US2416479A - Hydrocarbon conversion process - Google Patents

Description

Feb. 25, 1947. cQ J. HELMERS 2,416,479,

l HYDROCARBON CONVERSION PROCESS Filed May 27, 1943 C.J. H ELM ERS ATTO Patented Feb. 25, rl94'7 `HYDROCARBON CONVERSION PROCESSf Carra. nemers, Bartlesvillaokla., assigner-itc l ,y Phillips Petroleum Company, acorporation of,

v Delaware Application 2'7, ,1943,seriaiivd., 488,757

This invention #relates ment of hydrocarbon oils toproduce lower boiling products including gasoline.` In kone of its `more specific aspects, the invention embodies an improved process for the catalytic cracking of hydrocarbon oils to produce'gasoline,'wherein improved gasoline-yields are obtained by segregation offreshfeed and/ or recycle stocks according to optimum response to cracking conditions in two or moreindependently controlled catalytic treating zones. l

It is the primary objectfof the instantinvention to obtain improved Vyields, of hydrocarbons boiling within the gasoline Yrange by the cracking of hydrocarbon oils in the catalyst material. v 5

Another important object of myfinvention is the more complete catalytic conversion of hydrocarbon oilsfto other hydrocarbons of preferred composition and high quality than hasbeen economically feasible heretofore. l

This invention hasfor a further important object the catalytic cracking ofhydrocarbon gas oil in a manner whereby gasoline boiling range hydrocarbons of renhanced antiknock character-V istics are produced economically and efciently.

In the catalytic 4crachingof hydrocarbon voils ofthe nature of gas oil to produce maximum yields of high `.octane gasoline, 'the optimum-per pass conversion isvjordinarily limited:v by factors which vary with the relative depth of conversion. These factors include' the quality of the gasoline product1 the loss'tafixed gases, and the amount ofcarbonf deposited on the catalyst. .The latter two arejof particulariimportance from an economic standpoint as affecting process yields and thefrequency-and length of catalyst reactivation periods. In most cases, therefore,` the per pass conversion is adjusted to give van economic' balance between increased gasoline production and operating costs, with values of from about'25 to about bo'pervcent conversionoften selected for various feed stocks. c i

"Ihe production of additional amounts of gasoline of lsimilar quality from unconverted feed stock may involve further treatmentby recycling arrangements. The recycling of unconverted material to the original catalytic zone,v howevenis often unsatisfactory because of the decreased respense of 'the ence-treated o'ii to *the originar cracking conditions'ian'dla resultant-decrease in overallconversi'on, For tliisreason; simple recyciingfof unconverted material may result in reducedprocess efficiency.

` Itlmsbeenlfproposed 'to' pass .total unconverted feedfst'ock tofgoneprx more" successive` stages of to the catalytic treatpresence of suitable Y,

1 claim. icl. isc- 52) catalytictreatment atprogressively more severe cracking'conditions-in order to maintain the per- Such an operation, however,v

pass conversion. may result in products of decreasing qualityas passage of the more refractory cycle stock to thermal-cracking units where conversion is effectedl tol a generally lower qualitygasolineproduct but withless difficulty from coke andtar formation.-

v It has nowbeen discoveredthat the increased refractory characteristics of catalytically cracked cycle gasoil stocks areldue inlargepart to the formation and, under conventional recycling con' "ditions, therapid pyramidingof a relatively-nar-sV I have also found thatthe building upv ofthe quantitiesof this refractory fraction inthefeed stock ,to catalytccracking through a recycling operation reduces' proportionately the per pass conversion at optimum conversion conditions'. On the otherhand, when conversion is maintained by laltering conditiolflS,v there are yuneconomic' losses toy gasjandcoke ofthev less refractorycome,

ponents of both fresh feed andA recycle oil- 'I1 have additionallydiscovered that improvedv operation 'of a' catalytic cracking system and higherproduct quality arev obtained by a rela-l tively coniplete A segregation of thev refractory light gasoil fraction as it appears in fresh' feed, stocks" and/or aslit is formed in recycle gask oil stocks."

The process steps which achieve thissegregation and furtherl accomplish efficient conversion to high octane gasolineare described hereinafter.

