Membrane technologies for CO2 separation

Today, all the existing coal-fired power plants present over the world emit about 2 billion tons of CO2 per year. The identification of a capture process which would fit the needs of target separation performances, together with a minimal energy penalty, is a key issue. Because of their fundamental engineering and economic advantages over competing separation technologies, membrane operations are, now, being explored for CO2 capture from power plant emissions.The aim of this work is to provide people interested in the use of membranes in CO2 capture a general overview of the actual situation both in terms of materials studies and global strategy to follow in the choice of the membrane gas separation with respect to the other separation technologies. Firstly, an overview on the polymeric membranes currently studied for their use in CO2 capture and of their transport properties is proposed. Up to now, the most promising materials developed at laboratory scale show a selectivity of 100–160. Then, some important design parameters have been introduced in order to evaluate the advantages potentially offered by membrane systems with respect to the other separation technologies (adsorption and cryogenic). These parameters, based on specific considerations related to the output to be obtained as the product purity and the final destination of the product and to the feed conditions, might constitute guidelines for the choice of the separation technology.Considering as case study a flue gas stream containing 13% of CO2, some general maps of CO2 recovery versus permeate purity have been introduced. This might constitute a simple tool useful for an immediate and preliminary analysis on the membrane technology suitability for CO2 separation from flue gas, also on the light of specific considerations, strictly related to the output to be obtained.