Sulfite pulping active base

Although acidic pulping methods have largely been displaced over the past 50 years by neutral and alkaline processes, there is still a significant amount carried out. Acid sulfite pulping uses combinations of sulfur dioxide and water at high temperatures and pressures. An appropriate base is used to control the pH and, although usually acidic, it is possible to perform these reactions at neutral or even alkaline pH. The most active nucleophile present is the bisulfite ion,... 

Semi chemical pulps are usually prepared by the neutral sulfite semichemical (NSSC) process, although modifications of the full chemical processes can be used. Active pulping chemicals are (in the sodium-base NSSC process) sodium sulfite buffered with sodium bicarbonate (pH 7,0-9.0) and (in the ammonium-base NSSC process) ammonium sulfite with ammonium hydroxide used as a buffer. Defiberization is usually accomplished by attrition mills of the disk type. 

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