US2309986A - Motor fuel and preparation thereof - Google Patents

Description

Feb. 2, 1943. n.15. RUTHRUFF MOTOR FUEL .AND PREPARATION THEREOF Filed Nov. 15, 1959 :lll

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Patented Feb. 1943 )UNITED STATES Pliilfzly'r.l ori-Ica zoasss f tMoron FUEL, AND PBEPABATIQN 'rnEREoF Robert F. Ruthruii', Chicago, Ill. Application November-15, 1939, serial No. 304,600

4 claims. (ci. ies-1o) This invention relates to motor fue1 and the preparation thereof. More particularly, this invention relates to motor fuel of high octane number and controllable volatility and` the preparation thereof. Y

During the last few years the steady improvement in motor fuel quality as regards octane number, volatility and other characteristics is too well known to those skilled in the art to merit further discussion. While the possible limits to such improvements have not as yet been approached in all probability, nevertheless, in certain directions, additional improvements are .becoming increasingly diillcult to achieve and all the#l resources of petroleum technology must be applied to the problem. This is particularly true in the case of high octane motor fuels for aviation use.

In the past. high octane number motor fuels for aviation use have been prepared by the catalytic polymerization of olennes containing four carbon atoms to the molecule followed by hydrogenation of the polymer formed. Such olefines may be obtained, in admixture with the analogous paraiiins, from the gases produced during the cracking of various petroleum fractionsor by the catalytic dehydrogenation or the thermal pyroll ysis of the butane cut from natural gas. These olefines consist of isobutene and the normal butenes. 'When such a mixture is passed over a suitable catalyst under suitable conditions as regards to temperature, pressure and time of contact, polymerization occurs. In this reaction the isobutene reacts very rapidly while the normal butenes react at a much slower rate. By the' proper selection of operating conditions it is pos-:'-

sible to attain almost quantitative conversions of isobutene to polymer with conversions of normal butenes'varying from' practically zero to practically 100%. The polymer l,produced consists largelylof isomeric octenes and hasan octane number of 80 to 82. While an excellent motor fuel for automobile engines, this material is totally unsuited for aviation uses becauseof its high unsaturate content, low octane number and low lead response. By catalytic hydrogenatlon the polymer may be converted to isooctanes having an octane number of 90 to 98. The hydrogenated material is completely saturated and exhibits an excellent lead response. 'Ihe octane number of the hydrogenated product is largely a function of the amount of normal butenes reactingfl When the ratio of reacting isobutene to reacting normal butenes is -high the octane number of the resulting hydrogenated polymer is high and vice versa.

While hydrogenated catalytic polymer shows considerable promise as a high octane number aviation fuel and has been much used for the purpose, yet the material and the process for of butenes.

preparing the same xhibit n'umerousdisadvantages. t ,For example, the hydrogenated catalytic polymer is not sufiiciently volatile for aviation requirements, the unhyd'rogenated'polymer obviously suffering from the same disadvantage. If an attempt is made to increase volatility by the addition of light naphthas the octane number of the blend is considerably, lower than that shown by the straight hydrogenated polymer. Furthermore, the possible yield of hydrogenated polymer is quite low. It is obvious that the yield can` be no higher than the olenes present in the charge and actually, if a high octane product is desired, is usually much less. If a high octane hydrogenated catalytic polymer is to be made it is well to react not more than one mole of normal butenes per mole of isobutene present. Howfuric acid at room temperature or below. Under these conditions, parailins containing a tertiary carbon atom are alkylated by olenes, and when the hydrocarbons concerned contain four carbon atoms, isomeric octanes form.v It will be noted that in this process, in contrast to that previously described, no hydrogenation step is required.

Obviously, the alkylate does not exhibit the nec-A essary volatility for use alone as an aviation fuel and -on fortification with light naphtha the octane number -of the blend is considerably lower than that of the straight alkylate, Also, in alkyl'ation, the yield is a function of th isobutane content of the feed.

