Processes and apparatus for lignin separation in biorefineries

Abstract

The present invention generally provides methods of improving lignin separation during biomass fractionation with an acid to release sugars and a solvent for lignin (such as ethanol). In some embodiments, a digestor is employed to fractionating a feedstock in the presence of a solvent for lignin, sulfur dioxide, and water, to produce a liquor containing hemicellulose, cellulose-rich solids, and lignin. A solid additive is added to the digestor, wherein the solid additive combines with at least a portion of the lignin. Then a mixture of lignin and the solid additive is separated from the liquor, prior to hemicellulose recovery. Optionally, a solid additive may also be introduced to a hydrolysis reactor for converting hemicellulose oligomers to monomers, to improve separation of acid-catalyzed lignin. In some embodiments, the solid additive is gypsum or a gypsum/lignin mixture.

What is claimed is: 
     
         1 . A method of improving lignin separation during lignocellulosic biorefining, said method comprising the steps of (i) catalyzing fractionation or hydrolysis with an acid to release sugars into an acidified solution containing lignin, wherein said solution also contains a solvent for lignin; (ii) neutralizing said acidified solution with a base to form a salt in a neutralized solution; (iii) in a separation unit, separating said salt and said lignin, individually or in combination, from said neutralized solution; and then (iv) recycling a portion of said salt and optionally a portion of said lignin to step (i) to combine, physically or chemically, with said lignin, to improve lignin separation in said separation unit. 
     
     
         2 . The method of  claim 1 , wherein said acid is selected from the group consisting of sulfur dioxide, sulfurous acid, sulfur trioxide, sulfuric acid, lignosulfonic acid, and combinations thereof. 
     
     
         3 . The method of  claim 1 , wherein said separation unit is selected from the group consisting of a filter, a membrane, a decanter, a clarifier, a hydrocyclone, and a centrifuge. 
     
     
         4 . The method of  claim 1 , wherein said salt is selected from the group consisting of metal sulfates, metal sulfate hydrates, metal sulfate derivatives, ammonium sulfate, ammonium sulfate derivatives, and combinations thereof. 
     
     
         5 . The method of  claim 4 , wherein said salt is selected from the group consisting of anhydrite, calcium sulfate hemihydrate, calcium sulfate dihydrate (gypsum), and combinations thereof. 
     
     
         6 . The method of  claim 5 , wherein said salt comprises gypsum.