US2429205A - Alkylation of isoparaffins by means of olefins - Google Patents

Description

et. 21, WW. F. J. JENNY HAL.

KLKYLATION 0F ISOPARAFFJENSv BY MEANS OF OLEFINS 2 Sheets-Sheet 1 Filed March 11, 1942 muHFmm 2.533

MUWEIU uzEomm FRANK J. JENNY MYRLE. M. PERKINS MICHAEL J. CICALESE INVENTORS y Y V /& A/U W ATTORNEYS;

y 141 F. J. JENNY, ETAL 242,5

ALKYLATION OF 'ISOPARAFFINS BY MEANS OF OLEFINS Filed March 11, 1942 2 Sheets-Sheet 2 #4 ff YLA T/O/V FRESH FIELD I as 1 5.50 TQIWZE IN VEN TORS BY Sim ATTORNEYS Patented Oct. 21, 1947 ALKYLATION F ISOPARAFFIN S BY MEANS OF OLEFINS Frank J. Jenny, Forest Hills, Myrle M. Perkins, Plandome, and Michael J. Cicalese, Forest Hills, N. Y., assignors to The M. W. Kellogg Company, Jersey City, N. 3., a corporation of Delaware Application March 11, 1942, Serial No. 434,200

3 Claims. (Cl. HBO-683.4)

This invention relates to the alkylation of isoparaifin hydrocarbons with olefin hydrocarbons to produce higher-boiling paraflin hydrocarbons.

More particularly, the invention relates to the alkylation of low molecular weight isoparaffin hydrocarbons, such as isobutane and isopentane, with low molecular weight olefin hydrocarbons, such as propylene, butenes and pentenes, in the presence of acid catalysts, such as sulfuric acid, phosphoric acid and hydrofluoric acid, to produce paraffin hydrocarbons boiling within the gasoline boiling range and of high anti-knock value. Still more particularly, the invention relates to the treatment of a mixture of low molecular weight hydrocarbons containing isobutane, normal butane and olefin hydrocarbons capable of alkylating isobutane.

Acid catalysts, such as sulfuric acid, phosphoric acid and hydrofluoric acid, are employed to catalyze the alkylation of low molecular weight isoparafiin hydrocarbons with olefin hydrocarbons. The reaction preferably is carried out by bringing the reactants and the acid catalyst into intimate contact in the liquid state. Preferably, the reaction is carried out in a continuous manner in which the hydrocarbon reactants and acid are supplied continuously in the liquid state to a reaction zone in which intimate mixing of the catalyst and reactants is effected with the production of a body of emulsion. To promote the alkylation reaction the isoparafiin reactants are maintained in the reaction zone in substantial excess of the amount necessary to react with all olefin hydrocarbons present. For example, a molecular ratio of isoparaffin reactants toolefin reactants of :1 or higher in the reaction zone is desirable. A portion of the mixture of hydrocarbons in the reaction zone is withdrawn, preferably continuously, and fractionated to recover the alkylate and a fraction concentrated with respect to the isoparafiins. The last-mentioned fraction is recycled to the alkylation zone in order to maintain the excess of isoparafiins in the reaction zone.

' The mixtures of low molecular weight hydrocarbons are obtained from hydrocarbon gases produced in the thermal or catalytic treatment of petroleum hydrocarbons and classified generally as refinery gases. Such gases contain the low-boiling olefin hydrocarbons and also contain substantial quantities of isobutane. Refinery gases ordinarily contain hydrocarbons having from 1 to 5 carbon atoms per molecule and include paramn and olefin hydrocarbons in the normal and iso forms. Prior to conversion treatment such gases ordinarily are fractionated to separate therefrom mixtures consisting essentially of hydrocarbons having at least three carbon atoms per molecule. For example, a fraction consisting essentially of butanes and butenes may be treated.

Such refinery gases or suitable fractions thereof contain the necessary reactants for the alkylation process, but ordinarily the proportion of olefin hydrocarbons is substantially in excess of the amount necessary to react with all the isoparaifin hydrocarbons present. Consequently, and. in the absence of another source of isobutane, such gases ordinarily are subjected to a polymerization treatment, for example in the presence of a polymerizing catalyst, to convert a substantial proportion of the olefin hydrocarbons to higherboiling olefin hydrocarbons by polymerization thereof without the occurrence of any reaction by the normal parafiin and isoparafilns present. For

.example, in a refinery gas obtained from the cracking of hydrocarbon oils, the hydrocarbon constituents having three carbon atoms per mole-'- -5 cule, the C3 hydrocarbons, ordinarily consist of a... major proportion of propane and a minor pro-' portion of propylene. The hydrocarbon constituents containing four carbon atoms per molecule, the C4 hydrocarbons, ordinarily consist of butanes to the extent of at least one half, the remainder being butenes. The butanes ordinarily include isobutane only in a minor proportion. By subjecting such a mixture to catalytic polymerization the proportion of butenes in the C4 hydrocarbons is substantially reduced with an accompanying increase in the proportion of butanes.