As has been mentioned previously, the isobutane-normal butane ratio in natural gas is much.

less than unity so that on catalytic dehydrogenatlon or thermal pyrolysis of such a cut under commercial conditions, the isobutane content of the resulting gas mixture is less than the content Also, the isobutane content of uthe gas mixture of four carbon atoms obtained in the cracking 'of petroleum fractions is less than the content of butenes. Accordingly, an excess of butenes remains after reaction is complete. This tion. Since isopentane is the 'only low boiling ation fuels meeting current specifications cannot be prepared in this way. If the blend meets the As those skilled in the artare aware, avi- 10% oi specification, the 50% oif specication is a not satisfied. Likewise if the blend has the proper amount of isopentane to satisfy the 50% off specification, the minimum permissible temperature for 10% olf is far exceeded. To correct for these deficiencies, light naphtha has been added to the isopentane-isaoctane blend. When this is done the octane number is very much below that'shown by the .straight isooctane. recently, dimethyl butane (2,2) has been suggested as a blending agent for isooctane, with or without isopentane. While the use of this compound asa blending agent results in considerable improvement the fact remains that this hexane is very diflicult to obtain. 'At present this material is made by the thermal alkylation of isobutane with ethenel at extremely high pressures. To reduce ethene polymerization, the concentration of this olene must be keptat an extremely low level. 'Ihis means that the yield per'pass of the desired compound isvery low, which in turn necessitates an extremely high recycle ratio and the rseparation of the small vamount of the isomeric hexane from a large amount of unreacted material.

One object of this invention is to provide .anl

improved motor fuel and a process for producing the same. A further object f this invention is t provide an improved motor fuel of high octane number and a process for producing the same.'

An additional object of this invention is to provide an improved motor fuel of controlled volatilty and a process for producing the same. An-

Very

the like, a large part of the hydrocarbon fraction, charged is converted into gaseous products and.

these consist almost exclusively of isobutaner* To this process the term destructive isomerization is applied. Isomerization is used to designate reactions wherein a compound is4 converted into a second compound having the same chemical composition and molecular weight but different structure than that of the first. The classical synthesis of urea from ammonium cyanate and the conversion of normal butane to isobutane are examples of isomerization. In the presentinstance however, in addition to forming a compound of different structure than that of the charge, the new compound also has a different molecular weight. In the example cited, a conb siderable amount of the heavy naphtha charge,

having an average molecular weight of say 142, is converted into 'isobutane having a molecular weight of 58. In other words, in this reaction, the" charge was rst decomposed'and the resulting fragments were then isomerized-hence the term destructive isomerization.

It might be argued that the above reaction was entirely one of destruction without any isomerization. For example, it might be argued with no little merit that the isobutane resulted from the preferential decomposition of Z-methyl paraillns 'between carbon atoms 3 and 4. In'this way isobutane could lbe formed without any-isomerization. A mass of experimental data shows that this stand is not tenable.. For example, in the example cited, Mt. Pleasant heavy naphtha was used as charge. As is well known to those in the art, this material consists largely of straight chain parains. In addition, this stock was heavily acid treated before use so as to remove aromatics and similar compounds, so asA charged it consisted essentially of a mixture of straight chain paraiiins.

Supplementary experiments have also conrmed the fact that straight chain paraiilns are' destructively isomerized with the production o! parain, for example, isobutane, at least part of which was obtained by the destructive isomerization of a hydrocarbon fraction. The resulting alkylate is blended with a light naphtha of high volatility and high isoparaflin content, and hence high octane number, at least part of which was also obtained by the destructive isomerization of a hydrgcarbo'n fraction. The blend produces a motor fuel of high octane number and of controllable volatility. In the production of this ma-',

terial, the processes of alkylation and destructive isomerization cooperate to produce an unexpected and new result as will become manifest from the following description. A

For a description of the process of destructive isomerization reference may :be made to my ing from above isobutane up to the initial of the.

isobutane. For example, a heavily acid treated Mt. Pleasant heavy naphtha was exhaustivelytreated with chlorosulfonic acid. This last named reagent removes hydrocarbons having tertiary carbon atoms. Upon subjecting the thus treated material to destructive isomerization as before, large amountsrof isobutane formed. Furthermore, synthetic normal heptane and'synthetic normal heptane after exhaustive treatment with chlorosulfonic acid as previously described, when subjected to destructive isomerization gave isobutane in greater yields and with greater ease than the Mt. Pleasant heavy naphtha.

A further study of the products of destructive isomerization has revealed a most important but hitherto unnoticed fact. products obtained by the destructive isomerization of a heavy naphtha for example, one cut may be obtained representing the isobutane produced and a second containing a material boiling from above isobutane up to the endpoint of the heavy naphtha charge. The octane number of this second cut has been 4found to be materially higher than that of the heavy naphtha charge.

