Production of gamma-valerolactone from sugarcane bagasse over TiO2-supported platinum and acid-activated bentonite as a co-catalyst
Nowadays, biomass utilization has become the center of attention for researchers worldwide and is driven by the depletion of global petroleum supplies for the production of energy and valuable chemicals while easing the atmospheric CO2 burden. We propose here a green strategy for transforming sugarcane bagasse into gamma-valerolactone (GVL), an attractive platform molecule that can be further converted into a variety of chemical derivatives for wide use in industrial applications. Our recent strategy involves the solid acid-catalyzed hydrothermal conversion of cellulose and hemicellulose derived from biomass to give an aqueous solution comprising levulinic acid (LA), followed by catalytic hydrogenation of LA to GVL. Native and acid-activated bentonites were used as solid acid catalysts to promote hydrothermal conversion of cellulose and hemicellulose. The maximum achievable yield of LA was 159.17 mg per gram of oven-dried biomass for 60 min reaction at 473.2 K in the presence of a 2% acid-activated bentonite catalyst. Catalytic hydrogenation reactions of LA to GVL over 1% Pt@TiO2 and acid-activated bentonite as a co-catalyst were performed at temperatures of 393.2–473.2 K and residence times of 120–360 min. The combined solid catalyst gave an attractive performance with respect to LA conversion (∼100%) and GVL selectivity (95%) under milder reaction conditions in comparison to 1% Pt@TiO2 without an acid co-catalyst. The spent catalyst could be reused for five consecutive hydrogenation cycles with a marginal decrease in the catalytic activity and GVL selectivity. Coke formation was believed to be the main cause of catalyst poisoning and calcination of the spent catalyst under a stream of pure oxygen at 723.2 K was applied for removing coke deposits from the active catalyst sites, thus restoring the catalytic performance.