Efficiency o hyd ophobic phosphonium ionic
liquids and DMSO as ecyclable cellulose
dissolu ion and egene a ion media†
Ashley J. Holding,
ab
A no Pa iainen,
a
Ilkka Kilpel¨
ainen,
a
Ana So o,
b
Alis ai W. T. King*
a
and H´
ec o Rod ´
ıguez*
b
Hyd ophobic, long-chain e aalkylphosphonium ace a e sal s (ionic liquids) we e combined wi h a dipola
ap o ic co-sol en , dime hylsul oxide (DMSO), and he easibili y o hese sol en sys ems o cellulose
dissolu ion and egene a ion was s udied. A 60 : 40 w/w mix u e o he ionic liquid
e aoc ylphosphonium ace a e ([P
8888
][OAc]) and DMSO was ound o dissol e up o 8 w % cellulose,
whils ioc yl( e adecyl)phosphonium ace a e ([P
14888
][OAc]) dissol ed up o 3 w % cellulose. Wa e (an
an i-sol en o cellulose) was ound o gi e ise o biphasic liquid–liquid sys ems when combined wi h
hese mix u es, yielding an uppe phase ich in ionic liquid and a lowe aqueous phase. The liquid–liquid
equilib ia o he e na y sys ems we e expe imen ally de e mined, finding ha DMSO s ongly pa i ioned
owa ds he aqueous phase. Thus, a p ocess scheme in ol ing simul aneous egene a ion o cellulose
and ecycling o he sol en sys em was en isioned, and demons a ed on a la ge scale using [P
8888
]
[OAc]. A la ge po ion o he ionic liquid (ca. 60 w %) was di ec ly eco e ed ia phase sepa a ion, wi h
a u he 37 w % being eco e ed om he swollen cellulose phase and esidual ma e ials, b inging
eco e y o 97%. XRD analysis o he eco e ed cellulose ma e ials showed a loss o c ys allini y and
con e sion om Cellulose I o Cellulose II. Non-dissol ing composi ions o ionic liquid and DMSO did
no affec cellulose c ys allini y a e cellulose pulp ea men .
In oduc ion
Ionic liquids (ILs) a e widely s udied o hei abili y o dissol e
cellulose and o he lignocellulosic biopolyme s,
1–4
and ha e
been applied as media o homogenous de i a iza ion eac-
ions,
5–7
biomass p e- ea men ,
8–11
dissolu ion o wood and
o he biomass,
12,13
biomass ac iona ion ia ex ac ion o
selec i e p ecipi a ion,
3,14–19
ca aly ic p ocessing o lignocellu-
lose,
20,21
and spinning o egene a ed cellulose b es.
22–25
Ionic
liquids ha e been a bi a ily dened
26
as sal s which a e liquid
below 100 C and mos a e composed o a la ge, o ganic ca ion
and an ino ganic o o ganic coun e anion. The main basis o
hei in e ac ion wi h cellulose and o he biopolyme s is he
po en ial o hyd ogen-bonding ne wo ks o be b oken by
hyd ogen-bond basic
27
anions, such as ace a e ([OAc]

) and
chlo ide (Cl

) anions. Howe e , o he in e -molecula o ces
including coulombic and dispe sion in e ac ions should also be
conside ed, depending on he s uc u es o he sol en and
solu e. Imidazolium-based ionic liquids a e a guably he mos
s udied bo h in gene al and wi h espec o hei applica ion
owa ds cellulose and biomass, wi h ionic liquids such as
1-bu yl-3-me hylimidazolium chlo ide ([bmim]Cl),
28
1-e hyl-3-
me hylimidazolium ace a e ([emim][OAc]),
29
and 1-e hyl-3-
me hylimidazolium dime hylphospha e ([emim][Me
2
PO
4
])
27
being some examples.
O ganic elec oly e solu ions
30
o mix u es o ionic and
molecula sol en s o cellulose dissolu ion ha e been explo ed
ecen ly due o hei ease o dissolu ion a low empe a u e,
lowe ed iscosi y, and cellulose dissolu ion efficiency.
30–34
Typical
combina ions include imidazolium
30,31,34–38
o onium ca ion
39–42
ionic liquids pai ed wi h basic anions, mixed wi h DMSO
(dime hylsul oxide), DMI (1,3-dime hyl-2-imidazolidinone),
DMA (N,N-dime hylace amide), DMF (N,N-dime hyl o mamide),
TMU (1,1,3,3- e ame hylu ea),
34
as well as g-bu y olac one and
g- ale olac one.
43
Recen ly, esea che s ha e demons a ed he possibili y o
spinning egene a ed cellulose b es om ionic liquid solu-
ions, such as in he ‘IONCELL-F’p ocess,
24
based on Lyocell-
ype p ocess, whe eby s ong b es (ha ing a highe enaci y
han bo h he N-me hylmo pholine-N-oxide (NMMO) based
Lyocell and he sulphi e based iscose b es) can be p oduced
by d y-je we (ai -gap) spinning om an ionic liquid dope in o
a wa e ba h. In his case, he cellulose dissol ing ionic liquid
a
Depa men o Chemis y, Uni e si y o Helsinki, A.I. Vi asen Aukio 1, 00014
Helsinki, Finland. E-mail: alis ai .king@helsinki.
b
Depa amen o de Enxe˜
ne ´
ıaQu
´
ımica, Uni e sidade de San iago de Compos ela, E-
15782, San iago de Compso ela, Spain. E-mail: hec o . od ig[email p o ec ed]
†Elec onic supplemen a y in o ma ion (ESI) a ailable. See DOI:
10.1039/c7 a01662j
Ci e his: RSC Ad .,2017,7,17451
Recei ed 9 h Feb ua y 2017
Accep ed 12 h Ma ch 2017
DOI: 10.1039/c7 a01662j
sc.li/ sc-ad ances
This jou nal is © The Royal Socie y o Chemis y 2017 RSC Ad .,2017,7,17451–17461 | 17451
RSC Ad ances
PAPER
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online
View Jou nal
| View Issue
1,5-diazabicyclo[4.3.0]non-5-enium ace a e ([DBNH][OAc])
dissol es a ound 13–14 w % o cellulose pulp o o m he
spinning dope. O he ionic liquids ha e also been s udied wi h
espec o egene a ed b e spinning, such as [bmim]Cl
23
and
[emim][OAc].
22
The la e showed a ou able physical p ope ies
when compa ed o NMMO Lyocell. Ae he ionic liquid and
cellulose solu ion is “spun”in o wa e , he ionic liquid emains
and mus be emo ed om he spinning ba h ae a pe iod o
ime. Wa e ac s as an an i-sol en o cellulose by dis up ing
he hyd ogen-bond ne wo k be ween he cellulose hyd oxyl
g oups and he bound ionic liquid anion.
