Sulfite mill liquor

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. 

Since the prices of petroleum products have soared, valorization of natural resources has intensively attracted the attention of researchers in different fields. To fully utilize wood, which is a renewable raw material, one must make better use of its 25-30% lignin content which forms the principal dissolved material in the spent liquor of chemical pulping processes. The annual production of sulfite pulp in Canada is approximately 2.6 million tons (data based on 1979), thus, at least one million tons of lignosulfonate is produced, representing a potential resource of raw material for other uses. However, among 35 sulfite mills in Canada, only two or three of them possess a recovery system for spent liquor, that means a very small portion of lignosulfonate has been recovered. The recovered lignin has been... 

The requirements for water pollution control have been forcing a shift to concentrating spent sulfite pulping liquor by evaporation, followed by incineration with heat recovery (102). When calcium-base liquor is burned, the sulfur emerges as calcium sulfate and is not available for recycle to the pulping process. The flue gas from such furnaces in Sweden is reported to contain 0.2—0.3% sulfur dioxide, and in one Swedish mill a Bahco wet limestone scrubber is used to treat the gases (115). 

Fermentation methods have traditionally played a dominant role in the industrial processing of the carbohydrate fraction of sulfite spent liquors and have also served as an effective way to reduce the pollution load from the mill. Hence, liquors have mainly been used for producing ethanol and single-ceU protein although this kind of... 

Paper and pulp mill condensate - 189, 206 Paper and pulp mill gas, noncondensable 203 Paper, bleach solutions - 541, 693, 694, 724 Paper, groundwood pulp stocks - 541 Paper machine - 204 Paper mill liquor - 204, 206, 539, 724 Paper, neutral sulfite Cooking liquor - 541 Pulp stocks - 542 Spent liquor - 542 Paper, paperboard waste 542 Paper, parchmentizing - 542 Paper pulp, bleached - 694 Paper pulp slurry 694 Paper, sizing solution - 543 Paper stock 694 Paper, white water Acid - 543 Groundwood - 543 Neutral sulfite - 543 Newsprint - 543 Paperboard 544 Soda - 544 Sulfate - 544 Peracetic acid - 30 Parachloride 230... 

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. 

Several units are used for sulfite-paper-mill waste-liquor disposal. At least six units are used for oil-refinery wastes, whicdi sometimes include a mixture of liquid sludges, emulsions, and caustic waste... 

Milled wood lignin was mixed with the crude enzyme solution of Tram-ties versicolor extracellular phenoloxidases produced on spent sulfite liquor in a ratio of approximately 2 1. This comprised the main part of the two-component bio-adhesive. Industrial particles were bonded with 15% bioadhesive under conventional pressing conditions to have 19 mm particle boards (40 x 50 cm) of the properties described in Table IV. The bonding reaction (crosslinking) took place in aqueous solution at room temperature. If conventional pressing technology is applied, the temperature should be elevated in order to maintain water evaporation within a reasonable press time. 

Paper Products. Paper (qv) products account for about 2% of sulfur demand. The laigest single segment of demand is in the manufacture of wood pulp by the sulfite process (see Pulp). In this process, the main sulfur intermediate is sulfur dioxide, which is generally produced at the plant site by burning elemental sulfur. Some sulfur dioxide, however, is produced as a by-product at smelter operations, purified and liquefied, and shipped to the pulp mills. The sulfur dioxide is converted to sulfiirous acid, and the salt of this acid is a principal component of the cooking liquor for the sulfite process. 

For calcium-base liquor, the gas is passed through towers packed with limestone with water flowing down through the tower. Because of the limited solubility of calcium bisulfite [Ca(HS03)2], the pH of the liquor is very low (about 2), and free sulfurous acid is present. This usually is called the acid sulfite process. As mentioned before, calcium-base mills have essentially disappeared in the United States. 

Talodura. The Talodura process, used in syrup clarification, consists of using a combination of sulfite clarification followed by subsequent clarification of the evaporated liquor with lime and phosphoric acid to which a flocculant is added. It has led to improvements in the color of the mill white sugar, boiling house recovery, and chemical costs per ton of sugar.46... 

Composition of the adhesive One part spray-dried, milled sulfite liquor containing ca. 20% sugar and 1.5 parts concentrated culture filtrate of Trametes versicolor (grown on 0.1% organosolv lignin in a 25 L fermenter), containing 420 U/mL phenoloxidase activity. 

Mondi sulfite pulp mill South Africa Spent liquor (71 m /m) UF + RO [62] c a>... 

Borregaard Industries Norway, Sarpsborg Ca-sulfite pulp mill spent liquor Tubular UF (1120 mV PCI, GE Osmonics 1981 35.6.1.1 [47,67] "V... 

As early as in the 1970s, DOS reverse osmosis plants were installed in the Toten sulfite pulp mill in Norway and the Reed Lignosol mill in Canada. RO membranes were used to concentrate spent sulfite liquor to help the overloaded evaporation systems of the mill [1]. 

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