Lignin isolation from pulp

All residual lignins isolated by the enzymatic method are contaminated with enzymes to varying extents. This is especially true for the residual lignins isolated from semi-bleached pulps (Jiang et al. 1987). The contamination can be largely removed by the following procedure ... 

Contamination by enzymes is a main drawback of the procedure, especially in the isolation of residual lignin from semi-bleached pulps. The contaminants cannot be completely removed by the purification procedure described above. Consequently, it is important to determine the nitrogen content of the residual lignin. Typical values of nitrogen content are 2.5% and 7.3% before purification and 0.6% and 2.3% after purification for residual lignins isolated from an unbleached and a semi-bleached southern pine kraft pulp, respectively (Jiang et al. 1987). 

Jiang J-E, Chang H-m, Bhattacharjee SS, Kwoh DLW (1987) Characterization of residual lignins isolated from unbleached and semi-bleached softwood kraft pulps. J Wood Chem Techno 1 7 81-96... 

Fig. 8.1.3. High-performance size-exclusion chromatograms of acetylated samples of milled wood lignin from pine (—), pine kraft lignin (—) and two samples of residual lignin isolated from pine kraft pulp (-,----). (Yamasaki et al. 1981)...

T Iversen, S Wannstrom. Lignin-Carbohydrate Bonds in a Residual Lignin Isolated from Pine Kraft Pulp. Holzforschung 40 19-22, 1986. 

In the sulphite pulping process wood cut into pieces is subjected to kiering in a calcium bisulphite solution under a pressure of 3-8 kg/cm2, at 120-145°C for 7-30 hr. The higher the temperature, the shorter the time of boiling. Substances accompanying cellulose dissolve in the liquor. Lignin is converted into a soluble lignin sulphonic acid. Cellulose is isolated from the solution, known as sulphite cellulose lye, and washed with water. 

Vanillin structures can be considered to be minor lignin end groups and compounds containing vanillin moieties were isolated from all wood and pulp samples. The yields were, however, much lower than those of either coniferyl alcohol... 

Organosolv lignin was isolated from black cottonwood (P. trichocarpa) which had been pulped using a methanol/water (70/30) solvent system with NaHSC>4 as a catalyst (28). The chloroform-soluble fraction of this lignin was utilized in this study. lH-nmr broad peaks were observed at 3.7 and 6.7 ppm C-nmr 55.9 (-OCH3), and other typical lignin peaks were observed from 103 ppm to 152 ppm. 

Gierer J, Lindeberg O (1980) Reactions of lignin during sulfate pulping Part XIX Isolation and identification of new dimers from a spent sulfate liquor Acta Chem Scand B 34... 

The earliest expts devoted to the nitration of lignin, previously isolated from wood pulp by means of HC1, were reported by Hagglund (Ref 3). Lignin mixed with fuming nitric acid... 

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