Hydrogen Production by Sorption-Enhanced Steam Methane Reforming Using Lithium Oxides as CO2-Acceptor

The kinetics of CO2-capture on Li4SiO4 has been examined experimentally and described by a mathematical reaction-rate model. Sorption-enhanced steam methane reforming has been simulated with a fixed-bed reactor model using the formulated capture kinetics. At working conditions of 20 bar, 848 K, a steam-to-carbon ratio of 5, and a superficial inlet gas velocity of 1 m/s, a dry hydrogen mole fraction at the outlet of 0.87 can be reached. The performance of the process with Li4SiO4 is compared to that with Li2ZrO3 as CO2-acceptor. Li4SiO4 gives higher conversion and production capacity at lower steam-to-carbon ratios. A drawback for the process with Li4SiO4 as acceptor is that high conversion is only reached at low fractional conversion of the acceptor. This is due to the fact that the capture kinetics is second order with respect to unreacted solid. The total reaction is endothermic, and effective heat exchange is necessary to avoid a dramatic drop in the reactor temperature. A fluidized-bed reactor has also been simulated, and the results have been compared to those of the fixed-bed reactor. The fluidized-bed reactor has some advantages in terms of easier heat integration and continuous regeneration of CO2-acceptor, but compared to the fixed bed, a longer reactor is needed to reach the same conversion.