US2431500A

US2431500A - Alkylation process

Info

Publication number: US2431500A
Application number: US561889A
Authority: US
Inventors: Joe E Penick
Original assignee: Socony Vacuum Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1944-11-04
Filing date: 1944-11-04
Publication date: 1947-11-25
Anticipated expiration: 1964-11-25

Description

Nov. 25, 1947. J. E. PENICK ALKYLA'I'ION PRbcEss Filed Nov. 4, 1944 llllllll .llll'll .585 E ww Joe E. Pem'ck IN VENTOR WRQQKQQQQ AGENT Patented Nov. 25, 1947 r UNITED STATES PATENT OFFICE 1 2,431,500 Joe E. Penickt nansf zlf fii by mesne enta, to Socony-Nacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York Application November 4, 1944, Serial No. 561,889

4 Claims. (01. 260-683.4)

This invention relates to the production of higher boiling hydrocarbons from lower boiling hydrocarbons in the presence of catalytic agents and relates more particularly to the alkylation of isoparafiins with oleflns in the presence of acid catalysts.

As is well ,known, hydrocarbon products may be produced by alkylation reactions involving the combination or'condensation of two dissimilar hydrocarbon reactants in the presence of suitable catalytic agents. While various types of alkylate products may be obtained by employing various types of reactants, the alkylation of low boiling isoparamns such as isobutane and isopentane with low boiling olefins such as ethylene, propylene, the isomeric butenes, and the isomeric pentenes, for the production of aviation fuels and high grade motor fuels has become of particular importance. Sulfuric acid has been employed as a catalyst in isoparafin-olefln alkylation and more recently liquid hydrogen fluoride has found favor as a catalyst. The alkylation of isobutane with butenes is representative of these reactions and has been commonly carried out by feeding isobutane and butene feed stocks in the liquid state along with liquid hydrogen fluoride to a multi-pass alkylation reactor such as the reaction loop type reactor, wherein the hydrocarbons and catalyst are vigorously agitated and continuously circulated within a closed circuit. The reaction is exothermic and temperature control is important to prevent localized 01' general overheating of the reaction mixture with consequent deleterious efiect on the yield and quality of the alkylate product as a result of side reactions occurring at elevated temperatures. Temperature control is obtained by means of internal heat exchangers over-which the reaction mixture passes proper control of the reaction temperature and because of the belief that very high ratios of saturated hydrocarbons to unsaturated hydrocarbons were essential to prevent olefin polymerization therefore making it desirable to recirculate the saturated hydrocarbon products.

It is an object of this invention to provide an improved alkylation process. It is another object of this invention to provide a process for the alkylation of isoparaflins with olefins in singlepass reactors. It is another object of this invention to provide a method for controlling the temperature of isoparafin-oleiin alkylation mixtures in single-pass reactors. Further objects and advantages of the invention will become apparent from the following description thereof.

In accordance with the invention, the above objects are achieved by a process which involves or by passing a portion of the continuously circulating mixture through an external heat exchanger. A portion of the circulating reaction mixture is continuously withdrawn from the reactor and the acid allowed to settle therefrom, after which the hydrocarbon product is treated for removal of excess isobutane reactant and re-- moval of normal butane and any lighter hydrocarbons which may be present, the acid and the isobutane being recycled to the reactor. It has been proposed to carry out the alkylation reaction in single pass reactors, i. e., reactors in which the reaction mixture is not continuously circulated, but such reactors have not been extensively used, despite the fact that they possess advantages not possessed by multi-pa'ss reactors, primarily because of the difficulty of obtaining feeding to a single-pass reaction zone a, volumeratio of acid catalyst to total hydrocarbons of at least three to one, separating the acid catalyst from the reactor efiluent, recycling at least a portion of the separated acid, and cooling at least a portion of the recycled acid to maintain the temperature of the reaction mixture ata predetermined level.

