US2389342A - Catalytic dehydrogenation - Google Patents

Description

Nov. 20, 1945. CONN 2,389,342

CATALYTIC-DEHYDROGENATION Filed Aug. 10, 1942 CATALYST TOWERS 980 IO50F lo|5oo GAUGE PRESSURE MOTOR FUEL HOLVNOLLDVHJ HIGH OCTANE FRACTION TAR, ETC.

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F325;! zo 1 um: J QLL B 2 m INVENTOR 8 5 w. CONN Patented Nov. 20, 1945 CATALYTIC D-E-HYDROGENATIO-N Miller Wade Conn, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application August 10, 1942, Serial No. 454,311

1 Claim. (01. 196- 9) This invention relates to a process for preparing an improved high octane motor fuel or gasolinefrom any straight-run naphtha or gasoline stock, especially'the normally liquid hydrocarbon condensate known as distillate and obtainedby known methods of recovery from the hydrocarbon mixture naturally occurring in gas phase in so-called distillate wells'under very high pressures exceeding 1000 pounds per square inch. As is well known, this condensate or distillate maybe recovered from the well gas which is at a high pressure within the retrograde condensation range by lowering the pressure thereon and preferably by simultaneously scrubbing or contacting with an absorbent liquid. Methods of recovery of the condensate will be found for examplein Vaughan 2,133,774; Bays 2,135,319; Vaughan 2,151,248; Bays 2,156,234; Walker et al. 2,174,336; Vaughan 2,198,098; B'ays 2,212,143; Roberts 2,213,996; Buckley 2,242,173}

Farris 2,245,028; Walker 2,272,503; Walker 2,278,750.

This distillate is normally liquid and may be approximately water-white in color, or in some instances more orless colored, and may or may nothave been subjected to stabilization to remove the light end or wildness (C4 and lighter) so that the remainder willnot readily evaporate. Broadly speaking the distillate liquid has many of the properties of a medium to poor quality third-grade motor gasoline. It is practically water-white, sweet, non-corrosive, low in'sulphur and gum, and susceptible to tetraethyl lead for raising the octane number. Practically all of it shows 10 to 20% boiling above 400 F. That is, 80-90% of it is inthe gasoline boiling'range. Usually it has an initial boiling point in the neighborhood of 90 to 100 F. and is fairly well distributed over the gasoline boiling range. A summary of typical characteristics is given in the following tables:

2,262,744;. Bays TABLE A Summary of typical distillate characteristics Gravity, A P. I 54 to 70", average around 60 Reid vapor pressure TABLE B Distillation characteristics (A. S. 1'. M.)

I. B. P F 78-162 10% PL. 128-232 50% F 202-364 E. P. F 360-572 8 F 255-462 Per cent over 400 F. B. P. per cent 0- 38 This distillate is produced in large quantities on the Louisiana and Texas Gulf Coast, for example, at Corpus Christi,'Texas.

It is a serious disadvantage of the condensate just described that its octane number-is extremely low so that if it is attempted to use it as or in motor fuel it necessary to add tetraethyl lead thereto in substantial amounts in order to raise its octane number'to satisfactory levels. Other disadvantages are encountered 'in the use of the distillate as motor fueL-f 'Ihe distillate per se, of courseyis not suitable for use as motor fuel, and furthermore fractionation to give end-poin motor fuels results in pooryields of an inferior type fuel.

Other types of material known'as'straight-run naphtha or gasoline stock are subject to the same disadvantages as the condensate just described, and my invention-in its broader sense is applicable thereto. An' example-is straightrun gasoline made by the straight-run distillation of crude petroleum oil. Preferably the start- 2 ing material has been freed from butane and lighter hydrocarbons! It may contain substantial proportions of material higher boiling than. gasoline, such as kerosene, gas oil, and other components boiling up to 600 or 650 F. I may treat either'theentire distillate or naphtha or only that portion thereof which boils inthe gasoline range. 7

The principal object of the present invention is to provide a process for improving the motor fuel characteristics of the straight-run naphtha or gasoline stock and especially the condensate or distillate of the type described above. Another object is to manufacture an improved motor fuel of high octane rating from],the'c 0ndensate and thereby markedly reduce the quantity of tetraethyl lead that mustlbe added: Numerous other objects of the present invention will more fully hereinafter appear- The accompanying drawing portrays agram; matically one arrangement of equipment that has been found very satisfactory for carrying out the process of the present invention,

high octane materials will consist of the branched chain or isoparafiins and certain highpctane aromatic constituents such as benzene, toluene, etc 'l r 1}.1 j

The residual material comprises the low octane components and, where the original material was not within the gasoline range iasgwillgordinarily be the case, also contains a large proportion boil; ing over and above the gasoline range@ This fraction is then, after; admixture with recycle gases and with recycle stock as hereinafter describedfpassed to aprehea'ter where it is brought to the catalytic conversion temperature ranging frorn '9'00 to 1100-F., and preferably from 980 to 1650 and the heated stream is passed through a body of catalyst capable of efiectin the desired catalytic dehydrogenation and gas reversion of the-feed. The pressure in'the conversionstep will .usually range from about 10 to about 1500 pounds persquareinch gauge.

