Biomass hydrolysis

Abstract

High-yielding method for chemical hydrolysis of lignocellulose into monosaccharides. The process of the invention can additionally be applied to cellulose, xylan and related biomass polysaccharides, such as galactan, mannan, or arabinan. The method is employed for hydrolysis of a biomass polysaccharide substrate. The process is carried out in an ionic liquid in which cellulose is soluble in the presence of catalytic acid at a temperature sufficiently high to initiate hydrolysis. Water is added to the reaction mixture after initiation of hydrolysis at a rate controlled to avoid precipitation yet avoid undesired sugar dehydration products such as HMF. Hydrolysis product is useful as feedstock for fermentations including fermentation processes for ethanol, butanol and other fuels.

We claim: 
     
         1 . A method for hydrolyzing a biomass polysaccharide substrate to form monosaccharide comprising hydrolyzing a reaction mixture comprising the biomass polysaccharide substrate, acid and an ionic liquid in which cellulose is soluble and adding water to the reaction mixture wherein water is added at a rate such that the polysaccharide of the biomass polysaccharide substrate is not precipitated from the reaction mixture and hydrolysis is not substantially inhibited wherein hydrolysis is continued until the monosaccharide yield is 50% or higher. 
     
     
         2 . The method of  claim 1  wherein the biomass polysaccharide substrate is lignocellulosic biomass. 
     
     
         3 . The method of  claim 1  wherein the anion of the ionic liquid is chloride, trifluoroacetate, tri chloroacetate, tribromoacetate or thiocyanate. 
     
     
         4 . The method of  claim 1  wherein the ionic liquid is an ionic liquid wherein the cation is an imidazolium, or a pyridinium. 
     
     
         5 . The method of  claim 1  wherein the ionic liquid is an imidazolium chloride, or a pyridinium chloride. 
     
     
         6 . The method of  claim 1  wherein the ionic liquid is [EMIM]Cl, [BMIM]Cl, 1-ethyl-2,3-dimethylimidazolium chloride or 1-alkylpyridinium chloride. 
     
     
         7 . The method of  claim 1  wherein the reaction temperature is about 70 to 140° C. 
     
     
         8 . The method of  claim 1  wherein the biomass polysaccharide is cellulose, xylan, arabinan, or mannan. 
     
     
         9 . The method of  claim 1  wherein the total amount of added water is at least 35 weight % of the reaction mixture, but not more than 50 weight % of the reaction mixture. 
     
     
         10 . The method of  claim 1  wherein the total amount of added water is between 40 and 45 weight %. 
     
     
         11 . The method of  claim 1  wherein selected amounts of water are added in a step-wise fashion at selected times after reaction initiation. 
     
     
         12 . The method of  claim 1  wherein water is added continuously over a selected amount of time to achieve the desired total amount of water. 
     
     
         13 . The method of  claim 1  wherein water is added to achieve a total water level of 20 weight % with respect to the total reaction mixture from 3-10 minutes after initiation of hydrolysis. 
     
     
         14 . The method of  claim 1  wherein water is added to achieve a total water level of 40-45 weight % with respect to the total reaction mixture by 60 min after initiation of hydrolysis. 
     
     
         15 . The method of  claim 1  wherein water is added to achieve a total water level of 35-45 weight % with respect to the total reaction mixture within 30-60 min after initiation of hydrolysis. 
     
     
         16 . The method of  claim 1  wherein the yield of HMF in the hydrolysis product is 10% or less. 
     
     
         17 . The method of  claim 1  wherein the concentration of biomass polysaccharide substrate in the initial reaction mixture ranges from 5-10 weight %. 
     
     
         18 . The method of  claim 1  wherein acid is present in an amount between 10-25 weight % with respect to the amount of biomass polysaccharide substrate. 
     
     
         19 . A method for making a monosaccharide feedstock which comprises the steps of preparing a hydrolysis product as in  claim 1  and separating the hydrolysis product from ionic liquid. 
     
     
         20 . A method for generating ethanol by fermentation which comprises employing the monosaccharide feedstock of  claim 19  for fermentation by an ethanologenic microorganism.