Recently, cellulose has been regarded as a promising alternative to non-renewable resource for sustainable biofuels and biochemicals, as its most abundant content in original lignocellulosic biomass. In acidic conditions, cellulose can be transformed into glucose, 5-hydroxymethylfurfural (HMF), levulinic acid (LA) in aqueous solution, and glucoside, 5-alkoxymethylfurfural, levulinate ester in alcohol. The products distribution from cellulose was affected by the types of solvent and acid on solid catalyst, we found that the presence of Lewis acid in catalyst can promote cellulose conversion rate, no matter in water or in alcohol. At high reaction temperature (&gt;160 oC), the product in water was only levulinic acid because glucose and 5-hydroxymethylfurfural was unstable and can be further converted to LA; more importantly, the selectivity to LA was promoted by strong Lewis acid site on Al-doped NbOPO4 solid acid catalyst, up to 52% LA was obtained at optimal conditions[1]. However, in methanol or ethanol, the pathway was quite different. The carbohydrate would go through glucoside and 5-alkoxymethylfurfural as intermediate, and then converted into levulinate ester. The interesting thing is that high Brönsted acid ratio preferred the formation of levulinate over NbOPO4 catalyst, just the opposite to that in water, and the levulinate yield could up to 57%[2], almost the same as that from homogeneous catalyst. On the other hand, high Lewis acid ratio was responsible for other series of high yield products in alcohol, such as methyl lactate, 1,1,2-trimethoxyethane and 5-alkoxymethylfurfural, which were unfavorable for the main product formation.

Multiple reaction pathways and mechanisms of cellulose conversion into bio-platform molecules in water and alcohol medium

251st National Meeting (2016)

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