Pulping, liquors from kraft

Several hundred low molecular mass lignin-derived components containing one or two aromatic rings have been identified in kraft pulping liquors from spruce and birch respectively [86, 87]. Some prominent structures are shown in Fig. 9.16. 

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. 

Wood is the raw material of the naval stores industry (77). Naval stores, so named because of their importance to the wooden ships of past centuries, consist of rosin (diterpene resin acids), turpentine (monoterpene hydrocarbons), and associated chemicals derived from pine (see Terpenoids). These were obtained by wounding the tree to yield pine gum, but the high labor costs have substantially reduced this production in the United States. Another source of rosin and turpentine is through extraction of old pine stumps, but this is a nonrenewable resource and this industry is in decline. The most important source of naval stores is spent sulfate pulping liquors from kraft pulping of pine. In 1995, U.S. production of rosin from all sources was estimated at under 300,000 metric tons and of turpentine at 70,000 metric tons. Distillation of tall oil provides, in addition to rosin, neady 128,000 metric tons of tail oil fatty acids annually (78). 

This process also transfers heat from the flue gases to the black liquor so that it leaves the last stage of evaporation hot. At this point, it is referred to as strong black liquor. Addition of make-up chemicals, either sodium sulfate ( salt cake ) or sulfur as necessary is carried out at this stage to replace any losses of sodium and sulfur occurring elsewhere in the process. In fact, sulfate process is synonymous with kraft process because the primary make-up chemical requirement of the kraft process is sodium sulfate, although sodium sulfate is not an active constituent of kraft pulping liquor. 

FIydroxybutanoic acid is a major organic component of kraft black liquors from hardwood pulping, but is formed only in trace quantities from the degradation of glucose polymers. It seems likely that it arises from the xylan by a process along the lines of that illustrated in Figure 6.13. 

Research in modern times has identified many thousands of compounds in extractives research. These extractives are produced in varying quantities depending on the demand and their natures. Many classes of wood extractives are covered in other sections of this book natural exudates in Chap. 1.1 tail-oil constituents as extractives from softwoods by kraft pulping liquor in Sect. 10.1 and pharmaceuticals such as cascara extract in Sect. 10.6. In this section I will discuss successful softwood and hardwood extractives utilization and prospects for their continued and expanded uses. 

Alen R, MohanenV-P, Sjostrom E. Potential recovery of hydroxy acids from kraft pulping liquors. Tappi J1986 69(2) 76-8. 

Tall oil rosin is obtained from crude tall oil obtained from the Kraft (sulphate) pulping of various coniferous trees in the paper manufacturing industry. During the Kraft pulping process the fatty acids and the resin acids from the coniferous wood are saponified by the alkaline medium. On concentration of the resulting pulping liquor, the sodium soap of these mixed acids rises to the surface from where they are skimmed out. By acidification of this material with sulphuric acid, the crude tall oil is obtained. Fractional steam distillation of the crude tall oil allows the separation of the tall oil fatty acids and the tall oil rosins [21]. 

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... 

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

The kraft process evolved from the soda process. The soda process uses an alkaline liquor of only sodium hydroxide (NaOH). The kraft process has virtually replaced the soda process due to the economic benefits of chemical recovery and improved reaction rates (the soda process has a lower yield of pulp per pound of wood furnish than the kraft process). 

The addition of anthraquinone (a chemical catalyst produced from coal tar) to the pulping liquor has been shown to speed up the kraft pulping reaction and increase yield by protecting cellulose fibers from degradation. The anthraquinone accelerates the fragmentation of lignin, allowing it to be... 

The effect of color production from carbohydrate transformation in an alkaline pulping process, such as kraft pulping, is illustrated in Table III. Cotton linters, which originally had a brightness of 90.5%, were treated for 4 h at 180° with kraft liquor, with and without additives. Brightness was measured on paper made from the resulting, washed pulp. 

Wood chips are processed in mild chemical liquor and subjected to mechanical refining using disc refiners. Semichemical pulping liquors have variable composition ranging from sodium hydroxide alone, alkaline sulfite (sodium sulfite - - sodium carbonate), mixtures of sodium hydroxide and sodium carbonate, to Kraft green or white liquors [3]. Sodium sulfite/ sodium carbonate liquor is most commonly used and the pulp product obtained thereafter is referred to as neutral sulfite semichemical (NSSC) pulp. 

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]. 

Kringstad, K.P. Ljungquist, P.O. de Sousa, F. Stromberg, L.M. Identification and mutagenic properties of some chlorinated aliphatic compounds in the spent liquor from Kraft pulp chlorination. Environ. Sci. Technol. 1981, 15, 562-566. 

Dimethyl Sulfoxide, Dimethyl sulfoxide is manufactured from dimethyl sulfide (DMS), which is obtained either by processing spent liquors from the kraft pulping process or by the reaction of methanol or dimethyl ether with hydrogen sulfide,... 

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