Tuning bio-oil characteristics and applying a statistical modeling-optimization approach for bio-oil yield

This study investigates the catalytic pyrolysis of tomato waste conducted in a Heinze reactor using Co/Al2O3 catalysts to produce valuable chemicals via thermochemical conversion. The research began with the characterization of co-precipitated Co/Al2O3 catalysts using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), X-ray powder diffraction (XRD), and N2 physisorption analyses. Subsequently, the influence of various experimental parameters related to catalyst application on the properties of the liquid product obtained from pyrolysis at 500 °C was examined through elemental analysis, Fourier-transform infrared spectroscopy (FT-IR), liquid column chromatography, and gas chromatography-mass spectrometry (GC/MS). Key variables included the cobalt content in the alumina-supported catalyst (5 and 10 wt%), the catalyst addition ratios (0, 5, 10, 15, and 20 wt% of catalyst-biomass mixture), and pyrolysis heating rates (10 and 40 °C/min), all of which affected the distribution of pyrolytic products and bio-oil yield. Additionally, the study employed a multilevel factorial experimental design to statistically model the effect of Co/Al2O3 catalyst usage on bio-oil yield. Although increasing cobalt content led to a reduction in overall bio-oil yield, column chromatography revealed that the Co/Al2O3 catalyst promoted deoxygenation reactions, thereby enhancing the proportion of polyaromatic and aromatic compounds in the bio-oil. Notably, the total phenolic content in the asphaltene and aromatic sub-fractions of bio-oil produced at a heating rate of 10 °C/min with the 5Co/Al2O3 catalyst reached 26.92 %. Thus, despite a lower yield, the catalytic pyrolysis process improved the quality and selectivity of the bio-oil. Analysis of variance (ANOVA) indicated that the catalyst addition ratio was the most significant factor influencing bio-oil yield (P-value = 0.013). These findings demonstrate that tomato processing waste can be effectively utilized as a feedstock for the production of phenolic-rich bio-oil and other valuable chemicals.