CA2107492A1

CA2107492A1 - Integrated process for producing olefins from methane-containing gas mixtures

Info

Publication number: CA2107492A1
Application number: CA002107492A
Authority: CA
Inventors: Domenico Sanfilippo; Stefano Rossini
Original assignee: Individual
Current assignee: SnamProgetti SpA; Eni Tecnologie SpA
Priority date: 1992-10-01
Filing date: 1993-10-01
Publication date: 1994-04-02
Also published as: RU2100334C1; DE4333372A1; ITMI922280A1; ITMI922280A0; US5430219A; IT1255710B

Abstract

"INTEGRATED PROCESS FOR PRODUCING OLEFINS FORM
METHANE-CONTAINING GAS MIXTURES"
Abstract Disclosed is an integrated process for producing olefins by starting from methane containing gas mixture, which process essentially comprises the following steps:
-- converting methane into higher hydrocarbons by oxidative coupling carried out in the presence of air and/or oxygen;
-- dehydrogenating, with the aid of a catalyst, said higher hydrocarbons, with an olefin-rich mixture being obtained;
-- removing H2O, CO2, CO and H2 from the resulting olefinic mixture;
-- removing from said olefinic mixture any not converted methane, and recycling it upstream from the oxidating coupling;
-- separating ethylene form the olefinic mixture;
-- separating any not dehydrogenated ethane from the olefinic mixture.

Description

~107~92 .

"lNTEGRAT~D PROCESS FOR PR03UCIN~ OLE~N~ fROM
ME~HANE-CONT~INI~G GA~ ~XT~RES"
The prosent lnvontion relates to an integrated prooess for produo1ng r,l~ins by stsrt1n~ ~rom meth~ne conta;nlng ~as ~ixturas~ in part~cular from n~t~3l The ran~e of industr1~l u~es of eompour1ds cont~ln1ng ~ p~ur~L1ty of c~rbon ~oms is extremely w1de. Thc sources of c~rbon ~toms aro three:
petroleum, presently the m~or souree tp~trochem;stry); natura~ ~g, whose m~;n ao~Ponent ~5~ by far, ~eth~nc, and ~hlch 1s very often found to~ethcr ~lth petrolcum and coal ~part from the hlgher compr,nents presqnt in a wet natural gas, ~hich can be us~d as such, the industr1al-che~1cal explo;tation of m~thane and co~
ro~ulres that a b~ckbone ot at lou~t t~o oarbon atoms 1s bu~l~ and 8 rcactlvity slt~, e.g., ~ double bond, 1~ introduced: thercfor-, the mattor Is of converting them 1nto at loa~t ethylene.
A fe~1b~e roueo ~or sueh an up~r~dln~ 1g through s~n~as proparat10n. In ~uch ~ ~oy, m1xtures of var10u~
kl*ds of hiph~r ~1.e., contain1ng t~o or moro car~3n ~toms) p~ratf1n1c and oluf1nlc hydrocar~ons can b~
obtalned acGording to the so-sc1d "Fisoher-TroPsch"
roact10n, snd 1ts subse~uent modlflcations, over eat~ysts ot F-r Co, N1, us such, or ~s mixtures ~nd ... ..
v~r10usly ~odif1~d. ~eeordin~ to another route, syngas can bo converted lnto moth~no~ over Cu-, Zn-, Al-, C~
basod cataLysts o~ ox;de ~haracter ("oxidie -., ., : :
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eat~ysts ), aeeord1n~ to widely ~sed teehnologi~s on lndu~t~ c~e~ ~nd msthanoL c~n be eonvorted, in its turn~ lnto olef1ns, over zaollt~e mate~ials aeeordlng to the MTO prace~s.
The baslc problsm dlsplayed by the a~ove men~ioned proeesses i5 the ~me syngas preparation, ~hleh ts eeonomieally penal~21ng. ~elng 3ble to obtain ethy~ene d1rsetLy from th~ erlmary sourc- of e~rbon atom~ ~ithout hav~n~ to resort to ~ntermediate syn~s preparat10n~ ~s regariëd as ~ ~oal of the highest tnterest. Wh1~st such a dlrect rout~ apps~rs to bo ~mpo~s1~ in ths C~8e ot eoa~, methane can be caused to adv~nta~eously reaGt wlth air (oxy~en) on oxidic çataly~ts, w1th m1xtures ot hydroearbon3 o~ two or more carbon atoms bein~ obtal~ed: such a roaction ig kno~n as oxidative coupling .
Insido eaeh fr~ot~on eontalnln~ n carbon a~oms, the para~f1nle eomponent 1~ generally preva1l1n~ ov~r the o~et1n~e one. Only by oper~ting w1th Long contact time~, at the highe~t operating temperatures reported for ox~dat1ve eoup~lng, i.e., aSO-950~C, an~ in the presene~ o~ larger oxyg-n amount~ olefins can be obtained 1n an amount ~h1eh ~5 equal to~ or sLlghtl l~rger than, as of the corresponding paraffin.
~S Unfortun~tely, a lon~ eontaet time means poor throu~hput va~uos per eatalyst volume (or mass) ~nit ~nd t~m6 unlt, ~hilst larg~r ~ounts of oxy~en g~n~rate, 1n the pr~soncs of a higher methane converQion rate, lower s~lect1vity to hy~roearbons tor ox1datlve ~oupl1ng reaetion.