However, in catalytic polymerization of such a mixture the extent of conversion of the butenes and propylene, if any of the latter is present, frequently is insufficient to reduce the proportion of such olefin constituents of the mixture to or below the amount equivalent, on a molecular basis, to the amount of isobutane present. This occurs when treating a gas having a relatively low concentration of isoparaflins or when the permissible extent of conversion is limited in order to obtain a high yield of polymer per unit of polymerizing catalyst employed. Consequently, the low-boiling hydrocarbon mixtures available for use as feed to an alkylation process often contain a substantial excess of olefin reactants over the amount thereof necessary to alkylate all isoparafiins present in the mixture. While, in the above discussion of this condition, reference is made by way of example to the C4 hydrocarbons produced by hydrocarbon cracking, the same conclusions apply to other low-boiling fractions containing isoparaiiin alkylation reactants such as the C hydrocarbons.

In initiating the alkylation of low molecular weight isoparaflin hydrocarbons, such as isobutane, it is customary to fill the reaction zone with isobutane and the acid catalyst and emulsify the mixture by mixing means. Thereafter the introduction of the fresh feed to the process, containing the olefin reactants and normal and isobutane, is initiated with concurrent withdrawal of an equivalent volume of the hydrocarbon mixture from the reaction zone. Upon introduction of the fresh feed into the reaction zone at proper conditions of temperature and pressure reaction of the olefin hydrocarbons with isobutane proceeds rapidly with the complete absorption of the olefin reactants in the reaction zone by the alkylation reaction. The hydrocarbon mixture withdrawn from the reaction zone is fractionated to separate alkylate and an isobutane fraction substantially free of normal butane for recycling to the reaction zone in order to maintain the high ratio of isobutane to olefin reactants.

Necessarily, the introduction of normal butane into the reaction zone as a part of the olefincontaining fresh feed results in displacing a part of the isobutane so that normal butane builds up in the reaction zone to a stabilized concentration the actual value of which depends on the conditions of reaction, the composition of the feed, feed rate, etc.

In the absence of isobutane from an extraneous source, as is usually the case, it is necessary to react isobutane only at the rate at which this compound is introduced into the system with fresh feed.

It is evident that the processing of close-boiling mixtures of hydrocarbons in which the olefin reactants are substantially in excess of the amount necessary to react with all the isoparamn reactants present presents certain difficulties in maintaining the desired substantial excess of isobutane in the reaction zone.

It is an object of the present invention to pro vide a method for processing such mixtures in which the desired substantial excess of isobutane, or other isoparafiin hydrocarbons, in the reaction zone is maintained and in which isoparaffins are alkylated only in an amount equivalent to the amount of isoparamns introduced into the system in the olefin-containing fresh feed. Other objects of the invention will be made apparent from the following more detailed description of the process of the invention.

The invention will be described in detail by reference to a specific application of the invention to the processing of a C4 hydrocarbon fraction resulting from a catalytic polymerization operation. The C4 hydrocarbon fraction separated from a polymerization reaction product varies in composition, but the following may be considered as typical:

M01 per cent Propane-propylene 2 Butenes l8 isobutane 12 Normal butane 68 as fractions of refinery gas, and to the treatment of hydrocarbons other than the C4 fraction, such as pentane-pentene mixtures. It is to be understood, therefore, that the invention ls not necessarily limited to the treatment or C4 fractions from polymerization reaction products, although, for reasons which will be made apparent below, the invention is of particular advantage in the processing of such mixtures.

The invention will be described in detail by reference to the accompanying drawings in which Fig. l is a diagrammatic view in elevation of apparatus suitable for carrying out the alkylation process of the invention in the presence of a sulfuric acid catalyst and in which Fig. 2 is a similar diagrammatic view illustrating a preliminary polymerization process from which the charge gas for the alkylation step may be drawn. It is to be understood, however, that the invention is not necessarily limited to the particular mode of application indicated by the drawing but includes other modifications in its scope, including the use of other acid alkylating catalysts.