As is well known to those skilled in the art, octane number increases as volatility increases. To evaluate the effect of volatility on the octane number increase observed, this second cut` was again distilled, taking overhead a fraction boilnaphtha charge and leaving as bottoms a material having approximately the same boiling range as the heavy naphtha charge. 0n deter On fractionating the aaoaaeev mining the octane numbers of the two fractions.

thus made it was' found that the bottoms had an octane number not greatly different than that of the original heavy naphtha charge, while the light naphthaoverhead had an extremely high octane number; It is apparent that the reaction is predominantly one of destructive isomerizaa l tion only, any partsv of the original charge esisomerization of hydrocarbon fractions consisted largely. ofv isoparaiiins, these accounting for the unusually high octane numbers observed.

To summarize, in the destructive isomerizat'ion of heavy naphtha the following major products are obtained:

A. Isobutane.

B. Light naphtha of vvery high octane number and consisting largely of isoparaiilns. A

C.- Heavy naphtha of the same boiling range and approximately the same octane number as' the char e.

D. Ma erial having a higher boiling point than that of the charge. l

It will be evident to those skilled in the art that the process of destructive isomerization differs materially from both thermal reforming and catalytic reforming. In thermal reforming, the gas formed contains all gaseous parailins and oleiines together with hydrogen. In destructive isomerization the gas consists essentially of isobutane. In thermal reforming, theiight naphtha tha obtained in destructive isomerization operations is completely saturated or nearly s'o. The

' produced is highly unsaturated. The light naph Y product from thermal reforming having the same boiling range as that of the charge is highly olenic and has a much higher octane number than that of the charge. The same fraction from destructive isomerization contains no olenes or practically none and has an octane number diifering little from that of the orig-1 inal charge. In catalytic reforming, the gas produced consists largely of hydrogen, very little light naphtha is produced and the material having the same boiling range as that of the charge consists largely of aromatic hydrocarbons.

For a more complete understanding of the alkylation reaction reference mayv be made to.

British Patents t'rl9,345, accepted January 3l, 1938, and 479,827, accepted February l1, 1938.

increased two or more fold were sufficient v butane available.v

The excellent cooperation between destructive isomerization and alkylation for the manufacture of high octane motor fuels. particularly high octane number motor fuels for aviation use should now be evident. For maximum production of alkylate, additional isobutane over that found in the usual refinery is required. Destructive isomerization supplies this isobutane. To confer the proper volatility on the alkylate without at the Sametime greatly lowering the octane number shown .by the alkylate, a light naphtha of high octane number is required. Destructive isomerization furnishes such a light naphtha.

While the specic'details of'the destructive 'isomerization process and of the alkylation t process, such as temperatures, pressures, contact times and catalysts. form no part of the instant invention, some discussion of these details will be included to aid those skilled in the art to select processes best suited to any particular set of conditions.

With respect to destructive isomerization, a wide variety of hydrocarbon fractions may be used as charging stocks. A particularly suitable charging stock for the purpose comprises 'a virgin heavy naphtha having a boiling range from about' 250 F. to 400 F., more or less. Such naphthas as those fromv East Texas crudes, Mid-Continent crudes and similar average crudes are well suited to the process as are naphthas having an abnormally high amount of normal paraiiins'such as Michigan naphthas, Pennsylvania naphthas, liquid hydrocarbons produced by theinteractiojn ofcarbon monoxide and hyl drogen (kogasin) rafflnates from the solvent extraction of kerosenes and the like. Preferably, a light naphtha or a straight run gasoline of normal boiling range is not used as charge for in such cases the high octane number light naphtha formed by destructive isomerization would be diluted with uncoverted virgin light naph- 'tha, thus defeating the objects of this invention to a greater .or less degree. Also, `when aluminum halide type catalysts are employed it is preferable to use an olefine free charge in order to reducerpolymer formation to a minimum.