As catalystII usually-use granular bauxite, especially hard Arkansas bauxite, since it is comparatively inexpensive and easily obtainable and as effective a catalyst as any I have found. In-.

stead of 'bauxite, I may use chromium oxide, especially black unglowed chromium oxide, alumina, Activated Alumina, magnesia, catalysts of the type known as,silica alumina.prepared by co-precipitating aluminum hydroxide and hydrous silica followed by calcining or by treating a partially dried hydrous silica gel with an aqueous [solution of aluminum'salt such as aluminum chloride or sulfate followed by washing and drying or lprepared many other known manner, adsorbent Qclay such as fullers earth, acid-,

activated clay, charcoal, activated carbon, zirconium, oxide, either alone or in admixture with aluminum oxidebauxite impregnated with chromium oxidafbrucite, gypsum,.cadmium oxide, vanadium oxide, molybdenum oxide, tungsten oxide, zinc oxideycalic'he of the limestone type, so-called Houdry catalyst, etc. Any of the synthetic catalystssuch as alumina or zirconia may be rendered in porus formas 'by the process'of Schulze 2,112,931. In the. case of chromium o'xide, it may be present in intimate admixture with a difiiculty reducible oxide of aluminum, zir-' conium, titanium, silicon, thorium, boronor magnesium, as disclosed in Frey et a1. Reissue"21,911. It will alsobe understood that the metallic compound cataly ts may beisupporte'd on suitable ine'rt or active carriers; Moreover the catalysts mentioned-are not necessarily equivalents of one another.

"The reactions taking place in thecatalytic converter are not fully'understood. However it is established "that catalytic dehydrogenation and catalytic g'a's reversion '(polyform) ar'e'major reactions "occurring. The dehydrogenation "effects conversion of paraffins to olefins Some cyclization and aromatization mayalso accompany the dehydrogenation. Allo'f these reactions increase the anti knock 'r'ating of the hydrocarbon-mixture being treated. Theses i'evers'ion' isa processin which occurs a reaction between normally liquid hydrocarbons an normally gaseous hydrocarbons, and especially of Ca and C4 paraffins and olefins derived froin the catalytic efiiuent and that are recycled to the converter, to form materials of good anti-knock properties and in the gasoline boiling range. The catalytic as reversion which occurs simultaneously with the straight catalytic dehydrogenation involves reversion 'of-gaseous recycle with fresh feed, with unconverted recycle, and with polymerization products ordinarily formed in straight dehydrogenation. Due to the presence of substantial quantities of lighter material in the catalytic zon'e, increased yields are obtained. This gas reversion-is catalyzed by the catalyst employed.

In addition to the foregoing reactions, catalytic reforming also takes place to a considerable excracking and formation of lower molecular weight materials with incomplete recombination also take place so that normally gaseous hydrocarbons available for recycling are continuously formed anew.

Other reactions may also takeplace in the conversion zone, such as isomerization, polymerization and depolymerizati'on, hydrogenation, catalytic alkylation, etc. Where sulfur is present,

40 catalytic desulfurization also occurs.

By reason of the presence of recycle hydrogen in the catalytic step, hydroforming may also take place.

Preferably the conditions are so adjusted that the extent of conversion per pass through the catalytic converter is at 1east20% and does not exceed 40% by weight based on the weight of fresh feed tothe converter .plus recycled normally liquid material.

If desired any normally gaseous material separated inthe first fractionation Where unstabilized feed was employed, "and especially any Ca and C4 hydrocarbons such as propaneand butane, may be introduced as gas reactant to the catalytic conversion step.

The effuent from the catalytic conversion-zone is now fractionated into at least four fractions and preferably five or even six fractions.

