US2355588A - Extraction of hydrocarbons from natural gas - Google Patents

Description

Aug. 8, 1944. D G. BRANDT EXTRACTION OF HYDROCARBONS FROM NATURAL GAS Filed 001;. 9, 1940 NMN FUN-$05M M23020 5% m 5 J 5N INVENTOR ATTORNEY Patented Aug. 8, 1944 giax'rnAcrroN or nrnaocmnous FROM NATURAL GAS 'David G. Brandt, Westfl Cities Service Oil Com a corporationoi' Penna eld, N. J., asslgnor to pany. New York, N. Y., ylvania Application October 9, 1940, Serial No. 360,401

Claims. (Cl. 196-8) This invention relates to the extraction of hydrocarbons from high pressure gas and the separation and stabilization of the hydrocarbon products recovered.

More particularly the invention relates to the extraciton of hydrocarbon distillates from high pressure gas wherein the gas is removed from the earth under its natural high pressure, the hydrocarbons extracted, and the pressure of the gas again built up to be recycled back into the earth formation or into a place for utilization.

Distillate pools have been discovered among the petroleum formations wherein a hydrocarbon distillate, in sand beds varying from ten to hundreds of feet in thickness, is associated with high pressure natural gas. The natural gas sand pres-.

sure may vary from 2,000 to 6,000 pounds per square inch or higher and the distillate usually exists in the vapor state. Often this distillate occurs in suflicient quantities to make it economically feasible to distil or scrub it out or the sand formation. This operation consists in maintaining the pressure on the sands, circulating the gas from the distillate beds to an extraction apparatus where the hydrocarbon distillates .are separated from the gas and then the gas is recompressed and pumped back into the sand formation without materially reducing the pressure of the gas in the sands. This operationis carried out in a continuous cycle whereby the gas is continuously circulated in a closed cycle and the minimum amount of gas is removed in the extracting step of the, cycle. By maintaining the pressure at substantially the natural rock pressure the maximum amount of hydrocarbons may be extracted from the pool.

The hydrocarbon distillates which occur in the earth are mostly hydrocarbons which are not liquid at normal temperatures and pressures, such as methane, ethane, propane and butane, but the distillate also contains some hydrocarbons, such as pentane and hexane, and may have an end boiling point of from 530 to. 650 F. or higher. Many of these hydrocarbons are contained in gasoline and therefore the distillate is utilized principally for the manufacture of gasoline. Usually ethane will not be extracted from the gas becaus it is desirable to utilize the ethane in vapors in the gas do not act pressures of the hydrocarbon constituents and under these conditions the gas or hydrocarbon in accordance with well known gas laws. The densities of the hydrocarbons in the vapor state become equal to or greater than the same vapors in the liquid state and the heats of vaporization of the hydrocarbons at the critical temperature and pressures become, or approach zero.

Some hydrocarbon distillate is extracted from high pressure gas by retrograde condensation. The retrograde condensation is that condensation of hydrocarbons which takes place in the high pressure gas as the gas pressures are varied when the temperature is above the. critical temperature. For example, high pressure gas from a well may be materially cooled and then, by dropping the pressure, a substantial amount of condensation of hydrocarbons will occur. The efilciency of retrograde condensation for extracting hydrocarbons from high pressure gas is not very high and this efllciency varies appreciably as the composition of the hydrocarbons in the gas varies. v

