Direct conversion of ethane to acetic acid over H-ZSM-5 using H2O2 in aqueous phase

Partial oxidation of ethane on protonated pentasil-type zeolite (H-ZSM-5) was studied by using hydrogen peroxide (H2O2), an environment friendly oxidizing agent. Acetic acid (CH3COOH) and formic acid (HCOOH) were obtained with high yield and selectivity from ethane. In addition, the influence of reaction parameters such as temperature, pressure, amount of oxidizing agent, and reaction period was investigated. Yields of acetic acid and formic acid (based on ethane) were achieved up to values of 18.7% and 14%, respectively, under the optimized reaction condition of 393 K and 3.0 MPa. Selectivity to both compounds is 84% under this condition. The amount of oxidant (H2O2) was optimized to be 279 mmol for the reaction. A low silica to alumina ratio in H-ZSM-5 was favorable for the partial oxidation of ethane. CO2 formation was observed as a deep oxidation product at initial period. Partial oxidation was observed to occur within a short reaction period and was associated with the active oxygen species produced from H2O2 and CO2 formed through the deep oxidation of ethane. Since the yield of CH3COOH from ethane is much higher than that from ethylene, partial oxidation on H-ZSM-5 proceeds through a reaction mechanism different from that of a Wacker-type oxidation reaction.

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► Effective production of acetic acid of 19% and formic acid of 14% (based on ethane) was achieved.
► Protonated pentasil-type zeolite (H-ZSM-5) was used as an active solid acid catalyst.
► The acid site of the catalyst seems to be the active site for partial oxidation.
► Triphenylphosphine is useful additive for improving yield.