US2336005A - Motor fuel production - Google Patents

Description

Dec. 7, 1943. F. E. FREY MOTOR FUEL PRODUCTION Filed Marh 11, 1940 ATTORNEY Patented Dec. 7, 1943 UNITED STATE s ainrrEii'r orricE MOTOR FUEL PRODUCTION Frederick'n. Frey,

Delaware Bartlesville, Okla., assigner to Phillips Petroleum Company,

a corporation of Application Maren 11, im,v semina. ses-,in

(ci. 26o-683.4)

` 3 Claims. This invention relates to the production or manufacture of motor fuel from low boiling hygranted August 24, 1943, and Serial No. 315,063

iiled January 22, 1940, now Patent 2.322,800, granted June 29, 1943.A

Many processes have been proposed for converting normally gaseous hydrocarbons into hydrocarbons having higher molecular weights, such as motor fuels and lubricants. Some of these processes are dependent upon having olefin hydrocarbons present in large proportions in the charge stock, such as in well-known thermal and catalytic polymerization processes'for producing motor fuel from refinery gases containing unsaturated components from cracking stills. Still other processes are adapted to produce motor fuel from normally gaseous paralns, such as unitary` thermal conversion processes, or multistage processes employing a dehydrogenation step as a first part of the process, followed by a conversion of olens so produced. Still other processes have been proposed wherein a paraiiinic hydrocarbon stream and an oleiinic hydrocarbon stream are charged to a process, and the paramns and olens are caused to interreact, or as it is generally stated, the parans are alkylated by the oleiins to form paraftlns having higher molecular weights.

As disclosed in my abovementioned copendingl application Serial No. 315,063, now Patent No. 2,322,800, I have found that concentrated hydrofluoric acid will act as a catalyst to eiect a union of unsaturated hydrocarbons, such as olefins, with parafiins to form higher boiling par- 'atiin hydrocarbons. I have also found that concentrated hydrofluoric acid can be used as the sole alkylating catalyst, without the presence of such other materials as iinely divided metals, metal halides, and the like, and that it is preffraction in the presence of hydroiluoric. acid to f f charged to erable to use as a catalyst substantially anhydrous hydroiiuoric acid, or hydrogen iuoride.

` l'. have now found that when low boiling pari ains such as butane or pentane are reacted in the presence of concentrated hydro'uoric acid with certain higher boiling olens, especially those formed by the polymerization of simpler lower fboiling olei-lns, a parainic product results which, although higher boiling than the original paraiiin, is not necessarily higher-boiling than the like, solid high boiling olenn reacted, and in fact may at times be lower boiling than the olefin. Thus I have found that when between about 10 and presence of concentrated hydrofluoric acid with an olefin material such as triisobutyiene, boiling between about 345 and 355 F., a paraiiinic p'roduct results of which the predominant part boils between 200 and 240 F. and which appears to contain large portions of isomeric octanes. Similarly, isooctenes will react with such a butane produce a paraiiinic product containing large portions of isooctanes.

The process Aof one modification of the present invention involves a cooperation between a polymerization step, for the production of motor fuel range hydrocarbons by the polymerization of lighterl oleiins, and an alkylation step, for the production of motor fuel range hydrocarbons by the alkylation of lighter parafilns with oleiins which may be heavier land/or lighter than the final product. The polymerization step is preferably one carried out with the aid of a solid polymerization catalyst, such as silica-alumina or the phosphoric acid, acid copper phosphate, or the like; and the alkylation step is carried outl in the presence of concentrated hydroiluoric acid, using olenns which have been recovered #21pm-the eliiuent of the polymerization step. .It husasen found that the paramns the aikyiation step may be either isoparafns or normal paraillns, but preferably the parafiinic material should contain appreciable portions of isoparaiins such as isobutane (2- methyl propane) or isopentane (Z-methyl butano) or the like, and such may be separated from'the v forming propanev and isobutene, and hydrogenand methane are removed from the eiiiuent. A

