CA2000281A1 - Aromatics-non-aromatics separation by permeation through thermally crosslinked nitrile rubber membranes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Aromatic hydrocarbons are separated from mixtures of same with non-aromatics by permeation through a membrane of thermally crosslinked polyconjugated diene rubber containing from 15 to 50 wt% nitrile groups. Thermal crosslinking increases selectivity far beyond the level obtained when crosslinking is caused by other techniques. The separations are conducted under pervaporation or perstraction conditions.

Description

~_De~5b~

Aro~t ic hydrobarbonEI arQ ~eparated f rl~m mixturo~ of sa~ with non~aromatic~ b~ p~r~eation through.. ~ membran~ o~ th~r~ally c:ros31inked ~oly-con~usll~t~d di~n~ rubber containing ~roDI 15 to 50 ~% C
~ ~ group~s. A th~n ril~ o~ nitrils~ rubb~r 1~ prepared usirlg a ca~tlng ~olution containing 1 to 25 wt~, pr~PQrably 2 to 20 wt~, mos~ prs~rably 5 to 1~ ~% o~
th~ r ubb~3r in a di~ol~ring solv~rlt, ~pr~a.dirlg ths ca~ting solution on a ~ulta~ substrat~ for support, p~itting th~ ~olvent to ~vaporat~ and cro~linking th~ polylaer by ~xposing it to ~31iavat~d t~perature~ in ~hQ rangQ 140 to 200-C, pr~er~bly 160 to 180-C for fro~ 1 to 12 hours, pre~rably 3 ~o 9 hour~0 This th~r~al cro3~1inking is condu~ ed in the abs~nc~ o~ any cataly~t ~uah as peroxi~3. Th~s 3~3para~ion i~ conduct-ed u~ing khes~ ~e~rane~ und~r pQrvaporation or perYtraction condition~, pref~rably pervaporation condition~ .

~:~

Th~ ~paration of aromatic from non-aroma-tic~ i~ a proc~duxo oP i~portanc~ in the c:hemical and p~trol~u~ indu~t~. ~an~ t~chnique~ have b~n.inv~sti-ga'e~d and d~v~lop~d to porgona th~ ~paration. Di til-lation undar at~o~h~ric or vacuuDI condi~ions h~ be~n ~aploy~d when th~r2 i~ ~ ~u~icl~nt di~r~nco in boil ing point in th~ s:ompon~nt~ to be separated .
~lt~rnativ~ly ~xtractiv~ distillation or 21gs00trOpiC
di~tillation can ba~ pracl:ic~dJ For ~ixturl~ o~ mat0-rlAl~ ring llttl~ or no boillng polrl~ dl~ r0nti~

;~ . , , :, ,, ~o~

mor~ ~ophi~ticatad t~chniqueg ~nu8t be employed, such as extraction u~ing ph~nol, furfural, N-methyl pyrrolidone., ~ul~olan8, glycolgp SO~ ~tc. a~ extraction solvant~, or ad~orption u3ing natur;~l or synthetic mol*cular siav~ eolite~). All o~ l:he~o t~chnique~
are~ either 2nergy intensiv~ or r~quirl~ a ~nultitude o~
slt~ps ~.g. ~paration o~ th~ aroD~atic~ ProD~ the extrac~ion solvQnt~, or de~s)rption o:e aro~atics ~rom th~ 2Id30rbents).

Othor saparation techniqu~ ha~s b~an inve~-tigatad. Th~ 3~paratiotl Or aro~aticY~ rrO~ non-~roma-tic~ by per~eation through ~ ctiv~ mbran~s ha~
r~s:oivad ~ ant att~ntion $n th~ Eaat~nt litera-tur2. Variou m~mbranes~ hav~ bQen sugg~sted ~or he ~paration. Th~y include v~rious ce~llulos~a astars, c~llulo~e ethetrsl j 14ixtur~ o~ cellulo~ t3r~ and ~thers, polyurethanas, polyethyl~n~, polypropylene, polyvinyl idln~3 ~luorid~, and polyethylene styrene copolymer~ .

"Separation of benzene - n Hept2me Mixtur~s By Penraporation with Ela~tomeric Membranes, ( I . ) Per~ormanca of M2mbrana3" Lorchet et al., Journal of Membrane Science ~ (1983) 81-9~, shows aromatic/-~a~urate separation by penraporation through nitri.le rubb~r or polybutadien~ ac:rylonitrile mem~rane~. The nltr~lo Dl~mbraneR w~r~ lightly cros~linked wi~h from 0.5 to 6.09~ dis::umyl p~roxide at 160-C for 10 ~o 20 ~lnut~s. Th~ articl2 at page~ ~9 and 90 show~ that varying th~ peroscidQ cont~nt ~rou 0. 5 to 6~ did not appr~ciably chang~ th~ perfor~Qanc~a o~ th~ mbranes.

