Evaluation of lactic acid via heterogeneous catalytic dehydration

A highly selective, active and stable catalyst is developed for the industrial production of acrylic acid (AA) from a sustainable source, lactic acid (LA). Although it is a chemically simple process, obtaining high AA selectivity is challenging due to the two active functional groups of LA and its self-esterification structure. The most important parameter for the LA dehydration reaction is the balanced acid-base property of the catalyst, and the ZSM-5 zeolite catalyst with phosphorus promoter and alkali modified stands out as one of the best catalysts among the developed catalysts, exhibiting 83 % AA selectivity and 98 % LA conversion. According to the results of elemental analysis and characterization of surface acid-base properties, the phosphorus promoter increased the amount and density of acid sites on the catalyst surface. Desilication further increased the acid site amount and density of the surface. Due to the composition of the catalyst surface species, especially sodium species increased on the catalyst surface after alkali treatment. Sodium species on the catalyst surface play an important role in the formation of sodium lactate, which is the intermediate product in the LA dehydration reaction. LA conversion was unaffected during the reaction time of 50 h and performed still over 98 even after regeneration. The experimental design of the best-performing ZSM-5/P-Na catalyst was developed to understand the optimal values of the important operational variables in the LA dehydration reaction. Undoubtedly, the promoter effect on acidity and basicity is the key point of this thesis. The current investigation offers a fresh perspective on the development of heterogeneous acid-base catalysts for the LA dehydration reaction.