US3096273A - Recovery of hydrocarbons - Google Patents

Description

July 2, 1963 J. HANISIAN ET AL RECOVERY OF HYDROCARBONS Filed Aug. 5. 1960 MOmDm :0 m 0 INVENTORS JOHN HANISIAN EDWARD H. LIGHTCAP J.H.Gllwm, 2am n. W

ATTORNEYS United States Patent aware Filed Aug. 5, 1960, Ser. No. 47,728 12 Claims. (Cl. 208101) This invention relates to the separation and recovery of hydrocarbons. In a particular aspect, it relates to the recovery of relatively low boiling hydrocarbons from admixture with relatively high boiling hydrocarbons.

"In the production of ethylene and other normally gaseous unsaturated hydrocarbons for use as starting materials in the manufacture of plastics and the like, various hydrocarbon feed stocks, such as ethane, propane and naphtha, are pyrolyzed, i.e., subjected briefly to high temperatures in the presence of steam, to produce an efliuent of pyrolysis containing a spectrum of components ranging from hydrogen, methane, ethylene, etc., to high boiling hydrocarbons, tarry substances and solids. Thus, in addition to ethylene, propylene and butadiene, the pyrolysis effluent contains a gasoline fraction, i.e., a fraction boiling generally in the C C range, which is useful as a motor fuel. Regardless of the method used to separately recover individual constituents and groups of constituents of relatively narrow boiling range from a pyrolysis efiiuent of wide boiling range, it is advantageous to first remove substantially all of the solids and the C and heavier hydrocarbons which include tarry substances from the efiiuent in order to avoid such accumulation of solid deposits in subsequent equipment as would force periodic interruption of the process for cleaning. As used herein, tarry substances include high molecular weight polymeric materials and other hydrocarbons in the pyrolysis effluent, heavier than about C which under the influence of heat or pressure or both readily tend to polymerize or otherwise deteriorate forming fouling deposits.

It is therefore an object of the invention to provide a process for recovering C and lighter hydrocarbons from a vaporous mixture containing the same, C and heavier hydrocarbons.

It is another object of the invention to provide a process for the removal of entrained solids from the eflluent of a pyrolysis process.

Still another object of the invention is to provide a process for quenching the effluent of a pyrolysis process.

A further object of the invention is to provide a process for separating C and lighter hydrocarbons from the effluent of a pyrolysis process.

A still further object of the invention is to provide a process for quenching and cleaning the effluent of a pyrolysis process and for recovery of enhanced yields of C and lighter hydrocarbons therefrom.

Various other objects and advantages of the invention will appear from the following detailed discussion and description.

The above objects are accomplished in accordance with the invention by the process which comprises contacting a vaporous mixture containing C and lighter hydro-carbons, C and heavier hydrocarbons in a scrubbing zone with a scrubbing liquid predominantly containing hydrocarbons heavier than C separating a scrubbed-gas fraction containing a major portion of the C and lighter hydrocarbons and a minor portion of the C and heavier hydrocarbons and a liquid fraction containing a major portion of the C and heavier hydrocarbons and a minor portion of the C and lighter hydrocarbons, separating C and lighter hydrocarbons from at least a portion of the liquid fraction, cooling and partially condensing the scrubbedgas fraction so as to produce a hydrocarbon condensate Nice containing the minor portion of C and heavier hydrocarbons present in the scrubbed-gas fraction and some C and lighter hydrocarbons, separating C and lighter hydrocarbons from at least a portion of the hydrocarbon condensate separated after the cooling and partial condensing step, and recovering C and lighter hydrocarbons uncondensed from the cooling and partial condensing step and as separated from the liquid fraction and the hydrocarbon condensate.

For a better understanding of the invention, reference is had to the following detailed discussion and description read in conjunction with the accompanying drawing which is a diagrammatic illustration in elevation of equipment suitable for practicing a preferred embodiment of the invention.

