Integrated Processes for Purifying a Cellulosic Material

Abstract

A process for converting a starting material to a purified pulp material, comprising removing lignin from a starting material to form a wet pulp comprising at least 5 wt. % water, extracting hemicellulose from the wet pulp with an extractant, and separating the extracted hemicellulose from the extraction mixture to form a cellulosic product comprising less hemicellulose than the wet pulp. The extractant comprises a cellulose solvent and a co-solvent. The cellulosic product advantageously retains its cellulosic fiber morphology. The process involves separating and recovering hemicellulose and separating and recycling various process streams employed in the process.

We claim: 
     
         1 . A process for converting a starting material to a purified pulp material, comprising:
 removing lignin from a starting material to form a wet pulp comprising at least 5 wt. % water;   extracting hemicellulose from the wet pulp with an extractant, wherein the extractant comprises a cellulose solvent and a co-solvent, the cellulose solvent selected from the group consisting of an ionic liquid, an amine oxide, and combinations thereof; and   separating the extracted hemicellulose from the wet pulp to form a cellulosic product comprising less hemicellulose than the wet pulp.   
     
     
         2 . The process of  claim 1 , wherein the removing lignin comprises:
 combining the starting material and a cooking liquor to dissolve lignin to form a cooked pulp comprising cooking liquor, dissolved lignin and pulp; and   separating the cooking liquor and lignin from the pulp to form the wet pulp.   
     
     
         3 . The process of  claim 2 , wherein the separating further comprises washing the wet pulp. 
     
     
         4 . The process of  claim 1 , wherein the process further comprises partial bleaching of the wet pulp prior to the extracting and partial or complete bleaching of the cellulosic product. 
     
     
         5 . The process of  claim 1 , wherein the process further comprises pressing the wet pulp prior to the extracting. 
     
     
         6 . The process of  claim 1 , wherein the process further comprises complete or partial bleaching of the wet pulp and washing of the wet pulp prior to extracting. 
     
     
         7 . The process of  claim 1 , wherein the wet pulp comprises at least 7 wt. % water and the process further comprises filtering, deliquoring, and/or drying the wet pulp to no less than 5 wt. % water prior to the extracting step. 
     
     
         8 . The process of  claim 1 , wherein the wet pulp comprises at least 30 wt. % water. 
     
     
         9 . The process of  claim 1 , wherein the wet pulp is sent to the extracting step without drying. 
     
     
         10 . The process of  claim 1 , wherein the wet pulp is washed with one or more pre-extraction washes comprising a pre-extraction wash agent prior to the extracting. 
     
     
         11 . The process of  claim 10 , wherein the pre-extraction wash agent is selected from the group consisting of methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, tetrahydrofuran, dimethoxyethane, acetone, acetic acid, formic acid, acetonitrile, propionitrile, butyronitrile, chloroacetonitrile, dichloromethane, chloroform, triethylamine, N,N-dimethylformamide, toluene, pyridine, water, and combinations thereof. 
     
     
         12 . The process of  claim 10 , wherein the pre-extraction wash agent removes at least 30% of the water from the wet pulp. 
     
     
         13 . The process of  claim 1 , wherein the wet pulp is filtered and/or deliquored prior to the extracting. 
     
     
         14 . The process of  claim 1 , wherein the co-solvent is water and wherein the cellulosic solvent is added directly to the wet pulp prior to the extracting. 
     
     
         15 . The process of  claim 1 , wherein the separating comprises:
 removing an extraction mixture from the extracting step;   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.   
     
     
         16 . The process of  claim 15 , further comprising recovering hemicellulose from the flashed liquid stream. 
     
     
         17 . The process of  claim 1 , wherein the separating comprises:
 removing an extraction mixture from the extraction step;   concentrating the intermediate cellulosic material to form the cellulosic product, wherein the cellulosic product has an increased solids content; and   recovering the separated hemicellulose.   
     
     
         18 . The process of  claim 1 , wherein the process further comprises drying the cellulosic product to form a sheet product. 
     
     
         19 . The process of  claim 1 , wherein the co-solvent is selected from the group consisting of alcohols, esters, ethers, ketones, carboxylic acids, nitriles, amine, amide, halides, hydrocarbon compound or heterocyclic compound and combinations thereof. 
     
     
         20 . The process of  claim 1 , wherein the starting material is pre-treated or pre-hydrolyzed prior to the removing lignin from the starting material.