Simultaneous shift reaction and carbon dioxide separation for the direct production of hydrogen

Hydrogen production via the reversible water-gas shift reaction normally requires multiple catalytic reaction steps followed by CO2 separation in order to produce the required H-2 purity. Removal of CO2 as it is formed via the noncatalytic gas-solid reaction between CO2 and CaO provides the opportunity to combine reaction and separation into a single processing vessel. Resultant process simplications include elimination of the need for heat exchangers between catalyst beds as well as the absorption and stripping units required for CO2 removal (or the pressure swing adsorption unit). Process savings may be realized by reducing the quantity of excess steam to the reactor, and the expensive, sulfur-sensitive shift catalyst is not needed in the 500-600 degrees C range of interest. The combined shift and carbonation reactions were studied in a laboratory-scale fixed-bed reactor containing dolomite sorbent precursor. The effect of shift-carbonation temperature and pressure. synthesis gas composition, space velocity, and composition and properties of the sorbent were studied. The rapid rates of the combined reactions permit equilibrium CO conversion and CO2 removal to be closely approached. Greater than 0.995 fractional removal of carbon oxides was achieved over a range of reaction conditions.