A number ^of catalysts may be employed to pro'mote the destructive isomerization reaction. Among these may be mentioned aluminum halides, alumina and clays, both natural clays,

' treated natural clays and synthetic clays. The

I n alkylation, a mixture containing isoparamns and olefines is contacted with asultable catalyst, usually concentrated sulfuric acid, higher isoparaiiins being produced. Usually isobutane is alkylated with olenes containing four carbon atoms,'isooctanes being formed as the maiorA products. This material has an octane number from about 91 to 93, exhibits anrexcellent'lead response and is completely saturated.' All these factorsare much. to be desired in aviation fuels. However, as has been mentioned previously, the alkylate A is not suiiiciently volatile for use as an aviation fuel and when blended with the light naphthas ordinarily available the octane number of the blend is appreciably lower than that of the straight alkylate. `also, the manufacture of alleviated isobutane is not` eiilcient v because of the dearth .of isobutane. xIn` the operating conditions to be employed when operating at atmospheric pressure and when using aluminum chloride as a catalyst have already been outlined and further details may be obtained by vconsulting the previously mentioned United States'Patent 2,172,146. It has been found that aluminum bromide is much more effective in this reaction than aluminum chloride due to the lgreater solubility of the former in hydrocarbons.

In place of straight aluminum halides, aluminum halides containing various amounts of finely divided metals such as aluminum, magnesium and zinc maybe employed.. By varying the aluminum halide to metal ratio in the catalyst, the' isobutane to light naphtha ratio of the destructively isomerized product may'be changed. When large amounts of one of the finely'divided metals are incorporated into the repressed. :On the other hand, with straight aluminum halides the isobutane to light naphtha ratiirfi's maximum. 'By varying the composition ofzthe .catalyst in this manner, isobutane and lightnaphtha may b'e produced in any propertions desired. It should be obvious that in any case, the light naphtha formed'mayv be fractionated to give a fraction of the proper boiling i' range and volatility for use in the flnal motor fuelv blend and thatany excess isobutane over requirements may be discarded.

Destructive isomerization may be conducted batchwise or preferably in a continuous system wherein the charge is passed over any of the various catalysts mentioned or other suitable contacts which may be mounted on supports if desired. Temperature of operation is usually rather W, varying from say 100 F. to 800 F., usually from 200 F.. to 700 F. The exact temperature to be employed depends largely upon the catalyst selected. When aluminum halides and similar contacts are used temperatures ofA from 200 F. to 400 F. may be employed while less active catalysts require higher temperatures, for example in the range 400 F. to 700 F. ,If desired, the reaction may be conducted under superatmosphe'rlc pressure. Actually; because -of'the rather low velocity of this destructive isomerization reaction, for economy in reactor size and the like it may be desirable to run under high superatmospheric pressure, especially when thev less active catalysts are employed. A

The destructively `isomerized product is separated by fractionation or other suitable means into a low boiling isoparaflin cut, usually comprising isobutane, or isobutane and isopentane depending upon the exact nature of the alkylation run to be carried out subsequently with the material, a higher boiling isoparaflin cut which may boil from the end point of the lower boiling isoparaflnic cut up to the initial of the hydrocarbon charge, a cut having the same boiling range as the hydrocarbon charge and bottoms having a higher boiling point than the hydrocarbon charge. The cut having the same boiling range as the hydrocarbon charge may be reycycledif desired. ,Or, if desired, the hydro- "carbonl chargemay be added continuously to the reaction vessel for destructive isomerization, product boiling lower than the initial boiling point of Athe hydrocarbon charge may be taken overhead continuously and separated into a low boiling isoparaflinic cut and a higher boiling iso'- paraflinic cut.

From time to time, or continuously, liquid maybe withdrawn from the reactor to prevent accumulation of material boiling higher lthan the hydrocarbon charge, sludge, et cetera. If desired, fresh catalyst may be added with the charge to the reactor.

Before turning to a consideration of the alkylation reaction proper it will be well to devote a few words to the olefines employed'. Prac' tically any olefine will alkylate a paramn con-- taining a tertiary carbon atom. However, ethylene reacts very slowly, propylene at a 'much higher rate and the but'enes and higher olenes at a very satisfactory rate. taining' suitable olenes may be obtained as a lay-product from the thermal cracking of petroleunifractions or by the catalytic dehydrogenation or thermal pyrolysis of suitable natural gas other source'may be employed. If desired. the

asoaase .to the alkylation reactor. One ingenious method Gas mixtures conolenes may be concentrated prior to charging 75 of doing this is to polymerize the oleflnes catalytically, thus converting them into liquid olenes' easily separable from the' gaseous parafllns, 5 these last then'being recycled to .the dehydrogenation or pyrolysis zone if desired. The liquid olilnes are then employed to alkylate isopara s.

product formed by the alkylation of isobutane .10 with diisobutene consists of isooctanesrather than isododecanes.

