Comparative study of synthesis of methylamines from carbon oxides and ammonia over Cu/Al2O3

Methylamines have been synthesized from carbon dioxide, hydrogen and ammonia using Cu/Al2O3 catalysts with different copper loading. The reaction was performed in a fixed-bed micro reactor in the temperature range 473-573 K and at 0.6 MPa total pressure. The product amines were mono-, di- and trimethylamine (MMA, DMA, TMA). The distribution of the amines depended mainly on the reaction temperature and the NH3/CO2 ratio in the feed gas. At elevated temperatures and higher NH3 concentrations methanol synthesis is suppressed and MMA is the main amine product, reaching a ratio of MMA:DMA:TMA of 1:0.23:0.07. Conversion and product distribution were compared to that of the corresponding reaction starting from CO or methanol instead of CO2. With CO conversion was lower but the selectivity to MMA was higher. If CO2 was replaced by methanol, conversion increased and TMA was the main product. In all experiments a change of space velocity had relatively little influence on both conversion and distribution of amines.