Commercial Spent Pulping Liquors

Commercial lignosulfonates (also called lignin sulfonates and sulfite lignins) are by-products of the treatment of pulp. One of the methods of isolating and purifying them is to add excess slaked lime to spent sulfite liquor. This precipitates calcium lignosulfonates, which are removed by filtration [32.29]. 

The effect of various operating conditions on the recovery of the pulping chemicals and heat values in the case of a neutral sulfite semichemical (NSSC) spent liquor has been described recently (I). The thermodynamic equilibria and kinetics of gasification which seem to apply to this same set of experiments were discussed elsewhere (9). Gas compositions and yields examined in the latter study showed that under some of the operating conditions investigated, commercially significant quantities of ammonia and methanol synthesis gases could be produced from NSSC-type spent liquors. 

Lignin also is commercially used as a resin for paper laminates. Its low cost and availability as a by-product in pulp manufacture make it attractive. One of the most successful products is made with lignin recovered from the spent liquor of the soda pulping process. The lignin may be added to the pulp suspension in solution and precipitated directly among the fibers, or added in a preprecipitated form. 

The -SO3H (or Na) may be attached to the ring or the side chain of the phenylpropane structure of -> lignin but is still part of a polymeric network. Commercial 1., gained from sulfite pulping (- paper), may be either spent liquor or purified 1. or their derivatives. They are soluble in water over the total pH range but not in organic solvents. 

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