In the alkylation of isoparaflins with olefines,

the mixture of the two, witli the isoparaillns preterably in large excess, is contacted with a suitable catalyst, such materials as mercurio aluminum bromide, a'iitimonous,v aluminum bromide sodium aluminum chloride lithium aluminuni chloride, boron fluoride plus nickel plus water aluminum chloride, aluminum chloride-hydro: 2Q carbon complexes and concentrated sulfuric acid having been suggested, among others. for the purpose. The reaction products are separated, the alkylate is sent to storage and the excess isoparafln isla'dded to fresh feed and recycled to the reactor.

As concentrated sulfuric acid is the most u sed catalyst for the allwlation reaction, ftiheg discussion will relate to this contact agent. An isoparaflin-oleflne ratio of three or higher is preferably employed. The acid is' added to the reactor in a highly concentrated form, say 98% acid. I

product taking about 90% overhead and leaving- 10% heavy ends as bottoms.

aviation stock from the total alkylate with th higher boiling cut from destructive isomerlzation, or the desired portion of said higher boiling cut to produce a motor fuel of high octane numbei', high lead response, high and controlled volatility and low unsaturate content is a procedure obvious to those skilled in the art;

It is not absolutely essential to separate the destructively isomerized product into a low boiling fraction for alkylation and a higher boiling blending stock. If desired, the whole material may be employed in the alkylation reaction. -Loeweiv, grteatllyI improved results follow when eruciveisome' 'I .rated as described. nze'd .p-qduct i? sem'. For the better understanding of this invention reference may be had to the accompanying ligure, forming a part of this specification, which is a diatgrammaic representation of one form of .appara us suita le for use in accom lishingv I objects of this invention. l f) the Turning now .to a more detailed consideration of Athe ngure, .suitable liquid charge of; nature previously described is moved by pump I through line 2 to destructive isomerization reactor l. A su.i:ablev catalyst, for example, aluminf um chloride, is held in hopper 4 and is added to the liquid charge at a suitable rate through valvel, the addition being accomplishedv byv means of an Contrary to expectations, the major 'Ihe blending of either the total alkylate or the asoaaao f y desired, these may constitute the whole gaseous eductor or similarv device. Reactor itis supplied 'with'heatiiig means, for example, coil 8 through which steam, hot oi1, heated biphenyl, heated biphenyl-diphenyl oxide mixture or the like may be circulated. An activator such as water, steam, hydrogen chloride, an alkyl chloride, or the like, ma'y be supplied to reactor 3 at aepredetermined rate through valved line 1.- The reactor 3 may be provided with suitable agitation meansv (not i isobutan'e being taken overhead through line I3,

cooled in exchanger I4 and sent to separator I5. (Usually, when operating in accordance with the very speciiicscheme being described, tower 9 is at low pressure and hence water will not liquefy isobutane and accordingly a refrigerated exchanger is used at I4.) Uncondensed products leave through valved line I5. Liquid isobutane is moved by pump I8A. Part may be circulated through valved line I1 to tower 9 to provide ope'n reflux therein. Net isobutane passes through valved line I8 to the alkylation zone. Material boiling above isobutane but below the liquid charge is removed from an intermediate point of charge to the unit.I

Dehydrogenated butanes-from valved line 48 and isobutane from valved line I8 are Joined in' line 45 wherein they are mixed with concentrated sulfuric acid introduced through line 48. 'I'his mixture is passed through mixer 41 which `may be a cone mixer, an orifice mixer, an impeller mixer or the like. Olenes alkylate' isobutane in the presence of concentrated sulfuric acid and the reaction products are sent to settler 48. Sulfuric acid is withdrawn 'from the bottom loi' settler 48 by pump 49 and is recycled via 45.` A portion of this acid is withdrawn through valved line 58 and an equivalent amount of fresh acid is added through valved line 5I.

