k-Carrageenan-based composite as an efficient acidic bio-based catalyst for the synthesis of 5- hydroxymethylfurfural from fructose

A novel bio-based nanocomposite was designed based on modification of halloysite with k -carrageenan via precipitation polymerization with acrylic acid in aqueous media. Various analyses were conducted to verify the formation of the catalyst. Afterwards, it was tested as a solid acid catalyst for the dehydration of fructose, resulting in the production of 5-hydroxymethylfurfural. Effective parameters, such as catalyst amount, temperature, and the reaction time were optimized and it was revealed that 10 wt% catalyst at 100 °C gave the desired product in 97.9% yield in 35 min. The catalyst was also reusable and could be reused up to four runs. Comparison of the activity of the catalyst with halloysite and k -carrageenan confirmed superior activity of the former, which was attributed to its higher acidity and possible synergism between the components. Moreover, the composite with lower content of the polymeric moiety was less effective, approving the role of the conjugated polymeric part in the catalytic activity. Thus, the present protocol would open up an innovative opportunity for the preparation of a bio-based catalytic system from naturally occurring components. In fact, k -carrageenan as a carbohydrate containing acidic functionality in its backbone was successfully applied for improving the acidity of the nanocomposite.