US2373674A - Production of high octane paraffinic gasolines - Google Patents

Description

April 17,' 194s.

c. c. CRAWFORD ETAL 2,373,674y

PRODUCTION 0F HIGH OCTANE PRAFFINIC GASOLINES 'Filed Nov. 9, 1942 inve nTors {Clgxzsi'zr-CJ Crawford j Donald.' L. Fuller. f

Bernardl Greenslder Bg fifhler ATTorneg'.

Patented Apr. 17,

PRODUCTION PARAFFINI oF meu ocrANl:

c GAsoLINEs chester o. Crawford, nl cenno, `one Donald i.. Fuller and Bernard vS. Greensfelder, Oakland, Calif., assis-hors to Shell Development Company, San Francisco,

. Delaware Calif.. a corporation of Application November 9, 1942, serial No. 465,048

(c1. 19o-5s) f Y Crafts type isomerization catalysts, such inl pary This invention relates to a process for the production of anti-knockgasoline stocks consisting essentially of paramnic hydrocarbons.

'I'he objectl of the invention is to providel a process whereby paraiiinic gasoline stocks of betteranti-knock qualitiesmay be produced from straight run naphthenic distillates having poor- A further object of the anti-knock properties.

invention is to provide a process .whereby a great- .Y

er yield of fontane-barrels may be produced from a given quantity of straight run naphthenic gasoline.A A further object of the invention is to provide a vprocess whereby paraflnic gasolinev` aviation gasoline. In order to avoid deterioration of rubber linings of gasoline tanks and for other Vreasons such stocks are preferably of relatively non-aromatic character. Also, in order to avoid stocks substantially free of aromatic hydrocar- `There is a great demand for gasoline blending*y stocks suitable for use as base stocks for premium deterioration in storage. etc., they arepreferably substantially free of oleflns. In order 'to meet the requirements they must furthermore f have the proper volatility, a high anti-knock,

characteristic and highv lead susceptibility. present no base stocks having all of these desired characteristics, except those 'prepared by blending synthetic hydrocarbons, are available although some stocks such as certain fractions of gasoline produced by short cycle catalytic crackticular Vas -aluminum chloride. Considerable progress has been made in the isomeriza/tion of pure -normal paraffin hydrocarbons and some progress has been made in theV treatment of straight run-gasoline fractions. So 'far, however;

as far as we are aware, it has lnot been possible to economically produce base stocks of the dee, sired properties by these methods.

There is a great deal of art relating to the cataf lytic isomerization of hydrocarbons with aluminum chloride catalysts and a number. of processes and improvements have been patented. These various processes have` generally been developed in the isomerization of pure or relatively pure hydrocarbons such as butane, pentftne, hexane, heptane or octane and are primarily adapted straight run petroleum distillates are improved only slightly -by such treatment.' Thus, it is found that when the majority of straight run y distillates of the nature of gasoline are subjectedy to isomerization treatments known to be effectivev I for. they isomerization of pentane, hexane, heptane and the like, the increase in octane number realized is generally only about half of that exing approach the. desired propertiesin most respects. Y

Itjis apparent fromconslderation of the problem that about ther ,only material capable of meeting all of these requirements is a mixture of highly branched paraffin hydrocarbons. With this in mind considerable work has been done in attempts. to produce such base stocks from various available distillates. Except for'the production of synthetic branched chain paraflln hydrocarbons, for instance by alkylation, these at-V tempts have invariably involved the isomerization ofthe normal paramn hydrocarbons from straight run .distillates by means of Friedelpected andn many cases is substantially nil. This point is illustrated by the following table wherein there are'listed results obtained in the treatment of a variety of typical distillates under isomerization conditions in attempts to improve their octane numbers. The catalyst employed in the several examples was a 'molten mixture of 7.5% b. w. AlCh and92.5% b. w. SbCh. The isomerizationtreatment was in each case effected in the violent mixing of the hydrocarbon and catalyst phases in a` turbo mixer.' Thevolume ratio of catalyst phase to hydrocarbon phase was -in each'case about 0.2:1v and the contact 4time was in each case minutes. In the first case the temperature was about C. and-no hydrogen chloride was added. In all other cases about 2.2% b. W. of hydrogen chloride was added (based on the hydrocarbon) and the temperature was about 80 C. In all cases the conditions employed were capable of giving excellent isomerizatons of individual pure hydrocarbons such as n-hexane.