In the drawing a vaporized light naphtha feed is introduced to the process at 300 F. and at 79 p.s.i.g. through conduit 11. An equal weight proportion of steam is introduced through'conduit 12 and admixed with the naphtha feed in conduit 11. The steam-hydrocarbon admixture is introduced to pyrolysis furnace 13 wherein the admixture is indirectly heated to about 0 F. so as to pyrolyze the hydrocarbon and produce ethylene, propylene, butadiene, gasoline-boiling range materials, C and heavier hydrocarbons including tarry substances and solids. Heat for pyrolysis is generated by the combustion of fuel in furnace 13. The steam which is introduced to furnace 13 ,with the hydrocarbon feed reduces carbon deposition attendant to pyrolytic cracking. The hot pyrolysis effiuent is withdrawn from furnace 13 through conduit 14 and freezing the efiluent composition, and for recovery of substantial proportions of the heat in the pyrolysis efiiuent by generation of. steam.

In this regard, water is introduced through a conduit 17 into a steam drum 18 from which a portion passes through conduit 19 to the quench boiler 16 wherein steam is generated and returned through conduit 21 to drum 18. Additional steam is produced by passing water from drum 18 through a conduit 22 to indirect heat exchange coils located in the flue gas exhaust section of furnace 13. Steam thus generated is returned from furnace 13 to drum 18 via conduit 23. The total steam make of drum 18 which is at 400 p.s.i.g. is withdrawn through a conduit 24.

Pyrolyses, such as the one described, are preferably conducted at maximum temperatures between about 1100 F. and about 1600 F. and at relatively low superatmospheric pressures, normally between about 5 andlOO p.s.i.g. These conditions are normally used where the pyrolysis is conducted for the production of ethylene and other normally gaseous unsaturated hydrocarbons including olefins and vdiolefins, although some variation can of course be made.

The intermediate temperature to which the pyrolysis effluent is cooled in quench boiler 16 is preferably between about 500 F. and about 900 F. While it is desirable to 3 about 13 p.s.i.g. The feed to scrubber 27 in conduit 26 has the composition shown in Table I below:

TABLE I Pyrolysis Effluent in Conduit 26 In gas scrubber 27 feed gas from conduit 26 is directly contacted countercurrently with a relatively cold scrubbing liquid predominantly containing hydrocarbons heavier than C The scrubbing liquid is obtained and introduced as hereinafter described. Scrubber 27 contains suitable baffles, etc., by means of which efficient vapor-liquid contact is achieved. The cold scrubbing liquid substantially cools the effluent introduced through conduit 26 to about 225 F., scrubs out substantial amounts of the C and heavier hydrocarbons including substantially all of the tarry substances and solids in the efiluent. The temperature to which the pyrolysis eflluent is cooled in scrub ber 27 is important. The effluent should be cooled as extensively as possible from the standpoint of reducing extraneous cooling requirements and of transferring pyrolysis heat to the scrubbing liquid which, as a circulating medium, is subsequently and efliciently used to supply heat to the efiluent in the course of its fractionation. At the same time it is necessary to avoid condensing any of the steam present in the efiluent during its passage through scrubber 27 because steam condensate, if present, and the tarry substances in the scrubbing liquid would tend to emulsify and thereby present a difficult separation problem. Accordingly, the scrubbed-gas effluent from scrubber 27 should be at a temperature no lower than its water dew point which, at the steam to hydrocarbon ratios and pressures normally used in pyrolysis, is between about 170 F. and about 260 F.

The scrubbing method described is quite eflicient, particularly from the standpoint of tar and solids removal, and of cooling the pyrolysis efiiuent while avoiding an oilwater emulsion problem. However, the scrubbing process described tends to produce equilibrium concentrations of all the components in the system in both the liquid and vapor phases. Thus, a certain portion of the C and lighter hydrocarbons in the effluent will be lost from the vaporous fraction by absorption into the liquid fraction. Similarly, a certain portion of the C and heavier hydrocarbons including tarry substances will appear in the scrubbed-gas fraction. As will "appear hereinafter, these disadvantages are also overcome by the process of this invention.

