Comparative study on various alcohols solvolysis of organosolv lignin using microwave energy: Physicochemical and morphological properties

Solvolysis approach is an efficient pathway to covert solid biomass into different end products since it can provide a mild environment and a single-phase condition. A comparative study on various alcohols-assisted liquefaction of lignin has been carried out using sulfuric acid as catalyst under microwave condition. Methanol and ethanol showed a higher conversion rate compared to other alcohols. Both liquefied products and residues have been investigated using gel permeation chromatography–high-performance liquid chromatography (GPC–HPLC), Fourier transform infrared (FT-IR), Scanning electron microscopy (SEM) and Thermogravimetric (TG) analysis. The results showed that methanol and ethanol as solvents achieved a higher conversion rate, meantime, the molecular weight of liquefied products was dramatically lower than those of other alcohols. The FT-IR indicated that there were obvious differences in the contents of carbonyl, methyl and hydroxyl group in the liquefied products with various alcohols as solvents. The solid residue exhibited a big difference in microstructure morphology after depolymerization, in addition, the resulted solid residue from methanol solvents showed a higher thermal stability and char yield, which can be used as a fire retardant in composite materials.