US2324112A - Refining process - Google Patents

Description

July 13, 1943. w. H. RUPP :TAL

REFNING PROCESS Fired Agni l1a, 1940 MOL t Enit NQ Patented July 13, 1943 UNITED STATES PATENT OFFICE R-EFIN ING PROCESS Ware Application April 18, 1940, Serial No. 330,240

(Cl. ISG- 8) 6 Claims.

The present invention relates to the refining oi mineral oils. The invention is particularly concerned with an improved process for recovering valuable petroleum hydrocarbons which may e incorporated in motor fuels and utilized as feed stocks for alkylation and polymerization processes from feed gases containing the same. The invention especially relates to an improved method stituents which may be incorporated in motorv fuels. A usual process is to co-untercurrently treat the gases containing the recoverable hydrocarbon constituents with an absorption oil under temperature and pressure conditions adapted t remove the recoverable hydrocarbons therefrom. In these absorption operations the common procedure is to withdraw the rich absorption oil containing the dissolved hydrocarbon constituents from the bottom of the absorption tower and then to substantially completely rem-ove the dissolved hydrocarbon constituents -from the oil by distillation means which may comprise one or more distillation towers operated in series or parallel under identical or diierent temperature and pressure conditions. The absorption tower operating conditions in general are regulated to recover the desired amount of the lowest boiling desirable hydrocarbon constituent termed the key component with a minimum recovery of hydrocarbon constituents boiling in the range below the. boiling range of the key component. Heretofore the lowest boiling hydrocarbon constituent or key component usually recovered from hydrocarbon gases for incorporation in motor fuels was a hydrocarbon constituent containing four carbon 'atoms in the molecule. Thus, absorption towers were generally operated under conditions to recover from the feed gases the desired amounts of hydrocarbon constituents containing four carbon atoms in the molecule with a minimum absorption of lower boiling undesirable hydrocarbons containing three or less carbon atoms in the molecule.. Thus, the usual practice was to operate absorption towers in a manner to remove approximately 60% to 80% of the hydrocarbons containing four carbon atoms intheinolecule and substantialiy the entire amount of higher boiling hydrocarbons from the feed gases. However, under these conditions some lower boiling hydrocarbons such as propane and propylene and to a lesser extent some ethane and methane were also dissolved in the absorption oil. These latter gases were removed overhead in the still 'along with the butanes, butylenes, and higher boiling hydrocarbons and the entire fraction passed through a condenser and into a distillate drum. Fixed or recycled gases comprising essentially propane Iand lower boiling gases were removed from the distillate drum and passed to the burning line or recycled to the equipment. In operations of this character, particularly when the conditions were regulated on the absorber to recover a substantial proportion of or to secure substantially complete recovery of the key component or butane, an appreciable amount of lower boiling hydrocarbons were also absorbed which had to be removed from the absorption oil and segregated from the desirable hydrocarbons in the distillation equipment. Thus, the capacity oi the distillation equipment with respect to the yield of desirable hydrocarbons was materiallyA reduced.

We have now discovered a process` by which an absorption operation may be conducted in a manner `to secure substantially complete recovery of or the desired recovery oi the lowest boiling hydrocarbon and higher boiling hydrocarbon constituents and by which the overall capacity of the absorption operation may be substantially increased. In accordance with our process, the rich absorption oil containing `the dissolved hydrocarbons removed from the absorption tower is heated and passed to an initial separation sone in which separation occurs between gases and liquid. The liquid is withdrawn from the initial separation zone, further heated and passed to the distillation equipment which preferably comprises a high pressure and a low pressure still. The vapors from the initial separation zone are withdrawn, cooled, and introduced into a secondary separation zone in which a further separation of vapors and condensate occurs. The vapors are withdrawn from the secondary separation Zone and preferably recycled with the feed gas to the 'absorption tower. The condensate of the secondary separation zone is withdrawn and passed t0 the distillation equipment. The distillation equipment is operated to remove and recover the absorbed hydrocarbons from the absorption oil and to produce 'a lean oil substantially free of dissolved hydrocarbons suitable for recycling to the absorption tower.

