In black liquor

Table 4 shows the typical ranges of black liquor constituents and characteristics of Kraft evaporator condensates. The composition of liquors may vary significantly, depending upon the type of raw material used. Inorganic constiments in black liquor are sodium hydroxide, sodium sulfate, sodium thiosulfate, sodium sulfide, sodium carbonate, and sodium chloride [11]. 

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. 

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. 

Table 8.4.3. Molecular weight distribution of pine kraft lignin in black liquor measured by ultrafiltration...

Kraft pulping chemical recovery consists of passage of black liquor along with the slurry passes through evaporators, recovery boilers, and causticizers to eventually produce white liquor. Corrosion on the fireside of the recovery boiler is accelerated by the presence of reduced sulfur species. The hydroxide mixtures present in black liquor are extremely corrosive to the recovery boilers made of type 304 stainless steel (37). Several phenomena in the recovery section cause different forms of corrosion such as (i) corrosion under ash build-up (ii) corrosion in the thin condensation layers and (iii) high-temperature metal/gas interactions. 

Figure 3A.4 Abundant aliphatic carboxylic acids in black liquors (see also Table 3A.3).

The resin in the wood of resinous species is dissolved during pulping by alkaline processes with the formation of sodium salts of fatty and resin acids. The presence of these soaps in black liquors facilitates foaming, thereby reducing the efficiency of pulp washing and liquor concentration operations in the pulp mill. Removal of the soap for the production of tall oil reduces these problems. Foaming is encountered from time to time with other species but the causes are not known. 

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