The Pr~en~ Invent.ic; ~

It ha~ n di~cov~ that aroma ~ic hydro-carbons c21n b~ parat~ ~ro~ ~1XtUE~ of ~ 0 with non-aro~aticY by pe ~3ation o~ th~ aromatic~ through a th~ liy cro slinked nitrile ru~b~sr containin~ ~rom 15 to S0 ~ nitrile yroup~.

The m~mbran~ i~s a polydien~3 ~poly m~ria ~t~-rlal con~aining 15-50 ~t nitrils g:roupi~. Typical n~trils rubbar~ are copoly~rs o~ butadi~ and acrylonitrlle, but othd~r dian~, pr~erably polycon~ugated di~n~, such as isopran~ an al~o b~
poly~oriz~d with acrylonitril~ or oth~r nitrils Dlo~a~y containing D~ono~r~ to prc~duc~a a u~able polym~ric ~at~rial. All ~uch pQlyD~r~ ar~ }~r~ini~ter ldenti~l~d a~ nitril~ ~bber~ ~or th~ ~ak~ oP ~implic~ty.

FroDI 1 to ~5 wt%, pr~forably ~ to ~0 wt~, DlO~t pre~erably 5 to 18 ~ o~ th~ ni~ril~ rubb~
di~olv~d in a suit~bl~ ~olvent ~3uch a~ chloEobaIlzen~, chloro~or~, 1, 2 dichloroethane, dichloromathana, di~athyl ~orn aD~id~ thyl ethyl ketona, n-~ethyl pyrollidone, ethyl aceta~, t~trahydro~uron, etc. to for~ a ca3ting ~olution. Th~ ~olution is spread a~ a thin ~ilm on a uitabla substrate liXe metal, glass, or woven fabric like tePlon or other ~abric which is not attached by eith~3r the polyn ~r or its dissolving solvent. T2~e solv~nt is permitted to evaporate from th~ ~il~ producing a symmetric ~ilm.

The ~n~ran~ u~g~d in th~ present separation ar~ ca t wi~hout any catalytic cro~linkinq ag~ant b~ing prasent in the poly~ar ca~ting solution.

Th~ ms~bran~ aro cros~linked u~ing heat exGluslve~ly. Th~ 7ne~rzne~ ara hsated at a te~p-3~zlturs o~ about 140 to abou~ 200-C, pr~ra~ly 160 to 180-C, ~or ~ro~ about ~ to 12 hsur~, prs~orably 3 1:o 9 hours.

H~at treat~nt causes a degree o~
cro~linking which i9 unattainable u5in~ catalytic cros~linking agent3 ~uch a9 dic~yl p~roxid~, ev~n whsn high s:onc~ntration~ oP guch catalysts are employed.

Further~or-~, h~at treatm~nt wh~n no catalyat i~ pr~3~ent produce~ a 3~nbran~ which hal~ a ~2igh~r ~æl~ctivity f~ctor than that obt~in~d ~h~n he~at trQat-m~nt i3 practic~ on ~ m~nbran~ ih ldh~ch a cataly~t i~
pr~nt.

1~ s~paraSion proc~ using t21~ t2~ ally cro~linked nitril~ r ~Dbran~ pr~ 3rably condu<::ted unde~ p~r~tr~ct on or p~ pc~ration condi-tion~.
.
In p~rstrac:tion, th~ ed i9 c:ont~ct~d with one~ ~ide o~ th~ s~lective mo~bran~ at ~ teIIlp~ratura in ~ne r~n~ o~ about 20 to 200-~. Th~ aro~tic a~:~ponent ssl~ctiv~ly di~olves irlto th~ m~bran~ and p~ at~
~Arough tAa Dl~mbr~n~. sinc~ thi~ proc~ is driv~n by thQ ~3xistence oP a concentration gradi~3nt acros~ the membran~ it is~ neca~sary that th~ concentration o~
aromatic~ on th~ permeate side o~ the membrane be kep~
low. This i~ ac~oDlplished by use o~ a sweep liquid.
~h~ primary chzlr~c:t~ristic o~ thQ sweep l i~id is th~
~a~ by which it can be separated from th~ swept aro~tic.

