Computational Study and Detailed Kinetic Model of C₁–C₃ Aldehyde Formation from Cellulose-Based Anhydroglucose via Pyrolysis

Cellulose-based carbohydrates are critical precursors of hazardous C1–C3 aldehydes emitted during biomass combustion. Among these, 5,6-anhydroglucopyranose (AHGlu), a monomeric fragment of cellulose with a terminal methylene group, is expected to contribute significantly to the formation of formaldehyde, acetaldehyde, glyoxal, and methylglyoxal. This study aims to elucidate the elementary reaction pathways leading to C1–C3 aldehyde formation from AHGlu during pyrolysis by using density functional theory (DFT) and transition state theory (TST). After excluding kinetically unfavorable pathways, AHGlu is predicted to convert into straight-chain terminal-methyl carbohydrates, forming formaldehyde through a trifurcated pathway with a rate-limiting activation barrier of 205.2 kJ/mol. Acetaldehyde formation proceeds via a bifurcated pathway with a rate-limiting activation barrier of 195.9 kJ/mol, while glyoxal and methylglyoxal are generated through a single-step isomerization–scission mechanism, with rate-limiting activation barriers of 189.8 and 177.2 kJ/mol, respectively. The uncertainty in calculating energy at the basis set level and the perturbation of the pressure dependence of the reaction on the final results were evaluated. Using reaction rates at 1 atm, comparative reactor simulations deviated from experimental references by less than 20%, indicating that the proposed mechanism is applicable to cellulose pyrolysis. According to sensitivity analysis, promoting the conversion of AHGlu toward LVG prior to the ring-opening step or conducting pyrolysis at pressures below 0.1 atm may substantially suppress aldehyde formation, particularly FMAD and ACAD. The formation mechanism of C1–C3 aldehydes from AHGlu reported here provides a further solid foundation for the thermal decomposition of cellulose-based anhydroglucose, and considering the catalytic effect of water in relation to these research findings will lead to a deeper understanding.