Hydrogenation of Carbon Monoxide into Formaldehyde in Liquid Media

Formaldehyde is a bulk chemical which is produced in excess of 30 million tons per annum and is growing in demand. However, the current production process requires methanol production, which is oxidized in air to produce formaldehyde, which must then be absorbed into water. Our recent work introduced a novel method to produce formaldehyde through CO hydrogenation in the aqueous phase. However, the aqueous phase has certain limitations which must be overcome to make it commercially viable. By applying a deuterium labeling technique and investigating the potential intermediates, the reaction mechanism was established which showed that solvents play a vital role in determining the yield. Various solvents were used for formaldehyde production, and the highest formaldehyde yield was achieved by using pure methanol followed by methanol-water mixtures. Formaldehyde reacts with methanol and water to produce hemiacetal and methylene glycol, respectively, thereby shifting the equilibrium of CO hydrogenation toward formaldehyde production. Methanol and water stabilize the hemiacetal and methylene glycol molecules, respectively, via hydrogen bonding. The highest yield of formaldehyde in methanol solvent was found to be 15.58 mmol L-1 g(cat)(-1) at 363 K and 100 bar, which is four times higher than our previous report. The liquid phase method shown here has the potential to be greener and more sustainable than the commercial processes because it operates at low temperatures and results in 100% selectivity toward formaldehyde with no CO2 generation.