Graphical Comparison of Coupled Membrane Columns with Differing Selectivity

摘要

A continuous membrane column involves the recycle of some permeated material, and operates in a counter-current manner. Any column, no matter how complex its configuration, can be divided into column sections. A general form of the Difference Point Equation (DPE) has been derived to describe to retentate composition down the length of a section, allowing for non-constant molar overflow. For demonstration purposes, a simple non-selective membrane is assumed. Using this as the permeation model, in conjunction with the DPE, allows one to graphically plot a column profile for a given initial condition. This allows one to not only configure simple columns, but complex configurations too. As an example, a thermally coupled membrane column will be discussed, using the same membrane throughout. Through simplifying assumptions, the system can be reduced to coupled column sections. Material balance constraints have to be satisfied in order for the configuration to be feasible. The topological behavior of the column profile depends on the selectivity of the membrane. For a non-selective membrane, it was found that a thermally coupled membrane column is in fact not possible under any operating conditions. Although not a positive one, this is a very useful result, since both time and money can be saved by avoiding any further investigations.