Structure elucidation of prot, alkali and dealkaline lignin(s) by NMR, FT-IR and Py-GC/MS: effect of solid acid and base catalysts

Abstract

Structural insight into lignin(s) helps in understanding its breaking behaviour and is needed to overcome the real industrial lignin valorization problem. Here, one industrial lignin obtained from a mixture of biomass (sarkanda, wheat straw and bagasse) using the soda extraction method, and two commercial lignins were characterized by ultimate, proximate, FT-IR, XRD, and ¹H and ¹³C-NMR techniques. The use of 2D-NMR analysis provided more structural insight into lignin and showed a clear structural difference. Moreover, the effect of acidic (ZSM-5 and Y-zeolite) and basic (MgO and CaO) catalysts on the pyrolysis products have also been investigated. The observed GC-MS compounds were grouped as phenolics (H, G and S-type), heterocyclic, aromatic hydrocarbon, acidic and other types. The results indicated that the formation of phenolics mainly occurred during the pyrolysis of lignin(s). A maximum amount of phenolics (93.5%) was noticed from the pyrolysis of alkali lignin using CaO as a catalyst. In addition, 83.0% and 88.6% were found from the pyrolysis of prot and dealkaline lignin using the CaO catalyst, respectively. Among all the GC-MS compounds, ethanone, 1-(2-hydroxy-5-methylphenyl), 2-methoxy-5-methylphenol, mequinol, benzaldehyde, and 3-hydroxy-4-methoxy were found to be the major compounds formed with high selectivity.