fraction consisting of hydrocarbons having three and more carbon atoms per molecule and comprising predominantly propene,v isobutene and ,isobutane is passed at an elevated pressure over a solid polymerization catalyst under conditions such that essentially all of the isobutene is polymerlzed along with a substantial portion of the propene, forming polymers in the. gasoline boiling range. Under optimum conditions, consida butane fraction, boiling y 35 F., is reacted in the Atains higher boiling olenic polymers and some unreacted propone. In this particular case the material which is lower boiling than isobutane contains a large portion of propene and is readily separated from the polymerization eiliuent by fractional distillation in a depropanizer. Likewise, the higher boiling olenlc polymers are readily separated from the gasoline range polymers. Either, or both, of these olenic fractions constitute a valuable part of the charge to the alkylation step. In this particular instance the unreacted parafilns in the polymerization efuent are predominantly isobutane, and a portion of such a fraction may constitute the parainic portion of the hydrocarbon charge to the alkylation step. This fraction will contain a small amount of unreacted isobutene which will' also undergo a desirable reaction in tl'ze alkylation step. Isopentane may be blended with the isobutane fraction hargedto the alkylation step or may con.- stitute the entire isoparailinic portion of the charge, or isobutane from some other source may be charged to the alkylation step. Even when higher boiling oleilnic polymers are the sole olefinic charge to the alkylation, the alkylation products will be isoparains in the gasoline boiling range, since it appears that such high boiling polymers undergo concomitant scission reactions, substantially all of the fragments being oleflnic and taking part in the reaction, rather than that these higher boiling olefins join directly to the charged isoparafiin to form still higher boiling products. The gasoline boiling range isoparafilns have high antidetonating qualities land octane numbers, and the olefin polymers in the gasoline boiling range are also superior in these respects. These gasoline products may be used separately as motor fuels or blending stocks, the olen polymer may be hydrogenated before use; or these fractions may be blended together to form a premium motor fuel. In those cases where an oleflnic motor fuel is not undesirable, this latter procedure is especially effective, since the olens have blending octane numbers even higherthan their straight octane numbers in the pure state, and to blend them with isoparaillns gives a still more superior result. l

' While the catalystic polymerization produces a polymer which has a superior octane number, both as it is and after hydrogenation to form a paraillnic material, it fails to convert all of the oleflns charged and generally also produces a certain amount of polymer which may be undesirably heavy. Although catalytic alkylation of hydrocarbon material to` give a product inthe same boiling range produces a paraiilnic product directly which also hasl a superior octane number, the octane number will generally not be quite as high as that of the former lproduct resulting from polymerization.

The cooperative combination of the present invention not only gives a total product with a high' octane number, but also depletes the olen content of the hydrocarbon stream produced by dehydrogenation and'charged to the alkylation step, and thus aids in producing a desirable alkymer byraising the ratio of parailin to olen in this stream and facilitates control of this reaction. Thus, the combination gives a total product having an octane number higher than could vbe produced by alkylation alone, andalso results in a better utilization of olefin hydrocarin the gasoline range than would result from catalytic polymerization alone.

more dilute concentrations may be used, I prefer to use it in concentrations greater than per cent by weight, the othermaterial being water, and I have found that substantially per cent hydroiluoric acid, that is, substantially or completely anhydrous hydrofluoric aoid, or hydrogen fluoride, is very effective, and is particularly adapted to the process arrangements to be hereinafter described more fully.. As will be discussed, the process is generally carried out with the hydrocarbon material substantially in liquid phase; eiilcient reaction -results when suillcient hydroiluoric acid is employed to result in a substantial saturation of the liquid hydrocarbon material with hydrogen fluoride, and preferably sufiicient hydrogen iiuoride is used to form a separate liquidv phase which may be maintained emulsifledor intimately mixed with the hydrocarbon while reaction takes place. In most cases the hydrouoric acid charge should be at least 10 per cent o'f the-total charge, on a liquid volume basis, and hardly ever need exceed 50 or 60 per cent, though more can, at times, be used. In the concentratecll form, hydrofiuoric acid is substantially inert, or non-corrosive, toward numerous metals; such as copper, nickel, most steels, and various other alloys which can be used in the constructionof plant equipment.' Occasionalv fortuitous jfreactions may produce minor amounts of-` inorganic fiuorides but, as previously discussed, insofarffas this invention is concerned hydroiluoric acid is considered to be used in the substantial Aabsence of added metals or metal halides. The .reaction temperature may be varied over a widerange forany particular re action mixture,butappears to be most -dependent upon the paraflln hydrocarbon participtating in the reaction. Thus, in general, I may carry out an alkylation process at temperatures between about 0 and 300 or 400 F. For readily reacted parailin hydrocarbons, such as isobutane or isopentane,I may readily effect an alkylation at a temperature between about 35 and 100 F., while for less reactive paramns, such as normal parailins, higher` temperatures of the order of to 300 or 500 F. are necessary or more desirable.' Theuse-of hydrofiuoric acid has a distinct advantagein such cases, in that it can be used under these more extreme' conditions without promoting or entering into extensive undesirable side reactions.

