US2309987A - Motor fuel and preparation thereof - Google Patents

Description

Feb. 2, 1943. R. F. RUTHRUFF I MOTOR FUEL AND PREPARATION THEREOF Filed Nov. l5, 1939 lll Patented Feb. 2, .1943

UNITED STATES PATENT t OFFICE Moroa'rcm. AND PREPARATION 'rrmaacr Robert r. autumn, chicago. nl.

Application November 15, 1939, Serial No. 304,602 4 claims'. (a. 19e-1o) This invention relates to motor fuel and the preparation thereof. More particularly, this invention relates to motor fuel of high octane number and controllable volatility and the preparation thereof.

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 asyet been approached in all probability, nevertheless, in certain directions, additional improvements are becoming increasingly diicult to achieve and all the 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 aviationiuse have been prepared by the cat- Valy'ii polymerization of olenes containing four carbon atoms to the molecules followed by hydrogenation of the polymer, formed. Such olefines may be obtained, in admixture with the analogous parafns, from the gases produced during the cracking of various petroleum iractions or by the catalytic dehydrogenation or the thermal pyrolysis of the butane cut from natural gas. These olenes 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 possible to attain almost quantitative conversions of isobutene to polymer with conversions of normal butenes varying from practically zero to practically 100%. The polymer produced consists largely of isomeric octenes and has an octane number of 80 to 82. While an excellent motor fuel for automobile engines, this material is totally unsuited for aviation usesbecause 5 of its high unsaturate content, low octane number and low lead response. By catalytic hydrorated and exhibits an excellent lead response'.

The octane number of the hydrogenated polymer is largely a function of the amount of normal butenes reacting. When the ratio ci' reacting isobutene to reacting normal butenes is high the octane number of the resulting hydrogenated polymer is high and vice versa.

- While the 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 preparing the same exhibits numerous disadvantages. For example, the hydrogenated catalytic polymer is not suiiiciently volatile for aviation requirements, the unhydrogenated polymer obviously suffering from the same disadvantage. If an attempt is made to increase volatility by the addition of light naphthas the octane n'umber of' the blend is considerable lower .Y 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 Ano 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 hydrogenatedcatalytic polymer is to be made' it is well to react not more than one mole of lnormal butenes per mole of isobutene present.

However, as is well known to those skilled in the art, the isobutane-normal butane ratio in natural gas and the isobutene-normal butenes ratio in cracked gas is much less than `unity so if it is desired to make a hydrogenated catalytic polythermal pyrolysis of the isobutane to produce isobutene. While this procedure solves the partlcular problems mentioned, it is obvious that the volatility deciency o f the hydrogenated polymer still remains.

Many attempts have been made to increase the volatility of isooctanes formed by the catalytic hydrogenation of catalytic polymer. Since isopentane is the only low boiling liquid isoparaln readily available, iscpentane-isooctane blends have been proposed as aviation fuels. As those skilled in the art are aware, aviation fuels meeting current specifications cannot be prepared in'this way. If the blend meets -the 10% oi specification, the of! specification is not satf istled. Likewise, if the blend has the proper amount of isopentane to satisfy the 50% off specification, the minimum permissible temperature for oif is far exceeded. To correct for these deficiencies, light naphtha has been added ment the fact remains that this hexane is .veryy difficult toobtain. At present this material is made by the thermal alkylation of isobutane with ethene at extremely high pressures. To reduce ethene polymerization, the concentration of this olefine must be kept at an extremely low level. This means that the yield per pass of the desired compound is very low, which in turn necessitates an extremely high recycle ratio and the separation of the small amount of the isomeric hexane from a large amount of unreacted material.

One object of this invention is to provide an improved motor fuel and a process for producing the same. A- further object of this invention is to provide an improved motor fuel of highv octane number and a process for producingl the same. An additional object of this invention is to provide an improved motor fuel of controlled volatility and a process for producing the same.

- Another object of this invention is to provide an improved motor fuel of high octane number and controlled volatility and a process for producing the same. Further objects of this invention will become evident from the following description.

