Reversible chemisorption of carbon dioxide: simultaneous production of fuel-cell grade H2 and compressed CO2 from synthesis gas

Abstract

One vision of clean energy for the future is to produce hydrogen from coal in an ultra-clean plant. The conventional route consists of reacting the coal gasification product (after removal of trace impurities) with steam in a water gas shift (WGS) reactor to convert CO to CO2 and H2, followed by purification of the effluent gas in a pressure swing adsorption (PSA) unit to produce a high purity hydrogen product. PSA processes can also be designed to produce a CO2 by-product at ambient pressure. This work proposes a novel concept called “Thermal Swing Sorption Enhanced Reaction (TSSER)” which simultaneously carries out the WGS reaction and the removal of CO2 from the reaction zone by using a CO2 chemisorbent in a single unit operation. The concept directly produces a fuel-cell grade H2 and compressed CO2 as a by-product gas. Removal of CO2 from the reaction zone circumvents the equilibrium limitations of the reversible WGS reaction and enhances its forward rate of reaction. Recently measured sorption-desorption characteristics of two novel, reversible CO2 chemisorbents (K2CO3 promoted hydrotalcite and Na2O promoted alumina) are reviewed and the simulated performance of the proposed TSSER concept using the promoted hydrotalcite as the chemisorbent is reported.