US2182536A

US2182536A - Process for conversion of hydrocarbon gases and oils and absorption system therefor

Info

Publication number: US2182536A
Application number: US238019A
Authority: US
Inventors: Gerald L Eaton
Original assignee: Gulf Oil Corp
Current assignee: Gulf Oil Corp
Priority date: 1938-10-31
Filing date: 1938-10-31
Publication date: 1939-12-05
Anticipated expiration: 1956-12-05

Description

DeC 5, 1939- G. l.. EATON PROCESS FOR CONVERSION 0F HYDROCARBON GASES AND OILS AND BSORPTION SYSTEM THEREFOR Filed oct. 31, 193s M n M .w o y m d, L y W Arm NWN M u@ AIM N |l m w QQ W. e mNMu H QN G QN Nwwimu do @EEA mzowmw uw. M w Wwf E@ Q NW1 @WHW QM \\N @n KX JWML@ mm. IQN a@ @A Wm @NIW $2@ O@ l|\ Nm. Dl .IJIvwlLiv I @W l--- l ---l uw@ El- .NN ||l| QN lll!! MOHM. NJN. ,-...s QW ---Il l 1.0m .mmmm Il- A@ Wmv -ii ||||1 ---www ww i-- www@ 1 Nm, n Il Ill will! l -li lli www Il: \|--I momz MMV u@ HHNU -lll nvm, ilmN Il- MN N N wzEQO @hun HH www@ W @NNW I Il :l ||I QM. ...mme WN Mohmzoommw Tm/ Il-- NW. QW al mQ\ |II\W Mmwww mmNHdmHm Mmwzmnzoo Wh. Il- -Ji Nmmmowmm .WQ WQ Patented Dec. 5, 1939 A UNITED STATES PROCESS FOR CONVERSION OF HYDROCAB- BON GASES AND OILS AND ABSORPTION SYSTEM THEREFOR Gerald L. Eaton, Osborne, Pa., assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of APennsylvania application octoberial, 193s, serial No. 2213.019,

2 claims. (o1. 19e-fs) y h oil, and the thereby enriched oil,vcontaining Ca My invention relates to processes of conversion of hydrocarbon gases and oils and absorption systems therefor.

During the past few years, a number of processes havebeen developed for thermal conversion of normally gaseous hydrocarbons, such as propane, butane and the corresponding unsaturated hydrocarbons, to normally liquid gasoline-like hydrocarbons useful as motor fuel. Such conversion may be accomplished in conjunction with the pyrolytic conversion of hydrocarbon oil to gasoline, or separately. In the former instance, of which the so-called gas reversion processes are typical, the gases subjected to conversion along with the hydrocarbon oil to be cracked may consist entirely of. gases produced in the system as a result of the decomposition of the hydrocarbon oil, but an increase in the amount and anti-knock value of the gasoline product may be secured by introducing gases into the system from an outside source. In straight gaspolymerization processes, all of the gaseous charge must, of course, originate elsewhere.

In either case, it has been found that only those normally gaseous hydrocarbons containing three and four carbon atoms per molecule should ordinarily be recirculated to the conversion zone. Hydrocarbons of higher boiling point represent gasoline constituents valuable as such, and recirculation thereof to the conversion zone simply tends to result in degradation of the gasoline. product. On the other hand, hydrocarbons containing less than three carbon atoms per molecule, such as ethane, are too refractory in character. Consequently, in all such systems it is desirable to remove Ca and C4 hydrocarbons from the products of conversion as completely and sharply as possible, so that the normally gaseous hydrocarbons recycled to the` conversion zone will contain all or substantially all of the Ca and C4 hydrocarbons, and yet be as free as possible from heavier and lighter hydrocarbons. t

One of the objects achieved in accordance with my invention is to secure substantiallyfcomplete and sharp recovery of C3 and C4 hydrocarbons, for subsequent conversion, in a system of the character set forth hereinabove, and more particularly one in which gases are introduced into the system from an outside source.

In accordance with my invention, the products leaving the conversion zone `of agas-polymerizing or combined oil-and-gas cracking unit, after separation of stabilized gasoline and heavier products therefrom. are subjected to contact in a primary absorption zone with a suitable absorbent and C4 hydrocarbons thereby absorbed, is delivered to the conversion unit for pyrolysis. Theremaining gases are then delivered to a second absorber where any C3 hydrocarbons remaining therein are removed by absorption in a second absorbent oil. This usuallyentails the absorption of a small amount of ethane.

