Black liquor lignins

Wallberg O, Jonsson A-S, and Wimmerstedt R. Fractionation and concentration of kraft black liquor lignin with ultrafiltration. Desalination 2003 154 187-199. 

UF of Kraft Black Liquor. Lignin from kraft black liquor has for years been used to a limited extent as extender for binders in various board products. 

Sometimes known as the sulfate process, since the sulfur is added as sodium sulfate. It is then reduced to S ° by burning with the evaporated black liquor (lignin and carbohydrate fragments from a previous cook) in an insufficient supply of air. Water extraction yields green liquor , a solution of (largely) sodium sulfide and sodium carbonate and which is treated with slaked lime [Ca(OH)2j. Insoluble calcium carbonate precipitates and the resulting solution of sodium hydroxide and sulfide ( white liquor ) is used for a new cook. 

NMR analysis of black liquor lignins indicated increases in the ratio of substituted to unsubstituted aromatic carbons, suggesting that lignin from these bio-pretreatments may be more condensed than that obtained from a normal kraft pulp. 

Typical accuracy values reported in the literature for integrating the various functional groups by NMR range from 3-5% 102), In these experiments, the error analysis was based on reproducing the LMS biopretreatment utilizing VA as the mediator three separate times. The black liquor lignin from each was isolated and analyzed. The standard error calculated from these three treatments for the NMR experiments was 3%. 

Table IV. Black Liquor Lignin Analysis of Bio-Pretreatment Conditions...

Analytical data on kraft lignins obtained after solvent fractionation of isolated industrial softwood black liquor lignin [88]... 

Adler E. and Hagglund E.K.M., Method of producing water soluble products from black liquor lignin, US Patent 2,680,113 1954. 

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 use of the lignin fraction is much more cumbersome currently the best-known chemical of a real commercial importance is vanillin, which is obtained by oxidation of the black liquor. Another example is a product called spray-dried lignosulfonate (as sodium salt) obtained from the older, acidic sulfite pulping process. It is sold as a commercial product primarily as a concrete additive for enhanced strength. Since the cement industry is one of the big contributors of carbon dioxide emissions (due to the production of calcium oxide from calcium carbonate), the use of this renewable, wood-derived product not only is fossil-carbon neutral in itself but also reduces carbon dioxide emission due to the diminished need for cement in large infrastructures made of concrete. 

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

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. 

Keywords Black liquor, crystallization process, oil palm empty fmit bunches, soda lignin, vanillin... 

The pH of the obtained black liquor was 12. 45 and its density 1.02 g/iuL. The soda lignin was then precipitated from the concentrated black hquor by acidifying it to pH 2 using 20% concentrated sulfuric acid (H SO ). The precipitated hgnin was then filtered and washed with water adjusted to pH 2 using H SO. Then, the soda lignin was dried in a vacuum oven at 55°C for 24 hours prior to further analysis [12]. 

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]. 

Jain, R.K. Gupta, A. Dixit, A.K. Mathur, R.M. Kulkami, A.G. Enhanced biomethanation efficiency of black liquor througb lignin removal process in small agro based paper mills. Bioenergy... 

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

Fractionation on Sephadex G-25 using 0.5M sodium hydroxide as eluent causes the low molar mass lignin components in black liquor to elute in the relative retention volume range 0.3-1.3 with partial separation from each other, as shown in Figure 11. 

Figure 9. Influence of sodium hydroxide concentrations in the eluent on fractionation of lignins in draft black liquor. Column Sephadex G-50. (Reprinted with permission from ref. 3. Copyright 1976 Wiley.)...

Figure 11. Fractionation of low molar mass lignin components in kraft black liquor. Column Sephadex G-25. Eluent 0.5M NaOH.

Lignin Concentration. Lignin concentrations have been examined in the range of 10 to 100 g/L. These concentrations represent concentrations normally present in black liquors and therefore are of industrial relevance. Typical lignin concentrations in black liquor range from 50 g/L for 15% solids to over 300 g/L at firing. 

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