A gas-liquid separation occurs in scrubber 27. The cooled scrubbed-gas fraction contains steam, a major portion of the C and lighter hydrocarbons originally pres ent in the pyrolysis eflluent and a minor portion of the C and heavier hydrocarbons. The warm liquid fraction contains a major portion of the C and heavier hydrocarbons, tarry substances and solids and a minor portion of the C and lighter hydrocarbons absorbed from the pyrolysis effluent. The Warm liquid fraction is withdrawn through conduit 28 at a rate of 73,280 barrels per stream day and filtered in filters 31 and 32 so as to separate the larger particles of entrained solids. Filter 29 is cleaned while filters 31 and 3 2 are in operation, enabling continuous filtration. The appropriate isolating valves are not shown. The warm liquid now free of at least the larger entrained solids is passed from filters 31 and 32 through conduit 33 by pump 34. A major portion of the warm liquid fraction is passed through a conduit 43 to an indirect heat exchanger 44. In exchanger 44 the liquid fraction which is at about 350 F. is substantially cooled by indirect heat exchange with liquid introduced into exchanger 44 through conduit 46 .and withdrawn through conduit 47. The material in conduits '46 and 47 which is a propane fraction from the lower portion of a propane-propylene fractionator (not shown) in the recovery process subsequent to the instant process is partially vaporized in exchanger 44. Warm scrubbing liquid, as a circulating heat carrier medium, can be used of course in indirect heat exchange to supply heat at any convenient point to the pro-duct gas, obtained from the instant process, for and in the course of its subsequent fractionation. By virtue of the heat exchanges done in quench boiler 16 and exchanger 44, substantially all of the useful heat originally in the pyrolysis efiluent in conduit 14 is recovered. The now cooled major portion of the warm liquid fraction is passed from exchanger 44 through conduit 48 at a rate of 72,500 barrels per stream day, further cooled to about F. by indirect heat exchange with cooling water in exchanger 49 and split into three streams in conduits 51, 52, and 53, having valves 54, 56 and 57, respectively, and returned to the scrubber 27 as a major portion or the aforesaid relatively cold scrubbing liquid. Conduits 5 1, 52 and 53 are provided to permit control of the point or points in the scrubber 27 to which the scrubbing liquid is introduced. This control assures efiicient gas-liquid contacting.

Control of the composition of the circulating scrubbing liquid is obtained by supplying a make-up gas oil stream, free of tarry substances, through conduit 58 to the cycled scrubbing liquid in conduit 53, and by withdrawing from the system a minor portion of the warm liquid fraction through conduit 35. Such make-up and purge results in low concentrations of tarry substances in the scrubbing liquid and reduces the total time that such heat-sensitive materials present in the scrubbing liquid are subjected to high temperature. In this way, interruption of operation for the purpose of removing fouling deposits formed by deterioration of heat-sensitive materials is avoided.

The extraneous scrubbing liquid supplied in accordance with the invention can be any hydrocarbon or mixture of hydrocarbon which is a free-flowing liquid at the conditions of operation; which is free of tarry substances so that the high temperatures encountered will not cause substantial cracking, polymerization or other deterioration; and which is preferably relatively high boiling so as to permit continuous circulation without loss through vaporization. Such hydrocarbon liquids are those boiling generally in the gas oil range. In the example here given, the gas oil used is introduced at a rate of 1000 barrels per stream day and contains principally C and heavier hydrocarbons, having an average boiling point of 544 F. The initial temperature of the circulated scrubbing liquid should be below the temperature to which the scrubbedgas fraction is to be cooled, preferably between about 10 F. and 50 F. below the temperature of the scrubbedgas fraction for efiicient heat transfer. The temperature of the warm liquid fraction is influenced by the rate of circulation of scrubbing liquid, which rate should be maintained high enough to keep the temperature of the warm liquid fraction below those at which appreciable vaporization or deterioration of the scrubbing liquid would result.

