电渗析法制备硅溶胶过程中阳离子膜浓差极化行为的研究

Study on the Concentration Polarization of Cation-exchange Membrane in the Process Producing Silica Sols by Electrodialysis

首先给出了阳离子交换膜浓差极化物理模型 ,然后利用该模型分析了电渗析制备硅溶胶过程中Um -J曲线的特性 ,阐明了利用Um -J曲线确定浓差极化电流密度的理论依据 ,阐述了Um -J曲线上两个拐点的理化本质 ,其中的拐点 2所对应的电流密度是在该实验条件下(XSiO2 =4% ,θ=5 0℃ ,cNa+=0 1 1 89mol·L-1)的极限电流密度 ,并根据Jlim 和cNa+的关系 ,计算出电渗析法制备硅溶胶过程中的膜边界层厚度δ为 7 6 8× 1 0 -6m ,同时得出了电渗析装置应在极限电流密度下运行这一结论。

The characteristics of the current density\|membrane potential curve have been analyzed theoretically according to the physical model of concentration polarization of cation\|exchange membrane. The method for determining the limiting current density has been derived. The essences of two inflection points on U m -J curves have been explained and the current density at inflection point 2 is the limiting current density at the experiment conditions of X SiO\-2 =4%, θ =50 ℃, c Na + =0 118 9 mol\5L -1 . According to the relations between J lim and c Na + , the thickness of the boundary layer was calculated, named 7 68×10 -6 m. At the same time, when operating, the current density should be lower than the limiting current density.