Kraft spent liquor

TABLE 7-8. Typical Composition of the Organic Material in Pine Kraft Spent Liquor... 

Chemical recovery ia sodium-based sulfite pulpiag is more complicated, and a large number of processes have been proposed. The most common process iavolves liquor iaciaeration under reduciag conditions to give a smelt, which is dissolved to produce a kraft-type green liquor. Sulfide is stripped from the liquor as H2S after the pH is lowered by CO2. The H2S is oxidized to sulfur ia a separate stream by reaction with SO2, and the sulfur is subsequendy burned to reform SO2. Alternatively, ia a pyrolysis process such as SCA-Bidemd, the H2S gas is burned direcdy to SO2. A rather novel approach is the Sonoco process, ia which alumina is added to the spent liquors which are then burned ia a kiln to form sodium aluminate. In anther method, used particulady ia neutral sulfite semichemical processes, fluidized-bed combustion is employed to give a mixture of sodium carbonate and sodium sulfate, which can be sold to kraft mills as makeup chemical. 

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... 

After conversion to the use of sodium-based chemicals, spent liquor could be incinerated, and sulfur dioxide, sodium sulfate, carbonate, or sulfide could be recovered. These compounds could be sold for use at nearby kraft mills or for other industrial uses. 

Reducing smelting furnaces that produce a high-sulfidity, kraft-like green liquor are now employed at sodium-based sulfite mills. U.S. EPA anticipates that it would be necessary to replace the existing recovery boilers at ammonia-based mills if chemical substitution to a sodium base were employed. Additionally, it is likely that, because the heat value of sodium spent liquor is lower than ammonia spent liquor, evaporator modification may he required if excess capacity does not already exist. 

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

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. 

Figure 10. Fractionation of spruce spent sulfite liquor and pine kraft black liquor.

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,... 

The remaining pair of acidolysis products isolated from Sephadex fraction B, as already mentioned, consisted of 4,4 -dihydroxy-3,3 -dimethoxystilbene (XXV) and 1,2-bisguaiacylpropanone (XXVI). The stilbene (XXV) was isolated several years ago from sulfite-spent liquor which had been heated with alkali (37) as well as from alkali-heated wood (J7, J9, 40) it has also been detected in kraft liquor (10). The structure of the previously unknown ketone (XXVI) (m.p., 121-122°C.) was derived from analytical and spectral data and established by synthesis (30). 

An essential factor in the kraft process has been the recovery of the spent liquor from the cooking process. The black liquor removed from the... 

A furnace similar to the Tomlinson kraft recovery furnace is used for the combustion of magnesium-based sulfite spent liquors. In this case, however, no smelt is obtained instead the base is completely recovered as magnesium oxide in dust collectors the sulfur escapes as sulfur dioxide and is absorbed from the combustion gases in scrubber towers. However, because magnesium hydroxide has a very low solubility in water, a complete recovery of sulfur dioxide meets difficulties. 

Krmgstad KP, Morck R (1983) nC NMR spectra of kraft lignins Holzforschung 37 237-244 Landucci L (1984) nC NMR characterization of soda and soda/AO spent liquor fractions J Wood Chem Technol 4 171-186... 

A feature of the kraft process vital to continued success is its integral, well-tested chemical recovery system. The digestion liquor for each batch of chips to be pulped is mainly obtained from the chemicals recovered from the spent liquor of previous digestions, and has approximately the composition given in Table 15.8. For kraft pulping it is usual to specify all of the components of the digestion liquor on a NaiO equivalent basis. This puts all the active constituents on the same sodium ion content basis. Thus, the actual concentration of sodium hydroxide present for a 73 g/F, NaiO equivalent is given by Eq. 15.12. 

In the kraft pulping of softwoods the resin acids and fatty acid esters present consume alkali required for delignification and are therefore undesirable. These can be recovered as tall oil by concentration of the spent liquor, separating off the acid soap (which also contains neutral components) and acidifying the sodium salts with sulphuric acid from which a blend of resin acids, fatty acids and neutrals is obtained. 

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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