A dry gas is commonly referred to as a gas which does not contain hydrocarbons in the gasoline boiling point range. At the present time, however, dry gas usually is made up of methane and ethane wherein the methane content varies from 80 to 99% of the mixture. The C1 and C2 hydrocarbons are herein referred to as "undesired hydrocarbons and in some cases Ca and C4 hydrocarbons may be undesired hydrocarbons. The Ca hydrocarbons, such as .propane and propylene, and C4 hydrocarbons are now being quite extensively used in the industry. The C4 and higher hydrocarbons and often the C3 and C4 hydrocarbons are extracted from the gas according to) this invention and are herein referred to as, de sired hydrocarbons." In a gas absorption systhem therefore, it may be desirable to carry on the absorption so as to remove from thegas all hydrocarbons heavier than methane'and ethane,

or Cl and C: hydrocarbons. When the absorption is being carried on the absorption oil is preferably saturated with all 01' the various hydrocarbons in the natural gas. An absorption oil,

holding up the rock pressure. However, the propane and butane contents may have sufilcient value to be extracted. In many cases, however,

the propane and part of the butane will be returned to the sand formations for repressuring. The extraction of hydrocarbon distillate from high pressure gas is very diillcult because the natural pressure of the gas is above the critical such as highboiling. gasoline, kerosene, or gas oil, is selective in its operation in that it tends to absorb the C: to Ca hydrocarbons and to reject the C1 and Ca hydrocarbons. Furthermore, the vapor pressures of the Grand C2 hydrocar-- bons are so high that if the absorption is carried out at a comparatively low pressure to 200 lbs.) the amount of C1 and C2 hydrocarbons absorbed is comparatively small. However, as the pressure in order that -to the earth.

. bilization.

be held at a minimum duction in pressure in the oil sures (1000 to 2000 lbs.) the amount of C1 and C2 hydrocarbons absorbed in the absorption oil becomes 'quite large because these absorption oils can hold or absorb much more of these lighter hydrocarbons at the higher pressures. Furthermore the densities of the lighter hydrocarbon vapors become comparatively high at the high pressures.

' In a recycling process it is important that the absorption-of the hydrocarbons from the natural gas should be carried out at as high pressure as the process will be emcient and selective. The higher the absorption pressure the less compression will be required to recompress the treated gas to a point above the earth formation the gas may be returned The hydrocarbon distillate which is removed by absorption contains a large amount of 'low boiling hydrocarbons, such as Cl, Ca'and Ca hydrocarbons, that must be removed in order to make a marketable gasoline from the distillate. This process is usually defined as gasoline sta- The low boiling hydrocarbons removed inthe distillate extraction process should in order to prevent a resands in the gas repressuring or recycling operation. Accordingly it -is desirable to carry on the absorption operation in the extraction of "the hydrocarbon ing retrograde condensation.

distillate to remove the minimum amount of undesired hydrocarbons or gases .which are to be pumped back to the distillate pool for scrubbing out the distillate.

One-object of the present invention is to carry out the absorption of the hydrocarbon distillate in a high pressure absorption process .in a selective mannerto reject undesired hydrocarbons while efficiently recovering the desired hydrocarbons. I

In accordance with this object one feature of the invention consists in conditioning the lean "absorption oil by saturating it with the low boillng undesired hydrocarbons to such a point that a very small amount of undesired hydrocarbons will be absorbed by the oil in the main absorption system. This permits practically all of the undesired hydrocarbons to be recompressed and returned to the earth formation for maintaining the desired high rock pressure. Further by carrying on the absorption under a high pressurerthe, return of the'gas to the earth can be accomplished with the use of the minimum amount of mechanical recompression.

Another object. of the inventionis to presaturate the absorption oilused for recovering the hydrocarbons with undesired hydrocarbons under high pressures approaching the absorption pressure whereby the absorption of undesired hydrocarbons in a high pressure absorber will be substantially avoided. 4

With these and other objects and features in view, the invention consists in the gasoline ex- .traction process herein described indetail and particularly defined in the claims.

The drawing is a flow sheetofan apparatus for carrying out the absorption system-of the present invention -inits preferred form.

