In order to investigate the delignification mechanism during high-boiling solvent (HBS) pulping, softwood HBS lignin samples from todo fir (Abies sachalinensis) were analyzed by 1H–13C correlation NMR spectroscopy (HMQC). Nine lignin model compounds that may represent the substructures in HBS lignin were prepared. The 1H and 13C NMR spectral data were compared with HBS lignin samples. The HMQC spectra of HBS lignin samples showed the disappearance of β-O-4 structures. Introduction of a pulping solvent into lignin was plainly observed with new signals in aliphatic regions. Only the erythro β-1 structure was detected in softwood milled wood lignin from todo fir by HMQC spectra. The β-1 structure was very reactive and probably produced the stilbene structure. The β-β and β-5 structures remained in HBS lignin. The 4-O-5 structure was successfully detected by HMQC spectra, and it was found to be stable under the conditions used.

Summary Milled wood lignin as well as wood meal from todo fir (Abies sachalinensis MAST) was treated with 70% aqueous 1,4-butanediol solution at 220°C without acid catalyst in order to elucidate the delignification mechanism during high-boiling solvent (HBS) pulping. HBS lignin was recovered from black liquor by precipitation, and was subjected to gel permeation chromatography and quantitative 13C-NMR study. The average molecular weight of MWL decreased. The content of phenolic hydroxyl groups in MWL increased from 0.28 to 0.68/OMe. The decrease in the content of β-O-4 substructures was evident, which may be attributed to the homolytic cleavage of phenolic β-aryl ethers. The changes in the content of β-5 and β-β substructures were rather small. The benzyl ether formation of β-O-4 structures with 1,4-butanediol was also confirmed by 13C-NMR. However, the signals corresponding to Hibbert's ketones were not observed, which suggests that acidolysis was not an important degradation pathway during HBS pulping.

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Klason lignin or preacid hydrolysate of a poaceous biomass such as rice husk, rice straw ( Oryza sativa ), and wheat straw ( Triticum aestivum ) became a good source of highly pure silica by simple calcinations in the testing process for application of high-boiling solvent (HBS) pulping of agricultural byproduct. Especially, Klason lignin or preacid hydrolysis residue of rice husks offered highly purified silica, which was converted to an excellent Ni/SiO(2) catalyst for methanation of carbon dioxide. The Ni/SiO(2) catalyst showed superior properties after the following sequential treatments; preacid hydrolysis of rice husks, HBS pulping of the resultant residue, cellulase hydrolysis of the HBS pulp, calcinations of the resultant powder, impregnation of the silica sample with an aqueous solution of nickel nitrate, and final calcinations.