One issue in pa icula ha has ecei ed a lo o a en ion in
ecen yea s has been he eco e y and pu ica ion o ionic
liquids. Ionic liquids a e oen expensi e, some imes oxic and
as such, need o ha e high eco e y a es in o de o become
economically and en i onmen ally easible. In addi ion, non-
ola ile con aminan s including oligome ic o monome ic
suga s, ino ganics and o he s a e likely o build up and need o
be emo ed by a low cos pu ica ion me hod. Dis illa ion o he
ionic liquid is one me hod, which has been applied o [emim]
[OAc],
44
a well-known ionic liquid o dissol ing cellulose, bu
which equi es a he high empe a u es and educed p es-
su es. This ionic liquid has also been shown o eac wi h he
cellulose subs a e
45–47
ia a eac ion o he imidazolium ca -
bene a he C2 posi ion and he cellulose educing end, o ming
a 2-(hyd oxyme hyl)-subs i u ed imidazolium adduc
45,46
hus
emo ing sol en and cellulose om he sys em. Newe gene -
a ions o ionic liquids a e able o be dis illed a much lowe
acuum and empe a u es, including 1,1,3,3- e ame hylguani-
dinium ace a e ([TMGH][OAc])
48
and [DBNH][OAc]
49
which a e
also able o dissol e cellulose. Since wa e is oen used as
a p ecipi a ing an i-sol en , ano he possible ecycling o pu i-
ca ion me hod is phase-sepa a ion o he ionic liquid om
wa e , i i is p esen .
In a p e ious s udy,
40
we iden ied a se o ionic liquids,
based on e aalkylphosphonium ca ions pai ed wi h ace a e
anions which we e effec i e o dissol ing lignin and which
dissol ed cellulose upon he addi ion o a dipola ap o ic
sol en , such as dime hylsul oxide (DMSO). As such, hese
sol en s o cellulose should be conside ed as mixed molecula
and ionic sol en s o “o ganic elec oly e”solu ions.
30
Some o
he s uc u es s udied we e phase-sepa able om wa e . One
ionic liquid, me hyl ioc ylphosphonium ace a e ([P
8881
][OAc])
was s udied in mo e de ail. When pai ed wi h he dipola ,
ap o ic molecula sol en DMSO i was shown o be a highly
effec i e cellulose sol en , dissol ing la ge amoun o cellulose
when compa ed o o he ypes o cellulose dissol ing ionic
liquids and elec oly es.
A e na y phase sys em consis ing o [P
8881
][OAc], DMSO and
wa e was s udied as a model o a possible sol en and eco e y
sys em o a cellulose b e spinning p ocess. Howe e , he
esul ing e na y phase diag am showed a limi ed wo-phase
egion wi h a la ge amoun o ionic liquid undesi ably ge ing
in o he aqueous phase. Addi ion o kosmo opic sal s o he
aqueous phase, including sodium o po assium ace a e,
imp o ed he phase-sepa a ion bu complica ed eco e y e en
u he . O he s ha e ecen ly in es iga ed hyd ophilic and
hyd ophobic phosphonium ionic liquids as cellulose sol en s,
50
including he hyd ophilic e abu ylphosphonium ace a e
([P
4444
][OAc]) and he hyd ophobic e aoc ylphosphonium
ace a e ([P
8888
][OAc]), claiming ha hey dissol ed 0.1 w %
cellulose. Based on ou p e ious in es iga ions and om his
s udy, i is unlikely ha he nea ionic liquids (wi hou dipola
ap o ic co-sol en s) dissol e much mo e cellulose.
Two u u e pa hways a e en isaged o his class o cellulose
sol en s: he  s , is o use smalle -chain ionic liquids such as
[P
4444
][OAc] (less hyd ophobic)
40
in combina ion wi h dipola
ap o ic sol en s, wi h eco e y aking place by he addi ion o
“sal ing ou ”(kosmo opic) sal s; he second, is o use longe -
chain ionic liquids, such as [P
8888
][OAc] (which a e mo e
hyd ophobic)
40
wi h dipola ap o ic sol en s and phase-sepa a e
hem om wa e wi hou he use o any addi i es, hope ully
simpli ying he ecycling p ocess and educing ene gy demands
(compa ed o dis illa ion o wa e ). Howe e , we showed
ecen ly
51
how he oxici y o his class o phosphonium ionic
liquids inc eases wi h chain-leng h. A ade-offbe ween cellu-
lose dissolu ion capabili y, eco e y by phase-sepa a ion, and
oxici y is likely. The bes way o wa d should be o in es iga e
bo h ou es ho oughly and de e mine exac ly which ou es a e
easible and sus ainable. Doing so should gi e aluable in o -
ma ion o op imising cellulose b e spinning p ocess
24
based
on hese sol en s.
In his pape , we will concen a e on he la e ou e, whe e
hyd ophobic ionic liquids (pa o an o ganic elec oly e solu-
ion wi h DMSO) a e eco e ed om wa e wi hou u he
addi i es. Following om ou p e ious s udy,
40
we desi ed o
in es iga e ionic liquid-based elec oly es which we e p edic ed
o be much mo e hyd ophobic han any p e iously s udied ionic
liquids o elec oly es, bu s ill dissol ed cellulose. The aim was
o in es iga e he dissolu ion capabili y o wo specic ionic
liquids based on la ge e aalkylphosphonium ca ions ( e -
aoc ylphosphonium ace a e, [P
8888
][OAc] and ioc yl( e-
adecyl)phosphonium ace a e, [P
14888
][OAc]), in combina ion
wi h DMSO, whils using wa e as a p ecipi a ing an i-sol en
o cellulose. We aimed o s udy he easibili y o he phase-
sepa a ion ecycling me hod by measu ing phase diag ams o
hese e na y sys ems.
Resul s and discussion
The wo long-chain, hyd ophobic phosphonium ionic liquids
we e syn hesized: ioc yl( e adecyl)phosphonium ace a e
[P
14888
][OAc] and e aoc ylphosphonium ace a e [P
8888
][OAc]
(Fig. 1). Bo h ionic liquids we e ound o be immiscible wi h
wa e , a p ope y ypical o long chain phosphonium ionic
liquids.
50,52–54
Howe e , he pu e ionic liquids p epa ed in his s udy did
no dissol e cellulose o any app eciable deg ee, below a lowe
es ed limi o 0.5 w %, which  s o ou p e ious unde -
s anding
40
o some phosphonium ace a e ionic liquids
(including he ionic liquid [P
8881
][OAc]) and cellulose dissolu-
ion. Thus, we se ou o use a molecula co-sol en in
conjunc ion wi h hese ionic liquids o enable cellulose disso-
lu ion, as we p e iously showed his combina ion o enable
17452 |RSC Ad .,2017,7,17451–17461 This jou nal is © The Royal Socie y o Chemis y 2017
RSC Ad ances Pape
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online
some non cellulose-dissol ing ionic liquids o dissol e cellu-
lose.
