US 2598785 A
Description (OCR text may contain errors)
MOVING BED SELECTIVE ADSORPTION SEPARATION ZONE IN V EN TORS GROEBE KARBOSKY ATTORNEYS J. L. GROEBE ET AL Filed Jan. 4,
June 3, 1952 TREATMENT 0E GAsEoUs HYDRocARBoN MATERIAL STREAMS F/G. l
i" T.' BY
Mm MIM FEED t' lib Patented June 3, 1952 PATENT oFFl-CE TREATMENT or GAsEoUs HYDROCARBON MATERIAL STREAMS Jenni.; Groene 'and joseph T.'Kartosky,.arnes ville; Okla., assigfnr's to' Phillips Petroleum'- Co'inpany, a 'corporation of Delaware Aopncationnnua'y 4, 195o, serial No'. 136,822 s claims. (C1. cl2-175.5)
ThisV invention-relates to methods for separating nitrogen from'niethane and from-other mix-- tures,rparticularly -na-tural gas. In one particular aspect it relates to methods for increasing the heating value oi?A gasY streams containingnitrogen, particularly nat-uralgas;` In anotherA particular aspect -it relates -to-methods for decreasing the-*volume occupied vby naturalv gas` by lremoving inertV materials therefrom, and thereby greatlyreducing vthe cost of -pipe line transportation. In still another-aspect'it relates to a new method of treating.-natural"gas` to remove nitrogen'produce la-rnethane stream and an ethane Streami Natural;v gas asit comes from producing wells gasin-city gas'` systemsi The natural gas may be employed in .the form-inyvhich it ,is received inthe` cityV or lit maybe -usedto enrich ordinary manufactured gas to increase the heating value thereof.vv In'v either event and `especiallywhere the naturalr gas isV used-forrenrihment of manufactuijed gas; it isA desirable that thenatural gas have ashigha B. t. value aspossiblef.4 At the nsaine time it-iscustomary to remove from the natural. Ygas at or 'near the point of its productin, as..uch. ofk the heavier components as is..cic'ncallypossible.KVV This may ;be donefby the ordinary processes of making natural gasoline. The heavier-,components (especially propane. aaa heavier f hen separated. and lique-- ed,-b"1"irig a much-.higher pricevthan-they would if ,vvr and 'sold-in the gaseons form. it thle sainetime'- there are minimum spjecifloations...on theeheating value, ofA natural gas s`ld for fel purposes. Usually it isrequired that the gas have a minimumnheating value of 1000 Bit. i1 per' cubic foot.A This prevents the also, afg'a's ofthis!latter-rheatingvalewn.;60
yield a-considerable quantity of liqueable coni-v ponents (such as gasoline hydrocarbons) and yet maintain a heating vvalue of 1000B. t. u., A typical natural gas from thel TexasPanhandle areamay be analyzed as follows;
M 1 etmial Haimg* o u. u. l Y a ue Y g Component Fraction oi Pure Contributedv I Component to gas Nitrogen 0. 1288 0 Methane. O. 7 458 l, 013 756 Ethane. 0. 0634 1, 775 112 Propane 0. 0411 2,526 104 Butane 0. 0176 3, 276 58 Pentane 0. 0051 4, 025 20 Hexane 0.0019 4, 773 9 01+ 0.0013 5, 521 I ,Y 7
Total 1 1, 065
1 B, t. u./cu. Ft.
If" th nitrogen content of such a gas be re#-l movech the-resulting gas has Vtsheating value increased to'1215 B. t. u. per cubic foot as shown in the' followingk table:`
Heating Mol Value K Fraction Contributed to Gas Component 1 B. t. u./cu. Ft. `From the .foregoing itvwill be seen that th removal of nitrogen from natural gas is very important. Various means have heretofore been'f promedio @freeing www ofnffieenifwm natural gas. Previous proposals may -be divided broadly into tvvo classes whicl'iin turn maybe y subdivided broadlyl into tivo classes', ,as follow s (A). Chennai methods, 1 asiatica of mingen as by causing the nitrogen selectively to chemiedrof the unreaotd 'hydrocarbon residue gas,
(2)Y Selective reaction of the' hydoaiibo with al suitable -iatiaL such asreactir with Water fof th hydrate. Whieh may be Separated ,and ttd in kivv' lnner to lregenerate .thhydocarboh; and (B5 Physical methods (1)l sep? aration of nitrogen from hydrocarbonV as by scrubbing with a solvent which selectivelyfdis solves the nitrogen and is vrelatively a non-solvent forI the hydrocarbons, by a diffusion nrethocll taking advantage of the difference in diftus'ionq rates of the. nitrogen and the-hydrocarbon through a suitable membrane or diffusion member, (2) separation of hydrocarbon from nitro-V gen as by scrubbing the gas with a solvent which dissolves the hydrocarbon and is relatively a non-solvent for nitrogen, or by so-called deep refrigeration in which the natural gas is liqueed and fractionally distilled at low temperatures. For Various reasons no plan for the removal of nitrogen has been used commercially. Each of the previously advanced proposals has involved variousl disadvantages, such as excessive costs, insuiiicient separation factor, etc.