Briefly, the improved motor fuel of the instant invention comprises hydrogenated catalytic polymer .blended with a light, naphtha of high isoparaln content obtained by the destructive isomerization of a hydrocarbon fraction. `(Destructive isomerization is defined immediately hereinafter.) The hydrogenated catalytic polymer is prepared by catalytically polymerizing a mixture containing isobutene, `at least part of said isobutene being derived from the catalytic dehydrogenation or thermal pyrolysis of isobutan'e obtained by the destructive isomerization of ahydrocarbon fraction, followed by the catalytic hydrogenation of the polymer produced. The resulting hydrogenated catalytic polymer is blended with a light naphtha of high volatility and high isoparafiin content, and hence of high octane number, at least part of which was also obtained by the destructive isomerization of a hydrocarbon fraction. The blend comprises a motor fuel of very low unsaturate content, high octane number, high lead response and high and controllable volatility. In the production of this material the processes of destructive isomerization, catalytic polymerization, catalytic hydrogenation and catalytic dehydrogenation (or thermal pyrolysis) cooperate to produce a new and unexpected result as will become manifest from the following deinto United States Patent 2,172,146, issued September 5, 1939.- In this it is shown that when a hydrocarbon fraction, for example a straightl run heavy naphtha, is treated at lovvv temperatures, for example, 205-210 F., with a suitable catalyst, for example'aluminum chloride `promoted with water, hydrogen chloride, carbon stance however, in addition to forming a compound of different structure than that of the charge, the new compound also has a different 4molecular Weight. In the example cited, a considerable amount of heavy naphtha charge, having an average molecular weight of say 142, is converted into sobutane 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.

i 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 2 -methyl parains between carbon atoms 3 and 4. In this way isobutane could be formed witho-ut 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 skilled in the art, this material consists largely of straight chain paraflins. In addition, this stock was heavily acid treated before use so as to remove aromatics and similar Ycmnpcunds,gsoas-M`` charged it consisted essentially of a mixture of straight chain parafns.

Supplementary experiments have also conrmed the fact that straight chain parafns are destructively isomerized with the production of isobutane.l For example, a heavily acid treated Mt. Pleasant heavy naphtha was exhaustively treated 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 amounts of 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 Mt." Pleasant heavy naphtha.

A further study of the products of destructive isomerization has revealed a most important but hitherto unnoticed fact. On fractionating the 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 found 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 octane number increase observed, this second cut was again distilled, taking overhead a fraction boiling from above isobutane up to the initial of the naphtha charge and leaving as bottoms a material having approximately the same boil-` ing range as the heavy naphtha charge. On determining'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 naphtha overhead had van extremely ing destructive isomerization of thehydrocarbonv fractions consistedlargely of isoparafiins, these accounting for the unusually high octane numbers observed.

To summarize, in the destructive isomerization of heavy naphtha-the following major products are obtained:

A. Isobutane.

B. Light naphtha of very high octane numbe and consisting largely of isoparailns.

C. Heavy naphtha of the same boiling range and approximately the same octane number as the charge. Y

D. Material having a higher boiling point than that of the charge.

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 paraflins and olenes together with hydrogen. In destructive isomerization the gas consists essentially of isobutane. In thermal reforming, the light naphtha produced is highly unsaturated. The light naphtha obtained in destructive isomerization operations is completely saturated or nearly so. The product from thermal reforming having the same boiling range as that of the charge is highly olenic` and has a much higher octane number j than that of the charge. The same fraction from destructive isomerization contains no olenes or practically none and has an octane number differing little from that of the original 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 largelyl of aromatic hydrocarbons.

'I'he catalytic polymerization-hydrogenation process for the production of higher isoparafflns is soy Well known to those skilled in the art that only the .briefest mention is necessary. In the catalytic polymerization step a mixture containing oleflnes is contacted with a suitable catalyst, suchl as phosphoric acid on carbon, usually at elevated to high superatmospheric pressures and. moderate temperatures. Usually gas mixtures comprising hydrocarbons containing four carbon atoms to the molecule are employed, the isobutene and normal butenes present polymerizing to forrn isooctenes. then catalytically hydrogenated, usually at moderate temperatures and pressures in the presence of a highly active hydrogenation catalyst, for example, nickel, to form isooctanes, the resulting product having a very low unsaturate content, high octane number and a high lead response, all these properties being much desired The resulting polymer is in aviation fuels. However, as has been mentioned previously, the hydrogenated polymer is not sufficiently volatile for use as an aviation fuel and when blended with the light naphthas ordinarily available the octane number of the blend is appreciably lowerv than that of the straight hydrogenated polymer. Also, the manufacture of hydrogenated polymer is not efiicient because of the dearth of isobutene. In the ordinary renery the yield of high octane number hydrogenated v polymer could be increased two or more fold were suieient isobutene available to give, for exampie, an amount equal in volume to the normal butenes at hand.

