US1878849A - Art of cracking hydrocarbons - Google Patents

Description

Sept 20, 1932- E. c. HERTHEL ART OF CRACKING HYDROCARBONS Original Filed April 21, 1925 4 Sheets-Sheet l S 88 88h s@ ATTORNEYS 1925 4 Sheets-Shet 2 E. C. HERTHEL Sept. 20, 1932.

I ART OF CRACKING HYDROCARBONS original Filed Airil 2.1

lNvENToR ye//e C /ef//e/ B me 2 'ATTORNEYS ART OF CRACKING HYDROCARBONS Original Filed April 2l, 1925 4 Sheets-Sheet 5 Sept- 20, 1932- E. c. HERTHEL ART OF -CRGKING' HYDROCARBONS original Filed April 21, 1925 4sheets-Sheet 4 ATTORNEYS Patented sept. 2o, 1.932

UNITED STATES PATENT oEFlcE PANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE ART OF CRACKING HYDROCARBONS l Continuation of application Serial No. 2433A, iiled April 21, 1925. This application led J'uly 12, 1929.

` Serial No. 377,816.

- This invention relates to improvements in pressure distillation processes for cracking heavier hydrocarbon oils, such as gas oil, for the production of lighter `hydrocarbon oils, such as gasoline and pressure distillate, therefrom. This application is a continuation of a prior application filed April 21, 1925, Serial No. 24,734.

'When hydrocarbon'oils are distilled under pressure at a cracking temperature, they are broken up into lighter oils of less complex molecular structure. AIn .addition to these lighter oils, the products of the cracking reaction also include carbon, or tar or pitch constituents, and fixed gases. In condensing the vapors in the pressure distillation, the fixed gases escaping from the pressure still with' the vapors of the cracked oil\tend to carry a certain proportion of the condensible components of the vaporsvviththem through the `condenser uncondensed. These uncondensed vapors thus associated with the ixed gases escaping uncondensed from the condenser include particularly the very light constituents Whichare desirable components of motor gasoline. If the condensing operation is carried out under pressure,th e proportion of such vapors which are condensed may be increased, but, in this case, when the pressure on the condensed distillate is reduced to atmospheric pressure the very light constituents again escape as vapors from the condensed distillate. The proportion of suchl light constituents which escape from the condensed distillate when the pressure thereon `is reduced to atmospheric pressure varies with the degree of'pressure under which the .condensing operation is conducted. v 'Howf increment of pressure above atmospheric during the condensing operation. In addition to the gas mixtures prbduc'ed in pres- Y sure still operation, 'normal refinery operation is also accompanied bythe production of other gas mixtures including` condensible constituents suitable as components of gasoline or other commercial oils, such for example as the gas mixtures produced in coke still operation. Hitherto, it has been the: practice to recover such condensible constituents from these various gas mixtures, if at all, by separate and additional operations .s uch as those employed in the recovery of gasoline from natural gas and. casing head gas. This invention includes improvements in the recovery of gasoline constituents from` such gas mixtures, and especially from the gas mixtures produced in pressure distillation or other cracking processes; and includes particularly a cyclic method of operation elimi- A nating such. separate and additional operations as have previously been employed for the .treatment of such gas mixtures; Like- 'EUGENE C.' HERTHEL, OF CHICAGO, ILLINOIS, ASSIGNOR T0 SINCLAIR REFINING- COM- I I Wise, a considerable proportion of the prod-v ucts of the cracking distillation is composed of unsaturated hydrocarbons, many of which are undesirable as components of gasoline and other vc ommercial oils, because of unpleasant odor, instability, etc. Attempts have hitherto been made to saturate'these undesirable unsaturated constituents by the addition of hydrogen thereto, such as by maintaining the vapors from the pressure still under pressure, or by mixing them With` hydrogen or hydrogen containing gases, but

Without marked results. This invention' also` includes improvements inthe operation of pressure stills whereby such undesirable unsaturated constituents are treated in the pres'- sure still system to. form saturated or more saturated compounds improving the quality of the pressure distillate. The invention further includes improved methods of operating pressure stills for controlling the pressure therein and for promoting the vaporization therein ofc'onstituents suitable as components of the desired pressure distillate. Other 'features and advantages of the invention will" be apparent as the description proceeds.

