Sulfite pulping decomposition

Figure 2B shows a group of sulfite pulps with the cotton linters pulp shown again for comparison. The USS and BSS pulps, unbleached and bleached spruce sulfite, respectively, are quite similar and fall between the cotton linters pulp and the bleached pine sulfite pulp with respect to both initial decomposition and final residue. 

For the preparation of paper, the incrustations must be removed. To accomphsh this, there are two main processes decomposition with sodium hydroxide ( soda pulp ) or with calcium hydrogen sulfite ( sulfite pulp ). The soda pulp process generates water-soluble phenolates of lignin. In a remarkable manner, the hydrogen sulfite process yields benzylsidfonic acids (Holmberg decomposition). 

Solid Calcium Sulfite. Recent thermodynamic studies of calcium sulfite by mass spectroscopy indicated that calcium sulfite dissociates into calcium oxide and sulfur dioxide (12). Under atmospheric pressure, this dissociation reaction is slow in the range below 250°C. We find under these conditions substantial decomposition of sulfite, yielding sulfate, elemental sulfur as well as thiosulfate. These observations are consistent with experiments by Brewer (13), and confirm old observatons made by wet-analysis of these complex solids (14). Our work confirms seventy year old literature reports which suggested evidence for thiosulfate, trithionate and dithionate in old pulping sulfite liquor which yellows when kept in air-free, sealed ampules (15-18). 

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