Improved pervaporation performance of locally-produced chitosan membranes
Mohd Ghazali Mohd Nawawi1 and Hashim Hassan2
1,2
Department of Chemical Engineering, Faculty of Chemical & Natural Resources Engineering
Universiti Teknologi Malaysia, 81310 Skudai, Johor Malaysia
1
Tel: +6075535593, Fax: +6075581463, E-mail: ghazali@fkkksa.utm.my
2
Tel: +6075535522, Fax: +6075581463, E-mail: hashim@fkkksa.utm.my
Abstract
In this study, the pervaporation membranes were prepared from locally-produced
chitosan polymer. Chitosan were extracted from domestic shrimp shells which can be
found abundantly locally via a simple method using strong acid and alkaline treatments.
Chitosan membranes were prepared by solution casting method. Chitosan membranes
were modified by blending with Poly(vinyl alcohol)(PVA) and incorporation of zeolite
13 X in the membrane matrix. The membrane performances were studied in the
pervaporation dehydration of isopropanol-water mixtures. From our results, chitosan
membranes showed preferential permeation to water for the whole feed compositions.
The overall pervaporation performance of the modified membranes were compared based
on the pervaporation separation index(PSI). It was found that the chitosan membranes
performance were improved upon modifications: chitosan/ poly(vinyl alcohol) blended
and chitosan/ zeolite blended membranes showed a higher pervaporation separation
index(PSI) as compared to the unmodified chitosan membranes.
Key words : Pervaporation; chitosan; blending; zeolite; isopropanol-water
1. Introduction
Membrane pervaporation is a unique process in which a liquid mixtures are brought
into contact with one side and permeate components are removed from the other side of
the membrane as vapor by applying a vacuum or using inert gas. The application of
membrane pervaporation in the separation of liquid mixtures has become increasingly
important in these days and has been recognized as an efficient alternative to the
conventional means of separation such as distillation and extraction1. The separations of
liquid mixtures using those techniques are not efficient as in the case which involves
azeotropic mixtures, isomeric components, close boiling point system or heat-sensitive
mixtures.
Hydrophilic polymer has been well exploited as a pervaporation membrane material as
it is more efficient and suitable for removing the water from organic-water mixtures.
One of the materials that has gained interest in the preparation of hydrophilic
pervaporation membrane is chitosan. Chitosan is the partially deacetylated polymer of
chitin which can be found in abundant in a wide range of natural sources like shrimp
shells and crab. Chitosan has been studied as pervaporation membranes due to its high
affinity to water, having film-forming properties and can easily be modified despite of its
chemically stability2-4 .
Usually pure polymer could not meet the demand of pervaporation so it needs
modifications to improve its performance. The polymer blend is of great interest as it is
the simplest and easiest way of achieving materials with new desirable properties5.
Several studies on poly(vinyl alcohol)/chitosan (PVA/CS) blending membranes have
been reported6-9. Chitosan forms a clear homogeneous blend with PVA at any blend
ratios. Alternatively, improvement of chitosan membrane performance can also be
obtained by blending it with suitable zeolite-chitosan pairs. Works by Chen and coworkers10 revealed that the separation factor of chitosan membranes can be successfully
improved by blending it with zeolite HY.
In this work, chitosan membranes prepared from locally-produced shrimp shells were
modified by blending it with PVA and zeolite 13X at varying weight ratios to chitosan. In
the preliminary stage, the optimum chitosan blend ratios were determined. The modified
membranes were further tested for the pervaporation dehydration of isopropanol-water
systems.
2. Experimental
2.1. Materials
Chitosan used in this research is extracted from a local source of shrimp shells using
strong acid and alkaline. Acetic acid, sodium hydroxide, hydrocloric acid, isopropanol
and ethanol are obtained from commercial sources. Poly(vinyl alcohol) with average
molecular weight of 124,000 is purchased from Aldrich Chemical and Zeolite 13X is
purchased from Sigma-Aldrich.
2.2. Chitosan preparation
Chitosan(CS) prepared in our laboratory(from domestic source of shrimp shells) is
produced by the following procedures. First, protein is removed from ground shells by
treating it with sodium hydroxide aqueous solution (NaOH) at 2-3 M at temperature 8090 oC for 2 hours. Then it is washed thoroughly with distilled water. The shrimps shell is
subsequently treated in 2M hydrochloric acid (HCL) aqueous solution for 24 hours to
remove the calcium from the shells. The chitin thus obtained is washed with distilled
water and dried under the sun. The chitin flakes are then subsequently deacetylated in
50% NAOH solution at a temperature of 90-110 oC for 3 hours to produce chitosan. Then
the chitosan flakes are washed with distilled water, dried under the sun for three hour and
is further dried at room temperature.
