The Research Of Gas Stripping Assisted Membrane Separation Process And The Preparation Of PDMS/VTES Membrane By A Green Method

Small organic molecules in fermentation broth can be in-situ separated by coupling with pervaporation process, thus yielding a reduction in the effect of product inhibition and a higher productivity. However, the permeate concentration in the coupled process is low, which need a further purification process. Additionally, membrane fouling is another problem to be sloved. Thus, our research aims to improve the separating efficiency and eliminate membrane fouling and corrosion,which were carried out by two methods. One is by integrating gas stripping and membrane separation process,the other is by improving the hydrophobicity of the pervaporation membrane via modification.Firstly, The PDMS/PVDF membrane was prepared by using water as solvent in presence of surfactant. The separation performance for isopropanol/water solutions was evaluated. The results showed that the separation factor and the permeate concentration was only 17.5 and 36.2 wt.%, respectively, for separating 3 wt.% isopropanol.Secondly, a novel process, gas stripping assisted vapor permeation (GSVP) process was designed in this research. The effect of gas flow rate, feed temperature and feed concentration on the separation performance of GSVP process were investigated. The results indicated that low gas flow rates, low membrane module temperatures, and high feed temperatures were conductive to a high separation performance. In addition, with increasing feed concentration, the total flux increased while the separation factor fluctuated over a narrow range.Thirdly, the separation efficiency and the energy consumption of this process were also analyzed. Furthermore, the comparison of GSVP and other separation techniques was studied. The results showed that the separation factor, isopropanol flux, and permeate concentration in GSVP were higher than those in PV, although the total flux was low in GSVP compared with that in PV. For example, for separating 3 wt.% isopropanol/water solution, the isopropanol flux, separation factor, and permeate concentration in GSVP were 1.48,7.0, and 2.2 times than those in PV, respectively. Meanwhile, the energy required for GSVP was only 1.28 MJ/Kg, which was only 26% and 30% of the energy required for PV and simple distillation, respectively.Finally, VTES and PDMS, as membrane materials, were used to prepare a membrane with vinyl groups using water as solvent in presence of surfactant. In the contact angle (CA) analysis, this membrane possessed higher hydrophobicity, relative to PDMS membrane. The results indicated that low amount of water additive, two hour of hydrolysis time, and 50℃ of hydrolysis temperature were optimum conditions. The total flux and separation factor were 1022.81 g/m2h and 40.42, respectively, for recovering 1.5 wt.% n-butanol solution by using this membrane. Meanwhile the total flux and separation factor were 1223.14 g/m2h and 49.85, respectively, for separating 3 wt.% furfural/water solution. These results indicated that the PDMS/VTES membrane with high separation performance was successfully synthesized in a green way.