(462d) Integrated One Box Process for Hydrogen Production From Syngas
The world is becoming more and more dependent on fossil fuels to satisfy increasing energy demands. United States coal reservoir is almost equal to the total world oil reservoirs which if used, can supply its energy needs for up to two centuries at the current production rates.
Today, Global warming resulting from increasing concentration of greenhouse gases, mainly carbon dioxide, has become one of the key environmental issues. Hydrogen has been seen increasingly as a promising environmental-friendly alternative to fossil fuels. Producing hydrogen from coal is a great potential step toward U.S. energy independence as well as cleaner environment.
Currently, the process of hydrogen production from coal includes the following steps. First, coal converts to synthetic gas, so-called ?syngas? in a gasifier. Second, syngas is cleaned in order to take away impurities, mainly hydrogen sulfide which is detrimental to catalyst life in the next steps. To do that, the syngas should be cooled down from more than 980oC as it leaves the gasifier to almost ambient temperature and reheated again to 350oC to reach process temperature requirement of the next steps. Third, water-gas-shift catalytic reactions are being used in order to maximize hydrogen content. Water-gas-shift reaction requires several steps because of reaching chemical equilibrium at higher temperatures, and slow kinetics at lower temperatures. Fourth, hydrogen is getting purified by pressure swing absorption (PSA) or membrane systems.
These processes are expensive because of their energy consumption and it is difficult to improve their efficiency. Introducing a ?one box? process, in which gas cleanup, water-gas-shift reaction, and hydrogen separation are integrated into one process offers great advantages in scaling up and provides better efficiency and lower production costs.
In this report, the development of such process has been described. The process uses a catalytic membrane reactor which contains a hydrogen-selective carbon molecular sieve membrane and sulfur-resistant Co/Mo/Al2O3 catalyst. Experimental studies including determining the catalytic reaction kinetics and rate parameters and the membrane reactor performance has been shown. Membrane reactor's behavior for a range of pressures and sweep ratios has been studied and compared with simulation results. The reactor performance is discussed in terms of carbon monoxide conversion, hydrogen recovery and purity. The results successfully show that hydrogen sulfide does not affect the performance of the system.