to produce a plurality of condensates containing primarily'unreacted isowithin said iirst zone,to separate the unreactive l lower boiling hydrocarbons from a bottoms fraction containing unreacted isoparamn therein, j eliminating the separated lower boiling hydrocarbons from the system, recovering unreacted isoparailln from said condensates and from said bottoms fraction and recycling it to the alkylation zone to maintain said excess of isoparamn 3. The process of alkylating isobutane containing admixed propane witha normally gaseous olefln to form high antiknock motor fuel,

which comprises contacting the isobutane and the oleiln with concentrated sulfuric acid in an l alkylation zone to eiect alkylation of the isobuhead to form a condensate containing primarily normal butane and isobutane and to concentrate the major portion of the propane in the uncondensed portion of the overhead, separating such uncondensed portion of the overhead and condensing it, fractionating the resulting final condensate within a zone independent of the zone of said first fractionation, for control of fractionatparatlln and higher boiling unreactive hydrocar- 1 bons and to concentrate the greater portion of the ing conditions independently of fractionating conditions in said first zone to separate the propane and lower boiling hydrocarbons from iso- I butane vand normal butane .contained therein,

eliminating the separated' propane from the system, further separating the isobutane from the normal butane, collecting the separated isobutane and recycling it to the alkylation zone to maintain the excess of isobutane therein, and

- fractionating the alkylate to recover a high antitherein, and fractionating the alkylate to recover a high antiknock motor fuel.

tane with the olen, maintaining an excess of isobutane over that required to react with the conditions independently of fractionating conditions in said first zone, to separate the propane from a bottoms fraction containing isobutane therein, eliminating the separated propane from the system, recovering isobutane from said cona high antiknock motor 4. 'I'he processo! alkylating'isobutane with a -butene to form high antiknock motor fuel, said reactants containing normal butane and lower l olen during alkylation, separating the resulting I hydrocarbon mixture from the sulfuric acid, frac- 1 tionating the hydrocarbon mixture to separate the unreacted hydrocarbons as overhead from the I alkylate, partially condensing said overhead to form a condensate containing primarily unre- 1 acted isoparaln and to concentrate the greater j portion of the propane in the uncondensed portion of the overhead, separating such uncon. l i densed portion of the overhead and condensing n l it, fractionating the resulting final condensate y within a zone independent of the zone of said first fractionation, for control-of fractionating knock motor fuel. c

5. 'I'he process as claimed in claim 4, wherein the concentration of propane in the alkylation zone is maintained below 3% by weight.

6. The process of aykylating an isoparamn with an olefin to form high antiknock motor fuel, said reactants containing lower boiling unreactive hydrocarbons unavoidably admixed therewith, which comprises contacting the isoparaiiln and the olefin with an alkylation catalyst to effect alkylation of the isoparaftln with the olen, maintaining an excess ofisoparailin over that required to react with the oleiin during alkylation, separating the `resulting hydrocarbon mix- Vture from the alkylation catalyst, fractionating portion of the lower boiling unreactive hydrocarbons in theuncondensedportion of the overhead, separating the uncondensed portion of said overhead and subjecting it to further fractionation within a, zone independent of the zone of Y said first fractionation for control of fractionating conditions independently of fractionating conditions within the zone of said iirst fractionation, to separate the lower boiling hydrocarbons from a bottoms fraction containing isoparafiin therein, eliminating the separated lower boiling hydrocarbons from the system, passing said bot' toms fraction to a third fractionation zone independent of said other fractionation zones, passing to said third zone, independently of said second zone the isoparafiin and another portion of said lower boiling unreactive hydrocarbon obtained from said first fractionation, for recovery of the isoparailin as overhead from the third zone, recycling the recovered isoparaiiin to the alkylation zone, and fractionating the alkylate to recover a high antiknock motor fuel.

LUDWIG KNmr..

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