The process of our invention may be readily understood by reference to the attached drawing illustrating modifications of the same. For purposes of illustration, it is assumed that the feed gases comprise hydrocarbons produced in various rening operations. These gases comprise hydrocarbons containing from one to six and higher carbon atoms in the molecule. The feed gases are introduced into absorption tower I by means of feed line 2. The gases flow upwardly through absorption tower l and countercurrently contact downiiowing lean absorption oil which is introduced into tower I by means of line 3. Treated gases substantially free of hydrocarbons boiling in the boiling range of butanes, butylenes, and higher boiling hydrocarbons are withdrawn from absorption tower I by means of line 4 and handled in any manner desirable, usually by passing to a burning line. The rich absorption oil containing dissolved therein the desired recoverable hydrocarbons which may be included in motor fuels and utilized as feed stocks for various alkylation, polymerization and similar processes is withdrawn from absorption tower I by means of line 5. The absorption o-peration is conducted under conditions adapted to secure substantially complete recovery of hydrocarbons containing four carbon atoms in the molecule. Thus, the absorption oil likewise will contain appreciable quantities of hydrocarbons boiling in the propane and propylene boiling range. The rich absorption oil withdrawn from tower I is pumped by means of pump 6 through suitable heat exchanging means 1 in which the temperature of the oil is raised the desired degree and introduced into initial separation or flash drum B. The liquid product is removed from tank 8 by means of line 9 and pumped by means of pump IB through heating means II and introduced into a high pressure still l2 of the distillation equipment by means of line I3. The flashed gases are withdrawn from initial separation drum 8 by means of line I4, passed through condenser or cooler I5 and introduced into secondary separation drum I6. Uncondensed gases are withdrawn from secondary separation drum i5 by means of line I'I and preferably recycled with the feed gases to absorption tower I. These gases, however, if desired, may be discarded or passed to the burning line by means of line I8. The condensate is withdrawn from drum i6 by means of line I9 and pumped by means of pump 2li into fractionating tower I2 at a point above the point of introduction of the absorption oil feed which is introduced by means of line I3.

The rich absorption oil substantially completely free of hydrocarbon constituents containing 2 or less carbon atoms in the molecule which is removed from initial separation zone 8 andintroduced into high pressure still I2 and is handled in a manner adapted to completely recover the absorbed butanes, butylenes and higher boiling hydrocarbons from the absorption oil. The high pressure still is operated at temperatures and pressures under which it is possible to permit the recycling of any gas from the redux accumulator back to the absorber without any recompressing being necessary. Gases are removed overhead from high pressure still I2 by means of line 2 I, condensed in condenser 22 and passed to reflux accumulator 23. Although when operating in accordance with the present process substantially complete condensation of the overhead is secured, any uncondensed gases may be removed from reflux accumulator 23 by means of line 24 and recycled to the absorption tower with gases removed from the top of secondary separation zone I6. Reux is recycled to high pressure still I2 from reflux accumulator 23 by means of line 25 and pump 25. The desired temperature is maintained in high pressure still I2 by recycling bottoms through heating means II by means of line 21 and pump 28. Open steam may be introduced into high pressure still I2 by means of line 29. The amount of this steam may be adjusted to control the amount of recycle gas released from the still or to regulate the pressure on the still when no gas is released therefrom. Bottoms are withdrawn from high pressure still I2 by means of line 3U, passed through a pressure release valve 3! and introduced into low pressure still 32. The temperature and pressure maintained on low pressure still 32 may vary widely. The desired temperature is maintained in low pressure still 32 by means of reboiler 33. Open steam may be introduced into low pressure still 32 by means of line 34. The operating conditions of low pressure still 32 are adjusted so that absorption oil substantially free of dissolved hydrocarbons is removed by means of line 35 and pump 35. tower and handled as described. Condensed water is removed from the stills by means of dehydrators 31 and 38, respectively. Hydrocarbon vapors are removed overhead from low pressure still 32 by means of line condensed in condenser 4I) and passed to low pressure reflux Although, in general, substanaccumulator 4I. tially complete condensation is secured, any uncondensed gases may be removed overhead from reflux accumulator 4i by means of line 42 and disposed of in any desirable manner. Reflux is introduced into low pressure still 32 from reflux accumulator 4I by means of line 43 and pump 44. The remaining condensed overhead from. low pressure still 32 not utilized as reflux is recycled to reux accumulator 23 by means of line 45 and pump 46. The recovered liquid hydrocarbon product is removed from the distillation system absorption oil and to segregate a recovered hyy' drocarbon fraction substantially free of undesirable hydrocarbon constituents. Although the process may be adapted to the treatment of rich absorption oils derived from substantially all types of absorption operations, the process is particularly suitable for the treatment of absorption oils derived from absorption processes, the operating conditions of which are adjusted to absorb hydrocarbon constituents containing 4' carbon atoms in the molecule as the key component, especially when the absorption operations are conducted to secure substantial or relatively.

