US2923751A

US2923751A - Production of high octane alkylate using a permeable membrane separation system

Info

Publication number: US2923751A
Application number: US581497A
Authority: US
Inventors: Robert C Binning; Robert J Lee
Original assignee: American Oil Co
Current assignee: American Oil Co
Priority date: 1956-04-30
Filing date: 1956-04-30
Publication date: 1960-02-02
Anticipated expiration: 1977-02-02

Description

Feb. 2, 1960 R. c. BINNING ET AL PRODUCTION OF HIGH OCTANE ALKYLATE usmc;

A PERMEABLE MEMBRANE SEPARATION SYSTEM Filed 'April 30; 1956 Lower 0./V.

A/ky

Higher 0.1V. A/ky/a/e Q i IIWEIVTORS. Robert 6. Binnlng Robert J. Lee

* ATTORNEY P 2,923,751 United States... atent ice,

method for producing an alkylate blending stock of high 2,923,751 octane number for a non-leaded gasoline and a lower RRODUCTION. OF 'HIGH' OCTANE ALKYLATE j USING A 'PERMEABLE MEMBRANE SEPARA- f "-TION SYSTEM Robert (2.: Binning, 'lfexas City,-an d Robert J. Lee, La Marque, Tex., assignors to The American Oil Company,

. Texas. City, 'I ex., a corporation of Texas regatedfport'ions' of alkylate having differing octane numbers andinpartieular it concerns the combining of an"'alk 'yla'tion processan'd a permeation process whereby large quantities of high octane alkylate as well as lower octane alkylate can be produced.

"Thedernand for high octane number gasoline has required petroleum refiners to operate their alkylation units for the production of blending stocks for motor fuels. Alkylate has high lead'susceptibility-and is additionally a desirable component of motor fuels because it reduces the sensitivity of the gasolines which is ever increasing because of larger concentrations of aromatic components. While the oct'ahe'number of the raw nonleaded alkylate is generally not of crucial importance to the petroleum refiner because of its excellent lead response, it is extrer'nely important to the refiner who produces a gasoline which contains no tetraethyl lead. When petroleum refiners are producing approximately 100 octane number gasoline which contains no tetraethyl lead, the octane number of the alkylate must obviously be as high as possiblefi- The alkylate'generally produced, which has an F'-'I octane numberof' between 85 to 96, leaves something to be desired in this respect. 1

It has long been appreciated that when an alkylate process is operated at maximum production rates of alkylate (and even higher than design rates), the nonleaded octane number of the alkylate is appreciably lower than if the alkylation unit were operating under conditions for .the production of lesser amounts of alkylate. For example, a typical alkylation unit may *be' capable of producingl0,000 bbL/day of 380 F. E.P. alkylate having an F-l octane number of 92.6, whereas when the same unit is operated so as to produce 3000 bbl./day of alkylate the F-l octane number of the latter alkylate will be 96.8. While the advantage in octane number is highly desirable, the penalty in loss of production is very severe. An object of this invention is to. provide a process capableof producing segregated portions of alkylate which have differing octane. numbers. Another object is to provide a combined alkylation and permeation process whereby maximum production rates of alkylate are pos- 'sible while still producing portions thereof which have'a high'octaneuumber. Afurther object is to provide a combined alkylation and permeation process capable of producing one portion of alkylate having a volume and an octane number at least as great as the alkylate produced; at lower alkylateproduction rates and in addition @aia wm 1 5 sr: oct n nu e l ylate An ioctane number alkylateblending stock for a leaded gasp; line and a lower octane number alkylate blending stock for a leadedgasoline in which the alkylation process is operated to produce maximum quantities pf alkylate.

