Biphasic Production of 5-Hydroxymethylfurfural Catalysed by Sulphated Zirconia in H2O/Cyclohexanone: Kinetic Modelling and Green Metrics

Abstract

The production of 5-hydroxymethylfurfural (HMF) presents the challenge of mitigating the undesired side reactions in its production via fructose dehydration to insoluble humins and rehydration products. For this, biphasic systems for in situ HMF extraction have proven effective. Here, a H₂O/cyclohexanone biphasic system showed a remarkable partition ratio of 2.91 compared to other biphasic systems to separate HMF as the reaction occurs. Sulphated zirconia, SO₄²⁻/ZrO₂, was used as acid catalyst, chosen among other heterogeneous catalysts through activity and recyclability screening over six cycles, with return to the initial activity upon regeneration. A phenomenological approach to kinetic model development was implemented, wherein a total of 12 reaction models were constructed to investigate the complexity of humin formation. Based on statistical discrimination criteria, a Langmuir–Hinshelwood–Hougen–Watson model with variable reaction orders for the production of humins was deemed the most plausible (RMSE = 0.1075), with activation energy for dehydration of fructose to HMF of 137.97 ± 6.40 kJ mol⁻¹, and reaction orders towards humin formation between 0.71 and 1.60. The calculation and comparison of green metrics show the promise of this biphasic system to conduct the reaction in the context of a process, although catalyst selectivity remains key to enhancing mass efficiency.