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

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.