It has been found that the peculiar advantages of a permeation process can be keyed into the disadvantages of an alkylation process to overcome the unties irablcv features of the alkylation process and thereby yield. the, necessary high octane number gasoline as well asap; additional quantity of a lower octane number gasoline. In our invention an alkylation process is operated at highproduction rates, preferably at the maximum rate of'alkylate production, thus yielding a gasoline boiling range alkylate which generally has an F-l octane numb en er less than 96. This alkylate is passed to a permeation prota; ess wherein'it is'permeated in one or more stages into segregated portions of alkylate which have octane nurn bers difiering from each other and from the alkylate which is charged to the permeation process. Whilethe total gasoline boiling range alkylate produced in the alkylation process may be charged to the permeation proc ess, it is preferred to fractionate the alkylate into separate fractions which consist of hydrocarbons substantiallyall, of'which have the same number of carbon atoms intheir molecule. Thus a preferred fraction of the alkylate;

charged 'to the permeation process maybe the C ,;C

fraction or the C fraction, especially the latter whichboils over the range of about 205 to 260 F. In the permeation process, the alkylate is charged to a permea tion vessel which may consist of one or more vessels separated by a thin plastic membrane into two sections.

The alkylate is charged into the charge section, which operates usually at a temperature of 100 to 300 F. and a super-atmospheric pressure sufiicient to maintain the alkylate liquid. A portion of the alkylate, which may be as little as 10% or as high as 90% of the charge, is permeated through the plastic membrane into the permeate zone which operates generally at a sub-atmo'se pheric pressure so that as the hydrocarbons permeate the membrane they are immediately vaporized into the permeate zone. The permeated portion of the alkylate, which has a lower octane number than the alkylate initially in contact with the membrane, is removed from the permeate zone. The remaining nonpermeated portion of the alkylate is removed from the charge zone. This portion of the alkylate has a higher octane number than the charge to the permeation step. In the permeation process the plastic membrane used should be as thin as possible e.g. 0.1 to 5 mils or even less. It may be of any type through which paraffinic hydrocarbons permeate more rapidly the less the number of methyl side chains the paratfins contain, It may bejof a cellulosic type such as cellulose acetate-butyrate', ethyl cellulose, films prepared by casting from solutions con..- taining blends of cellulose ester and ethers, etc. The process of our invention is characterized by the produc-f tionof segregated portions of alkylate, one portion of which has at least as high an octane number as the similar boiling range alkylate producedwhen an alkylation process'is operated at a lower production ratel'anda second segregated portion of alkylate having -,ja ;jl'ower octane number than the first segregated portion, but the 3 combined volume of these segregated portions being greater than that of the equivalent boiling range alkylate which is produced at the lower alkylate production rate.

As illustrative of our invention a preferred embodiment thereof will be described hereinafter.

Figure 1 is a diagrammatic representation of our combined alkylation-permeation process for producing alkylate at high production rates while also producing segregated portions of alkylate having high and low octane numbers respectively. Numerous valves, pumps, heaters, coolers etc. have been omitted from this diagrammatic representation for purpose of clarity. 7

Referring toFigure 1, the charging stock to the alkylation process consists of a depropanized refinery butanesbutenes-stream from catalytic cracking. It contains about 50% olefins and is composed essentially of isobutane, normal butane, and butenes with minor amounts of pro-' pane' and pentanes. Butanes and butenes from other sources-may obviously be used also. The butanes-buteues charge stoek is passed under pressure from source 11 by way of line-12 into vessel 13 which contains an aqueous caustic solution for removing mercaptans and hydrogen -snlfide. The caustic washed hydrocarbons are removed from vessel 13 and passed through line 14 wherein they meet recycled isobutane in an amount such that the isobutanezbutene ratio is then approximately 4:1 to :1 e'.-g'. 6:1. Thebutanes-butenes stream is passed by way of line 14 into water settler 15 from which water is removed and discarded by way of line 16. The hydrocarbon stream is removed from settler 15 and passed by way of line 17 to chiller 18. Thereafter the chilled hydrocarbons are passed by way of line 19 into the alkylation reactor 21.