Low temperature fractional distillation toV remove nitrogen from natural gas or methane has not proven practical or economical because the i reux to the column is substantially pure nitrobe adsorbed and this requires a high circulation rate of adsorbent, such as activated-charcoal, and large equipment to handle a comparatively small amountof gas.
We have invented a combination process for treatinga gaseous mixture comprising nitrogen, methane and Cz and higher-boiling hydrocarbon materials which can advantageously be applied to removing nitrogen from natural gas. In carrying on the process of our inventionin treating a gas containing C2 and higher-boiling hydrocarbon materials as well as nitrogen and methane, we compress and cool the gaseous mixture to condense Cz and higher-boiling hydrocarbon materials. The resulting gaseous mixture of nitrogen and methane is then fractionally distilled at low temperature to yield an overhead mixture of niltrogen and methane and a bottoms of methane. The overhead mixture contains sufficient methane so as to have permitted condensation of a methane-rich reflux, thereby reuxing the lowtemperature fractional distillation zone with a reflux stream which is rich in methane and in equilibrium with the overhead mixture of nitrogen and methane, permitting operation at' a higher temperature than normal with far less refrigeration. The resulting overhead methane and Vnitrogen stream is then separated in a selective adsorptionseparation zone, preferably a continuous moving bed selective adsorption separation zone utilizing activated-charcoal, to produce a nitrogen streamY and a methaneV stream. Since the quantity of methane has been greatly re- `duced by the low-temperature fractional distillation operation, the capacity of the selective adsorption separation equipment has been increasedA or, rfor example, less circulation of adsorbent inV moving bed systems is required. vIn addition, the low-temperature fractional distillation stepprovidesa nitrogen and methane feed stream to thev selective adsorption separation `zone at a low temperature, `thus aiding adsorption and-increasing the capacity of the selective adsorbent. Y 1
'In a modification of the process of our invention, the condensate of C2 and higher-boiling hydrocarbons resulting from compressing and cooling the Yfeed gas mixture, for instance, natural gas, is fractionally distilled to yield an overhead `methane and Cz .hydrocarbons stream .which is fed to the selective adsorption separation zone of our invention. If a natural gas is being treated deethanization results in recovering methane `unavoidably condensed along with ethane and higher-.boiling hydrocarbon materials in the compressing and cooling step of the process of our invention. The selective adsorption separation step of our invention is then operated to recover an overhead nitrogen stream, a side product methane stream and a bottoms C2 hydrocarbon stream. Thus, a AC2 hydrocarbon stream, for instance ethane if a natural gasis being treated, is made available for cracking to or recovery of ethylene which can be used in the many chemical synthesis processes known inthe prior art.
It is an object of our invention to provide a method for the separation of nitrogen from methane and from other mixtures, such as natural gas, in a simple and economical manner.
Another object of ourinvention is to provide Va method in which refrigeration requirements are very muchV lower than in so-called deep refrigeration or low-temperature fractional distillation processes for nitrogen removal.
Anotherobject of our invention is to provide a process whereby nitrogen removal is accomplished while at the same time a methane stream and a C2 hydrocarbon stream are produced.
Other objects andadvantages of the process of this invention will become apparent, to one skilled in the art, upon reading thisY disclosure.
The drawings which accompany 'and are a part of this disclosure are diagrammatic flow sheets' setting forthv preferredspecific embodiments of the process of our invention. Figure 1 depicts an embodiment of the process of our invention used to removenitrogen from a gaseous mixture comprising nitrogen, methane and C2 and higherboiling hydrocarbon materials, such Vas a natural gas, and to produce a methane stream'and a C and higher-boiling hydrocarbon stream. Figure 2 depicts an embodiment of the process of our invention used to produce a C2 hydrocarbon stream, `"an ethane streamif naturalgas is'treated, as well as to remove nitrogen andproduce a methane stream.