A minor portion of the warm liquid fraction withdrawn through conduit 33 and pump 34 is passed, as purge, through conduit 35 to filters 36 and 37, arranged for alternating operation, wherein substantially all of the entrained solids are removed. Complete separation of entrained solids is not practiced in filters 29, 31 and 32 because the passages in the circulating scrubbing system are large and no problems arise from the presence therein of relatively small particles of entrained solids. It is, however, necessary for the minor portion passing in conduit 35 to be substantially freed of entrained solids in view of the subsequent treatment of this minor portion. Use of filters 36 and 37 avoids, therefore, the need for fine filtration of the whole circulating scrubbing liquid in filters 29, 31 and 32. The filtered minor portion is passed in conduit 38 to the upper portion of a stripping tower 39 operated at about 14 p.s.i.g. Steam is introduced into the lower portion of stripping tower 39 which contains a number of suitable liquid-vapor contact trays. The steam strips C and lighter hydrocarbons from the purge stream introduced in conduit 38 so that the vaporous over-head from tower 39 withdrawn through conduit 42 constitutes recovered C and lighter hydrocarbons originally in the pyrolysis efliuent and lost therefrom incident to scrubbing in scrubber 27. A gas oil purge stream containing tarry substances is withdrawn from tower 39 through conduit 77 at 348 F., cooled by indirect heat exchange in ex changer 68 to 226 F., and discarded from the process through conduit 78. Operation in the foregoing manner permits a continuous purge of undesirable tarry substances from the process without the loss of C and lighter hydrocarbons.

The cooled and cleaned pyrolysis eflluent is withdrawn as a scrubbed-gas fraction from scrubber 27 through a conduit 59 at a rate of 172,035 lbs. hydrocarbon/hr., combined with the vaporous overhead recovered from stripping tower 39 in conduit 42 and cooled and partially condensed by indirect heat exchange with cooling water in exchanger 61. The cooling and partial condensing in exchanger 61 is such as to condense substantially all of the C and heavier hydrocarbons, steam and a minor portion of the C and lighter hydrocarbons. A sharp liquidvapor separation between about Q and C hydrocarbons is again precluded by the equilibrium character of the liquid-vapor separation. Separation of this mixture is effected in drum 62, operated at about 105 F. and 9 p.s.i.g., wherein a water layer and a hydrocarbon layer develop as well as an uncondensed fraction. Water is withdrawn from drum 62 through conduit 63 and discarded from the process. Hydrocarbon condensate is withdrawn from drum 62 through conduit 64 and is passed by pump 66 in conduit 67 to heat exchanger 38 wherein it is indirectly heated to about 250 F, The heated condensate from exchanger 68 passes in conduit 69 to the upper portion of a stripping tower 71 to which steam is introduced through a conduit 72. Stripping tower 71 which also contains a number of suitable liquid-vapor contacting trays is operated at about 9' p.s.i.g. The condensate delivered in conduit 69 is stripped by steam to recover C and lighter hydrocarbons as a vaporous overhead fr-action withdrawn from tower 71 through conduit 73. The bottoms fraction comprising C and heavier hydrocarbons is withdrawn from tower 71 and discarded from the process through conduit 79. This operation of tower 71 permits a continuous rejection of the C and heavier hydrocarbons contained in the scrubbed-gas fraction incident to the scrubbing in scrubber 27, without the loss of C and lighter hydrocarbons. The uncondensed portion of the scrubbed-ga fraction in drum 62 is withdrawn through conduit 74, combined with the vaporous overhead fraction from tower 71 in conduit 73, and delivered through conduit 76 as the principal product of the process. This product stream delivered at a rate of 164,891 lbs. hydrocarbon/hr. contains substantially all of .the C and lighter hydrocarbons originally present in the 6 pyrolysis efiiuent. It hasbeen cooled and cleaned of entrained solids and heavy hydrocarbons which might prevent fouling problems in the subsequent recovery process, and therefore, is in a suitable condition to be treated under high pressures and low temperatures for the recovery of ethylene, propylene, butadiene, gasoline,

etc. The product in conduit 76 has the composition shown in Table 11 below. I

TABLE II Product in Conduit 76 Component: Mol percent Hydrogen 16.5 Methane 22.7 Acetylene 0.5 Ethylene 29.0 Ethane 7.8 Methyl acetylene 0.3 Propadiene 0.1 Propylene 10.7 Propane 0.3 But-adiene 1.9 Butylene 3.2 Butanes 0.1 C s 2.5 C5S 3.4 C-fs 0.6 C878 CgS-C13S 0. 1 C sand heavier 0.0 100.0

scope of the invention. For example, instead of introducing steam into stripping towers 39 and 71, convention- -a1 reboilers could be used to produce stripping vapors. Also, instead of cooling the effiuent to an intermediate temperature in quench boiler 16, this step could be omitted and all the requisite cooling could be done in scrubber 27.

