Sorption Enhanced Methane Steam Reforming Reaction For Hydrogen Production

Sorption enhanced steam reforming technology for hydrogen production was widely investigatied by researchers for high H2 purity and simple process. However, only a few studies have reported relative method to prepare the CO2 captor, the sorption-desorption reaction mechanisum. Sorption enhanced methane steam reforming was analyzed in this paper using Li4SiO4 as the CO2 captor.At first, thermodynamic equilibrium of steam methane reforming (SMR) reactions were studied by Gibbs free minimization using AspenPlusTM, as a function of pressure (0.1-2MPa), reforming temperature (300-1100℃), steam to carbon ratio (S/C=0.5-6). As both the H2 yield and system efficiency are concerned, the optimal operating condition is S/C=3-4 at 700-750℃and 0.1 MPa. The theoretical compositions of the sorption/desorption reactions were calculated using FactSage and the conversion of Li4SiO4 is 100% in each sorption/desorption temperature range.The sorption/desorption process on Li4SiO4 was investigated by comparing the shrinking core, double exponential, and Avrami-Erofeev models based on the kinetic experimental data obtained by TG experiment. The Avrami-Erofeev model fits the kinetic TG experimental data well and, together with the double-shell mechanism, clearly explains the sorption/desorption mechanism. For the sorption process, the reaction occurs rapidly on the particle surface and forms a double-shell structure consisting of Li2CO3 and Li2SiO3 firstly. The process is limited by the rate of the formation and growth of the product crystals. With the increase in double-shell thickness, the limiting-step becomes the diffusion control when the conversion of Li4Si04α>0.1 below 650℃and whenα>0.84 at 700℃. When the C02 partial pressure is 0.1 atm, the inflexion between the two stage changed to be 15min, but the Li4SiO4 conversion of the inflexion is 0.1, which is the same as the inflexion in pure CO2. The whole desorption process is found to be controlled by the rate of the formation and growth of the Li4SiO4 crystals.At Last, pure Li4SiO4 were synthesized using Li2CO3 and SiO2 with Li/Si=4.1 by calcined at 750℃for 6hr. The CO2 sorption properties of the sample were confirmed to be the same as the commercial Li4SiO4. Thus, the sorption/desorption kinetic model for the commercial Li4SiO4 can be used in the synthesized sample and used in the simulation of the sorption enhanced methane steam reforming system.