PERMEATION EQUATIONS DEVELOPED FOR PREDICTION OF MEMBRANE PERFORMANCE IN PERVAPORATION, VAPOR PERMEATION AND REVERSE-OSMOSIS BASED ON THE SOLUTION-DIFFUSION MODEL
PERMEATION EQUATIONS DEVELOPED FOR PREDICTION OF MEMBRANE PERFORMANCE IN PERVAPORATION, VAPOR PERMEATION AND REVERSE-OSMOSIS BASED ON THE SOLUTION-DIFFUSION MODEL
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DOI：
10.1252/jcej.24.326
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发表时间：
1991-06-01
影响因子：
0.8
通讯作者：
KIMURA, S
中科院分区：
文献类型：
--
作者：
KATAOKA, T;TSURU, T;KIMURA, S
在假设膜内压力梯度为平面梯度（情形1）和线性梯度（情形2）的情况下，提出了渗透汽化（PV）、蒸汽渗透（VP）和反渗透（RO）的基于溶液-扩散模型的一般渗透方程。利用这些方程，一旦膜的传输参数已知，就可以估计出PV、RO和VP的渗透特性。通过对乙醇-水体系中水选择性膜和乙醇选择性膜的样品计算，估计了上游压力对RO和PV的选择性和通量的影响。RO中的通量和选择性较小，在无限大压力下达到PV中的通量和选择性。在情形1和情形2中，这个极值是不同的，在情形2中，渗透剂的摩尔体积比变得很重要。对PV中下游压力的影响进行了估计，并与多孔膜的真空增强膜蒸馏（MD）进行了比较。随着压力的增加，PV和MD的分离系数接近汽液平衡。随着压力的降低，MD的分离系数由膜内扩散系数的比值决定。由于水的Knudsen扩散系数大于乙醇，因此随着下游压力的降低，乙醇-水分离的分离系数减小。用PTFE膜进行了实验验证。
General permeation equations based on the solution-diffusion model were proposed for pervaporation (PV), vapor permeation (VP) and reverse osmosis (RO) on two different assumptions about the pressure gradient inside a membrane: a flat gradient (case 1) and a linear gradient (case 2). With these equations the permeation properties in PV, RO and VP can be estimated once the transport parameter of a membrane is known.The effect of upstream pressure on selectivity and flux in RO and PV was estimated by sample calculations for water- and ethanol-selective membranes in ethanol-water system. Flux and selectivity in RO is smaller and, reaching that in PV at infinite pressure. This ultimate value is different in cases 1 and 2, and in the latter the molar volume ratio of the permeants becomes important. The effect of downstream pressure in PV was also estimated and compared with the case of vacuum-enhanced membrane distillation (MD) with a porous membrane. With increasing pressure the separation factor approaches that of vapor-liquid equilibrium in both PV and MD. With decreasing pressure that in MD is governed by the ratio of diffusion coefficients inside the membrane. Since the Knudsen diffusion coefficient of water is larger than that of ethanol, the separation factor decreases in ethanol-water separation with decreasing downstream pressure. This was verified by experiment, using PTFE membranes.