Comparative study of the thermo-catalytic reforming of agricultural and forest residue and advanced characterization of final products in a cold climate

Abstract

Global agricultural and forest residues hold promise for renewable fuel production through thermo-catalytic reforming (TCR). Limited data exists on TCR outcomes for regions known for cold conditions like Canada. This study used a 2 kg h⁻¹ TCR unit for the intermediate pyrolysis/reforming of agricultural (wheat straw pellet, WSP) and forest (softwood pellet, SWP) residues. Maximum bio-oil yields were 8.43% for wheat straw pellets and 7.99% for softwood pellets at 400 and 500°C reactor and reformer temperatures. Feedstock, bio-oil, and biochar properties were analyzed through proximate and ultimate analysis. At 550°C reactor and 700°C reforming temperatures, 70.73% of the wheat straw pellet-based gas yield contained 36.11 vol.% H₂ and 11.08 vol.% CH₄, giving a higher heating value (HHV) of 12.54 MJ kg⁻¹. A high concentration of CH₄ (22.02 vol.%) in the softwood pellet-based gas gave an HHV of 17.94 MJ kg⁻¹. The low viscosity (3.9 mPa · s⁻¹) and total acid number (7.3 mg KOH g⁻¹) wheat straw pellet-based bio-oil had an O/C molar ratio of 0.09 and an HHV of 35.80 MJ kg⁻¹. The 400/600°C reactor/reformer temperatures gave the lowest area percentage of mono-aromatic (16 vol.%) and polycyclic aromatic (11.20 vol.%) compounds in the softwood pellet bio-oil. The O/C molar ratio (0.5–0.6) in softwood pellet biochar elevated the higher heating value from 32.37 to 34.57 MJ kg⁻¹. The study results guide optimal TCR unit operation in cold climates like Canada with local feedstocks, emphasizing its notable hydrogen production over bio-oil and biochar.