Adsorption-enhanced steam-methane reforming with intraparticle-diffusion limitations

Abstract

The adsorption-enhanced reaction (AER) process is theoretically analyzed for hydrogen production by steam-methane reforming (SMR). It uses a fixed-bed packed column of an admixture of a SMR catalyst and an adsorbent for selective removal of CO 2 from the reaction zone. A mathematical model taking into account multicomponent (six species) mass balances, overall mass balance, Ergun relation for pressure drop, energy balance for bed-volume element including the heat-transfer to the column wall, and nonlinear adsorption equilibrium isotherm coupled with three main reactions was derived to describe AER process with the intraparticle-diffusion limitations. The numerical solution of the model equations for this process was obtained by using the method of orthogonal collocation. The validity of the model prediction was checked by comparing the simulated results with experimental data from literature. The mechanism of the adsorption-enhanced SMR is studied by analysis of the profiles of the bed concentrations, temperature, velocity, pressure, and reaction and adsorption rates. The intraparticle-diffusion limitations on the adsorption-enhanced SMR are evaluated by the effectiveness factors. The effect of the operating conditions (reaction temperature, pressure and length of adsorptive reactor) on the hydrogen purity, hydrogen productivity and methane conversion is studied by numerical simulation; a high purity of hydrogen product gas (90–98%) with methane as the prime impurity and traces of CO 2 (below 400 ppm) and CO (below 30 ppm) can be produced directly from the adsorptive reactor under conditions of 450–490 °C and 222.9–891.4 kPa.