Processes for Purifying a Cellulosic Material

Abstract

A process for treating a cellulosic material comprising extracting hemicellulose from the cellulosic material with an extractant comprising a cellulose solvent and a co-solvent to selectively extract hemicellulose therefrom and separating the extracted hemicellulose to form a cellulosic product comprising less hemicellulose than the cellulosic material. The extractant comprises a cellulose solvent and a co-solvent. The cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide and combinations thereof, and the co-solvent may preferably have a boiling point less than 120° C., or less than 100° C. The cellulosic product advantageously retains its cellulosic fiber morphology. The processes involve separating and recovering the hemicellulose and separating and recycling various process streams employed in the process.

We claim: 
     
         1 . A process for purifying a cellulosic material, comprising:
 extracting hemicellulose from the cellulosic material with an extractant comprising a cellulose solvent and one or more co-solvents to form an extraction mixture;   separating the extraction mixture to form an intermediate cellulosic material and a liquid stream containing hemicellulose; and   flashing at least a portion of the liquid stream to form a vapor stream enriched in the co-solvent and a flashed liquid stream comprising the hemicellulose, the cellulose solvent, and the co-solvent.   
     
     
         2 . The process of  claim 1 , wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof, and wherein the co-solvent has a boiling point of less than 120° C. 
     
     
         3 . The process of  claim 1 , wherein the co-solvent comprises acetonitrile and/or water. 
     
     
         4 . The process of  claim 3 , wherein the co-solvent has an acetonitrile to water weight ratio from 6:1 to 500:1. 
     
     
         5 . The process of  claim 1 , wherein the intermediate cellulosic material comprises at least 10% less hemicellulose than the cellulosic material. 
     
     
         6 . The process of  claim 1 , further comprising concentrating the intermediate cellulosic material by at least partially drying the intermediate cellulosic material and optionally washing the intermediate cellulosic material one or more times with one or more washes prior to the drying operation. 
     
     
         7 . The process of  claim 6 , wherein the one or more washes are selected from the group consisting of an alcohol, a ketone, a nitrile, an ether, an ester, a carboxylic acid, a halide, a hydrocarbon compound, an amine, a heterocyclic compound, water, and combinations thereof. 
     
     
         8 . The process of  claim 6 , wherein the one or more washes are selected from the group of methanol, ethanol, isopropanol, acetone, methyl isobutyl ketone, propionitrile, butyronitrile, chloroacetonitrile, ether, tetrahydrofuran, acetone, acetic acid, formic acid water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, a mixture of water and alcohol, and combinations thereof. 
     
     
         9 . The process of  claim 6 , wherein the one or more washes are enriched in co-solvent. 
     
     
         10 . The process of  claim 9 , wherein the one or more washes enriched in co-solvent comprise a condensed portion of the vapor stream of the co-solvent from the flashing. 
     
     
         11 . The process of  claim 9 , wherein the one or more washes comprise the co-solvent and water, wherein the one or more washes are recovered after washing and the one or more washes are directed to a vaporizer to separate the co-solvent from the water, and further wherein the co-solvent is directed to the extractor. 
     
     
         12 . The process of  claim 6 , further comprising separating the co-solvent from the one or more washes using distillation. 
     
     
         13 . The process of  claim 1 , further comprising:
 combining the liquid stream with a precipitation agent in a precipitator to form a precipitation slurry; and   separating the precipitation slurry to form an intermediate hemicellulosic material.   
     
     
         14 . The process of  claim 1 , further comprising:
 separating the liquid stream in a distillation column to produce a distillate comprising water and a residue comprising hemicellulose, co-solvent and ionic liquid;   combining the residue with a precipitation agent in a precipitator to form a precipitation slurry; and   separating the precipitation slurry to form an intermediate hemicellulosic material.   
     
     
         15 . The process of  claim 14 , wherein the precipitation agent is the same as the co-solvent used in the extracting. 
     
     
         16 . The process of  claim 15 , wherein acetonitrile and/or water are used as both co-solvent and precipitation agent and the concentration of co-solvent in the precipitation slurry is at least 1% higher than in the extractant. 
     
     
         17 . The process of  claim 1 , wherein the extracting is conducted at a pressure at least 3% greater than the pressure of the flashing. 
     
     
         18 . The process of  claim 1 , wherein the extracting is conducted at a temperature from 20° C. to 150° C., the flashing is conducted at a temperature from 0° C. to 300° C., and the separating comprises filtering at a temperature from 10° C. to 150° C. 
     
     
         19 . A process for purifying a cellulosic material, comprising:
 extracting hemicellulose from the cellulosic material with an extractant at a pressure from 20 to 20,000 kPa to form an extraction mixture;   filtering the extraction mixture to form an extraction filtrate and an intermediate cellulosic material comprising at least 10% less hemicellulose than the cellulosic material; and   concentrating the intermediate cellulosic material to form a concentrated cellulosic material having an increased solids content;   wherein the liquid extractant comprises an ionic liquid, a co-solvent comprising acetonitrile, and secondary co-solvent.   
     
     
         20 . A process for purifying a cellulosic material, comprising:
 extracting hemicellulose from the cellulosic material with an extractant to form an extraction mixture;   filtering the extraction mixture to form an extraction filtrate and an intermediate cellulosic material comprising at least 10% less hemicellulose than the cellulosic material; and   concentrating the intermediate cellulosic material to form a concentrated cellulosic material having increased solids content;   wherein the liquid extractant comprises an amine oxide and a co-solvent comprising acetonitrile.