Likewise, the vaporous overhead fraction of tower 39 could, alternately, pass directly to product in conduit 76. Instead of passing the vaporous overhead fraction of tower 71 directly to product, it could be combined with the scrubbed-gas fraction in conduit 59 and thereby be subjected to an additional cooling and separation. The point at which each of the vaporous overhead fractions of towers 39 and 71 is recombined with the scrubbed-gas fraction is principally a matter of engineering expedience, i.e., in accordance with relative pressures. Generally the arrangement illustrated by tower 39 and conduit 42 is preferred because sharper separations result from repeated partial condensing and separation.

The foregoing example presents an embodiment of the invention in which several objectives are achieved: separation of higher boiling hydrocarbons, tarry substances and solids from the vaporous feed and cooling of the vaporous feed. It should be understood that the invention is of equal applicability embodied in any process in which a hydrocarbon vapor is directly contacted with a hydrocarbon liquid so as to accomplish only one or a few of the above objectives.

Various alterations in and modifications to the process of the invention may be made as will be evident to one skilled in the art without departure from its scope.

taining a major portion of said C and lighter hydrocarbons and a minor portion of said C and heavier hydrocarbons and a liquid fraction containing a major portion of said C and heavier hydrocarbons, tarry substances and a minor portion of said C and lighter hydrocarbons, separating C and lighter hydrocarbons from at least a portion of said liquid fraction, cooling and partially condensing said scrubbed-gas fraction, separating hydrocarbon condensate containing said minor portion of C and heavier hydrocarbons present in said scrubbedgas fraction and C and lighter hydrocarbons from said cooled and partially condensed scrubbed-gas fraction, separating C and lighter hydrocarbons from at least a portion of said hydrocarbon condensate, and recovering C and lighter hydrocarbons uncondensed from said cooling and partial condensing step and as separated from said liquid fraction and said hydrocarbon condensate.

2. In a process 'for the production of ethylene by the pyrolysis of a hydrocarbon feed in which the pyrolysis effluent contains ethylene, gasoline, tarry substances and solids, the process for recovering the gasoline and lighter materials which comprises contacting said pyrolysis efiiuent in a scrubbing zone with a hydrocarbon scrubbing liquid predominantly comprising hydrocarbons heavier than C separating a scrubbed-gas fraction containing a major portion of said gasoline and lighter mate- 'rials and a minor portion of said C and heavier hydrocarbons and a liquid fraction containing a major portion of said C and reavier hydrocarbons, said tarry substances and said solids and a minor portion of said gasoline and light materials, separating gasoline and lighter materials from at least a portion of said liquid fraction, cooling and partially condensing said scrubbed-gas fraction, separating hydrocarbon condensate containing said rninor portion of C and heavier hydrocarbons present in said scrubbed-ga-s fraction and gasoline and lighter materials from said cooled and partially condensed scrubbed-gas fraction, separating gasoline and lighter materials from at least a portion of said hydrocarbon condensate and recovering gasoline and lighter materials uncondensed from said cooling and partial condensing step and as separated from said liquid fraction and said hydrocarbon condensate.