As just''men'tioned, higher temperaturesl are necessaryifrigthe alkylation of normal paramns, and they .nittyl be caused to react with ole'ns in the presence. of' concentrated hydroiiuoric acid at temperatures above about 10o to 120 v ,.pref.,

erably withinathe range of 150 to 300 F., but in ried out lunder only slight superatmospheric presf sures, itis preferable to operate under substantial superatmospheric pressures, such as about I g n ',100 toi,000or2,000poundspersquareinehor more. The process is preferably conducted with at least an appreciable portion of the reactant material in liquid phase, although this is not necessary for all reactants.- When the process is conducted with a substantial portion 4of the vreactants in liquid phase, the reaction temperature should not be above the critical temperature of the highest boiling reactant, and the pressure should be at least no less than the vapor pressure ofthis reactant, and preferably should be at least 500 pounds per square inch. Since the alkylation temperatures, even in the -upper part of the range indicated, are still rather'modcrate, the pressures ordinarily need not be excessively above the vapor pressure of the reacting mixture and can, of course, be as low ascan be shown by trial to permit effective alkylation. In many instances normal paraflins can be alkylated in the presence of hydroiiuorlc acid at pressures between 50 and 500 pounds per square inch. With some of the lower boiling and less reactive f of the parailins, it may be desirable to conduct the alkvlation at a temperature in the upper part of the range indicated and such that the reactants are predominantly in gaseous phase, even under substantial elevated pressures.'

It is an object of my invention to react normally liquid unsaturated hydrocarbons with low boiling paraiin hydrocarbons to form paraffin hydrocarbons in the'motor fuel boiling range.

Another object of my invention is to react polymeric oleflns with low boiling paraflns in the presence of' concentrated hydroiluoric acid to form paraffin hydrocarbons boiling in the motor fuel range.

A further object of my invention is -to provide a process for the production of hydrocarbons boiling in the motorfuel range from low boiling hydrocarbonsby a combination of an olen polymerization step and an olefin-paraffin alkylation step conducted in the presence of concentratedA hydrouoric acid.

A still further object of this invention is to react polymeric olens boiling in or above the motor fuel range with low boiling parafiins, especially low boiling isoparains, in the presence of concentrated or anhydrous hydrouoric acid to form parafiin hydrocarbonsboiling near or below such as a butane fraction of natural gas containing a high concentration of isobutane, enters the system through pipe I and valve- I I and is passed by pump I2 through the coil I3 in the dehydrogenating furnace I4. In many cases where such a hydrocarbon stream comes directly vfrom a fractional distillation process or from some other separation step it may be under a pressure suiliciently high' to obviate the necessity of the pump I2 and in such a case, of course, the pump may be omitted. The dehydrogenation which takes place in the unit represented by the coil I3 and the furnace I4 may be any type of dehydrogenati'on process known to the artand may* be either thermal or catalytic or a combination of both. The pressure will generally not be in excess of about 200 pounds per square inch,, and prefer-l gen and any ught nvamcarbons formed in che dehydrogenation are removed from the system through pipe 23V and valve 2l; and any heavy' hydrocarbons, tar and/or carbon may be removed from the system through pipe 25 and lvalve 26. This separation may be aided by the use of cooled, unreacted hydrocarbons, (which may be flashed to provide direct vaporization and refrigeration as has been more fully described by Hays et at. in their copending application 'Serial No. 336,250, filed May 20, 1940), introduced through pipe 19 and expansion valve 80. A hydrocarbon stream, -comprising unreacted paraiiins and oleiins produced by the dehydrogenation, passes from the separating means 20 through pipe 21 and valve 28, and is passed at a suitable` polymerization pressure, preferably between 200 and 2000 -pounds per square inch, by

