US2226467A - Utilization of petroleum refinery gas - Google Patents

Description

E.'B. HJERPE ETAL l UTILIZATION OF PETROLEUM REFINERY GAS' Dec: 24, 1940.

Filed May 7, 193e NNJOOU MzSM Q21 MIMJL lkw eifpes 2 use,

.vt/fiamma v .f www* Patented Dec. 24, i

UNITED STATES PATENT OFFICE Y n 2,226,461 e e 4 U'rI'LIzA'rIoN or PETnoLEUM REFINERY ons, A

. Eric B. Hjerpe, Port Arthur, Tex. and William A. Gruse, Wilkinsburg, Pa., assigner: to Gulf Oil Corporation, Pittsburgh, Pa., acorporation of Pennsylvania Application May '1. 193e, sei-iai no. 78,480

e 1 claim. (ci. zoo-ssa) This application is in part a continuation of vour application Serial No. 613,774, illed May 26,

1932, now U. S. Patent No. 2,099,480.

The invention covered by this continuation-inpart application relates to the utilization of pevtroleum refinery gas, and comprises a continuous process wherein renery gas containing methane,

. ethylene, ethane. propylene, propane, butylene,

butane, pentanes and higher boiling constituents, lo 1s stripped yof its contained gasoline vapors (pentanes and higher boiling components); the residue is next strippedof methane for deposition as desired; and the residue from the last mentioned separation is further subjected to successive fractionation for isolation of cuts containing individual oleilns such as ethylene, propylene and butyle ene; the charging stock for a polymerization or gas conversion operation conducted for the purpose of producing motor fuel.

More specifically, this invention provides a continuous process wherein uncondensed gas from the customary water-cooled condensers of petroleum cracking stills and/or coke stills and/or steam stills (said gas comprising methane. 25* ethylene, ethane, propylene, propane, butylene,

butane and higher boiling components) is subjected to compression and/or absorption steps to liquefy and thereby separate and remove higher boiling constituents, leaving a residue of stripped 8 refinery gas. This stripped reilnery gas is chilled to a temperature sumcient to liquefy all components (higher boiling than methane and is introduced into a tower and the methane fractionated out, the necessary chilling of the gas being eiectas ed by expanding it through an expansion valve after compressing it to the necessary degree and cooling it with water. The liquid residue from lthe last mentioned tower is expanded into the second tower and the ethylene and ethane are similarly fractionated out; the liquid residue of the last mentioned separation, now freed .of ethylene, ethane and methane. is expanded into a fractionating tower and the propylene and propane are fractionated out from residual butylene and butane. e l

In particulanour invention relates to a method of fractionating gases of the character indicated, in which the gases after fractionation thereof, are passedthrough a series of fractionating steps in which constituents or fractions of successively higher boiling points are removed, residual liquid from anyone of the aforesaid'towers beingemployed to assist in the fractionation and sep?- aration taking place in a preceding'tower;

,. ,u v In order that our invention maybe clearly-.set

forth and understood, we now describe, with reference to the drawing accompanying and forming a part of this specification, a preferred manner in which our invention may be practiced andem ployed. Y 5 In the drawing the single figure is a more or. less diagrammatic view of apparatus for carrying out our invention arranged primarily as a ilow sheet.

Referring to the drawing, the numeral I indicates a stream of charging stock to a conventional cracking still comprising a cracking coil 2, separating and dephlegmating tower 3, condenser l, and separator 5. These elements do not constitute a portion of this invention but are included4 for clarity of presentation. After condensa- 15 tion of `cracked distillate in the condenser 4 the distillate is separated from accompanyingiincondensed gasin separator 5. This gas, conducted away through line 8, is raw material used in the process which constitutes our invention. Other raw material for our process is the corresponding uncondensed gas from petroleum ooking stills, lubricating stills, and steam stills. Any one of these gases alone or any mixture of them is acceptable raw material and this raw materialwill 25- hereinafter be referred to as still gas', or petroleum renery gas.