PerYapor~tion i~ a D~ore ~icient s~paration proc~s~. It i~ conduct~d at an ~l~Yated t~pQrature, a t~peratur~ high enough to pro~viq~ th~ h~t o~ vapori-zatlon o~ th~ aroma~ic co~pon~tnt. The mixtur~ ~ea~d i contac:t~dL with on~ 31d~ o~ ctiv m~nbrane.
contacting i~ at: a ta~p~raturo in th~ rzmg~ 0 to 200 ~ n~ al~ ~ppli~ pro~ur~ O~e 0 to lOOû p~, Th~
~roD~atic~ scti~ly di~olv~ua $nto th~ bran~ and 8:~

migr2lt~ to th2 parm~a~ ~ide. A~ in parstraction, p~rvapora~ion i5 driv2n by the exi~tence o~ a concen-tration gradi~ant. In th~ ca~ o~ per~raporation this gr~diQnt i~ maintain~d ~y applying a valcu~ or pas~ing a sw~ep ga~ on the perm~t~ ~id~ o~ th~ membran~ to dr~ away tha p~rmeat~d aromati~ hydrocarbon. Vacuu drawn on tha p~ ate sidQ is such t~t th~ pres~ure i~
than th~ equilibriu~a vapor pr~urq o:e th~ liquid ~d. Vac~ ax on th~ order oX 0.1 to 50 ~m ~g are typic~l at th~ tQ~np~r~tur~ employsd.

Th~ proc~sa i~ u~e~ I n ~h~ p~trole~ indu~try to s~parat~ aromatic hydrocarbons ~ro~ ~ixturas Or aroD~atic hydrocarbon~ and non-arom~tic hydrocarbon~.
Typical non~ iting exzmpla~ oS ~e~d~ which are or ccntain mix~ur~s o~ aro~atic and non-aromatic hydro~r-bons are naphtha, catalytic nap~ha, ga~ oil~, heavy cat naphtha, light g~8 oil9, light cat. ga~ oils, etc.
The sQpar~tion proc~ can also bs used in t~e chemical industry for r~cov~ry/concentration of aromatic~ ~uch a~ b~nzens, toluen~, xylen~s, etc. fro~ chemical proc~ strea~s.

The invention is illu~trated in detail by ref~renc~ to thQ following non~ iting examples and compari~on~.
xa~
:' This ~ampl~ dl~cu~ses tae effect o~
crosslinking tim~ and te~p~ra~ur~ on th~ p~rfor~anc~ o~
m~branes containing 20% dicumyl p~roxide and explains why th~rcal cro~linking, no~ th~ p~roxide content, is th0 d~termining factor in pr~parinq high salectivity nitrilQ rubb~r membrane~.

~no~

Tha pol~er 501ution was prepared by co-di~;-~olving nitrile rubb~r (45 wt% acrylonitrile content) and d~ cumyl peroxid~ in chloroben2ena . The total sclids in ~olution wer~ kept con3t~nt at 18 wt;t. Tha ~olution~ wer~ ca~t on porou~ 0. 2~L t~3~1c~n membrane3.
The g:'llm~ w~r- d~ied and th~n h~a~d al: v~riou~ t~mp2r-~tur~ 135'C) for ~rarlousl p~riods oi~ ti~e (> 1 hour) in a vacuu~ ov~n und~r a nitrog~n purg~3. Th~ m~DIbr~ne thickn~s~ vari ~d grom 50 to 80 Dlicrons. q~h~5~ ~m-bram~ w~r~ t~st~d und~r p~rv~poration condltion~ u~ing an 80~0 b~nz~na~cycloh~xan~ f~d at 28 - C wi~ th~
down~rQaDI pres~ure maintained at 1 mbar. Th~a r~sults ar~ ted in Table 1.

Ini~ially, thQ~Q m~3~brane~ wer~a cured at 137 C Por 1 and 2 hour~ . Tha~ ~neD~ran~ demon~trat~d s~l~ctivity ~actors o~ 3 . 06 tc~ 3 . 15 at parD~aabil ity value~ og 750 and 870 kgu/~2d~y. According to lit~ra-tur~ docu~entating th~ U!~Q oi~ dicumyl peroxid~ with nitrile rubber (H~rcule3 Technical ~ata bulletin~
ORC-105B, ORC-~OlC, O~C-lOlB) at 137-C~, an appr~ciable aDIount o~ peroxid~ would be und~composed even af~er 2 hour~ .

Acc:ording to the lit~ratllre, at a cure t~mp~rature of 160-C, a curQ ~ime of 1 hour would r~.ult in Dlors than 99% o~ the p~roxide d~composing.
Tho ~lectivity ~actor for a ~bran~ treat~d under thi~ condit~on was only ~l~ghtly higher at 3.31 which 1~ cloo~ to the valu~ of 3 . 5 ob3~rved in litera1:urs.
Fror3 thi~ rQ~ult, i~ is ~hown that meD~ranQs with a high dicu~yl p~roxidel content o~ 20% do not show any hlgh~ 3~12ctiviti~s than th~ literatur~ nbrane3 containing 0 . 5 to 5% dicumyl poroxida.