`pump 29 through pipe 30, heater 3I and pipe 32 to the polymerization unit 33. Normally gaseous unsaturated hydrocarbons, such' as propylene and/or butenes as may be recovered from an oil cracking process, may be introduced through pipe 34 and valve 35, and such a stream may constitute the only hydrocarbon material charged to this part of the process. In such a case the dehydrogenation part of the system just described may not be used, or may be used only to dehydrogenate parain hydrocarbons in the stream .entering through pipe 34 `which pass through the polymerization system and are ultimatelypassed. through pipe 63 to the pipe I0. The polymerization carried out Vin unit 33 will preferably be a catalytic polymerization rather than a thermal one and may be carried out with any known polymerization catalyst which promotes-the formation of simple, low boiling polymers from light clef-ins such as propylene and/or butylenes. Such' catalysts may be silica-alumina, solid phosphoric acid, diluted aqueous solutions of liquid acids such as sulfuric acid, or the like. If the hydrocarbon stream charged to this polymerization step contains two or more species of olens such as the mixture of propylene and isobutene which results from the thermal dehydrogenation of isobutane, the unit may be so operated as to secure interpolymerization of these oleflns, one such method being described in Freys copending application Serial No. 294,377, i'lled September 11, 1939.

The polymerization eilluent passes through pipe 31 and `valve 38 to separating means represented' by the fractionating column 40, supplied with la heating coil 4I at the bottom and a cooling coil 42 at the top. The entire polymer fraction, comprising olen polymers boiling in the motor fuel range and also higher boiling polymers, passes from the bottom of means 40 through pipe 43 and valve 44 to fractionating column 45, wherein a separation is made bef tween light polymers suitable for motor fuel or as a motor fuel blending stock wh'ich is removed from the system` through pipe I6 andv valve 41, and heavier polymers which may be removed through pipe 48 and valve 49. Extremely heavy .polymers or tar and the'like may bev removed 4- assapou from the system through'pipe 50 and valve 5|. Separation and fractionation -in the column 45 is aided by heating coil 52 in the bottom and cooling coil 52 in the top.

Light hydrocarbons which havev passed through the polymerization step unailected, including paraflinhydrocarbons along with unreacted oleiins, pass from the means 40 throughrplpe 55 and valve 58 to the Iractionator 60, wherein a separation is made between unreacted hydrocarbons and heavier unreacted hydrocarbons, the separation being aided by a heating means Bifand cooling means 82. Heavier unreacted hydrocarbons, which will be substantially entirely paraiilns, pass from the bottom oi fractionator 60 through pipe 0 3 controlled by a valve 84, andv may be passed through valve 05 to pipe i0 and the dehydrogenation step, or any part or all of this stream may be withdrawn from the system through pipe 66 and valve 81. A stream of light unreacted hydrocarbons, which will contain the majority of the unreacted oleilns, is removed from the top of fractionator 60 through pipe 10, and part vor all of the stream may be removed through valve 1| when it is not possible or desirable to take care of this stream by the methods to be hereinafter described, or when the content of parafiins is sufhciently high to warrant a discard of a part of this stream or to warrant a separation of paraillns from oleins` in apparatus not shown, .with subsequent reintroduction tothe process of either one or both of these fractions as will be readily appreciated. A portion of the oleiin-containing stream passing through pipe may be diverted through pipe 12 and valve 13 `and returned t0 the polymerization stepby pump 14.` This may be done by addition of this str eam through pipe 15, and valve 16 directly to pipe.r30, or by passing a part or all of the stream through pipe 11, cooler 18, pipe 19 and valve 80 as a refrigerat- 'aues or in the motor mei range.

When the polymerization is so conducted that substantially all'the light oleilns charged are polymerized, the only olens unsuitable for motor fuel will have high molecular weights,l but generally, the polymerization conditions will not be so drastic'and both light and heavy olens can be sent to the alkylaton step and reacted there,

. and a'process involving this modification is also a part of my invention.