According to the present invention, charging stock supplied to the pressure still is first employed as an absorbing medium for scrubbing the uncondensed vapors and gases from the pressure still, or other gas mixtures including condensible components suitable as components of the desired pressure dlstil- I 4-5' stood that this further more detailed description is to introduce the supply of fresh harglate, andthe absorbed constituents are then distilled from the charging stock as it is supplied to the pressure still system, and the absorbed condensible vapors distilled in the pressure still system are taken off andcondensed with the vapors forming the pressure distillate. The gas mixture supplied to the scrubbing operation may be that produced in the same or other pressure stills, or the gas mixture produced in other cracking operations, or other refinery gases including constituents suitable as components of the desired pressure distillate, or a mixture including various of these lgases and gas mixtures. The' gas mixture supplied to the scrubbing operation advantageously includes all com-e ponents which escape from the pressure distillate when the pressure is reduced to a substantially lower pressure than that maintained in the pressure distillation or to atmospheric pressure. The charging stock containing/the absorbed constituents therein may be introduced into the charge of oil undergoing distillation in thel pressure still, or it may be supplied to the pressure still through a relluxing operation. lOne particularly advantageous way of carrying outthe invening stock containing the constituents absorbed in the scrubbing operation into direct contact with the vapors from the'pressure still in a reflux tower through which the pressure still -vapors'pass to the condenser. All or part of the charging stock containing absorbed constituents may thus be introduced into a reluxing operationin accordancewith the present invention, or part of the charg ing stock may be elsewhere introduced into the pressure still system. v Y The invention will be further described more lparticularly in connection with the pressure distillation of gas oil character charging stocks for the' production of-gasoline, or gasoline containing pressure distillates,'but it is intended and will be undertion vof' one way of carrying out the invention is illustrative of the invention and fthat the invention is not limited thereto. Reference willbe made, in connection with this further description `of the invention, to the accompanying drawings, which illustrate in a diagrammaticand conventional manner one type of apparatusv adapted for"carrying out the process of the invention.f The pressure still illustrated in the drawings is of the general construction and operatlonfdescribed in United States Letters Patent No. 1,285,200 granted to the Sinclair Refining Company November 19, 1,918 on the application of Ed-A ward Isom.l The -invention is applicable in connection with other pressure distillation systems, but this particular type of'pressure still has been chosen for the purpose of illustration as representing a type of pressure` still, and of pressure still operation, to which the invention is applied with advantage.

In the accompanying drawings Figs. 1 and 1A, taken together, represent in 4elevation and partly in section with parts broken away a pressure still system and associated apparatus adapted for carrying out the rocess of the invention,

Fig. 2 represents in elevation and partly in section a modiedarrangement of the conbulk supply tank being varranged away from the furnace, and a circulating ump 4 and circulating connections 5, 6 and connecting successively the bulk supply tank, the circulating pump, the lower end of the heating tubes, and the upper end of the heating tubes, and the bulk supply tank. Arranged abpve the bulk supply tank is a reflux tower 8 having a plurality of baiiies 9 therein. A vapor line 1-0 is arranged to conduct vapors from the.

vapor dome 11 on the bulk supply tank to the lower end of the reflux tower and a reflux return line 12 is arranged to conduct reflux, and admixed `fresh oil, from -the lower end of the reflux tower to the upper end of the of the circulating pump 4. The reflux tower,

the bulk supply tank, and theA circulating .heat insulating jackets of material such as mineraLwool thereon. A connection 13 is circulating connection 5 on the suction side les provided for pumping out and charging the c still and a tar draw-olf connection 14 is arrarliged for use during the'operation of the sti l. r'

Vapors escape from the upper end of the reflux tower 8 through theY vapor line 15 to a condenser 16. e condenserA discharges through connection 17 into the receiver 18 which isA provided with a distillate outlet 19 and a gas outlet 20. The gas outlet from the receiver connects to a header 22 (thegas line being connected at D-D as shown). Gas mixtures fromother pressure stills,or from other cracking operations, or other refinery gases containing 'condensible hydrocarbon vapors, may be supplied through the header 21. From this point the gas mixture is con'- ducted to the scrubbing tower through con-` The pressure 'in the pressure` nection 22. stlll may be controlled by theregulating valve 23 arranged in the vapor 'line'l l be.-