The excellent cooperation between destructive isomerization and catalytic polymerization-hydrogenat-ion for the manufacture of high octane motor fuels for aviation use, should now be evident. For maximum production of high oc-v tane number hydrogenated polymer, additional isobutene over that found in theusual refinery is required. Destructiveisomerization supplies isobutane which is easily converted to isobutene .by catalytic dehydrogenation or thermal pyrolysis. To confer proper volatility on the hydrogenated polymer `without at the same time greatly lowering the octane number shown by f the straight hydrogenated polymer,. a light naphtha of high octane number is required. Destructive isomerization .furnishes such a light naphtha. Also inthe conversion of isobutane from destructive isomerization into the isobutene required in the catalytic polymerization reaction, hydrogen is produced as a by-product while in the conversion of' catalytic polymer into isooctane hydrogen is required.

While the specific detailsof the destructivecharging .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 from East Texas crudes, Mid- Continent crudes and similar average crudes are well suited to the process as lare naphthas having an abnormally high amount of normal paraffins such as Michigan naphthas, Pennsylvania naphthas, liquid hydrocarbons produced by the interaction of carbon monoxide andhydrogen (kogasin) rafllnates 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 naphthas formed by destructive isomerization would be diluted with unconverted virgin light naphtha,

.thus defeating the objects 0f 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 reduce polymer formation to a minimum.

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

treated natural clays and synthetic clays. The operating conditions 'to be employed when operating at atmospheric pressure and when using aluminum chloride as a catalyst have alreadyv been outlined and further details may be obtained by consulting the previously mentioned United States Patent 2,172,146. vIt has been found that aluminum bromide is muchmore effective in this reaction than aluminum chloride due to the greater solubility of the former in hydrocarbons. i

In place of straight aluminum chloride or bromide, aluminum halides containing various amounts of-ne1y divided metals such as aluminum, magnesium and zinc may be employed.

` miuin oxide on alumina.

of the catalyst in this manner, isobutane and light naphtha may be produced in any proportions desired. Itshould be obvious that in any case, thelight naphtha formed may be fractionated to give a material of the proper boiling range and volatility for use in the final motor fuel blend and that any excess isobutane over requirements may be discarded.

Destructive isomerization maybe 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 bev mounted on supports if desired.I Temperature of operation is usually rather low, varying from say 100 F. to 800 F., usually from 200 F. to 700 The exact temperature to be employed depends largely upon the catalyst selected. When aluminum halides and similar contacts'are used temperatures of from 200 F. to 400 F. may be em-ployed 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 superatmospheric 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 inhydrocarbon charge, a cut having the same boiling range as the hydrocarbon charge and botl product' boiling lower than th'e initial boiling lpoint of the hydrocarbon charge may be taken overhead continuously and separated into a low boiling isoparaaflnic cut and a higher boiling isoparainic cut. From time to time, or continuously, liquid may be withdrawn from the reactor to prevent accumulation of mate-rial boiling higher than the hydrocarbon charge, sludge,

the Voleiines produced being isobutene.

et cetera. If desired, fresh catalyst may be added with the charge to the reactor.

Before turning to a consideration of the catalytic polymerization-hydrogenation reaction proper it will be well to devote a few words to the charging stock employed in the catalytic polymerization step. As has been mentioned previously, at least part of thisl stock comprises isobutene formed by the catalytic dehydrogenation or thermal pyrolysis of the isobutane pro.- duced during destructive isomerization. As the conversion of isobutane to isobutene by catalytic dehydrogenation is preferably employed, the. process whereby this change is accomplished by thermal pyrolysis will not be considered. In catalytic dehydrogenation, the isobutanev is charged to a reactor containing a highly active dehydrogenating catalyst, for example, chro- An operating temperature of from 1000 F. to 1100 F., more or less, may be employed and' while theoretically low pressures are preferable, actually moderate superatmospheric pressure, for example-30 pounds per square inch, may be used Without appreciable harm and with considerable savings in reactor cost and the like. Depending upon the space velocity of the charge and the operating temperature, up to 40% or more of the entering isobutane is converted to oleflnes, about of The resulting product is preferably subjected to allsuitable separation process, for example, the well known absorption-fractionation process to remove vhydrogen and produce a cut consisting largely of isobutane and isobutene, suitable for charging to the catalytic polymerization unit. If a refinery butano -cut is available containing appreciable isobutene and normal butenes, this may be added to the isobutene-isobutane fraction obtained as described heretofore. On the other hand, if a natural gas butanecut is available, mixing this with the isobutane produced by destructive isomerization prior to charging to the catalytic dehydrogenation zone is the obvious and proper procedure. Obviously, suitable oleflnes from other sources may also be employed in the charging stockto the polymerizer.