Referring to the drawing, the alkylation reactor I is divided into a reaction zone 2 and a settling zone 3 by means of a suitable weir 4 which extends across the cylindrical reactor to a height corresponding to the desired liquid level. To facilitate mixing of the reactants in reaction zone 2 the latter may be divided into a plurality of separate mixing zones 2a, 2b and 20 by means of suitable baffles or weirs 5 with means, such as suitable beaters 6a, 6b and 6c, provided in each separate mixing zone, to mix the reactants and acid catalyst. Reaction zone 2 is filled to the top of weir 4 with the emulsion of reactants and acid catalyst and, due to the continuous introduction of fresh reactants, there is a continuous flow of the mixture from zone 2a to zone 2b and then to zone 2c and over'weir 4 into settling zone 3.

Settling zone 3 is maintained at a lower liquid level than zone 2 by means of a weir I which extends to a height lower than that of weir l and separates a small part of reactor I at the end thereof from the remainder of section 3.' In settling section 3 the mixture of hydrocarbons and acid catalyst separates into an upper hydrocarbon layer and a lower acid layer.

The acid collecting in the lower portion of settling zone 3 is withdrawn through line 8, provided with a pump 9, and returned to reaction zone 2, preferably at a plurality of points along the length thereof, and in each of zones 2a, 2b and 20 by means of branch lines 8a, 8b and 80. A portion of the acid passing through line 8 may be diverted through line I 0 for revivification or other handling, and an equivalent amount of fresh or revivifled acid is introduced through line Ii, provided with pump l2, which connects with line 8.-

The hydrocarbons separated in settling zone 3 flow over weir l and are withdrawn from reactor I through line I3, provided with a Pump it. The alkylation reaction product passes in indirect heat exchange at IS with incoming fresh feed to cool the latter and thereafter is mixed with a caustic solution introduced into line l3 through line i6. The alkylation product and caustic solution pass through mixer l1, located in line l3, whereby acid entrained in or absorbed by the hydrocarbons passing through line I3 is absorbed by the caustic solution. Line i3 connects with caustic settler I8 in which the caustic solution separates as a lower layer while the treated hydrocarbons separate as an upper layer. The caustic solution is withdrawn from settler 18 through line is, provided with a pump 20, for regeneration or other treatment, or all or a portion of the caustic solution passing through line I9 may be recycled, through line 2| which connects line l9 with line IS.

The treated hydrocarbon mixture separated in settler I8 is withdrawn through lin 22, provided with heating means 23, and introduced into an isobutane fractionator 24. In fractionatbr 24 fractionating conditions of temperature and pressure are maintained to effect substantially complete separation between isobutane and normal butane whereby the condensate collected in the bottom of fractionator 24, consisting essentially of the alkylate and normal butane, contains a very small proportion of the isobutane introduced into fractionator 24. Condensate collected in the bottom of fractionator 2A is transferred through line 25 to debutanizer 26 in which the mixture is fractionated to separate overhead a normal butane fraction withdrawn from the system at 21 and to separate a condensate, containing the alkylate, which is withdrawn at 28 for further fractionation treatment or other treatment for the recovery of gasoline therefrom.

The isobutane fraction, which may include propane, passing overhead in fractionator 2d, as'a vapor, is withdrawn through line 29. The vapors passing through line 29 are condensed by cooling means at 30, and the condensate is collected in reflux drum 3|. A portion of the condensate at 3| is returned by means of line 32 and pump 33 to the upper portion of fractionator 25 as reflux.

The fresh feed to the system is introduced through line 3%, provided with a pump 35. Line 36 connects with a water settler 35.

The hydrocarbon mixture flowing through line 36 is cooled by heat exchange at it with the alkylation reaction product and, if necessary, by additional cooling means at 31 prior to introduction into water settler 36. The isobutane fraction collected in reflux drum Si is withdrawn therefrom through line 38, provided with a pump 39, and introduced into line 34 as shown whereby the isobutane fraction containing recycled isobutane is mixed with the fresh feed to the operation prior to the cooling steps at E5 and 3? and prior to introduction of the mixture into settler 35.

In settler 3B the hydrocarbon mixture is mainexample 85 pounds per square inch and the combined feed to the operation is maintained in water settler 36 at a pressure suificiently high to prevent vaporization, for example, 90 pounds per square inch. The reduction in pressure of this material at 43 to the reaction pressure maintained in accumulator 42 efiects a separation into condensate and vapors as described.

The vapors sepaarted in accumulator 42 pass overhead through line 44 to compressor 45. From compressor 45 the compressed hydrocarbons pass through line 46, in which is located cooling means 41, to a condensate drum 6%. The vapors are compressed at $5 under a substantial pressure of, for example, 65 to 75 pounds per square inch whereby they are increased in temperature from approximately F. to approximately 125 F. The compressed mixture is then cooled at ill to a temperature sufficiently low to effect complete condensation, for example, 100 F. Condensate collected in drum 58 is then expanded to the reaction pressure, and the remaining condensate is transferred to the reaction zone. This is accomplished advantageously by transferring the contained relatively quiescent to permit separation of water which is withdrawn from the system through line 40.