As a preliminarystep, the gas is first stripped of pentanes and all higher boiling constituents. Some butane and butyiene may be removed at this point, if it is ldesired to retain this mate, rial as suchin the cracked gasoline. This separation may be effected in various ways and we have found compressionr and absorption methods very satisfactory, with subsequent controlled u fractionation ofthe absorbed material. Absorption is-most effective when we maintain a'superatmospheric pressure of the order of 250 pounds or 300 pounds in theabsorber. 'I'he compression can be effected in two stages as shown in the o drawing, with recooling of the gas after each compression stage. This compression andy subsequent cooling will liquefy some of the' higher boiling constituents oi the gas and so a separator is placed 'in the line which conducts the cooled gas from one compression stage to another compressor. Liquefled material removed from this separator is termed compression gasoline. drawing depicts two-stage compression with compressors 1 and in, followed by recooling in coolers o 8 and- Il respectivelyf and removal of compresarator 9 through line I3. After compression to u gas, leaves the absorber through line I5.

dissolved constituents of the gas, leaves the bottom of absorber l2 through line I6 and is introduced through line I8 into a tower I9 where the absorbed constituents of the gas are distilled off and fractionated. Tower I9 is preferably opervated under a superatmospheric ,pressure and 1 should its pressure not be suiciently below that Per cent Methane 45 'Ethylene 5 Ethane 20 L Propylene I 8 Propane 15 Butylene 3 Butane 4 of the absorber to cause the necessary iiow through lines I6 and I8, a pump l1 can be inserted in the line to effect the transfer of the liquid. Heat for distilling the absorbed constituents of the gas out of the absorbent oil in tower I9 is provided by a closed steam coil or equivalent heating means in the lower portion of the tower. The upper portion of tower I9 is designed to ei'- fect clean fractionation ofthe absorbed material from the absorbent and the so-fractionated vaporsfrom tower I9 pass to, andare condensed by, condenser 20. The eii'iuent of the condenser passes to gas separator 2I where any unliquefled components of the gas are separated from the liquefied components. The condenser and gas separator 2| are maintained under the same pressure and the pressure and temperature of the condenser are chosen to assure liquefaction of normally liquid constituents without liquefaction of normally gaseous constituents, for example, propane and propylene. Any higher boiling fractions of the refinery gas which are liqueed in condenser 20 and separated from accompanying gas in separator 2l are conducted away through line 22. 'I'hat portion of the petroleum refinery gas which passes through condenser 20 without being liquefied therein passed out of the top of gas separator 2| through line 23. This line joins line I 5, previously described, and the combined stream is termed stripped refinery gas. This stripped refinery gas contains butylene and butane and all of the lower boiling constituents of the pertoleum refinery gas. The relative proportions of the various constituents vary widely according to the kind of oil from which it originates, the kind of still in which it is produced, the temperature, pressure, and other conditions attending its creation, and the condensation of accompanying vapors in the still condenser (condenser 4 or its equivalent). One typical analysis of the stripped refinery gas-insofar as any analysis could be termed typical--was the following, observed in operation of the process herein described and claimed:

Our next step is to fractionate out the methane. We do this by introducing the `stripped reiinery gas at a sufficiently low temperature into a fractionatlng tower and the low temperature is obtained by self-coolingr 'incident to expansion' through an expansion valve or work engine. Further details follow. 'Ihe stripped refinery gas in line I5 is compressed to whatever degree is necessary to effect that cooling at the expansion valve which is requisite for liquefaction at tower pressure of all constituents of the gas which boil at higher temperatures than methane. The tower pressure is advantageously chosen to permit further pressure drop in subsequent fractionating steps and yet maintain suitable'worklng pressure at the last fractionating step. The