40
In gene al, any molecula o ganic sol en s in combina-
ion wi h an ionic liquid mus be bo h pola and ap o ic o ac as
a so called “co-sol en ” o cellulose dissolu ion. Fi s ly, he
sol en mus no dis up hyd ogen bonding be ween he
hyd ogen-bond basic anion and cellulose, and hus mus no be
a hyd ogen-bond dona o (ap o ic) and mus be highly pola in
o de o effec i ely sol a e he anions and ca ions. F om ou
p e ious s udy, i appea ed ha DMSO was he mos effec i e
co-sol en , and has been he mos widely s udied so a .
33,55–58
I s
high boiling poin (i.e. ole ance o he high cellulose dissolu-
ion empe a u es), low hyd ogen bond acidi y, and e y high
pola i y make i an ideal co-sol en . The use o DMSO is no
wi hou i s disad an ages –al hough i is non- oxic, i s biolog-
ical sol en ac ion is a pa icula conce n, pa icula ly in
combina ion wi h ionic liquids. O e all, DMSO plays a syne -
gis ic ole enabling p e iously non-dissol ing ionic liquids
(such as e aalkylphosphonium ace a es), o dissol e cellulose
o an ex emely high deg ee when compa ed o o he ionic
liquid based sol en s.
40
The mos posi ed mechanism o ac ion
o his “co-sol en effec ”is he s ong abili y o he highly
dipola DMSO (o o he dipola ap o ic sol en ) o sol a e bo h
he ca ion and anion, inc easing ion pai sepa a ion and hus
‘ eeing’ he hyd ogen-bond basic anion o bond o cellulose
hyd oxyl g oups.
35,36,56,58
The ole o p e e en ial sol a ion is
deba ed, wi h Xu e al. sugges ing he p e e en ial sol a ion o
he ca ion plays an impo an pa in he co-sol en effec in he
[bmim][OAc]/DMSO sol en sys em.
59
The ca ion is also specula ed o play a majo ole which
diffe s acco ding o i s s uc u e. Imidazolium-based ionic
liquids, o example, a e able o dona e hyd ogen bonds om
he acidic p o on on he C2 posi ion o he imidazolium ing, o
he hyd oxyl oxygens and hemiace al oxygen. Phosphonium
ionic liquids, on he o he hand, lack such an acidic p o on bu
ha e ypically long and non-pola alkyl chains, which we ha e
p e iously sugges ed
40
o con ibu e o he dissolu ion o
cellulose by inc easing he s eng h o he non-pola in e ac-
ions be ween he ca ion and he non-pola , hyd ophobic
su ace o cellulose. Recen compu a ional wo k has shown he
impo ance o he con ibu ion o hese dispe sion o ces
60
on
cellulose dissolu ion and he e has been much discussion on
he signicance o cellulose amphiphilici y
61,62
on i s solubili y
beha iou .
Two iews o he cellulose dissolu ion in hese sys ems a e
p esen ed: a weigh (weigh pe cen age, w % –Fig. 2) based iew
and a mola based iew (Fig. 3), whe e we use he me ic
“AGU : IL” a io, o moles o anhyd oglucose uni s “AGU” o
moles o IL. Such a me ic allows us o compa e easily he
amoun o cellulose dissol ed pe ionic liquid ion be ween ILs
o diffe en molecula weigh s and sizes. We compa e bo h o
he ionic liquid elec oly es om his s udy o [P
8881
][OAc],
which was s udied p e iously.
40
The cellulose dissolu ion capabili ies in hese o ganic elec-
oly e sol en sys ems a e ypically affec ed by concen a ion o
he co-sol en componen , usually ising and alling a ound
a maximum (Fig. 2, 40–50 w %). Bo h ionic liquids ha e his
simila esponse o DMSO concen a ion as he p e iously
s udied ionic liquid, [P
8881
][OAc]. [P
14888
][OAc], wi h an
ex emely la ge ca ion, dissol es less cellulose han [P
8888
][OAc]
a all DMSO concen a ion anges, wi h maxima o ca. 3 w %
Fig. 1 S uc u e o ionic liquids used in his s udy.
Fig. 2 Cellulose (MCC) sa u a ion poin as w % in [P
8888
][OAc]/DMSO
and [P
14888
][OAc]/DMSO solu ions, as a unc ion o he DMSO
concen a ion, in w %.
This jou nal is © The Royal Socie y o Chemis y 2017 RSC Ad .,2017,7,17451–17461 | 17453
Pape RSC Ad ances
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online
and ca. 8 w % cellulose dissol e in solu ion, espec i ely. Ideal
le els o dissolu ion o cellulose depend hea ily on he appli-
ca ion – o analy ical pu poses o small scale cellulose de i a-
iza ion eac ions, smalle amoun s will be enough, bu o
Lyocell-like b e spinning, la ge amoun s will be necessa y.
In he la e case, he heological pa ame e s would need o be
adjus ed by uning he cellulose, DMSO and ionic liquid
concen a ion. Thus, i is likely ha only [P
8888
][OAc] would be
able o be applied o Lyocell-like b e spinning, al hough
[P
14888
][OAc] may s ill be use ul in niche applica ions.
When conside ing he mola dissolu ion me ics (Fig. 3), a
he maximum poin , [P
8888
][OAc]/DMSO can dissol e up o
0.44 mol o AGU pe mol o IL (o 2.2 mol o IL pe mol o AGU)
whils [P
14888
][OAc]/DMSO can dissol e up o 0.30 mol o AGU
pe mol o IL (o 3.3 mol o IL pe mol o AGU). Wha is qui e
su p ising is ha ca ions o such size and bulkiness, in
combina ion wi h dipola ap o ic co-sol en s such as DMSO,
compa e a ou ably o ionic liquids wi h much smalle ca ions.
Howe e , i is clea ha solu ions con aining ca ions la ge han
[P
14888
]
+
a e app oaching he poin o insolubili y, as he e is
a clea nega i e end in he mola dissolu ion a io (AGU : IL)
wi h inc ease in ca ion size om [P
8881
]
+
h ough o [P
14888
]
+
.In
compa ison, [emim][OAc] wi hou any dipola ap o ic co-
sol en s is ypically desc ibed as being able o dissol e up o
0.33 mol o AGU pe mol o IL, o 3 mol o IL pe mol o AGU (ca.
25 w %). Essen ially, i has been specula ed
57
ha his is he
dissolu ion limi , whe e each hyd oxyl is bound by 1 ionic liquid
ion, specically he hyd ogen-bond basic anion.