From settler 35 the hydrocarbons are transferred by line iii to a feed preparation zone maintained in accumulator 432. The pressure on the hydrocarbon mixture introduced into accumulator 42 through line a l is released, for example by means of pressure reduction valve 53, to the lower pressure maintained in accumulator 62, which is ordinarily the pressure of the alkylation reactor. As a result of such expansion the hydrocarbons introduced into accumulator 52 through line All separate into a vapor and a condensate at a temperature at least as low as that of the alkylation reaction zone.

Alkylation reactor 1 is operated preferably at a pressure which permits substantial vaporization of unreacted hydrocarbons from the reaction mixture at the desired reaction temperature. Since it is desired ordinarily to maintain the alkylation reaction zone at a relatively low temperature to inhibit polymerization of olefins the pressure necessary to maintain the reaction mixture in the desired condition is ordinarily rather low. The pressure necessary is affected also by the proportion of the low-boiling hydrocarbons densate from drum it through line 9 to accumulator t2 and releasing the pressure by means of pressure reduction valve 5@ located in line Q9.

The condensate collected in accumulator i2 is withdrawn therefrom through line 5 i. Line 54 is provided if necessary with a pump 52 to efiect transfer of the condensate from accumulator t2 to the alkylation reaction zone 2. Line 5! is provided with three branch lines 5m, 5!!) and lilo which connect line 55 with zones 2a, 2b and 2c of reaction zone 2. By this means the charge to the reactor may be introduced entirely into zone 2a through line 5 id, or the charge may be distributed in any desired proportions to zones to, 2b and 2c. Preferably, uniform distributionis employed by introducing the fresh feed and the recycled isobutane in equal amounts through each of lines Eta, Eib and Sic.

As is pointed out above, the reactor 2 is maintained under conditions permitting vaporization of unreacted hydrocarbons at the reaction temperature. By this means the reaction mixture is maintained at the desired reaction temperature since the heat of the exothermic reaction is abstracted through such evaporation and by the removal of such vapors from the reactor'through line 53. Such vapors ordinarily are condensed externally of the reactor, and condensate thus obtained is returned to the reaction zone. In connection with this operation the recovery treatment of such vapors may be combined with treatment of vapors separated from the feed introduced into accumulator at through line til. This combination of the vapors is efiected advantageously by connecting line '53 with accumulator 42 whereby the vapors are passed through accumulator Q2 and substantially freed of entrained liquids through contact with suitable bafiies, etc, contained therein. By this method of operation the combined vapors withdrawn through line it are treated in the manner described above,

Alternatively, or in addition to the transfer of condensate directly from drum 43 to accumulator 42, all or a portion of the condensate from drum 48 is transferred through line 54, provided with pump 55, to depropanizer fractionator 56. In depropanizer fractionator 56 conditions of temperature and pressure are controlled to separate overhead a propane fraction substantially free of isobutane and containing propane in an amount equivalent to the amount being introduced into the system through line 34. This is a convenient method of eliminating propane from the system since the mixture passing through line 5! is more concentrated in propane than any other mixture in the system. Fractionation is thereby rendered relatively simple since it is necessary ordinarily to eliminate a part only of the propane introduced into depropanizer 56.

The condensate separated in the bottom of depropanizer 55 consisting essentially of butanes, and ordinarily containing propane, is withdrawn therefrom through line 51, provided with pump 58, and introduced into line 34 into admixture with the fresh feed. When the feed introduced through line 34 is derived from the fractionation of a catalytic polymerization product the depropanizer fractionator of such an operation may perform the function of depropanizer 56 in which case the disposal of the condensate as indicated by line 51 is essentially similar.

Instead of combining the treatment of the fresh feed with the treatment of the recycled isobutane and the handling of the vapors evolved in the reaction zone, in a single system comprising accumulator 42, drum 48 and the various connections thereto, the fresh feed containing the olefin reactants may be separately handled for introduction into the reaction zone. In this modification of the process the fresh feed introduced into the system through line 34 is passed wholly or in part through line 59 which connects with a separate fresh feed accumulator 6|]. The fresh feed passing through line 59 is cooled by suitable means at El and is released to approximately the reaction zone pressure by pressure-reducing valve 62 in line 59. In accumulator 60 the hydrocarbons separate into a vapor and a condensate having a temperature which is approximately the reaction temperature. Vapors separated in accumulator 60 are withdrawn overhead through line 63 which connects with a compressor 64. At 64 the vapors are compressed to'a relatively high superatmospheric pressure, for example 65 to 75 pounds per square inch, and the compressed material is then introduced into drum 65. Cooling means are provided at 66 to effect complete condensation of the vapors prior to introduction into drum 65. Condensate from drum 65 is then returned to accumulator 60 through line 61, the pressure being reduced by means of pressure-reducing valve 68. Any vapors, separated from the condensate introduced through line 61 into accumulator 60 are combined with other vapors therein and treated in the manner described.