In alkylation reactor 21, the liquid mixture of butanes and butenes at a temperature between about 30 and 50 F. is intimately contacted with sulfuric acid having a concentration between 90 and 100%, preferably about 95 to- 98%. The ratio of acid to hydrocarbon should be between about 0.721 and 121. An internal isobutane to olefin ratio of between 25 and 1000 (the higher the internal ratio, the higher the octane number of the alkylate) is used. An olefin space velocity of 0.15 to 0.50 and a hydrocarbon-acid contact time of about 10 to 20 minutes is employed. The influence of the various operating conditions described above are well-known in the art and may be adjusted accordingly to produce the optimum results of alkylate production and octane number with minimized usage of sulfuric acid.

When the rate of production of alkylate is increased, the operating conditions are changed usually in the following manner. The external ratio of isobutane to olefins is approximately the same, the olefin space velocity is greatly increased, for example, it may be increased to 0.4 or thereabouts and the hydrocarbon acid contact time is reduced. The recycle of isobutane is constant. In

;such an operation, the internal ratio of isobutane to olefins is decreased (because of the constant isobutane -recycle ratio and the greater throughput of olefins) and th s causes the octane number of the alkylate to be reduced. The increase in the olefin space velocity and the reduction in contact time also appear to contribute to reducing the octane number of the alkylate. The alkylate product does not appear to have the more desirable higher octane number isomers, some chain breaking of the hydroca'rbon occurs, and more of the higher molecular weight lower octane number components are formed. Because the alkylation units are usually designed to produce a defined quantity of a given end point alkylate having a prescribed minimum octane number, such units will be operated at less than designed capacity to produce a higher octane number alkylate or operated at greater than designed capacity to produce a lower octane numher alkylate:

In the embodiment illustrated herein the design capacity of the alkylation process is about 7500 bbL/day of 94.2 F-l octane number alkylate having an end point of 380 F. The alkylation process in this embodiment is operated at maximum throughput to produce 10,000 bbl./ day of 380 E.P. alkylate having an F-l octane number of 92.6. Thus in the embodiment illustrated herein the alkylation unit is operating in excess of the designed capacity and it produces an additional 2500 bbL/day of alkylate, but the entire alkylate has a lower octane number by 1.6 units. Although the alkylate herein has an octane number of 92.6, the alkylate may have an even lower octane number, for example, it may be between and 96. In general, the lower the octane number of the alkylate charge to the permeation process, the greater the improvement in octane number of the non-permeated portion per permeation stage, and therefore it is greatly preferred to produce the largest possible volume of alkylate even though its octane number is as low as 85 F-l or thereabouts; v y 7,

Alkylation reactor 21 may be any of a number of varied types such as the impeller type reactor system as is diagrammatically indicated herein, the jet type, timetank system or others. Reactor 21 is provided with a bayonet tube cooling bundle 22 through which refrigerant flows to remove the heat of reaction liberated in the process. The hydrocarbon-acid emulsion leaves reactor 21 and is passedby way of line 23 into an acidsettler 24. The settled acid is removed and recycled by way of line 26 into reactor 21. To maintain the desired strength of the acid, a portion thereof may continuously be withdrawn and replaced with higher strength acid or an entirely fresh batch of acid may be charged batchwise as is necessary. The hydrocarbon layer from settler 24, which consists of alkylate, excess isobutane, and the inert diluents introduced with the feed, is passed by way of line 27 into vessel 28 which contains an aqueous caustic solution for removing. components such as so; which are formed in small quantities by catalyst de-' generation. The caustic washed hydrocarbons are then removed from vessel 28 and passed by way of line 29 into the fractionation section of the alkylation plant. Wh le a sulfuric acid catalized butene alkylation process has been described, a different-catalyst such as HF, A101 or complexes thereof, or anethylene alkylation process may be substituted therefor.