, Hydrocarbons are withdrawn from the top separator 48 and pass by line 52 to fractionator 53 which is similar to tower 9 with the exception that an intermediate withdrawal point is not necessary. moved by pump 5,4I through valved line 55 to line I9 wherethey. mix with light isoparaillnic naphA .tha to form the ultimate'product. Conventionally, alkylate bottoms are caustic washed before use. To accomplish this, valve 55 is closed and the bottoms pass throughazalved lines 56 and -51 to line 58 wherein they are blended with caustic tower 9 through line I9 to be utilized aswill be explained'sub'sequently. Bottoms falling within 1 are removed from reactor 8 at a predetermined rate through valved line 2|. l

Natural gas butanes are passed through line 22 to coil 23 in furnace setting 24. On passage through coil 23 the gas stream is heated to catalytic dehydrogenation temperature and is then passed to reactor 24A, which, if desired, may take the form of an upper manifold 25, a lower manifold 28 and a plurality of connecting tubes 21. These tubes Vare lled with a suitable hydrogenation catalyst, for example, chromium oxide on alumina, andare preferably placed in a furnace setting to supply vthe endothermic reactionheat. Reaction products pass via 28 and through a suitable cooler (not shown) to the bottom of absorber 29 wherein they are contacted with a da scending stream of absorber oil introduced through til. Absorber 29 is provided with means to promote liquid-vapor contact, for example,

bubble trays- 3i.` Hydrogen and any small amounts of lower gaseous hydrocarbons,.e. g., methane, ethane and ethylene, are eliminated through valved une s2. Rich absorber 011 is moved by pump 33` through exchanger 34 to stripper 35. Stripper 35 is provided with means to promQtejliquid-vapor contact, for example solution introduced by pump` 59. The blend is intimately mixed in mixer and is settled in 8|,

the aqueous layer being withdrawn through l valved line 82. The hydrocarbons are moved by pump 63 to line 54 wherein they meet water ir'itroduced by pump 85. The blend is intimately contacted in mixer 85, is settled in 81 and water is:` withdrawn through valved line .88. Washed alkylate is, moved by Dump, 59'through valved line 10 to line I9 to form the ultimate blend.

If desired, alkylate may be fractionated to give a cut of more desirable boiling range prior to incorporation with light isoparainic naphtha.. To accomplish this, crude alkylate is moved by pump 54 via valves 58 and 1I, through heater 12 to fractionator 13, -which is similar to tower 9 except that an intermediate withdrawal point is not essential. Unwanted, high boiling alkylate bottoms are removed through valved line 14 while overhead of the desired boiling range is moved by pump'15 through valves 16 and 11 to line I9. By closing valve 11 and opening valve \18, the fractionated` alkylate may be caustic bubble trays 36, and with bottom heating means,

for example, coil 31. Stripped absorber oilis moved by pump 38 through exchanger 34, cooler 39 and line 30 back to absorber 29. Dehydrogenated butanes, comprising butane, isobutane, isobutene and the butenes, lare discharged from stripper 35 through line 40, are liquefied in cooler 4I (refrigeratedif necessary) 'and are moved by pump 42 into valved line 43. If available, C4

' hydrocarbons from cracking still gas may be introduced `through valved line 44. Obviously, if

washed prior to entering line i9. Ii desired,

Tower 8| is highly eillcient and is provided withmeans to promote liquid-vapor contact, for-'example, a large number' of bubble trays 82, and

with bottom heating'means 83 and top cooling means 84. Isobutane 'is taken yoverhead-#and passed by lines 85 and 88 tol line 45. Normal butane `is removed as bottoms and passed by yline s1 to une' 22. l f

By a very convenient modification, 'separation of normal butane from isobutane may be avoided 'but thisv modification requires a catalytic polymerization unit, which is however `frequently available. Valve 43 is closed and 88 is opened. the

^ catalytically dehydrogenated. butanes thereby Alkylate bottoms from tower 53 are passing through coil 89 in furnace setting 90 whereinv they are heated to a catalytic polymerization temperature.v The heated mixture passes to reactor 9| wherein it is contacted with a polymerization catalyst, for example, copper pyrophosphate. Products pass via vvalve 92 `(where some pressure reduction is accomplished) to fractionator 93 which is similar to tower 9 except that an intermediate withdrawal line is not necessary. Olene polymerization products are moved by pump 94 to line 45 while overhead from tower 93 passes through valve 95 and line 96 to line 22 for recycling. Conditions are so regulated in the catalytic polymerization zone so 4as to achieve asA nearly complete oleiine conversion as is conveniently possible.