The amount of heat evolved in alkylation reactions isga function of the type of alkylation reactants, i. e., the heat of alkylation will vary with different reactants, and the temperature rise of the reaction mixture will be a function of the heat of alkylation and the relative amounts and specific heats of the reactants, acid catalyst, alkylate product, and any inert hydrocarbons which may be contained in the hydrocarbon feed stocks. The acid catalyst has a relatively high specific heat and when employed in volumeratios of at least three to one is capable of absorbing the exothermic heat of reaction and preventing an undesirably large increase in the temperature of the reaction mixture. The acid catalyst separated from the reactor eilluent and recycled to the reactor will contain the heat absorbed from the alkylation reaction minus or plus, of course, that heat which may be conducted to or taken from the atmosphere through the walls of the reactor, separator, pipe 1ines,-etc., and the cumulative effect of the heat contained in the recycle acid increasing the temperature of the reaction mixture with repeated recycling is avoided by cooling the recycle acid, or a portion of the recycle acid, to a sumciently low temperature.

The efiect of acid catalyst-hydrocarbon ratio on the rise of temperature of the reaction mixture is shown in the following table. The data were obtained by alkylating isobutane feed stock with butene feed stock in a single-pass reactor and employing varying volume ratios oi. hydrofluoric acid to total hydrocarbons. The isobutane and butene feed stock combined analyzed propane, 60% isobutane, 12% butene. 21% normal butane, and 2% pentane by volume.

m a Woods Acid to ma Hydrocarbons Tm nor. are 3tol 1a1 4.1m 1.2 Dtole0 l9tol 24 temperature of the reaction mixture may be continuously maintained.

The use of hydrofluoric acid-hydrocarbon ratios of at least three to-one results not only in minimizing localized and general overheating of the reaction mixture by absorbing the exothermic heat oi reaction but has the additional efiect of improving the quality of the alkylate product through the catalytic eflect oi the large volumes of acid catalyst. Heretoiore,

'isoparaflin-olefln alkylations, particularly isobutane-butene alkylation, have been carried out by employing hydrofluoric acid-hydrocarbon ratios of about one to one or slightly higher, 1. e., the volume 0! hydrofluoric acid employed, including the recycle acid, has been equal to or slightly greater than the volume of isobutane and butene feed stock, including any normal parafflns or other inert hydrocarbons contained therein, plus the recycled isobutane. It

has been recently discovered, as disclosed in my co-pending application with Urban H. Wagner and Carl S. Kuhn, Jr., Serial No. 561,888, filed November 4, 1944, that significant increases in the octane numbers of the alkylate products are obtained by employing hydrofluoric acid-hydro carbon ratios of at least three to one. As the copending application discloses, it appears that the controlling factor in isoparaifln-olefin alkylation producing high yields of branched chain compounds having high octane numbers, for example, high yields of 2,2,4-trimethyl pentane (iso-octane) by the alkylation of isobutane with butenes, is a low concentration of olefin dissolved in the acid phase of the reaction mixture or, which is the same thing since isoparafllns are only slightly soluble in the .acid phase, a. high ratio of dissolved lsoparaflin to olefin. As the co-pending application further discloses, eflectively low concentrations of dissolved olefin or high ratios of dissolved isoparaflln to olefln are obtained by employing volume ratios of acid catalyst to total hydrocarbons fed to the alkylation reactor of at least three to one. Thus, the use of acid to hydrocarbon ratios of at least three 4 to one is an important feature or the present invention when employing hydrofluoric acid as the catalytic agent in the alkylation 0! isoparaflina from the standpoint of obtaining the catalytic effect of the high ratios of acid to bydrocarbons on the quality or the product and the eflect of minimizing localized and general rise in temperature or the reaction mixture.

While satisfactory results may be obtained by employing ratios oi acid to hydrocarbon or at least three to one, it is desirable to employ higher ratios, as, for example, ratios of 10 to 1 to to 1. Even extremely high ratios, such as ratios of 200 to l and higher, may be employed since both the catalytic effect and the temperature controlling eflect oi the acid increases with increasing acid ratios,

The entire amount of acid being fed to the reactor may be cooled or only a portion or the acid may be cooled. For example, the recycle acid alone or only a portion of the recycle acid may be cooled, or the entire amount or only a portion or the recycle acid plus fresh or regenerated make up acid may be cooled. The extent to which the acid is to be cooled will depend upon the temperature rise 01' the reaction mixture and the amount of acid being cooled. Thus, where the entire amount of acid is cooled the extent oi cooling will be less than where only a portion of the acid is cooled. Preferably, the entire amount of acid is cooled or the cooled portion thoroughly premixed with the rest 01' the acid going to the reactor in order to avoid localized under-cooling at the inlet portion of the reactor. The extent of cooling required will vary for each particular case and can be determinedby those skilled in the art by actual operation or by calculation.