Howe e , om ou and o he pas s udies,
40,58
i is appa en
ha he e is a clea “co-sol en ”effec on he dissolu ion o
cellulose, e en upon imidazolium ionic liquids like [emim]
[OAc]. Al hough i dissol es cellulose o a high deg ee, he
amoun o cellulose able o be dissol ed wi h he addi ion o
DMSO is d ama ically inc eased when compa ed o he nea
ionic liquid, up o 0.79 mol AGU : IL, o 1.7 mol IL : AGU –
sugges ing ha no e e y hyd oxyl is being bound by one
anion.
40
Equally, in his s udy we see ha [P
8888
][OAc]/DMSO a
i s AGU : IL dissolu ion maximum displays simila cha ac e -
is ics, wi h less moles o ionic liquid han he amoun o
cellulose hyd oxyls. Howe e , i is a g ea deal less powe ul as
a sol en han he p e iously s udied ionic liquid sol en sys em
[P
8881
][OAc]/DMSO, which dissol ed up o 1 mol AGU : IL
(Fig. 3).
40
Taking all he da a in o accoun , he change in he
alkyl chain leng h clea ly has a huge impac on he cellulose
dissolu ion capaci y. In compa ison, he ionic liquids used in
his s udy ank jus below some o he classes o cellulose dis-
sol ing ionic liquids in e ms o ‘w %’cellulose dissolu ion
capaci y. Acid–base conjuga e ionic liquids including [TMGH]
[OAc] (1,1,3,3- e ame hylguanidinum ace a e) and [DBNH]
[OAc] (1,5-diazabicyclo[4.3.0]non-5-enium ace a e) ha e dis-
sol ed as much as 15–16 w % o cellulose.
49
Howe e , o he
onium ca ion ionic liquids ha e been s udied which we e
compa able o he sol en s in his s udy, such as [N
4444
][OAc]
( e abu ylammonium ace a e) which was ound o dissol e up
o 8 w % cellulose in he p esence o DMSO.
41
In his espec , i
is qui e ema kable ha he much la ge ca ion p esen in he
sol en [P
8888
][OAc]/DMSO leads o he same le el o cellulose
dissolu ion.
The dependence o he mola o weigh a io o ionic liquid
o co-sol en is eec ed in o he li e a u e ega ding mixed
ionic and molecula cellulose sol en s o o ganic elec oly e
solu ions wi h cellulose dissolu ion capaci y oen ising and
alling a ound a maximum and he addi ion o he co-sol en
inc easing he amoun o cellulose able o be dissol ed in
some ins ances.
34,58,59
As a gene al conside a ion o he mechanism o dissolu ion
in hese mixed ionic-molecula sol en sys ems, i is likely ha
he inc eased size o he ca ion o ces hyd ogen-bonds om he
ace a e anion o become sha ed, as he e a e now less anions
pe uni o cellulose in he  s sol a ion shell. This is a iew
ha was ecen ly p oposed in Rabideau e al.'s compu a ional
s udies o cellulose dissolu ion
60,63
whe e he au ho s ound ha
inc eases in alkyl chain leng h o imidazolium based ionic
liquids led o a dec ease in he amoun o single, non-b idging
hyd ogen bonds and an inc ease in sha ed, b idging hyd ogen
bonds. In he phosphonium ionic liquids, his effec mus in
some way be media ed o offse jus enough by he inc ease in
he alkyl chain leng h and he s eng h o he dispe sion o ces
be ween he non-pola ca ion and he non-pola su ace o
cellulose (in addi ion o he inc eased ion pai sepa a ion and
sol a ion affo ded by he dipola ap o ic componen ) o allow
o dissolu ion. In solu ions wi h ca ions signican ly la ge
han [P
14888
]
+
, i is unlikely ha much dissolu ion will occu a
all, wi h he ca ions being simply oo la ge ( hus unable o
s abilise he non-pola su ace o cellulose) wi h he effec i e
concen a ion o hyd ogen-bond accep ing anions in he  s
sol a ion shell being oo low.
Liquid–liquid equilib ia
The liquid–liquid equilib ia o e na y sys ems composed o
a mix u e o a e aalkylphosphonium ace a e ionic liquid,
Fig. 3 Mola dissolu ion a io (AGU : IL a io) e sus w % o DMSO.
Displayed a e lines showing he poin s a which each cellulose
hyd oxyl is bound by one ionic liquid ion (o 3 mol o IL pe AGU) and
by 1/3 ionic liquid ion (o 1 mol o IL pe AGU).
17454 |RSC Ad .,2017,7,17451–17461 This jou nal is © The Royal Socie y o Chemis y 2017
RSC Ad ances Pape
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online
DMSO, and wa e was s udied o e alua e he ecyclabili y o he
sol en sys ems ia phase-sepa a ion. Such e na y sys em is
a ep esen a ion o he s a e o he mix u e ae dissolu ion o
cellulose and i s subsequen egene a ion wi h wa e , he an i-
sol en . The expe imen al liquid–liquid equilib ium da a o
he e na y sys ems [P
8888
][OAc] + DMSO + wa e and [P
14888
]
[OAc] + DMSO + wa e , a 25.0 C and a mosphe ic p essu e, a e
epo ed in ESI Tables 1 and 2†and a e p esen ed as iangula
phase diag ams in Fig. 4 and 5. Bo h sys ems we e ound o be
o Type I acco ding o he classica ion by Sø ensen e al.,
64
wi h
wa e and he ionic liquid showing a la ge mu ual immiscibili y
and he o he wo bina y combina ions (DMSO + wa e , and
DMSO + ionic liquid) being o ally miscible in any p opo ion.
A la ge 2-phase egion was iden ied in bo h sys ems, con-
sis ing o an uppe ionic liquid- ich phase, and a lowe aqueous
phase, wi h he a ea o he wo-phase egion being la ge wi h he
ionic liquid [P
14888
][OAc]. The e is a clea effec o he alkyl chain
leng h, o size (mola olume) be ween he wo ionic liquids on
he dis ibu ion a io o he DMSO, on he wa e con en o he
ionic liquid phase, and on he ionic liquid con en o he
aqueous phase. As he ca ion size inc eases, he ionic liquid
con en in he aqueous phase d ops, as does he wa e con en o
he ionic liquid phase. These effec s would be consis en wi h he
inc ease in “hyd ophobici y”as affo ded by he longe alkyl
chains, by inc easing he size and non-pola cha ac e o he
ca ions. An in e es ing ea u e is he e y low o e en negligible
concen a ion o ionic liquid in he aqueous phase o bo h ionic
liquids, pa icula ly [P
14888
][OAc]. The eco e y o ionic liquid is
he limi ing ac o o scale-up o cellulose dissol ing and
biomass ac iona ion p ocesses wi h ionic liquids, and hus his
is a e y impo an conside a ion. F om he liquid–liquid equi-
lib ium da a, we can see ha he ionic liquid has e y low solu-
bili y in he aqueous phase in he e na y sys ems s udied; hus
minimising he loss o he expensi e ionic liquid componen in o
he aqueous was e s eam.
