www.rsc.org/polymers - KAUST Repository - King Abdullah University of Science and Technology

33 Pages·2015·3.83 MB·English

Fabrication of Polyacrylonitrile Hollow Fiber
Membranes from Ionic Liquid Solutions
Item Type Article
Authors Kim, Dooli; Moreno Chaparro, Nicolas; Nunes, Suzana Pereira
Citation Fabrication of Polyacrylonitrile Hollow Fiber Membranes from
Ionic Liquid Solutions 2015 Polym. Chem.
Eprint version Post-print
DOI 10.1039/C5PY01344E
Publisher Royal Society of Chemistry (RSC)
Journal Polym. Chem.
Rights Archived with thanks to Polym. Chem.
Download date 10/04/2019 09:51:29
Link to Item http://hdl.handle.net/10754/579600
View Article Online
View Journal
Polymer
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: D. Kim, N.
Moreno and S. Nunes, Polym. Chem., 2015, DOI: 10.1039/C5PY01344E.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/polymers
Page 1 of 32 Polymer Chemistry
View Article Online
DOI: 10.1039/C5PY01344E
Fabrication of Polyacrylonitrile Hollow Fiber Membranes from Ionic
Liquid Solutions
5. DooLi Kima, Nicolas Morenoa,b, and Suzana Pereira Nunesa*
0
9:
0
1: a Biological and Environmental Sciences and Engineering,
1
15 King Abdullah University of Science and Technology, Saudi Arabia
0
10/2 b Center for Numerical Porous Media NUMPOR, King Abdullah University of Science and t
3/ Technology, Saudi Arabia p
1
n
o i
y *Corresponding author: [email protected] r
g
olo c
n
h s
c
e
d T ABSTRACT u
n
e a n
c
n The interest in green processes and products has increased to reduce the negative impact
cie a
S
of M
v of many industrial processes to the environment. Solvents, which play a crucial role in the
ni
U
h d
ulla fabrication of membranes, need to be replaced by sustainable and less toxic solvent e
d
b
A t
ng alternatives for commonly used polymers. The purpose of this study is the fabrication of p
Ki
y e
b
ed greener hollow fiber membranes based on polyacrylonitrile (PAN), substituting c
d
a
o c
wnl dimethylformamide (DMF) by less toxic mixtures of ionic liquids (IL) and dimethylsulfoxide
o A
D
5.
1 (DMSO).
0 y
2
ber r
cto A thermodynamic analysis was conducted, estimating the Gibbs free energy of mixing to t
O s
8
on 0 find the most convenient solution compositions. Hollow fiber membranes were manufactured mi
d
e
h
s
bli and optimized. As a result, a uniform pattern and high porosity were observed in the inner e
u
P h
surface of the membranes prepared from the ionic liquid solutions. The membranes were C
coated with a polyamide layer by interfacial polymerization the hollow fiber membranes were r
e
m
applied in forward osmosis experiments by using sucrose solutions as draw solution.
y
l
Key words: Green solvents, membranes, ionic liquid, hollow fibers, forward osmosis. o
P
Polymer Chemistry Page 2 of 32
View Article Online
DOI: 10.1039/C5PY01344E

1. Introduction
5. Volatile organic compounds (VOC) resulting from many toxic or hazardous solvents are
0
9:
0
1:
5 1 discharged in the air at an estimated rate of 20 million ton per year from the industry 1. These
1
0
2
10/ emissions cause serious environmental issues such as contamination of the atmosphere and t
3/ p
1
n
o i
y the contamination of aqueous effluents 2 posing a high risk to the environment and human r
g
olo c
n
ch health. As concerns of regulatory authorities related to environmental impact grow, interest in s
e
d T u
n
e a green processes and products, by the usage of harmless chemicals, has increased through the n
c
n
cie a
S
of past decade. M
v
ni
U
h Green chemistry aims to reduce the usage of harmful chemicals and was summarized by d
a
ull e
d
Ab Anastas et al. 3 in twelve principles, which are important considerations in the design of t
ng p
Ki
y processes and products 4. Using safer solvents and auxiliaries is one of the main aspects of e
b
ed c
d
oa green chemistry 5. The European Chemicals Agency (EACH), which is governed by EU c
nl
w
o A
D
5. public law, classified harmful or toxic solvents into a list regulated by the Registration,
1
0 y
2
ber Evaluation, Authorization and Restriction of chemicals (REACH) 6. In this list, chemicals r
cto t
O s
n 08 which are commonly used to fabricate membranes such as DMF, NMP, and DMA, appeared i
o m
d
e
h as toxic compounds. This means that the commonly used solvents may soon be withdrawn
s
bli e
u
P h
from the market and will not be able to be utilized in Europe due to their high toxicity and
C
risk for human health and the environment. This is a strong motivation to consider
r
e
alternatives to conventional chemicals used as solvents, and replace them by sustainable and
m
alternative solvents, which are less toxic to the environment and human health; such solvents y
l
o
are frequently referred as “green” solvents.