The caustic washed product is passed by way of line 29 into deisobutanizer 31 from which an overhead stream of recycle isobutane is taken and passed by way of line 32 into line 14 for the purpose of fortifying the butanesbutenes stream with respect to isobutane. A slip-stream portion of the isobutane recycle is removed from line 32 and passed by way of line 33 into depropanizer' 34 from which an overhead stream of propane is removed by way of line 36 and sent to storage means not shown, and a' stream of purified isobutane is removed by way of line 37 and returned to isobutane recycle line 32. A bottoms stream is removed from deisobutanizer 31 and passed by way of line 38 into debutaniz'er 39 from which an overhead stream of n-butane is removed by way of line 41 and-sent to storage means not shown. A bottoms stream from fractionator 39 is removed and passed by way of line 42 into fractionator 43 from which an overhead stream of about 2550 bbL/day containing substantially all of the pentanes, hexanes, and heptanes is removed and passed by way of line 44 to storage means not shown. A bottoms fraction of about 7450 bbl./day is removed from fractionator 43 and passed by way of line 46 into fractionator 47. From fractionator 47 a bottoms fraction of about 2250 bbL/day whichboils at 260 F. and higher is removed and sent by way of line 48 to storage means not shown. The overhead stream from fractionator 47, which amounts to about 5200 bbl/day, haslan T -I, Bohemians; of 94,. almost exclusivelyofbranched chain paraflins having 8- The permeation process which segregates the alkylate.

into portions having differing octane numbers canbe described, in its simplest form, as a. single stage operation using a single closed vessel which is separated into two sections by a thin pIast-icmembrane. The two sections formed by the dividing membraneare termed a charge section and a permeate section. The alkylate, which consists almost exclusively of branched chain paraffins, is charged to the charge zone and a portion of the alkylate is permeated through the'm'ernbrane. The parafiinic hydrocarbons which'have a lesser degreeof branching, i.e. those' having fewer methyl side chains permeate the membrane more rapidly than do the branched chain paraflinic hydrocarbons having a greater number of methyl substituents. Fortuitously the parafi'inic hydrocarbons in alkylate which have fewer methyl side chains also have a lower octane number than the. paraflins having a greater number of methyl side chains. .Consequently the-per meated portion of alkylate will have a lower octanenumher than the charge and the non-permeated portion will have a higher octane number than the charge. The fraction of the charge,which is permeated through the membrane may be between 10% and. f9.0% thereof, for

example about 50% of the charge may be permeated.

The permeation process may be carried out in a batchtype operation wherein, the charge is introduced into the charge section and permeated without adding additional charge thereto until the desired fraction of the charge has been permeated. When the charge is a fraction of alkylate (substantially all of the hydrocarbons having the same number of-carbon atoms per molecule) the first portion of permeate will have the lowest octane. number and successive incremental portions of the permeate will have progressively higher octane numbers. Or, the process may be operated in a continuous fashion by continuously introducing alkylate into thecharge section while continuously withdrawing the permeated portion from the permeate section and the non-permeated portion from a point in the charge section which is remote from the point of introduction ofthe charged alkylate.

A wide variety of operating conditions may be employed in the permeating process.- To achieve high rates of permeation through the membrane'it is desirable to employ as high a temperature as is possible since the rate of permeation increases with increasing temperature. A temperature of from 100 to 300 1*. may conveniently be used. The alkylatevin the charge zone should be maintained in the liquid state. I Because at least a portion of the alkylate charge' may boil, at the operating temperatures used, the charge zone should be operated at asuper-atmospheric pressure sufficient tornaintain the charge in the liquid state; Pressures of from 5 to 50 or even 100 p.s.i.g. may be used. The permeate zone should be operated at a sub-atmospheric pressure such that as the hydrocarbons are permeated through the membrane they are immediately vaporized from the permeate side of the membrane into the permeate zone and then rapidly removed from the permeate zone. Absolute pressures in the permeate zone of from to 400 mm. Hg may be used. The plastic membrane used should be as thin as possible because the permeation rate increases as the thickness of the membrane is diminished. It may be between 0.1 and 5 mils or thereabouts, preferably less than one mil in thickness. The plastic membrane may be composed of a cellulosic material such as a cellulose ester or a cellulose ether. Celluloseacetate-butyrate (having an acetylcontent of 5-15% by weight and a butyryl content of 35-50% by; weight) ethyl cellulose (having an ethoxyl content of about 40- 50% by weight) attain and films which are formed by casting from a solutioncontainingcellulose esters and/ or ethers such as cellulose acetate-butyrate and ethyl cellulose are very satisfactory,