tween the reux tower-and the'lccondensen I or the pressure 'may be reduced and regu` lated beyond the condenser or receiver. When the receiver 1s maintained under' any l39 tower 27 where the pressure is reduced subrelease line 28 and a Adistillate discharge line 29. The line 29 connects to a header 30 into which the distillate from a number of p ressure stills may be discharged. An auxlliary distillate discharge connection 31 is also provided for use as required. Here the pressure may be reduced and regulated by control valve 32, or the condenser may be operated under substantially the pressure pre- /vailing in the still and the pressure reduced and regulated beyond the condenser, for example by control valve 33, or the receiver 26 may also be maintained under the pressure prevailing in the still. From the header the condensed distillate is discharged through connection 34 `into the gas release stantially to atmospheric. Excess gases and vapors absorbed in the distillate under the -higher pressure in the receiver or condenser are then liberated andv escape through connection 35 and the distillate free from such constituents is discharged through connection 36 under substantially atmospheric pressure.

' The released gases and vapors escaping from the receiver through connection-28 and escaping from the gas release tower through connection 35 pass together to the scrubbing tower through connection 25.

Again referring to Figs. 1 and 1A, the gas mixture from connection 22 is introduced into the lower end of the scrubbing tower 37 through connection 38 and passes upwardly therethrough over the bailles'or other gas and liquid contact promotingmeans with which the scrubbing tower is provided. The stripped gases escapefrom the upper end of the scrubbing tower through connection 39 and are discharged into a gas holder 40 through connection 41. A valved by-pass connection 42 is also provided between gas line 22 and the gas line 41. Fresh oil is pumped from the charging stock tank 43 by I means of pump 44 through connection 45 to the upper end of the scrubbing tower 37 through which it iows downwardly in countercurrent contact with the gases and vapors iowing upwardly therethrough. From the lower end of the scrubbing tower, the oil .together with the constituents absorbed therein in the scrubbing tower is'discharged into 5 storage tank 46 .through connection 47. A

header 48a may connect to this storage tank 46 from which a number of pressure stills may be supplied with fresh oil containing the` constituents absorbed lin the scrubbing tower. A pump 49 is provided for supplying fresh oil from this tank to the pressure still system illustrated in F ig.'1. From the pump -49 one feed oil line 50 leads to the bearings of the circulating pump (the feed line being connected at C-C as shown), and another feed oil line 51 leads to the upper end of the reflux tower 8 (this feed line being connected at B-B as show-n). The feed line 51 connects to a spray head 52 arranged in the upper end of the reflux tower for spraying fresh oil downwardly therethrough in direct contact with the rising vapors from the pressure still. The flow of oil through the feed lines 50 and 51 may be controlled by valves 54 and 53 respectively. Fresh oil may also be supplied to other pressure stills ythrough connection 48by means of the same pump. Thel major proportion of fresh oil is supplied to the upper end of the reflux tower and the'minor proportion is introduced through the bearings of the circulating pump. The supply of oil introduced into direct contact with the vapors in the reflux tower is regulated to control the reiluxing operation therein, and additional oil required to maintain the still charge is supplied through the bearings of the circulating pump, a minimum sufficient to cool and protect the 'bearings `of the'circulating pump being at all times supplied thereto.

As an illustration of 'one way of carrying out the present invention for the production of gasoline from gas oil in the apparatus illustrated, the still ischarged with 8,000 gals. of gas oil and brought to cracking conditions of temperature and pressure in the usual way. After being brought to operating conditions, the introduction of fresh oil into the reflux tower is begun and the vapors escaping from the reflux tower are condensed and the distillate discharged through the condenser to the receiver. With a gas oil character charging stock, pressures in the neighborhood of to 125 lbs. per sq. in. :may b'e employed; but the pressure employed may vary, for example, with lighter charging stocks such as' kerosene character charging stocks pressures up ,to 300 lbs. per sq. in. or more may be used. This pressure may be maintained throughout the condenseran'd" 3 Ireceiver but separation 'of the distillate and gases is advantageously effected at a substantially lower pressure than that mainoil is supplied at approximately the rate at which distillate is taken oif, for example with a distillate rate of 1,000 gals. per hour fresh oil may be supplied at a rate of about 1,000 gals. per hour. Before the pitch content of the charge reaches saturation, the supply of -fresh oil`is increased and 4the withdrawal of tar laden oil from the still charge is begun, the rate of supply of fresh oil and of withdrawal of tar laden oil being regulated to maintain the pitch content of the charge below saturation. For-example, with a distillate rate of 1,000 gals. per hour fresh oil may be supplied at a rate of about 2,500 gals. per hour and tar withdrawn at a rate of about 1,500 gals. per hour.V Sufficient fresh oil is suppliedl to the upper end of the reflux tower to maintain the head temperature therein at the desired point for the production of the desired character distillate and the balance of the fresh oil is introduced into the circulating charge in the still. By providing a heat insulating jacket on the reflux tower, a large proportion of the fresh oil may be supplied through the reflux tower in direct contact withl the vapors therein.

