409 / 2018-07-25 17:13:08

Conversion of C5 carbohydrates into furfural catalyzed by Lewis/Brønsted acidic ionic liquid in renewable γ-valerolactone

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In this study, an aqueous solvent system including Lewis/Brønsted acidic ionic liquid as catalyst and renewable γ-valerolactone (GVL) as co-solvent was developed for high-efficiency transformation of C5 carbohydrates to produce furfural(FF). The conversion process of two important pentoses in hemicellulose, namely xylose and arabinose, were investigated in detail at different conditions. The results showed that the introduction of GVL greatly improved the reactivity of pentoses and inhibited the secondary decomposition reaction of FF compared to pure-water reaction system. NMR analysis suggested that the distribution of pentose conformers was optimized significantly in favor of FF formation. It was found that the Lewis acidic ionic liquid could facilitate the 1,2-hydride shift in the isomerization process in which aldopentoses isomerized to ketopentoses. The sulfonated Brønsted acidic ionic liquid could donate protons as a Brønsted acid and accept protons as a conjugate base, and therefore it could efficiently promote the enolization of xylose and the subsequent dehydration of the intermediate to FF. The influence of reaction parameters on pentose conversion was also studied. Results showed that arabinose had less reactivity than xylose, leading to its lower conversion rate and FF yield. Furthermore, xylan and real biomass materials were tested in the proposed reaction system, and decent FF yields of up to 70% were obtained from these complex polysaccharides, indicating that the proposed reaction system had great potential for producing FF from real biomass materials under mild conditions.