'- although of course membranes composed of other plastic will have different permeation rates and also may exhibit a. different selectivity for permeating the less' highly branched in preference to the more highly branched parafiins and thereforeachieve different amounts of octane number improvement.

I In the embodiment of the permeation process illustrated herein, the process consists of five .permeation stages (whichare represented herein as five permeation vessels), each stage being operated at a temperature of about 230 F. with a pressure in the charge zone of about 1 p.s.i.g. and an absolute pressure in the permeate zone of about 30 mm. Hg. Thus the charge is maintainedinthe'liquid state and the permeated hydrocarbons are recovered from the permeate zone in the vapor state. The membrane used is one mil in thickness and is a film prepared by casting from a solution of ethyl acetate,

ethylene dichloride, and cyclohexanonecontaining ethyl cellulose (having an ethoxyl content of-45 weight percent) and cellulose acetate-butyrate (-havingan aeetyl content of 6% and a butyryl content of 41% by weight) in a weight ratio of 5 parts of the former per 3 parts'o the latter. Approximately one-half of the charge to each of the stages is permeated through the membrane and one-half of the charge is recovered as the nonpermeated portion. 4

The octane fraction, in the amount of about 5200 bbL/day, from the alkylation process is passed by way of line 49 into the charge zone 50 of permeation vessel 51 which constitutes the first-permeation stage. Permeation vessel 51 is divided into a charge zone 50 audapermeate zone 52 by plastic membrane 53. vWhile the first stage is illustrated herein as consisting of one permeation vessel, obviously a number of separate permeation vessels may be used. A portion of the octane fraction charged is permeated through the membrane at the rate of approximately 30 gallons of permeate/hour/ 1000 sq. ft. of membrane surface. This permeated portion has an F-l octane number of about 92.2. It is removed from permeate, section 52 and passed by way of line 54 into the charge zone of the second permeation stage i.e. into charge zone 56 of permeation vessel 57. Approximately one-half of the charge introduced into charge 61 as charge to the third permeation stage i.e. into charge zone 62. In this third permeation stage the plastic membrane 63 separates the charge zone 62 from the permeate zone 64. The non-permeated portion, which has an F-l octane number of 92.9, is recycled by way of-line 6.6

into line 54 whereby it is recycled as a portion of the blended with the stored fraction of alkylate boiling below 205 F. and with thestored fraction boiling above 260. F. to Emma balanced alkylate which can .be usedv for blending with a leaded gasoline, the alkylate fraction 7 responding excellently to the tetraethyl lead which is added.

