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

Abstract 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 H 2 O over a 2.5% Ba 2.5% La 0.5% Ni 0.1% Ru/SiO 2 catalyst, methane was converted to CH 3 Br and CO (CH 3 Br/CO molar ratio = 1/1) with a CH 4 single-pass conversion of 70% at 660 °C. Our results showed that CH 3 Br was formed via the interaction of methane with bromine radicals whereas CO was generated in the oxidation of CH 3 Br. Through the carbonylation of CH 3 Br over RhCl 3 -KI or RhCl 3 -PPh 3 (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 CH 3 Br). The promotional action of PPh 3 and KI is realized via the direct coordination of PPh 3 to Rh and the conversion of CH 3 Br to CH 3 I by means of Br–I exchange, respectively.