The essential feature of single pass reactors is a substantially steady forward flow of the reaction mixture from the inlet to the outlet of the reactor and the process of the invention is applicable to any type of reactor fulfilling this condition. The reactor maybe a straight chamher or may be a curved tubular reactor. It desired, the reactormay be provided with baiiies or other flow distributing means of such nature as to increase the turbulence of the reaction mixture without substantial interference with its predominantly forward flow through the reactor.

The process of the invention may be employed for the alkylation of isobutane with ethylene,

'. propylene, butenes, pentenes, etc., and the alkylation of isopentane with these same oleflns. However, the process of the invention may be employed in connection with any type of alkylation. The feed stocks may consist entirely of the pure reactants such as pure isoparaflln and pure olefin, or mixtures of pure isoparafllns and pure olefins, or may contain normal paraflins or other inert hydrocarbons. Refinery butane-butane mixtures obtained, for example, by the fractionation of gas mixtures from cracking operations or by the partial dehydrogenation of butane fractions obtained from natural gas or from stabilization of natural or straight run naphthas and containing normal butane and hydrocarbons heavier and lighter than 4-carbon atom hydrocarbons may be employed in isobutane-butene alkylation. However, it is desirable to carry out the alkylation reaction with feed stocks containing minimum amounts of inert hydrocarbons.

Conventional alkylation conditions with respect to temperature, pressure-and isoparafllnolefln ratio may be employed. For example, the

alkylation of isobutane with butenes may be carried out at temperatures betweerr about F. and 150 F; at pressures at least sufllciently high to keep the hydrocarbons and hydrofluoric acid in the liquid phase and with isobutane-butene ratios of between 2 to 1 and 15 to 1, preferably between about 6 to 1 and to 1. Ratios of isobutane to butenes of at least 2 to l'are essential since lower ratios tend to cause polymerization of the butenes with resultant decrease. in yield of the alkylate product and/or excessive reaction between the butenes andthe primary alkylate product because of the relatively low ratios of isobutane to alkylate product in the reaction mixture. The hydrofluoric acid may be anhydrous hydrofluoric acid or may have a titratable acidity as low as 70% by weight. Following alkylation, the reaction products may be treated in known manner for separation and reuse of hydrogen fluoride catalyst, separation and recycling of unreacted isoparafiin and recovery and purification oi alkylate product. I

The accompanying drawing is a flowsheet illustrating one mode of carrying out the-process of the invention in connection with the alkylation of isobutane with butene.

Referring now to the drawing, isobutane in the liquid state enters the system through line i0 provided with a suitable control valve H and is admixed in line I 2 provided with a suitable control valve l4 with recycle isobutane obtained in the manner hereinafter described. The isobutane is admixed with liquid butene feed entering the system through line l5 provided with a suitable control valve i6, and the combined feeds passed to alkylation reactor IT. The volume of isobutane fed to the alkylation reactor is regulated by means of flow controller i8 operating valves I! and I4 and activated by flow responsive means [9, and the volume of butene is regulated by means of flow controller 20 operating valve I 6 and activated by flow responsive means 2|.

Fresh and/or regenerated liquid hydrofluoric acid enters the system through line 22 provided with a suitable control valve 24 and is admixed in line 25, also provided with a suitable control valve 26, with recycle hydrofluoric acid obtained in the manner hereinafter described. The volume of hydrofluoric acid is regulated by means of flow controller 21 operating valves 24 and 2B and activated by flow responsive means 29. The acid in line 25 passes through acid cooler 30 where it is cooled to the desired temperature and'then passes to reactor i i. The mixed hydrofluoric acid and hydrocarbon feeds pass through the reactor and are withdrawn through line 3i and passed to separator 32 for gravity separation of the acid from the hydrocarbons. Recycle acid catalyst is withdrawn from the lower portion of separator 32 and returned through line 25 to the reactor, fresh and/or regenerated acid entering through line 22 as necessary. Line 34 provided with valve 35 is connected to the line 25 for continuous or intermittent removal of a portion of the recycle acid for regeneration. After regeneration, the acid may be returned to the system through line 22.