The non-permeated portion from the first permeation stage (permeation apparatus 51) is removed from charge Zone 50 and passed by way ofline 68 into charge zone 69 of permeation apparatus 71 (which is the fourth permeation stage and'which operates on the non-permeated portions of the fraction of original alkylate charged). The permeation apparatus 71 is divided into charge zone 69 and permeate zone 72 by membrane 73. Approximately one-half of the charge is permeated through the membrane, the permeated portion having an F-l octane number of about 93.7 and the non-permeated portion having an F-l octane number of about 96.9. The permeated portion isremoved. from permeate zone 72 and passed by way of line 74 into line 58 by which it is recycled as a portion of the charge to the first permeation stage. The non-permeated portion is removed from permention vessel 71 and passed by way of line 76 into the charge zone 77 of permeation vessel 78 (which is the fifth permeation stage and which operates on the nonpermeated portion of the original alkylate charged to the permeation plant). In permeation vessel 78 plastic membrane 79 separates the charge zone 77 from the permeate gone 81. from permeate zone 81 and passed by way of line 82 into line 68 by'which it isrecycled as a partof the charge .to the preceding permeation stage. This permeated portion has an F 1 octane number of about 96.2. The non permeated portion, which in the continuous operation described herein amounts. to about 2600 bbl./day, is removed from permeation vessel 78 and passed byway of line 83 to storage means not shown. This non-permeated portion has an F-l octane number of about 97.5. Because of its very high octane number it is an excellent stock for blending to produce a high octane number nonleaded premium gasoline.

A number of examples were carried out which demonstrate methods of, carrying out the process of this invention. In the first example an alkylate (380 F. E.P.). having an F-l octane number of 92.6 was produced by the sulfuric acid catalytic alkylation of isobutane with butenes (using the butane-butenes streams from catalytic cracking plus additional high purity isobutane) at the rate of 10,000 bbl. of alkylate/day. This rate of production was higher than the designed capacity of the alkylation unit by about 2500 bbl./day. A portion of the-depentanized alkylate boiling between about 120 and 260 F. was then charged to a permeation apparatus. The amount charged to the apparatus was about 13 liters. The permeation apparatus was operated in a batch fashion and three permeation stages were employed.

The permeation apparatus used consisted of a sealed chamber in which was suspended a box like membrane holder. The sealed chamber was the charge zone into which the alkylate was introduced. The membrane holder had five open faces which were tightly covered (leakproof) with a membrane consisting of ethyl cellulose having an ethoxyl content of about 45% by weight and which was one mil in thickness. The total amount of membrane surface effective for permeation was 22 sq. in. The chamber was maintained at atmospheric pressure and at a temperature of 212 F. The membraneholder, into which hydrocarbons could not pass from the charge chamber except'bypermeation through the membrane, constituted the permeate zone. A sub atmospheric pressure of 30 mm. Hg was maintained within the membrane holder by a vacuum pump. The permeation apparatus was operated until approximately half of the alkylate charged was permeated through the membrane and recovered as vapors of permeated hydrocarbons withdrawn from the membrane holder. The un-. permeated portion of the hydrocarbons was then segresis ed, Therea r: the on -h lf of the lky w ch The permeated portion is removed Table I Octane Number Portion of the alkylate- Alkylate charged to first stage Permeatotrom first stage :(and charged to second stage) Non-permeated portlon tromfirst stage Permeate from second stage (and charged to third stage) Non-permeated portion from second stage Permeate from third stage Non-permeated portion from third stage.

From the above table it is apparent that the permeated portion has a lower octane number than the charge and the non-permeated portion has a higher octane number than the charge to the permeation stage- By this batchwise operation it is possible to segregate permeate fractions having incrementally different octane numbers. Thus the permeate from the third stage could be discarded and the remaining portions of permeated and non-permeated alkylate could be blended to produce an alkylate having a higher octane number than the original alkylate charged'to the first stage, i.e. 94.0, and'which blend would constitute about 90% of the original alkylate.

In another'example ofithe manner in which the permeation of the alkylate may be carried out, a portion of the depentanized' alkylate produced in the manner previously described was fractionated in a three foot hypercal column at a refiux ratio of 10:1 and four fractions were collected as follows: (1) a C fraction boiling between 122 and 165 F, (2) a C fraction boiling between 165 and 205 F, (3) a C fraction boiling between 205" and 260 F,'and (4) a C and higher fraction boiling between 260 and 380 F. Each of the individual fractions of ployed was approximately one mil in thickness.

