Study on characteristics of carbonyl compounds from pyrolysis of holocellulose catalyzed by coal gasification fine slag

The resource utilization of biomass and coal gasification fine slag (CGFS) is considered crucial for ensuring national energy security, mitigating environmental pollution, and achieving China’s “dual carbon” target. Pyrolysis, as the fundamental thermochemical conversion of biomass, enables the rapid transformation of biomass into bio-oil, biochar, and small-molecule gases within milliseconds, representing one of the most promising technologies for high-value biomass utilization. However, direct application of bio-oil is hindered by its complex composition and poor stability. The conversion pathways of biomass pyrolysis vapors are dynamically regulated through ex-situ catalytic fast pyrolysis technology, thereby enhancing carbonyl compound content in bio-oil. This carbonyl-enriched bio-oil serves as a critical platform intermediate for synthesizing gasoline/diesel and lubricants via aldol condensation and reductive etherification reactions. Nevertheless, existing catalysts are constrained by complex synthesis procedures and prohibitive costs. Thus, CGFS was innovatively employed in biomass catalytic fast pyrolysis, and a novel strategy termed “holocellulose rapid pyrolysis coupled with CGFS-directed catalysis” was proposed for producing carbonyl-enriched bio-oil, achieving synergistic utilization of biomass and CGFS. Systematic investigations were conducted using corn stalk holocellulose as feedstock and CGFS as catalyst through ex-situ fast catalytic pyrolysis. The effects of pyrolysis temperature, catalytic temperature, and catalyst-to-feedstock mass ratios on product distribution and composition were comprehensively analyzed. Catalyst characterization was performed using XRD, SEM–EDS, and XPS, with additional evaluation of cycling stability and regeneration capacity. Key findings demonstrated that: bio-oil and biochar yields were reduced with increasing pyrolysis temperature, peaking at 49.8% bio-oil yield at 450 ℃. A progressive decrease in bio-oil yield from 40.1% to 32.2% was observed as the catalytic temperature was elevated from 400 ℃ to 550 ℃, while gas yield was enhanced from 36.8% to 45.4%. This thermal transition was accompanied by significant increases in H₂+CH₄, CO₂, and CO yields, rising from 5.3, 40.7, and 53.1 mL/g to 57.2, 55.9, and 124.3 mL/g, respectively. Increasing mass ratios of catalyst to holocellulose from 0.5 to 2 reduced bio-oil yield from 46.6% to 36.2%, while CO₂ and CO yields rose from 36.4 and 46.3 mL/g to 51.7 and 59.9 mL/g. A marked enhancement in carbonyl compound content was achieved through catalyst loading optimization, with relative abundance increasing from 48.9% to 81.9% as the catalyst-to-feedstock ratio was elevated from 0 to 2. Concurrently, ketonic species exhibited similar amplification from 41.4% to 81.2%. The carbonyl fraction was predominantly composed of linear ketones (e.g., 1-hydroxy-2-propanone), cyclic ketones (e.g., 2-cyclopenten-1-one), and furan derivatives including furfural and 5-hydroxymethylfurfural. Notably, peak area ratio of 1-hydroxy-2-propanone was elevated from 1.41% to 48.98% as the catalyst-to-feedstock ratio was elevated from 0 to 0.5. The crystallographic phases of CGFS remained unaltered after use, while the surface O and C atomic ratio was reduced. The fresh CGFS exhibited an Fe²⁺ content of 60.08%, and the value decreased after use. After five catalytic cycles, carbonyl content declined from 75.7% to 67.6%, primarily attributed to oxidation of surface metallic species.