Surpri~ingly, m~bran~ trGat~d at 160-C for 3 an~ 9 hours ~howo~ signi~ie~ntly high~r D~ c1:ivity 20a~'2~

factors o~ 3 . 84 and 4 43 and reduced permeability valuQ~ o~ 530 ancl 3~0 k~ h~2day. Thi~ lncreased sel~ctivity and r~duced permeability cannot b~ attri-but~d to p~roxids catalyzed cro~linkirlg as all o~ the p6roxide would hav~a be~n des::ompo~d after 1 hour~ It i~ known (}~ubber C:heDIi3try and TQchnology 31 (1958) 132-146) t~at n~trll~ rubb~r can ~h~ ally cro~31ink at an el~vat~d te~peratur~ o~ 180C. Tho incrsased ~1QCtiVitY at: long~r tr~at~ent ti~ is attributed to ~h~aal cro~linklng~ Th~s degr~ o~ thermal cro~linking ~rould continu~lly incr~a~ a~ th~ curQ
time i3 incr~a~ed.

~Q~ , Thi~ ~xaDIpl~ discu~th~ ~fg~ct o~ th~
dlcu~yl pQroxid~3 cont0nl: on the performanc~ o~ thar~al-ly cros~link~d ni~ril~ rubber malubranla~ and ~how~ that no peroxid~ i9 raquir~d to achi~3v~ high se1ectivity therma11y cro~1inked nitril~ rubb~3r m~mbrane~.

'rh~ m~D~rana3 wera pr~parad and tested as detai1ed in Examp1e 1. The results ar~ listed in Table 2.

As ~hown for membrane~ heat treat~d at 160 ~ c ~ox 9 hour~, th~ ~1ectivity factor increase~ a~; the di~yl paroxid~ cont~nt` d~creased. For membrane~
con~inlng 20, 15, 10, and 5~ dicu}:ly1 p~roxid~ at 28~C, thq~ ~sQ1~ctivity rac~or~ increa~ed ~roDI 4 . 43 ~o 5. 8 and th~ permsabi1ity va1ua~ stay~d r~latively con~tant ranging ~o~tly ~atw~an 330 and 390 kgu/~day, A ~eDlbran~ containing no dic:u~ny1 p~roxid~
h~at tr~at~d at 165 C for 2 . 5 hour~, was al~o te~t2d and ~ho~ s~ iv1ty actor o~ 5.4 with a per~-abllity valuo o~ 320 kgu~2day. This~ 3-~10ct:1vity 20~ 2l31 ~actor is significantlY higher than that o~ the litera-tur ~ DlQDlbrane~ at a ~lectivity ~actor of 3 ~ 5 Clearly, no dicu311~1 p~3roxide~ i9 r~quir~d in preparing high s~l~ctlvity ~abran~ Th~ ctivity and p~rmea~ility o~ nitril~ rubb~r me~mbrz~n~ can b~
Gontroll~d by th~ dQgree . o~ t~l~al cros~l inlcing that th~y un~argo.
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Claims (10)

1. A method for separating aromatic hydro-carbons from mixtures containing aromatic hydrocarbons and non-aromatic hydrocarbons, the method comprising selectively permeating the aromatic hydrocarbon through a membrane of thermally crosslinked polyconjugated diene rubber containing from 15 to 50 wt% nitrile group.

2. The method of claim 1 wherein the aroma-tic hydrocarbon permeation is conducted under perstraction conditions.

3. The hod method of claim 1 wherein the aroma-tic hydrocarbon permeation is conducted under perstraction conditions.

4. An aromatic separation membrane compris-ing a thermally crosslinked polyconjugated diene rubber containing from 15 to 50 wt% nitrile groups.

5. The aromatic separation membrane of claim 4 comprising a thermally crosslinked copolymer of butadiene and acrylonitrile.

6. A method for producing a thermally crosslinked polyconjugated diene rubber membrane containing from 15 to 50 wt% nitrile groups comprising preparing a copolymer by mixing a polyconjugated diene with a monomer containing a nitrile moiety, dissolving the copolymer in a dissolving solvent to form a casting solution, spreading a thin film of the casting solution on a substrate, evaporating the dissolving solvent to produce a symmetric film and having the symmetric film in the absence of any catalytic crosslinking agent at a temperature of about 140 to about 200°C for from about 1 to 12 hours.

7. The method of claim 6 wherein the symme-tric film is heated at a temperature of about 160 to 180°C.

8. The method of claim 6 wherein the heating is conducted for from 3 to 9 hours.

9. The method of claim 7 wherein the heating is conducted for from 3 to 9 hours.

10. The method of claim 6 wherein the casting solution contains from 1 to 25 wt% of the copolymer.