Modification of multi-walled carbon nanotubes for pervaporation nanocomposite membrane
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Date
2011
Authors
Yit Thai, Ong
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Journal ISSN
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Abstract
Owing to its low energy consumption, operational simplicity and ease of
control, pervaporation has gained increasing interest in membrane separation
technology. Due to the requirement of high performance pervaporation membrane
and the emergence of biodegradable polymer, chitosan has become one of the most
studied biodegradable pervaporation membrane. Unfortunately, the pure chitosan
membrane often suffers from low selectivity caused by excessive swelling. In this
research work, it is proposed to incorporated multi-walled carbon nanotubes
(MWCNTs) into chitosan matrix as an outcome to reduce the excessive swelling
behaviour of chitosan. Producing a high quality MWCNT/chitosan nanocomposite
membrane becomes a daunting task as it requires a homogenous dispersion of
MWCNTs in uniform orientation. Therefore, the present research work focus on
functionalized the MWCNTs with poly(3-hydroxybutyrate) (PHB), a biodegradable
polymer which is miscible with chitosan in order to increase the compatibility and
dispersion of MWCNTs in chitosan matrix. The result from thermogravimetric
analysis (TGA) and transmission electron microscopy (TEM) showed that about 40
wt.% of PHB has been successfully attached to MWCNTs by wrapping on their
surface. As to optimize the reinforcing effect from functionalized MWCNT (PHBMWCNT),
it was bulk aligned using simple filtration method. The bulk alignment is
found to offer advantages in reducing the amount of MWCNTs required in achieving
desired mechanical properties. When applying the PHB-MWCNT/chitosan
nanocomposite membranes in dehydration of 1 ,4-dioxane, the nanocomposite
membrane exhibited an increased in selectivity towards water and decreased in
permeate flux when the concentration of 1 ,4-dioxane in feed solution was increased.
However, increasing feed temperature reduced the selectivity of the nanocomposite
membranes but improved the permeate flux. When subjected to higher permeate
pressure (low vacuum), both the selectivity and permeate flux were decreased due to
the reduced driving force. As compared with the chitosan membrane, the
incorporation of PHB-MWCNT significantly enhanced the permeability of the
membrane but trade off its selectivity. Eventually, the optimum conditions of the
nanocomposite membrane in 1 ,4-dioxane dehydration process were obtained using
Response Surface Methodology (RSM). It is suggested that an optimum permeation
flux of 69.48 g/m2·h can be obtained at 59.7°C feed temperature, 5.00 rnrnHg
downstream pressure and 18.88 wt.% of water concentration in feed solution. As for
selectivity, the optimal value of 2292.09 was predicted at 30°C feed temperature,
5.00 mmHg downstream pressure and 1.00 wt.% of water concentration in feed
solution. A balance between the optimum permeation flux and selectivity was
estimated to be simultaneously occurred when the pervaporation process was running
at 30°C feed temperature, 5.00 mmHg downstream pressure and 10.92 wt.% of water
concentration in feed solution. The optimal value of 40.57 g/m2·h and 1668.48 were
obtained for permeation flux and selectivity respectively under this operating
conditions.
Description
Keywords
Multi-valled carbon , Nanocomposite