Catalytic Conversion of Chitin Biomass to 5-Hydroxymethylfurfural in Lithium Bromide Molten Salt Hydrates

Abstract

5-Hydroxymethylfurfural (5-HMF) is one of the top valuable platform chemicals that can be derived from biomass. Herein, a facile, mild, and efficient catalytic conversion method was developed to convert chitin biomass into 5-HMF in lithium bromide molten salt hydrates (LiBr MSHs) with boric acid (BA) as the catalyst. About 49.6% 5-HMF yield was obtained from glucosamine (GlcN) in 65 wt % LiBr MSHs at 130 °C for 2 h with 800% BA addition. The system is applicable to other sugars, and the C2substituted group of sugars played a significant role in the 5-HMF yield. The 5-HMF yields were 81.3, 40.3, and 3.9% from fructose, glucose, and N-acetyl glucosamine (GlcNAc), respectively, under identical conditions. Combined with acid addition and Box−Behnken experiment designs, the direct conversion of chitosan and chitin were achieved at 140 °C for 5 h to produce 5-HMF with 21.6 and 15.3% yield. Ammonia quantitative analysis and NMR tests have been conducted, based on which a plausible reaction pathway was proposed. The LiBr MSHs and the BA catalyst facilitated the hydrolysis, deacetylation, and ringopening of chitin biomass. Especially, the catalyst BA played a key role in the formation of 5-HMF, as it was found to promote dehydration at the last step. The study put forward new avenues for chitin refinery to produce high-value furanic platform chemicals in cheap and green solvent systems.