The charging stock supplied to the pressure still may, for example, be ai gas oil havi e' a gravity in the neighborhood of 28 to B. On its way to the pressure still, this charging stock is passed through the scrubbing tower in countercurrent to the hydrocarbon gas mixture rising therethrough. The relative supply of fresh oil and of gas mixture to the scrubbing operation will vary with the character of the fresh oil and with the amount of gases available, but in normal operation from 150 to 250pgals. of oil per thousand cubic feetof gasv mixture will be employed. This ratio, however, may vary from somewhat less than 100 `to more than 400 gals. per thousand cubic feet of gas mixture. The gas mixture supplied to the scrubbing operation may include the uncondensed vapors Iand gases produced in pressure stills l in lthe renery together with uncondensed both the composition andthe amount' of unvapors and gases from other cracking operations and other hydrocarbon refinery gas mix- 4tures in varying proportions. Not only the amount, but alsothe character of the gases and gas mixtures available lin the refinery may vary from time to time, for example condensed vapors and gases may vary at different periods in the same pressure distillaition operation. These variations tend to be oifset by the relatively large amount of oil supplied to the scrubbing operation. In the y, scrubbing tower approximately 20% to 30% of the total gas mixture is absorbed in the oil. Normally, the supply of oil required for pressure still operation is so much in excess of that required for absorption that substantially all absorbable constituents of the and 13.5%.

the gas mixture supplied to the scrubbing op.

eration may amount to as much as 3 to 5 gals. per thousand cubic feet of gas mixture or more. These condensible constituents are liberated from the fresh charging stock in the pressure still system and are condensed and collected with the pressure distillate.

The gas mixture discharged from the pressure still, or pressure stills, either from the receiver or from the receiver and the. gas release tower, includes both saturated and unsaturated hydrocarbons together with minor proportions of hydrogen, and sometimes carbon dioxide or carbonmonoxide in very small amounts.) As a typical analysis, the pressure still gas mixture may have a content of unsaturated hydrocarbons of about 31.7% and of saturated hydrocarbons of about 66.6% by volume; successive absorption'in '70% H2SO4, 80% HZSO. and finally in fuming sulfuric acid removing the unsaturated constituents of this gas mixture successively to the extent of 3.9%, 13.5%,

which may be supplied to the scrubbing tower in carrying out the present invention is the mixture of uncondensed vapors and vgases from colle still operation. As a typical analysis, such gas mixtures may have a content Another refinery gas mixture of about 32.2% of unsaturated hydrocarbons y and about 65.7% of saturated hydrocarbons together with Aminor proportions of hydro-` gen, .and sometimes very small amounts .of carbon dioxide and carbolf monoxide; 70% H2SO4`, 80% HZSO.. and fuming sulfuric acid removing successively about 4.8%, 12.2% and 15.4% of the gas mixture. As atypical analysis of the stripped gases escaping from the scrubbing tower, for example, when a mixture containing from 50 to 60% of pressure still gases'together with coke still gases making up the balance of the foregoing typical analyses is' passing thrugh the scrubbing tower, the stripped gas mixture may have a content of unsaturated hydrocarbons of about 14.8% and of saturated hydrocarbons of about 82.3%: 70% H2SO4 80% HQSO. and fuming sulfuric acid removing successively 0.8%, 6.6% and 7.0%. The stripped gas is` also substantiallyreduced in volume as compared to the volumel of gas mixture supplied to the scrubbing operation. v

plied to the pressure still system,l and is ad- 10 absorbed constituents are liberated in a gradual and progressive manner as the, oil flows downwardly through the reflux tower. The absorbed condensible and non-reacting constituents are thus vaporized and escape and are condensed with the pressure distillate. The absorbed unsaturated constituents tend to combine with the unsaturated constituents of the vapors forming the pressure distillate, and particularly with the less 'stable and e more unsaturated hydrocarbons, forming more stable and more saturated hydrocarbons. The unsaturated constituents supplied to the pressure still system ab-y sorbed in the fresh charging stock may 5 be in part condensible and in (part incondensible under conditions of practical operation, and part of these constituents may be condensed as such or part of them may combine with unsaturated constituents of the vapors and gases in the pressure still system,