alkylate was then employed separately as the charge to the permeation process using the previously described permeation apparatus. The pressure in the charge zone and the temperature during the permeation of each fraction were as follows: fraction (1), 3'0 ,p.s.i.g. and F.; fraction (2), 0 p;s.i.g. and F; fraction (3), 0 p.s.i.-g..and 230 F; and fraction (4), 0 p.s.i.-g. and 240 F. An absolute pressure in the permeate zone of 30 mm. Hg was used in each case. The membrane em- It was prepared by casting the film from a solution of 5 grams of ethyl cellulose (having an ethoxyl content of about 45% by Weight) and 3 grams ofcellulose acetate-butyrate (havingan acetyl content of 6% and a butyryl content of 41% by weight) in a-solvent consisting of 41 grams ethyl acetate, 41 grams ethylene dichloride, and 10 grams cyclohexanone. The permeation procedure consisted of permeating approximately 20% of the alkylate fraction charged, segregating this permeated portion, separately recovering the next 20% of the alkylate permeating the membrane, then separately recovering the third20% portion of the alkylate permeated, and then removing &' non-permeated portion which approximated 40% of the original fraction of the alkylate charged to the permeation apparatus. The F-l octane number of each of the three permeated portions and the non-permeated portions was then determined. This procedure was used for the separate permeation of each of the fourv fractions of alkylate. The octane numbers of the permeated and non-permeated portions of the various fractions of alkylate are shown Table II which follows:

It is evident from the above table that fractions of alkylate which consist of hydrocarbons substantially all of which have the same number of carbon atoms in their molecule can be segregated by permeation into portions having diifering octane numbers. The first portion permeated will generally have the lowest octane number and the portion last to be permeated will generally have the highest octane number. By combining various permeated and non-permeated portions of the various boiling range fractions, a very high octane number alkylate can be produced which is highly desirable for blending with non-leaded premium gasolines, and a low octane number alkylate satisfactory for blending into leaded gasolines can be made.

While the invention has been described in detail with reference to specific operating examples, other modifications will be apparent therefrom to those skilled in the art.

What is claimed is: a

1. A process which comprises contacting under permeation conditions an isobutane-butene alkylate boiling in the gasoline boiling range which has an F-l octane number of less than 96 with one side of a permeable plastic membrane and thereby permeating a portion of the alkylate through the membrane, separately recovering a portion of the alkylate which permeates the membrane and a portion of the alkylate which has not permeated the membrane, the non-permeated portion having a higher octane number than the permeated portion.

2. A process for producing segregated portions of isobutane-butene alkylate having differing octane numbers which process comprises operating an isobutane-butene alkylation process under conditions of high production rates whereby an alkylate boiling in the gasoline boiling range which has an F-l octane number of less than 96 is produced; contacting a fraction of the alkylate under permeation conditions with one side of a permeable plastic membrane and permeating a portion of the alkylate through the membrane; separately removing from opposite sides of the membrane a portion of the alkylate which permeated the membrane and a portion of the alkylate which has not permeated the membrane, the permeated portion having a lower octane number than that of the alkylate initially contacting said membrane and the nonpermeated portion having a higher octane number than that of the alkylate initially contacting the membrane; which process is characterized by the production of segregated portions of alkylate, a first segregated portion having at least as high an octane number as does the similar boiling range alkylate produced when the alkylation process is operated at a lower production rate and a second segregated portion of alkylate having a lower.

octane number than said first segregated portion, the combined volume of the segregated portions produced in the combination process of alkylation and permeation exceeding the volume of equivalent boiling range alkylate produced at the lower alkylate production rate.

3. The process of claim 2 wherein the first segregated portion has an octane number at least as high as does the corresponding boiling range alkylate which is produced at the lower alkylate production rate and the volume of .the first segregated portion is at least as large as the volume of the equivalent boiling range alkylate produced at the lower alkylate production rate.

4. The process of claim 2 wherein the alkylate contacted with the membrane under permeation conditions contains hydrocarbons substantially all of which have between 6 and 8 carbon atoms, inclusive, in their molecules.