The condensate collected in accumulator B is withdrawn therefrom for transfer to the alkylation reaction zone by means of line 69 and pump 10. Conveniently, line 59 connects with line If it is desired to mix the condensate from ascumulator 50 with that from accumulator 42, in order to distribute the resulting mixture among mixing zones 2a, 2b and 20, line 69 is connected with line 5| at a point between accumulator 42 and branch line 5la. However, it may be desirable to distribute the olefin-containing condeninteroduced into zone 2a and the smallest amount being introduced into zone in order to minimize difierences in the residence time of the reaction mixture in each mixing zone.

The process of'this invention is particularly applicable to the treatment of hydrocarbon mixtures containing an excess of olefin reactants reaction zone.

over the amount necessary to alkylate all isoparaffins present. In the handling of such a mixture, introduced into the system through line 34, all or a portion of the mixture is diverted from line 34 through line 12 which connects line 34 with line 22 whereby the material diverted through line 12 is introduced directly into fractionator 24. If the freshfeed to the system flows from line 34 into line 59, the necessary diversion of fresh feed occurs at the junction of lines 34 and 59 with the diverted portion passing through lines 34 and I2.

The amount of material diverted from the fresh feed through line 12 is regulated whereby it includes olefin reactants higher boiling than the isoparaffins in the mixture in an amount equivalent to the excess of olefins in the mixture introduced through line 34 over the amount required to alkylate all the isoparafiins present. Preferably, a sufiicient amount of material is thus diverted from the fresh feed to divert olefin reactants higher boiling than the normal paraffin corresponding to the isoparamn to be alkylated in an amount equivalent to a major proportion of the said excess of olefin reactants in the mixture introduced into the system through line 34. Referring specifically to the alkylation treatment of a mixture including isobutane as the isoparailln to be alkylated, the amount of the fresh feed diverted is regulated to pass through line I2 a quantity of butenes equivalent to the amount by which the olefin reactants are in excess of the amount required to react with all isobutane introduced through line 34. Preferably, the mixture diverted through line 12 contains butene-2 in an amount equivalent to all or a major proportion of the excess of the olefin reactants in line 34. By this method of operation butene-2 introduced into fractionator 24 is included in the condensate withdrawn through line 25 with at most a small proportion of other butenes and is thus excluded from the alkylation reaction zone. Fractionator 24 is controlled to effect separation overhead of butene-l and isobutene along with isobutane whereby all or most of these olefin reactants are included in the hydrocarbons recycled to the Alternatively, fractionator 24 is operated under conditions effective to include all or a substantial proportion of the butene-l and isobutane in the condensate whereby only a portion, or none, of these olefin reactants diverted through line 12 is included in the hydrocarbons separated overhead in fractionator 24 for recycling to the alkylation reaction zone. Under either method of operation of fractionator 24 the quantity of material diverted from the fresh feed through line I2 is regulated whereby the proportion of the olefins separated as condensate in fractionator 24 is a quantity equivalent to the excess of olefins over isoparamns in the fresh feed introduced through line 34. Preferably, however, fractionator 24 is operated to eiiect a separation between butene-l and normal butane whereby all or nearly all butene-l and isobutene in fractionator 24 are included in the isobutane fraction separated overhead because of the greater ease of fractionation and because this method requires the diversion of a greater proportion of the fresh feed through line 12, thereby excluding from the reaction zone a greater proportion of the normal butane content of the fresh feed. Inasmuch as the alkylation reaction is promoted and otherwise favorably influenced by maintaining the concentration of isobutane therein at a maximum, it is preferred to handle the fresh feed in a manner which eliminates the greatest amount of normal butane.

In certain mixtures of butanes and butenes the quantity of butene-2 may be substantially less than the amount of excess olefins in the mixture over the amount required to alklate the isoparam s present. In that case diversion of all of the fresh feed through line 112 would not be sufficient to include in the condensate a suflicient quantity of olefins when operating fractionating tower 2d to include all or nearly all isobutene and butene-l in the overhead mixture. In that case it is desirable to subject such a fresh feed to a preliminary isomerizing treatment in which butene-l is isomerized to butene-2.