which in turn might be condensible or in condensible under conditions of practical opera! tion, to form constituents which are condensed and taken off with the pressure distillateL The unsaturated hydrocarbons absorbed in the fresh oil and supplied to the pressure still system therein do not again appear, but there is an actual decrease in the content of unsaturated hydrocarbons and an increase in the content of saturated hydrocarbons of the final stripped gas mixture re leased from the scrubbing operation. This is illustrated by the typical analyses given above. .i In the operation of a battery of pressure stills in accordance with the present invention in which the gas mixture from the pressure stills and the gas mixture from the coke stills in the refinery were scrubbed in the fresh oil supplied to the pressure stills, the following average results were obtained over a 42 day period.

Gas mixture from pressure stills per day Cubic feet` 1,696,600 Pounds 120,100 Gas mixture from pressure stills per barrel charged Cubic feet 123.8 Pounds l8.8 Gas mixture from coke stills per day Cubic feet 1,187,000

Pounds 87,600

Gas mixture ,from coke stills per. barrel charged r Cubic feet i 74.1 Pounds 5.46 `70 Total gas mixture per day Cubic feet 2,883,600 Pounds 207,700l Total stripped gas from absorber per day `Cubic feet 2,345,500 75 i `Pounds 143,000 Tot-a1 gas mixture constituents absorbed per Cubic feet V538,100 80 Pounds 64,700

One of the important advantages of the present'invention is that it combines with the pressure still operation the recovery of condensible hydrocarbons from the various hydrocarbon gas mixtures available in the relinery, such as the gas'm'ixtures produced in' the pressure still itself or in other refinery operations. With the exception of the scrubbing operation and the apparatus therefore, additional and separate apparatus and operations are eliminated; and the scrubbing operation in the combined system is greatly simplified.

With reference to the scrubbing operation of the present invention, the pressure still charging stock is a good absorbing medium and because of the relatively large flow of oill through the scrubbing tower as compared to the flow of gas no particular care and regulation of the relative flow of gas and oil are necessary. Moreover, gas production in a given still corresponds roughly to th@ rate ofdistillation so that with high rates of distillation-more fresh oil is required compensatin for increased gas production. AThe relatively large quantity of fresh oil supplied to the pressure stills also avoids any necessity for a multiplicity of scrubbing towers or recirculation of the'absorbing medium. compared to separate oil absorption recovery systems, special still and handling equipment to recover the absorbed condensible hydro- `Carbons from-the absorbing medium is eliminated, asis the operation of such apparatus, and there is no necessity for providing special absorbing mediums of high initial boiling point to avoid contamination of the recovered light oils.. Moreover, as the recovered light oils are vaporized in the pressure still system and condensed with the pressure distillate, the provision of separate storage means is not necessary; and, as the recoveredlight oils may be refined with the pressure distillate, special refining operations carried out uponthe gas mixture before it is subjected to ab- Sorption treatment, hitherto employed .to avoid the high evaporation losses incident to the refining of the very light oils as recovered in separate operations, may also be eliminated.

As illustrated in a diagrammatic manner in 1 3 refiuxing operation in direct contact with the the How sheet constituting Fig. 3 of the drawings accompanying this application, in carrying out the present invention for the production of gasoline,to which the present invention is particularly applicable, gasoline con- A stituents suitable as components of the desired, pressure distillate are scrubbed from the gas mixtures in Which they occur and absorbed in fresh charging'stock, and the absorbed gasoline constituents are distilled from the fresh oil as itis supplied to the pressure still system and are taken off and condensed with the cracked vapors produced in the still.

Another important advantage of the present invention is the improvement in the quality of the pressure distillates produced in pressure distillation processes which it makes possible. As has been pointed out above, the charging stock to the pressure still absorbs a large amount of unsaturated constituents from the gas mixture supplied to the scrubbing operation. The heavier more condensible constituents of the gas mixture, for example, may be predominantly unsaturated in character so that saturated constituents are concentrated in the unabsorbed gases. As the fresh oil is heated in the pressure still system, these absorbed unsaturated constituents are liberatedvvithin the pressure still system Where they tend to combine with unsaturated constituents of the vapors forming the pressure distillate, and particularly with the less stable and more objectionable unsaturated hydrocarbons, forming morestable and more saturated hydrocarbons. `In this aspect of the invention, it is particularly advantageous to supply to the scrubbing opration gas mix tures containing a considerable proportion of unsaturated components, such as the gas mixture produced in pressure distillation processes or in otherv cracking processes.