3. A process for recovering C and lighter hydrocarbons from a vaporous mixture containing the same, C and heavier hydrocarbons which comprises contacting said vaporous mixture in a scrubbing zone with a hydrocarbon. scrubbing liquid predominantly comprising hydrocarbons heavier than C separating a scrubbedgas fraction containing a major portion of said C and lighter hydrocarbons and a minor portion of said C and heavier hydrocarbons and a liquid fraction containing a major portion of said C and heavier hydrocarbons and a minor portion of said C and lighter hydrocarbons, separating C and lighter hydrocarbons from at least a portion of said liquid fraction, cooling and partially condensing said scrubbed-gas fraction, separating hydrocarbon condensate containing said minor portion of C and heavier hydrocarbons present in said scrubbed-gas fraction and C and lighter hydrocarbons from said cooled and partially condensed scrubbed-gas fraction, separating C and lighter hydrocarbons from at least a portion of said hydrocarbon condensate, and recovering C and lighter hydrocarbons uncondensed from said cooling and partial condensing step and as separated from said liquid fraction and said hydrocarbon condensate.

4. A process for recovering C and lighter hydrocarbons from a vaporous mixture containing the same, C and heavier hydrocarbons which comprises contacting said vaporous mixture in a scrubbing zone with a hydrocarbon scrubbing liquid predominantly comprising hydrocarbons heavier than C separating a scrubbedgas fraction containing a major portion of said C and lighter hydrocarbons and a minor portion of said C and heavier hydrocarbons and a liquid fraction containing a major portion of said C and heavier hydrocarbons and a minor portion of said C and lighter hydrocarbons, passing at least a portion of said liquid fraction from said scrubbing zone to a first stripping zone, separating a vaporous fraction containing C and lighter hydrocarbons in said first stripping zone, cooling and partially condensing said scrubbed-gas fraction, separating hydrocarbon condensate containing said minor portion of C and heavier hydrocarbons present in said scrubbed-gas fraction and C and lighter hydrocarbons from said cooled and partially condensed scrubbed-gas fraction, passing at least a portion of said hydrocarbon condensate to a second stripping zone, separating a vaporous fraction containing C and lighter hydrocarbons in said second stripping zone, and recovering C and lighter hydrocarbons uncondensed from said cooling and partial condensing step and as the vaporous fractions of each of said stripping zones.

5. A process as defined in claim 4 where that portion of said liquid fraction which is passed from said scrubbing zone to said first stripping zone is a minor portion and where a major portion of said liquid fraction is returned to said scrubbing zone as at least a major portion of said scrubbing liquid.

6. A process for recovering C and lighter hydrocarbons from a vaporous mixture containing the same, C and heavier hydrocarbons and entrained solids which comprises contacting said vaporous mixture in a scrubbing zone with a hydrocarbon scrubbing liquid predominantly comprising hydrocarbons heavier than C separating a scrubbed-gas fraction containing a major portion of said C and lighter hydrocarbons and a minor portion of said C and heavier hydrocarbons and a liquid fraction containing a major portion of said C and heavier hydrocarbons, a minor portion of said C and lighter hydrocarbons and said entrained solids, filtering said liquid fraction to remove solids, returning a major portion of said filtered liquid fraction to said scrubbing zone as at least a major portion of said scrubbing liquid, passing a minor portion of said filtered liquid fraction from said scrubbing zone to a first stripping zone, separating -a vaporous fraction containing C and lighter hydrocarbons in said first stripping zone, cooling and partially condensing said scrubbed-gas fraction, separating hydrocarbon condensate containing said minor portion of C and heavier hydrocarbons present in said scrubbed-gas fraction and C and lighter hydrocarbons from said cooled and partially condensed scrubbed-gas fraction, passing at least a portion of said hydrocarbon condensate to a second stripping zone, separating a vaporous fraction containing C and lighter hydrocarbons in said second stripping zone, and recovering C and lighter hydrocarbons uncondensed from said cooling and partial condensing step and as the vaporous fractions of each of said stripping zones.