Heavy oleiins are passed from pipe 48 through pump |08, pipe |'0| and valve |02 to the alkylation process,- and light olens are passed ing agent to the top of the*fractionato'r4 20, as

previously mentioned. Alternatively, or concomitantly, a portion of the streampassing through pipe 10 may be passed through-pipe 85 and valve 06 to the hydrofluoric acid alkylation step to be more fully hereinafter discussedy.. When the dominantly paraffin hydrocarbons such as bu- :l

tanes, while the stream passinglirom this fractionator through pipe 10 will coritainfthe major part of the unpolymerized "olens, Ymainly propene, at least a part, of wlriiclrcan conveniently be recycled to the polymerization] step. If the polymerization step has beenso conducted that practically all of the olefin material charged has undergone polymerization, the stream passing through pipe may be passedVv directly to pipe 63 through pipe 58 and valve v58, with suitable control of valves 56 and 84. g Y

As has been previously discussedpit is an object of this invention to react olens, which are present in the polymerization eiiluent and which are unsuitable' by reason of their boiling range or molecular weight for direct inclusion in motor fuel, with low boiling paramns and especially low -boiling isoparafilns in the presence ofl a concencharge to the polymerizationgstcpcontains apfrom pipe through pump |03, pipe |04 and valve |05 to thejalkylation process. A suitable hydrocarbon stream, such as one consisting of or comprising large quantities ci isoparailins such as isobutane and/or pentane is passed through pump |01 and pipe |08 to the alkylation process. The paratln hydrocarbons in the etlluent of. the polymerization step may comprise 'or consist of a portion of the stream passing through pipe 53, which is passed through pipe ||0 and valve to pump |01. II such is not the case, or if additional paraffin charge is needed, paramns may be introduced through pipe H2 and valve ||2 into pipe ||0. Light olens separated from the stream discharged through valve 1I and in. a more concentrated form may also be introduced through pipe ||2, or through pipe 81 and valve 88 into pipe 85. Polymeric olens from some suitable outside source may also be introduced'to the process through pipe 81 or ||2, and may at times constitute the sole olen charge to the process.

Hydroiluoric acid is charged to the process through pipe'ii5, valve lli, pump ||1 and pipe ||8, which in this case leads into pipe |08. .As

one method of performing the alkylation, the' paranlns, olensand hydrofluoric acid may be rapidly and intimately mixed 'at the juncture of pipes |08 and ||8, and the mixture is rapidly passed through the tube coil |20 in the reactorheat-exchanger |2|. Since the'alkylation reaction is exothermic, it is preferable that this initial part of the reaction should be carried out withv a removal of heat suicient to maintain a desired operating temperature. A tube coil of a type similar to that usedv in tube stills eiects' a turbulent mixing of the material passing through it, and thus contributes to the emciency of the alkylation reaction. This reaction may be continued and completed in an enlarged chamber |22, which may be insulated and which affords an extended reaction time` to the mixture with-- out much mixing or turbulence. It may at times be desirable to have a part or all or the light olen's enter the alkylation system at some intermediate point or points, and in such an event this may be accomplished bypassing any desired portion of the stream from pipe |00 through one or more pipes illustrated by pipe IIS, controlled by a value |28, to one or more intermediate 'points of the coil |20, with suitable control of The hydrocarbon material, containing the hydrocarbons is removed from the top of the separator |24, either as a liquid or as a vapor,