In one specific embodiment the invention comp-risesthe followinggsteps: (l) `a vsuitable gas oil x feed is catalytically'cracked in a first cracking zone to produce partial conversiontcgasoline and lighter products;-(2) v,the reactionfproducts are continuously fractionated to separate heavy,

intermediate and light fractions all higher boilingthan the desired gasoline end `point while the gasoline andv lighter 'products are removed asproducts of the process; (3) the relatively narrow boiling rangey intermediate fraction` of thellnversion products being passed to the fractionation and/on recoverywsystem provided fori-the first;

` heated to conversion temperature. then passthrough a line 4 to a catalytic reactor i 5. Suitable conversion conditions are maintained in the reactor, and further quantities of super--` light gas oil fraction is recycled to the rst cata- 4 lytic zone along with the heavy recycle stock.

These Vas well as other process steps are illustrated on the annexed drawing which is a diagrammatic representation of a suitable arrange- 1 ment of processrequipment, In the drawing, gas oil feed entering by a line Iis preheated in a furnace 2, admixed with suitable diluent, such as superheated steam from aline 3, and furtherV The vapors heated steam may be added as a heat carrier l during conversion, as required. v The efuent from the reactor flows through a line 6to a separator 'I where tar may be removed through a line 8. The vapors then pass through a line 9 to a column IB which is the first section I VI of the gas oil fractionating equipment. From the bottom of column Il) a stream of heavy gas oil is 1 withdrawn through a line II while uncondensed material passes overhead through a line I2 to a second column I3. i This latter column is operated to separate gasoline vapors from higher boiling oil; The bottoms product. a light gas oil 1 fraction', is `removed through a line I 4, whiler a I lower boiling naphtha cut may also be removedas I a side stream from the column through a line I5.

The gasoline vapors passingoverhead in coll umn `I3 are condensedin passing through a line IB to an accumulator I'I from which water may be l withdrawn through aline I8. T he hydrocarbon condensate is stabilized in column I9 by separation of light gases overhead through a line 20.

The stabilized gasoline passes through aline 2| to a unit 22 for clay treatment (or its equivalent) before being sent to storage.

Thelight gas oil cutwhich is obtained as the bottoms product of column I3 is passed through a line 23 as charge stock to the second catalytic treatment. In this second cracking step the oil is preheated in a furnace 24 and passes through a line 25 to a reactorv 26. Superheated steam may lbeadded from, a line 21 to the oi1 vapors either Y j before or during the catalytic treatment. Other suitable diluents may be employed with or without steam Ywith proper adjustment of treating conditions and/or separation steps. Such dilu-4 I ents may include light refractory hydrocarbon gasesor hydrogen-containing recycle gases from the process or from associated operation. The

i of the gasoline and/orgases produced in the sec- Y ond stepY (as described hereinafter) the second .4 of the temperature in the separator 1. In Va similar manner a portion of the light gas oil in line I4 may be withdrawn through a line 33 to avoid accumulation of material too refractory to crack satisfactorily. The boiling range of the light gas oil is effectively controlled by the temperature at the top of column III and the location of the side stream vindicated by line I5 on column I3. While a single fractionating unit is indicated by column I3, this fractionation may be done in a plurality of separate columns, if desired.

Many alternative operations and modifications arepossible in carrying out the process illustrated by the flow diagram. While no attempt will be made to discuss all such modifications, two alternative operations are of particular interest in connection with the illustrated operations. First, the fresh gas oil feed instead of passing to the preheating furnace of the rst catalytic cracking step may pass rst to the fractionating system for wseparation into the diiferent boiling ranges. This is indicated by aline 3| through which a full range gas oil charge may pass (after preheating if de-V sirable) on the fractionating system which it en-V ters ahead of the separator 1. I The second modification comprises a prelimi` nary fractionation of an original wide boiling range gas oil charge in suitable fractionating equipment (not shown) so that fresh feed streams step wherein the less refractory stocks are treated under usually milder conditions. The reactor may be any suitable type other than the xed bed chamber illustrated, such as multitu- 4bular reactors, moving catalyst reactors and the like. reactor with provisions for the injection of a heat carrier diluent is often preferred because of the relatively higher temperatures and/or pressures employed and the fact thatr some other types of.. reactors have temperature and pressure lirnitay tionsV of a mechanical nature.

InV the practice of this invention vron variety of gas oil stocks from different sources, the

rst catalytic cracking treatment is ordinarily'A carried out at temperatures in the range of about( 800v to about 1100 F., depending on thecatalyst employed, the reaction time andther desiredper passV conversion. The pressures are'usually low superatmosphericpressures of about l5 to aboutv l 500 pounds gage and iiow rates may range from.

