Hydropyrolysis of various biomass materials on coals with catalysts

Abstract

An extensive study of intrinsic and extrinsic factors on biomass pyrolysis reactions is needed if valuable hydrocarbon gases are to be produced from pyrolysis of biomass. In the first phase of this study a spent coffee waste material was pyrolysed in a stainless steel batch reactor at 500 to 900°C with both N2 and H2 carrier gases. The use of H2 gas did not affect the product distribution. Yields of pyrolysis gas products reached 61 and 74 wt% of the feed at 900°C for N2 and H2 carrier gases. Corresponding mass balance closures were obtained at 86 and 98 wt% of the feed. Catalytic effect of the stainless steel wall was confirmed. Maximum conversion of CO was found at pyrolysis zone temperature of 700°C. Pyrolysis experiments with spent coffee performed in a quartz (inert) batch reactor proved that the carrier gas had negligible influence on the primary pyrolysis product distribution. Pyrolysis with K2CO3 at 650, 700, and 800°C, showed catalysis of cracking reactions of pyrolysis tars and the water-gas shift reaction. Copyrolysis of biomass materials and coals were performed in the quartz reactor with the objective of producing a higher hydrocarbon content gas product. Copyrolysis of spent coffee and lignite coal at 800°C in a hydrogen atmosphere resulted in gas production of more than 45 wt% of the feed, compared with only 27 wt% for pure coal sample. Increases in production of CH4 and C2H4 were 15.9 wt% and 21.3 Wt%. For copyrolysis with sub-bituminous coal, these synergistic increases were 36.5 wt% and 23.9 wt%. In the final phase of this research, a fluidized bed reactor was used to study hydropyrolysis of cellulose, spent coffee, aspen-poplar, bagasse and lignite coal in presence of sand (inert medium), ã-alumina catalyst, Engelhard US-260 (a silica alumina catalyst), 10 wt% nickel-ã-alumina, 10 wt% cobalt-ã-alumina and a 40 wt% nickel-refractory support catalyst. Over the temperature range of 500 to 600°C, the 10 wt% nickel catalyst was most effective in conversion of biomass. Overall it was found that the combination of cellulose with 10 wt% Ni catalyst at 550°C was the optimum catalyst-feed system for conversion of carbon content of biomass to methane. In this case the yield of CH4 was 46.7 wt% of cellulose. Rate constants for (primary) pyrolysis, (secondary) tar-cracking and (tertiary) hydrogenation reactions at 550°C were determined. Rate constants for the above mentioned reactions were estimated to be k1=2.88 s-1 (pyrolysis model), k1=2.88 and k2=1.31 s-1 (pyrolysis-cracking model), and k1=2.88, k2=13.1 and k3=12.96 s-1 (pyrolysis-cracking-hydrogenation model).