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

Abstract

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.