US2224840A - Conversion of hydrocarbon oils - Google Patents

Description

Dec; 10, 1940. LE ROY G. sToRY y 2,224,840y

v y CONVERSION oF HYDRocARBoN oILs Filed July 24, 19:59

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LEROY G.STORY Rs ATTORNEYS Patented Dec. 10, 1940 UNITED STATES PATENT oFl-lcE i coNvEasloNzoF maocsaononls u Le Roy G. story, White Plains, N. Y., signor to The Texas Company, New York, N. `Y., a corporation of Delaware i Application July 24, 1939, lserali No. 236,106

claims.u (cl. 19a-9)J This invention relates to the conversion of hydrocarbon oils and has to'do particularly with a process of conversion for. the production of gasoline hydrocarbons suitable inthe manufacture of `5 motor fuel.

Broadly, the invention contemplates a process of conversion 4wherein hydrocarbon oils are sub= jected to catalytic cracking such that the products of. conversion contain a substantial amount i of a low-boiling isoparaiiin such as isobutane.-

The catalytically cracked oil is separated into a gas oil fraction and a naphtha fraction containing gasoline hydrocarbons, including isoparains. The gas oil fraction is subjected to thermal conversion in the presence cfa low-boiling isoparamn hydrocarbon such as isobutane separated from the naphtha produced'in the catalytic conversion.

The products of thermal conversion are likewise fractionated to separate a naphtha fracbons, and a gas oil fraction, which may be recycled. The naphtha fraction is stabilized to rey move low-boiling constituents which may include both normal and isoparaiiin hydrocarbons. The low-boiling isoparafn hydrocarbons are recycled through the thermalA conversion. operation, while the low-boiling normal paraffin hydrocarbons, as' 4well as any unsaturated low-boiling hydrocarbons. are recycled tothe catalytic conversion operation.

IMore specifically, the invention linvolves operating a catalytic cracking unit in commotion 'with a thermal cracking unit whereinA the isobutane produced from the catalytic unitis recycled to the thermal unit and the normal butane from the vthermal unit is recycledto the catalytic,

Y unit. The gas oil produced from the catalytic unit forms all or a portion of the gas oil charge to the thermal unit.

The catalystv employed in the catalytic unit 40 may be a metallic halide such as aluminum. chloride, although other catalysts having a cracking and isomerizing eiect may be used,l 'including phosphoric acid, antimony and molybdenum suliides, etc. The catalyst ymay be supported on an adsorptive solid such as activated alumina or silica, or acid treated clays, Hydrogenmay also -be used in the catalytic cracking step. l

In the cracking of oil with a catalyst such as aluminum chloride there is a substantial amount of isobutane evolved, whereas-in the conventional thermal cracking there is .a considerable amount of normal butane and 'butylenes produced. The normalbutane and the butylenc's may be used to advantage vin the catalytic cracking operationto obtain isomerization of the normal butane and polymerization of the butylenes. On the other hand, the isobutane is useful for injection into the thermal cracking operation.

As described in pending application Serial No. 274,514 iiled May 19, '1939 relating to improve-l 5 ments in Conversion of hydrocarbon oils it has been found highly beneficial to inject a comparatively high proportion of isobutane in the oil which is undergoing thermal conversion. Moren over, it is desirable that the isobutane so injected vl0 be in a relatively concentrated form; that is, relae tively free from normal butane and other gaseous hydrocarbons, When thermal cracking is carried out in the presence of isobutaneiin this many ner substantially no coke or tar formation occurs. 15 The reactions are not understood fully, but may include splitting of hydrogen from the isobutane and hydrogenation of the products which otherwise would tend to be converted into tar or coke. Substantial alkylation` by the isobutane, or products thereof, may occur. yIt is also possible'that the lsobutane has a direct or indirect inhibiting effect on reactions tending to form tar and coke.

The beneficial eiect of the presence of isobutane in thermal cracking is illustrated in the 25 case of cracking an East Texas gas oil having a gravityof 34.6 A. P, I. and a' boiling range of 454 F. to 704 F. In one instance a portion of this oil was cracked ata temperature of about 750 F. under a pressure of 4,150 pounds, with a ratio su oi isobutane to oil of about 6.721, Vthe time of re-s action being one hour. Under these conditions there was obtained about 31% of 410 F. end point stabilized gasoline, on the basis of the total stabilized liquid product, without any tar or coke 35 formation. f

In another instancea portion of this same oii was cracked under the same conditions of tems perature and time under a pressure o' 2,35@ pounds, but with an isobutane to oilratio of only 4o 45:1. Under these conditions the yield of 400 F. end point gasoline was only 10.6% and was ac companied with considerable tar and coke formation, indicating that the ratio of isobutane to oil was insunicient for this temperature. 45

Cracking the same oil under a temperature ci 825 F. and a pressure of6000 pounds with a ratio of isobutane to oil oi 20:1 produced :1.70% yield of 460 F. end point gasoline 'with nov coke or tar formation. 50? l The process is applicable to the cracking oi' Yvarious types of oils, either distillate or', residual..

as well as to the reforming oi naphtlla or certain constituents of naphtha.

The invention will be 'understood more iully from the following description read in connection with the accompanying drawing, which shows a diagrammatic sketch of one arrangement of ow for carrying out the process of the invention.

Referring to the drawing, the oil to be cracked as, for xample, a reduced crude, is charged l through a line I to a heating coil 2 wherein it drocarbons are removed in vapor form through pipe 1 leading to a fractionator 8. High-boiling hydrocarbons of a tarry nature are drawn off from the bottom of the separator S'through a pipe 9 and may be disposed of as ldesired.