Conveniently, such preliminary treatment is carried out in the presence of a catalyst having both a polymerizing and isomerizing action whereby the olefins are reduced in quantity and at the same time conversion of butene-l to butene-2 is efiected. For example, the polymerizing treatment of a refinery C4 or C304 gas mixture in the presence of a copper pyrophosphate polymerizing catalyst as described in U. S. Patents Nos. 2,189,655 and 2,259,755 apparently effects isomerization of olefins, apparently through the shift of the double bond from an end position to a central position, while at the same time polymerizing olefins to higher-boiling hydrocarbons. Other catalysts which apparently have this combined polymerizing and isomerizing action include phosphoric acid and silica gel activated with alumina.

Fig. 2 illustrates the polymerization-isomerization process from which may be obtained the fresh feed introduced into the alkylation operation through line 3t. Referring to Fig. 2 a refinery gas mixture consisting of hydrocarbon gases, in which propane, propylene, butane and butylenes predominate, is introduced through line 13 to a suitable heater la in which the gases are heated to the temperature desired for the polymerization treatment. The exact composition of such gases varies somewhat but the following may be considered typical:

The gas feed is heated in heater l4 approximately to the desired reaction temperature which is preferably in the range of 375 to 450 F. The heated fresh feed is withdrawn from heater it through line 15 which connects with the upper 10 P rtion of a reactor 16. Reactor 18 contains a granular mass of polymerizing catalyst preferably in the form of pellets consisting of mixtures of finely divided carbonaceous material and copper pyrophosphate, as described in the above-mentioned patents and also in U. S. Patent No. 2,310,161. Preferably also the catalyst is supported within reactor 16 on suitable trays, etc.

The reaction gases pass through reactor 16 in contact with the catalytic material to effect substantial conversion of propene and butene. While reactor 16 may be sufficiently large to provide a reaction time sufiiciently long to eiiect the desired conversion of the olefins it is preferred ordinarily to utilize a plurality of reactors arranged in series. In Fig. 2 such a series is represented by the arrangement of reactors l6 and H, but it is to be understood that these are representative of a series of any desired number of reactors which may vary from two to six. Reactor i6 is connected to reactor II by line 18 through which the reaction mixture passes from the bottom of reactor it to the top of reactor ll.

Reactors l6 and Ti are maintained under a substantial superatmospheric pressure which is ordinarily higher than 500 pounds per square inch, an operating pressure of 900 pounds per square inch being a. typical condition. The reactants are passed through the reaction zone represented by reactors it and H at a rate of approximately 5 to 15 cubic feet (measured as gas at standard conditions of temperature and pressure) per pound of catalyst per hour, a feed rate of approximately 9 cubic feet per hour being a typical value for this factor.

The reaction products are withdrawn from the bottom of reactor ll through line l9 which connects with a fractionator which serves as a depropanizer. A cooler may be provided in line is. In fractionator all the reaction product is subjected to fractionating conditions of temperature and pressure effective to separate overhead a gas mixture containing all but a minor proportion of the propane and lower boiling constituents and containing at most a minor proportion of hydro carbons higher boiling than propane. The remainder of the reaction product, including the polymers and unconverted butenes and butanes, is separated as a condensate in the bottom of fractionator at.

The gases separated overhead in fractionator 80 are withdrawn through line 82 which is provided with cooling means 83 and connects with reflux drum M. The gases are cooled at 83 sufficiently to condense substantially all propane and propylene and the condensate thus produced is separated from uncondensed gases in drum 84. The uncondensed gases are withdrawn overhead through line 85 and the condensate is withdrawn through line 86 by means of pump 81. A portion of the condensate withdrawn through line 86 is returned to the top of fractionator 80 as reflux liquid through line 88.

A suitable trap-out tray 89 is provided in the upper portion of fractionator 80 to separate a condensate consisting primarily of butanes and butylenes. This condensate is withdrawn through line 90 by means of pump 9i. Line 90 is connected by .branch lines 92 and 93, by the multiple connections shown, to intermediate points along the length of reactors i6 and Ti. Through lines 92 and 93, and their various connections to the reactors, condensate collected at 89 is introduced into the reaction zone to absorb the heat de- 75 veloped by the exothermic polymerization reaction and to assist in maintaining the reaction temperature at the desired level. The liquefied gases are thus introduced through each of the connections with the reaction zone in the amount necessary to absorb, by vaporization of the liquefled gases, the heat developed in that part of the reaction zone adjacent the connection. The condensate in line 96 may be employed also for this purpose but the arrangement shown is preferred.

The depropanized condensate is withdrawn from the bottom of fractionator 89 through line 94 which connects with a second fractionator 95. Fractionator 95 is maintained under conditions of temperature and pressure effective to debutanize the condensate introduced through line 94 whereby a gaseous overhead product is separated which contains a substantial proportion if not all of the butanes and butenes introduced into fractionator 95. The debutanized polymer product is separated as a condensate in the bottom of tractionator 95 and is withdrawn for further treatment elsewhere through line 99.