Referring to the'drawin'g the preferred form or the process may be outlined as follows:

-High pressure gas, which may be natural gas from the earth formation and in which may be included liquid hydrocarbons that have been condensedby retrograde condensation, is intro-.

duced into an absorber l0 through a line H. 'Th gas may be at the natural rock pressure of the pressure of the gas may be reduced in effect- In any case, however, 'the absorption in the absorber I0 is carried out under a high pressure of 1200 to 2000 lbs. so that a valve' H in the line I! is provided for controlling the pressure in the absorber. The 'gas'passes through the absorber l0 countercurrent to the flow of absorption oil which is introduced at the top of the tower through a line 16. Dry gas is removed from the top of the absorber and this gas then passes through one or a series of compressors l8 where it is recompressed to a pressure above be recycled back into the earth. The absorption pressure preferably should be as high as possible, particularly for a gas recycling operation, to reduce the. cost of repressuring the gas for return to the earth formation or to the place of utilization. This pressure is controlled by and limited to those densities and partial pressures of the gas which will not act to carry the absorption oil out of the "tower during the countercurrent circulationof the gas and oil in the tower. When treating a gas containing percent methane, pressures as high as 2000 lbs. may be used in the absorption.

Although the gas entering the absorption tower lll may preferably comedirectly from the well, the present invention contemplates the use of retrograde condensation along with absorption for the extraction of hydrocarbon distillate from the natural gas. Preferably the retrograde condensation is carried'out'before the gas enters the absorber ill.

from the gas but passes in admixture with the gas directly into the absorber I0. In case retrograde condensation is carried out it may not be necessary to use the valve I! to regulate the The present process is carried out to separate from the gas being treated only thedesired hydrocarbons, that is hydrocarbons having a molecular carbon-content of C3 and higher. In some cases the desired hydrocarbons may be 04 and higher and the process is controlled to se-' lectively reject theundesired hydrocarbons which .may be C1 and C2, C1 to C3, or C1 to C4 hydrocarbons. The. selective absorption is accomplished by presaturating the absorption oil which enters the tower"! through the line IS with the undesired hydrocarbons. 'This presaturated oil then rejects substantially all undesired hydrocarbons in .the gas being treated. The amount'of absorption oil used is controlled.

so that substantially all of the desired hydrocarbons will be absorbed and at' thesame time the partial pressures of all of the hydrocarbons absorbed in the absorption oil will be such as to reject the undesiredhydrocarbons while retaining all desired hydrocarbons. The rejected, undesired hydrocarbons pass out of the tower II to a compressor III to be recompressed so that they may be recycled back to theearth reservoir or to a point'of utilization.

from the undesired hydrocarbons in.,the absorption. oil, the absorption oil is subjected to dis-. tillation or stabilization to selectively remove -t undesired hydrocarbons :at high pressure.

the rock pressure so that it may Preferablythe retrograde condensate' after being produced is not separated Y proved types of fractionating equipment.

desired, propane, and these vapors rise through the tower to be separated from the absorption oil. To carry on the separation, the absorption oil in the bottom of the stabilizer is circulated through a line 26 to a reboiler 28 from which vapor returns by line 30 to the stabilizer. This heating operation is carefully controlled in con junction with the pressure reduction to act to free undesired hydrocarbons fromthe absorption oil. As the undesired hydrocarbon vapors pass upwardly through the stabilizer tower they pass in countercurrent circulationto condensed hydrocarbons for the purpose of scrubbing from the vapors any desired hydrocarbon vapors that may be set free in the bottom of the tower. The stabilizing tower may be a filled tower, a bubble cap tower, a plate contact tower, or any of the ap- The reflux for carrying on the fractional distillation operation in the tower 24 is obtained by passing hydrocarbon vapors flowing through the tower 2% through a line 32 to a cooler 34. Part of the hydrocarbon vapors are condensed in the cooler and pass into a receiver 38. passes from the receiver 36 through a line a distributor 40 located in the top of the stabilizer. The amount of condensate returning to the .top of the tower is controlled by means of a valve 42, which in turn, is controlled by a thermostat 44 positioned in the vapor in the line 32. The amount of condensate returned to the top of the stabilizer, therefore, will depend upon the temperature of the vapors in line 32, and on. the temperature of the condensate which, in turn, will depend upon the temperature of the water or cooling medium used in the cooler 34. Uncondensed, undesired hydrocarbon gases which pass through the cooler 34 flow into the receiver 36 and pass from the receiver 36 through a line 45 into the bottom of an absorption tower section 46 located on the top of the stabilizer 24. The stabilizer section is separated from the amorber 44 by means of a solid partition 41. The line 45 is preferably used as an ovefiow line so that if more condensed undesired hydrocarbons are collected in the receiver 36 than are required as reflux in the stabilizer 24, this condensed hydrocarbon distillate will fiow from the receiver 35 into the bottom of the absorber 46 to be mixed with the absorbing oil, as hereinafter described.