` In the fractionator 3 the vg-asoline hydrocarbons and gaseous constituents are separated as a vapor fraction which is drawn off throughpipe I0 leading to an accumulator II. The higherboiling constituents comprising gas oil hydrocarbons are drawn off from the bottom of the fractionator through a pipe I2 leading to thethermal cracking unit, to which reference will be made later.

In the accumulator I I gaseous constituents, including ilxed gases and normally gaseous hydrocarbons, separate and are withdrawn through a pipe I3. The gasoline hydrocarbons'are drawn off through a pipe I4 to a stabilizer I5 operated under suitable conditions of temperature and pressure -to remove gaseous hydrocarbons, including C4 hydrocarbons' and lighter. The .operation may be regulated so as to retain in the gasoline any desired proportion of the C4' hydrocarbons in order to produce a fuelof the desired volatility and boilingl point characteristics. The stabilized gasoline is drawnv olf through a pipe IB.

The gaseous hydrocarbonsseparated in the stabilizer I5 are removed overhead through a pipe I1 and these gases together with all or a portion of the gases removed from the accumulator I I are introduced to a fractionator I 8` for the purpose of recovering C4 hydrocarbons, particularly normal butane and isobutane. This butane fraction is drawn oi from the bottom of the fractionator Ithrough a pipe I9 leading to another fractionator 20 wherein kit is resolved into-an isobutane fraction anda normal butane fraction.

uid form from the bottom of the fractionator 20 through a vpipe 2I and returned, all or in part, to

the pipe I leading tothe heater 2 .wherein thel Arecycled butane and any butylnes associated The mixture of hydrocarbons passing through the heater 25 is heated to a temperature which may range from about 650-1000 F. and under pressure which may range from 300-7000 pounds. Advantageously, the ratio of isobutane to oil passing through the heater 25 is maintained between about 2:1 and 50:1. The higher pressures and higher ratios of isobutane to oil rare ordinarily associated with the higher temperatures, while the lower pressures and lower ratios of isobutane to oil are more suitableV for the lower temperatures.

g It is contemplated that the more common conditions will be pressures of about 2000-4000 pounds and temperatures of about '100-850 F. with ratios of isobutane to oil of between about 10:1 and 30:1.

'Ihe reaction time will vary with the temperature and may range between about two minutes and two hoursA and, preferably, between about twenty and forty-five minutes.

The heated hydrocarbons are discharged from the heater 25 into a reaction vessel 21 wherein they are subjected to cracking conditions for the desired length of time. The high-boiling tarry constituents formed in the reaction vessel `are withdrawn from the reaction vessel through pipe 28. The lower-boiling cracked hydrocarbons are removed from the vessel 21 through a pipe 29 leading to a separator 30 wherein the gasoline and lighter constituents are separated from the higher-boiling gas oil constituents. 'I'he gas oil constituents are drawn o5 from the 1 separator through a pipe 3| communicating with the inlet to the heater 25.

The vaporized gasoline and gaseous hydrocarbons are drawn oif from the separator 30 through a pipe 32 leading to an accumulator 33. Gaseous constituents separating in the accumulator 33 are drawn of! through a pipe 34, while the gasoline hydrocarbons are drawn off through a pipe 35 leading to a stabilizer 36. I

Gaseous constituents, including all or a portion of -the C4 hydrocarbons, are removed from the gasoline in the stabilizer 38 and conductedv through -a pipe 31 leading to a fractionator 38.

Gaseous constituents removedfrom the accumulator through pipe 34 also may be passed through pipe 31 leading to the fractionator 38.

f The stabilized gasoline is drawn oir from the bottom of the stabilizer through a pipe 39. l

Inthe fractionator 38- 'gaseous constituents, commonly referred to as dry gas, are separated and discharged through the pipe 33 while a fraction comprising C4 hydrocarbons is formed and drawn oiI through a pipe -40 leading to the previously described fractionator 20. In this way the C4 fractionv is resolved intonormal butane' and isobutane, which are separately recycled,.as previously described.

Obviously many modifications and variations -of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

1. In the conversion of hydrocarbon oil for production of motor fuel, the steps comprising subjecting the'oil to catalytic cracking such that the products ofconversion contain a substantial amount of C4 hydrocarbons, including isobutane, separating .the catalytically cracked oil into a catalytic gas oil fraction and a catalytic naphtha fraction, removing from said naphtha fraction fractions respectively rich in normal and isobutane, recycling the normal butane fraction to the catalytic conversion step, and subjecting the catalytic gas oil fraction to thermal cracking in l the presence of said isobutane fraction.

2. In the conversion .of hydrocarbon oil for production of motor fuel, the steps comprising subjecting the oil to catalytic cracking such that the products of conversion contain a substantial amount of C4. hydrocarbons, including isobutane, removing from the catalytically cracked oil a catalytic gas oil fraction and a catalytic naphtha fraction, removing from said naphtha fraction a fraction comprising C4 hydrocarbons, subjecting said C4 'fraction to fractionation to, produce an isobutane fraction and a fraction comprising normal butane, subjecting the catalytic gas oil fraction to thermal cracking in the presence of said isobutane fraction, removing from the thermally cracked oil a thermal gas oil fraction and a thermal 'naphthafraction, separating C4 hydrocarbons from said thermal naphtha fraction, subjecting said C4 fraction to fractionation with the C4 fraction produced in the catalytic cracking step land recycling the normal butane produced ing step.

` 3. The method according to claimz in which the thermal, gas oil fraction is recycled throug the thermal cracking step. 4. The method according to claim 1 in whichr the thermal cracking is eiectedunder superat- 1 of a catalyst comprising in said fractionation through the catalytic crack-

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