Steam reforming of a clean model biogas over Ni/Al2O3 in fluidized- and fixed-bed reactors

Simultaneous steam, carbon dioxide reforming of methane was conducted over 11.5 wt.% Ni/Al2O3, at 1 atm in micro-fluidized- and fixed-bed reactors using a constant molar ratio of CH4/CO2 approximate to 1.5 as a model biogas. The performance of a fluidized reactor was compared to that of a fixed-bed reactor under similar conditions (feed gas to steam ratios of 1.5 and 0.75 at a reactor temperature of 750 degreesC, GHSV of 300 min(-1)). Conversions of CH4 and CO2 were 75 and 67%, respectively, in a fixed-bed reactor under the ratio of 1.5. Overall higher conversions (7-15%) were observed in the fluidized-reforming reactor. The initial activity of the fixed-bed reformer decreased rapidly and massive carbon deposition caused reactor blockage at the low steam concentration. Decreased the feed gas to steam ratio to 0.75 reduced carbon deposition and the nature of the carbon was suggested not to be the cause of the catalytic enhancement of the fluidized reforming. A study of the fluidized-bed reformer under decreasing feed gas to steam ratios from 3.0 to 0.3 showed an almost complete CH4 conversion (98% for feed gas to steam ratios below 1.0). With decreasing feed gas to steam ratio the H-2/CO ratios increased as expected from 1.5 to 2.7. At the highest feed gas to steam ratio, a poor catalyst fluidization was observed due to massive carbon deposition, which was reduced dramatically when steam was provided in excess. Increasing temperatures from 650 to 850degreesC enhanced both conversions and lowered H-2/CO ratios. (C) 2002 Elsevier Science B.V. All rights reserved.