through pipe |30 and valve |3|. It will gener- 'I ally be desirable to eiect an intimate contact of this hydrocarbon material with`- an acidneutralizingl agent such as sodiuml hydroxide or carbonate or the like, and such material as an aqueous solution or a slurry in some hydrocarbon-miscible material can be introduced through pipe |32 'and valve |33 and the combined mixture passed to separator |34. Any excess neutralizing agent and products of the neutralization are removed, as through pipe |35 and valve |33, while hydrocarbon material is passed through pipe |31, valve` I 38, and through pump |36 to hydrocarbon separating. means illustrated by the fractionator |40 which is equipped with a heating coil |4| at the bottom and a cooling coil |42 at the top. A hydrocarbon fraction comprising a large proportion of hydrocarbons lin the motor fuel boiling range produced by the alkylation, or in other words the alkymer fraction, is removed from a low point of the fractionator |40 through pipe'l43 and valve |44, and may be used directly as a premium motor fuel; or it may be used as a blending stock, or maybe subjected to further' fractionation to recover certain narrow boiling fractions of simple composition comprising certain highly desirable individual hydrocarbons. Heavier hydrocarbons are removed from a lower point of the fractionator through pipe |45 and may be discharged from the system through valve |46. This fraction may at times contain an appreciablev proportion of higher boiling olefin polymers, suitable for reaction in the alkylation step. In such cases, a portion of the stream may be passed from pipe |45 through pipe |41 and valve |48 to pipe 48, where it is mixed with the heavy polymer passing from the polymerization step to the alkylation step.

A hydrocarbon steam lighter than the alkymer, and comprising low-boiling unreacted paramns, is removed from an upper part of the fractionator |40 through pipe |50, and may be passed through valve |I, pump |52 and pipe |53 to pipe v H0 for further passage through the alkylation stem. A portion or all of this stream may be passed to the dehydrogenation step by being passed from pipe |50 through pipe |55 and valve i56 to pipe i0. If desired, this stream may be discharged from the system throughv pipe |51 land valve |58. Any light hydrocarbons which it may be passed from this pipe through pipe 90 and valve to pipe |50 and is passed by pump |52 to the alkylation step.

` When isopentane is a. part of the'hydrocarbon material charged to the alkylation step and is present in excess so that an appreciable portion passes through this step unreacted, a part or all of this unreacted isopentane may be retained lin the'fallqrmer fraction removed through pipe |43, and at times a part may also be recycledto this step through pipe |50,pump |52 and pipe |63 and H0, as is readily understood. `:isopentane -asaaoos V 5 produca or the alkylation along with unreacted in itself is va valuable ingredient of premiiimfnoto: fuels. m 'introduction 'to une Aaumenta step thus producesa'fuel'having a desirably wide boiling range. and` having a good volatility. A combination motor fuel having a bightantiknock rating may be formed by blending thematerial produced in the polymerization step witlrthe fuel discharged from the alkylation step. This may I be accomplished by passing all or any part ofthe fuel flowing through pipe-46, through pipe |65 and valve |66, and mixing it with a stream withdrawn from pipe I43'through pipe |61 and valve |68, with suitable control of valves 41 and |44. Both these streams comprise motor fuel hydrocarbons `having high antiknock qualities, and since one, the alkyner, is paraiilnic and the other. the polymer, is olenic, the resultant blend will be quite high as to antiknock value or octane number, since the blending octane number of the oleiinic component when blended with a parailinic stock, is not infrequently much higher than the octane number of the olenic component by itself.

' Example I sure of about 1500 pounds per square inch and` at a temperature of about 350 F. The silicaalumina catalyst was prepared by treating a hydrous silicagel with an aluminum sulfate solution, whereby alumina was adsorbed, and

washing and drying the resultant material, as described in U. S. Patent 2,142,324. vThe reaction time of the polymerization was such that about percent of the olens in the charge were polymerized, forming an olenic polymer of which over 80 percent boiled below 360 F.

From this olenic polymer a fraction `was separated, by fractional distillation, which -boiled between 345 and 355 F., and which consisted essentially of dodecenes. of a liquid butane fraction from natural gas, containing a predominant portion of isobutane, were mixed with about one volume of substantially anhydrous liquid hydrouoric acid and tothe mixture was added about 0.76 volume of the above described polymer fraction. The mixture was vigorously agitated and maintained under a pressure between 45 and 55 pounds per square inch gauge. and the olefin fraction was added during.

Boiling` A Refrac- Weight Per pproximate Denrange, tive index per cent cent F. @mma mty at 68 F. of total unsat.