2.3. Homogeneous dense chitosan preparation
Homogeneous dense chitosan membranes were prepared by the solution casting
technique. First a preweighed quantity of chitosan flakes was dissolved in a dilute
aqueous acetic acid solution and stirred well for 24 hours to form a homogeneous
solution. The polymer solution comprising of 2.0 wt% chitosan, 9.8 wt% acetic acid and
88.2 wt% water. Then, the polymer solution was first filtered to remove trace amount of
undissolved chitosan to give a clear homogeneous casting solution. The resulting casting
solution was cast onto a horizontally position petri-dish, allowing the casting solvent to
evaporate for 48 hours at ambient conditions. The formed membrane was then peeled off
from the petri dish before being immersed in a coagulation bath containing 3 wt% NaOH,
47 wt% ethanol and 50 wt% water for 24 hours at room temperature, then washed
thoroughly with deionized water to completely remove NaOH and finally is air-dried at
room temperature.
2.4. Chitosan/PVA blend preparation
For chitosan/PVA blends preparation, PVA(poly[vinyl alcohol]) solution were
prepared by dissolving a preweighed quantities of dry PVA in deionized water, followed
by a continuous heating at 90oC for 6 hours. A blend solution was prepared by mixing the
PVA and chitosan solution at various blend compositions at room temperature for 24
hours. The blended casting solutions were poured onto glass petri dish and air-dried at
room temperature for 24 hours. Then, the film were peeled off from the glass, treated in 3
wt% sodium hydroxide solution containing 50 wt% isopropanol for 24 hours at room
temperature, washed thoroughly with deionized water to completely remove sodium
hydroxide. The modified membrane were finally air-dried at room temperature.
2.5. Zeolite-filled chitosan preparation
A calculated amount of zeolite was first dispersed in acetic acid solution. Chitosan
solution and zeolites solution were mixed at desired ratios and stirred overnight to form a
homogeneous solution that are ready for casting. The solution was then casted on a petri
dish, allowed to dry under room condition. Finally the dry membrane was peel off from
the petri dish in the similar way as that used in the preparation of homogeneous chitosan
preparation.
2.6. Pervaporation experiments
Pervaporation experiments were carried out by conventional pervaporation techniques
using a lab scale unit as shown in FIGURE 1. Membrane with an effective area of 52 cm2
was supported by a sintered stainless steel. The permeate pressure was maintained about
3-5 mm Hg by a vacuum pump. The isopropanol solution was stirred well during
experiments. The permeate collected in the cold trap was weighed to determine the
permeation flux. The permeate compositions were analyzed using a Kalfisher equipment.
The separation factor was calculated from:
 YH 2O / YIsopropanol 

 X H 2O / X Isopropanol 
α H O / Isopropanol = 
2
(1)
whereYH 2O , YIsopropanol and X H 2O , X Isopropanol are the weight fractions of water and
isopropanol in the permeate and feed, respectively.
Circulation
pump
Circulation
pump
Feed
Tank
Heating Tape
1
Temperature
Controller
Pressure Gauge
Control Valve
Control Valve
Cold Trap with
Dewar Flaks
Relief Valve
Cold Trap
Vacuum Pump
Pervaporation separation indexes (PSI) were determined from equation:
PSI= J (α − 1)
(2)
Figure 1: Schematic diagram of the pervaporation experimental apparatus
3. Results and discussion
3.1. Pervaporation performance of chitosan/PVA blends
Chitosan was blended with PVA at various compositions. All of the blend solutions
were optically clear to the naked eyes. They showed neither separation into two layers
nor any precipitation. So, the blends film were transparent. Pervaporation performance of
CS/PVA blended membranes were tested in the dehydration separation of 90 wt% of
isopropanol in isopropanol-water mixture. Early studies was aimed at finding the optimal
blended composition. The permeation flux and separation factor versus weight fractions
of chitosan are presented in FIGURE 2. As can be seen from the figure, increasing the
chitosan in the blend will result in the increase in the permeation flux since the increase
of chitosan in the blend will act a plasticizer. This will facilitate the permeation of both
components. It is also shown that membrane with composition CS/PVA: 30/70 exhibites
the best trade-off between flux and separation factor suggesting that CS/PVA blend
composition is optimal at 30/70. The membrane was further investigated on its
performance in the pervaporation system for the whole concentration range of
isopropanol in feed for comparative study.
3.2. Pervaporation performance of
zeolite-filled chitosan(CS/13X)
180
180
160
160
140
140
120
120
Flux
Separation factor
100
80
100
80
60
60
40
40
20
20
0
0
10
30
50
70
Separation factor
.
