Sulfite pulping free sulfur dioxide

The free sulfur dioxide in the sulfite pulping liquor promotes hydrolysis of the more easily hydrolyzable constituents of wood. A wood such as spruce, which contains 70.1% carbohydrate substances, of which 85.3% are potentially fermentable, gives a 50% yield of a pulp containing 97.7% carbohydrate, of which about 80% is fermentable. The... 

A technique known as flash roasting was developed in the 1920s. Finely ground pyrites or other sulfide ores fall through a chamber in which air is introduced countercurrenfly from the bottom. The particles bum at 1000—1100°C yielding sulfur dioxide free of sulfur trioxide at a concentration suitable for making sulfuric acid or for sulfite pulping (260). 

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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