有机相纳滤分离过程中浓度、电荷、溶剂对溶质截留行为的影响

Effects of concentration, molecular charge and solvents on solute rejection with solvent-resistance nanofiltration membranes in non-aqueous system

研究了浓度、电荷和溶剂对膜通量和溶质截留率的影响．结果表明,在有机相中,溶质的截留率随浓度的增加而增加,该结果与水相纳滤的规律相反,通量衰减系数的分析结果发现,浓差极化是导致该结果的原因之一．溶质所带电荷对水相中的溶质截留率影响显著,但对有机相中的截留率影响很小,有机相中纳滤膜分离的主要机理为筛分效应。溶剂的粘度和极性是影响膜通量的主要因素,对于疏水性纳滤膜MPF-50,通量随黏度的增加而降低,溶剂极性与通量关系不明显;对于亲水性纳滤膜MPF-44,通量随极性的降低而降低,而与黏度关系不明显．在纯有机溶剂中,大豆异黄酮D的截留率随溶剂极性的增加而升高．但在甲醇-水的混合溶液中,大豆异黄酮D的截留随溶剂极性的增加而降低．目前普遍认为对于同种纳滤膜,相同有机分子在有机相中的截留率低于水中的截留率,但本文的研究发现,对MPF-50膜,大豆异黄酮D在甲醇和丙酮中的截留率反而显著高于水中的截留率,对该现象的解释有待进一步研究．

The effect of solute concentration, molecular charge and solvents on membrane performance （flux and rejection） in organic solvents was investigated. It was found that solute rejection increased with the rise of concentration which is different from that in aqueous. The investigation of membrane flux decline demonstrated that membrane concentration polarization was one of the likely major causes of the result. Although charge effect influence on the rejection greatly in aqueous, no charge effect on the rejection was observed in organic solvents. In aqueous solutions both sieve and charge effects are dominating separation mechanisms while sieve effect is the major separation mechanism in methanol solutions. The study also shows that solvent viscosity and polarity are the important factors on membrane flux. As for the hydrophobic membrane MPF - 50, solvent viscosity has more effect on membrane flux than polarity does. While for hydrophilic membrane MPF - 44, solvent polarity has more effect on membrane flux than viscosity does. Moreover, solvents also have great effect on solute rejection. In pure organic solvents, the rejection of Soybean daidzin increased with the rise of solvent polarity. On the contrary, in methanol- water mixture, the rejection of Soybean daidzin decreased with the rise of solvent polarity. In addition, it was reported by most researchers that the rejection of the same organic molecular always higher in aqueous than in non - aqueous. However, higher rejection in methanol and acetone than in water was observed in the nanofiltration of soybean daidzin through hydrophobic MPF- 50 membrane in this work.