The hydrocarbon phase from the separator 32 is taken overhead through line 36 and sent to hydrofluoric acid stripping column 31 where a major portion of dissolved and suspended hydrofluoric acid carried over in the hydrocarbon phase is vaporized and returned after condensation in analyzed as follows:

condenser 39 to the separator 32 through line 40 4 provided with valve 4|. The bottoms from stripper 31 are passed through line 42 to deisobutanizer 44 for removal of isobutane. Residual traces of hydrofluoric acid and organic fluoride contained in the bottoms from stripper 3'! may be removed by chemical treatment, as with bauxite, prior to introduction of the hydrocarbons in deisobutanizer 44. The isobutane is removed as overhead through line 45 and passed to condenser 48 maintained under such conditions of temperature and pressure that the isobutane condenses while any lighter hydrocarbons which may have formed during the alkylation reaction or which may have been contained in the hydrocarbon feed remain in the gaseous state. The gases pass out of the condenser through line 41 provided with valve 49 and the liquid isobutane is recycled through line l2 to the alkylation reactor 11. The bottoms from deisobutanizer 44 are passed through line 50 to debutanizer 5| where normal butane formed during the reaction or which may have been contained in the feed hydrocarbons is removed as overhead through line 52. If desired, the normal butane from line 52. may be isomerized to isobutane and recycled to the reactor H. The debutanizer bottoms are passed through line 54 to iractionator '55 where the alkylate product is separated into aviation alkylate and heavy alkylate. The heavy alkylate is removed as hottoms through line 55 and the aviation alkylate is removed as overhead through line 51 and condensed in condenser 59.

The following examples are illustrative of the results obtainable by the process of the invention. In these examples, isobutane feed stock was alkylated with butene feed stock employing hydrofluoric acid as the catalyst. The feed stocks Volume Per Cent Hydrocarbon Examplel Propane and Propylene isobutane";

Pentane, Pentenes, and heavier and were used in proportions to give the isobutane-butene ratios indicated in the-table below. The reaction was carried out in a single-pass reactor comprising a section of straight pipe one inch in diameter and twenty-feet long. The reactor eiliuent was sent to a separator where the hydrofluoric acid was allowed to settle from the hydrocarbon phase and the separated acid was recycled to the reactor. The entire amount of recycle acid plus the make-up acid was cooled before entering the reactor. The hydrocarbon phase was stripped of dissolved hydrofluoric acid and chemically treated for removal of any remaining hydrofluoric acid and was then deisobutanized, the isobutane being recycled to the reactor. Thereafter, the hydrocarbon phase was fractionated for removal of normal butane and lighter hydrocarbons. The resulting product was regarded as the total alkylate product. The total alkylate product was then fractionated into heavy alkylate and aviation alkylate, the aviation al- Example 2 Table Example Number.-. l 2

l operamn-oleiin Ratio 1: Volume 6. 9 6. 4 H droflilioric Acid-Total fiydrocarbon Ratio 39 to l 190 to 1 V ume Titl ltflblb Acidity oi HydrofluOrio Acid,

Weight Per cent 89. 6 89. 3 Residence Time of Reactants in Reactor,

Seconds l 3 Mrs Velocity of Reactants in Reactor, Pounds r Square Foot per Second 79 m In at Temperature of Reactants, F 90 00 Outlet Temperature of ctauts, F 9i. 1 90. 2 Yield oi Total Alkylate on Basis of Butenes Consumed, Volume Per cent 179 184 Yield of Aviation Alkylate on Basis of Butenes Consumed, Volume Per cent 166 174 F-& Octane Number of Aviation Alkylatc:

Clear 1 90. 8 91. 2 F-i Octane Number of Aviation Alkylate S-l-cc. oi Tetraetbyl Lead per Gallon 2. (B 2. 71

lead r llon.

(T I 3 and F-4 octane numbers were determined by the standard Aviation Fuel Division motor methods.)

It will be seen from the above table that high yields of high octane number alkylate product are obtained by the process of the invention.

Having thus described my invention, it is to be understood that such description has been given by way of illustration and example only and not by way of limitation, reference being had for the latter purpose to the appended claims.

