Sulphite Pulping Processes

In the sulphite pulping process wood cut into pieces is subjected to kiering in a calcium bisulphite solution under a pressure of 3-8 kg/cm2, at 120-145°C for 7-30 hr. The higher the temperature, the shorter the time of boiling. Substances accompanying cellulose dissolve in the liquor. Lignin is converted into a soluble lignin sulphonic acid. Cellulose is isolated from the solution, known as sulphite cellulose lye, and washed with water. 

Rychtera, M., Barta, J., Fiecter, A., and Einsele, A. A. (1977). Several aspects of the yeast cultivation on sulphite waste liquors and synthetic ethanol. Process Biochem. 12(2), 26-30. Rydholm, S. A. (1965). "Pulping Processes." Wiley (Interscience), New York. 

Chemical pulps are prepared by the digestion of wood chips with chemicals at high temperature (170-180°C) until much of the lignin has been removed. There is a concomitant loss of hemicelluloses, because of polysaccharide degradation due to chemical attack. Therefore yields are low, from 45-50%. Chemical pulping falls into two main classes, those based on pulping with sulphite liquors at various pH levels, and alkaline pulping of which the kraft process is by far the most important. 

Semichemieal pulps produced by the sodium bisulphite and neutral sulphite-anthraquinone pulping processes at 75% yields have properties that are rather similar to a lower yield chemical pulp shown in Table 13.4. The pulp eharaeteristies from this proeess are of considerable interest, since it has been shown that ehemical pulps made by the so-ealled ASAM process, in which the wood is delignified with a liquor containing sodium sulphite, sodium carbonate or sodium hydroxide and methanol (c. 40% of the liquor by volume) with a trace of anthraquinone ean be delignified more rapidly and to a lower kappa number (this surrogate measure of the lignin content of pulp is explained in the appendix) than pulps made in the absenee... 

Conventional sulphite pulping processes use aqueous solutions of sulphur dioxide at various pH levels. Sulphite solutions differ in their content of sulphur dioxide, bisulphite ions and sulphite ions, as shown in Figure 13.9. At a low pH of between 1 and 2 the sulphite liquor contains about 50% sulphurous acid and bisulphite ions respectively at a pH of 4 to 5 it contains approximately 100% bisulphite ions and at a pH of 8 to 10 it consists almost entirely of sulphite ions. When allowance is made for chemical charge, it is the pH and the relative amounts of bisulphite and sulphite ions that chiefly control the mode of pulping. In the original acid sulphite process... 

The soda method was also attempted in Finland in the 1870s and early 1880s. Theodor Hoffding and another Danish engineer were involved in setting up the first two pulp mills close to Viipuri, near the eastern border. However, commercial production first started in 1886 in the Walkiakoski paper mill, a Finnish company in the western part of the country that employed the sulphate process. Due to technical setbacks, the output remained modest for many years. Paper mills in Nokia and Kuusankoski adopted the other process, sulphite pulping, in 1885, and succeeded much better. Imitators followed, and for several decades that process dominated chemical pulping in Finland. ... 

Pulping of hgnocellulosic materials results in fibres termed pulps. Pulping of wood can generally be divided into mechanical and chemical pulping or mixtures of both types. In chemical pulping, nowadays the alkaline Kraft sulphate pulp process is predominant compared to the sulphite process. 

Both fungi and yeasts have been grown commercially on sulphite waste liquors. However, the gradual change in pulping from sulphite to Kraft processes has reduced availability to such an extent that most commercial yeast plants in North America have closed down. One commercial plant to produce 10,000 tons of fungal protein has been set up in Finland. Similarly, a process to use starch wastes is operating in Scandinavia. 

The direct measurement of pH at elevated temperatures and pressures has been made possible through the development by Ingruber of high-temperature electrode systems for use in the sulphite pulping process of the paper industry [68]. Lietzke and Tarrant have demonstrated the applicability of Ingruber s electrode system to the measurement of the pH of... 

Alternatively cellulose is produced from wood via wood pulp. A number of processes are used in which the overall effect is the removal of the bulk of the non-cellulosic matter. The most widely used are the sulphite process, which uses a solution of calcium bisulphite and sulphur dioxide, the soda process using sodium hydroxide and the sulphate process using a solution of sodium hydroxide and sodium sulphide. (The term sulphate process is used since sodium sulphate is the source of the sulphide.) For chemical purposes the sulphite process is most commonly used. As normally prepared these pulps contain about 88-90% alpha-cellulose but this may be increased by alkaline purification and bleaching. 

Cellulose produds There is little scope for the use of austenitic steels in the alkali processes for the digestion of wood pulp, but both molybdenum-free and molybdenum-bearing steels are extensively used for sulphite pulp digestion, choice depending on concentration, temperature and working experience. 

The second option involves the use of a CIO2 scrubber. This is a technique presently used in the paper and pulp industry. In the scrubber, the chlorine dioxide reacts with another chemical, such as a sulphite, DMSO, white spirit or an alkaline hydrogen peroxide solution. The hydrogen peroxide solution is most suited to the process described in this chapter as there are no waste streams. The reaction of chlorine dioxide with the alkaline hydrogen peroxide solution is rapid [10]. The reaction equation is as follows ... 

Provincial Papers Inc. is located on Lake Superior at Thunder Bay, Ontario. Sulphite/mechanical processes are used in the production of coated and uncoated fine papers from purchased kraft pulp and groundwood from softwood sources. Secondary treatment is carried out in an aerated lagoon system (a serpentine basin) and was installed at the mill in late 1995 (see Fig. 2). Effluent flow rates ranged from 25,000 to 35,000 m3/day in the two years following installation of secondary treatment. Treated effluent is discharged into the inner basin of Lakehead Harbour, a sheltered embayment created by a series of breakwaters. The Current River is the other major discharge to the immediate area of the mill outfall. A description of the EEM study is found in ESG (2000). 

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