P
Membrane technologies have a crucial role as green processes in terms of energy
efficiency, with their simple operation process; high performance, such as selectivity and
permeability; low energetic requirement, compared to other separation processes; and high
2
Page 3 of 32 Polymer Chemistry
View Article Online
DOI: 10.1039/C5PY01344E
stability under operating conditions 7. However, this only considers one side of “greenness”
in membrane technology. It is important to think in other aspects as how can membranes be
5.
9:0 fabricated without the usage of any toxic compounds? Figoli et al. 8 recently summarized
0
1:
1
5
1 very well the concept of greener membranes: Firstly, the use of new and renewable materials
0
2
10/ t
13/ to replace oil derived chemicals was considered; secondly, the hazard or toxicity of the other p
n
o i
y r
g
olo chemicals involved in the fabrication of membranes such as solvents, additives, and c
n
h s
c
e
d T modification agents, needs to be minimized as possible. This study focuses on the fabrication u
n
e a n
nc of greener membranes by the usage of chemicals with less toxic properties.
cie a
S
v of Solvents which play a crucial role in the fabrication of membranes are derived from M
ni
U
h d
a petroleum and generate volatile organic compounds during their production, which can cause
ull e
d
b
ng A health and environmental problems 9. Alternative or green solvents need to have low toxicity, pt
Ki
y e
ed b be non-volatile, be easy to recycle, inert, and should not contaminate the product 10. Over the c
d
a
o c
nl past decade, water, ionic liquids, supercritical fluids (SCFs), and fluorous solvents have been
w
o A
D
15. reported as possible alternatives and green solvents 11.
0 y
2
ber r
cto Ionic liquids (IL) are considered green solvents in many aspects, such as lack of t
O s
8
n 0 measurable vapor pressure, non-flammability, reusability, high thermal stability 12 and low i
o m
d
e
h
blis corrosiveness 13. Due to their high solubility in water, toxicity to aquatic organisms has been e
u
P h
a matter of some concern 14, but the substitution of hazardous volatile organic solvents C
frequently used for membrane fabrication by less toxic mixtures containing ionic liquids r
e
m
could be very beneficial. The term ionic liquid refers to liquids composed entirely of ions that
y
are fluid at temperatures below 100 ºC 10, 15 and do not lead to hazardous VOC generation in
l
o
contrast to common organic solvents 15, 16. P
Many studies have focused on dissolving cellulose using hydrophilic ionic liquids such as
1-butyl-3-metylimidazolium chloride [BMIM]Cl and 1-allyl-3-methylimidazolium chloride
[AMIM]Cl 17. Swatloski et al. 18 showed that ionic liquids can be used as non derivatizing
3
Polymer Chemistry Page 4 of 32
View Article Online
DOI: 10.1039/C5PY01344E
solvents for cellulose. They also reported, that ionic liquids with anions, which are strong
hydrogen bond acceptors, were most effective for dissolving cellulose 19. S. Livazovic et al. 20
5.
9:0 recently reported a membrane manufactured based on cellulose/ionic liquid. Wang et al. 21
0
1:
1
5
1 reported the dissolution of polybenzimidazole (PBI) in 1-ethyl-3-methylimidazolium chloride
0
2
10/ t
13/ ([EMIM]Cl). However, very few studies related to the preparation of membranes have p
n
o i
y r
g
olo focused on ionic liquids. Xing et al. dissolved cellulose acetate (CTA) in 1-butyl-3- c
n
h s
c
d Te metylimidazolium thiocyanate ([BMIM]SCN) to fabricate flat sheet membranes 22. In a u
n
e a n
nc following study, they also fabricated hollow fiber membranes using the same polymer, but
cie a
S
v of dissolved in a different ionic liquid, 1-ethyl-3-metylimidazolium thiocyanate ([EMIM]SCN) M
ni
U
ah 23. Similarly, UF membranes were also fabricated but using only polybenzimidazole (PBI) 24 d
ull e
d
b
ng A or blends of PBI and P84 polyimide 25, both studies used the same ionic liquid, 1-ethyl-3- pt
Ki
y e
ed b metylimidazolium acetate ([EMIM]OAc). Only few polymers have been used for the c
d
a
o c
nl fabrication of membranes with ionic liquids due to their poor activity as solvents for the
w
o A
D
5.