,: .~: . : . . . : , . . .

3. 2107~92 ;

~ ccording to an alternative proce~s it uas found that th~ ~ddlt10n of vol~tile chlor1n~-conta1nin~
or~anic compoun~s oar favo~r the ~ormat1On of ~thyl~n~
from ethane. The pro~cnce of such ~hlorin~ted compounds 1mpLi~s the presence of oh~or~ne in the end product. Suoh a prosenc~ wouLd cons1d~rab~y l~mit the poss1ble use of olef~ns o~ing to ~aterlal sp~cif1cat1On ~nd corrosion Prob~em~
The pr~sent Appli~ant~ have fo~nd no~ a p~ocess . .
wh1ch makes it poss1ble thc o~etin/paraftin ratio to be aonsid~rably ~noroa~ed 1n e~ch fraction of n carbon atoms where n is to be understood as mostly be1rg ~qua~ to two ant three and somtimes al50 four~ obta1ned by comb1n;ng a typical first ~tep ot ox~dstive coupl~ng w1th a ~econd st~p of c~talYtic dohydrogenat10n.
The ~ntegrated process for produc~ng olefins by start1n~ tro~ ~as m1xtures conta~ning mothane ~hich 1s the ~ub~oct matter of the present lnvention is oharaoterlzsd in that ~sid 1ntegrated prooes3 essent1a~y ompris~ the followln~ steps~
convert1ng methane 1nto h~gher hydro~arbons by oxldative o~up~n~ carr1e~ out ~n the presenco of ~ir andlor oxygen u~th mo~ar rat~o of CH~102 selocted ~-w1th1n the rango of from 1 to lO0 preferab~y of from 1.5 tO 20 at ~ temper~ture ~ompr~sod w1thin the range of from S00 to 1000~C~ preferably of fro~ 700 to 9SOoC~ under a prss~ure oomprlsed ~ith1n the ran~e of ~-trom 0.01 to 10 atm prqforably of from 0.5 t~ 5 atm and durlng a oontaot t1me comprlsed ~th1n the ran~o : .

