Kinetic modelling of acid-catalyzed liquid-phase dehydration of bio-based 2, 3-butanediol considering a newly identified by-product and an updated reaction network

Study on the acid-catalyzed dehydration of bio-based platform chemical 2, 3-butanediol (BDO) to produce methyl ethyl ketone (MEK) has a relatively long history. However, the reaction networks of the system have not been completely elucidated yet. In this work, a new by-product formed during acid-catalyzed liquid-phase dehydration of BDO was detected, which was wrongly identified by the GC–MS NIST database or previous research works. The new compound was finally identified as 2-isopropyl-4, 5-dimethyl-1, 3-dioxolane (IDMD), formed by acetalization between 2-methyl propanal (MPA) and BDO under the catalysis of Bronsted acids. MPA was an intermediate product of acid-catalyzed dehydration of BDO, but its life was short primarily due to the formation of IDMD. Prepared IDMD with high purity was further characterized by FTIR, MS and NMR spectroscopy, providing data which have not been previously reported in literatures. The reaction mechanisms of acid-catalyzed dehydration of BDO were thus updated with consideration of the new side reaction. New kinetic models were further developed based on the updated reaction network. Observed kinetic constants were fitted with experimental data, and the observed rate constants were correlated with reaction temperature and acid concentration by an extended Arrhenius equation. The results revealed that the acetalization between BDO and MPA had much higher observed activation energy (191.5 kJ/mol) than the ketalization between BDO and MEK (59.7 kJ/mol). The observed reaction equilibrium constants was also affected by reaction temperature as well as acid concentration. Increasing reaction temperature was beneficial for the formation of ketalization and acetalization products, while increasing acid concentration seems to more significantly accelerated the hydrolysis of the ketalization and acetalization products.