Enhancement of the production of chemicals and liquid fuels from grass biowaste via NaOH-Fenton pretreatment coupled with fast pyrolysis

Abstract

Biomass waste pyrolysis has taken an increasing interest in producing biofuels and bio-based chemicals, but the complex compositions of pyrolytic liquid hinder its development and utilization. To address these challenges and improve the yield of target chemicals (levoglucosan) and aromatics, a novel two-stage process based on NaOH-Fenton pretreatment coupled with fast pyrolysis is firstly proposed. Firstly, rice straw was pretreated by dilute alkali to separate lignin fractions, and then the residue was further treated via Fenton reaction at room temperature to obtain cellulose-rich substrate. The fast pyrolysis of raw rice straw produced the complex compositions in the pyrolytic liquid. After NaOH-Fenton pretreatment, the target platform chemicals in the pyrolysate were effectively concentrated. The cellulose-rich substrate exhibited a very high absolute yield of levoglucosan (201.9 mg/g) as compared to raw rice straw (not detected). The lignin fractions recovered from this process were catalytically fast pyrolyzed for preparing aromatic fuels. Furtherly, the maximum removal rates of nitrogen (76.5%) and sulfur (93.3%) were achieved by the coupled process. A short-chain cellulose-rich substrate with similar dissociation energy of glycosidic bonds was formed by the NaOH-Fenton process based on the analytical results of the DFT calculation and mechanism. The similar dissociation energy of C–O bonds from the short-chain cellulose-rich substrate favors the formation of high-yield levoglucosan in subsequent fast pyrolysis. This work introduces a simple and highly efficient strategy to convert grass biowaste into value-added chemicals and liquid fuels.