Gases from an outside source, containing C3 and C4 hydrocarbons which it is desired to introduce into the conversion zone, are introduced into the system in a third absorber where they are scrubbed with a third flow of absorbent oil. This oil maybe similar in character to that employed in the two absorbers mentioned hereinabove. In this third absorber, C: and C4 hydro' carbons in the third absorber, vaporization of un.

desirably light material contained in the enriched absorbent from the second absorber occurs. The

combined flow of absorbent oil leaving the third which is introduced from an outside source intothe system to be cracked, and the' absorbent oil employed in the second and third absorbers com-f prises a distillate oil produced in the system, the enriched oil from these absorbers being recirculated into the system ata point subsequent to the,

conversion zone. In such a system, it will be obf vious that the normally gaseous hydrocarbons contained in the enriched oil leaving the'third absorber are not delivered directly to the conversion zone, although they are ultimately picked up v in the first absorber and .delivered to the conversion zone for crackingand polymerization.l l

One of the advantages of this type of system rerendered more eilicient.

My invention may, however, be applied to otherv specific types of units. such, for example, as a unit in which fresh oil from outside the system is available for use as an absorbing medium in the second and third absorbers as well as in the first absorber, or to a system in which heavy naphtha or gas oil is produced in such quantity that such oil (after enrichment in the second and third absorbers referred to hereinabove) is delivered to a second conversion zone, the vapors being combined with those from the primary conversion zone for fractionation and condensation and recovery of normally gaseous constituents therefrom. y

In addition to the improvements referred to hereinabove, other improvements in operative advantages and results will be apparent from consideration of the remainder of this specification.

In order that my invention may be more fully set forth and understood, I now describe, with reference to the drawing illustrating and forming part of this specification, a preferred form and manner in which my invention may be practiced and embodied. In this drawing,

The single figure is a more or less diagrammatic and conventionalized elevational view of apparatus for the thermal conversion of hydrocarbon oils and gases, adapted for the performance of my invention.

As shown in the drawing, this apparatus primarily comprises a cracking furnace I, a tar separator 2, a fractionator 3, a condenser-stabilizer Y 4 and absorbers 5, 6 and l, together with various conduits, pumps, valves and heat exchangers, to be described more fully hereinbelow. This particular system is especially suitable for the combined conversion of a light oil charging stock, such as naphtha or light gas oil, in conjunction with hydrocarbons containing three and four carbon atoms per molecule, in part derived from an outside source and in part produced in the system.

A mixture of the oil charging stock and normally gaseous hydrocarbons containing three and four carbon atoms per molecule, derived in a manner to be shown hereinbelow, enters the cracking furnace I through a line I0 and traverses an elongated pipe coil II of restricted cross-sectional area, wherein thermal conversion is effected at high temperatures and pressures. Various temperatures and pressures may be used, so long as they are :effective to promote a sumcient degree of conversion per pass of the charging stock, such as temperatures of from 900 to 1200 F. and pressures of from 200 to 3000 pounds per square inch. However, optimum results are secured by employing temperatures suiliciently high to effect an increased degree of conversion per pass of the oil, over that which could be obtained, without serious carbon deposition. if the oil were cracked alone in the same apparatus and under otherwise similar conditions of time and pressure, in the absence of normally gaseous hydrocarbons, all as set forth and described in the prior application of Povl Ostergaard Ser. No. 151,743, filed July 2, 1937, now Patent No. 2,135,014, dated Nov. 1, 1938.`

The hot products of conversion leaving the coil II then pass through a transfer line I2 having a pressure-reducing valve I3 into the tar separator .2, which mav be o more or less conventional design. It is usually desirable to check the reactions initiated in the coil II by introducing relatively cool oil to the products leaving the coil II. In the instance shown, such quenching is effected by delivering a owof relatively cool oil and normally gaseous hydrocarbons into the transfer line I2 through a quenching line Il. A similar flow of relatively cool material is also introduced into the tar separator 2 through a line I5. By virtue of this cooling and also by virtue of the pressure reduction effected by means of valve i3, tari-y constituents contained in the hot products o f conversion are caused to separate out and are withdrawn from the tar separator 2 through a valved outlet line I5.

In the instance shown, in which the main charging stock is a light oil which upon conversion produces a relatively small amount of gas oil, such conditions are maintained in the tar separator 2 that all gas oil produced in the system is ultimately withdrawn in the tar leaving the systemthrough the line lli. However, not all of the gas-oil constituents contained in the vapors traversing the tar separator 2 are initially condensed at this point; on the contrary, these vapors contain substantial quantities of uncondensed gas-oil constituents, which must be condensed later in the system.

