Separation of Lignin From Lignocellulosic Materials

Abstract

A method is described for separating lignin from liquid solutions resulting from the pretreatment of lignocellulosic materials such as switchgrass with ammonium hydroxide. The method involves a sequence of steps including acidification, evaporation, and precipitation or centrifugation that are performed under defined conditions, and results in a relatively pure, solid lignin product. The method is tested on ammonium hydroxide solutions containing lignin extracted from switchgrass. Experimental results show that the method is capable of recovering between 66-95% of dissolved lignin as a precipitated solid.

1 . The process of recovering lignin from a biomaterial comprising the steps of:
 providing a lignin-containing cellulosic biomaterial;   treating said cellulosic biomaterial with a solution of ammonium hydroxide, thereby extracting lignin from cellulosic biomaterial and providing an ammonium hydroxide lignin solution;   separating the treated cellulosic biomass from the solution of ammonium hydroxide lignin solution;   evaporating ammonia from the separated ammonium hydroxide lignin solution while maintaining a pH greater than 7.0;   acidifying the separated ammonium hydroxide lignin solution to a pH level below 4.0, thereby forming a colloidal suspension of lignin;   reducing a volume of said colloidal suspension of lignin by evaporation of water, thereby forming a coagulation of particles of lignin within said reduced volume solution;   separating the lignin from the reduced volume solution;   optionally washing the separated lignin with dilute sulfuric acid; and,   drying said lignin.   
     
     
         2 . The process of  claim 1  wherein said treating step with a solution of ammonium hydroxide further includes supplying the ammonium hydroxide at a volume to mass ratio of between about 1:1 to about 16:1. 
     
     
         3 . The process according to  claim 1  wherein said step of evaporating ammonia further includes the step of heating the separated ammonium hydroxide within the solution until a boiling point of the solution reaches about 96 to 98° C. at ambient pressure. 
     
     
         4 . The process according to  claim 3  wherein said acidifying the step is carried out prior to the cooling of the separated ammonium hydroxide lignin solution following evaporating of ammonia. 
     
     
         5 . The process according to  claim 1  wherein said step of reducing a volume of said colloidal suspension of lignin further includes reducing the volume by about 50%. 
     
     
         6 . The process according to  claim 1  wherein said step of separating the lignin from the reduced volume solution further includes separating the lignin by at least one of a centrifugation step or a filtration step. 
     
     
         7 . The process according to  claim 1  wherein said drying step further includes drying the lignin in a vacuum oven at a temperature of less than about 65° C. 
     
     
         8 . The process according to  claim 1  wherein said step of separating the treated cellulosic biomass from the ammonium hydroxide lignin solution is via a filtration step. 
     
     
         9 . The process according to  claim 1  wherein said treating step with a solution of ammonium hydroxide further includes supplying the ammonium hydroxide at a volume to mass ratio of at least about 6:1. 
     
     
         10 . The process according to  claim 1  wherein said treating step with a solution of ammonium hydroxide further includes supplying the ammonium hydroxide with a volume to mass ratio of between about 8:1 to about 16:1.