Synthesis of Formaldehyde from CO
Formaldehyde is an intermediate in the synthesis of edible carbohydrates from CO2, O2, and H2 derived from crew member metabolic wastes on spacecraft missions. Methods of accomplishing the synthesis of formaldehyde were studied, and the CO2 → CH4 → CH2O route was selected as the most suitable for spacecraft conditions.
Partial oxidation of methane using heterogeneous solid catalysts, ozonated oxygen, and gaseous nitric oxide was investigated. The highest yield achieved was with nitric oxide, amounting to 2.5% of the methane admitted to a single pass reactor.
The feasibility of converting CO2 into formaldehyde was demonstrated with a recycle system entailing two reactors. A methanation reactor converted feed and by-product CO2 into CH4; the CH4 in turn was oxidized to formaldehyde in an oxidation reactor. With recycling, essentially 100% conversion of CO2 to formaldehyde was achieved at ambient pressures. The product formaldehyde and water were separated and removed either as solid paraformaldehyde and ice or adsorbed on solid adsorbents. The system is compatible with zero gravity operation.