Continuous membrane column

Figure 19.13. Continuous membrane column with reflux from both product streams.

Earlier papers on the continuous membrane column (28,29) have discussed the separation of CO2-N2, CO2-O2 and O2-N2 (air) mixtures in stripper, enricher and total column units composed of 35 silicone rubber capillaries. A characterization of the membrane column using a membrane unit concept (analogous to transfer unit concept — HTU, NTU) has also been presented. The purpose of this paper is to present some new data and discussions on the extended study of continuous membrane column. Specifically, the topics of multicomponent separations, Inherent simulation difficulties, composition minima in the enriching section, variation of experimental parameters, and local HMU variation along the column will be covered. 

One of the next steps in developing the continuous membrane column will be to obtain extensive data on multicomponent systems. Some preliminary experiments with a C02 CH -N2 mixture using a stripper have already been conducted. The results of two such experiments are presented in Figures 3 and 4. The agreement between experiment and model is excellent. 

The performance of the continuous membrane column was characterized earlier (28) in a manner analogous to the transfer unit concept for packed columns. The expressions developed for NMU (difficulty of separation) and HMU (efficiency) were... 

Inherent difficulties accompany some simulations of the continuous membrane column. Perturbation of boundary conditions within the range of experimental error may be necessary in certain Instances to achieve a proper fit of experimental data. 

Thorman, J.M. "Engineering Aspects of Capillary Gas Perme-ators and the Continuous Membrane Column," Ph.D. Thesis, University of Iowa, Iowa City, Iowa, 1979. 

S. T. Hwang and S. Ghalchi, Membrane Separation by a Continuous Membrane Column, /. 

Separator arrangements (a) parallel flow (6) series flow (c) two-stage flow (d) continuous membrane column. 

To get higher purity permeate, the product from the first stage can be compressed and sent to a second stage, as shown in Fig. 26.11c. Two or more stages could be used in this fashion to get the desired purity, but the cost of recompression and the increased complexity of the system makes this scheme generally uneconomical. A novel approach that uses two separators and one recompression step is the continuous membrane column. As shown in Fig. 26.1 Irf, part of the permeate product from the second separator is compressed and sent back to the other side of the membrane, where it flows countercurrently to the permeate. This reflux action permits very high purity permeate to be obtained. The reflux steam loses the more permeable component as it flows through the separator and is combined with the feed to the first separator. This scheme was demonstrated in pilot units but has not yet been used commercially. 

Continuous Membrane Column., Dissertation, University of Iowa (1979). 

FIGURE 9 1 (a) A continuous membrane column, (b) Membrane column section break down [1]. 

Hwang, S.andJ.M.Thorman, The continuous membrane column. A/C/iEyourwa/, 1980,... 

Tsuru, T. and S. T. Hwang, Permeators and continuous membrane columns with retentate recycle. Journal of Membrane Science, 1995, 98(1 2) 57 67. 

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