Catalysts for vapor-phase dehydration of ethylene glycol and their application to pyruvic acid synthesis

Abstract

Vapor-phase dehydration of ethylene glycol over acidic catalysts such as η-Al 2O 3, SiO 2MgO, H 3PW 12O 40, P 2O 5/AI 2O 3, AIPO 4, and K 2S 2O 7/SiO 2 has been examined as a probe reaction for attempted conversion of tartaric acid into pyruvic acid. The reaction was carried out by a conventional fixed-bed flow apparatus at 200–400°C with a space velocity of 1000 or 3600 h −1 for 10 vol% ethylene glycol in feed. η-Al 2O 3 gave 1,4-dioxane as a major detectable product at 200–250°C. The yield passed through a maximum (35%) at 280°C and then decreased with increasing temperature. Formation of the intramolecular dehydration product, acetaldehyde, was observed at above 250°C, showing a plateau of yield (55°-60%) at higher temperatures. The lack of balance was presumably due to formation of linear polymers. Similar behavior was also observed for H 3PW 12O 40, but no dioxane was detected for SiO 2MgO. Dioxane activity showed a shift to higher temperature for P 2O 5/Al 2O 3 and AlPO 4, and thus both dioxane and acetaldehyde were obtained in the same temperature region above 250°C. It is of interest to note that AlPO 4 prepared from sulfate showed high selectivity to acetaldehyde, while dioxane was the predominant product for AlPO 4 from nitrate. K 2S 2O 7/SiO 2 was another favorable catalyst for the intramolecular dehydration of glycol similar to AlPO 4 from sulfate, and revealed excellent activity for conversion of ethyl tartrate into ethyl pyruvate through dehydrative decarboxylation (yield 60% at 300°C with SV 500 h −1).