The dis ibu ion a io o DMSO in he phases in equilib ium,
b
DMSO
, was calcula ed by means o eqn (1):
bDMSO ¼
wII
2
wI
2
(1)
whe e w
2
is he mass ac ion o DMSO, and supe sc ip s I and II
e e o he ionic liquid- ich phase and he wa e - ich phase
espec i ely. Fo bo h e na y liquid–liquid equilib ia, he
alues o b
DMSO
a e p esen ed along wi h he liquid–liquid
equilib ium da a in ESI Tables 1 and 2.†In bo h sys ems he
DMSO dis ibu ion a ios a e g ea e han uni y, indica ing he
p e e en ial pa i ion o DMSO owa ds he aqueous phase. The
dis ibu ion a ios a e pa icula ly high a low concen a ions o
DMSO in he sys ems, hen dec easing oughly in an exponen-
ial ashion as a unc ion o inc easing DMSO con en (Fig. 6).
As a measu e o he sepa a ing powe ha wa e has on he
mix u e o he ionic liquid and DMSO, a selec i i y pa ame e S
can be dened as:
S¼
wII
2
wI
2

wI
1
wII
1
(2)
wi h subsc ip s 1 and 2 s anding o he ionic liquid and DMSO
espec i ely, and he es o a iables ha e he same meaning as
in eqn (1). These S alues we e calcula ed only o he e na y
sys em wi h [P
8888
][OAc], as he e na y sys em wi h [P
14888
][OAc]
displays nume ically inni e alues on accoun o he lack o
ionic liquid de ec ed in he aqueous phase. Selec i i ies a e
no ably la ge o he sys em [P
8888
][OAc] + DMSO + wa e (ESI
Table 1 and Fig. 6†), and inc eases as he global concen a ion
o DMSO dec eases and he global concen a ion o wa e
inc eases. Wi h he high S alues displayed, a high efficiency o
sepa a ion is demons a ed o be possible wi h he ionic liquid
and DMSO using he an i-sol en wa e ; especially a low DMSO
concen a ions. This means ha in any possible p ocess, he
Fig. 4 Expe imen al ie-lines o he liquid–liquid equilib ium o he
e na y sys em [P
8888
][OAc] + DMSO + wa e a 25.0 C and a mo-
sphe ic p essu e, in weigh ac ions.
Fig. 5 Expe imen al ie-lines o he liquid–liquid equilib ium o he
e na y sys em [P
14888
][OAc] + DMSO + wa e a 25.0 C and a mo-
sphe ic p essu e, in weigh ac ions.
This jou nal is © The Royal Socie y o Chemis y 2017 RSC Ad .,2017,7,17451–17461 | 17455
Pape RSC Ad ances
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online

DMSO is e y likely o be easily emo ed as pa o he aqueous
phase, pe haps ae mul iple ex ac ions, and he eae
eco e ed om he aqueous was e s eam.
Cellulose egene a ion and ionic liquid eco e y
We conduc ed a la ge -scale demons a ion o he cellulose
dissolu ion and egene a ion capabili ies o media based on
[P
8888
][OAc] and DMSO, since his was he ionic liquid wi h he
g ea es cellulose dissolu ion capabili y. The o e all p ocess is
illus a ed in Fig. 7. Taking a 5 w % solu ion o cellulose in
a solu ion o 40 w % IL and 60 w % DMSO, wa e was used as an
an i-sol en o p ecipi a e cellulose. The eco e y global
composi ion was 80 w % wa e , 12 w % ionic liquid, and 8 w %
DMSO. E en hough wa e and [P
8888
][OAc], a his concen a-
ion, a e immiscible, cellulose p ecipi a ion s ill occu s.
Ini ially, he cellulose p ecipi a es as a gel, and equi es s ong
o e head s i ing in wa m wa e o b eak up he gel in o a solid
suspension, wi h he ionic liquid and aqueous phases appea -
ing as an emulsion. The amoun o wa e was de e mined based
on he e na y phase diag am and in o ma ion om he equi-
lib ium expe imen s, in o de o maximize po en ial eco e y
and minimize excessi ely s ong emulsion o ma ion. The ionic
liquid, DMSO and wa e mix u e is sepa a ed om cellulose ia
cen i uga ion, wi h wo liquid phases and he solid cellulose
phase sepa a ing e enly, enabling he ionic liquid- ich phase o
be eco e ed wi h ela i e ease om he op phase. Howe e ,
since he solid cellulose oa s a he in e ace o he wo phases,
a po ion o he ionic liquid is abso bed in o he op o he
swollen cellulose ma e ial, and mus be washed wi h a miscible
sol en o be ully eco e ed.
Thus, he aqueous phase and he solid cellulose was sepa-
a ed ia l a ion wi h he cellulose being washed wi h e hanol.
Ae phase-sepa a ion and emo al o he cellulose phase,
a small amoun o ionic liquid emained on he op o he
aqueous phase. This po ion was ca e ully decan ed and
ex ac ed and he side o he ask washed wi h e hanol o
eco e mo e esidual ionic liquid. The e hanol wash l a e was
e apo a ed combined wi h he ionic liquid- ich phase o he
nal eco e y mass balance. Typically, in a eal b e spinning
p ocess, only a small amoun o ‘dope’is spun in o a spinning
ba h a one ime, wi h he b es being con inually emo ed,
ae which hey a e aken h ough mul iple s ages o washing
ba hs o emo e esidual sol en . This is in con as o ou lab
scale demons a ion, whe e he whole mass o cellulose is
p ecipi a ed a once (appea ing be ween he phases) necessi-
a ing such eco e y echniques. Doing hese expe imen s,
howe e , enables us o gain a easonable mass balance as an
e alua ion o he po en ial o his eco e y echnique on a lab
scale.
The yield o eco e ed cellulose was high, wi h 99 w % being
eco e ed. The yield o ionic liquid eco e ed om he ionic
liquid- ich o ganic phase in he liquid–liquid sepa a ion was 60
w %, wi h he bulk o he es being eco e ed om he cellulose
e hanol wash, a ound 30 w %, whils a small amoun o ionic
liquid, a ound 7 w %, was eco e ed om he op o he aqueous
phase ae emo al o he ionic liquid and cellulose phases
(b inging he o al eco e y o ionic liquid o 97 w %), and he
es , a ound 3 w % was unaccoun ed o , wi h a po ion (<0.1
w %, om he phase diag am) o be in he aqueous phase and
he es due o expe imen al losses, likely du ing he l a ion
s age. F om he phase diag am, he eco e ed ionic liquid- ich
phase should ha e a small amoun o DMSO and wa e
(a ound 10 w % espec i ely). The esidual wa e and DMSO can
Fig. 6 DMSO dis ibu ion a io (b
DMSO
) o he e na y sys ems [P
8888
]
[OAc] + DMSO + wa e (blue) and [P
14888
][OAc] + DMSO + wa e ( ed),
a 25.0 C and a mosphe ic p essu e, as a unc ion o he mass ac ion
o DMSO in he ionic liquid- ich phase.