With a high pressure system, the hydrocarbon separated from the absorption oil in the stabilizer 24 will be a portion of the undesired hydrocarbon and be principally methane and some ethane. To further separate undesired hydrocarbons the rich absorption oil is distilled ina. second stage. To accomplish this, oil from the reboiler 28 pases through a line 48 in which its Condensate a line 54 to a reboiler 56 from which vapors pass through a line 58 into the stabilizer 52. The vapors set free in the stabilizer pass upwardly through filling in the stabilizer countercurrent to reflux condensate introduced through a distributor 60 located at the top of the stabilizer. Thi condensate is produced by condensing hydrocarbon vapors which pass through a line 62 -the temperature of pressure is reduced by a valve 50. The oil passto a coler' 64. Condensed hydrocarbon vapors,

enter a receiver 66 and flow back through a line 68 to tick distributor 60. The return of condensate to the distributor 60 is controiled by a thermostatic valve lll'which controls the amount of condensate returned depending upon the temperature of the vapors flowing through the line 62, the amount returned also depending upon the condensate. Uncondensed vapor accumulating in the receiver 66 pass through a line 12 into the'bottom of an absorber tower section I4 positioned on top of the stabilizer 52 above a solid the receiver 66 above that required for reflux in the stabilizer 52 passes through the line 12 along with the vapors and mixes with the absorption oil in the bottom of the absorber 14.

Depending upon the pressure at which the primary absorber is operated two or more stages of stabilization may be required for separating the undesired hydrocarbons from the desired hydrocarbons. -The number of stabilizer required. however, depends more directly upon the pressure being used and upon the desired degree of presaturation of the absorption oil with the undesired hydrocarbons before the absorption oil is returned to the primary absorption tower. If the primary absorption is carried out at pressures from 1200 to 1600 lbs. three stages of stabilization may be eflectively used.

To efl'ect a further separation of the undesired hydrocarbons from the rich absorption oil, the oil is passed through a line 18, through a pressure reducing valve to the lower portion of a third stage stabilizer 82. in the lower portion of the stabilizer 82 by passing oil through a line into a reboiler 86 and passing vapors through a line 88 to the stabilizer. In the illustrated apparatussubstantially all of the remaining undesired hydrocarbons which are not condensible at the existing pressure are separated from the absorption oil in the stabilizer 82. The vapors rising through the stabilizing tower pass through a condensate distributor 90 positioned in the top of the stabilizer. This condensatc'is produced from vapors'passing through a line 92 to a. cooler 94 where vapors are condensed, the'con'densate being collected in a receiver 90. The condensate flows from the receiver througha line 98 back to the distributor 90. The amount of condensate returned to the stabilizer is controlled by' a thermostatic valve I00 which controls the flow depending upon the temperature of the vapors passing through the line 92. Uncondensed gases collecting in the receiver 00 pass through a line I02 into the bottom of an absorber tower section I04 positioned on the top 01' the stabilizer 82 and separated therefrom by a solid partition I 00. Any condensate accumulating in the receiver 96 which is not returned to the stabilizer 02 flows through the line I02 to be mixed with absorption oil in the bottom of absorber I0 a .When the mixture of absorption oil and distillatehas been stabilized to separate thenon-compartition I6. Any. excess hydrocarbon distillate accumulating in The absorption oil is heated tillation, oil from then passed through a line I08, provided with apressure reducing valve IIO, into a still II2. In this still desired hydrocarbons are driven overhead and lean absorption oil removed from the lower portion of the still. To carry on the disthe still is. removed through line 4 and passed into a reboiler II6, from which vapors pass through a line 8 back to the still. Vapors of the desired hydrocarbons distilled off in still II2 pass through a line I20 intoa condenser I22 and then into a receiver I24."