The gases separated overhead in fractionator 95 are withdrawn through line 91 which is provided with cooling means 98 and 'connects'with a reflux drum 99. Substantially complete condensation is effected at 98 and the condensate is collected in drum 99. This condensate, which represents a suitable charging stock for the alkylation step illustrated in Fig. 1, is withdrawn from reflux drum 99 through line 34 which is connected with the alkylation system as shown in Fig. l. A portion of the condensate from drum 99 may be diverted from line 34 through line I90, provided with pump I01, for return to the top of fractionator- 95 as reflux.

The invention thus includes the combination of a polymerizing-isomerizing operation and an alkylating operation in which the polymerizingisomerizing operation is employed to treat a gaseous mixture containing olefins and isoparaffins and corresponding normal parafflns to reduce the quantity of olefins in the mixture and at the same time isomerize the olefins to increase the proportion of higher-boiling olefins, apparently through shifting of the double bonds from outside positions to central positions in the molecule. The extent 01' conversion in the polymerizing operation may be regulated to produce a resulting unreacted mixture in which the quantity of olefins higher boiling than the corresponding normal paraifln is at least equal to the amount by which olefin reactants are in excess of the amount necessary to alkylate all isoparaffin present. Referring, for example, to the treatment of a gaseous mixture containing butenes, isobutane and normal butane. and possibly propane and propylene, it is desirable to operate the polymerization step to effect a degree of conversion suflicient to produce in the resulting unreacted gases a quantity of butane-2 substantially equivalent to the excess of olefin reactants in the alkylation feed prepared from such a mixture. Ordinarily, the products of polymerization of a CaC4 mixture are fractionated to separate a C4 fraction for use as feed to the alkylation step. Consequently, the propene concentration is relatively negligible in the alkylation fresh feed. If the C4 fraction from the polymerizing step is controlled to produce in the C4 fraction of the reaction product a quantity of butene-Z equivalent to or only slightly less than the excess of all butenes in the mixture over the amount required to alkylate the isbutane or, expressed otherwise, if the polymerizing step is regulated to produce in the fraction a quantity of isobutene and butene-l sufllcient to alkylate all isobutane present such a fresh feed may be introduced in toto into the fractionating zone of the alkylation step whereby normal butane is substantially completely excluded from the alkylation reaction zone. This method of operation of the polymerizing'step may involve a lower conversion per pass than would otherwise be desirable, but this effect may be compensated for by the increased efliciency of operation of the alkylating step and by a greater yield of polymer per unit of polymerizing catalyst employed.

However, the requirement for polymer may require operating the polymerizing zone to effect a greater degree of conversion than in the combined operation described above. Under such cir- M01 per cent Propane-propylene 2 Isobutene 4 Butene-l 4 Butene-2 l0 Isobutane 12 Normal butane 68 In processing the foregoing mixture in accordance with the present invention no more than 60 mol per cent of the fresh feed should be diverted through line 12 and introduced directly into fractionator 24. In fractionator 24 this mixture, along with other hydrocarbons therein, is separated into a condensate including substantially all normal butane, butene-2 and alkylate and an overhead fraction including substantially all isobutane and at least a major proportion of the butene-l and isobutene. When employing a fractionating system previously designed for mere fractionation between isobutane and normal butane a minor proportion of the butene-l and isobutene may be included in the bottoms. In such case the amount of fresh feed diverted is made slightly less than the amount containing butene-2 in an amount equal to the said excess of butenes.

for example, 50 to 55 per cent of the total fresh feed. By this method of operation the excess 6 mol per cent of butenes over the amount required to react with all isobutane in the fresh feed is eliminated from the system along with normal butane. This method of operation also improves the process by the reduction in the amount of normal butane introduced into the reaction zone to the extent of 50 to 60 per cent. This reduction in the amount of normal butane in the reaction zone effects a corresponding increase in the concentration of isobutane therein with resulting improvement in the alkylation reaction as to speed of reaction and the octane number of the gasoline obtained from the alkylation product.