These vapors leave the tar separator 2 through aline I'I and enter the lower portion of the fractionating column 3, the interior of which is provided with suitable cooling means such as a watercooled coil I8 and suitable gas-and-llquid-con tact devices, such as a plurality of bubble trays I9. By means of cooling supplied through the coil I8 or otherwise, condensation of gas-oil constituents is effected, the gas-oil condensate being withdrawn from the bottom of the fractionating column 3 through a line2II having a valve 2l. 'This condensate is withdrawn at a rather high temperature, which must be lowered before the condensate can be used as an absorbent, and its further disposition will be shown hereinbelow.

Vapors leaving the top of the column 3, and now free from constituents having boiling points above the desired gasoline boiling-point range, then pass through a line 22 into the mid-section of the combined condenser-stabilizer 4. While various means may be employed for this purpose, the stabilizer-condenser 4 illustrated in the draing, and which is preferred for use in this operation, is of that improved type set forth and described in the prior applications of Povl Ostergaard Ser. No. 52,717, filed Dec. 3, 1935, now Pat ent No. 2,134,926, dated Nov. 1, 1938, and Ser. No. 103,947, led Oct. 3, 1936, now Patent No. 2,134,836, dated Nov. 1, 1938.

This unit, as shown, comprises an upper or condensing section 25 and a lower or stabilizing section 26. Unstabilized condensate is withdrawn from the lower portion of the upper sec,

tion 25 through a line 21, is cooled in a heat ex-v4 changer 28 and is then delivered by a pump 2l through a line 30 into the upper portion of the condensing section 25, to serve as a cooling and reiiuxing medium therefor. Another portion of the unstabilized condensate condensed in'the upper section 25 passes through a down-flow pipe 3i into the stabilizing section 25, where rectification and stabilization occurs, assisted by l a re-boiler 32 which is in communication with the bottom of the stabilizing section 2i through a liquid line 33 and a vapor-return line u. Heat for the operation of the re-boiler 32 may be supplied in various ways, but in the instance shown this heat is supplied by hot gas oil leaving the bottom of the fractionator I, the gas-oil line 2l communicating with a heating coil 35 located in the re-boiler 32. stabilized gasoline is withdrawn from the re-boiler 32 through a line 88 having a valve 31 and passes out oi the system.

Vapors liberated in the stabilizing section 26 pass upward into the condensing section 25 through a vapor line 38. Vapors leaving the top of the condensing section 25, and consisting of hydrocarbons having up to fourcarbon atoms per molecule, pass through a line l0 to a condenser 4l and thence into a separator 42, from which uncondensed vapors and condensate flow through lines 43 and M, respectively, into the lower portion of the absorber 5.

Light gas oil or naphtha charging stock enters the system through a line 45 and is delivered by means oi a pump 46 and a line l1 into the upper portion of the absorber 5. As this oil ows downward through the absorber 5 it extracts from the gases and vapors passing upward therein hydro- 0 carbon constituents having three and four carbon atoms per molecule. Conditions within the absorber 5 are so maintained as to prevent absorption of substantial quantities of ethane in the absorbent oil, so that the enriched absorbent oil 3" leaving the bottom of the absorber 5 is substantially free from hydrocarbon constituents having less than three carbon atoms per molecule. This enriched oil then passes through a line I8 to a pump 49, which in turn delivers it through the une lo into the con n located within the cracking furnace i.

The gases remaining unabsorbed inthe absorber -5 pass through a line 5l to the lower portion of the absorber 6, where they are scrubbed d with a suitable absorbent liquid. In the instance shown, this liquid is provided by picking up hot gas oil leaving the coil of the re-boiler 32 in a pump 52 which delivers it through a line 53 to.

