Pyrolysis-catalytic hydrogenation of cellulose-hemicellulose-lignin and biomass agricultural wastes for synthetic natural gas production

The production of methane from the biopolymers; cellulose, hemicellulose and lignin, and also four different agricultural waste biomass samples was investigated using a two-stage pyrolysis-catalytic hydrogenation reactor. The biomass agricultural waste samples were rice straw, willow, sugar cane bagasse and ugu plant. Pyrolysis of the biomass samples was carried out in a 1st stage reactor while the catalytic hydrogenation was carried out the 2nd stage reactor using a 10 wt.% Ni/Al2O3 catalyst maintained at 500 °C with heating rate of 20 °C min−1 and a H2 space velocity of 3600 ml h−1 g−1catalyst. The thermal degradation characteristics of the biomass components, mixtures of the components and the biomass waste samples was also conducted using thermogravimetric analysis (TGA). TGA of the mixtures of the biomass components showed interaction, illustrated by a shift in the thermal degradation temperatures for hemicellulose and lignin. The results from the pyrolysis-catalytic hydrogenation revealed that the methane yield increased in the presence of the catalyst; the methane yield obtained from the hemicellulose (7.9 mmoles g−1biomass) and cellulose (7.65 mmoles g−1biomass) was significantly higher than that produced from lignin, (3.7 mmoles g−1biomass). The pyrolysis-catalytic hydrogenation of the mixtures of the biopolymers showed clear interaction, producing higher total gas yield and methane yield compared to calculated values. Pyrolysis-catalytic hydrogenation of the agricultural biomass wastes suggests that the product methane yield was influenced by the percentage of hemicellulose and cellulose content in the biomass.