Table I C. F. R C F R Octane Boiling octane octane Material treated range No. of No. of gi feed product C. Stlriflght run Penn. gaso- 15-200 52. 5 49. 0 -3. 5

e. Straight run Calif. gasoline. 3-136 73 76 +3 Parafllnic solvent 12B-176 3l. 5 40 +8. 5 Hyldiogenated cracked gas- 40-126 08. 5 73. 5 +5 Do 25-168 49. 5 50. 5 +1 East Texas straight run 15-100 7l 70 -l gasoline.

Do 15-70 72. 5 83 +10. 5 Do 15-150 04 67. 5 +3. 5 Ventura (Calif.) straight 6-150 68 68 0 run gasoline.

It will be appreciated that better results may be obtained with certain .disti1lates. The above results, however, illustrate the relatively poor results generally obtained when it is attempted to produce base stocks of the character described from the majority of typical distillates by the known isomerization methods.

We have now invented an improved Aprocess wherebythe various disuuates such as shown in comprises molybdenum oxide supported upon an adsorptive alumina. The alumina may be either in the form of alumina alpha monohydrate or gamma alumina, or in the form of one of the stabilized aluminas produced by reacting an adsorptive gamma alumina with a small amount of an oxide of an alkali or alkaline earth metal.

'The catalyst may also contain relatively small and 30% by Weight.

, lyst is effected under conditions quite similar to those employed in catalytic reforming with this catalyst. The temperature of the treatment may bevaried between about 425 C. and 550 C. and is preferably between about 450 C. and 525' C. The pressure may be from atmospheric pressure up to about 60 atmospheres but is preferably between about 2 and 25 atmospheres. The process is preferably effected in the presence of a substantial concentration. of recycled hydrogen-rich gas. Suitable partial pressuresof hydrogen are, for example, between about l and 50 atmospheres. The conditions of temperature, pressure and hydrogen concentration 'are so adjusted-within the above limits that little or no destructive hydrogenation of the gasoline is effected.

line from naphthenic or mixed base petroleum.

- Such gasolines invariably -consist of a complex mixture of paraiiinic hydrocarbons and naphthenic hydrocarbons usually containing minor amounts of oleflns and aromatic hydrocarbons. The gasoline fraction employed` in they process preferably has a boiling range below about 180 C. Thus, a fraction boiling up to about 180' C. or any more narrowly cut fraction may be suitably employed. A preferred fraction aiording a blending stock of superior volatility, for example, has a maximum boiling point of about *95 C.110 C.

- obtained with this specific catalytic agent. Other catalytic agents of the same general .type such as During use the catalyst becomes coated with carbonaceous deposits and these are periodically removed byfbu-rning in the known manner.

In the above-described treatment with the molybdenum oxide catalyst aromatic hydrocarbons are formed in the gasoline fraction, for instance, by the dehydrogenation of cyclohexane (a hydroaromatic naphthene) and its homologues. These aromatic hydrocarbons are known to be harmful to the subsequent isomer-ization step and are therefore removed. This may be effected in any of the known manners. For example, the gasoline fraction may be treated with a solvent which selectively removes aromatic hydrocarbons or it may be extractively distilled. Since the removal of aromatic hydrocarbons from petroleum fractions may be effected in a number of efllcient ways and these are all well known in the art, this step of the process will not be described in further detail.