The overhead or first fraction is normally gaseous and containsthe non-condensible gases, n'am'ely Czhydrocarbons andlighter, i. e., ethane, any ethylene, methane, and hydrogen. It may or may not contain thecaand C4 hydrocarbons, 1. e., butane, any butenes, propane and any propylene. This overhead fraction, whether or not it contains the Ca an'd C4 components, maybe further fractionated to separate essentiallylpure hydrogenjwhich' is especially suitable for recycling. Where the C3 andC-i components are removed in this-overhead fraction, the fractionation may also separate a fraction consisting of'the C3 and C4 materials, these materials beingpar ticularly desirable as recycle stock, in addition tol the hydrogen. 1 i

A second fraction of intermediate "boiling" point and boiling in the motor fuel range is separated. This fraction constitutes the principal product of the process, it being of very good anti-knock quality, much higher than thefeed orthe gasoline portion of the feed. This fraction may be used as such as motor fuel, with or without blending, but preferably is blended with the high octane fraction initially separated as described above, since these two fractions have difierent characteristics and compositions and mutually beneficial blendingproperties so that the resulting motor fuel is more rounded or balanced, more complex and a better fuel. The product is a high octane end poin motor: fuel and has improved lead susceptibility.

A third fraction consists of material heavier than the motor fuel fraction just described and comprises mainly unconverted material, incompletely converted material and other materials lighter than tars and suitable for recycling. This third fraction is recycled in toto to the catalytic conversion step for further conversion along with fresh feed from the first fractionation-step.

A fourth fraction comprising tars and the like heavy material undesirable for recycling is separated in the fractionating step under discussion and discarded from the system.

As pointed out above, if'desired, the fractiona tion of the conversion-effluent may be so conducted as to separate afraction consisting of the -C3 and C4 hydrocarbons which together with the pure hydrogen or a suitable portion thereof or with a portion of the entire C2 and lighter fraction is passedpto the catalytic step' as the gas reactant for the gasreversion reaction therein. Usually an excess of this Ca and C4 fraction will be formed and it will be necessary to bleed off a portion thereof continuously from the system.

As will be obvious, the fractionation of the catalytic eflluent may be conducted in one or a plurality of fractionators as necessary to give the desired separation. .So-called superfractionation may be employed, if desired, for giving extreme closeness of cuts.

Referring now to the accompanying drawing, the raw distillate is fed via line I into the first fractionator 2 (which may be one or several columns) where a cut containing the high octane materials is separated and passes out via line 3 whence it may be removed as such from the 'system via line 4, though it is preferably blended with the main product of the process to form motor fuel as will appear below.

The low octane and heavy cut formed in fractionator 2 passes via line 5, which traverses heat exchanger 6 where it is heated by the hot catalytic converter efiluent flowing in line H], through heater I where it is brought to conversion temperature preferably from about 980 to about 1050 F., and thence via line 8 into one of catalyst towers 9 which are filled with an appropriate solid catalyst.

The effluent from catalyst towers 9 passes via line I through heat exchanger 6 and thence into fractionator l I where it is fractionated into at least four cuts now to be described. A normally gaseous overhead (C4 and lighter) fraction is taken off via line 12 whence it may be split, a portion passing via line I3 as recycle gases into the feed in line and the balance passing via line I4 to fuel or any other use. A fraction in the motor fuel boiling range (from about 100 F. to about 400 F.), and which is the main product of my process, is taken off via line l5 and passed into admixture with the overhead cut from fractionator 2 to form the preferred motor fuel prod'uctbf my invention.- :A third fraction higher boiling than the fraction leaving via line l5 and comprising mainly unconverted or incompletely converted material is removed via line l6 and recycled to line 5 for further treatmentin catalyst towers 9.

Occasionally it will be found desirable to effect a further separation in fractionator H (which may be either a single? column or a series of columns as necessary" to'effect' the'desired fractionation) whereby the C3 and C4 are separated as a fractionby themselves, removed via line IT and a portion passedvia line l8 as the recycle gas into 1ine5', the excess leaving via line l9. This C3 and C4 fraction will be composed mainly of propane. and butanes though propylene and butylenes may also be present in significant proportions. When this Ca and C4 fraction is used as the recycle gas for effecting the gas reversion in towers 9, no, or only asmall proportion of the non-condensible gases (C2 and lighter hydrocarbons. and hydrogen) removed via line I2 will be recycled via line l3.

,Inany case, the excess gas leaving the system via line 14 may be passed to the flare, employed as fuel in the refinery, compressed and pumped back into the formation whence the distillate was recovered, or put to any other desired use.

It'is desirable to always recycle a substantial amount of hydrogen in order to protect the catalyst against premature carbonization and deterioration, especially in the initial portion thereof. Thus, an especially desirable way to operate is to recycle C3 and C4 material vialine l8 and to treat the C2 and lighter non-condensible fraction takenoif via line l2 (or a suitable portion of this fraction) in a unit 2| to segregate substantially pure hydrogen from the hydrocarbon content thereof, and recycle this essentially pure hydrogen in suitable amount to line. 5, the hy drocarbon gases so separatedleaving via line 22. However, hydrocarbons lighter than C3, such as ethane, ethylene and methane, may also be recycled, inwhole or only in part, if desired. 'Provision is made in fractionator II to withdraw as a bottom product via line 20 any accumulation of unconverted products, tars and the like not desirable to recycle to the system.

