“High Temperature Gas Separation Membranes in Coal Gasification”

Abstract

Abstract In this work we investigate the proof of concept of metal (Cobalt) doped silica membranes for H 2 /CO 2 separation in single and multi tube membrane modules, in addition to a membrane reactor (MR) configuration for the high temperature water gas shift (WGS) reaction. The membranes were prepared by a sol-gel process using tetraethylorthosilicate (TEOS) in ethanol and H 2 O 2 with cobalt nitrate hexahydrate (Co(NO 3 )26H 2 O). The membranes delivered high H 2 /CO 2 single gas selectivity up to 131. A multi tube membrane module was tested up to 300 ∘ C and 4 atmospheres for 55 days (1344 hours) for binary feed gas mixtures containing H 2 and CO 2 at 40:60 concentration ratio. The best membrane performance delivered H 2 purity in excess of 98%. For the high temperature water gas shift reaction and a ternary mixture of 40% (H 2 ), 40% (CO 2 ) and 20% (CO), which is equivalent to 67.5% CO conversion, the membrane delivered a permeate stream containing 92.5% H 2 . The membranes complied with a flux temperature dependency mechanism, as H 2 permeation had a positive energy of activation whilst CO 2 was negative. As a result, H 2 permeation and separation to other gases increased with temperature. In turn, this effect was combined with high CO conversion for the water gas shift reaction, thus allowing for high throughput of H 2 production and separation in a single processing step. The process integration provided by this work is potentially beneficial for the next generation of high temperature processing unit operations in low emissions coal gasification.