' about 1 to 10 barrels of oil per ton of catalyst' per step eiiiuent may wholly or partially be lpassed to a separate fractionating line 30. c v

The heavy gas oil fraction according to the I drawing is wholly or partially recycled through line' II to the gas oil charge line I to theA first I, catalytic step. Uncycled heavy oil may'bewithdrawn through a line` 34 Aor the volume and end point of recycle materialI controlled. `by CQllIfol system through a hour. as suitable for cracking of heavy hydrocarbons,

nesia preparations promoted kwith various metal oxides, synthetic silica-alumina compositions, Vor

the like;

The second catalytic treatment to which the,V light refractorygas oil is charged is usually carried out at somewhat higher temperatures than, the rst step, for` example, in the range of about1 -L 950 to about 1300 F. The type and activity ofY the catalyst employed as well as other conditions suchv asthe reaction time and theproportionsof- Various types of catalytic reactors i may be employed, particularly in the first catalytic In the second cracking step, a fixed bed ,a WideV The catalysts employed are VVthose knowny diluent employed Willfiin'manyicases determine tionsifnfethenefractm fraction funderlsfordinary the-optimum conversion,temperatura direct leCyClIZticcmditirms.J:v

Icomparative ...'terms,..the.refractory.,gas,4 011;`I Inmate cases. the octane ratings and yield-sofvv fraction requires higher?,crackingtemperatures J gasoline..prod1ced by catalytic crackingbf the and/0r longer.contacttimelandless..dilutionwth-- 5 ...heavy gas O-VSUkS-ale highestwhen the reac-n steam4 or `otliendiliient thantherlesarefractory, tiO'n time isreletively` shlt and the lerici/hof th stocksatvthesarneaconversion level..v For exam DlOceSs :perio'd islim'ited: vThus/in' treating heavy -f ple, yvhenemployingrthe Same catalysngf, modgasroil .fractions 'over: fbauxitievrcatalyst atiftemi.. I erateactivity .inbotlrcatalytic..stepstoprofilu.ce` Deratiis irl''th neighborhood-1 of 975to`10010 maximum,V quantities .oigasoh'ne the secon-d stenvv '10@moderat'e:pressuresnand 'relatively ihighlpropore" may be carried out at temperaturesfabout '50 to tions-fof steamnorliother diluents-'arefbenefiial' 100.F. above the .temperatures in the rst step, andi/thenoptimumiprocessiperiodimay Abe in-the with reduced proportions of steam diluent, or even lange'lofvaboutl tov'' hoursr 'I'h'ese-` conditions in the .absen ce 0f, a diluent produce. :suitable: per. lpass fconverson and Y 'aid dn s In certain instances, the light refractory gas 011,215 E(themaintienanceroflcatalyst aCtivity'bysuppres-f.. may be treated ,under'conditions of-ftemperature, sion offcarbon.fo'i'matlomH pressure and contact timey which ,producede'ep In contrast, the treatmentrofsthe light refracconversion to valuable normallygaseous product-srs' 1301's' gas Oil -SOCkS under Similar COndiiiOnS may and propcrticnately reduced 'yields' of gasolinezfactornnii'shfper'pass@conversionsubstantiallyfluei The. refractory ,nature and 10W coke forming ite'nd-" o 310W im i BCQHOmNOD'GmUm? Thse' TS'ICOTY" en'cy of the stock make possible conversioninzthe S'O'GKS i'eSl'Orld-wivaialyticprocessing With rela-- temperature range of 1100-1300 F." without untifefl-yldne-reactiowtimes; henca'condtions may economic formation 0f Carbon-and fixed gases-s0 includeffele'vated pressures,-= lo'wer charge yrates thattreactions favored bysuchshigh temperatures and/ori-smallr'prOpOriiOnS' Ofeiiilllents. The 1e^- mayebe,fcayyipd.Y