Kraft spent pulping liquors

COMPOSITION OF SPENT PULPING LIQUORS 10.4.1 Kraft Pulping Liquors (Black Liquors)... 

While sulfite pulping is less popular than Kraft pulping, it is more prevalent in the production of dissolving pulps. Further, sulfite pulping permits recovery of ethanol from the spent pulping liquor before incineration, as is... 

A problem with NSSC pulping is the difficulty of either recycle or disposal of the waste (spent) pulping liquor. It can be concentrated and burned but this produces sodium sulfate, not sulfite suitable for reuse. If there is a kraft pulping operation near the semichemical pulping operation, the sodium sulfate may provide both sodium ion and sulfate make-up chemical for the kraft... 

FIGURE 15.8 Cyclic process for recovery of chemicals and energy from the spent pulping liquor of the kraft process. 

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. 

TABLE 8-4. Composition of the Organic Material in Spent Bleach Liquor from Chlorination and Alkali Extraction Stages (Pine Kraft Pulp)a... 

The spent black liquor from the kraft pulping of pines contains the less volatile products of the wood resin in the form of sodium salts or soaps. The liquor first is concentrated in multiple-effect evaporators, and then the concentrate is sent to settling tanks. The soaps rise to the surface, are skimmed off, and then are acidified with sulfurous or sulfuric acid. The crude tall oil rises to the top and is mechanically separated. Crude tall oil from southern pines contains 40-60 percent resin acids and 40-55 percent fatty acids with 5-10 percent neutral substances. These components are separated by fractional distillation under vacuum. 

The process is conducted at the high pH in the presence of sodium sulfide, sodium hydrosulfide, and sodium hydroxide at 150-180°C for about 2 hours (Fig. 33.26). Along with the primary cellulose product, the process generates a solution containing dissolved lignin, most of the wood s hemicellu-loses, and spent pulping chemicals ( black liquor ). This solution is used in the kraft recovery boiler as a source of power for the mill and fuel for chemical recovery operations crucial to economic operation. The chemistry of pulping reactions has been the subject of much study, and summaries are available the literature.425 127... 

Calcium Lignosulfonate occurs as a brown, amorphous polymer. It is obtained from the spent sulfite and sulfate pulping liquor of wood or from the sulfate (kraft) pulping process. It may contain up to 30% reducing sugars. It is soluble in water, but not in any of the common organic solvents. The pH of a 1 100 aqueous solution is between approximately 3 and 11. 

Occurrence of alkyl polychloronaphthalenes (RPCN) in spent bleach liquors was first time reported in 1979 [8], Their structure was deduced to contain one methyl and one isopropyl group [8] which indicates origin from wood. Later analyses indicated that most common RPCNs in kraft pulp mill effluents and sludges were mono- to tetramethyl polychloro naphthalenes (C1-4PCN) [41-45]. In sludges their total contents were 28-72 ng g1 dw and in effluents only trace levels of a few ng 1 1 [42, 45]. Their origin was suggested to be chlorination of alkyl naphthalenes abundant in oil-based defoamers used in pulp mills [42]. 

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). 

A cooperation agreement was made in 1973 between DDS-RO and the Finnish Pulp and Paper Research Institute with the aim to develop products and processes on the basis of membrane filtration of effluents from the pulp and paper Industry. The cooperation with Dr. Kaj Forss section at FPPRI has been very successful. For instance, through an extensive development program UF has been found to be a feasible tool for the preparation of lignin for the Karatex ( ) plywood binder. This adhesive, which is made from ultrafiltered spent sulfite liquor (SSL) or kraft black liquor (KBL), can be used for partial replacement of the much more expensive petroleum based phenol-formaldehyde resin in plywood and other wooden boards. 

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