In the catalytic lpolymerization of olenes, a mixture containing these reactive compounds is passed over a suitable catalyst at moderate to highsuperatmospheric pressure and at moderate temperatures. As catalysts, such materials as phosphoric acid on carbon, the solid obtained by calcining a mixture of phosphoric acid and kieselguhr (the so called solid phosphoric acid) copper pyrophosphate, copper orthophosphate plus cadmium orthophosphate plus phosphoric acid, sodium aluminum chloride, lithium aluminum chloride, antimonous aluminum bromide, mercurio aluminum bromide and similar contact agents have been suggested. Operating pressures of from 200 to 1500 pounds per square inch, more or less, have been suggested and temperatures of vfrom 200 F. to 550 F., more or less. Specifically, excellent results have been obtained when,operating at a. temperature of 350 F. to 375 F. and a pressure of 1500 pounds per square inch, the olene containing charge being passed over the catalyst at. a; rate of 20 cubic feet (measured -at standard conditions) per hour per pound of catalyst.

Thus far in the discussion major emphasis has been placed on the. polymerization Aof mixtures containing. olenes having four carbon atomsto the molecule. 'Sur olefines are most-suitable 'like may be circulated.

for polymerization. Ethylene polymerizes at a very slow rate' and while inthe presence of r y largely by conducting the polymerization in two or more steps with product separation between steps but obviously this greatly increases the cost of the apparatus. polymerization unit charge Abut perfectly satisfactory results may be'obtained using an isobutene-normal butenes mixture and either limiting the amount of normal butenes polymerization or having an isobutene-normal butenes ratio of about one or more. f

The polymer produced is separated lfrom the gaseous components of the reaction mixture. These last are preferably recycled to the zone wherein paraiiins are converted into olenes. The polymer is hydrogenated. This may be accomplished by Vsubjecting a vpolymer-hydrogen mixture to a high superatmospheric pressure at moderately elevated temperatures in the presence of a. relatively inactive but highly stable hydrogenation catalyst such as a sulfide or oxide of molybdenum or tungsten. Usually however the hydrogenation is accomplished under milder conditions, for example, 200 pounds per square inch pressure and a temperature of 400 F. to 600 F., more or less, in the presence of a more active catalyst, for example, nickel. Y

The blending of either the total'hydrogenated polymer or any suitable fraction thereof with the higher -boiling cut from the product of the destructive isomerization of a hydrocarbon fraction or any suitable fraction obtained from said higher boiling cut, to produce a motor fuel of high octane number, high 1ead response, high-and controllable volatility and low unsaturate content is a procedure'obviou's to those skilled in the art.

For the better understanding of this invention reference may behad to the accompanying gure,

forming a part of this specication, whichis a diagrammatic representation of one form of apparatus suitable for use in accomplishing the objects of this invention.

Turning now to a more detailed `consideration of the gure, suitable liquid charge of a nature previously described is moved by pump I through line 2 to the destructive isomerization reactor 3. A suitable catalyst, for example, aluminum chloride, is held! in hopper 4 and is added to the liquid Vcharge at a predetermined rate through valve 5, the addition being accomplished by means of an eductor or similar device. Reactor -3 is supplied with heating means, for example,

coil 6 through which steam, hot oil, heated biphenyl, heated biphenyl-diphenyl oxide or the water, steam, hydrogen chloride, an alkyl chloride orthe like may be supplied to reactor 3 at a predetermined rate through valved line 1. The

through ,conduit 8.and pass toy fractionator 9 which is conventional, .being provided with means to promote liquid-vapor contact, for example bubble trays Ill, With bottom heating means,'f or example, heating coil I I and upper disposed cooling means, for example, cooling coil I2; The volatile reaction products are fractionated in 9,

isobutane being taken overhead through line |3,`

Isobutene is about ideal as a partially condensed in exchanger I4 and sent to .separator ,I5. Condensedisobutane is moved by pump I6. .Part may be circulated through valved line I1 to tower 9 to provide open reflux therein.