complete recovery of hydrocarbons having 4 carbon atoms in the molecule. In general, these conditions are preferably secured by maintaining a pressure on the absorption zone from 50 to lbs. per square inch, and an oil rate in the range from 30 to 100 gals. of absorption oil per 1,000 ouv ft, of gas.

This oil is recycled to the absorptionv 'I In 1 general, theY temperaturey of th'e rich `ab'- sorption .oil withdrawn-from the absorption system and containing.: the ldissolved hydrocarbons should-not exceed about 120 F. tol30 F., and

preferablyshould be below-'about 110-Fi Therich absorption oil'is passed through a heating zone which maycomprise suitable heat exchanging or` equivalent'means by which the temperature of the oil is raised to'above about 250 F., preferably to atemperature in the range from about 300 F. to 350 F. The heated rich absorption oil-is passed to an initial separation Zone, in whichv a separation is .made between the vapors andithe'liquid.y It: is preferred that the initial separation be madeunder flash conditionsat pressures in the -rangefromaabout 60 lbs. to 125' erablytoja temperature .in the range from about 320 F. to 360 F. Thevapors from the initial separation zone are-passed through a cooling zone adapted to produce substantial condensation of the same. In general, itis desirable to cool the vapors from the initial separation zone to a l temperature below about 100 F., preferably to a temperature in the range from '70 F.^to 85 F. When processing a rich absorption oil derived from a process in which substantially complete removal of butane from the. feed gas is eiected, itisfpreferred; to adapt conditions to remove as a `vaporousproduct from the initial 'separation Zonefrom about 40% to 60% of the hydrocarbons dissolved in' the rich .absorption oil and to condense in the subsequent cooling zone from about 40% to 60% of-thevapors which are then separated from theremain-ingvapors in the secondary separation Zone. The cooled vapors in the secondary separation zone are separated and preferably recycledtothe'absorption zone with the feed gases. The,condensatev from the secondary separation zone alongwith the heated condensate from the primary separation Zone is introduced into the distillation equipment. It is preferred that the condensate from the secondary-separation Zone be introduced into the distillation'equipment at a. point'above thev point of introduction of theh'eated liquid from the initial separation zone;v The distillation equipment preferably comprises a high and low pressure still arrangementiinwhich the pressure on the high pressure stillv is in :the range from about 80 lbs. to 120 lbs. per square inch, and the pressure on the low pressure still is in the range from about 3 lbs. to 10 lbs. per square inch. A desirable bottoms temperature on the high pressure still is in the range from about 350 F. to 450 F., while the preferred temperature on the low pressure still is in the range from about 320 F. to 380 F.

In order to further illustrate the invention, the following example is given which should not be construed as limiting the same in any manner whatsoever:

Eample I Feed gases of the following composition derivedfrom petroleum distilling, cracking andreforrning .operations werer passed'into an absorption tower asdescribed.

Mols

Per cent *Denotes number of carbon atoms in hydrocarbon molecule.

These gaseswere countercurrently contacted.

with an absorption oil which had a gravity of 43 A. P. I., a mid-boiling point of about 425 F., a boiling range from about 350 F. to 475'F.-and an air equilibrium vapor pressure of about'5 mms. at F. The oil gals. per 1,000 cu. ft. of gas, and the pressuremaintained on the 70 lbs. per square inch.A

The rich absorption oil was withdrawn fromV the absorption tower at a-temperature of. about' F., passed through a heating zone in which the temperature of the rich absorption oil `was raised to about 340 tion oil was then passed into an initial separation zone in which uncondensed vapors were separated'.`

The liquid was removed from the initial separation Zone,

The pressure maintained onV the high pressure still 'of the distillation equipment was about 80.

lbs. per square inch andthe bottoms temperature was about 400 F.' The pressure maintained on the low pressure still was about 5 lbs. per square` inch and the 360 F.

