Lignin Dewatering Process

A process for treating a substantially spent, alkaline and non-sulphite digestion liquor obtained from digestion of a cellulosic biomass, said digestion liquor containing lignin as a potential precipitant upon acidification of said digestion liquor, leaving substantially clarified residual liquid, said process comprising:

• mixing into said spent digestion liquor a water soluble, surface active, polymeric, coagulant agent;
• acidifying the so mixed liquor to a pH below 7 to separate the lignin and other organic compounds and to coagulate them as solids which tend to float to the surface of the residual liquid to form a lignin plastic mass having a moisture content above about 60%;
• heating the lignin plastic mass to a temperature above a critical temperature;
• cooling the heated lignin plastic mass to a temperature below the critical temperature thus causing the lignin plastic solids to agglomerate into lower moisture granular lignin solids and a residual liquid, said lower moisture granular lignin solids having a moisture content of less than about 60%;
• and
• separating at least a portion of the residual liquid from the lower moisture granular lignin solids to obtain dewatered granular lignin solids.

A process for treating a substantially spent, alkaline and non-sulphite digestion liquor obtained from digestion of a cellulosic biomass, said digestion liquor containing lignin as a potential precipitant upon acidification of said digestion liquor, leaving substantially clarified residual liquid, said process comprising:

• mixing into said spent digestion liquor a water soluble, surface active, polymeric, coagulant agent;
• making a heated acidified dilution liquid comprising an acid and clarified residual liquid;
• mixing the heated acidified dilution liquid and the spent digestion liquor into which the water soluble, surface active, polymeric, coagulant agent has been mixed to produce a mixture having a pH below 7 and a temperature above a critical temperature;
• cooling the mixture to a temperature below the critical temperature thus causing the lignin to agglomerate into granular lignin solids as a precipitant in a residual liquid, said granular lignin solids having a moisture content of less than about 60%;
• separating at least a portion of the residual liquid from the granular lignin solids to obtain dewatered granular lignin solids and clarified residual liquid;
• and
• adding acid to at least a portion of the separated clarified residual liquid and heating at least one of the portion of the separated residual liquid, the acid, and the mixture of the separated residual liquid and the acid, to form additional heated acidified dilution liquid.