A Novel Membrane Reactor for Direct Hydrogen Production from Coal

Gas Technology Institute is developing a novel concept of membrane gasifier for high efficiency, clean and low cost production of hydrogen from coal. The concept incorporates a hydrogen-selective membrane within a gasification reactor for direct extraction of hydrogen from coal-derived synthesis gases. The objective of this project is to determine the technical and economic feasibility of this concept by screening, testing and identifying potential candidate membranes under high temperature, high pressure, and harsh environments of the coal gasification conditions. The best performing membranes will be selected for preliminary reactor design and cost estimates. To evaluate the performances of the candidate membranes under the gasification conditions, a high temperature/high pressure hydrogen permeation unit has been constructed in this project. The unit is designed to operate at temperatures up to 1100 C and pressures to 60 atm for evaluation of ceramic membranes such as mixed ionic conducting membrane. Several perovskite membranes based on the formulations of BCN (BaCe{sub 0.8}Nd{sub 0.2}O{sub 3-x}) and BCY (BaCe{sub 0.8}Y{sub 0.2}O{sub 3-x}) were prepared by GTI and successfully tested in the new permeation unit. During this reporting period, two different types of membranes, Eu-doped SrCeO{sub 3} (SCE) and SrCe{sub 0.95}Tm{sub 0.05}O{sub 3} (SCTm) provided by the University of Florida and the University of Cincinnati, respectively were tested in the high pressure permeation unit. The SCTm membrane, with a thickness of 1.7 mm, showed the highest hydrogen permeability among the perovskite membranes tested in this project so far. The hydrogen flux measured for the SCTm membrane was close to 0.8 cc/min/cm{sup 2} at a hydrogen feed pressure of about 4 bar at 950 C. SEM and EDX analysis for the tested SCTm membrane showed a separate Ce-rich phase deposited along the grain boundaries in the region towards the feed side of the membrane. No such phase separation was observed towards the permeate side. Partial reduction of the SCTm perovskite material by the high pressure hydrogen, especially in the feed side of the membrane, was postulated to be the possible reason for the phase separation. Further investigation of the stability issue of the perovskite membrane is needed