(570d) Comparative Evaluation of Pyrolysis and Hydrothermal Liquefaction of Cucumber Plant Residue: Effect of Temperature on Bioproducts Yield and Characteristics

The controlled environment cultivation generates substantial post-harvest biomass, which at present is often neglected or their potential is inadequately addressed. Effectively managing these residues is essential for overall resource recovery and reduced environmental impact. Thermochemical conversion processes offer a viable avenue by converting waste residues into valuable products such as biochar, bio-oil, and syngas. This study compares and evaluates the impact of two thermochemical conversion pathways, namely pyrolysis and hydrothermal liquefaction, on yield and characteristics of bioproducts derived from greenhouse-grown cucumber plant residues. Pyrolysis was conducted at temperatures 500 to 700 °C, whereas hydrothermal liquefaction was conducted at 290,300 and 320°C. The resulting products were analyzed for their yield and compositions. The yield composition of the pyrolysis indicated that increasing pyrolysis temperature boosted biochar and gaseous yield, with the highest char yield (~30 wt.%) obtained at 700 °C, and gas yield of (~47 wt.%) at 500°C. This suggests the biomass potential for carbon sequestration and soil amendment. Similarly, biocrude yield peaked (9 wt.%) at 600°C, after which it declined to 7 wt.% at 700°C. On the other hand, the yield composition of hydrothermal liquefaction indicated the highest biocrude yield (~11 wt.% at 320°C) with minimal gas formation (~4 wt.%), indicating more efficient carbon solubilization into liquid phase under wet conditions. Bio-oil elemental composition shifted with temperature, suggesting a higher concentration of light hydrocarbons (phenols and methyl phenols, C6-C8) and aromatics at elevated temperatures. Furthermore, the liquefaction-derived biocrude exhibited a higher energy density and lower oxygen content indicating improved thermal and storage stability compared to pyrolysis oil. Elevated gaseous fuels yield (CO₂, CO, H₂) at higher temperatures indicates active thermal cracking and gasification reaction, which can be utilized for energy recovery through combustion, or energy integration in the greenhouse for developing self-sustaining systems. This study demonstrates that temperature significantly affects product distribution and properties, providing insights into the potential of different thermochemical processes for efficiently managing greenhouse residues.