Sis-167-.- 1. 3689 4. 2 o. oo 167-203.. 1. 3841 5. 8 0. 10 203-257- 1. 3951 61. 6 0. 05 257-306.. CnHzo.. O. 7183 1. 4065 5. 8 0. 05 306-365-- CIDH and Cul-124- 0. 7445 1. 4219 12. 7 0. 36 365..- CNH and heavier 0. 7670 l. 4312 9. 9 0. 60

About three volumes It is of considerable interest to note that the predominant fraction of the total product was a mixture of octanes, formed by the general reaction clearly understood at this time, but which also appear to produce paraillnic products. Well over 90 percent of the total product was in the present day gasoline boiling range, and possessed good motor fuel properties.

Example II As an example of the operation of another modification of my invention, 'a hydrocarbon stream containing about 95 percent isobutane was thermally dehydrogenated by being passed through a tube coil maintained at a temperature between 1100 and 1220 F., and under an inlet pressure of about 150 pounds per square inch gage, for a period of time sulcient to produce an eiiluent stream containing about 20 mol percent of gaseous oleilns which were about half isobutene and half lighter oleilns predominantly propene.- All but a negligible fraction of the material lower boiling than propene was `removed Ffrom this dehydrogenation eiiiuent, a portion of unreacted propene was added as a recycle stock,

andthe mixture was passed under a pressure of about 1410 pounds per square inch over a granular silica-alumina catalyst at a temperature between 300 and 475 F. for a period sufficient to convert over 90 percent of the isobutene in the charge to polymers; about 50 percent of the total propene in the charge also entered into the reaction producing some interpolymers such as isoheptenes with the isobutene. The normally liquid hydrocarbons, that is, the polymer fraction, were readily separated from the butanes and lighter portion of the effluent.v About one-third of this polymer had more than eight carbon atoms per molecule, and about one-eighthof it was too heavy to be included in a motor fuel having 'an end-point of 400 F. The normally gaseous fraction separated from the polymers consisted of Cz and C4 hydrocarbons, which were readily separated by fractionation into a saturated part containing` about 2 percent olefins and over 95 Apercent isobutane, and an unsaturated partcontaning about 40 p ercent propene. A portion of this latter fraction was returned to the polymerization step as recycle stock.

The polymer material was separated by fractionation into two parts, one boiling below about 360 F.A constituting about 82 percent of the total polymer. 'I'his material, after being saturated by non-destructive hydrogenation, is a premium blending stock for aviation fuel, having an octane number of about 91 and a high response tothe addition of an antiknock agent such as tetraethyl lead. The second portion contained the Ahigher boiling polymers and, although a substantial portion would have been included in a gasoline having a higher endpoint, such as about 400 F., such a fraction is considered as a higher-boiling polymer fraction for the purpose o`f thi speciilcation.

This liquid higher-boiling polymer lfraction is blended with approximately an equal liquid volume of the light unsaturated, unreacted hydrocarbons mentioned above, and the combined stream is mixed with about 4 liquid volumes of the above mentioned isobutene fraction. 'I'he combined hydrocarbon stream, as a liquid, is continuously and intimately mixed with concentrat- ,ed hydroiiuoric vacid of a strength greater than percent in a ratio of about 2:1 and is passed through a tube coil at a velocity sufficient to insure turbulent flow. The tube coil is immersed in a bath to regulate the temperature and keep it below F., and is of sulcient length that the reaction time is about 40 minutes. The eiiiuent is passed as a liquid to a separator, wherein a separation takes place between the heavier liquid hydroiiuoric acid and the hydrocarbon material. The hydroiluoric acid is removed and returned to the inlet of the tube coil. The hydrocarbon fraction is neutralized by being passed over soda ash, and from ita liquidy product is separated, boilingbelow 400 F. andf'constituting about 95 percent of the total normally liquid product. It is over 98 percent saturated, contains a large proportion of isoparafilns, has an initial octane number ofnearly 90 and has an excellent response to the addition of tetraethyl lead.