'Ihe -present invention has several further additional advantages when carried out in connection With-.pressure distillation processes in which the vapors; are subjected. to a retluxing o eration and when the fresh oil containing a sorbed constituents recovered in the scrubbing operation is supplied to the vapors therein. By carrying out the operation in this Way, absorbed condensible constituents, such as uncondensed gasoline constituents, are liberated'from the fresh oil in the refluxing operation by the heat given up by the vapors and these vaporized` constitu- I ents pass 0E from the refluxing operation torso gether with the vapors of the cracked oil without being subjected to the higher temperature prevailing in the pressure still proper. Likewise, -in such operations, absorbed unsaturated constituents are progressively liberated from the fresh oil as it is heated up by contact with the vapors in the refluxing operation and are thus intermingled with the vapors of thecracked oil in a particular ly advantageous Way and at a temperature which apparently promotes the combination of the various unsaturated components of the vapors and gases. The absorbed unsaturated constituents are thus also intermingled with the vapors from the pressure still proper Without being subjected to thehigher temperature prevailing in the pressure still proper. The introduction of light absorbed constituents into the fresh oil supplied to the reuxing operation also assists in promoting therefluxing operation, the vaporizationand liberation of the absorbed constituents from the fresh oil assisting in cooling the vapors therein.

Another advantage of the present invention is that it' provides an improved method of controlling the pressure in the pressure still operation. In addition to the condensible constituents and the reacting unsaturated constituents which are absorbed in the fresh oil supplied to the pressure distillation in accordance with the present invention, a certain amount of saturated xed gases are absorbed as Well as a certain amount of unsaturated fixed gases Which may not react, and these latter gases are liberated from the charged fresh oil as it is supplied to the pressure still system, assisting in maintaining the pressure therein and providing a readily controlled partial pressure of fixed ases in the pressure still by reason of WhicIi vaporization of the desired lighter condensible constituents takes place therein at lower temperature than if the condensible constituents driven off alone were relied on to maintain this pressure. When the charged fresh oil is supplied through a reliuxing operation, the absorbed fixed gases introduced with the fresh oil are quietly and progressively released in the reiuxing operation Without disturbing the oil in the pressure still proper and there is no tendency for the liberated gases in escaping 11oA to entrain heavier oil constituents as in the case where fixed gases are introduced beneath the surface of the liquid charge in a pressure still. In this way, the pressure still may be continuously kept charged with a, fresh supply of fixed gases sufficient to maintain the desired pressure on the system.

I claim:

1. In the pressure distillation of heavier hydrocarbon oils for the production of lighter hydrocarbon oils, subjecting the heavier oil to a cracking temperature and taking olf under pressure the gas and vapor mixture generated thereby, subjecting the gas and vapor mixture to a condensing operation, separating condensed distillate from the remaining uncondensed vapors and gases at substantially atmospheric pressure, scrubbing uncondensed vapors and gases from the separating operation with fresh heavier oil and introducing the heavier oil containing the constituents absorbed from the vapors and gases therein directly into the hot gas and vapor mixture generated in the cracking operation, separately discharging unabsorbedy gases from the scrubbing operation, and taking o together absorbed constituents liberated from the fresh heavier oil and the vapors of the cracked oil Without again subjecting them to the cracking temperature. 2. In the pressure distillation of'heavier hydrocarbon oils for the production of lighter hydrocarbon oils, subjecting the heavier oil to a cracking temperature and taking oft' under pressure the as and vapor mixture generated thereby, su jecting the gas and vapor mixture to a condensin operation, separating condensed distillate om the remaining uncondensed vapors and gases at substantially atmospheric pressure, scrubbing uncondensed vapors and gases from the separating operation with fresh heavier oil and introducing the heavier oil containing the constituents absorbed from the vapors and gases therein to the cracking operation, and discharging unabsorbed gasesfrom the scrubbing operation.

In testimony whereof I aix my signature. K

EUGENE C. HERTHEL.

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