An efficient, high-yield synthesis of 5-hydroxymethylfurfural from red macroalgae (Eucheuma cottonii) using HCl/AlCl₃ as the catalyst

Macroalgae are attractive feeds for biobased platform chemicals like 5-hydroxymethylfurfural (HMF) and levulinic acid (LA). We here report an experimental study to obtain HMF from a representative red macroalgae using a biphasic water/MIBK system and a dual catalyst consisting of HCl and AlCl₃ in a batch set-up. The highest HMF yield was 64.0 mol% based on C6 sugars in the feed, corresponding with a carbon yield of 37.9 % (30 min, 153 °C, 0.04 M of AlCl₃ and 0.04 M of HCl, 5 wt% macroalgae (Eucheuma cottonii, EC), intake on water). A reaction network is proposed based on major and minor products identified in the liquid phase during reaction and involves both D-galactose and 3,6-anhydro-D-galactose. The experimental data were modeled using a statistical approach, and good agreement between the experimental results and the model was obtained. The model predicts that particularly the temperature has a significant effect on HMF yield. The data were also modeled using an appropriate kinetic model and the kinetic model was used to optimize the batch processing of EC.