A safety valve I26 is preferably mounted in a gas line at the top of the receiver I24 to control the discharge of gas therefrom. 4

It is not essential to operate the stabilizing towers in order to separate all .of the undesired hydrocarbons from the mixture of desired hydrocarbons and absorption oil. It is necessary.

only that all non-condensible'undesired hydrocarbons should be separated bythe time the oil has passed through the lowest pressure stabilizer 82 and any undesired hydrocarbons that are condensible may be carried over to-the still H2 and these hydrocarbons will be condensed and collected in the receiver I24. I v

The condensed desired hydrocarbons are fur ther stabilized, particularly when manufacturing gasoline, in order to obtain a product of the desired vapor pressure; To accomplish this, condensate from the receiver I24'passes through a line I28, and is forced by means of a pump I30 through a heat interchanger I32 into a stabilizer I34. Innormal operation, the still H2 would be operated at a pressure of approximately 100 lbs. per square inch while the gasoline stabilizer I34 would preferably be from 200 to 400 lbs. tion the desired product is passed from the bottom of the stabilizer I34 through a reboiler I36.

'Light hydrocarbons driven ofi overhead in the stabilizer I34 pass through a vapor line I38 to a condenser I40 and then'into a receiver I42. A pressure control valve I44 is mounted in the gas discharge line from the receiver I42. The cooling by the condenser I40 is controlled by a pressure operated based upon the pressure in the receiver I42. The desired product, or hydrocarbons, which is, for example, a stabilized gasoline is removed through a cooler I48 and passes through a line I50 to storage.

The distillation the desired hydrocarbons, such as gasoline, overhead and the higher boiling absorption oil is held in the still; This higher boiling product is the absorption oil and may contain all hydrocarbons between the end boiling point of gasooperated at a pressure of- To assist in the stabilizavalve. I46 which control is drocarbons entering the bottom of the absorber through the line I02. The absorption oil will take up the undesired hydrocarbons entering the absorber I04, and the resulting absorption oil collecting in the bottom of the absorber I04 is then passed to the next higher pressure stage for absorption of undesired hydrocarbons in that stage.

When two or more separating the undesired hydrocarbons from'the desired hydrocarbons it is' not necessary to separate any one specific light hydrocarbon in a single stabilizer, but a mixture of the lighter undesired hydrocarbons may be separated in each stabilizer and a sumcient number of stabilizers used so that all of the noncondensible undesired hydrocarbons will be removed by the time the rich absorption oil has passed through the last stabilizer. The larger number ofstabilizers aids the operation of the stabilizers so that latitude can be given in the temperatures and pressures in the stabilizers in order to effectively remove all of the undesired hydrocarbons j sorber I04 is cool and may act as a condensing bilizer 82. To avoid medium when absorbing thelight hydrocarbons therein. If the absorption is carried too far the pressure in the absorber will tend to fall and thus upset the operating condition in the stathis condition a bypass line I58 controlled by a valve I60 is connected with the line I56, by which lean absorption oil may be bypassed around the absorber I04. The valve I60 is connected through line I62 bilizer 82 so that the pressure in the stabilizer can' be used to control the amount of liquid pass-' ing through the bypass line I58. If the pressure in thestill H2 acts to force the absorber I04 line and the end point of, the-heavy ends of the distillate removed from thegas which may be up to 650 F. This absorption oil distillate i removed from the still H2 through a line I52 and passes through an interchanger I32 from which it is forced by means of a pump I54 through a line I56 into the top of absorber I04. Practically all. of the absorption oil remains in cyclic circulation so that a portion of the high boiling distillate removed from the gas may be drawn out of the line I56. through a valved line I55 to pass to storage.