I claim:

1. In an alkylation process of the type wherein a liquid isoparaffin, a liquid olefin, and hydrofluoric acid catalyst are fed into the inlet of a single-pass reaction zone wherein substantially forward flow of reaction mixture is maintained, the reaction mixture including alkylate product,

'isoparaflin, hydrofluoric acid, and any unreacted olefin is withdrawn from the outlet of said reaction zone and sent to a separation zone for separation into a hydrocarbon 'phase and an acid phase, and the acid phase recycled to the inlet of said reaction zone for admixture with fresh isoparaflin and olefin, the improvement in controlling the temperature of the reaction mixture in the reaction zone which comprises regulating the volume of hydrofluoric acid fed to said reaction zone including that recycled from said separation zone to the volume of total hydrocarbons fed to said reaction zone such that the volume of hydrofluoric acid in said reaction zone is at least ten times as great as the total volume of hydrocarbons in said reaction zone and cooling by indirect heat exchange at least a portion of the hydrofluoric acid to a temperature such that the average temperature of the entire portion of hydrofluoricacid entering said reaction zone is sufliciently below the maximum temperature desired therein that substantially the entire heat of reaction will be taken up by the reaction mixture without raising the temperature thereof in excess of the predetermined maximum value desired. 2. In an alkylation process of the type wherein a liquid isoparaflin, a liquid olefin, and hydrofluoric acid catalyst are fed into the inlet of a single-pass reaction zone wherein substantially forward flow of reaction mixture is maintained, the reaction mixture including alkylate product, isoparaflin, hydrofluoric acid, and any unreacted olefin is withdrawn from the outlet of said reaction zone and sent to a separation zone for separation into ahydrocarbon phase and an acid phase, and the acid phase recycled to the inlet' of said reaction zone for admixture with fresh isoparaflin and olefin, the improvement in controlllng the'temperature of the reaction mixture in the reaction zone which comprises regulating the volume of hydrofluoric acid fed to said reaction zone including that recycled from said separation zone to the volume of-total hydrocarbons fed to said reaction zone such that the volume of hydrofluoric acid in said reaction zone is between ten and fifty times as great as the total volume of hydrocarbons in said reaction zone and cooling by indirect heat exchange at least a portion of the hydrofluoric acid to a temperature such that the average temperature of the entire portion of the hydrofluoric acid entering said reaction zone is sufllciently below the maximum temperature desired therein that substantially the entire heat of reaction will be taken up by the reaction mixture without raising the temperature thereof in excess of the predetermined maximum value desired.

3. In an alkylation process of the type wherein a liquid isopara'filn, a liquid olefln, and hydrofluoric acid catalyst are fed into the inlet of a. single-pass reaction zone wherein substantially forward fiow of reaction mixture is maintained, the reaction mixture including alkylate product, isoparamn, hydrofluoric acid, and any unreacted olefin is withdrawn from the outlet of said reaction zone and sent to a separation zone for separation into a hydrocarbon phase and an acid phase, and the acid phase recycled to the inlet of said reaction zone for admixture with fresh isoparafiin and olefin, the improvement in controlling the temperature of the reaction mixture in the reaction zone which comprises regulating the volume of hydrofluoric acid fed to said reaction zone including that recycled from said separation zone to the volume of total hydrocarbons fed to said reaction zone such that the volume of hydrofluoric acid in said reaction zone is between ten and fifty times as great as the total volume of hydrocarbons in said reaction zone and cooling by indirect heat exchange the entire portion of hydrofluoric acid entering said reaction zone to maintain the inlet and outlet temperatures of the reaction mixture at predetermined values.

4. In an alkylation process of the type wherein a liquid isoparaflin, a liquid olefin, and hydrofluoric acid catalyst are fed into the inlet of a single-pass reaction zone wherein substantially tion zone including that recycled from said separation zone to the volume of total hydrocarbons fed to said reaction zone such that the volume of hydrofluoric acid in said reaction zone is 200 times as great as the total volume of hydrocarbons in said reaction zone and cooling by indirect heat exchange the entire portion of hydrofluoric acid entering said reaction zone to maintain the inlet and outlet temperatures of the reaction mixture at predetermined values.

JOE E. PENICK.

(References 611 following page) REFERENCES CITED The following references are of record in' the file of this patent:

UNITED STATES PATENTS Number Name Date Gibson Apr. 25,- 1944 Frey Dec. 7, 1943 Grosse et al July 27, 1943 10 Grosse et al Dec. 30, 1941 Taylor et a1 Feb. 8, 1944 Bowles Nov. 23, 1943 Number Number OTHER REFERENCES Gerhold et al., Nat. Pet. News, Tech. Sec., March 1, 1944, pages R-146, R-148, R-150, R-151, R-154 and 55-155. Patent Offlce Library.