The synthesis of acetic acid from methane via oxidative bromination, carbonylation, and hydrolysis Original Research Article

Acetyl bromide and acetic acid (AA) were synthesized from methane by an energy-saving process. By reacting methane with oxygen in the presence of HBr and H2O over a 2.5% Ba 2.5% La 0.5% Ni 0.1% Ru/SiO2 catalyst, methane was converted to CH3Br and CO (CH3Br/CO molar ratio = 1/1) with a CH4 single-pass conversion of 70% at 660 °C. Our results showed that CH3Br was formed via the interaction of methane with bromine radicals whereas CO was generated in the oxidation of CH3Br. Through the carbonylation of CH3Br over RhCl3-KI or RhCl3-PPh3 (triphenyl phosphine) catalyst in propanoic acid, acetyl bromide could be synthesized and readily hydrolysed to acetic acid at room temperature (with more than 99.7% yield based on CH3Br). The promotional action of PPh3 and KI is realized via the direct coordination of PPh3 to Rh and the conversion of CH3Br to CH3I by means of Br–I exchange, respectively.