Fig. 7 Illus a ion o la ge (lab)-scale dissolu ion and egene a ion
expe imen showing he ecycling scheme.
17456 |RSC Ad .,2017,7,17451–17461 This jou nal is © The Royal Socie y o Chemis y 2017
RSC Ad ances Pape
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online
be emo ed unde high- acuum, lea ing a pu e and d y ionic
liquid. Howe e , om he phase equilib ium da a, i should also
be possible o emo e he esidual DMSO by mul i-s age o
coun e -cu en ex ac ion wi h wa e due o he ex emely
a ou ably dis ibu ion a io and selec i i y o DMSO ex ac ion
in he aqueous phase. Howe e , a small amoun o wa e would
s ill emain, which may need o be emo ed wi h some so o
app op ia e d ying me hod. The eco e ed cellulose showed no
signs o con amina ion by he ionic liquid, when compa ing he
in a- ed spec a o ha o pu e cellulose (ESI†).
The c ys allini y o he eco e ed sample om he la ge-scale
dissolu ion and egene a ion was analysed ia XRD (X-Ray
Diff ac ion) measu emen s (Fig. 8). As ound wi h he
p e ious s udies on phosphonium ionic-liquid and DMSO-
based elec oly es,
40
he egene a ed cellulose ma e ial was
ound o con e om he Cellulose I o he Cellulose II poly-
mo ph wi h a co esponding ela i e loss in c ys allini y and
inc ease in amo phous con en .
We also explo ed he use o he phosphonium ionic liquids
as cellulose dec ys allisa ion agen s – ha is, he abili y o
emo e cellulose c ys allini y (Cellulose I o na i e cellulose)
and eco e amo phous cellulose om high molecula weigh
dissol ing pulp (Enocell PHK Pulp). This was es ed by simple
hea ing (a 100 C) o 4 hou s, ollowed by emo al o he ionic
liquid wi h e hanol. I was ound ha hea ing in he nea ionic
liquid (0 w % DMSO) and “non-dissol ing”composi ions o
[P
8888
][OAc] and DMSO (i.e. 5 and 90 w % DMSO, based on
Fig. 2) lead o e y li le change in he XRD in e e og am, wi h
Cellulose I emaining as he dominan cellulose c ys alline
o m. When iewed unde a mic oscope, he b ous s uc u e o
he pulp emained (ESI Fig. 11 and 13†). This adds u he
e idence o he non-dissol ing abili y o hese kinds o hyd o-
phobic phosphonium ionic liquids in he absence (o excess) o
a dipola -ap o ic co-sol en (such as DMSO) as desc ibed by
Fig. 2. Howe e , a “dissol ing”composi ion (40 w % DMSO)
wi h an excess o cellulose (10 w %, being jus o e he
measu ed sa u a ion poin o ca. 8 w % cellulose, meaning
a po ion o he cellulose is swollen and no dissol ed) leads o
an in e media e mix u e o Cellulose I and Cellulose II poly-
mo phs (Fig. 9), which would be consis en wi h undissol ed
b e agmen s being p esen along wi h dissol ed and egen-
e a ed Cellulose II (likely wi h inc eased amo phous con en )
(ESI Fig. 12†). The XRD in e e og ams o cellulose (p e-hyd o-
lysis k apulp) ea ed wi h pu e [P
8888
][OAc] and a ying
amoun s o DMSO a e displayed in Fig. 9.
T acking dissolu ion, egene a ion and eco e y wi h NMR
spec oscopy
We ha e shown p e iously he excellen abili y o his class o
cellulose sol en s in obse ing lignocellulosic biopolyme s,
including high molecula weigh cellulose, by NMR spec os-
copy.
65
P o on NMR spec a o he ionic liquid be o e dissolu-
ion, ae dissolu ion o 5 w % cellulose in 60 : 40 w % [P
8888
]
[OAc]/DMSO-d
6
,ae phase sepa a ion o an ionic liquid- ich
phase, and ae d ying and ull eco e y shows he p ocess o
dissolu ion and eco e y in hese sol en s (Fig. 10). Ae
dissolu ion o cellulose in he sol en , i is clea ly isible in he
1
H spec a. The spec al a ea o
1
H signals a ising om
ca bohyd a es is a ound 5–3 ppm, wi h no majo conic ing
signals om he ionic liquid sol en . Howe e , mino sol en
impu i ies a e also isible wi h low in ensi y in he cellulose
egion, bu hese a e easily dis inguished om he cellulose
backbone peaks. These a e isible wi h e y low in ensi y in he
spec um o he ionic liquid p io o dissolu ion (ESI Fig. 5†). No
esidual ca bohyd a es a e isible in his egion in he
1
H
spec um o he eco e ed ionic liquid, indica ing minimal
con amina ion wi h oligosaccha ides, monosaccha ides o
esidual cellulose in he ionic liquid, such as om deg ada ion
p ocesses. Ae addi ion o wa e , and ex ac ion o an NMR
sample om he ionic liquid- ich phase, we can see he disap-
pea ance o he cellulose peaks, along wi h a new wa e peak
and a DMSO peak o inc eased in ensi y. The eco e ed ionic
liquid is ee om DMSO, wa e , and shows no signican
changes o he s a ing ma e ial.
Fig. 8 XRD in e e og ams o wo samples: MCC cellulose dissol ed
and egene a ed om [P
8888
][OAc] : DMSO 40 : 60 w % (wi h wa e ,
and washed wi h e hanol) and un ea ed MCC.
Fig. 9 XRD in e e og ams o Enocell PHK Pulp (10 w % in solu ion)
swollen (no ully dissol ed) in [P
8888
][OAc] and a ying composi ions
o IL and DMSO.
This jou nal is © The Royal Socie y o Chemis y 2017 RSC Ad .,2017,7,17451–17461 | 17457
Pape RSC Ad ances
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online
Conclusions
Two hyd ophobic, long chain phosphonium ionic liquids we e
ound o dissol e cellulose in he p esence o DMSO. Howe e ,
he ionic liquid [P
14888
][OAc] dissol ed signican ly less cellu-
lose a he mos op imum DMSO concen a ion han [P
8888
]
[OAc] –so a limi on he effec i e chain leng h o phosphonium
ionic liquids, and ionic liquids in gene al o cellulose disso-
lu ion, is appa en . Te na y sys ems including basic and
hyd ophobic phosphonium ace a e ionic liquids o a se ies
[P
R888
][OAc] wi h DMSO and wa e we e shown o be phase-
sepa able om wa e , showing a Type I phase diag am. The
high DMSO dis ibu ion a ios and high selec i i y alues
demons a e ha he ionic liquid and DMSO may be efficien ly
sepa a ed wi h a minimum o he sepa a ing sol en , wa e . The
low solubili y o he ionic liquid in he aqueous phase allows
quan i a i e eco e y o he ionic liquid when wa e (as
a p ecipi a ing an i-sol en o dissol ed cellulose) is added o
an ionic-liquid and DMSO mix u e. Thus, he inc eased eco e y
by simple phase-sepa a ion compa ed o p e ious gene a ions
o his sol en class (and o he ionic liquids) is a signican
ad ance in he sea ch o a phase-sepa able sol en medium o
cellulose dissolu ion and egene a ion, which could lead o
lowe ed ene gy demands and hus mo e sus ainable p ocesses.
