Patent ID: 8613781

Claim:
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; 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 precipitate in a residual liquid, said granular lignin solids having a moisture content of less than about 60%; and separating at least a portion of the residual liquid from the granular lignin solids to obtain dewatered granular lignin solids and clarified residual liquid.