Design considerations in the application of membrane reactors for use in steam-carbon dioxide reforming environments.

摘要

This study examines some of the design considerations of the application of ceramic membranes to the production of hydrogen by the reforming of methane with steam and carbon dioxide. Two different classes of membranes have been studied: ceramic alumina membranes, which are utilized in the high temperature reforming environment; and carbon membranes, which are used in the purification of reforming mixtures. Finally, a perovskite-type membrane is applied to the glass manufacturing process, where it is found to dramatically increase the thermal efficiency of the process.; Membranes are typically used in reacting systems to selectivity remove one or more of the reaction products, driving the reaction further to completion. For the temperatures involved in steam-methane reforming this requires the use of either dense metallic membranes or porous, inorganic membranes. Unlike the dense metallic membranes, which are permeable only to hydrogen, the ceramic membranes used were permeable to all of the gas species present. These membranes were shown to increase the conversion of methane over that obtainable by equilibrium. A model for the reactor utilizing the Fickian description of diffusion was developed and used to identify the optimal operational variables.; The second class of membranes studied in this work were carbon-based membranes. These membranes, formed by the pyrolysis of specially prepared polymer films on a porous substrate were not intended for high temperature reactions. Rather, these membranes show a very high selectivity towards carbon dioxide at ambient temperatures. These may prove to be useful in the purification of CO2-rich gas streams. The application of carbon membranes and the ceramic membranes to the design of hydrogen plants is briefly discussed in this study.; Finally, a perovskite-type membrane, which is selectively permeable to oxygen, is applied to the glass manufacturing process. In this process, the membrane reactor uses the waste heat from the glass melting process to convert CO2 to CO and oxygen. The recovered CO and oxygen is then fired in the furnace. This utilization of waste heat dramatically improves the overall efficiency of the process.