离子交换膜分离机制的理论分析

Abstract

本文以Donnan dialysis原理和化学势平衡机理为基础，从理论上分析离子交换膜无外加电场分离离子时可能存在的3种状态：膜中离子迁移速率是控制步骤，速度较慢，边界层溶液中离子的迁移速率极快，远高于膜中离子迁移速率；膜中离子迁移速率远大于边界层溶液中离子的迁移速率，边界层溶液中离子的迁移速率是控制步骤；膜中离子迁移速率和边界层溶液中离子的迁移速率均为控制步骤。讨论了3种状态下各区域离子浓度的变化规律，并得出结论：在假定温度、压强等其他影响速率的参数不变的情况下，上述3种状态中，第一种适用于待分离离子及补偿离子浓度高时的情况，第二种适用于待分离离子及补偿离子浓度低的情况，第三种适用于中间范围浓度。浓度范围与3种状态的定量对应关系，可能与离子种类，离子所带电荷数以及膜本身性质有关，需要进一步研究。 This paper, based on Donnan dialysis and chemical potential equilibrium principle, theoretically investigates the three states of ion exchange membrane without external supply of electricity: the rate of ion transport is slow thus is the deterministic step, while the transport in the boundary layer is rapid and much faster than that in the membrane; the transport rate in the membrane is much faster than that in the boundary layer, which is the deterministic step; both the transport rates in membrane and boundary layer are the deterministic steps. And in this paper, the three states are discussed and the conclusion is reached that assuming temperature, pressure and other influential factors remains constant, among the three states mentioned above, the first state is suitable when the concentration of driving ion and feed ion is very high, the second is suitable when the concentration of the two ions is very low and the third is suitable when the concentration is medium. The relationship between the range of concentration and its corresponding state may relate with ion type, ion charge and the nature of membrane itself, and needs further investigation.