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of fro~ 0.01 to 10 seconds, pref~rab~y of ~rom 0.03 tb 3.6 seconds;
-- dehydrogenatln~, w1th the aid of a catalyst, sa~d h~gher hyarocarbon~ at a temperature comprisod wlth1n the ran~e o~ from 400 to 9500C, proferably of from 500 to oOOoC, under a pressure compria~d w1thin the ran~e of from 0.01 to lO ~tm and duriny ~ con~act t1me compr~s~d ~th~n the r~n~e of from 0.01 to 50 seconds, pref~rabLy of trom 0.1 to 20 seconda, ~ith an ol~ftn rich mlxtur~ bein~
obtained;
-- removin~ HzO, Co2, C0 And H2 from the res~Lting ol~f~ntc ~ixture;
-- romov~ng from th~ oleftntc m~xture ~ny not oonvqrsed ~ethane, and r~cycltn~ it upstream from ~
the oxldat1n~ aouplin~ step, ---- separattnU ethyl~no from the olç~tnic mixtur6 -- separat~n~ fro~ the oLefinic mixturo any non-dehydr~genated eth~ne, possibLy recyclin~ it do~nstreom from the ox1dativc aoupling atop and up3tre~m from the dehydro~enation step, -- po~bly~ subdtv1din~ 1n one or more stcps, th~
~ heaviar hydrocarbon~ remaln1ng in the mixture, so ¦ as to obt~in paratttn1c hydrooarbons conta~n~ng ~5 three or more ~rbon atoms, wh1ch can be at Least parti~l~y reoyaLed upstraam from the dehydrogen~tton st-p; and ole~tn1c hydroo~rbons conta~nin~ thro~ or more oarbon atom~.
The ~resh, m~thane ~onta1ntng foed~tock can be fed upstroam from ehe ox~dative coupLin9 stop, or 5- 2~7~2 downstream from the ox~dattve coupling step ~nd uPstrea~ from ~he dohydrogenatton step, sGcordiny to the contatned amount of methanel feeding s~td frcsh fe~dstock upstrcam from the oxid~tlve coupling st~p 1s recommonded ~hen s~ld fresh feedstock 15 a n~tural ~as essentl~Lly oonstituted by mcthane; the dounstre~m feed ts recommended ~hen the fresh feodstock is a wet naturaL ~as ~ontaln~na hydroça~bon3 w1th t~o or more carbon atoms.
Purthermore r~cyc;inj at least a port10n of ~zO
removed from the oleftn;c mixt~re ~nd/or at least a partton ot C02 removed trom the olefinia m1xt~re upstream from the oxtdRtive coupltng stop, miyht prove to b~ advantagebUS. ~ -RecycLtn~ COz increases the selecttvitY to hydrocarbons ln the oxidative aeuplin~ step, by at Least 15%, ho~ever to the ~amage of the rat1O ~f C~ /C2, ~htch ts any~ay restor~d by the dehydrogenDt~on. -~ ~-Recyc~tng H20 sl1~htly lncreas~s the seLectivlty to hydrocarbons ~n the oxtdat~n~ coupllng step ~tthout any negat1ve outcomes on C2~/Ca ratioS suh a rat;o can be then 1nere-sed by the dehydro~enatton.
The methane convers1On ~tcp ~ox1dat~v~ oouplin~) can be carrled out by t~king sdvant~ge ot the aotalysts ~lre~dy known from the prior art, su~h ~, e.g., those ~s d1sclosed in patent applicbtloh IT~
! 19284 A90, to thc ~ame Appltcants, ~htch aatslysts conta1ns -- an eLement seLected from ae, St, Sn, tl, Z~;