As previously mentioned the dehydrogenation step should be conducted at a pressure below about 200 pounds per square inch and "may be either thermal or catalytic or a combination of both. Thermal dehydrogenation is preferably carried out between about 1000 and 1250 F., and catalytic dehydrogenation may be carried out between about 850 and 1100 F. In a combination of both, the thermal dehydrogenation should precede the catalytic. It has been found that the most desirable catalysts comprise orl consist of chromium oxide, preferably the black, unglowed variety. Suitable modications are disclosed in U. S. Patents 1,905,383 and 2,098,959, and in the copending applications, Serial Numbers 113,091 of Morey, (now Patent 2,2t8,320, granted June 30, 19.42) 173,708 of Matuszak et al., (now Patent 2,294,414, granted September 1, 1942) 173,709 of Morey et al., (now Patent 2,312,572, granted March 2, 1943) and 263,000 of Schulze (now Patent 2,291,581, granted July 28, 1942) The polymerization step, while it may be thermal or catalytic, is preferably a-catalytic one carried out in the presence of solid granular catalysts. A preferred catalyst is a silica-alumina catalyst, such as described in U. S. Patent 2,142,324 or 2,147,985; or a catalyst of somewhat similar properties may be prepared by intimately mixing anacidic hydrous silica jelly and hydrous alumina jelly, preferably with the latter being present only to an extent of about 1 to 5' percent by weight,'and subsequently drying and granulating the resultant material. As mentioned, other solid catalysts may be used. The pressure will generally be at least 200 pounds per square inch and need not be in excess of ,about` 2000 pounds per square inch. Pressures sufilcient to am a coinventor.

insure a substantially liquid phase operation are the most desirable, as brought out in the copending application, Serial No. 747,964, now Pat necessary to give a more or less constant or steady polymerization of the oleiins.

Many modications and variations of this invention may obviously be used, and can be adapted by one skilled in the art without departing from the spirit of the disclosure. The restriction used in the examples, and in connection with the drawing, need not necessarily be-used as limi its for all particular operations or sets of conditions, since they are presented primarily as illustrative examples. It will be understood that the ilow diagrams presented and described as a part of the disclosure are schematic only, and that many additional conventional pieces of equipment, such as pressure gauges, valves, pumps, heat exchangers, reflux lines and accumulators, heaters and coolers, and the like,.wi1l be necessary for any particular installation, and can be supplied to meet the requirements of any particular case by anyone skilled in the art. The essential equipment and conditions have been described and the modiilcations discussed in sufli Icient detail to serve as efllcient guides..

I claim:

1. A process for the production of premium aliphatic hydrocarbons boiling in the motor fuel range from isobutane, which comprises dehydrogenating isobutane to produce isobutene and a moving same from the process as a product thereof, separating also a fraction comprising higher boiling polymers, a fraction comprising unreacted isobutane, and a fraction comprising unreacted propene, passing through an elongated reaction zone a stream comprising an intimate liquid mixture ofl concentrated hydrouoric acid and said isobutene fraction and said heavy polymer fraction, removing heat from said mixture in said zone during a reaction period to maintain an alkylation temperature, adding at a plurality of points along the length of said reaction zone said propene fraction to supply additional olen reactant to said zone and in amounts such as -to maintain a relatively low olen concentration, and recovering from an effluent of said zone a hydrocarbon fraction contalning-paraillns boiling in the motor fuel range so produced.

2. A process for alkylating a low-boiling isoparafiln hydrocarbon of four to ve carbon atoms per molecule to produce isoparaffinsboiling in the motor fuel range, which comprises passing a stream comprising an intimate, liquid admixture of such an isoparafiin, concentrated hydroiluoric acid and oleiin polymers boiling above the motor fuel range through an elongated reaction zone under alkylating conditions to produce isoparaffins in the motor fuel range, adding at a plurality of points subsequent to the inlet of and along the length of said reaction zone a normally gaseous oleiln of at least three carbon atoms per molecule to supply additional olefin reactant to said zone and in amounts such as to maintain a relatively low oleiin concentration in said reaction zone, and recovering from an efuent of said reaction zone a hydrocarbon fraction containing isoparaffins boiling in the motor fuel range so produced.

3. A process for reacting a low-boiling isoparthe inlet of and along the length of said reaction zonea normally gaseous oleiln to supply additional olefin reactant to said zone and in amoimts such asto maintain a relatively low oleiln concentration in said reaction zone. and recovering from an eilluent of said zone a hydrocarbon fraction containing isoparafllns boiling in the motor fuel range so produced.

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