Acetalization of 5-hydroxymethyl furfural into biofuel additive cyclic acetal using protic ionic liquid catalyst- A thermodynamic and kinetic analysis

Abstract

This work investigates the thermodynamics and kinetics of the synthesis of 5-HMF-cyclic acetal, a fuel additive, from 5-HMF and 1,3-propanediol using lab synthesized, environmentally benign Brønsted acidic ionic liquid (IL) catalyst. Firstly, a thermodynamic study of the acetalization of 5-HMF with different mono and polyalcohols was carried out to evaluate the thermodynamic properties of critical temperature (Tc), critical volume (Vc), critical pressure (Pc), Gibbs free energy of formation (ΔGf0), enthalpy of formation (ΔfH0), and heat capacity (Cp) using group contribution methods. Then, kinetics of 5-HMF acetalization with 1,3-propanediol was investigated in a batch autoclave using Brønsted acidic IL catalyst and effect of reaction parameters temperature, molar ratio of reactants and time were investigated on the conversion of 5-HMF into 5-HMF-cyclic acetal product and optimized for high 5-HMF conversion and cyclic acetal yield. A first-order pseudo-homogeneous kinetic model with a squared regression coefficient R2 > 0.99 fitted well with experimental data. The activation energy of the acetalization reaction is estimated to be 83 kJ/mol for the 1st order kinetics. Based on the catalyst activity, a plausible reaction mechanism was proposed for the acetalization reaction of 5-HMF and 1,3-propanediol. Finally, this manuscript reports an efficient method for the production of fuel-additive compound and valuable information for predicting the thermodynamic properties for the pure organic components.