Separation of black liquor to produce lignins substantially free of sodium

Abstract

The method described herein will produce depolymerized lignins substantially free from sodium compounds. Black liquor supplied from a pulping process is utilized for providing a mixture of depolymerized lignins dispersed and dissolved in a solution containing sodium hydroxide. The mixture is then separated to form depolymerized lignins and a solution containing sodium hydroxide. Following separation, the depolymerized lignins are then extracted with water to produce an extractate containing sodium compounds. The extracted depolymerized lignins, containing sodium compounds, are then reacted with an acid to form sodium salts to form a slurry. The slurry containing sodium salts is, by means of a salt splitting method, separated from the extracted depolymerized lignins to produce substantially sodium free depolymerized lignins. The separated solution containing sodium hydroxide is combined with the extractate, and the combination, subsequent to removal of water, is suitable for recycle to depolymerize, disperse and dissolve additional lignins. As a result, depolymerized lignins substantially free of sodium compounds are produced, in addition to a solution to produce black liquor.

What is claimed is:  
     
         1 . A method to produce depolymerized lignins substantially free from sodium compounds, which comprises: 
 providing black liquor containing depolymerized lignins and sodium hydroxide and,    providing membrane means for separation of depolymerized lignins from said black liquor, and    separating said black liquor from said depolymerized lignins and producing a filtrate containing sodium hydroxide, and    extracting with water the heretofore separated depolymerized lignins containing sodium compounds to provide an extractate containing sodium compounds and a raffinate containing depolymerized lignins, and    combining said filtrate containing sodium hydroxide with said extractate to form a solution containing sodium hydroxide, and    combining an acid with said raffinate of heretofore extracted depolymerized lignins to form a slurry of sodium salts and the depolymerized lignins, and    subjecting said slurry to salt spiting to substantially remove salts and produce depolymerized lignins substantially free of sodium whereby depolymerized lignins substantially free of sodium compounds is produced and a solution of sodium hydroxide is produced suitable for recycle to produce black liquor.    
     
     
         2 . The method as described in  claim 1  wherein said membrane means for separation of said black liquor is selected from the group of membranes including diffusion membranes and nano filtration membranes including an individual or a combination thereof.  
     
     
         3 . The method as described in  claim 1  wherein said slurry containing sodium salts is dependent on salt splitting bipolar membranes to create sodium hydroxide and create an acid from the slurry containing sodium salts and produce depolymerized lignins substantially free of sodium.  
     
     
         4 . The method as described in  claim 3  wherein the depolymerized lignins substantially free of sodium is subjected to ion exchange resins to scrub remaining sodium salts from depolymerized lignins to create depolymerized lignins presumably free of sodium salts.  
     
     
         5 . The method as described in  claim 1  wherein said slurry, containing sodium salts, is subjected to salt splitting ion exchange resins to remove sodium salts and produce depolymerized lignins presumably free of sodium salts.  
     
     
         6 . The method as described in  claim 1  wherein said acid is selected from the group of inorganic acids including sulfuric acid and hydrochloric acid including an individual or a combination thereof.  
     
     
         7 . The method as described in  claim 1  wherein the extraction with water is accomplished by weak black liquor obtained from pulp washing.  
     
     
         8 . The method as described in  claim 1  wherein said slurry is of Ph about 2 to about 4.  
     
     
         9 . The method as described in  claim 1  wherein said solution containing sodium hydroxide is combined with sodium hydroxide to increase concentration of sodium hydroxide within the solution.  
     
     
         10 . The method as described in  claim 1  wherein said solution containing sodium hydroxide contains sodium sulfide.  
     
     
         11 . The method as described in  claim 1  wherein heretofore combined sodium hydroxide solution is reacted with hydrogen sulfide to form sodium sulfide.  
     
     
         12 . The method as described in  claim 1  wherein said black liquor is supplied from kraft pulping digestion.  
     
     
         13 . The method as described in  claim 1  wherein said black liquor is supplied from soda pulping digestion.  
     
     
         14 . The method as described in  claim 1  wherein said depolymerized lignins substantially free of sodium are subjected to flue gas to remove water from the depolymerized lignins.  
     
     
         15 . The method as described in  claim 14  wherein the depolymerized lignins are utilized as a fuel.  
     
     
         16 . The method as described in  claim 1  wherein said solution containing sodium hydroxide is concentrated by removal of water by a multiple-effect evaporator to produce a concentrated solution containing sodium hydroxide.  
     
     
         17 . The method as described in  claim 16  wherein the concentrated sodium hydroxide solution contains about 40% sodium hydroxide to about 10% sodium hydroxide.  
     
     
         18 . The method as described in  claim 16  wherein the heretofore concentrated solution is substantially separated from tall oil contained in the concentrated sodium hydroxide solution.  
     
     
         19  The method as described in  claim 18  wherein the heretofore separated tall oil is reacted with an acid to form a phase of sodium salts and a phase of crude tall oil.  
     
     
         20 . The method as described in  claim 1  wherein the extraction with water is accomplished by counter flow of water.