1 polymers which are commonly used for membrane fabrication, such as polysulfone (PSf),
0 y
2
ber r
cto polyacrylonitrile (PAN), and polyetherimide (PEI). t
O s
8
n 0 DMSO, a good solvent for commercial polymers and commonly used for membrane i
o m
d
e
h
blis fabrication, is considered of low toxicity according to the GSK’s guide 26, 27 and is not in the e
u
P h
REACH solvent list under concerns 6. Low toxicity, high polarity, and water miscibility are C
good characteristics for a solvent in membrane manufacture, making DMSO a good r
e
m
candidate to replace DMF, dimethylacetamide (DMA), and 1-methl-2-pyrrolidone (NMP).
y
The purpose of this study is the fabrication of PAN hollow fiber membranes using solvent
l
o
mixtures of ionic liquids and DMSO, which has lower toxicity than other commonly used P
polar organic solvents, with good pore morphology. First, the suitable composition was
estimated considering their thermodynamic interactions expressed by the Flory-Huggins
parameter, χ and the Gibbs free energy of mixing. Theoretical and experimental phase
4
Page 5 of 32 Polymer Chemistry
View Article Online
DOI: 10.1039/C5PY01344E
diagrams were constructed to validate the proper solvent composition. Once identified the
adequate solvent and polymer compositions membranes were manufactured using such less toxic
5.
0
9: solvent mixture. The performance of hollow fiber membranes prepared from IL/DMSO, pure
0
1:
1
5
1 DMSO, and pure DMF were compared for FO systems.
0
2
10/ t
13/ p
n
o i
y r
olog 2. Experiments c
n
h s
c
e
d T u
n
e a n
nc 2.1 Materials
cie a
S
v of Polyacrylonitrile (PAN, Mw = 324,000) was used as the polymer in the form of fine M
ni
U
h d
a power. The ionic liquid (IL) was 1-Ethyl-3-methylimidazolium acetate ([EMIM]OAc,
ull e
d
b
A t
ng ≥95.0% ), supplied by Sigma-Aldrich. Dimethyl sulfoxide (DMSO, ≥99%), and p
Ki
y e
ed b dimethylformamide (DMF, 99.8%) were also purchased from Sigma-Aldrich. The used c
d
a
o c
wnl materials are summarized in Table 1. For the interfacial polymerization (IP), M-
o A
D
5.
1 phenyldiamine (MPD, >99%), 1,3,5-benzenetricarbonyltrichloride (TMC, 98%),
0 y
2
ber r
cto triethylamine (TEA, >99.5%) and (1S)-(+)-10-camphorsulfonic acid (CSA, 99%) were t
O s
8
n 0 supplied by Sigma-Aldrich. Polyethylene glycol (PEG) (Sigma-Aldrich) and i
o m
d
e
h
s
bli polyethyleneoxide (PEO) (Sigma-Aldrich), whose molecular weights were 300 g/mol, 1,500 e
u
P h
g/mol, 6,000 g/mol, 10,000 g/mol, 35,000 g/mol, 100,000 g/mol, and 600,000 g/mol, were C
used for the solute rejection evaluation and determination of the molecular weight cut-off r
e
m
(MWCO). Sucrose (Sigma-Aldrich) was used as draw solution which was applied in the
y
lumen side of the thin film composite (TFC) hollow fiber membranes for testing the
l
o
performance in a FO system. P

5
Polymer Chemistry Page 6 of 32
View Article Online
DOI: 10.1039/C5PY01344E
Table 1. Polymer and solvents used in this study
5. Materials Structures
0
9:
0
1:
1 Polyacrylonitrile (PAN)
5
1
0
2
10/ t
3/ p
1
n
o i
y r
g
olo 1-Ethyl-3-Methylimidazolium acetate ([EMIM]OAc) c
n
h s
c
e
d T u
n
e a n
c
n
cie Dimethyl sulfoxide (DMSO) a
S
v of M
ni
U
h d
a
dull Dimethylformamide (DMF) e
b
A t
ng p
Ki
by e
ed c
d
a
o c
nl
ow 2.2 Thermodynamic analysis A
D
5.
1
0 y
2
ber Prediction of the Gibbs free energy of mixing (∆ Gm) and the Flory- Huggins parameter r
cto t
O s
8
n 0 Understanding the polymer-solution system from the thermodynamic standpoint is an i
o m
d
e
h
blis important tool to optimize the ionic liquid composition in the dope solution for the fabrication e
u
P h
of membranes. The free energy of mixing for polymer dissolution can be written as C
∆ G = ∆ H –T ∆ S (1) r
m m m
e
m
where, T is the absolute temperature, whereas ∆ H and ∆ S are the enthalpic and entropic
m m
y
change of mixing, respectively. According to Flory-Huggins theory28, the Gibbs free energy l
o
of mixing can be approximated by the expression: P
∆ G / N = kT [χφ φ + φ / x ln φ + φ / x ln φ ] (2)
m 0 1 2 1 1 1 2 2 2
6
Page 7 of 32 Polymer Chemistry
View Article Online
DOI: 10.1039/C5PY01344E
where k is the Boltzmann constant, φ and x are the volume fraction and number of segments
ι i
of the ith component, respectively. Spontaneous dissolution processes take place only if ∆ G
m
5.
