Metal oxides-based catalytic pyrolysis of lignocellulosic biomasses for bio-oil development: a comparative assessment...

This study investigated the conventional fixed-bed catalytic pyrolysis using metal oxides (CaO, Fe₂O₃, and TiO₂) to enhance bio-oil yield from three lignocellulosic biomasses: safflower press cake (SPC), coconut press cake (CPC), and coconut shell (CS). The primary characterization, using ultimate, proximate, and compositional analyses, as well as TGA-DTG-DSC, was carried out in the experiment. SPC biomass had a high hemicellulose content (50.8 ± 0.11%), which is suited for bio-oil applications. An initial non-catalytic pyrolysis experiment was conducted at 550 °C with a heating rate of 25 °C/min for 30 min; the bio-oil yields were 34% (SPC), 29% (CPC), and 26% (CS), respectively. During the catalytic pyrolysis, TiO₂ showed its strongest catalytic activity, primarily combined with SPC biomass. Under optimized conditions 550 °C, 25 °C/min heating rate, and a 30-minute reaction time SPC with TiO₂ yielded a maximum bio-oil output of 71.75 ± 0.16%. In contrast, under the same conditions without a catalyst, SPC produced 34 ± 0.16% bio-oil, indicating a significant 37.5% improvement with the addition of TiO₂. Among the three biomasses, SPC showed the greatest responsiveness to catalytic enhancement, while CPC offered a better balance between oil quality and char usability. The GC-MS analysis of TiO₂-catalyzed SPC bio-oil confirmed TiO₂'s selective catalytic influence on bio-oil compound distribution by revealing a predominance of phenolic compounds, such as Guaiacol (19.8%), 2,4-Dimethoxyphenol (31.12%), and hydroxy ketones such as -Hydroxy-2-butanone (29.49%) and 1-Hydroxypropan-2-one (26.36%), confirming the superior Lewis acid catalytic mechanism of TiO₂ for the production of phenolic compounds and ketone - rich bio-oil from lignocellulosic agro-industrial wastes.