Po en ial oadblocks o la ge scale applica ions o hese
sol en sys ems include he sepa a ion o DMSO om was e
wa e s eams and oxici y o he componen ionic liquids (due
o he long alkyl chain leng h o he ca ion). Howe e , a dec ease
in ca ion alkyl chain leng h (and i s associa ed lowe ed oxici y)
comes a he expense o he eco e y abili y by phase-sepa a ion
–so a balance be ween hese wo ac o s is needed. Fu u e wo k,
including enginee ing simula ions and LCA analyses may be
able o elucida e exac ly which pa hway is mo e sus ainable.
Expe imen al sec ion
Chemicals and aw ma e ials
T ioc ylphosphine (CYTOP 380) was a gi om Cy ec L d. Oc yl
chlo ide, e adecyl chlo ide, po assium ace a e (99.8%, anhy-
d ous c ys alline powde ), me hyl ace a e (HPLC g ade, >99.8%)
and 2-p opanol (HPLC g ade >99.5%) we e pu chased om
Sigma Ald ich L d. Mic oc ys alline cellulose (MCC) was also
pu chased om Sigma Ald ich L d. Enocell PHK pulp was
kindly supplied by S o ¨
a Enso Oyj.
Ionic liquid syn hesis
Fo bo h syn hesized ionic liquids, ioc ylphosphine was
cha ged unde a gon in o a pu ged 3 necked ound bo om
ask, wi h an a gon balloon capped condense and sep um on
he side neck. The co esponding alkyl chlo ide, 1.01 equi alen
was in oduced in small po ions h ough he sep um whils
s i ing, wi h he empe a u e o he mix u e being moni o ed
wi h a he mome e (Scheme 1i). The empe a u e o he eac-
ion mix u e was slowly inc eased o 145 C and s i ed o 16
hou s. Excess eac an s and any small-molecula weigh by-
p oduc s we e emo ed unde high acuum a ca. 90 C,
p oducing a ligh yellow, highly iscous liquid.
The e aalkylphosphonium chlo ide ionic liquid in e media e
was dissol ed in isop opanol, in a 1 : 5 olume a io and hea ed o
80 C wi h s i ing. Po assium ace a e, 1.01 mola equi alen , was
added in small po ions (Scheme 1ii) and s i ed o ensu e
comple e dissolu ion and homogeniza ion in he mix u e. Ae
s i ing a 80 C o onehou , hemix u ewass i eda oom
empe a u e o 16 hou s, and e ige a ed o a u he 16 hou s o
ensu e comple e p ecipi a ion o KCl. The KCl by-p oduc was
acuum l e ed o e a glass sin e l e and celi e and he iso-
p opanol was emo ed unde educed p essu e. Cold ace one was
added o he c ude p oduc o p ecipi a e any emaining sal s,
including KOAc and KCl, and again l e ed wi h a glass sin e
l e and celi e. Ace one was e apo a ed unde educed p essu e,
and he p oduc was d ied unde high acuum and high empe -
a u e (ca. 90 C) o p oduce a highly iscous, da k ambe liquid.
T ioc yl( e adecyl)phosphonium ace a e [P
14888
][OAc]
T ioc ylphosphine (83.1 g, 2.24 10
1
mol), e adecylchlo ide
(52.62 g, 2.27 10
1
mol), po assium ace a e (21.28 g, 2.17 
Fig. 10
1
H NMR spec a illus a ing dissolu ion and egene a ion
p ocesses: (a) ionic liquid p io o dissolu ion in CDCl
3
; (b) 5 w % MCC
cellulose in [P
8888
][OAc]/DMSO-d
6
,(C
N
e e s o he cellulose ca bon
numbe , NRE ¼non educing end); (c) [P
8888
][OAc]/DMSO-d
6
solu ion
a e addi ion o wa e and egene a ion o cellulose; (d) [P
8888
][OAc],
a e phase-sepa a ion, eco e y and d ying, in CDCl
3
. No e: in DMSO-
d
6
, some chemical shi s, no ably he peak a ising om he ace a e
CH
3
, shi upfield.
Scheme 1 Syn hesis o phosphonium ionic liquids. (i) Menshu kin
qua e niza ion, (ii) anion me a hesis.
17458 |RSC Ad .,2017,7,17451–17461 This jou nal is © The Royal Socie y o Chemis y 2017
RSC Ad ances Pape
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online
10
1
mol). Final p oduc : 135.90 g, 2.17 10
1
mol, 96.7%
yield.
1
H: (600 MHz, CDCl
3
)d2.41 (m, P–CH
2
), 1.94 (s,

OOC–CH
3
),
1.63 (m, –CH
2
–), 1.48 (m, –CH
2
–), 1.36 (m, –CH
2
–) 1.24 (m,
–CH
2
–), 0.86 ( , J¼6.9 Hz, CH
3
).
13
C: (600 MHz, CDCl
3
)d179.21 (s, CH
3
CO
2

), 33.52 (s, CH
2
),
33.42 (s, CH
2
), 32.29 (s, CH
2
), 32.26 (s, CH
2
), 32.22 (s, CH
2
),
32.14 (s, CH
2
), 31.96 (s, CH
2
), 31.94 (s, CH
2
), 31.58 (s, CH
2
),
27.86 (s, CH
3
CO
2

), 25.29 (s, CH
2
), 25.20 (s, CH
2
), 24.61 (d, J¼
4.78 Hz, CH
2
), 21.46 (d, J¼46.7 Hz, P–CH
2
), 16.72 (s, CH
3
),
16.65 (s, CH
3
).
Te aoc ylphosphonium ace a e [P
8888
][OAc]
T ioc ylphosphine (83 g, 2.24 10
1
mol), oc ylchlo ide
(33.56 g, 2.27 10
1
mol), po assium ace a e (22.02 g, 2.24 
10
1
mol). Final p oduc : 117.6 g, 2.17 10
1
mol, 96.7% yield.