methane is fractionated out ln the tower 35 and in our practice of the invention we have found a pressure of 500 pounds per square inch above atmospheric, before expansion, to be suitable for a gas such as the one which an analysis is shown above, and a pressure of seven atmospheres within the tower to be quite satisfactory. This pressure is generated by compressor 24 and the heat generated in compression is removed from the gas by a cooler 25. The compressed land recooled gas is then in condition for chilling by expansion, for introduction into the towerl at 33 and for fractionation therein. Expansion and consequent cooling is effected at expansion valve 3l. Maincontent of the gas with a tower head temperature of minus 140 C. and the remainder of the gas leaves the base of the tower in liquid form at a temperature of minus 60 C. The fractionation in the tower is more easily controllable if we have a chilling means in the tower head and a warming means in the tower base. These are readily provided for by closed coils 21 and 32 in the' tower base and head, respectively, and bypass connections in the incoming gas line, to admit of circulating this gas therethrough in such quantity as' is necessary to obtain the required control. Three valves 28 are shown for permitting the use of regulated amounts of the unexpanded gas for controlling the temperature of the tower base and similar by-pass connection and valves are provided to permit the use of regulated amounts of the expanded gas for controlling the temperature of the tower head. 'Ihe by- Pass connection and valves 28 have been illustrated in\c,onnection with coil 21, their similar arrangement in connection with head coil 32 has been yomitted from the drawing for simplicity of illustration. These same remarks apply as to the head coils in towers 40 and 15, each of which is.

therewith through a. pierced diaphragm 36. The.

methane nnally ows away through line 31 for utilization.

The liquid residue leaves tower 35 through line 34 and comprises ethylene, ethane, propylene. propane, butylene and butane. This liquid is discharged into tower 40 at 42 for fractionation of ethylene and ethane from the propylene, propane, butylene. and butane. Tower 40 may be provided with coils 33 and 39 ior assisting in controlling the head and base temperatures thereof, and these coils are connected with line 3l in by-pass arrangement and sequence as already fully described in connection with coils 2 1 assess? j Y and. 32. A pressure of `six-atmospheres is maintained in'tower 40 and the ethylene and ethane leave the top of the tower through line 4C at a temperature of minus 50 C., while the propylene,

propane, butylene, and butane leave the base of the tower .through line `43 at a temperature of minus C.

A mixture of propylene, propane, butylene, and

i butane is removed from the base of tower 40 through line 43 under a pressure of six atmospheres. This is conveyed through line 4I to 4tower 15, and is expanded at expansion valve 1I prior to its introduction thereinto at 14. Tower 15 is provided with base coill y12 and head coil 13 similar to coils 21 and 32 oi tower 35 and completely described in vthat connection. The contents of line 43 or a portion of them may be by-passed through coil 12 for regulation of the A temperature .of the tower base, and all or a portion of them, after expansion through valve 1I. may be by-passed through coil 13 for regulation of the tower head temperature. As previously stated the by-pass connections for coil 1l have been omitted from the drawing 'for purpose oi simplicatlon. We operate tower 15 at a pressure of live atmospheres andv maintain therein a head temperature of 0 C. and a base temperature of plus C. Thereby we effect fractionation of the incoming stream and take off from the tower head, through line 16, a mixture of propylene and propane, and from the tower base we take olf a residue of butylene and butane through line D. The butylene-butane fractionis conducted away through line D for further utilization as desired. J

Throughout the various fractionations in the process illustrated. we may improve the separation by discharging a portion of the more closely separated/product of one tower back to the head of the previous tower, to constitute an open reflux stream therein. Thus, a portion of the liquid product removed from the tower ,4D through the line 43 may be returned through a line 80 having a pump 8l and a valvev 82 to the upper portion of the tower 35, to serve as a reflux and absorbing and concentrating medium. By means of the valve 82 and a further valve B3 located in the line 43, the proportions of the liquid withusual manner.

Similarly, a portion of the butane containing fraction removed from the bottom of the tower l 15 through the line D, may be delivered to the tower 40 as reflux. For this purpose, we provide a line 85 having a valve 86 and a pump 81 and communicating at one end with the line D and terminating at the other end in the upper portion of the tower 40. An additional valve 88 may be provided in the line D which with the valve 85 may be employed for the purpose of regulating the proportion ofthe liquid returned as reflux to the tower 40 and such excess liquid as may b e withdrawn through the line D.