out-L; I thfhigh: temperature- 25 yfraotoryigas oilstoclrsv are usually -lesssusceptiblef lowfpre'ssure'conversionisteps;` principal `products t0 Cai'ii'Orl fOImaf/iCn-and thewprocess periods 'may maybeflight olensr(ethylenefpropylene and oftenvbecXtendd-'fto sixhurs* or' more without* butylenes) y ,bulla-diene, cgdiolens and highly substantiali'depreciationffinlgasoline quality. evenv aromatic'gasoline Whichvmay'be utilized irrava. hfiujg-hifafrelatveiif!fdep'Der v'IJSiSSlfCOIlVeiSiCin ist" tion'gasolin'e.Jv Whenthe-light-gas -oil is treated 30Q@m1119615 'i undef.those.conditions.,the products (-J-tl,1e.secu FilTif/hel'mOrefbheflighteflfactl'y gaSO'SO'Ck ondfcatal-ytic stepareordinarily paSsedfto-sepaproduce gaiso'lme products ofl'substantauy :higher rate ,rfmctonatnrrequpment, forsegregation of. octane rating under conventional catalytic crack- Y .v l. ,n ,l 1 `ey. g'lotrliagiritlct geerelatively narrow boiling range refractory stock' 011 Chrg e d may be subjected to special 'conversion treatments The behavmnofwhe light renactorymgasv on: wherein the predominant concentration of cyclic fraction andthe' circumstanc'eslunder whichit'is loigpg alvlhlghdcapon'lydrof bum im@ .theunmeried porti@ of a filnmnge maticgasoline stocks-ornaat; pgdililcrm; o ai? gas,k 011 indicate that this fractlo'n contains rela- 1.26 d. S p C" o Spea" tivelydarge `proportions of 'jcyclc hydrocarbons. i Fnhwfor'e om discu .u b Tli'isis further sulfostantiated.bythegelatively low. M thalnfh. feren fragctidnssfqgsl Gi/iw 0550612 A..P ."I.' `gravity o'r the observedoiling range i Y A. andthe extensive cracking and/cr dehydrogenase. lksnpldg; atalytlc Crikmg are. utilized' tion .tovfo'rm hilgh octaneiaromatic .type gasoline essofutejfipreselt flrllx'tlcorrilneg fflizglge Wtrignegagrgpgateenege Ovemplaryfoperations will further illustratathe. which includes the totalrefractory fraction may Igil?Ccllsgiggtgolblvv Sctr fr the scope of tne'disclosure, no limitation to the p* .us n e p' p ous" specic stocks treating conditions orproducts of fractionationtof a gas oil stock,1the-iprincipa-l'porn said examnles.' intend-'d i tionsoi-fthe refractory 4material ordinarily;-boi1sv 55%` "1S e betweenfa'bout 47E-and 575? Fb Stillhigher con-n centrations .off refractory material may .often': bewobtainedfbygcloser-fractionation to aboilingrange'r AY gasoil cutafromWVest Texasfcrudeaoil had Eample I ofvabout 490 lto about 550 F.,but ingmostifoper,a'e` the ,following,gharacteristics` tions the Wider boiling 'rangeris .ientirelylsatisfac-f 6@ tween about 400 and 'about 475i F. is less refractoryandfisnsually convertedlto,gasolinein satis--- af''iiis 'S0Ck`WaS lcatalyticallycracked bKPaSSagG factory? yields under relafm/elyV @packingw OVeIbauX-lte Catalyst alt` F." LV1-)ragev Catalyst and/ordehydrogenation.conditionsn Similarly., temperature, "75'houndsgagepressure, anda 110WV the ,neavy .gas on fractioniboninebetween about, rate 0f 'about -b'arrels" pertonf .catalyst per 575 .to about.725? or higher maybe. relatively; 4 hOurn' The biLLwasiadmixed 'withv steamahead easily convertedtc `lowerboiling` products com-. v7c Of'h CatalystftOLpnoduce ,asteameoil .mollratiof prising. gaso1ine.gases..and a;substantial prop,r., of v,14:1. Tlflecpr VDass. Conversion.v to. products;V tionof materialize the above `described refractory '-f boiling lbelo'fw 40G-L Was ,about v,'25 ,Weight ..1per boiling range .of abut 475 tu 5'7 5f3 'F This formam, cent `of thesoilchargedjand therprincipaleproduct..,