1
H NMR (600 MHz, CDCl
3
)d2.38 (m, P–CH
2
), 1.90 (s,
CH
3
CO
2

), 1.60 (m, –CH
2
–), 1.46 (m, –CH
2
–), 1.33 (m, –CH
2
–),
1.21 (m, –CH
2
–), 0.82 ( , J¼7 Hz, CH
3
)
13
C: (600 MHz, CDCl
3
)d179.24 (s, CH
3
CO
2

), 34.27 (s, CH
2
),
33.48 (s, CH
2
), 33.38 (s, CH
2
), 31.53 (s, CH
2
), 27.95 (s, CH
3
CO
2

),
25.15 (s, CH
2
), 24.56 (d, J¼4.59 Hz, CH
2
) 21.6 (d, J¼46.4 Hz, P–
CH
2
), 16.60 (s, CH
3
).
Cellulose dissolu ion expe imen s
Dissolu ion expe imen s we e conduc ed in a simila manne o
ou p e ious wo k,
40
wi h cellulose being dissol ed in a p e-
mixed ionic liquid–DMSO solu ion a a cons an empe a u e,
120 C and cellulose being added in small inc emen s un il
a cloud poin is eached. The uppe bounda y is aken as he
midpoin be ween he cloud poin and he las addi ion o
cellulose, whe e each addi ion is ca. 0.5% o he o al mass.
Cloudy solu ions can be con med by op ical mic oscopy o
con ain b e agmen s.
Liquid–liquid equilib ia
Mix u es o DMSO, wa e and ionic liquid ([P
8888
][OAc] o
[P
14888
][OAc]), wi h global composi ion lying in he immisci-
bili y domain o he co esponding e na y sys em, we e
p epa ed and in oduced in o jacke ed glass cells especially
designed o liquid–liquid equilib ium expe imen s. The
empe a u e o he cells was kep a 298.2 K by means o an
Ul a he m-200P Selec a wa e -ci cula ing he mos a ic ba h,
wi h an unce ain y o 0.1 K. All mix u es we e igo ously s i ed
(magne ic s i ing) o a minimum o 2 h, and hen allowed o
se le un il comple e sepa a ion o he phases in equilib ium (a
minimum o 12 h, and ypically se e al days). I was ound ha
a lowe DMSO concen a ions, he he e ogeneous mix u es
o med s ong emulsions and phase sepa a ion imes we e
un easonably la ge. To o e come his p oblem, such mix u es
we e placed in cen i uge ubes, hen cen i uged wice o 15
minu es each a 4000 pm, and he cen i uge ubes we e placed
in o he he mos a ic wa e ba h a 298.2 K. In all cases, ae
equilib a ion and sepa a ion, bo h phases we e sampled wi h
sy inges a ached o needles, wi h a oidance o minimisa ion o
he dis u bance o he liquid–liquid in e ace. The eae , hese
samples we e placed in glass ials, weighed, and mixed wi h
known amoun s o an ex e nal s anda d and a sol en , as
desc ibed in he ollowing pa ag aph, o composi ional anal-
ysis by gas ch oma og aphy.
The composi ions o he samples we e analysed using a HP
6890 se ies gas ch oma og aph, equipped wi h a he mal
conduc i i y de ec o and a HP-FFAP capilla y column (25 m 
0.2 mm 0.33 mm), coupled wi h an emp y p e-column o
collec he ionic liquid ha was no e ained by he line . To
allow calcula ion o he ionic liquid concen a ion by diffe ence,
me hyl ace a e was used as an ex e nal s anda d. An o ganic
sol en , namely 2-p opanol, was used as sol en o he
mix u es o sample and ex e nal s anda d. Helium was used as
he mobile phase, and he injec ion olume was 1 mL wi h a spli
a io o 50 : 1 and a p essu e o 20.42 psi. Injec ion empe a u e
was 250 C. The ini ial o en empe a u e was 50 C held o 2.7
minu es. The e we e wo hea ing amps, he  s om 50–
175 Ca 12C pe minu e, and he second om 175–240 Ca
120 C pe minu e, leading o a o al un ime o 18.16 minu es.
Unde hese condi ions, an adequa e sepa a ion be ween he
signals o he ex e nal s anda d, sol en , wa e , and DMSO was
obse ed. Calib a ion cu es we e cons uc ed wi h samples
p epa ed by weigh and wi h composi ions in he (homoge-
neous) icini y o he solubili y cu e, p e iously de e mined ia
he “cloud poin ”me hod. The wa e con en o he ionic liquids
was measu ed ia Ka l-Fische i a ion in a Me Ohm 737 KF
coulome e , and was ac o ed in o he mass balance o ionic
liquid and wa e . The peak a eas a io o he analy es DMSO
and H
2
O o e he ex e nal s anda d we e co ela ed wi h he
mass a ios o he analy es o e he in e nal s anda d. The
s anda d mass ac ion e o s associa ed wi h he composi-
ional analysis p ocedu e desc ibed we e ound o be: 0.006 and
0.007 o he ionic liquid- ich phase and wa e - ich phase
espec i ely in he sys em [P
8888
][OAc] + DMSO + wa e ; and
0.006 and 0.005 o he ionic liquid- ich phase and wa e - ich
phase espec i ely in he sys em [P
14888
][OAc] + DMSO + wa e .
La ge scale dissolu ion- egene a ion expe imen
D y [P
8888
][OAc] (8.7 g) was mixed wi h DMSO-d
6
(5.8 g), o
which cellulose (0.77 g) was added, and he solu ion s i ed
un il a homogenous dispe sion was achie ed. The solu ion was
hea ed a 100 C o ca. 1 hou and 120 C o ca. 30 minu es,
un il a clea solu ion was obse ed. To he cellulose/ionic
liquid/DMSO solu ion wa e was added (10 mL), ini ially
inducing cellulose egene a ion o a homogenous gel s a e.
O e head mechanical s i ing was used o s i he mix u e
igo ously, whils he emaining po ion o wa e (13 mL) was
added, o ming he p ecipi a ed cellulose as a suspension. The
mix u e was s i ed o ca. 2 hou s wi h mechanical s i ing a
oom empe a u e. The mix u e was ans e ed o a cen i u-
ga ion ube and cen i uged o 45 minu es a 40 C o sepa a e
he ionic liquid, aqueous and solid cellulose phases. F om he
esul ing 3-phase sys em, he ionic liquid laye was ex ac ed
om he op wi h a needle and sy inge lea ing he cellulose
phase, oa ing a he op o he aqueous phase, swollen wi h he
ionic liquid phase. The mix u e was cen i uged once again, o
This jou nal is © The Royal Socie y o Chemis y 2017 RSC Ad .,2017,7,17451–17461 | 17459
Pape RSC Ad ances
Open Access A icle. Published on 20 Ma ch 2017. Downloaded on 6/16/2020 9:40:34 AM.
This a icle is licensed unde a
C ea i e Commons A ibu ion 3.0 Unpo ed Licence.
View A icle Online