Process for lowering molecular weight of liquid lignin

Abstract

Processes and systems for lowering molecular weight of lignin generally includes first isolating a dense liquid lignin phase from black liquor and subjecting the dense liquid lignin phase to a temperature and pressure for a period of time to effect an average molecular weight distribution of the lignin. Solid lignin produced with the lowered molecular weight is then isolated. The systems and processes may further include an oxidation unit for oxidizing the black liquor and intermediate streams to remove or mitigate malodorous or toxic emissions.

What is claimed is: 
     
         1 . A process for reducing molecular weight of lignin comprising:
 carbonating a black liquor stream at a temperature between about 80° C. and 200° C. and adjusting the pH above 10;   recovering a dense liquid-lignin phase, wherein lignin within the dense liquid-lignin phase has a first average molecular weight; and   exposing said dense liquid-lignin to heat and pressure for a predetermined period of time to reduce an average molecular weight of said dense liquid-lignin to a second average molecular weight, wherein the second average molecular weight is less than the first average molecular weight.   
     
     
         2 . The process according to  claim 1  further comprising, acidifying the dense liquid lignin with an acid to a pH between 1.5 and 3.5. 
     
     
         3 . The process according to  claim 1 , wherein said carbonating of the black liquor is effective to adjust the pH to between 11 and 13. 
     
     
         4 . The process according to  claim 1 , wherein exposing said dense liquid-lignin to heat and pressure is at a temperature of about 150° C. to about 300° C. 
     
     
         5 . The process according to  claim 1 , wherein exposing the dense liquid lignin to heat and pressure is at a temperature of about 150° C. to about 190° C. 
     
     
         6 . The process according to  claim 1  where a strong base is added to the dense liquid-lignin to raise its pH and catalyze lowering of the average molecular weight. 
     
     
         7 . The process according to  claim 1 , further comprising adding an oxidizing agent to said black liquor prior to carbonating in an amount effective to eliminate or substantially reduce the odor of the resulting lignin product. 
     
     
         8 . The process according to  claim 7 , wherein said oxidizing agent is a member of the group consisting of oxygen, air, a peroxide, or mixtures thereof. 
     
     
         9 . The process according to  claim 1 , wherein exposing said dense liquid-lignin to heat and pressure for the period of time to reduce the average molecular weight of the lignin to a second average molecular weight comprises introducing the dense liquid-lignin into a plug-flow reactor. 
     
     
         10 . The process according to  claim 1 , wherein said black liquor has a solids content between 10 to 70 weight percent. 
     
     
         11 . A process for reducing molecular weight of lignin, comprising:
 acidifying a black liquor stream to a pH above  10  to form a dense liquid-lignin phase;   isolating the dense liquid-lignin phase from the black liquor stream, wherein lignin within the dense liquid-lignin phase has a first average molecular weight; and   exposing said lignin to heat and pressure at a temperature of about 150° C. to about 250° C. for a period of time to reduce an average molecular weight of the lignin to a second average molecular weight, wherein the second average molecular weight is less than the first average molecular weight.   
     
     
         12 . The process according to  claim 11 , wherein subsequent to exposing the dense liquid-lignin to heat and pressure for the period of time to reduce the average molecular weight of the lignin to the second average molecular weight acidifying the dense liquid-lignin with an acid to a pH less than  4 . 
     
     
         13 . The process according to  claim 11  wherein a strong base is added to the dense liquid-lignin to raise its pH and catalyze lowering the average molecular weight. 
     
     
         14 . The process according to  claim 11 , further comprising adding an oxidizing agent to the black liquor prior to acidifying the black liquor in an amount effective to eliminate or substantially reduce the odor of the resulting lignin product. 
     
     
         15 . The process according to  claim 11 , wherein said oxidizing agent is a member of the group consisting of oxygen, a peroxide, or mixtures thereof. 
     
     
         16 . The process according to  claim 11 , wherein said black liquor has a solids content between 10 to 70 weight percent. 
     
     
         17 . A process for reducing molecular weight of lignin comprising:
 carbonating a black liquor stream at a temperature between about 80° C. and 200° C. and adjusting the pH above 10;   recovering a first dense liquid-lignin phase, wherein lignin within the first dense liquid-lignin phase has a first average molecular weight;   exposing the first dense liquid-lignin to heat and pressure for a pre-determined period of time to reduce a first average molecular weight of the lignin to a second average molecular weight, wherein the second average molecular weight is less than the first average molecular weight,   further carbonating the less dense liquid stream isolated from the first carbonation to lower a pH to a range of about 9 to about 10 recovering a second dense liquid-lignin phase.   
     
     
         18 . The process according to  claim 17  further comprising, acidifying the dense liquid-lignins, either combined or separately, with an acid to a pH less than  6 . 
     
     
         19 . The process according to  claim 17 , further comprising, acidifying the dense liquid-lignins, either combined or separately, with an acid to a pH between 1.5 and 3.5. 
     
     
         20 . The process according to  claim 17 , wherein said carbonating of said black liquor is carried out by contacting said black liquor with carbon dioxide countercurrently. 
     
     
         21 . The process according to  claim 17 , wherein said carbonating of the black liquor is effective to reduce the pH to between 9.0 and 10.5. 
     
     
         22 . The process according to  claim 17 , wherein exposing the dense liquid lignin to heat and pressure is at a temperature of about 150° C. to about 300° C. 
     
     
         23 . The process according to  claim 17 , wherein exposing the dense liquid-lignin to heat and pressure is at a temperature of about 150° C. to about 190° C. 
     
     
         24 . The process according to  claim 17  where a strong base is added to the dense liquid lignin to raise its pH and catalyze lowering of the average molecular weight. 
     
     
         25 . The process according to  claim 17  further comprising, adding an oxidizing agent to the black liquor prior to carbonating the black liquor in an amount effective to eliminate or substantially reduce the odor of the resulting lignin product. 
     
     
         26 . The process according to  claim 17 , wherein the oxidizing agent is a member of the group consisting of oxygen, air, a peroxide, and mixtures thereof. 
     
     
         27 . The process according to  claim 17 , wherein exposing the dense liquid- lignin to heat and pressure for the period of time to reduce the average molecular weight of the lignin to a second average molecular weight comprises introducing the dense liquid lignin into a plug-flow reactor. 
     
     
         28 . The process according to  claim 17 , wherein said black liquor has a solids content between 10 to 70 weight percent. 
     
     
         29 . A process comprising the steps of pH fractionation, using controlled acidification of black liquor to separate a first liquid-lignin fraction of relatively high molecular weight, further acidification of produce a second liquid-lignin fraction of lower molecular weight, heating the first liquid-lignin fraction to lower its molecular weight, and blending the resulting two fractions to produce a blend of desirably lower molecular weight. 
     
     
         30 . A process according to  claim 29 , where said black liquor feedstock is oxidized. 
     
     
         31 . The process according to  claim 30 , wherein said oxidizing agent is a member of the group consisting of comprises oxygen, air, a peroxide, and mixtures thereof.