fractionscausesthe rapidincrease, irilthe proper-75 number.

2,416,479 rf i The recycle gas oil from this rst pass operation had the following characteristics:

Gravity 1 A. y2P. 1 35.2 Boiling ranger. F-- 460-748 Volume per cent in fraction 475-'-5'75 F 36 A second-pass cracking operation on this recycle stock under substantially the same conditions gave a per pass conversion', only about 60 per cent of the rst pass conversion, with the octane rating of the butane-free gasoline slightly lower than that of the first pass gasoline. The gas oil residuum from the second pass treatment contained 50 volume per cent of the fraction boiling between 475 and 575 F. so that a third pass treatment at the original condition was impractical.

Example II A full range Mid Continent gas oil was cracked over bauxite catalyst at an average catalyst temperature of 985 F., 35 pounds gage pressure and a flow rate of 8 barrels per ton of catalyst` per hour. Steam was admixed with the oil charge prior to and during the catalytic treatment in an oil-steam weight ratio of 2:1. The optimum process period -was about 3 hours while carbon deposits amounted to about 1 weight per cent of the oil charged. Conversion per pass was 35 f weight per cent of the oil charged and the butanefree gasoline had an ASTM octane rating of 78.

The fresh feed and recycle stocks had the following characteristics: Y

Fresh feed ARecycle Y Vol. percent of fraction 475-575 F 38 I l Gravity A. P. I-- 36. 0 34. 5 Boiling range F-- 1150-750 Mil-7gg Light Heavy recycle recycle Gravity A. vP. I.. 37. o 31. 5 Boiling ralllge...V lG-620 550-740 Vol. percent in fraction 475575 F. 75 2 The heavy recycle stock was returned to the orig-v inal catalytic treatment along with an intermediate naphtha fraction boiling between about 400 and450 F, andY original conversion conditions were substantially maintained.

The light recycle stock was charged to a separate cracking unit where it was admixed with steam in an oil-steam weight ratio of 5:1 and passed over bauxite catalyst at an average catalyst temperature of 1010 F. and a iiow rate of 6 barrels Yper hour per ton of catalyst. The per pass conversion was 40 weight per cent of the oil charged during a six hour process period and the corresponding gasoline yield was 34 weight per cent. The gasoline `after stabilization to remove C4 and lighter material had ASTM and Research octane numbers of 80 and 92, respec,

tively.

Example III A full range Mid Continent gas oil similar to that of Example II was given a preliminary fractionation to produce light and heavy stocks.

These stocks were treated over bauxite catalyst under substantially identical cracking conditions at a temperature of 960 F. anda reaction time of 5 seconds. The following comparative results were obtained in three hour process periods with i steam-oil mol ratios in the charge of about 8:1.

Light gas Heavy gas oil oil Charge characteristics:

Gravity A. P. I.- 38 31 Boiling range F 450-635 540-740 Vol. percent in fraction 475-575 F 62 1 Per pass conversion, wt. percent of charge 18 Octane rating of B. F. gasoline (A. S. T.

M.) 79 77 Residuum characteristics:

Gravity 37. 1 30.1 Boiling range F" 467-637 450-740 Vol. percent in fraction 475-575 F 65 30 A second pass treatment at the same conditions of the unconverted heavy gas oil stock increased the refractory portion boiling between 475 and 575 F. to 42 volume per cent, while the per pass conversion dropped to about 20 per cent.

The unconverted gas oil from the cracking of I periods at a'catalyst temperature of 985 F. The

steam-oil mol ratio was reduced to 2:1 and the reaction time increased to 15 equivalent seconds at 960 F. The per pass conversion was 41 weight per cent of the gas oil charged with a gasoline yield of about 85 Volume per cent of the gas oil converted. The butane-free gasoline had ASTM and Research octane ratings of 78 and 90, respectively.

Example IV The light gas oil stock of Example IV was cracked by passage over bauxite catalyst at an average catalyst temperature of 1175 F., 6 pounds gage pressure and a contact time of 0.8

, second. The steam-oil mol ratio was 9:1. About 80"`weight per cent of the oil charged was converted to gasoline and light gases including large yields :of ethylene, propylene and butylenes, and butadiene equivalent to about 2 weight per cent of the oil charged. p The gasoline yield was about 30 weight percent ofthe oil charged and was 9 highly aromatic. The fraction boiling between 150 and 350 F. had an ASTM octane number of 89 and was segregated for treatment and employed as aviation gasoline stock.

I claim:

A process for the catalytic conversion of hydrocarbon gas oil to gasoline which comprises catalytically cracking a stream of gas oil in first cracking step at a temperature in the4 range of about 800 to 1,100 F., fractionating the eilluents thereof to thereby obtain a plurality of hydrocarbon fractions comprising a rst heavy fraction substantially boiling at a temperature above about 575 F., a second intermediate relatively refractory fraction substantially boiling within the temperature range of about 475 to 575 F., a third less refractory fraction substantially boiling within a temperature range of about 400 to 475 F., and a fourth fraction Within the gasoline boiling range; recycling said first and third fractions to said first cracking step, catalytically cracking 'said second fraction in a second cata- 19 lytic cracking step under more drastic cracking conditions than said rst step at a temperature in the range of about 950 to 1,300 F., and fractionating the eiiiuents of said second catalytic cracking step to obtain therefrom a fraction boiling within the gasoline range.

CARL J. HELMERS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,203,850 Tropsch June 11, 1940 2,235,133 Zimmerman Mar. 18, 1941 2,303,107 Benedict Nov. 24, 1942 2,327,510 Day Aug. 24, 1943 2,236,083 Alther Mar. 25, 1941 2,281,881 Keith et al. May 5, 1942 2,249,595 Benedict July 15, 1941

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