The operation of. the pump I54 is such as to raise the pressure of the absorption oil to a pressure only slightly lower than that being maintained in stabilizer 82. As the absorbing oil passes downwardly through the absorber I04 it comes into countercurrent contzt with undesired hy- 0f the light falls below a predetermined point the valve will open.

-The light hydrocarbons which are separated from the desired hydrocarbons stabilizer I34 collect in receiver I42. This prodnot is preferably returned to the lean absorption oil by means of a pump I64 and line I66, the pump I64 being operated to raise the pressure hydrocarbon distillate to the pressure prevailing in the absorber I04, and this distillate is introduced tmough the line I66 into the bottom of the absorber.

The absorption oil which has'absorbed the undesired hydrocarbons from the stabilizer 82. and the stabilizer I34 flows from the bottom of through a line I68,- through a cooler I10, to a pump I12 which forces the oil through a line I14. into the topof. the absorber 14. The oil'passing through the line I68 may contain absorption oil which passesthrough the tion oil passes countercurrent to the undesired hydrocarbons separated in the stabilizer 52, this absorption being carried. on at about the pressure which is maintained in the stabilizer 52.

. The pressure in the stabilizer 52 and absorper 14 is controlled similarly to that on the stabil16 controlled by a pressure operated valve I18 will permit oil to be bypassed around the absorber 1.4 in order to prevent the drop of the pressure therein.

lizer 82. A by-pass line The partially saturated, lean absorption oil flows from the bottom of theabsorber 14 through I a line I80, through a. cooler N32 to a pump I84 which forces the cool oil through a line I86 into .the top of the absorber 46, the .operation of the pump being. such that the oil'will be introduced stalibilizers are used for with the stain the gasoline into the absorber 46 at about the pressure prevailing in the stabilizer 24. The lean absorption oil passing downwardly through the absorber 46 passes countercurrent to rejected undesired hydrocarbons removed by the stabilizer 24. The bypass line I16 is connected with the line. I80 to permit the lean absorption oil to flow around the absorber I4. The pressure in the absorber 46 is maintained or controlled by a bypass line I88 having a pressure controlled valve I90 therein. The valve I90 is connected with the stabilizer 24 to control the bypass line in accordance with the pressure in the stabilizer 24. The line I88 connects with a lineI92 by which presaturated ab-' sorption oil flows from the absorber 46 through a cooler I93 to a pump I94 for forcing the presaturated oil through the line It into the top of the primary absorber I0.

The operation of the absorber units 46, I4 and I04 is preferably carried on so that all of the lean absorption oil which is introduced into the primary absorber will be saturated with hydrocarbons of the type of the undesired hydrocarbons. To accomplish this the lean oil has been freed of all light hydrocarbons prior to being introduced into the first unitof the absorber system. The pressures in the absorbers I04, 14 and 46 arestepped up in stages to carry out the absorption at the highest practicable pressure in order to insure that the absorption oil will be saturated with the light undesired hydrocar- N In the present invention three stabilizer bons. towers are used for removing the undesired hydrocarbons and three absorbers are used for presaturating the absorption oil. Ifvery high absorption pressures are used more stabilizer and absorption towers may be employed. n the other hand if lower pressures (800 to 1200 lbs.) are used two stabilizers and two absorption towers generally will be suflicient. By having the lean oil saturated with the light undesired hydrocarbons there will be substantially no absorption of the same type of light undesired hydrocarbons in the primary absorber. To assist in controlling the temperature and pressure in the stabilizers 24, 52 and 82, connections may be made to introduce fresh lean absorption oil directly into any of the absorbers 46, 74 or I04. Presaturation tends to cut down the heat of solution in the primary absorber and therefore cuts down materially the amount of absorption 011 required for separating the desired hydrocarbons from the gas. With the higher pressures in the primary absorber the heat of vaporization (or the heat of solution) of the gas hydrocarbons in the absorption oil approaches zero so that less cooling to take care of the heat of souution is required and less oil is necessary for the absorption.

