A Low-Energy, Hybrid Distillation / Membrane Separation Process Design for Solvent Dehydration

There are approximately 40,000 distillation columns of various types in operation in the United States.  These columns use about five quads of energy.¹  Distillation is widely used in solvent (e.g., ethanol) dehydration processes because of its simplicity, low capital cost and reliability.  The key disadvantage of distillation is its poor energy efficiency.  The use of vapor permeation membranes as a low-energy alternative to distillation has been proposed for more than 30 years, yet the current U.S. market for this technology is no more than $20 million/year due to a number of issues with the vapor permeation technology itself.  In our earlier paper, we introduced an energy-efficient, hybrid distillation and membrane vapor permeation process as an alternative to conventional distillation.²  This separation process can be applied to any liquid mixture for which appropriate selective membranes are available.   We have shown that the combination distillation / membrane vapor permeation process reduces the energy consumption of the separation to half that of simple distillation for most applications.

In this paper, the designs of such low-energy processes are further illustrated using ethanol dehydration as an example.  The effect of permeate side pressure and membrane selectivity on the separation performance and economics of the hybrid process will be thoroughly discussed.  The membranes developed for ethanol dehydration will also be described.

 

REFERENCES

1. J.L. Humphrey and G.E. Keller II, Separation Process Technology, McGraw-Hill, New York (1997).
2. Y. Huang, R. W. Baker and L. M. Vane, Low-Energy Distillation Membrane Separation Process, Ind. Eng. Chem. Res, 49, 3760-3768, 2010.