Heteropolyacids combined with Y zeolite as superior solid acid catalysts to accelerate lactic acid esterification

BACKGROUND

Ethyl lactate, produced through lactic acid and ethanol esterification is extensively used in plastics, polymers, and food industries and renowned for its biodegradability and low toxicity. However, lactic acid self-catalyzed esterification presents a slow reaction process and to accelerate this reaction catalysts are being used. Traditional catalysts like H2SO4 exhibit strong corrosion and difficult recovery, therefore increase the need for efficient and effective catalyst. In this study, two kinds of heteropolyacids-zeolite catalysts, involving loading silicotungstic acid and phosphotungstic acid onto Y zeolite were synthesized, characterized using XRD, NH3-TPD and SEM and analyzed for their catalytic efficiency.

RESULTS

Results showed that the Keggin structures of heteropolyacids retained during the preparation process and strong acid sites of Y zeolite were enriched, which made the main contribution to the esterification of lactic acid and ethanol. Furthermore, the initial-stage reaction rate of esterification significantly enhanced. During the 1st hour of esterification, the conversion of lactic acid increased from 18% to 65%. Exp Dec1 index model was employed to determine the activation energies of 60HSiW-Y and 60HPW-Y, which exhibits the values of 29.3 kJ/mol and 28.2 kJ/mol, respectively.

CONCLUSION

This study indicates that Keggin structure of heteropolyacids plays a key role in the esterification and heteropolyacids zeolite catalysts can effectively catalyse the esterification. Meanwhile, the results of the kinetic experiments can be of reference significance for large scale industrial processes involving esterification.