As an example of an operation of the apparatusillustrated in the drawing the primary absorber I0 maybe operated at 1600 Has; the first stabilizer may be operated at 1000 lbs., the second stabilizer at 700 lbs. and the third stabilizer at 300 lbs. The 'still II2 may be operated at approximately 100 lbs. and the gasoline stabilizer I 34 operated at 300 lbs. In such an operation ethane and methane will hydrocarbons and the C3 and higher boiling hydrocarbons are the desired hydrocarbons.

While theoretically the system illustrated in the drawing might be used for giving a full presaturation of the lean absorption oil, practically this does not occur. Furthermore some of the light hydrocarbons will be exhausted through be the undesired control valves I96, I and 200 mounted respectively in gas discharge lines from the top of the -absorption towers 46, I4 and I04. These valves furthermore operate in conjunction with the valves I90, I18 and I60 for controlling the pressures in the stabilizers 24, 52 and I32. The valves I90, I18 and I60 tend to maintain the pressure up to the desired maximum,- while the 'valves I96, I98 and 200. tend to control the pressure if it exceeds a desired maximum.

When using the process described herein on a gas recycling system the amount of gas. which would be exhausted through the valves I06, I98 and 200 should not be more than would be required for fuel to furnish the heat for operating the reboilers 28, 56, 86, H6, and I36. It will be seen furthermore that the absorption system does not require the use of compressors for compressing a large amount of residue gas from a low pressure up to high line-pressure. The undesired hydrocarbons are absorbed in the lean absorption oil and therefore they are brought up to the absorber pressures pumps, the operation of a liquid pump being relatively cheap compared to the operation of high pressure gas compressors.

In some cases where the rock pressure in the earth formation is reduced condensation of vapors occurs in the formation. Under such circumstances distillate is often carried out of the formation with the gas and taken to the absorption system. This distillate may also be supplemented by distillate condensed outof the gas by retrograde condensation. In the present process it is contemplated that the mixture of gas with distillate, whether the distillate is produced by condensation in the earth or by retrograde condensation after the gas is removed from the earth, shall be absorbed sorption oil andthe mixture then treated to sepor mixed with the abgas comprising passing the gas through a hydrocarbon oil arated to absorb the desired hydrocarbons of the gas, continuously removing the rich absorption I the. primary absorber to contact. the gas therein sired hydrocarbons contained in gas comprising by means of liquid 6 hydrocarbons of the gas, continuously removing the rich absorption oil from the absorber and gradually reducing the pressure in a series of stages while heating the oil to separate only undesired hydrocarbons from the oil, separating and stabilizing desired hydrocarbons from the rich absorption oil after the pressure reduction, absorbing undesired hydrocarbons separated in each stage in relatively lean absorption oil in a corresponding absorption stage maintained at apressure at least as high as the pressure of the stage in which the hydrocarbons were separated, lean absorption oil being introduced into the lowest pressure absorption stage and passed consecutively through said absorption stages to the highest pressure absorption stage of the series, i

the rich saturated oil from the absorberand reducing the pressure of the oil in a succession of stages while heating the oil in each stage to stabilize the absorption oil mixture, controlling the pressure reduction and the heating .of the oil in each stage to distil overhead only the undesired absorbed hydrocarbons, removing desired hydrocarbons from the absorption oil after the pressure has been reduced, passing the lean absorption oil through absorbers in'the successive stages and successively increasing the pressure on the lean oil as it advances through theabsorbers in the respective stages to correspond to the pressures in the respective stages of the absorption oil stabilization, absorbing separated undesired hydrocarbons in the lean absorption oil in each stage and forcing the presaturated absorption oil from the highest pressure stage back to the primary absorber to 4. The process defined in claim 2 wherein condensable low boiling hydrocarbons recovered in stabilizing the desired hydrocarbons is added to the lean absorption oil before it is introduced into the primary absorber.

