Atomistic insights into formaldehyde (HCHO) high-temperature treatment and syngas production via ReaxFF MD simulations

Formaldehyde (HCHO), typically known as an industrial waste gas, can be recycled to generate syngas. Our study focuses on the high-temperature and high-pressure treatment of formaldehyde, including pyrolysis, oxidation, and supercritical H2O/CO2 (scH2O/scCO2) co-pyrolysis via reactive molecular dynamics. Results showed that in the pyrolysis, the primary final products are H2 and CO. The formation of CO occurs through the double dehydrogenation of HCHO, and H-abstraction reaction leads to the formation of H2. In the oxidation, scH2O and scCO2 co-pyrolysis systems, the corresponding global reactions vary. HCHO can be oxidized to HCOOH, ultimately producing CO2. Another pathway for CO2 generation involves the formation of the COOH radical from CO. Oxidative treatment is more powerful in handling formaldehyde pollutants, while the supercritical condition is more effective in producing syngas. The order of carbon emission is oxidation > scH2O > pyrolysis. In the scCO2 system, scCO2 participates in the reaction, increasing CO production. Moreover, reaction kinetics models are proposed and agree well with experimental results. Under high-temperature conditions, the reaction rate in the oxidation system is the highest. Based on the activation energy for formaldehyde consumption and the energy barriers of the sub-reactions, the pyrolysis process is the easiest, whereas the oxidation process is the most difficult.