Optimization and Fuel Property Characterization of Bio-Oil From Catalytic Pyrolysis of Achyranthes Aspera Wood Residue Using Zeolite Y Catalyst

Abstract

The growing demand for renewable alternatives to fossil fuels has intensified interest in biomass pyrolysis for bio-oil production. Despite the wide availability of Achyranthes aspera wood residue as an underutilised tropical lignocellulosic biomass, its pyrolytic bio-oil properties remain entirely unreported, limiting evaluation of its renewable fuel potential. This study investigated bio-oil yield distribution and physicochemical fuel properties from catalytic pyrolysis of Achyranthes aspera wood residue in a fixed-bed reactor at 400 °C and 500 °C, using four biomass-to-zeolite Y catalyst ratios (100/0, 95/5, 90/10, and 85/15 weight percent (wt.%)). Product yields were quantified by mass balance and analysed using descriptive statistics and two-way ANOVA. Bio-oil yield was optimised via a desirability function, maximising liquid yield (weight = 0.5) while minimising biochar and syngas (weight = 0.25 each). Fuel properties: flash point, pour point, pH, density, kinematic viscosity, American Petroleum Institute (API) gravity, and higher heating value (HHV) were determined per ASTM standards (D445, D4052, D93, D97, D2500, D7946-19), with HHV estimated from elemental analysis correlations. Desirability optimisation identified 95/5 at 500 °C as optimal, achieving a score of 88.77, with 52.95 wt.% bio-oil, 22.00 wt.% biochar, and 25.05 wt.% syngas. ANOVA indicated that temperature significantly affected biochar yield (p < 0.05) and catalyst ratio significantly influenced syngas yield (p < 0.05), noting that these results are based on a single observation per treatment combination using the interaction term as a proxy error term. Flash points of 76–82 °C exceeded diesel (50 °C), indicating improved storage safety. Pour points of −3 to −4 °C confirmed adequate low-temperature flow. pH rose from 7.50 (non-catalytic) to 8.50 (85/15 ratio), demonstrating deoxygenation and reduced corrosion risk relative to typical bio-oil pH of 2.0–3.8. Densities (0.78–0.85 g/mL), viscosities (4.00–4.30 cSt), and API gravities (40.00–45.58) fell within petroleum fuel specifications. HHVs increased from 29.04–29.07 MJ/kg (non-catalytic) to 32.07–32.80 MJ/kg (catalytic), confirming energy density improvement with catalyst loading. Zeolite Y catalytic pyrolysis at 95/5 and 500 °C delivers near-diesel fuel properties, establishing Achyranthes aspera wood residue as a promising renewable feedstock for industrial energy applications.