Processes Starting with Sulfite Waste Liquor

Processes Starting with Sulfite Waste Liquor 

The basis of the sulfite pulping process is the discovery by Tilghman in 1866 that white cellulose fibers are obtained by cooking wood under pressure in an aqueous solution of calcium bisulfite Ca(HS03)2. In chemical terms, the process is founded on the fact that lignin, the solid binder of wood, reacts with sulfite to form water-soluble sulfonic acids. In this fash- 

The reaction requires a temperature in the order of 140 °C, and as it is acid, pentosan in the wood is hydrolyzed to pentose, and some of this pentose is dehydrated to furfural. Against this background, there has been a persisting interest in converting the pentose of sulfite liquor to furfural, and to recover the furfural already existing in the liquor. 

Strictly speaking, the interest for furfural in the pulping industry is essentially limited to the given calcium sulfite process, where disposal of the spent liquor is a problem. In the more modem magnesium process, the spent liquor is readily thickened and then burnt to fully recover MgO and SO2 used in starting the process  

in the magnesium process the agents required to digest the wood can be used in a closed circle, so that there is no effluent. Thus, there is no interest for doing anything with the pentose and the furfural in the magnesium liquor. They are simply burnt. 

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Processes Starting with Sulfite Waste Liquor... 

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