Referring 'now to Figure 1, the following is a discussion of-a preferred specific embodiment of the Vprocess of our invention wherein a feed gas stream comprising nitrogen, methane and C2 and higher-boiling hydrocarbon materials, such as a natural gas, is treated to remove nitrogen, produce a methane stream and a C2 and higherboiling hydrocarbons stream. The feed gas stream is passedv v ia line Minto compression and cooling zone 6 wherein it is compressed and cooled to condenseV C; and higher-boiling hydrocarbon materials. Resulting condensedv materials are withdrawn via line 8 for further treatment, as dis-v `c ussed hereinafter withregard to the modificaerated to produce a nitrogen and methane stream I which is withdrawn overhead viav line I4' and a methane bottoms stream which is withdrawn via line I k6. 'I'hisrme'thaneAv stream which is preferably substantially free of nitrogen' is combined f Wthanother methane str'eamfpro'duce'd ashereinafter set? fo'i'ftlfi,Y a-n-d- Withd'rawnfrom the system'A or'it canbe `used afs-.desiredi.` y Fractionationgzone I2- is operatedso that considerable vi'ethanels i carried cverheadwith the nitrogenand-since this'` overhead gas s'trea-misi-n equilibriumwith liq'uidk reilu'x to fractionation- Zone-112, the liquid refill-X l isf relatively rich methanevtlfius requiring less refrigeration and 'allowing for higher oper-ating temperatures than would possible inmakinga relatively finite separation bet-Ween nitrogen f and methane. y
'Il'ie'nitrogenA and methane mixture-Withdrawn overhead from fractionation'- zone l2 via linel I4- is passed-intoV selectivegadsorptioi-r separation zone I8 which is preferably a continuous moving` bedselective adsorption' separation zone; Therein Anitrogen and methane aIeseparatedf The* nitrogenL is removed fromV selective" adsorption'V separation zone 18? via` line 2t and the :methane tion4 vof the methaner stream, stripped `from ythe selective adsorbent; preferably activated-charcoaLin the stripping-section of selectiveladsorp': tion separation1 zone ij8`; as they stripping mediumj.' However,V otherstrpping mea-ns can bef'used.v A`
portion of the-.methane streamin lines22'jiswith'- drawn via linev 24,9; heated' in indirect heat ex-n change means 28"and' passed'` into the lower portion' of theV stripping section'thus furnishing heat to strip methane from theselective adsorbent.
On' Figure 1- a gais-liftsystem,` using nitrogen Withdrawn fromV linei ZlYVi'ak line' ZSand pres-Y sured by kblower 30', is used toelevatesel'ective ad; sorbent back into the upper'portionofse'l'ective adsorption separation zone IB'via line'32. However,other'elevating` means, su'chas mechanical elevating means,` canbe used. Methane remaining on the-'selective adsorbentpassed backri'nto the upper portion ofselective adsorption separation zone lis removed by passing a. portion of the' nitrogenoverhead gas Aup through'tlie-se'- lective adsorbent prior toits" introduction intoV hereinbefore discussed', is' treated't remove ni.A trogen, producea methaneV stream and, in addifA tion,` recoverniore methane and produceafCzhydrocarbon stream, an ethane strearnif riaturalI gas isbeing treated. The same lreference.numerals" are used on Figure 2 as usedon'Figure 1 WhereA the equipmentA performs the same operation or the same operation is carriedout. In this embodiment of the process of our invention, the Cz and.higher-boiling'hydrocarbon materials Withdrawn from compression and cooling zone 6 via line 8 are fractionally distilled in fractionation zone t,A which, if a natural gas is being treated, would be a deethanizer, toV produce a methane and C hydrocarbon stream overhead, which is withdrawn via line 40, and a higherboiling hydrocarbon material stream as bottoms, which is Withdrawn via line .42? to be treated'oi used as desired. 1
The methane and Cz hydrocarbon stream; which contains methane condensed.'` in comprese? sionl and 'cooling zone 6, is passedvialinewm.. into selective adsorption separation Zone` 141,11;
which is designed to make a= methane .side'epro'duct stream and is preferably'a continuous'fimv; f.
