文档介绍：A Review of Reverse Osmosis Theory
Michael E. Williams, ., ,
Williams Engineering pany, Inc.
Many mechanistic and mathematical models have been proposed to describe reverse osmosis
membranes. Some of these descriptions rely on relatively simple concepts while others are far more
complex and require sophisticated solution techniques. Models that adequately describe the
performance of RO membranes are very important since these are needed in the design of RO
processes. Models that predict separation characteristics also minimize the number of experiments
that must be performed to describe a particular system. Excellent reviews of membrane transport
models and mechanisms include Jonsson (1980), Soltanieh and Gill (1981), Mazid (1984), Pusch
(1986), Dickson (1988), Rautenbach and Albrecht (1989), and Bhattacharyya and Williams (1992c).
Reverse osmosis models can be divided into three types: irreversible thermodynamics
models (such as Kedem-Katchalsky and Spiegler-Kedem models); nonporous or homogeneous
membrane models (such as the solution-diffusion, solution-diffusion-imperfection, and extended
solution-diffusion models); and pore models (such as the finely-porous, preferential sorption-
capillary flow, and surface force-pore flow models). Charged RO membranes theories can be used
to describe nanofiltration membranes, which are often negatively charged; these models (such as
Donnan exclusion and extended Nernst-Planck models) include electrostatic effects. The transport
models focus on the top thin skin of asymmetric membranes or the top thin skin layer posite
membranes since these determine fluxes and selectivities of most membranes (Bhattacharyya and
Williams, 1992c). Also, most of the membrane models assume equilibrium (or near equilibrium) or
steady state conditions in the membrane.
A fundamental difference exists between the assumptions of the homogeneous and porous
membrane models. The homogeneous