Valorization of humins from food waste biorefinery for synthesis of biochar-supported Lewis acid catalysts

To close the carbon loop of biomass waste valorization, it is imperative to utilize the unavoidable by-products such as humins, a carbonaceous residue with complex and heterogeneous composition. In this study, starchrich rice waste was effectively converted into value-added chemicals (e.g., 5-hydroxymethylfurfural) under microwave heating at 160 degrees C using AlCl3 as the catalyst. The solid by-products, i.e., humins, were then valorized as a rawmaterial for fabricating biochar-supported Lewis acid catalysts. The humins were collected and pretreated by AlCl3 as the impregnation agent, followed by carbonization. Detailed characterization revealed several Al-O species on the biochar surface plausibly in the amorphous state. The oxygen-containing functional groups of humins might serve as anchoring sites for the Al species during impregnation. The humins-derived biochars exhibited good catalytic activity toward glucose-to-fructose isomerization, a common biorefinery reaction catalyzed by Lewis acids. A fructose yield of up to 14 Cmol% could be achieved under microwave heating at 160 degrees C for 20 min in water as the greenest solvent. Such catalytic performance was comparable with the previously reported Al-based catalysts derived from wood waste and graphene/graphitic oxide. This study herein highlights humins as a low-cost alternative source of carbon for the preparation of renewable solid catalysts, proposing a novel practice for recycling by-products from food waste valorization to foster circular economy and sustainable development. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study demonstrates the effective conversion of starch-rich rice waste into value-added chemicals using AlCl3 as a catalyst under microwave heating. The solid by-products, humins, were further valorized as raw material for biochar-supported Lewis acid catalysts with good catalytic activity. This novel practice offers a low-cost alternative for preparing renewable solid catalysts from by-products, fostering circular economy and sustainable development.