7. A process for cooling and recovering C and lighter hydrocarbons from a relatively war-n1 vaporous pyrolysis effluent containing the same, C and heavier hydrocarbons which comprises contacting said relatively warm vaporous efiluent in a scrubbing zone with a relatively cold hydrocarbon scrubbing liquid predominantly containing hydrocarbons heavier than C1 separating a cool scrubbed-gas fraction comprising a major portion of said C and lighter hydrocarbons and a minor portion of said C and heavier hydrocarbons and a warm liquid fraction containing a major portion of said C and heavier hydrocarbons and a minor portion of said C and lighter hydrocarbons, cooling a major portion of said Warm liquid fraction, returning the thus cooled portion of said warm liquid fraction to said scrubbing zone as at least a major portion of said relatively cold scrubbing liquid, passing a minor portion of said warm liquid fraction from said scrubbing zone to a first stripping zone, separating a vaporous fraction containing C and lighter hydrocarbons in said first stripping zone, further cooling and partial condensing said cool scrnb'bedrgas fraction, separating hydrocarbon condensate containing said minor portion of C and heavier hydrocarbons present in said cool scrubbed-gas fraction and C and lighter hydrocarbons from said further cooled and partially condensed scrubbed-gas fraction, passing at least a portion of said hydrocarbon condensate to a second stripping zone, separating a vaporous fraction container C and lighter hydrocarbons in said second stripping zone, and recovering C and lighter hydrocarbons uncondensed from said further cooling and partial condensing step and as the vaporous fractions of each of said stripping zones.

8. A process as defined in claim 7 in which said relatively warm vaporous pyrolysis effiuent further contains steam and in which the temperature of said cool scrubbedgas fraction is maintained above the dew point of steam whereby said warm liquid fraction separated in said scrubbing zone is substantially water-free.

9. A process as defined in claim 7 in which the temperature of the cool scrubbed-gas fraction is above about 170 F. and the temperature of said relatively cold scrubbing liquid contacting said pyrolysis effiuent in said scrubbing zone is initially between about 10 F. and 50 F. cooler than the temperature of said cool scrubbed-gas fraction.

10. A process for recovering C and lighter hydrocarbons from a vaporous pyrolysis efiluent containing the same, C and heavier hydrocarbons and entrained solids which comprises contacting said vaporous effluent in a scrubbing zone with a hydrocarbon scrubbing liquid predominantly comprising hydrocarbons heavier than C and obtained as described below, separating a scrubbedtgas fraction containing a major portion of said C and lighter hydrocarbons and a minor portion of said C and heavier hydrocarbons and a liquid fraction containing a major portion of said C and heavier hydrocarbons, a minor portion of said C and lighter hydrocarbons and said entrained solids, filtering said liquid fraction to remove solids, combining a major portion of said filtered liquid fraction with a hydrocarbon liquid stream predominantly comprising hydrocarbons heavier than C and free of tarry substances, passing said combined stream to said scrubbing zone as the above-mentioned scrubbing liquid, passing a minor portion of said filtered liquid fraction to a first stripping zone, separating -a vaporous fraction containing C and lighter hydrocarbons in said first stripping zone, cooling and partially condensing said scrubbed-gas fraction, separating hydrocarbon condensate containing said minor portion of C and heavier hydrocarbons present in said scrubbed-gas fraction and C and lighter hydrocarbons from said cooled and partially condensed scrubbed-gas fraction, passing at least a portion of said hydrocarbon condensate to a second stripping zone, separating =a vaporous fraction containing C and lighter hydrocarbons in said second stripping zone, and recovering C and lighter hydrocarbons uncondensed from said cooling and partial condensing step and as the vaporous fractions of each of said stripping zones.

