Processes for Purifying a Cellulosic Material

Abstract

A process for treating a cellulosic material comprising 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:
 extracting hemicellulose from the cellulosic material with an extractant to form an intermediate cellulosic material having a reduced hemicellulose content;   concentrating the intermediate cellulosic material to form a concentrated cellulosic material having an increased solids content; and   recovering the separated hemicellulose;   wherein the extractant comprises a cellulose solvent and a co-solvent, and the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide and combinations thereof.   
     
     
         2 . The process of  claim 1 , wherein the extracting forms an extraction mixture and wherein the extraction mixture is separated in a filter to form the intermediate cellulosic material and an extraction filtrate comprising the hemicellulose, the cellulose solvent and the co-solvent. 
     
     
         3 . The process of  claim 2 , further comprising:
 directing the extraction filtrate to a membrane to remove at least a portion of the cellulose solvent and the co-solvent from the extraction filtrate; and   precipitating the extraction filtrate with a precipitation agent in a precipitator to form a precipitation slurry;   wherein the precipitation agent is selected from the group consisting of 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.   
     
     
         4 . The process of  claim 3 , wherein the precipitation agent is selected from the group consisting of methanol, ethanol, isopropanol, butanol, acetone, 2-butanon, acetonitrile, propionitrile, butyronitrile, chloroacetonitrile, tetrahydrofuran, diethyl ether, dibutyl ether, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, propylene carbonate, acetic acid, formic acid, formamide, dichloromethane, chloroform, 1-chlorobutane, 1,2-dichlorethane, hexane, 2,2,4-trimethylpentane, benzene, toluene, ethylamine, butylamine, ethyldiamine, pyridine, pyrrole, pyrrolidine, piperidine, water, and combinations thereof. 
     
     
         5 . The process of  claim 2 , further comprising:
 directing the extraction filtrate directly to a precipitator to precipitate the extraction filtrate with a precipitation agent to form a precipitation slurry.   
     
     
         6 . The process of  claim 1 , wherein the extracting further comprises extracting impurities from the cellulosic material, wherein the impurities include degraded cellulose, resins, rosins, and/or other dichloromethane extractables. 
     
     
         7 . The process of  claim 1 , wherein mono-, di-, and oligo-saccharide and other side products formed in the process are removed from the process. 
     
     
         8 . The process of  claim 1 , wherein the concentrated cellulosic material is dried to recover a finished cellulosic product. 
     
     
         9 . The process of  claim 1 , wherein the intermediate cellulosic material comprises at least 10 wt. % less hemicellulose than the cellulosic material. 
     
     
         10 . The process of  claim 1 , wherein the extracting occurs from between 5 minutes and 180 minutes. 
     
     
         11 . The process of  claim 1 , wherein the ionic liquid is selected from the group consisting of 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1,3-diethyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate, 1,3-dimethylimidazolium dimethyl phosphate and combinations and complexes thereof. 
     
     
         12 . The process of  claim 1 , wherein the co-solvent is selected from the group consisting of dimethyl sulfoxide, tetramethylene sulfone, tetramethylene sulfoxide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl formamide, piperylene sulfone, acetic acid, water, and mixtures thereof. 
     
     
         13 . The process of  claim 1 , wherein the amine oxide is selected from the group consisting of trimethylamine N-oxide, triethylamine N-oxide, tripropylamine N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide, N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide, and combinations thereof. 
     
     
         14 . The process of  claim 1 , wherein the extracting hemicellulose comprises:
 directing the cellulosic material and the extractant to an extractor;   extracting hemicellulose from the cellulosic material in the extractor to form an extraction mixture; and   filtering and washing the extraction mixture with an extractant wash to form the intermediate cellulosic material and an extraction filtrate.   
     
     
         15 . The process of  claim 14 , wherein the extractant wash is 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. 
     
     
         16 . The process of  claim 14 , further comprising:
 concentrating hemicellulose from the extraction filtrate in a hemicellulose concentrator to form a recovered extractant and a hemicellulose concentrate; and   recycling the recovered extractant to the extractor or using it as an extractant wash.   
     
     
         17 . The process of  claim 16 , further comprising:
 precipitating the hemicellulose concentrate with a precipitation agent in a precipitator to form a precipitation slurry;   filtering the precipitation slurry to form a precipitation agent filtrate and filtered hemicellulose;   washing the filtered hemicellulose with a precipitant wash to form washed hemicellulose; and   drying the washed hemicellulose to form a finished hemicellulose product.   
     
     
         18 . A process for purifying a cellulosic material, comprising:
 extracting hemicellulose from the cellulosic material in an extractor with an extractant to form an intermediate cellulosic material having a reduced hemicellulose content;   filtering and washing the intermediate cellulosic material to form a washed intermediate cellulosic material and an extraction filtrate;   recovering recovered extractant from the extraction filtrate; and   directing the recovered extractant to the extractor;   wherein the extractant comprises a cellulose solvent and a co-solvent, and the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide and combinations thereof.   
     
     
         19 . A process for purifying a cellulosic material, comprising:
 extracting hemicellulose from the cellulosic material in an extractor with an extractant to form an intermediate cellulosic material having reduced hemicellulose content;   filtering and washing the intermediate cellulosic material to recover an extraction filtrate comprising extractant and separated hemicellulose;   precipitating the separated hemicellulose in a precipitator with a precipitation agent; and   returning recovered extractant from the precipitator to the extractor;   wherein the extractant comprises a cellulose solvent and a co-solvent, and the cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide and combinations thereof.   
     
     
         20 . The process of  claim 19 , further comprising concentrating and drying the hemicellulose material to form a finished hemicellulose product comprising from 5 to 20 wt. % cellulose, from 70 to 95 wt. % hemicellulose, and from 3 to 20 wt. % water.