The results of this operation are summarized in the following material balance, excluding the absorption oil, based upon 100 mols of 'feed gas to the absorption zone:

bottoms temperature was about Mols of H d h absorbgd y roy rocar ons flaless carbons. removed from absorption absorbed in lnltial separatowcr absorption tion zone oil Liquid Vapors Mols Mols rate was approximately; 29`

absorption tower was about" F. The heated 'richabsorp--- passed through afsecondary heating zone. and then introduced into` a high pressureI When operating as described above it was possible to process 28.4 unit volumes of feed gas per day.

Example II In a similar operation conducted under conditions described with respect to Example I utilizing the same feed gas and operating under conditions `to produce products substantially identical in character with the exception that the rich absorption oil was passed directly to the high pressure still of the distillation equipment, it was found possible to process only 21.4 unit volumes of feed gas per day.

What we claim as new and wish to protect by Letters Patent is:

1. Process for the removal of absorbed hydrocarbon from absorption oil containing the same, comprising passing the absorption oil through a heating zone, introducing the heated oil into an initial separation zone under iash conditions to secure a separation between vapors and liquid, withdrawing the liquid from the initial separation zone and further heating the same, introducing said liquid at an intermediate point of a distillation tower, withdrawing the vapors from the initial separation zone, treating the same in a cooling zone and passing the same to a secondary separation zone, effecting a separation between vapors and condensate in said secondary separation zone, introducing the condensate from said secondary separation zone into said distillation tower at a point intermediate the point at which said liquid is introduced and the top of the tower, removing absorbed hydrocarbons overhead from said distillation tower, substantially fully condensing said overhead, withdrawing a portion of said condensate as a recovered product, and returning va portion of the same to the top of said distillationy tower as reflux.

2,l Process in accordance with claim 1 in which said absorption oil is heated to a temperature of in the range above about 250 F. prior to introducing the same into the initial separation zone and in which the vapor is removed from said initial separation zone and cooled to a temperature below about 100 F. prior to introducing the same into said secondary separation zone.

3. Process for the removal and recovery of hydrocarbon constituents which may be included in motor fuels from hydrocarbon gases containing the same comprising countercurrently contacting the feed gases containing the hydrocarbon constituents which may be included in motor fuels with an absorption oil under temperature and pressure conditions whereby said hydrocarbon constituents are absorbed in said absorption oil, withdrawing the absorption oil containing the absorbed hydrocarbons from the absorption zone, passing the absorption oil through a heating zone, introducing the heated oil into an initial separation zone under flash conditions to effect a separation between vapors and liquid, withdrawing the liquid from the initial separation zone and further heating the same, introducing the heated liquid into an intermediate point of a distillation tower, withdrawing vapors from the initial separation zone, treating the same in a cooling zone and passing the same to a secondary separation zone, effecting a separation from between vapors and condensate in said secondary zone, introducing the condensate from said secondary separation zone into said distillation tower at a point between the top of said tower and the point at which said heated liquid is introduced, removing overhead from said distillation tower the ab` densing said overhead, withdrawing a portion of the condensate as a nal product, and introducing the remainder thereof to the top of said disl tillation tower as reiiux.

4. Process in accordance with claim 3 in which said hydrocarbon constituents may be incorporated in motor fuels containing 4 or more carbon atoms in the molecule.

5. Process according to claim 3 in which the rich absorption oil is removed from the bottom of absorption zone at a temperature below about 120 F. and in which said absorption oil is heated to a temperature above about 250 F. prior to introducing the same into said initial separation zone and in which the vapors removed from said initial separation zone are cooled to a temperature below about 100 F. prior to passing the same to said secondary separation zone.

6. Process according to claim 3 in which said distillation tower is a high pressure still operated at a pressure of from to 120 lbs. per square inch, and is utilized in conjunction with a low pressure still operated at a pressure of about 3 to 10 lbs. per square inch and under conditions whereby the overheads from the respective stills are substantially fully condensed at temperatures in the range below about F.

WALTER H. RUPP. KENNETH E. THORP.

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