ing bedv selective adsorption .separation zone',y usingr activated-charcoal as the `selective a'dsorb' ent. Y This streamfisintroduced ata: pointJb'elo'vv" the point of- Withdr'awal ofthe methanel 'side'. product stream whichv in A turn belowthe point.-
ofl introduction ofthe -nitrogenand methanefeed stream introduced via linel i4; The'fmethane y trodu'ced inthevfe'edstreams isseparated," re# moved via lin'e441as" a-..side'product 'str'ea'xY and l withdrawn from the system, ori-it can 'be-.come l bined with the methane stream from f-r"actirn'ia".--A
tion zone IZ via line 46 and Withdraw'nlfo-m'fthe system.- Inthis methodor operation tliemethane in the gas stream treated is substantially'- conpletely recovered f-r'e'e off nitrogen to be avail# .able for sale or use as fuel-gas. C2' hydrocarbonv isl separated and withdrawn yfrom selective ad-` Y sor-ption zone 42r -via linerdl Any suitable strip# ping medium can be used to strip the C; hydro# car-bons fromv the selectivegadsorbent in thelovver' 'stripping section of selective adsorption separation.' zone 42 but We prefer to'use a portionof thei Czlhydrocarbon stream inline 48: A portionf of this. stream-,is withdrawn via line 50, heated indirect heat exchange means 52 .and-passedinto" the lower'portionY of Athe' stripping-A section. C2- hydrocarbon. remaining 1 on: the'v selective adsorbent elevated back into Ythe upper section ofi-'zonel 42 is removed by passinga-porti'on of the nitro-'- gen overheadlgas up through .-theselectiveadsorbent prior to itsLintroduction-mw the a'd'sorpl-v tion zone; This .nitrogen gas .andi removed/C21 hydrocarbon is VWithdrawn via line 3'4 to` lie-fused as desired, such as a low. Bft. u. fuel-gas.-
l Carrying On the-.processfof-ourf ir'ivention5A and `its modication, .as- Iset `forth hereinbefore,
We ndA it particularly r ad'va'nt'ageou'slyl applied-totreating al natural gascontaining'- froriiilft 30v mol per cent or morenitrogen, from 55vto'- '75111101 per cent methane andthe remainder Ce and v higher-boiling hydrocarbon'- materials". We lp're-r` fer to. compress and? cool-.to a pressure ofv 200' to 1000 poundsV per square inch absolute andV atemperature of front-50oA F. 200 F., more preferably toa temperatureof from SOP-*Fitto 1659 F. Compression and cooling is preferably' carried out to an'Y extentthat the nitrogen and methane'. stream passed to the'denitrogenation zone, fractionation zone HKv contains o"inoie" than 1-.5-mo1 per cent Cz'and `higher-boiling'hyed'rocarbonjmaterials.
Weprefer'to operate fractionation zone' I'2at a pressureof'from 200 to 500 pounds :per square inch" absolute and a top temperature off'rom.
-8'0` FI to 2506 F. to producean overhead feed gas stream for selective adsorption separation..
zones1I-8 and l2Y containing from 55 to; 75.moi percent nitrogen and 25to 45 mol per-"centVA methane. Such'an overhead. gas'tstre'amwprovides ya methane rich reuxf stream,v Witha which itisinequilibrium, to reflux fractionationvzon'e. l2. Selectiveadsorption separation -zones .1I 8;'ar'1`d 42-are1preferably' operated at a: pres'sure.orf-*frontv 200' to .500p`ou-nds .per square inch absolute I` the modification.- f" our invention asdel picted:r byFig'ure 27,- frac'tionatic'n'i -Zne 38v -isf rior#l mall-y arid-preferably- Opla'ted-to produce overhead gasto feedselective I adsorption separa#y tiorr-y Zone 42' containing from 35 "to f 750" mol-"pe cenemethanev. and :from-A so.. tof Sv mor per' centi- C2 hydrocarbon or ethane, if natural gas is being y treated.
i The discussions set forth hereinbefore of the y preferred specificembodiments of the process of l our invention and the drawings will serve as examples of the process of our invention. However; such discussionsdrawings, operating conditions, compositions, materials, etc. are not to unduly limit the scope of our invention.
As will be evident to those skilled in the art,
l various modifications of this invention can be made, or followed, in the light of this disclosureV and discussion, without departing from the spirit or scope of this disclosure or from the scope of the claims. f
We claim: 1. A process for treating a gaseous mixture comprising nitrogen, methane, and C2 and higherboiling hydrocarbon materials which comprises:
` fractional distillation zone, passing same into a selective adsorption separation zone and therein separating nitrogen and methane; land withdrawing aresulting overhead nitrogen stream' and a bottoms methane stream from said selective adsorption separation zone.