The advantages of the described mode of operation are many. Among them are: An overall inferior distillate or straight-run naphtha is initially separated into its high and low octane fractions for separate treatment, thereby eliminating the necessity or disadvantage of cracking or processing branched chain high octain hydrocarbons by processing catalytically only the low octane fraction. The process results in a 94-98% yield of motor fuel hydrocarbons with a much improved octane number as compared with a previous yield of about of motor fuel hydrocarbons having an inferior octane number when using simple fractionation of the distillate to recover only the gasoline range material. By recycling normally gaseous products derived from the fractionation of the catalytic effluent and also by recycling the heavier-than-motor fuel fraction similarly derived, under the conditions of temperature and pressure shown, catalytic reforming is obtained whichmay involve hydrogenation, catalytic reversion, catalytic cracking, catalytic dehydrogenation, catalytic alkylation and catalytic desulfurization or any possible hydrocarbon reactions to give better yields 01' a superior qualit motor fuel. The process gives a gself-contained, economically operated methodof converting fdis'tillate to a high grade the advantages of the invention. Ofthetotal 50 octane :raw condensate Y or distillate charged to asystem as described above approximately 180% falls withinthe motor fuel range and has an cetane number of around58, which with 1 cc. of tetra ethyl ;1ead.gives 72 octane motor lfuel. :By treatmentin accordance with the'foregoing so as to .obtain catalytic dehydrogenationand gas treversion of "the :low \octane out of this material, there .is obtained "an 85 to 90% yield of motor fuel which withl cc. of=tetraethyl leadgives an SOlQctanemateria-I. i

,The process :is applicable toany gasoline stock of the type known as fstraighterum that :is, to condensate or f distillate 'of the type described at length above. Ordinarily "the stock "treated comprisesa Predominant proportion of material in the gasoline range,1that from 'about 90 F. toabout 400 Fuor 425 F. Theastock may cover a range of from an initial ".point Lranging anywhere fromaabout 190 F. to about 200F. to an end point iranging anywhere "from -about .400 F. or 425 up to 2650 F iand ordinarily -.is .fairly well distributed over sucha range. Ordinarily the stock treated bythe process of'my invention consists essentiallyofparafl'ins most of which are unbranche'd and therefore very'low'in octane'rating. However, small amounts ofunsaturates, i.e., olefins, cyclo-o'lefins, 'etc., small amounts of arcmati'cs, cycloparaflin's, naphthenes,-etc., and substantial amounts of isoparafilns of high octane rating maybe present.

As used herein, by the term high octane I mean having "an octane number above 60 and usually at least 70 and by low' octane I mean having an octane number not over "60,Wlthllt using lead.

It "will be understood that the :foregoing disclosure is illustrative only 'andnot limitative, and

that the invention is to be taken as byzthe terms 'ofithe appended claim.

. A process which comprises subjecting a norw mally liquidcondensate obtained from the hydrocarbon :mixture occurring naturally in the gaseousphase in distillate 'wells under a pressure in excessof 1000 pounds ,persquare inch to fracticnation to separate a first fraction containing the high octane'components in the motor fuel boiling rangeand a second fraction containing the low octane and heavier components, passing said second fraction in the presence of recycled hydrogen and C3 and C4 hydrocarbons formedin this step in contact with'agranular bauxitecatalyst at a temperature within the range of approximately 900 to approximately l100 Fhand ataipressurewithin the [range of approximately 10 tosapproximately 1500 pounds ;per square inch gauge, .fra'ctionating athe efiluent from the .lastnamed-step to recover at least six fractions .as follows: a (1) 'a fraction consisting of essentially pure hydrogen, (2) a fraction containing'C2 and lighter :hydrocarbons, ('3) a fraction containing Ca and cifhydrocarbons, (4) a normally liquid fraction'containing the high octane components -in the motor fuel boiling range, (5) a second liquid fraction containing ithelow octane components and components heavier than those in the motor fuel boiling :range; includingunconverte'cl and (incompletely convertedrnormally .liquid components of the charge to said last -named step, and (6) a:fraction containing tars andheav-y material unsuitable for recycling, recycling :at least a "portion of said hydrogen :fraction (fractional) :andat least ;a portion of said C3 and C4 fraction .(fraction'3) to said catalytic conversion step lrecyeling said second liquid fraction (traction '5) to-said catalytic conversion step for additional conversion along with fresh'material, and blending rsaid first-named .high octane fraction with :said second-named high octane fraction (fraction .4) .togive a high octane motor fuel.

MILLER WADE 'COlllV;

limited only;

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