Processes for pretreating and purifying a cellulosic material

Abstract

A process for treating a cellulosic material comprising pretreating the cellulosic material and then extracting the cellulosic material with an extractant 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 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:
 pretreating the cellulosic material to form a pretreated cellulosic material;   extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and   separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the cellulosic material;   wherein the cellulosic material has been delignified prior to the pretreating; and further wherein the pretreating comprises water pretreatment, dilute acid pretreatment, steam explosion, ammonia fiber explosion, carbon dioxide explosion, alkaline hydrolysis, sodium hydroxide pretreatment, calcium hydroxide pretreatment, or combinations thereof.   
     
     
         2 . The process of  claim 1 , wherein the cellulosic material is a pulp with a water content from 1 wt. % to 50 wt. %. 
     
     
         3 . The process of  claim 1 , wherein the pretreating is conducted at a temperature from 90 to 250° C. 
     
     
         4 . The process of  claim 1 , wherein the pretreating comprises water pretreating conducted at a pulp to water weight ratio from 1:5 to 1:100. 
     
     
         5 . The process of  claim 1 , wherein the pretreating comprises dilute acid pretreating conducted at a pulp to dilute acid solution weight ratio from 1:5 to 1:100. 
     
     
         6 . The process of  claim 1 , wherein the pretreating comprises water pretreating at a temperature from 50 to 250° C. 
     
     
         7 . The process of  claim 1 , wherein the pretreating comprises dilute acid pretreating at a temperature from 20 to 150° C. 
     
     
         8 . The process of  claim 1 , wherein the pretreating comprises dilute acid pretreating at a pressure from 50 kPa to 10,000 kPa. 
     
     
         9 . The process of  claim 1 , wherein the acid is selected from the group consisting of an organic acid selected from the group consisting of formic acid, acetic acid, propionic acid, oxalic acid, and maleic acid; an inorganic acid selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid and hydroiodic acid; and combinations thereof. 
     
     
         10 . The process of  claim 1 , wherein the acid is present in an aqueous solution in a concentration from 0.0001 to 10 wt. %. 
     
     
         11 . The process of  claim 1 , wherein the acid is dilute sulfuric acid at a pH from 1 to 6. 
     
     
         12 . The process of  claim 1 , wherein the cellulosic product has a measured UV value for purity at 277 nm of less than 2. 
     
     
         13 . The process of  claim 1 , wherein the co-solvent is selected from the group consisting of alcohols, esters, ethers, ketones, carboxylic acids, nitriles, amines, amides, halides, hydrocarbon compounds, heterocyclic compounds, and combinations thereof. 
     
     
         14 . The process of  claim 1 , wherein the co-solvent is selected from the group consisting of methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, tetrahydrofuran, acetone, acetic acid, formic acid, acetonitrile, propionitrile, butyronitrile, chloroacetonitrile, dichloromethane, chloroform, triethylamine, N,N-dimethylformamide, toluene, pyridine, water, and combinations thereof. 
     
     
         15 . The process of  claim 1 , wherein the cellulose solvent comprises an ionic liquid selected from the group consisting of ammonium-based ionic substances, imidazolium-based ionic substances, phosphonium-based ionic substances, and combinations thereof. 
     
     
         16 . A process for purifying a cellulosic material, comprising:
 subjecting the cellulosic material to a dilute acid pretreatment to form a pretreated cellulosic material;   extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and   separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the pretreated cellulosic material.   
     
     
         17 . A process for purifying a cellulosic material, comprising:
 delignifying the cellulosic material to form a wet cellulosic material comprising at least 5 wt. % water;   subjecting the wet cellulosic material to a dilute acid pretreatment to form a pretreated cellulosic material;   extracting hemicellulose and degraded cellulose from the pretreated cellulosic material with an extractant to form an extraction mixture; wherein the extractant comprises a cellulose solvent and a co-solvent and wherein the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and   separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the pretreated cellulosic material.   
     
     
         18 . The process of  claim 17 , wherein the delignifying comprises:
 combining a starting cellulosic material and a cooking liquor to dissolve lignin to form a cooked cellulosic material comprising cooking liquor, dissolved lignin and cellulosic material; and   separating the cooking liquor and lignin from the cellulosic material to form the wet cellulosic material.   
     
     
         19 . The process of  claim 17 , wherein the process further comprises complete or partial bleaching of the wet pulp prior to the extracting. 
     
     
         20 . The process of  claim 17 , wherein the process further comprises complete or partial washing the wet pulp prior to the extracting.