While the invention is particularly applicable to a combination polymerizing and alkylating treatment of a C4 refinery gas fraction because of the relatively large volume of such raw materials which are available, it is evident that the principles of operation of the invention are also applicable to the processing of other hydrocarbon mixtures in a preliminary isomerizing treat- 13 ment, with or without polymerization, of an olefin-normal paraflin-isoparaflin mixture followed by alkylation in the manner described above. For example, a pentane-pentene fraction may be subjected first to an isomerizing treatment to effect isomerization of olefins to increase the proportion of higher-boiling olefins, apparently through shifting of the double bond from an outer to a central position, and then to an isopentane alkylating process in which a suflicient proportion of the alkylation fresh feed is diverted to the fractionating system of the alkylation process to exclude high-boiling pentenes, such as pentene-2 and 2-methyl butene-2, from the alkylation reaction zone in an amount equivalent to the excess of olefin reactants in the alkylation feed over the amount necessary to alkylate the isopentane. The isomerizing step may involve polymerization to reduce the concentration of olefins. This method of operation also excludes from the alkylation reaction zone a substantial proportion of normal pentane in the feed if not all of that hydrocarbon with resulting benefits, as described above.

We claim:

1. A process for the conversion treatment of a low-boiling mixture of hydrocarbons comprising an isoparaflin, the corresponding normal paraifin and low-boiling olefins capable of alkylating said isoparaflfin in substantial excess of the amount necessary to alkylate all of said isoparaflin which comprises first subjecting said mixture to an isomerization treatment to effect isomerization of olefins to increase the proportion of higher-boiling olefins, separating from the isomerization product a. low-boiling fraction suitable as fresh feed to a catalytic alkylation process, contacting isoparafllns and olefins in a catalytic alkylation reaction zone to effect alkylation of the isoparaflins by said olefins, fractionating the alkylation products to separate a fraction comprising unreacted isoparaflins and substantially free of higher-boiling normal parafifins and a fraction containing said corresponding normal paraflin, recycling isoparafl'lns thus recovered to the alkylation reaction zone to maintain a substantial excess of isoparafllns in the reaction zone, introducing directly into the zone of fractionation of the alkylation reaction products a portion of the said alkylation fresh feed which contains olefins higher boiling than said isoparaflins in an amount at least equivalent to the excess of olefins in said alkylation fresh feed over the amount required to alkylate all said isoparaflin contained in said fresh feed whereby the isoparafiln content of said material thus introduced directly into the fractionating zone is included in the said fraction comprising unreacted isoparaffin and olefins are included in said normal paraffin fraction in an amount equivalent to said excess, and introducing the remainder of the said alkylation fresh feed into said alkylation reaction zone.

2. A process for the conversion treatment of a low-boiling mixture of hydrocarbons comprising an isoparaflin, the corresponding normal paramn and low-boiling olefins capable of alkylating said isoparaifin in substantial excess of the amount necessary to alkylate all of said isoparaflln which comprises first subjecting said mixture to an isomerization treatment to eifect isomerization of olefins to increase the proportion of higher-boiling olefins, separating from the isomerization product a low-boiling fraction suitable as fresh feed to a catalytic alkylation process, contacting isoparafiins and olefins in a catalytic alkylation olefins in said alkylation fresh feed over the amount required to alkylate all said isoparaflin contained in said fresh feed whereby the isoparafiln content of said materialthus introduced directly into the fractionating zone is included in the said fraction comprising unreacted isoparafiln, and introducing the remainder of the said alkylation fresh feed into said alkylation reaction zone.

3. A process for the conversion treatment of a low-boiling mixture of hydrocarbons comprising an isoparamn, the corresponding normal paraffin and low-boiling olefins capable of alkylating said isoparaflin in substantial excess of the amount necessary to alkylate all of said isoparaflin which comprises first subjecting said mixture to a polymerizing and isomerizing treatment to effect polymerization of olefins to higherboiling products and isomerization of other olefins to increase the proportion of isomerized higher-boiling olefins, separating from the polymerization and isomerization product a low-boiling fraction suitable as fresh feed to a catalytic alkylation process, contacting isoparaflins and olefins in a catalytic alkylation reaction zone to effect alkylation of the isoparaflins by said olefins, fractionating the alkylation products to separate a fraction comprising unreacted isoparaflns and substantially free of higher boiling normal parafilns and a fraction containing said corresponding normal paraflins, recycling isoparaffins thus recovered to the alkylation reaction zone to maintain a substantial excess of isoparaflins in the reaction zone, introducing directly into the zone of fractionation of the alkylation reaction products a portion of the said alkylation fresh feed which contains olefins higher boiling than said isoparafllns in an amount at least equivalent to the excess of olefins in said alkylation fresh feed over the amount required to alkylate all said isoparaffln contained in said fresh feed whereby the isoparaffln content of said material thus introduced directly into the fractionatlng zone. is included in the said fraction comprising unreacted isoparaflin and olefins in an amount equivalent to said excess are included in said normal parafiin fraction, and introducing the remainder of the said alkylation fresh feed into said alkylation reaction zone.

' FRANK J. JENNY.

MYRLE M. PERKINS. MICHAEL J. CICALESE.

REFERENCES CITED The following references are of record in the file of this patent:

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