Net condensdrisobutane passes through valved' line I8 wherein it is mixed with uncondensed isobutane from valved line I9. The mixture passesto the catalytic dehydrogenation zone. Material boiling above isobutane but below liquid charge is removed from an intermediate point of tower 9 through line 20, tovbe utilized as will be explained. Bottoms falling within the boiling range of the liquid charge are removed from l' tower 9 through valved line 2l and are returned An activator such as to reactor 3. Sludge andpolymer are removed ,from reactor 3 at a predetermined rate through valved line 22.

Isobutane passes through valved lines I8 and I9 to line 23 and thence to coil 24 in furnace setting 25. If desired, natural gas butanes may be added to the isobutane stream via valved line 26. On passage through coil 24 the gas stream Vis heated to catalytic dehydroegnation temperals provided with means to promote liquid-vapor contact, for example, bubble trays 34. Gas, consisting essentially of hydrogen, is eliminated through valved .line 35. Rich absorber oil ls moved by pump 36 through exchanger 31 to strip-- per 38. -Stripper38 is provided with means to promote liquid-vapor contact, for example, bubble trays 39, and with bottom heating means, for example coil 40. Stripped absorber-oil is moved by pump 4I through exchanger 31, cooler 42 and line 33 to absorber 32. Dehydrogenated products comprising isobutane and isobutene (plus normal butane and the normal butenes if natural gas was introduced through 26) are discharged from stripper 38 through line 43, are .cooled and preferably liqueed in cooler 44 and are moved by pump 45 to coil 46 in furnace setting 41.l If available, 64 hydrocarbons from cracking still gas may be introduced through valved line 48. Catalytically dehydrogenated products are heated to catalytic polymerization temperature in coil 46 and are passed to reactor 49 wherein they are contacted with a polymerization catalyst, for example, copper pyrophosphate. Products pass via valve 50 (where some pressure reduction is accomplished) to fractionator 5I which is similar to tower 9. Olene polymerizate may be removed by line 52 and valved line 53 to line 54, or, if desired, an intermediate cut of olene polymers may be removed via valved line 55 to line 54 lwhile olene polymer bottoms may be removed via line 52 and valved line j56, valve 53 being closed. Overhead from tower 5I is recycled via line 51 to the catalytic dehydrogenation zone. 'Conditions are regulated in the catalytic polymerization lzone so as to achieve as nearly complete olene conversion as is conveniently possible. f Polymer-liquid in line 54 is brought to a catalytic'- hyrogenation pressure by pump 58 while hydrogen in line 35 is brought to a similar pressure in compressor 59, the two streams being mixed in line 50 and sent through coil 6i in furnace setting 02. During passage through coilv 6| the mixture is brought to catalytic hydrogenation temperature and is then Isent to reactor 63 containing a suitable hydrogenation catalyst, for example, nickel on kieselguhr. Products leave reactor 63 by line 64, are cooled in 65 and pass to separator 66 from which hydrogen is removed via valved line 6l and is sent to compressor 59 for recycling. Hydrogenated liquids are removed from separator 66 via valved line 68, are heated in heater 69 and are sent to fractionator 10. If the polymer liquid was fractionated in tower i, then tower 'i0 need do no more than stabilize the hydrogenated polymer fraction. However, if total vpolymer was hydrogenated, then the hydrogenated total polymer may be fractionated in l0. If desired, no fractionation need be clone in either tower, but as a rule it is preferable to remove and discard heavy ends of the liquid, either before or after hydrogenation.. Tower. 'l0 is provided with means to promote liquid-vapor contact, for example, bubble trays 1|, with bottom heating means, for example, heating coil 'l2 'and with upper disposed cooling means, for example, cooling coil 13. Gas, consisting essentially oi hydrogen, is taken overhead from tower 'l0 by line 14 and may bel sent by valved line 15 to line 35' for recycling. Ii' desired, prior and the total liquid charge to tower l0 may be removed by valved line 80, thence to line 18 and finally to line 20 wherein the material is blended with light isoparaiiinic naphtha to form the ultimate product of the process.