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~' ' 6 2107~92 -- an e~ement s-lected f~om ~a, Scr Y~
-- an alk~l1 or alka~1n~ rth m~t~l~
The deh~dro~enat1On by me~ns of a c~talyst can be eith~r ~ cata~yt~c dehydrogon~tlon with hydrogen tormat1On, or an oxidatlve cata~ytlc d~hydrogenat1On The cat~lrt1O dehydrogenat~on ~ith hydrogen formatlon, of olef1ns ~1th a ~mall number of carbon atoms is bein~ curr~ntly operato~ ~t an industrial ~-~evel for tho hydrocarbon~ of C~ cut, ma1nly lsobùt~ne, accordlno to the teohnolog1~s developed by Snamprogett1, Oleflex, Houdry.
By m~ns of the ~ame techno~ogios, also othane and propane cDn be proce~sed by sultably changing the operated condttions, ln order to obtain the corresponding olet1ns Use~b~e cat~lyst6 for the ox~dative catalyti~
dehydrogen~t1On are those known from ths prior ~rt, ~.9 , that cata~y~t ~hich 1~ describe~ in the proceed1ngs o~ tho "Sympos1um on Natur~ G~s Up~r-ding 2û II", S. Franrtsco, ~1~9Z), pa9~ 200 ~Ferelra P.R., Dç
Gouvei~ V , Ro~a f.) The pro~ent Applirants have furthermore ¦ surpr1sln9Ly tound th~t by us~ng ~uitable ! dehydrogenation cat~lyst~, 1n the ~econd step ot th~
2S proc~ss accordin~ to ehe present lnvention, the reaction of dehYdrosenat~on 1nto olofin~ of the paratt1n~ cone~1ned in the eft~uen~ ~Qav~n9 the ox1d~t1vo co~pllng 5teP c~n be obtained ~ith th~
poss1b~ compet1t1ve reactions, such ~s ste-m reforming, wator g-s sh1ft, and so forth, beln~ k-pt .

7 2107~92 ' to the very m1nimum.
Sal~ sultable cataLysts are those as d1~close~ in Italian pstent applications IT-Z1 180 A85, It-1~ 283 A90 and IT-M~ 92A 000 556 to the samr Appliaant.
~y selectlng ~a1d catalysts, th~ cat~lytie dehydro~en~t~on ~ith hydrogen format10n appears to y1eld optimal rssultsr because it i9 not aff~cted by th~ pre3~nce of methane hh1ch, wlthin most r,perating range, oan be re~ardod as an in~rt accompanying ~pec1es, ~u1tabLe process des1gn~ make 1t furthermore po~atb~e ~et natural g~es (~.e., oontain;n~ C2, C3, and ac ~orth, hydrocarbons) to b~ treated without hav1ng to resort to specific soparation lines for hydrocarbons different from methane, and up~radin~
such higher com~onents a~ olef1ns.
In the ~irst patent appllcat10n tlT-21 180 A85)~
, :
the used cat~yst ~s based on alu~1num, chromi~m, potas~ium and si~1con; the preparation of sa1d catalyst start~ tro~ alum;num oxide ln microsPhere Z0 to~m, ~hich 1s ttrst ign~ted at temper~turoa compri6ed ulth1n thv rango of from 500 to 7000C, then at tehperatures h1gher than 10000C for many hours, th~n th~ resultin~ c~cine~ product is imprcgnated with a -~
solut10n contain~n~ chromium and potas~ium compounds, ¦ Z5 or separatc oolut~on~ o~ ~aid coumpound, i5 dried, and .15 1mpregnat~d agaln u1th a solut~on conta;ntng a s1licon compound, and f1nally 1g ~ried and 1gnited oncc more at temperaturcs ot up to 700~C.
In the s~cond p~tent appl1cat10n, a oatalytic 3~ compos1tion ig c~aimed ~hich je ~ormed by:

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-- plattnum ln an amount of from 0.1 to 3X by we1ght;
possi~ly t1n, 1n ~n amount ~f from 0 to 1.5% by h e1ght;
-- ~ carr~er selccted from titanatcd ~lumina, t1tanated siL1ca and/or t1tan~um s;lical1te, in wh1ch the t;t~n1um amount 1n the samo c~rr1er ;~
comprised ~ithln the range of from 0.05 to 3% by weight.
In the th1rd patent ~pplicat~on, cataLytic compos~t1Ons aro d1sclosed wh1ch contain ~allium, ~um1na, poss1bi~y s1~1ca ~nd/or one or morc alkall or alkal1n~-ear~h meta~s, ~h1ch ~re act1vated by means of ~ th~rmal 3ct1~at1On 1n a~r at ~ temporature oompr;sed h1thin the ran~e of from 450 to 1000a¢, followod by a post-activat~on oarrled out bY mean~ of ehe toLlowin~
stç~S;
-- ox1dat10n w1th air and~or oxygen, or a m1xture conta1ning at ~east 5% by volume ~f oxyg~n, in an ~nert yR~, dur1ng ~ tlme aompriscd w1thin th~ range ~0 ot ~rom 1 to 18û mlnutes, at a tqmperatur~
compr1sed w1th1n the range of from 500 to 1000OC
and proterably dur1ng a t1me comprised w~thin the rango of from 30 to 90 m~nutes;
-- w~h1ng with an ~nert sas durin~ a t;me comPrisod Z5 ~lth1n the range of trom 1 to 10 m1nutes;
-- roductlon w1th hydro~en or a mi~turo contain1ng at lea~t 10X by vo~ume of hydrogen, and an inert or reduc1ng ~as, dur1n~ a time compr1sed with1n the range of from 1 to 120 minutes and at e temperature compr~sed ~ithln the ran~e of from ~50 t~ 8000C.

9. 2 ~ 0 7 4 c~ 2 In partlcular~ pref~rr~d catalytl~ compo~ition 1n sald p~tent appllcatlon contalns~
-- gall~um in on amount co~prlsed ~lthln the rangs of from 0.1 to 33,6X by welght twhen oxpress~d at S Ga2~3), -- sllico 1n ~n amount comprlscd wlthtn the ran~e of from 0.08 to 3X by wqi~ht, -- posslbly one or more ~lkali or al~a~ine-earth metals in ~n amo~nt comprised uith~n the ran~e of from 0 to 5X by weight, -- alum1na, the balance to 100, as dqlta or thet~
ph~se, or ~g a m1xturQ of delt~ I theta or delt~ + the~ + ~Lpha pha~es.
The cL~lmed Process 1~ dlsaLosed no~ uith the 31d of the two accompanylng f~ur~5.
ln the flow d~agram ot Fl~ure 1, th~ ~resh focd~tock ms1nly conta1nlng methan~ (1) ls m1~ed u~th the oxid1~r (2) ~alr and/or oxy~en~ and rccyoLed methane 117) ~nd, lns1de reactor ~3), 1s convorted, by ox1dat~ve coupl1ng, 1nto higher hydrocarbons.
The eff~uent (4) from ths reaetor, admixed wlth any posslb1Le rocyc~qd ~than~ t~2) and propane t24) 1s fed to the dehydrogenatlon reactor ~5), 1n uhlch the h1ghor paraffln1c hydroc~rbons are then cataly~lcaLLy 2S dehydrogenatcd 1n such a way as to obtain a stream whlch 15 rlcher ot oLefins l6).
from such ~ 3tre~m (6), ~2 ~8) 1s first r~moved, ~n the steP (7), then in the step ~9) CO2 ~10) is removsd, ~nd fina~Ly, in (11), C0 and H2 ~12) ~re removcd.

