Search

Lignin was isolated from wheat straw via organosolv process and further transferred to monophenolic compounds via oxidative conversion. Wheat straw lignin (WSL) with purity at 91.4 wt% was acquired in the presence of heterogeneous and recyclable catalyst of Amberlyst‐45. WSL was characterized by infrared spectrometer (IR), nuclear magnetic resonance spectroscopy (NMR) including 1H NMR and 13C NMR spectra. The results showed that WSL possesses typical syringyl (S), guaiacyl (G), and p‐hydroxyphenyl (H) units, and it is mainly composed of S and G units. The product distribution was dependent on the composition of WSL. Derivatives from S and G units were found to be the main products. The oxidative conversion of WSL was performed by varying oxidant and catalyst. Both the formation of monophenolic compounds and aromatic aldehydes were enhanced by combining oxidants and catalysts. The composite catalyst composed of NaOH/NaAlO2 was effective for the oxidation of WSL in the presence of nitrobenzene and atmospheric pressure air. The total yield of monophenolic compounds reached up 18.1%, and yields at 6.3 and 5.7% for syringaldehyde and vanillin were achieved, respectively.

Convertible cellulose and lignin were simultaneously isolated from wheat straw using a two-stage process via simply varying temperature and H2SO4 concentration. At the first-stage, cellulose was obtained by pretreating wheat straw at lower temperature and acid concentration using an organosolv process. The purity, yield and recovery rate of cellulose reached 86.8 wt%, 55.2 and 92.8% at 150 °C with 1 wt% H2SO4. At the second stage, the residual liquid was further treated at higher temperature and acid concentration, giving 17.4% lignin yield with 86.6% recovery rate and 93.2 wt% purity at 180 °C with 1.5 wt% H2SO4. The conversion of the as-isolated cellulose and lignin into chemicals was further investigated. The total yield of 5-hydroxymethylfurfural and glucose derived from wheat straw cellulose reached 82.5%, and 18.3% yield of monophenolic compounds from lignin were obtained, respectively. These results indicated that the two-stage process was effective for obtaining high-quality cellulose and lignin from wheat straw. Both of them displayed excellent convertible property.