Water density dependence of formaldehyde reaction in supercritical water

The water density dependence of formaldehyde (HCHO) reaction in supercritical water (SCW) was studied with batch experiments. Major products from the reaction were methanol (CH₃OH), formic acid (HCOOH), hydrogen (H₂), carbon monoxide (CO) and carbon dioxide (CO ₂). It was found that the Cannizzaro reaction mechanism was the preferred reaction pathway for HCHO reaction in SCW. At higher water densities, CH₃OH yields increased confirming the predominance of the Cannizzaro reaction mechanism. At low water densities, CO yields increased and CH ₃OH yields decreased, which indicated that monomolecular decomposition became the main reaction pathway. Addition of base to the reacting mixtures was found to promote the Cannizzaro reaction path whereas addition of acid promoted monomolecular decomposition.