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~, ~ ' , , 10. 2iO7~92 A port10n of H20 ~13) and ~ portion of Co2 ~14) can posslbly be recycl~d Upstredm from tho oxidetive co~pling step ~3).
The purifled oleflnic stream ~15) ~s sent to a soparator tl6) in ordcr to recov~r any unconverted methane (17), to be re~ycLed up~troam from the oxl~htlve aoupllng ~tep (3).
Sa1d ~;xture from whlch ~sthane uas removed ~18) ts sep~rat~d, 1n t19), ~rom ethyL~ne ~20); then, in ~21), 1s separ~ted from ethane ~ZZ); and flnally, in (23), lg s~bd1v1dsd into a stream essentia~Ly contajning propane ~24), o stream essent;ally contaln1ng C3 olefln~ ~25), a stream mainly co!l~ainin~
C4 ol~fins ~26), and a stream containin~ C~ paraffins 1S ~Z7).
~ccordln~ to the aases, the paraffinic streams C~th~ne ~2), prop~ne ~24), C~ paraff1ns ~27)~ can b~
e1ther part1aL~y or totaLly recycled upstream fro~ the catalytlc dehydrouenat1rJn reactor (5).
The f~ow dl-gram of ~lgure 2 is sub~t~ntially ana~o~ous to the f~o~ dla~ram of Floure 1, but for ths fe~d of the me~han~ cont~nlng feedstock not tak1ng pl~ae upstream from the ox~d~t1ve ooupllng step, but, on the contrary, do~n~teeam trom lt ~nd upstr~am from the catalyt1c dehydrogen~tlon ~tep ~5).
Thls ~econd op~ratlng ~odal1ty ls Preterred ~hen th~ fresh f~edstock ~s ~ wst gss: in such ~ ~ay, lt is not nece~sarY that meth~rle 1~ ~eparated fro~ Cz~
fract~ons and tho Lattor are upgraded by transforming thelr p~rrfflnlc fraction lnto the carrespandin~

11 . 2 l a 7 ~ 9 2 olefln.
Some examples ~re 91ven nou In order to b~tter ;llustrat~ the invent~on.
a -Some tests were cdrr1ed out in the laboratory, ~lways by start~ng ~rom a fe~dstorrk which es~entiaLLy conta1ne~ mcthane~ by adopting the operat;ng mo~ality of Fiyure 1~ ~ithout recycL~g the ethane ~2Z) sepa~ated from the olef~nir mix~Ure drJwnstream ~ro~
the ronvers1On st~p, and using the follo~lng 03t~lytic systems for the conv~rs1On: * Zr-La:Na = 1:1:1, by moL;
and, a~ re~ards the dehydrogona~ion:
-- the cat~lytlc dehydrogen~eion lExampLes 1, ~, 4, S, 7, 8, 10)~
Al:~r:K:S1 ~ 5:1:0.110.1, by moLJ
- ox1dat1ve dehydro~enat~on ~Example MnO2 lOX w~ Na20 0.5~ s~; SiO2 8~,5% ~1 ~% u ~ peroent ~y uelght~.
In ~xample~ 1, Z, 4, 5, 7, 8~ 10, 18, the str~ams ot H20 (13) and C02 tl4) uore not recycled, ~hilst in Example 1Z ~n~y C02 ~3bX by voLume) ~a~ recyc~ed to the ox~d~tive coupl1n~ ste~ ond, in ~xample 15, on~y HzO ~20X by volume) uas rccycLed to the oxid~t~ve ooupl~ng ~tcp.
xamplcY 3, 6, 9, 13, 14, 1~, 17, 19 ~re compar~son examples, bccause ~n these examples the ~ehydro~-nat1on step ~as not carr1ed out, ~ith only the oxidat~ve couPltng step being carried o~t, by us~ng th~ same catrlytic ~ystem; in parttcular, in the .
,. .

12. 2107~92 co~parlson Exa~ples 3,-6, 9, 13, 1~, 19 the streams of H20 ~nd C02 w~re not rocycled, uhil~ in the oo~par~son Examples 14 and 17, the recycLed streams aro snalo~ous to those as of the oorrespondin~
ExampLes 12 and 15.
The obtstned resuLts ~re r~ported in T~ble 1.
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Claims

