Energy Requirements in Membrane Separation Processes

Abstract

Due to a strong increase in the world’s population and a continuous growth of industrial productivity the world energy consumption continues to increase. On the other hand, the fossil energy resources such as oil, gas and coal are gradually exhausted. In order to secure the energy supply for the near future energy saving measures should be taken and the development of energy-saving technologies should be stimulated. In this respect membrane technology is an emerging technology with many prospects as an energy saving separation technology. In a number of classical separation techniques such as distillation, evaporation, refrigeration, condensation, a phase change occurs and the energy consumption is relatively high. Membrane technology is one of the new separation techniques with a relatively low energy consumption since no phase change takes place, except for pervaporation.

In this paper the energy aspects of membrane separation processes will be emphasized. First the thermodynamic minimum energy consumption of a separation process will be described and the minimum consumption of various membrane processes will be given. To calculate the actual energy requirements, relations are given for the energy consumption of a mechanical device which applies the driving force, e.g. a pump and a compressor. A classification of the energy consumption of the various membrane processes will be given according to their driving force; pressure driven processes (microfiltration, ultrafiltration, nanofiltration and reverse osmosis), partial pressure driven processes (gas separation, vapour recovery and pervaporation) and electrically driven processes (electrodialysis). Some examples will be given where membrane processes will be compared with competing processes in terms of energy requirements. Finally, hybrid processing, the combination of various separation processes, will be considered as an energy saving option, and some examples will be given.