Method of separation of hemicellulose and cellulose from polysaccharide sources

Abstract

A method of separating hemicellulose and cellulose by dissolution of hemicellulose from a hemicellulose-rich source, such as a pulp of any origin or from holocellulose. In the method, hemicellulose is dissolved in a solvent system comprising a cellulose solvent, which is either a ionic liquid or another direct cellulose solvent, and a molecular solvent (co-solvent), wherein said co-solvent does not dissolve cellulose, and wherein the solvent basicity and acidity of said ionic liquid or other direct cellulose solvent are adequately adjusted by the co-solvent. The present invention enables quantitative separation of cellulose and hemicellulose without any depolymerization and yield losses as occurring during conventional dissolving pulp manufacturing processes.

What is claimed is: 
     
         1 . A method of separating hemicellulose and cellulose by dissolution of hemicellulose from a hemicellulose-rich source, such as a pulp of any origin or from holocellulose, characterized in that wherein hemicellulose is dissolved in a solvent system comprising a cellulose solvent, which is either a ionic liquid or another direct cellulose solvent, and a molecular solvent (co-solvent), wherein said co-solvent does not dissolve cellulose, and wherein the solvent basicity and acidity of said ionic liquid or other direct cellulose solvent are adequately adjusted by the co-solvent. 
     
     
         2 . The method according to  claim 1 , characterized in that wherein hemicellulose is dissolved in a solvent system comprising a ionic liquid and a molecular solvent (co-solvent), wherein said co-solvent does not dissolve cellulose and wherein the solvent basicity and acidity of said ionic liquid are adequately adjusted by the co-solvent. 
     
     
         3 . The method according to  claim 1 , wherein the solvent basicity and acidity are characterized by the Kamlet-Taft solubility parameters, particularly by the β- (H-bond basicity) and α- (H-bond acidity) values. 
     
     
         4 . The method according to  claim 1 , wherein said co-solvent is miscible with the ionic liquid. 
     
     
         5 . The method according to  claim 1 , wherein said co-solvent is capable of lowering the β-value and/or raising the α-value of the solvent system. 
     
     
         6 . The method according to  claim 1 , wherein
 i) the ionic liquid is a direct cellulose solvent, which preferably has
 a cation selected from the group of cationic moieties depicted in  FIG. 2 , wherein the residues R 1-5  are independently linear or branched alkyl- (typically C1-C6), alkoxy-, or alkoxyalkyl groups, residues containing aryl moieties, or hydrogen, and 
 an anion selected from the group consisting of halides (fluoride, chloride, bromide and iodide), pseudohalides (cyanide, thiocyanide, cyanate), carboxylates (formate, acetate, propionate, butyrate), alkyl sulphite, alkyl sulphate, trifluoromethane sulfonate, phenyl sulfonate, dialkyl phosphite, dialkyl phosphate, dialkyl phosphonites, and dialkyl phosphonates, or 
   ii) the ionic liquid is replaced by NMMO.H 2 O or LiCl/DMAc.   
     
     
         7 . The method according to  claim 1 , wherein the co-solvent is selected from the group consisting of water, methanol, ethanol, propanol, iso-propanol, butanol, acetone, acetonitrile, dimethylsulfoxide, dimethylformamide, dimethylacetamide and dimethylimidazolidione, preferably the co-solvent is water or ethanol. 
     
     
         8 . The method according to  claim 1 , wherein the co-solvent comprises another ionic liquid which itself is not capable of dissolving cellulose, so that this co-solvent-IL-mixture consists of an aforementioned cation and any anion not mentioned above, preferably of the type hexafluorophosphate, tetrafluoroborate, bis(trifluoromethane)sulfonimide. 
     
     
         9 . The method according to  claim 1 , wherein the ionic solvent has a net basicity (β−α) in the range 0.11-0.47; and a β-value in the range 0.57-0.95; preferably a net basicity (β−α) in the range 0.24-0.39; and a β-value in the range 0.70-0.88. 
     
     
         10 . The method according to  claim 1 , wherein the ionic liquid is an [emim]-based ionic liquid. 
     
     
         11 . The method according to  claim 1 , wherein the ionic liquid is [emim][OAc], [bmim][OAc], [emim][DMP], [DEP], [DBNH][OAc], [DBNH][EtOAc], preferably [emim]OAc, or [emim][DMP], the co-solvent is water or an alcohol, preferably water, wherein the water content preferably is in the range 10-30 wt-%, and the solvent has a net basicity (β−α) in the range 0.11-0.47; and a β-value in the range 0.57-0.95; preferably a net basicity (β−α) in the range 0.24-0.39; and a β-value in the range 0.70-0.88. 
     
     
         12 . The method according to  claim 1 , wherein the method is carried out at a temperature ranging from 20-150° C., preferably 40-80° C. for a time ranging from 10-400 min, preferably 60-180 min. 
     
     
         13 . The method according to  claim 1 , wherein the pulp consistency is 1-25 wt-%, preferably 5-15 wt-%. 
     
     
         14 . The method according to  claim 1 , wherein the hemicellulose-rich pulp used as starting material is bleached or unbleached paper pulp of any lignocellulosic raw material derived from any commercial (sulphite, kraft, Soda-AQ) or non-commercial processes, such as organosolv, carboxylic acid, ASAM, ASA or MEA. 
     
     
         15 . The method according to  claim 1 , wherein the dissolved hemicellulose fraction is regenerated by the addition of a non-solvent, preferably water or alcohol, and the precipitate is separated by filtration or centrifugation. 
     
     
         16 . The method according to  claim 1 , wherein
 the dissolved hemicellulose fraction is separated by pressure driven membrane processes, and/or   a non-solvent is added to the hemicellulose-enriched retentate to initiate precipitation of the hemicellulose, and   the hemicellulose is recovered as a pure powder after washing and drying.   
     
     
         17 . The method according to  claim 1 , wherein
 the final cellulose product obtained has a residual hemicellulose content of 1.0 to 10 wt-%, preferably between 2.0 and 5.0 wt-%, and   the isolated and purified hemicellulose has a residual cellulose content between 1.0 and 10 wt-%, preferably between 2.0 and 5 wt-%, wherein the cellulose and hemicellulose contents are calculated by the Janson formulae, and the neutral sugar contents are determined by HPAEC-PAD as described in reference [10].   
     
     
         18 . The method according to  claim 1 , wherein the cellulose-rich residue is dissolved in a cellulose solvent. 
     
     
         19 . The method according to  claim 1 , wherein oxidants or acids are added to the cellulose dope to adjust the degree of polymerization suitable for the subsequent forming and regeneration processes. 
     
     
         20 . The method according to  claim 1 , wherein oxidants are added to the cellulose dope to remove chromophores such as residual lignin, HexA and extractives prior to the conversion processes. 
     
     
         21 . The method according to  claim 17 , wherein the treated cellulose dope is subjected to filtration to remove undissolved impurities. 
     
     
         22 . A dissolving cellulose pulp, obtained by a method according to  claim 1 , wherein said cellulose pulp has a residual hemicellulose content of 1.0 to 10 wt-%, preferably between 2.0 and 5.0 wt-%. 
     
     
         23 . The dissolving cellulose pulp according to  claim 22 , obtained by a method in which the isolated and purified hemicellulose, withdrawn from a hemicellulose-rich source, has a residual cellulose content between 1.0 and 10 wt-%, preferably between 2.0 and 5 wt-%, and wherein the cellulose and hemicellulose contents are calculated by the Janson formulae, and the neutral sugar contents are determined by HPAEC-PAD.