The gasoline is then subjected to a catalytic isomerization treatment with a' Friedel-Crafts type metal halide isomerization catalyst. The preferred catalysts of this type are valuminum chloride, aluminum bromide and/or zirconium chloride. The catalyst may be employed in any one of several forms. Aluminum chloride, for example, may be employed per se, in the form of a complex of the Gustavson type, or supported upon or 4mixed with an inert support or filler such as active carbon, active alumina or the like. Any of the known isomerization catalysts of this general type may be employed. Also, catalysts consisting of a liquid melt of a mixture of metal halides comprising free aluminum chloride may be employed. Suitable catalysts of this latter type are described in United States Patents 2,279,-

' 291 and 2,279,292.

chromium oxide, titanium oxide, vanadiumoxide,

iron oxide, nickel oxide. platinum oxide, e'tc., do not give thev desired results. While the process is specific to the use of molybdenum oxide, this catalytic agent may be'applied in any of the conventional forms. Thus, it may be used per se, as

; a mixedgel, or supported upon a suitable carrier 'or supportingl material. The preferred catalyst --ca-rbos, for example neohexane (2,2-dimethyl The isomerization. treatment is effected under relatively. severe conditions to effect a substantial production of doubly branched paraflin hydrobutane) Temperatures ranging from about 50 C. up to about 200 C., depending upon the particular catalyst, are employed. When using a ticulars Aregarding the method of contact of the' chloride, the temperature is preferably between about 60 C. and 150 C., and with aluminum chloride complexes of the Gustavson type, the

temperature is preferably between aboutu100 C.

land. 200 C. The isomerization may be effected at atmospheric pressure but is preferably effected undersuperatmospheric pressure. Any superatmospheric pressure maybe employed.- Generally, however, pressures between about 2 and 50 atmospheres are suitable and most practical. 'I'he isomerization is effected in the presence of one of the known promoters such vas boron fluoride vor a hydrogen halide. Generally, the promoter is hydrogen chloride. This may be generated in the isomerization system in a known. manner but is usually added directly. The partial pressure of hydrogen chloride may range from traces up to several atmospheres. Preferred partial pressures of hydrogen chloride are from about 1 to about 20 atmospheres. Under these conditions, the isomerization is eiected in the liquid phase. The

isomerization is also preferably effected in the presence of added hydrogen. Preferred partial pressures of hydrogen are, for example, between about 1 and 20 atmospheres. Also, if desired, the isomerizationmay be effected under a pressure of an added normally gaseous parain hydrocarbon in order to allow more drastic isomerization conriitions without causing excessive degradation. The contact time is adjusted according to the conthe Asame time affording the desired isomerization. In general, under the relatively drastic conditions described, contact times -in the order of to 30.minutes are usually sufllcient to attain Somewhat longer or shorter contact times may, however, be sometimes' advantageously employed. It is observed that under these conditions a ccnsiderable production of -doubly branched parain hydrocarbons is realized which is not the case whenA operating under the relatively mild conditions .usually employed in theisomerizationof pure hydrocarbons such aspentane. The parcatalyst and the gasoline, the method of recovering and ,recycling the hydrogen halide promoter, andthe like do not differ from those known in the art and used in the isomerization of pure hydrocarbons, and their detailed description here will not serve any'useful purpose.

The above-described combinationv of process visomerization is low and the life of the isomerizationcatalysts is appreciably increased. These advantages are due to a, muchmore emcient and clean-cut. isomerization treatment Aproducing large amounts of doubly branched hydrocarbons such as neohexane and are, in turn, made possible by the above-described specific treating steps, to

bound by any theories, it is our belief that the generally unsatisfactory results hitherto obtainedl in attempts to produce base stocks of the type described by subjecting typical straight run gasoditions to avoid excessixe degradation, while at 35, a maximum improvement in octane number. v

lines to known catalytic isomerization processes are due to the composition ofthe majority of straight run distillates and, more particularly, to

the type and concentration of hydrocarbons o1l naphthenic character.' The naphthenic hydrocarbon.; normally present in appreciable concenv trations in such distillates, it is found,play an important role in such isomerization treatments and materially affect the results obtained. One of the 10 unexpected properties of these naphthenic hydrocarbons in such isomerization treatments is their ability in small. concentrations to repress the degradation. of the paraffin hydrocarbons which normally takes 4place to a substantial extent. This is illustrated by the following experiments: l