Throughout the various steps of our process for utilizing petroleum refinery gas we can of course reduce the number of steps in fractionating out a. cut containing any particular olefin when it does not disadvantageously ailect the usefulness of adjacent fractions or where, under the particular circumstances, the adjacent fraction is not to be used. Likewise, where it does not affect the usefulness of adjacent fractions, we can fractionate to get the desired olefin as the principal scription that in our process refinery gases which 5 are to be separated into twofractions relatively high and relatively low respectively in a lowboiling and refractory constituent, such as ethane or ethylene, are introducedinto a fractionating tower, to the upper portion or which is-supplied `10 'as reflux a liquid free orsubstantially freeV of such constituent and comprising, for example,`

butane and butylene.` The bottoms from this 'fractionating tower are then subjected to a second fractionation for the purpose of removing any constituents absorbed by the reflux and the bottoms from the second tower, thus stripped of said absorbed constituents, are returned at least in part to the first fractionating'tower as a reriuxing and absorbing medium. it being understood that the function of absorption is inherent inthe action of a liquid reflux. y Asa result of this absorbing 4and stripping action, the overhead from the second tower is substantially richer in high boiling and hence less refractory constituents. for example propylene and propane, than the overhead separated from the first fractlonating tower.

It will further be understood that the proporf tions ofy any of the oleflns to the corresponding 30 paraiins (for example the proportion of butylene to butanel may vary considerably in accordance with the particular gases initially fed to the process and that such gases may comprise largely paramnic constituents, this `being largely a function oi' the type of cracking operation from which the gases have been initially derived. Thus, where the gases are largely paraiiinic in character, the overhead from the tower 40 will comprise largely ethane, the overhead from the tower 15 will comprise largely-propane and the liquid effluent from thebottom of the tower 15 will consist largely oi' butane. In general however, both parainic and oleflnic constituents will be present, as both paraiflnic and oleilnic constituents are found at least to some extent in the gases resulting from all oil-cracking operations.

The process of our invention is adapted to be employed wherever it is desired to separate mixed hydrocarbon gases of the character indicated into ay plurality of fractions, such for example as an Aethane-ethylene fraction.. a propane-propylene fraction and a butane-butylene fraction. These various fractions, being different in character, may then be advantageously subjected to different types of conversion operations, or may be subjectedwto conversion operations maintained under diierent optimum conditions according to thev natures of the individual fractions treated. Thus, the ethane-ethylene fraction and the propane-propylene fraction may be utilized for the production of ethyl chloride and propyl chloride, respectively, whereas the butane-butylene fraction maybe subjected to elevated temperature and pressure. with or without the assistance of suitable catalysts, in order to eifect the conversion thereofv to polymer gasoline.

Moreover, as has been indicated herein above, by reducing a number of steps inthe fractionation operation, we may similarly reduce the number of fractions segregated. Thus, by conducting the operation in two stages, we may removemethane as overhead from the tower 25 and may then complete the fractionation in a second l tower'. withdrawing as overhead therefrom a fraction comprising ethane, ethylene, propane and propylene.

It will be understood that our invention is not limited to the illustrative details set forth herein. but may variously be practiced and embodied within the scope of the claim hereinafter made.

What we claim is:

The process of recovering gases relatively free from low boiling parafiinic gaseous constituents such as ethane from hydrocarbon gases containing the same in addition to higher boiling nor: mally gaseous constituents, which comprises introducing said gases in at least partly liquefied form into a fractionating column, supplying to the upper portion of said column a reuxing andl scrubbing medium, removing from the upper portion of said column a gaseous fraction relatively rich in said low-boiling paramnic gaseous constituents, removing from the lower portion of said column a. liquid fraction, introducing the liquid fraction withdrawn from the first column the second column to the upper portion oi the iirst mentioned column to constitute the refluxing and scrubbing medium supplied thereto.

ERIC B. HJERPE. WILLIAM A. GRUSE.

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