Kraft pulping cooking 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... 

Consid - the Kraft pulping process shown in Fig. 8.8 (Dunn and El-Halwa, 1993). The first step in the process is digestion in which wood chips, containing primarily lignin, cellulose, and hemicellulose, are cooked" in white liquor (NaOH, Na2S, Na2C03 and... 

Black liquor is 13 to 17% strength, rinsed extract from washed and cooked woodchip pulp, produced in the Kraft pulping process. This... 

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]. 

Hodson PV, Maj MK, Efler S, Bumison BK, van Heiningen ARP, Girard R, Carey JH. 1997. MFO induction in fish by spent cooking liquors from kraft pulp mills. Environ Toxicol Chem 16 908-916. 

Figure 7-32 illustrates the glucomannan and xylan losses during kraft pulping of pine wood. As can be seen, an appreciable portion of the lost xylan is actually not degraded but dissolves in the cooking liquor as a polysaccharide. The amount of dissolved xylan reaches a maximum around the midpoint of the delignification process. 

Of the stabilization methods, the polysulfide pulping process is of practical importance. The influence of polysulfides is based on a specific oxidation of the end groups to carboxyl groups via glucosone intermediates (cf. Section 8.1.3). Polysulfides can be prepared by catalytic oxidation of sulfide in the white liquor or by adding elemental sulfur into the kraft cooking liquor ... 

In kraft pulping, the resin and fatty acids which are either free or liberated in the hydrolysis of fats and waxes are dissolved as sodium salts ("soaps") in the cooking liquor. Especially the resin acid salts are effective emulgators... 

Fourdrinier machine—The machine that forms paper from pulp, named after the English family that financed its development in the early 1 800s. Furnish—Specific combination of pulp and other ingredients used to make a particular kind of paper. Kraft process—process in which sodium sulfate is reduced by heating with carbonaceous matter in a furnace to form sodium sulfide, which is then used in a water solution with sodium hydroxide as a cooking liquor. The wood pulp is then cooked under pressure and at high temperatures. The kraft process, also known as the sulfate process, has a less corrosive influence on iron and steel than the sulfite process. 

FIGURE 10.3 A laboratory flow-through kraft cook of softwood with a lowered concentration of hydrosulfide ions present in the cooking liquor during the time interval of 60-105 min, after the start at 70°C, corresponding to a temperature interval of 130-170°C -H 5 min at 170°C. Pulping selectivity is measured as pulp viscosity as a function of kappa number. (Sjdblom, K., Mjdberg, J., and Hartler, N., Pap Puu, 65, 227-240, 1983.)... 

---