a cooler 54 and thence through a line 55 and a branch line 56 having-a valve 51 into the top of the'absorber 6 5 In order to insure complete removal of Cs hydrocarbons from the gases traversing the absorber 6, conditions are so maintained within'the 4;,vabsorber 5 that a small amount of ethane is also gases', cracking plant gases, natural gases orv other .gases containing substantial quantities oi' C3 and C4 hydrocarbons, enter the system through a line 66 communicating with the bottom of the absorber 1. A portion of the cool gas oil flowing through the line 55 is diverted into the upper part of the absorber 1 through a line 6I having a valve 62 and communicating with the line 55. As this oil flows downward through G0 the absorber 1, it absorbs C: and C4 hydrocarbons from the gases, such conditions being maintained as to prevent any substantial amount of ethane from being contained --.-in the enriched eilluent leaving lthe bottom of the absorber 1 t5 through a lirie 63. Enriched absorbent leaving the bottom of the absorber 5-is withdrawn therefrom through a line 6l, wherein is located a heat exchanger or cooler 65, andenters the absorber 1. This oil is introduced intolthe absorber 1 at T0 such a point that the composition of the introduced oil approximates the composition ofthe liquid flowing down through the Eabsorber 1 at the point of introduction, and sufilcient cooling is ordinarily provided in the coolei so that the 15 temperature of the introducedoilfwill also correspond rather closely to the temperature o! the oil flowing down through the absorber 1 at the point of introduction. Additional cooling for the absorber 1 may be provided by withdrawing a side stream from a trap-out tray 68 through a 5 line 81 and returning this side stream through a cooler 68, a line 88, a pump 13 and a line 1i back to a higher level in the absorber 1.

However, due to the heat of absorption oi.' normally gaseous constituents in the absorbent oil, 10 which is considerable on account oi.' the relatively small amount of absorbent oil ordinarily -employed, vaporization o! ethane contained in the enriched absorbent oil introduced from the absorber 6 is readily eiected, and the combined 15 absorbent oil leaving through the line 83 is substantially free from ethane, but contains lsubstantial amounts of hydrocarbons having three and four carbon atoms per molecule as well as any `heavier constituents which may be present in the gases introduced through the line 60.

A portion of the enriched absorbent oil from the absorber 1, leaving through the line 63, then passes through a branch line 15 having a valve 16 to a pump 11 which in turn delivers it through 25 the line I4 into the transfer line I2. as a cooling and quenching medium. The remaining portion of the enriched absorbent oil passes through a branch line 18 having a valve 18 to a pump 80 which in turn delivers it through the line I5 30 Ainto the tar separator 2 as a cooling and reiuxing medium. Normally gaseous hydrocarbons contained in the oil thus re-introduced into the system are eventually picked up in the absorber 5 and recirculated to the conversion coil Il. $5 n Gases remaining unabsorbed in the absorbers 6 and 1 are removed from the upper portions thereof through

lines

82 and 83, respectively, and pass out of the system through an exit line 84 having a pressure control valve 85. By means of 40 the valve 85, a suitable pressure is maintained 'throughout the `system yso that the condensation and .abs'o tion operations referred to hereinabove may be conducted without dilculty and without 7the necessity for refrigeration. Such pressure It will be understoodv that in referring hereinabove to normally gaseous hydrocarbons, I means those hydrocarbons which, in isolated w form, are'gaseous at atmospheric conditions of temperature and'pressure. lThey may, however. lsubsist in liqueiied form in various parts of the cycle, due to the lpresence of absorbent oil,` to

will ordinarily runirom to 500 pounds per pressure, or both. 55

While I have illustrated my invention hereinabove with reference to a speciiic embodiment and with reference to various operating and apparatus details, it will be understood by those Vskilled in the art that my invention is not limso ited to such details but may variously be practiced and embodied within the scope o! the claims hereinafter made.

What I claim is:

1. The process of obtaining gasoline of high a5 anti-knock value from petroleum oil, which comprises: subjecting a mixture of petroleumoil and hydrocarbons containing three and four carbon atoms per molecule to cracking in a heated conversion zone, fractionating the vaporous products '1o of conversion to recover gasoline, tar and intermediate condensate contacting the remaining gases in a rst absorber with said petroleum oil, prior to cracking the latter, to recover from said gases the bulk of the hydrocarbons containing 7s' three and four carbon atoms per molecule, and cracking the resultant mixture of oil and absorbed hydrocarbons as aforesaid. contacting gases leaving said rst absorber with a portion of said intermediate condensate in a second absorber to absorb substantially al1 of the propane contained therein, together with some ethane, contacting a second flow of hydrocarbon gases in a third absorber with a further portion of said' intermediate condensate to remove hydrocarbons containing three and tour carbon atoms per molecule therefrom, introducing enriched condensate from said second absorber into said third absorber and thereby vaporizing ethane from the enriched condensate by the heat of absorption in said third absorber, withdrawing condensate enriched with hydrocarbons containing three and n @massa If 35 four carbon atoms ,per molecule but substantially i'ree of hydrocarbons containing one or two carbon atoms per molecule from said third absorber, and recirculating said condensate into the cle at a point intermediatesaid heated conversion zone and the point of recovery of said intermediate co densate from said products of ctm-v absorber.

GERALD L. EATON.