Permeation flux, g/m 2 hr
The pervaporation performance of zeolite-filled chitosan membranes at 90 wt%
isopropanol in the feed solution was investigated in terms of their permeation flux and
separation factor. The results are shown in FIGURE 3. For the entire range of zeolite
content, the total permeation flux increases with the increase of zeolite content in the
membrane. The increase in the total permeation flux become more drastic after zeolite
content in membrane is above 16.67 wt%. The increase in the permeation flux is due to
the facilitation of transport of penetrant molecules through the membrane filled with
zeolites. For the filled membrane, the penetrant can have two different channel for the
transport to occur: transport through polymer matrix and through the zeolite pores. At
high zeolite content(above 16.67 wt%) there is more chances for the imperfection of the
membrane structures to occur. Any defects occurred in the structure would increase the
permeation flux of the membrane. As for the separation factor, the filled-membrane
showed a maximum value at zeolite content of 4.76 wt% in membrane. The separation
factor then decreases with increasing zeolites. The reduction in separation factors were
very drastic above 16.67 wt% zeolite content.
90
Weight percent of chitosan (%)
Figure 2: Effect of chitosan weight percent on flux and separation factor
3.3. Unmodified Versus Modified Membranes
FIGURE 4 shows the pervaporation separation index (PSI) for homogeneous chitosan,
chitosan/PVA blend and zeolite-filled chitosan membranes respectively. The modified
membranes(CS/PVA and CS/13X) show higher PSI value over the
unmodified(homogeneous chitosan) membrane for the entire feed compositions of
isopropanol-water mixtures. However, a very promising results are exhibited by
membrane CS/13X especially at very high isopropanol concentrations. This membrane
ahows a good potential to be used for the pervaporation dehydration of isopropanol-water
at azeotropic conditions.
350
700
300
Permeation
flux
500
250
Separation
factor
400
200
150
300
100
200
Separation factor
Permeation flux,g/m2.hr
600
50
100
0
0
0.00
4.76
9.09
16.67
23.08
Zeolite content, wt %
-50
28.57
Pervaporation separation
index(PSI), g/m2.hr
Figure 3: Effect of zeolite content lin CS/13X membranes on permeation flux and separation
factor
100000
CS-Homo
CS/PVA
CS/13X
80000
60000
40000
20000
0
10
30
50
70
90
95
Weight percent of isopropanol in feed (%)
Figure 4: Pervaporation separation index for homogeneous chitosan, CS/PVA and CS/13X
membranes
4. Conclusions
In this work, chitosan membranes produced using locally available shrimp shells were
found to be water-selective in the pervaporation separation of isopropanol-water
mixtures. Chitosan membranes were further modified by blending with PVA and the
incorporation of zeolite 13X in the membrane matrix. Both modified membranes:
CS/PVA and CS/13X showed better pervaporation performance than the homogeneous
chitosan membrane. Among them, membranes CS/13X has the best performance
especially at high concentration of isopropanol in the feed.
Acknowledgement
The financial support by Ministry of Science, Technology and Environment of
Malaysia for funding this research through IRPA project is gratefully acknowledged.
References
[1] Huang, R.Y.M. Pervaporation Membrane Separation Processes; Elsevier Amsterdam,
1991.
[2] Feng, X. and Huang, R.Y.M. Pervaporation With Chitosan Membranes. I. Separation
of Water from Ethylene Glycol by a Chitosan/Polysulphone Composite Membrane.
Journal of Membrane Science, 116: 67-76, 1996.
[3] Kubota, N. Permeability, Perstilation and Percrystallization. Journal of Membrane
Science, 100:61-64, 1995.
[4] Mohd. Nawawi, M.G. Pervaporation Dehydration of Isopropanol-Water Systems
Using Chitosan Membranes. Ph.D Thesis, University of Waterloo, 1997.
[5] Paul, D.R., and Newman, S. (Eds.), Polymer Blends, Acedemic Press, New York,
1978.
[6] Wu, Li-Guang, Zhu, Chang-Luo, Moe Liu. Study of a New Pervaporation Membrane.
Part 1. Preparation and Characteristicd f the new Membrane. Journal of Membrane
Science, 90: 199-205, 1994.
[7] Wu, Li-Guang, Zhu, Chang-Luo, Moe Liu. 1994. Study of a New Pervaporation
Membrane. Part 2. Performance Test and Analysis of the New Membrane. Journal of
Membrane Science, 90: 207-212, 1994.
[8] Kim, Jin Hong, Lee, Kim, J Young, Lee, Young Moo, and Kim, Kea Yong. Properties
and Swelling Chaeracteristics of Cross-linked Poly(vinyl alcohol)/Chitosan Blend
Membrane. Journal of Applied Polymer Science. Vol. 45: 1711-1717, 1992.
[9] Mohd. Nawawi, M.G. and Huang, R.Y.M. Pervaporation Dehydration of Isopropanol
with Chitosan Membrane. Journal of. Membrane Science, 124:53-62, 1997.
[10] Chen, X., Yang, H., Gu, Z., and Shao, Z. Preparation and Characterization of HY
Zeolite-filled Chitosan Membranes for Pervaporation Separation. Journal of Membrane
Science, 79: 1144-1149. 2001.