Kraft lignin precipitation

Two Streptomyces strains, S. badius and S. viridosporus, were found to be able to grow on kraft lignin (In-dulin ATR) as sole carbon source. The resulting APPL (Acid Precipitable Polymeric Lignin) was characterized by FTIR and elemental analysis for C, H and N, and was found to contain proteins in addition to a relatively demethoxylated lignin component. The proteins were further characterized by amino acid analysis, while the lignin component was separated by solvent extraction and its molecular weight distribution determined by HPSEC. 

Figure 4. Infrared spectra of kraft lignin, Indulin AT (D), and the precipitates collected in the first trap (at 1 bar) after methylamine extraction of Indulin AT (C), methylamine extraction of red spruce (B), and ammonia extraction of red spruce (A). Extraction conditions 2 h extraction at 185 ° C, 275 bar, and 1 g/min solvent flow rate.

Figure 10. Molecular weight calibration curves for kraft lignin samples differing in degree of association eluted from Sephadex G100 with aqueous 0.10A/ NaOH ( ) associated sample after 385 h at 180 gL 1 in 1.0 M ionic strength aqueous 0.40 M NaOH (O) orig nal preparation ( ) dissociated sample precipitated upon acidification to pH 3.0 after 2000 h at 0.50 gL 1 in aqueous 0.10 M NaOH.

Kraft Lignin. A softwood kraft lignin (KL) was isolated from a partly evaporated, industrial kraft black liquor by precipitation through the addition of dilute sulfuric acid as described elsewhere (7). The lignin was thereafter fractionated by successive extraction with organic solvents (7). The KL fraction used in the present investigation was the second of five fractions obtained (propanol soluble - methylene chloride insoluble). 

Based on alkali-soluble methylolated kraft lignin which was precipitated by acidification and blended with an acid-curing phenolic resin. 

Reaction of cyanamide-peroxide with a soluble kraft lignin was more rapid than the corresponding alkaline peroxide oxidation [101], When cyanamide-peroxide was used in eight-molar excess at 60°C, after one hour only 30% of the kraft lignin was recovered by acid precipitation. This compared with an 80% recovery for the alkaline peroxide treatment. The peroxide in the cyanamide-peroxide system was totally consumed, whereas more than 70% residual peroxide was obtained in the alkaline peroxide experiments. Most of the peroxide in the cyanamide-peroxide system was consumed within 10 minutes. 

Uloth V, Wearing J. Kraft lignin recovery acid precipitation versus ultrafiltration. Part I laboratory test results. Pulp Pap Can 1989 90(9) 67—71. 

---