1. Integrated process for producing olefins, in particular ethylene and propylene, by starting from methane containing gas mixtures characterized in that said integrated process essentially comprises the following steps:
-- converting methane into higher hydrocarbons by oxidative coupling carried out in the presence of air and/or oxygen with a molar ratio of CH4/O2 selected within the range of from 1 to 100, at a temperature comprised within the range of from 500 to 1000°C, under a pressure comprised within the range of from 0.01 to 10 atm, and during a contact time comprised within the range of from 0.01 to 10 second, preferably of from 0.03 to 3.6 seconds;
-- dehydrogenating, with the aid of a catalyst, said higher hydrocarbons, at a temperature comprised within the range of from 400 to 950°C, under a pressure comprised within the range of from 0.01 to 10 atm and during a contact time comprised within the range of from 0.01 to 50 seconds, with a mixture being obtained which contains the corresponding olefins; --removing H2O, CO2, CO and H2 from the resulting olefinic mixture;
-- removing from the olefinic mixture any not converted methane, and recycling it upstream from the oxidating coupling step;
-- separating ethylene from the olefinic mixture;
-- separating from the olefinic mixture any non-dehydrogenated ethane.

15.

2. Process according to claim 1, in which the oxidative coupling is carried out with a molar ratio of CH4/O2 comprised within the range of from 1.5 to 20, at a temperature comprised within the range of from 700 to 950°C, under a pressure comprised within the range of from 0.5 to 5 atm, and during a contact time comprised within the range of from 0.03 to 3.6 seconds.

3. Process according to claim 1, in which the dehydrogenation with the aid of a catalyst is carried out at a temperature comprised within the range of from 500 to 800°C, during a contact time comprised within the range of from 0.01 to 20 seconds.

4. Process according to claim 1, in which, after ethane separation, the heavier hydrocarbons remaining in the mixture are subdivided, in one or more steps, so as to obtain paraffinic hydrocarbons with three or more carbon atoms, which, at least partially, can be recycled upstream from the dehydrogenation step, and olefinic hydrocarbons with 3 or more carbon atoms.

5. Process according to any of clams from 1 to 4, in which the ethane separated from the olefinic mixture is recycled downstream from the oxidative coupling and upstream from the dehydrogenation step.

6. Process according to claim 1, in which the methane containing gas mixture is fed upstream from the oxidative coupling.

7. Process according to claim 6, in which the gas mixture is a natural gas essentially constituted by methane.

16.

8. Process according to claim 1, in which the methane containing gas mixture is fed downstream from the oxidative coupling and upstream from the dehydrogenation step.

9. Process according to claim 7, in which the gas mixture is a wet natural gas containing hydrocarbons with 2 or more carbon atoms.

10. Process according to any of claims form 1 to 9, in which at least a portion of removed H2O is recycled upstream from the oxidative coupling step.

11. Process according to any of claims from 1 to 10, in which at least a portion of the removed CO2 is recycled upstream from the oxidative coupling step.

12. Process according to any of claims form 1 to 11, in which the catalyst of the dehydrogenation step is based on aluminum, chromium, potassium and silicon.

13. Process according to any of claims from 1 to 11, in which the catalyst of the dehydrogenation step is formed by:
-- platinum, in an amount comprised within the range of from 0.1 to 3% by weight;
-- possibly tin, in an amount comprised within the range of from 0 to 1.5% by weight;
-- a carrier selected from titanated alumina, titanated silica and/or titanium-silicalite, in which the titanium amount in the same carrier is comprised within the range of from 0.05 to 3% by weight.

14. Process according to any of claims from 1 to 11, in which the catalyst of the dehydrogenation step 17.
contains gallium, alumina, possibly silica and/or one or more alkali or alkaline-earth metals.

15. Process according to claim 14, in which the catalyst contains:
-- gallium, in an amount comprised within the range of from 0.1 to 33.6% by weight (when expressed as Ga2O3), -- silica, in an amount comprised within the range of from 0.08 to 3% by weight, -- possibly one or more alkali or alkaline-earth metals, in an amount comprised within the range of from 0 to 5% by weight, -- alumine, balance to 100, as delta or theta phase, or as a mixture of delta + theta or delta + theta + alpha phases.

16. Process according to any of claims from 1 to 15, in which the catalyst of the oxidative coupling step contains:
-- an element selected from Ce, Si, Sn. Ti, Zr;
-- an element selected from La, Sc, Y;
-- an alkali or alkaline-earth metal.