Abstract
The key challenges for converting chitin to 5-hydroxymethylfurfural (5-HMF) include the low 5-HMF yield. Moreover, the disadvantages of traditional acid–base catalysts including complex post-treatment processes, the production of by-products, and severe equipment corrosion also largely limit the large-scale conversion of chitin to 5-HMF. In this view, herein we have demonstrated a microwave aided efficient and green conversion of chitin to 5-HMF while using polyoxometalate (POM) as a catalyst and DMSO/water as solvent. Chitin treated with H2SO4 followed by ball-milling (chitin-H2SO4-BM) was selected as the starting compound for the conversion process. Four different POMs including H3[PW12O40], H3[PMo12O40], H4[SiW12O40] and H4[SiMo12O40] were used as catalysts. Various reaction parameters including reaction temperature, amount of catalyst, mass ratios of water/DMSO and reaction time have been investigated to optimize the 5-HMF conversion. The H4[SiW12O40] catalyst exhibited the highest catalytic performance with 23.1% HMF yield at optimum operating conditions which is the highest among the literature for converting chitin to 5-HMF. Significantly, the disadvantages of the state of the art conversion routes described earlier can be overcome using POM-based catalysts, which makes the process more attractive to meet the ever-increasing energy demands, in addition to helping consume crustacean waste.
Highlights
IntroductionAmong the various high-value chemicals, 5-hydroxymethylfurfural (5-HMF) is one of the most promising valuable bio-based platform compounds and is considered to be the key intermediate to bridge the gap between biomass and fossil fuel resources.[12,13,14,15] In a general view, 5-HMF can be used to synthesize many chemicals including furan derivatives and nonfuranic compounds
The mechanical forces imported by the ball mill act to alter the crystalline structure of chitin to increase the ratio of amorphous structure which is more reactive and has less tensile strength, and greatly
The green conversion of chitin-based biomass to a value-added platform chemical holds enormous potential to contribute as a renewable energy source to meet the increasing energy demand in addition to help consuming crustacean waste
Summary
Among the various high-value chemicals, 5-hydroxymethylfurfural (5-HMF) is one of the most promising valuable bio-based platform compounds and is considered to be the key intermediate to bridge the gap between biomass and fossil fuel resources.[12,13,14,15] In a general view, 5-HMF can be used to synthesize many chemicals including furan derivatives and nonfuranic compounds. The use of chitin for direct conversion to 5 HMF is largely limited to their poor solubility and very low yield of product.[20,21,22,23] For example, a very low 5-HMF yield of only 1.9% was reported by Zhang and coworkers using an ionic liquid ([Hbim]Cl) catalyst.[21] In a separate study, Wang et al observed 5-HMF yield of 9.0% with ZnCl2 as a catalyst and at 190 C for 6 h hydrothermal condition.[22] The highest conversion efficiency to date of chitin to 5-HMF was achieved as 19.3% using FeCl2$4H2O as a catalyst by Yu and coworkers.[23] In addition to the low 5-HMF yield, these processes are limited with critical post-treatment issues. The H4[SiW12O40] catalyst shows better 5-HMF conversion efficiency over the other three catalysts
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