`Normal hexane containing various concentrations-of methyl cyclo-pentane was prepared and subjected to a catalytic isomerization treatment exactly as described above for the examplesgiven in Table I, except. that the contact time was in l each case 30 minutes and the amount of hydrogen chloride charged was about 4.2%. Since the primary degradation product observed in the degradation of the normally liquid paraiiin hydrol carbons is isobutane, the production of this hydrocarbon can be used as a measure ofthe extent of degradation. The precentages of'isobutane found in the products. of the isomerization of these -hexanes-containing various amounts of methyl cyclopentane were as follows:

Table -II Concentration of methyl Isobutane cyclopentane Per cent Per cent In the' case of the isomerization of normal pentane'at a temperature of 72 C. and contact f' time of 10 minutes, extensive degradation was tof tally repressed 'by the addition of as little as 3.1% of methyl cyclopentane.

It isseen from the above thatwith respect to the suppression of degradation, the presence of a certain 'amount of naphthenic hydrocarbons is apparently highly desirable. It is found, however, that naphthenic hydrocarbons exert certain ,detrimental effects and that for optimum results 55 the concentration of naphthenic hydrocarbons is quitelow and, in general, much lower than the concentrations normally present .in available petroleum fractions. 'Ihus,it is found Vthat while v naphthenic --hydrocarbons greater than small optimum amounts eectively in concentrationsv repress degradation of the paraffin hydrocarbons they materially sliertenv the active life of the cata-y lyst.v This vleads to the unexpected finding-that the catalyst life is not necessarily dependent upon the amount of degradation as has been hitherto whichthe gasoline fraction is subjected prior to V'm the isomerization of branched' chain paraiiins" to 7 isomerization. While we do not desire to 4be the highy octane doubleffbranched isomers. This is illustrated by the following experiments:

Normal hexane in admixture with various con- .centrations of methyl cyclopentsmel swas prepared and subjected to a catalyticisomerization as described above for the examples given in Table II. The percentages of the charge converted to neohexane (2,2-dimethy1 butane) and the percentages of neohexane in the hexane fractions were The relatively poor increase in octane number obtained when treating stocks containing the usual excessive concentrations of naphthenic hydrocarbons is also partly due to the isomerization of non-hydroaromatic naphthenic hydrocanbons such as methyl cyclopentane, etc., to their hydroaromatic isomers with a consequent depreciation in octane number which partly offsets the increase in octane number eilected by the isomerization of the paraffin hydrocarbons. The overall effect of the naphthene concentration upon the increase in octane number obtained is illustrated by the following experiments:

Normal hexane in admixture with various concentrations of methyl cyclopentane was prepared and subjected to a catalytic'isomerization as described above for the examples given in Talble III. The increases in C. F. R. octane number obtained with the various mixtures were as follows:

Table IV Increase in F. R. octane number Concentration of methyl cyclopentane The results tabulated in the above Table II, III and IV are plotted graphically in the attached graph, Figure I, II, III, and IV forming a part of the specification. From these figures the effects of naphthenic' hydrocarbons upon the isomeriz'ation of hexane are readily apparent. It is believed upon this and other evidence that the effects of this naphthenic hydrocarbon aswell as other naphthenic hydrocarbons in the isomerization of petroleum distillates comprising a mixture of such hydrocarbons is analogous.