0
09: is negative. The enthalpy change of mixing can be calculated from the Flory-Huggins
1:
1
5
1
0 parameter, χ, which can be estimated from the solubility parameters of the species according
2
10/ t
3/ p
n 1 to equation (3) 29-32:
o i
y r
g
olo χ = V (δ− δ)2 / RT + 0.34 (3) c
n ij i i j
h s
c
e
d T u
n
ce a where, χij is the Flory-Huggins parameter; Vi is the molar volume of the solvent, (cm3 / mol); n
n
cie a
of S δ is the Hildebrand solubility parameter for the solvent (i) and the polymer (j), (Mpa1/2); R is M
v
ni
U
h the ideal gas constant (8.314 cm3 Mpa K-1 mol-1); T is the absolute temperature, (K); and 0.34 d
a
ull e
d
b
A is an empirical constant absent in the original theory that has been found important for t
ng p
Ki
y polymer systems 29-32. According to the Flory-Huggins approximation, if χ is smaller than 0.5, e
b
ed c
d
a
nlo homogeneous polymer solutions are expected 30. Taking into account the inherent c
w
o A
D
5. simplifications in the Flory-Huggins model28, the value of χ = 0.5 is used as an initial guess
1
0 y
2
ctober to decrease the experimental solvent-composition space to study. The solubility parameters tr
O s
8
n 0 can be computed using the Hansen solubility parameters 31, given by the contribution of i
o m
d
e
h
blis dispersive, dipole-dipole, and hydrogen bonding interactions as e
u
P h
δ2 = δ2 + δ2 + δ2 (4)
D P H C
r
In particular, for ionic liquids the electrostatic33 and Coulombic interactions may have an e
m
important contribution that is not included in the traditional Hansen approach. Therefore,
y
l
experimental or computational based estimations are suitable for improving the free energy
o
P
calculation. Xing et al. 22, 23, 25 calculated the solubility parameter of the ionic liquids,
[EMIM]OAc and [EMIM]SCN, using molecular dynamic simulations 34, leading finally to
∆ G values.
m
7
Polymer Chemistry Page 8 of 32
View Article Online
DOI: 10.1039/C5PY01344E
Phase diagram
Polyacrylonitrile solutions with the following solvents or solvent mixture were
5.
0
9: investigated for membrane preparation: (20/80, 30/70, and 40/60) (wt%/wt%) IL/DMSO;
0
1:
1
15 pure DMSO; and pure DMF. Each point in the phase diagrams for each polymer solution
0
2
10/ t
3/ was plotted after detecting cloud points, i.e. the abrupt increase of turbidity while titrating the p
1
n
o i
y r
olog originally homogeneous solution with addition of water as a non-solvent at 25ºC ±1. c
n
h s
c
d Te u
n
e a n
nc 2.3. Fabrication of membranes
cie a
S
of M
niv PAN was dissolved in a 3-neck flask in each solvent at 60 ℃ for 12 hours. The polymer
U
h d
a
ull solutions were prepared with the ionic liquid (IL), 1-Ethyl-3-methylimidasolium acetate, e
d
b
A t
King (HF-20IL 1, 2, and 3); with pure DMSO (HF-DMSO ); or pure DMF (HF-DMF ). In the case p
y e
b
ed of HF-20IL 1, 2, and 3, the ionic liquid was added after complete polymer dissolution in c
d
a
o c
nl
w
o DMSO and all polymer solutions were stirred for 12 hours at room temperature. The prepared A
D
5.
1
0 y
2 dope solutions were degassed inside the reservoir of the dope solution during 24 hours. Then,
ber r
cto t
O hollow fiber membranes were prepared by using a double spinneret with 0.34 µm inner s
8
n 0 i
o m
d diameter (ID) and 0.64 µm outer diameter (OD) at room temperature. After spinning, the
e
h
s
bli e
u
P hollow fiber membranes were immersed in a mixture of 50% glycerol and 50% 2-propanol h
C
for 2 hours and were dried again. The spinning conditions are summarized in Table 2. These
r
spinning conditions were designed to fabricate hollow fiber membranes with thin walls with e
m
thicknesses of approximately 100 µm, which is convenient in forward osmosis to improve
y
l
water flux. In case of the composition of the bore fluids, the concentration of water was o
P
always 10 wt%; 90 wt % DMSO or DMF was used, depending on solvent used in the dope
solutions.

8