Kraft black liquor lignin from

The following steps can be used to isolate fractions of kraft lignin from black liquor. 

Figure 1. Deposition of lignins from black liquor on cotton wool during kraft cooking.

Recovery of inorganic chemicals is crucial to the cost effectiveness of the Kraft process. The black liquor which is obtained from delignification is rich in solubilised lignin and carbohydrate degradation products and, after concentration, is combusted in a recovery furnace. The Carbon dioxide which is produced during combustion converts unused sodium hydroxide into sodium carbonate. In addition, the sodium sulfate is converted, under the reducing atmosphere of the furnace, to sodium sulfide. 

Condensation reactions of lignin have been mentioned 22) in connection with sulfite pulping as being responsible for color formation. However, most of the likely condensation reactions occurring during a kraft cook do not lead directly to chromophore formation. One potential condensation reaction which would give a chromophore is the formation of a chalcone (XIX) from vanillin and acetoguaiacone, both of which have been isolated by Enkvist 12) from black liquor. 

Kraft pulping is a common process in the paper industry. Figure 8.4 shows a simplifled flowsheet of the process. In this process, wood chips are reacted (cooked) with white liquor in a digester. White liquor (which contains primarily NaOH, NaiS, Na2C03 and water) is employed to dissolve lignin from the wood chips. The cooked pulp and liquor are passed to a blow tank where the pulp is separated from the spent liquor weak black liquor which is fed to a recovery system for... 

The feasibility of electrochemically recovering pure sodium hydroxide and lignin from kraft black liquor has been explored in several studies. Electrodialy-... 

Kraft pulping involves the cooking of wood chips at 340-350°F and 100-135 psi in liquor that contains sodium hydroxide, sodium sulfide, and sodium carbonate. This process promotes cleavage of the various ether bonds in lignin and the degradative products so formed dissolve in alkaline pulping liquor. The Kraft process normally incorporates several steps to recover chemicals from the spent black liquor [3]. 

Hagglund and Enkvist (6) developed a laboratory scale method for manufacturing methyl sulfide from kraft black liquor by pressure heating after addition of sodium sulfide. This process was later taken over by Crown-Zellerbach in the United States and developed in pilot plant and full scale. However, the yield is only about 7% of the initial lignin utilized in the process. 

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). 

In addition, the discovery of phthalic acid as a major oxidation product is theoretically important with respect to the linkages in alkali lignin obtained from kraft black liquor and, therefore, to the mechanism of the kraft cook. 

In addition to in situ soil applications, Fenton reagent has also been studied for treatment of industrial waste streams. For example, the treatment of residual Kraft black liquor from the pulp-and-paper industry has been shown to be effective [42]. Near-complete degradation of lignin (95-100%) and decolorization were achieved under optimized conditions. Basic oxygen furnace slag was evaluated as a source of iron for degradation of 2-chloro-phenol in industrial wastewater [43], and favorable results were achieved. 

Numerous attempts have been made to produce other low molecular weight products from lignin by subjecting concentrated kraft black liquors directly to various treatments, including hydrogenation, oxidation, or only heating in the presence of excess alkali. 

AI6n, R., Patja, P., and Sjostrom, E. (1979). Carbon dioxide precipitation of lignin from pine kraft black liquor. Tappi 62(11), 108-110. 

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