| The U.S. Department of Energy is investigating technologies for removing trace amounts of ammonia from the high temperature, high pressure synthesis gas produced by advanced coal gasification power systems such as the integrated, gasification combined cycle process (IGCC). Catalytic decomposition of ammonia to hydrogen and nitrogen is a potential method for removing the ammonia. However, use of a conventional packed bed reactor is not feasible because ammonia conversion is limited by chemical equilibrium due to the high concentrations of nitrogen and hydrogen in the synthesis gas. The objective of this project was to investigate the catalytic decomposition of ammonia in a packed bed membrane reactor. The purpose of the membrane reactor was to shift the equilibrium of the ammonia decomposition reaction by selectively removing hydrogen from the feed gas. A hydrogen selective membrane capable of operating at large transmembrane pressure differences and high temperatures was developed in the study.; Composite palladium-ceramic membranes with palladium films ranging from 11.4 to 20 {dollar}mu{dollar}m were made by depositing palladium on the inside surface of asymmetric tubular ceramic membranes. Electroless plating was used to deposit the palladium film. Membranes were characterized by conducting permeability experiments with hydrogen, nitrogen, and helium at temperatures from 723 to 913 K and feed pressures from 160 to 2445 kPa. The hydrogen permeability for a composite membrane with an 11.4 {dollar}mu{dollar}m palladium film was {dollar}3.23{lcub}cdot{rcub}10sp{lcub}-9{rcub}{dollar} {dollar}rm moles{lcub}cdot{rcub}msp2{lcub}cdot{rcub}s{lcub}cdot{rcub}Pasp{lcub}0.602{rcub}{dollar} at 823 K. The hydrogen/nitrogen selectivity for this membrane was 380 at 823 K at a transmembrane pressure difference of 1500 kPa.; Membrane reactor experiments were conducted with a gas stream that simulated the temperatures, pressures, hydrogen, nitrogen, and ammonia concentrations in IGCC synthesis gas. An ammonia conversion of over 94 percent was achieved in the membrane reactor at 873 K. Since the equilibrium conversion of the feed gas was only 58 percent, a significant equilibrium shift was obtained with the membrane reactor. The equilibrium shift was even higher at lower temperatures.; A membrane reactor model was developed to predict the ammonia conversion in a membrane reactor. The effect of interphase and intraparticle mass transfer was included in the model. Predicted and experimental ammonia conversions generally showed good agreement. |