The ability of the above-described process to produce high octane base stocks of the class described irom the typical distillates-such as shown in Table I above is, We believe, due largely to the extent of removal of the naphthenic hydrocar-bons normally present in such distillates. Molybdenum oxide, it is found, when employed under the above-described hydroforming conditions possesses the unique ability to simultaneously isomerize non-hydroaromatic naphthenic hydrocarbons and convert them to aromatic hydrocarbons. Since under these conditions the isomerized non-hydroaromatic naphthenes are converted to aromatic hydrocarbons, the isomerization reaction is favored with the result that the concentration of naphthenic hydrocarbons is reduced to a low and apparently optimum concentration. It is also, of course, possible and probable that other effects of the treatment with a molybdenum oxide catalyst contributetoward the improved results. For example, certain of the parailin hydrocarbons may undergo mild isomerization which facilitates subsequent treatment with th-e Friedel-Crafts type metal halide isomerization catalyst.

While the process of the invention is primarily directed to the production of improved paraffin blending stocks in a more economical manner, it is also to be noted that the process allows the yproduction of a'maximum yield of octane barrels per given quantity of gasoline treated. Thus, the aromatic hydrocarbons removed after the treatment of the molybdenum oxide catalyst constitute a high octane material suitable for lblending in motor'fuels or for other uses. Also, if desired, a maximum yield of gasoline having a maximum octane number may be produced by blending the aromatic fraction with the isomerized parainic blending stock. The resulting product may not however, have all of the desired properties of the paraflinic Iblending stock to the production of which the process of the invention is particularly directed but under certain circumstances the use of the aromatic fraction in whole or in part may be warranted.

We claim as our invention:

1. A process for the production of high octane parafiirn'c blending stocks suitable for use in aviation gasoline from substantially saturated naphthenic petroleum fractions of gasoline constituents containing non-hydroaromatic naphthenes and parailns which comprises treating said naphthenic petroleum fraction under hydroforming conditions with a molybdenum oxide catalyst, removing aromatic hydrocarbons from the hydroformate, and treating the substantially aromaticfreeremainder with a Friedel-Crafts type isomerization catalyst vunder isomerization conditions to produce a saturated parafnic stock of improved. octane number.

2. A process for the production of high octane paralnic blending stocks suitable for use in aviation gasoline from substantially saturated naphthenic petroleum fractions of gasoline constituents containing non-hydroaromatic naphthenes and lparaiins which comprises treating said naphthenic petroleum fraction with a molybdenum oxide catalyst at a temperature between about 425' C. and 550 .C., a pressure between about 1 'and 60 atmospheres, apartial' pressure of hydrogen between about l and 50 atmospheres and a .liquid hourly space'velocity of about 0.1 and 2.

removing aromatic hydrocarbons from the thustreated distillatek and treating the substantially aromatic-free distillate with an aluminum chlorideV isomerization catalyst at a temperature between about 50 C. and 200 C., at a pressure between about 1 and 50 atmospheres, at a contact time between about 10 and 30 minutes under. a partial pressure of hydrogen between about 1 and 20 atmospheres, and in the presence of a partial pressure of hydrogen chloride between about 1 and 20 atmospheres to produce a saturated hydrocarbon distillate of improved octane numlber.

3. Process according to claim 1 wherein the molybdenum oxide catalyst consists essentially of an activated alumina impregnated with from about 4% to 30% of molybdenum oxide.

4. Process according to clailr` 1 wherein the isomerization catalyst consists essentially of a molnmixmrcof'nnulmudescomvrisincfree :umril'mtion uw comida a aluminum chloride. muitenmixtreofmel hslid free 5.Proccsaccordinsltoclaim2whereithe aluminum chloride.

moiyb'denum catalyst essenticliy of an activated alumina. impregnnbed with from-chant 5 -CHES'I'ERCgCRAWFORn 4% to 30% of molybdenum oxide. DONALD n FULLER. 6. Proceas-accordinstoclaim2whereintheiSO-- BERNARD S. GER.

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