Sulfite process, wood pulping

Highly bleached and purified sulfite process wood pulp suitable for conversion into products such as rayon, viscose, acetate, and cellophane... 

Sulfite process wood pulp with or without bleaching used for products such as tissue papers, fine papers, and newsprint... 

Paper Products. Paper (qv) products account for about 2% of sulfur demand. The largest 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 andUquefied, and shipped to the pulp mills. The sulfur dioxide is converted to sulfurous acid, and the salt of this acid is a principal component of the cooking Hquor for the sulfite process. 

Sulfite pulps have less color than kraft pulps and can be bleached more easily however, they are not as strong. The efficiency and effectiveness of the sulfite process is also dependent on the type of wood furnish and the absence of bark. For these reasons, the use of sulfite pulping has declined in comparison to kraft pulping over time. 

Attisholz A process for recovering valuable waste products from the sulfite process for making wood pulp. This includes methanol, cymenes, and furfural. Developed in Switzerland. 

Detailed discussion of the classical wood pulping processes - e.g., the Sulfite and Kraft processes - is available in the literature [14]. Pre-treatments that aim to facilitate the fermentation of lignocellulosic materials are also discussed elsewhere [49, 62-64]. 

Wood chips are processed in mild chemical liquor and subjected to mechanical refining using disc refiners. Semichemical pulping liquors have variable composition ranging from sodium hydroxide alone, alkaline sulfite (sodium sulfite - - sodium carbonate), mixtures of sodium hydroxide and sodium carbonate, to Kraft green or white liquors [3]. Sodium sulfite/ sodium carbonate liquor is most commonly used and the pulp product obtained thereafter is referred to as neutral sulfite semichemical (NSSC) pulp. 

Chemical pulping of wood is commonly carried out according to the Kraft (sulfate) or sulfite processes [13]. These methods are described in the following subsections. 

VIII. Hydrolysis of Wood During Sulfite Process Pulping... 

High-yield chemical pulps can be produced by the soda, kraft, or sulfite processes, in which chemical use and digestion time and/or temperature are suitably reduced to effect a milder cook than used for full chemical pulps. Mechanical defibrators are used to complete the separation of wood fibers not accomplished by the chemical action... 

SULFITE PULP PROCESS. See Pulp (Wood) Production and Processing. 

Chemical Wood Pulp Pulp obtained from wood by the sulfite, sulfate or soda process(See Wood Cellulose under CELLULOSE)... 

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