Formaldehyde production via hydrogenation of carbon monoxide in the aqueous phase
Formaldehyde (HCHO) is an essential building block in many industries for producing value-added chemicals like resins, polymers and adhesives. Industrially, formaldehyde is produced via partial oxidation and/or dehydrogenation of methanol. Methanol is produced from natural gas in a series of processes, with synthesis gas as an intermediate. This study presents for the first time, formaldehyde production via hydrogenation of carbon monoxide in the aqueous phase, which eliminates the need for methanol synthesis, which may potentially save capital costs and reduce energy consumption. Gas phase hydrogenation of CO into formaldehyde is thermodynamically limited and therefore, resulted in a low CO conversion of only 1.02 × 10−4%. However, the aqueous phase hydrogenation of CO into formaldehyde was found to be thermodynamically favourable and kinetically limited. The highest CO conversion of 19.14% and selectivity of 100% were achieved by using a Ru–Ni/Al2O3 catalyst at 353 K and 100 bar. The rapid hydration of formaldehyde in the aqueous phase to form methylene glycol shifts the CO hydrogenation reaction equilibrium towards formaldehyde formation. Increasing the pressure and stirring speed increased the yield of formaldehyde, whereas increasing the temperature above 353 K resulted in a lower yield.