5. The process defined by claim 1 wherein the be passed in contact ,with the gas introduced thereinto.

- said overhead fractions improvement which comprises passing the retrograde condensate with the remaining gaseous constituents at high pressure into the absorber and carrying out the absorption operation at high pressure, passing the resulting mixture of rich absorption oil and retrograde condensate through a series of rectifying zones of progressively decreasing pressure. andremoving an undesired gas fraction overhead from each zone, passing said overhead fractions into separate absorbers held at approximately" the pressure under which the fraction is produced, passing a lean absorption oil into the absorber of lowest pressure and then in seriesthroughthe said absorbers in contact to saturate the lean absorption oil, and introducing the saturated absorption oil into the first-mentioned absorber.

9. A process of separating desired hydrocarbons from undesired hydrocarbons contained in gas comprising passing the gasthrough a hydrocarbon oil absorbing menstruum in a primary absorber maintained at a high superatmospheric pressure ing the oil to separate substantially only tradey from said absorptionstages amount of lean oil passing through the absorber in each stage is controlledby the pressure of the stage to maintain a predetermined maximum pressure therein.

6. The process desired hydrocarbon vapors that are not absorbed in the lean oil are expelled from the stage absorbers when the pressure tends to exceed a predetermined rnaximum.

'7. The process defined in claim 3111 which the stabilization of the absorbed hydrocarbons is controlled to remove all. undesired hydrocarbons which are non-condensable at the pressure at which the desired hydrocarbons are separated from the absorption oil by distillation.

8. In a process for separating and recovering desired hydrocarbons from a high pressure gaseous mixture in which the mixture is subjected to pressure reduction to produce a retrograde condensate and in which the remaining portion 0! defined by claim 1 wherein unsired hydrocarbons from the oil, separating and stabilizing desired hydrocarbons from the rich absorption oil after the pressure has been reduced to provide a lean absorption oil, successively absorbing undesired hydrocarbons separated in" each stage in the lean absorption oil while conducting the lean absorption oil consecutively through a series of absorption stages, controlling the amount of absorption oil passing through the absorption stages and the pressure therein so that the-absorption oil leaving the series of absorption stages will have absorbed enough of the undesired hydrocarbonsto be substantially saturated, and forcing the substantially saturated absorption oil into the primary absorber to be passed in contact with the gas therein.

10. In a process for separating and recovering desired hydrocarbons from a high pressure gaseous mixture in which the mixture is subjected to pressure reduction to produce a retrograde condensate and in which the remaining portion of the gaseous mixture is subjected to the action of an absorption oil in an absorber for the recovery of further quantities of desired hydrocarbons,

the improvement which comprises passing the retrograde condensate with the said remaining portion of thegaseous mixture at high pressure into the absorber and carrying out the absorption operation at high pressure, subjecting'the resulting mixture of rich absorption oil and-retrograde condensate to' a fractionating operation in a-series of fractionating zones .of progressively decreasing pressure in which the absorbed undesired hydrocarbons'are separated out in the form of gas in each zone and passed in intimate contact with a the gaseous mixture is subjected tothe action of an absorption oil in an a of further quantities of desired hydrocarbons, the

osorber for the recovery.

lean absorption oil in separate absorbers, one of which is associated with each zone, to saturate the lean absorption oil withthe undesiredhydroc'ai'bons, and introducing the resulting saturated absorption oil into said first-mentioned absorber tobe brought in contact with the said remaining portion of the gaseous mixture, whereby the undesired hydrocarbons in the absorption oil introduced into said first-mentioned absorber are replaced.

DAVID G. BRANDT.-

with

to saturate the-absorbing oil, continuously removing the rich saturated oil from the

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