As has been mentioned heretofore, oleflnes 'from any convenient source may be used as one component of the alkylation pair and the prep'- i aration of olenes by the catalytic dehydrogenation of gases containing isobutane has been mentioned. Obviously, oleiines may be prepared by dehydrogenating pure isobutane and by so doing' many apparatus simplifications are possible. Valve I8 is closed and the isobutane is passed via valved line 91 to the catalytic dehydrogenation zone, this gas representing the sole charge to this zone.A After absorption and stripping, the resulting isobutane-isobutene mixture passes through valved line 43 to line 45 where alkylation occurs as usual. Overhead from tower 53, consisting essentially of isobutane, passes through valved line 99 and line 86 back to line 45 for recycling. Part or all of this isobutaneA may be recycled to the catalytic dehydrogenation zone via valved line 99. It will be noted that by this method of oper-A ation both the catalytic polymerization zone and the tower to separate butane and isobutane may be eliminated. A For the better understanding of the instant invention a single example illustrating the same is given. It is to be understood that this example is illustrative only and in -no way limits the scope of the instant invention.

Example 1 A heavy naphtha obtained from East Texas crude and having a boiling range of from 250 F. to 400 F. and a motor octane number of about 45 was mixed withy about 1% aluminum bromide and the resulting material was passed continuously to a liquid phase reactor operating at about 210 F. Overhead'fromfthe reactor was partially condensed to produce agaseous fraction comprising essentially isobutane and a liquid containing large amounts of isoparailins and' asoaase to an alkylation reactor containing concentrated sulfuric acid and operating at 35 F.' Hydrocarbon reaction products were fractionated to prot duce a cut consisting largely of isobutane, a cut consisting largelyof normal butane, and alkylate of an endpoint vof 275 F. and bottoms. The isobutane rich cut was recycled to the alkylation reactor afterbeing mixed with fresh feed tothe same zone, the normal butane rich cutv was recycled to the catalytic dehydrogenating zone, the bottoms were diverted to premium automobile motor fuel while the major alkylate fraction was blended with a sufficient amount of the liquid, highly isoparaiiinic material produced in the destructive isomerization step to give an aviation fuel of high octane number, high lead response, high and proper volatility and low unsaturate content. By adding tetraethyl lead to thisblend it was easily possible to achieve 100 octane number with less than 3 cc. per gallon and well over 100 octane number with 6 cc. per gallon, this larger quantity of lead tetraethyl being permissible in some aviation fuels for military purposes.

The foregoing description and example serve to outline the scope and spirit of thepresent invention and manifest its advantages to those skilled in lthe art to which it `pertains but itis noty intended that these shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

I claim:

1. In the preparation of motor fuel, the steps comprising subjectingia heavy naphtha to destructive isomerization, separating' the destructively isomerized product into a relatively low boiling fraction and a relativelyhigh boiling fraction having a maximum boiling point lower than the initial boiling point of said heavy naphtha, alkylating said relatively low boiling fraction with oletines, and blending the resulting alkylate with said relatively high boiling fraction.

2. In the preparation of motor fuel, the steps comprising subjecting a heavy naphtha to destructive isomerization, separating the destructively isomerized product into a relatively low boiling fraction and a relatively high boiling fraction having a maximum boiling point lowerthan the initial boiling point of said heavy naphtha, alhvlating said relatively low boiling .fraction with butenes and 'blending the resulting alkylate with said relatively high boiling fraction.

3. In Athe preparation of motor fuel, the steps comprising subjecting a heavy naphtha. to destructive isomerization, separating the destructively isomerized product into a fraction comprising isobutane and a higher boiling fraction having a boiling point lower than the initial vboiling point of said heavy naphtha, alkylating said fraction comprising isobutane with olenes and blending the resulting alkylate with said higherl boiling fraction.

4. In the preparation of motor fuel, the steps comprising subjecting heavy naphtha to destructive isomerlzation, separating the destructively isomerized product into a fraction comprising attained. The resulting gas mixture was subisobutane and a higher boiling fraction having a maximum boiling point lower than the initial boiling point of said heavy naphtha, alkylating said fraction comprising isobutane with butenes and blending the resulting alkylate with said higher boilingfraction. was mixed with the isobutane produced in dey structive isomerization and the whole was passed ROBERT F. RU'IHRUFF.

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