Dehydration of lactic acid to prepare acrylic acid over Hβ zeolite modified by acid treatment and Rb ion-exchange

The catalytic dehydration of bio-derived lactic acid into acrylic acid is one of the research hotspots in the field of green chemical industry, but the selectivity of acrylic acid and the stability of catalyst still face great challenges. In this work, a modified Hβ zeolite catalyst was prepared by sequential nitric acid treatment and Rb ion-exchange for the gas phase dehydration of lactic acid to prepare acrylic acid. The nitric acid treatment increased the content of Lewis acid sites together with the decrease of the content of Bronsted acid sites, which enhanced the dehydration and hindered the decarboxylation/decarbonylation of lactic acid. Consequently, the selectivity of acrylic acid was improved. The Rb ion-exchange not only significantly decreased the density of acidic sites but also regulated the density of basic sites of the catalyst. The optimal 0.1NA-6.8Rb/Hβ catalyst treated by 0.1 mol/L of nitric acid and 6.8 wt% of Rb ion-exchange contributed to a 99.28 % conversion of lactic acid and 76.72 % yield of acrylic acid. The catalyst showed a better stability and was easy to regenerate, maintaining 87.35 % conversion of lactic acid and 62.49 % yield of acrylic acid, respectively, after two cycles of consecutive 48 h reaction.