Modification of multi-walled carbon nanotubes for pervaporation nanocomposite membrane

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Date
2011
Authors
Yit Thai, Ong
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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.
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Keywords
Multi-valled carbon , Nanocomposite
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