High-Yield Synthesis of 5-Hydroxymethylfurfural from Untreated Wheat Straw Catalyzed by FePO4 and Organic Acid in a Biphasic System

It is of great significance to develop an affordable and environmentally friendly method for producing 5-hydroxymethylfurfural (HMF) and furfural from inexpensive and abundant agricultural waste. Herein, FePO4 combined with organic acids such as mandelic acid were used as catalysts in a one-pot catalytic conversion of untreated wheat straw into HMF and furfural in a two-phase system of THF/H2O saturated by NaCl. H+, Fe(OH)2+, and Fe(OH)2+ originated from partially dissolved FePO4 in hot water together with organic acids provided Brønsted and Lewis acid sites for the cascade conversion of wheat straw. Whereas organic acid could regulate the concentrations of Lewis and Brønsted acid sites to promote the dehydration process of fructose and hinder the production of by-products and humins, boosting the yield of HMF and furfural. The response surface methodology (RSM) was used to optimize the reaction conditions. The highest yield of HMF was 62.9% at 200 °C and 120 min, which is higher than the reported yield of HMF using lignocellulose as raw material in the current literature. Furfural has also achieved a higher yield (93.9%) at 180 °C and 90 min. This study demonstrates the rationality of the deployment of lignocellulose to produce furan compounds by organic acids and FePO4, providing the possibility for efficient production of HMF and furfural from recalcitrant agricultural waste.