2. The process of claim 1 wherein said lowtemperature fractional distillation zone is re- Aa C2 and higher-boiling hydrocarbon materials stream resulting from said compressing and cooling into a second fractional distillation zone, therein effecting a fractional separation and withdrawing an overhead stream comprising methane and C2 hydrocarbons, passing said nitrogen and methane stream withdrawn from saidV first fractional distillation zone and said methane and C2 hydrocarbons stream withdrawn from said 'second fractional distillation zone into a selective adsorption separation zone and therein effecting separation of nitrogen, methane and C2 hydrocarbons; and withdrawingan overhead nitrogen stream, a side product methane stream and a bottoms C2 hydrocarbonstream from said selective adsorption separation zone.
5. A process for treatingv a gaseous mixture comprising nitrogen, methane and saturated Cz and higher-boiling hydrocarbon materials which comprises: compressing and cooling said mixture to a pressure of from 200 to 1000 pounds per square inch absolute and a temperaturei` offromV F. to 200 F., thereby condensing'said C2 and higher-boiling hydrocarbon materials; passing resulting uncondensed nitrogen and methane into a first fractional distillation zone operating at a pressure of from 200 to 500 pounds per square inch absolute and a top temperature of from 250 F. to 80 F., therein effecting a fractional separation of Anitrogen and methane and withdrawing an overhead stream containing Vmethane and from to 75 per cent nitrogen; passing a C2 fluxed with a methane rich redux in equilibrium Y l with said overhead stream containing nitrogen and methane 'withdrawn from said low-temperature fractional distillation zone. Y
Y3. A process for treating a gaseous mixture comprising from 10 to 30 per cent nitrogen, from 55 to 75 p er cent methane` and C2 and higherboiling hydrocarbon materials which comprises: compressing said mixture to a .pressure of from 200 to 1000 pounds per square inch absolute and cooling same to a temperature of from 50 to 200 F., thereby condensing said C2 and higherboiling hydrocarbon materials; passing resulting uncondensed nitrogen and methane into a lowtemperature fractional distillation zone oper-- ating at a pressure4 ofA from 200 to 500 pounds per square inch absolute and a top temperatureV oflfrom 250 F. to 80 F. and therein effecting afractional separation of nitrogen and methane; withdrawing an overhead stream containing 'methane and from 55 toY 7 5 per cent nitrogen from `said low-temperature fractional distillation zone,
passing same into a continuous moving bedV selective adsorption separation zone, operating `at a pressure of from 200 to 500 -pounds per square inch absolute and therein separating nitrogen and methane; withdrawing a resulting overhead nitrogen stream anda bottoms methane stream fromV said selective adsorption separation zone. 4. A process for treating a gaseous mixture comprising nitrogen, methane and 'C2 and higherboiling hydrocarbon materials which comprises: compressing and'cooling said mixture, thereby Vcondensingl said C2 and khigher-boiling hydrocarbon materials; passing resulting uncondensed nitrogen and methane into a rst fractional distillation zone operating at low-temperatures, therein effecting a fractional separation of nitrogen and methane and withdrawing an overhead` stream comprising nitrogen and methane; passing and higher-boiling hydrocarbon materials stream resulting from said compressing and cooling into a deethanization zone, therein effecting a fractional separation and withdrawing an overhead stream containing from 35 to '70 per cent methane and from 30 to 65 per cent ethane; passing said nitrogen and methane stream Vwithdrawn from said first fractional distillation zone and said methane and ethane stream withdrawn from said deethanization zone into a continuous moving bed activated-charcoal selective adsorption separation zone operating at a pressure of from 200 to 500 pounds per square inch absolute and therein effecting separation of nitrogen, methane and ethane; and withdrawing an overhead nitrogen stream, a side product methane stream, and
a bottoms ethane stream from said selective adsorption separation zone.
6. A process for separating a gaseous mixture comprising nitrogen and methane which comprises, passing said mixture into a low-temperature fractional distillation zone and therein effecting a fractional separation of nitrogen and methane, thereby producing an overhead stream `of nitrogen and methane in equilibrium with a methane rich stream, using said methane rich stream to reflux said low-temperature fractional distillation zone, separating said overhead nitro- A gen and methane stream in a selective adsorption separation zone to produce an overhead nitrogen stream and a methane stream.
JOHN L. GROEBE. JOSEPH T. KARBOSKY.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,230,219 Carey Feb. 4, 1941 2,475,957 Gilmore July 12, 1949 2,519,343 Berg Aug. 22, 1950