Catalytic Dehydration of Lactic Acid to Acrylic Acid over Phosphorus Promoted and Alkali Modified ZSM-5

Abstract

We have developed a selective and active catalyst for sustainable industrial production of acrylic acid (AA) from lactic acid (LA). The phosphorus-promoted and alkali-modified ZSM-5/P-Na catalyst exhibited the best performance, achieving 83% AA selectivity and 98% LA conversion. We have successfully demonstrated that the acid-base properties of the zeolite can be easily modified by adding a promoter during synthesis. To elucidate the structural and acid-base properties of the ZSM-5/P-Na catalyst, comprehensive analytical techniques were employed, including XRD, BET, FT-IR, ICP-MS, TGA, NH₃, and CO₂-TPD. It was found that the distribution of aluminum, silicon, phosphorus, and sodium species in the catalyst structure significantly affected its acid-base properties. Additionally, the alkaline treatment method used in this study caused desilication in the ZSM-5 zeolite structure. Desilication enhanced weak and medium acidity of the phosphorus-promoted ZSM-5 zeolite, while a high alkali concentration promoted mesopore formation. The results showed that the ZSM-5/P-Na exhibited not only higher selectivity and LA conversion but also a longer catalytic lifetime (50 hours) in the LA to AA reaction. Finally, an experimental design of the catalyst was developed to understand the optimal values of the important operational variables in the LA dehydration reaction.