Isomerization of glucose into fructose with homogenous amine-type base catalysts: amine structure, chain length, and kinetics

Abstract

Three homogeneous organosilanes amine and aliphatic primary amine were used as amine catalysts to evaluate their catalytic activity and kinetic towards glucose isomerization. Catalysts structure (primary, secondary, tertiary amine), terminal groups and alkyl chain length were investigated and compared elaborately. Result showed organosilanes tertiary amine behaved the best and amine generated OH− and amine itself contributed the isomerization reaction. The generated acidic by-product not only decreased fructose selectivity but also affected glucose conversion kinetic. The effect of siloxane (–Si–O–CH3) substituent with methyl (–CH3) can be insignificant, but it provided guiding significance for selecting amine-type homogeneous or grafted amine catalysts for glucose isomerization reaction. Longer alkyl chain resulted in lower glucose conversion because of the alkyl chain curls that would weaken the amine catalytic effect and hydration ability. Catalyst loading and initial glucose concentration investigations further showed that amine would effectively catalyze the isomerization reaction under varied operational conditions. This work will provide more details about organic amine catalysts on glucose isomerization into fructose and promote synthesis of platform chemicals in the applications of biorenewable chemicals and fuel.