非电解质溶液扩散系数的理论研究评述

Review on theoretical calculation of diffusion coefficients in non-electrolytic solutions

许多过程都涉及扩散控制的传质,相应的扩散速率计算对过程工程的精确量化具有重要意义.本文简述了扩散速率的理论表述模型,并着重介绍了非电解质溶液内扩散系数的理论分析计算途径.分子动力学模拟正处于发展中,并用于估算自扩散系数,但进入实用化阶段尚需时日,唯象模型仍为最重要的理论计算手段.作为最常用的方法,由无限稀释浓度下的扩散系数以及合适的插值方法可计算特定浓度下的扩散系数;自由体积理论是半经验性模型,可以计算自扩散系数,并借助混合规则计算相互扩散系数;最后,对扩散系数的理论研究作了展望.

The knowledge of diffusion is crucial in many processes because reactions and separations are often limited by a diffusional process. Different approaches to describing diffusion transfer are presented, and the existing models for estimation of the diffusion coefficients in non-electrolytic solutions are discussed in this paper. The most widely applied models are combinations of interpolation schemes, with the diffusion coefficients at infinite dilution. The phenomenological approach is capable of modeling variations of diffusion coefficients with molar fraction. Another series of models for the estimation of diffusion coefficients are based on the concepts of free volume and activation energy. However, all the variations of this approach operate in term of self-diffusion coefficients, and the self-diffusion coefficients may be related to mutual diffusivities by mixing rules. The approach of molecular dynamics simulation is developing, and widely used for the estimation of self-diffusion, but the strong influence of fluctuations makes it difficult to estimate the mutual diffusion coefficients with good accuracy in a reasonable time. Finally, the evaluation of diffusion coefficients for multi-component mixtures is also presented, and the future research in this area is proposed.