For the better understandingof the instant invention the following examples illustrating the same are given. It is to be understood that these examples are illustrative only and in no way limit 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 with about 1% aluminum bromide and the resulting material was passed continuously t a liquid phase reactor operating at about 210F. Overhead from the reactor was partially condensed to produce a gaseous fraction comprising isobutane and a liquid fraction containing large amounts of isoparailins and having a motor octane number of about 80. From time to time a very small amount of steam was added to the reactor to activate the catalyst. From time to time sludge was withdrawn from the reactor. The isobutane fraction from the destructively isomerized product was cpmpressed to a pressure of about two atmospheres and was passed through a catalytic dehydrogenation zone containing a catalyst comprising chromium oxide mounted on alumina and heated to a temperature of somewhat above 1025 F. On charging the isobutane at a rate of about 250 cubic genation zone.

feet (measured at standard conditions) per hour per cubic foot of reactor volume, a gaseous product containing 30% hydrogen, 40% unconverted isobutane, 25% isobutene and 5% of various minor components was obtained. This was subjected to absorption-fractionationto remove hydrogen andthe resulting hydrocarbon mixture,

having an olefine content of over 35% was compressed 1:01500 pounds per square inch pressure and passed at 365 F. over a catalyst comprising solid phosphoric acid, the flow rate being 35 cubic feet of charge (measured at standard conditions) per pound of catalyst per hour. The product, after partial pressure release, was stabilized to eliminate hydrocarbons containing four carbon atoms to the molecule. These were mixed with isobutane from destructive isomerizture from the hydrogenation zone was separated, l

hydrogen 'being recycled and the hydrogenated polymer being blended with a sumcient amount of the light highly isoparaftinic naphtha produced in the destructive isomerization zone 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 this blend 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 tetraethyl4 being permissible in some aviation fuels for military purposes.

Example 2 The procedure was similar to that described in Example 1 except thatithe isobutane, formed during the destructive isomerization of the East Texas heavy naphtha, was mixed with 1.5 times its volume oi' the butane cut from natural gas, containing normal butane and 20% isobutane, priori-,o passage to The procedure was similar to thaty described in Example 1 except that the isobutane-isobutane fraction, prior to passage to the catalytic polymerization zone was mixed with three volumes of a refinery gas fraction containing hydrocarbons of four carbon atoms and showing on analysis 15% isobutene and 30% normal butenes.

It is obvious that in all of the above examples operations are continuous, in other words. the appropriate materials are charged continuously and at suitable rates to the destructive isomerization zone, the catalytic dehydrogenation zone,

Vthe catalytic polymerization zone and the catalytic hydrogenation zone. l

' The foregoing description and examples serve to outline the scope and spirit-oi the present invention and manifest its advantages to those skilled in the art to which it pertains but it isv not intended that these shall be regarded as limitations upon the scope of the invention except the catalytic dehydroinsofar as included in the accompanying claims.

I claim: 1. In the preparation of motor fuel, the steps comprising subjecting a heavy naphtha to detively isomerized product into a relatively lowv boiling fraction and a relatively high boiling traction having a maximum boiling point lower than the initial boiling point of said heavy naphtha, dehydrogenating said relatively low boiling fraction with the production of olenes l dd structive isomerization, separating the destrucand hydrogen, separating said oleilnes and said y hydrogen, polymerizing said separated olenes, hydrogenating the polymer produced with said separated hydrogen and blending the resulting hydrogenated polymer with said relatively high boiling fraction.

3. In the 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 maximum boiling point lower than the initial boiling point of said heavy naphtha, dehydrogenating said fraction comprising isobutane with the production of isobutene and hydrogen, polymerizingsaid isobutene, hydrogenating the polymer produced and blending the resulting hydrogenated polymer with said higher boiling frac-- tion. i

il. In the preparation of motor fuel, the steps comprising subjecting a heavy naphtha to de structive isomerization, separating the destruc tively isomerized product into a fraction com prising isobutane and a higher boiling fraction having a maximum boiling point lower than the initial boiling point of said heavy naphtha, dehydrogenating said fraction comprising isobutane with the production of isobutene and hydrogen, separating said isobutene and said hydrogen, polymerizing said separated isobutene, hydrogenating the polymer produced with said separated hydrogen and blending the resulting hydrogenated polymer with said higher boiling fraction.

ROBERT F. RUFE'.

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