Synergistic catalytic effect of zirconium chloride and Brønsted acid salt for conversion of agarose to 5-hydroxymethylfurfural in aqueous media

A facile and highly efficient method for converting seaweed-derived agarose to 5-hydroxymethylfurfural (HMF) in aqueous media using combined metal salts as catalysts is proposed. A series of combined metal salts were investigated under different conditions. The combination of ZrCl 4 and KHSO 4 was the most efficient catalyst; it was capable of achieving a high HMF yield of 71.4% under optimized conditions. The charge density or counter anion possibly affected the ionization degree of the metal cations in the aqueous solution, thereby influencing the HMF yield. ZrCl 4 promoted the cleavage of the C–O–C bond in agarose and galactose to ketose isomerization , which is the key step for HMF formation. KHSO 4 increased the conversion rate of ketose to HMF. This work offers a convenient method for converting seaweed-derived agarose to HMF and improve the utilization of marine biomass.