5. The process of claim 2 wherein the membrane is a plastic cellulosic material.

6. The process of claim 2 wherein a number of permeation stages are used and wherein permeated and nonpermeated portions of alkylate which have approximately the same octane number are combined and used as the feed in the later permeation stages.

7. The process of claim 2 wherein the alkylate which is contacted with the membrane under permeation conditions consists of hydrocarbons substantially allof which have the same number of carbon atoms in their molecule.

8. The process of claim 7 wherein the fraction of al kylate which is contacted with the membrane consists of hydrocarbons substantially all of which have 8 carbon atoms in their molecule.

9. A process for producing segregated portions of isobutane-butene alkylate having differing octane numbers which process comprises operating an isobutane-butene alkylation process under conditions of high production whereby an alkylate boiling in the gasoline boiling range which has an F-l octane number of less than 96 is produced, fractionating said alkylate and recovering an octane fraction thereof consisting of hydrocarbons substantially all of which have 8 carbon atoms in their molecule, contacting the octane fraction under permeation conditions in five separate permeation stages with one side of a permeable plastic membrane and permeating about one-half of the charged octane fraction through said membrane in each stage and recovering permeated portions from each permeation stage which have a lower octane number than the feed to the particular permeation stage and also recovering non-permeated portions from each permeation stage which have a higher octane number than the feed to the particular permeation stage, wherein the permeation stages are carried out in the following man-1 ner: (1) permeating the octane fraction in a first stage and recovering a permeated portion and a non-permeated portion therefrom; (2) permeating the permeated portion from (1) in a second stage and recovering a permeated and a non-permeated portion therefrom, the latter non-permeated portion being recycled as a part of the charge to the first permeation stage of (1); (3) permeating the permeated portion from the second permeation stage in a third permeation stage and recovering a permeated and a non-permeated portion, the permeated portion being recycled as a part of the charge to the second permeation stage of (2), and the permeated portion being a segregated portion of the octane fraction of alkylate from (4) in a fifth permeation stage and recovering therefrom a permeated and a non-permeated portion, the permeated portion being recycled to the fourth permeation stage of (4) as a part of the charge stock thereto, and the non-permeated portion being a segregated portion of the octane fraction of alkylate which has an octane number substantially higher than the charge to the first permeation stage of (1).

10. The process of claim 1 wherein a plurality of permeation stages are used and wherein non-permeated portions of selected stages are blended to produce an alkylate 12 having a higher octane number than the original alkylatc charged to the first stage.

References Cited in the file of this patent UNITED'STATES PATENTS 2,475,990 Robertson July 12, 1949 2,591,367 McAllister Apr. 1, 1952 2,653,982 Kennedy et al Sept. 29, 1953 10 2,758,960 Kelly et al Aug. 14, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No; 2,929,351 February 2, 1960 Robert C. Binning et a1.

It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 lines 4 and 5 strike out "and a lower octane number alkylate blending stock for a leaded gasoline"; column 3, line 16 for "50 read 50% column 4 line 11, after "alkylatei r, insert produced Signed and sealed this 16th day of August 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting ()fficer Commissioner of Patents

Claims

1. A PROCESS WHICH COMPRISES CONTACTING UNDER PERMEATION CONDITIONS AND ISOBUTANE-BUTENE ALKYLATE BOILING IN THE GASOLINE BOILING RANGE WHICH HAS AN F-1 OCTANE NUMBER OF LESS THAN 96 WITH ONE SIDE OF A PERMEABLE PLASTIC MEMBRANE AND THEREBY PERMEATING A PORTION OF THE ALKYLATE THROUGH THE MEMBRANE, SEPARATELY RECOVERING A PORTION OF THE ALKYLATE WHICH PERMEATES THE MEMBRANE AND A PORTION OF THE ALKYLATE WHICH HAS NOT PERMEATED THE