11. A process for cooling and recovering C and lighter hydrocarbons from a hightemperature vaporous pyrolysis efiluent containing the same, C and heavier hydrocarbons and entrained solids which comprises cooling said high temperature vaporous pyrolysis efiluent by indirect heat exchange to an intermediate temperature, directly contacting the partially cooled efiluent in a scrubbing zone with a relatively cold hydrocarbon scrubbing liquid predominantly comprising hydrocarbons heavier than C and obtained as described below, separating a cooled scrubbed-gas fraction containing a major portion of said C and lighter hydrocarbons and a minor portion of said C and heavier hydrocarbons and a warm liquid fraction containing a major portion of said C and heavier hydrocarbons, a minor portion of said C and lighter hydrocarbons and said entrained solids, filtering said warm liquid fraction to separate solids, cooling a major portion of said filtered liquid fraction, combining said cooled major portion of said filtered liquid fraction with a hydrocarbon liquid stream predominantly comprising hydrocarbons heavier than C and free of tarry substances, passing said combined stream to said scrubbing zone as the above-mentioned relatively cold scrubbing liquid, passing a minor portion of said filtered liquid fraction to a first stripping zone, separating a vaporous fraction containing C and lighter hydrocarbons in said first stripping zone, further cooling and partially condensing said cooled scrubbed-gas fraction, separating hydrocarbon condensate containing said minor portion of C and heavier hydrocarbons present in said cooled scrubbedgas fraction and C and lighter hydrocarbons from said further cooled and partially condensed scrubbed-gas fraction, passing at least a portion of said hydrocarbon condensate to a second stripping zone, separating a vaporous fraction containing C and lighter hydrocarbons in said second stripping zone, and recovering C and lighter hydrocarbons uncondensed from said further cooling and partial condensing step and as the vaporous fractions of each of said stripping zones.

12. A process as defined in claim 11 wherein said hightemperature vaporous pyrolysis effluent is at a temperature between about 1100 F. and about 1600 B, said intermediate temperature to which said vaporous pyrolysis efiluent is partially cooled is between about 500 F. and about 900 F., said cooled scrubbed-gas fraction is at a temperature above about F. and said relatively cold scrubbing liquid contacting said partially cooled effluent in said scrubbing zone is initially at a temperature between about 10 F. and 50 F. below the temperature of said cooled scrubbed-gas fraction.

References Cited in the file of this patent UNITED STATES PATENTS 1,824,947 Davis et al. Sept. 29, 1931 2,313,940 Hirsch Mar. 16, 1943 2,619,450 Fleming Nov. 25, 1952 2,768,124 Berg et a1 Oct. 23, 1956 2,777,802 Peet Jan. 15, 1957 2,780,580 Kniel Feb. 5, 1957 2,804,488 Cobb Aug. 27, 1957 2,989,459 Eastman et a1. June 20, 1961

Claims (1)

1. A PROCESS FOR RECOVERING C13 AND LIGHTER HYDROCARBONS FROM A VAPOROUS MIXTURE CONTAINING THE SAME AND TARRY SUBSTANCES WHICH COMPRISES CONTACTING SAID VAPOROUS MIXTURE IN A SCRUBBING ZONE WITH A HYDROCARBON SCRUBBING LIQUID PREDOMINANTLY COMPRISING HYDROCARBONS HEAVIER THAN C13, SEPARATING A SCRUBBED-GAS FRACTION CONTAINING A MAJOR PORTION OF SAID C13 AND LIGHTER HYDROCARBONS AND A MINOR PORTION OF SAID C14 AND HEAVIER HYDROCARBONS AND A LIQUID FRACTION CONTAINING A MAJOR PORTION OF SAID C14 AND HEAVIER HYDROCARBONS, TARRY SUBSTANCES AND A MINOR PORTION OF SAID C13 AND LIGHTER HYDROCARBONS, SEPARATING C13 AND LIGHTER HYDROCARBONS FROM AT LEAST A PORTION OF SAID LIQUID FRACTION, COOLING AND PARTIALLY CONDENSING SAID SCRUBBED-GAS FRACTION, SEPARATING HYDROCARBON CONDENSATE CONTAINING SAID MINOR PORTION OF C14 AND HEAVIER HYDROCARBONS PRESENT IN SAID SCRUBBEDGAS FRACTION AND C13 AND LIGHTER HYDROCARBONS FROM SAID COOLED AND PARTIALLY CONDENSED SCRUBBED-GAS FRACTION, SEPARATING C13 AND LIGHTER HYDROCARBONS FROM AT LEAST A PORTION OF SAID HYDROCARBON CONDENSATE, AND RECOVERING C13 AND LIGHTER HYDROCARBONS UNCONDENSED FROM SAID COOLING AND PARTIAL CONDENSING STEP AND AS SEPARATED FROM SAID LIQUID FRACTION AND SAID HYDROCARBON CONDENSATE.

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