Methods for detoxifying a lignocellulosic hydrolysate

Abstract

The present disclosure relates to methods for detoxifying a hydrolysate obtained from a lignocellulosic biomass and methods of producing ethanol from the detoxified hydrolysate. The present methods provide detoxified hydrolysates in which the quantity of compounds that are deleterious to fermenting microorganisms are substantially reduced relative to the starting hydrolysate and in which the amount of fermentable sugars loss is minimal.

What is claimed is: 
     
         1 . A method of reducing the toxicity of a lignocellulosic hydrolysate towards a fermenting organism, or for reducing at least a portion of one inhibitor to a fermenting organism from a lignocellulosic hydrolysate, comprising the step of mixing a starting lignocellulosic hydrolysate solution, said starting lignocellulosic hydrolysate solution comprising a mixture of fermentable sugars, furan aldehydes and aliphatic acids, with a magnesium base selected from magnesium hydroxide, magnesium carbonate and magnesium oxide for a period of time and under conditions that result in the formation of a detoxified hydrolysate solution comprising at least 90% of the total fermentable sugars present in the starting lignocellulosic hydrolysate solution and no greater than 40% of furan aldehydes present in the starting lignocellulosic hydrolysate solution, thereby reducing the toxicity of the lignocellulosic hydrolysate. 
     
     
         2 . The method of  claim 1 , wherein the starting hydrolysate solution is prepared by hydrolyzing a lignocellulosic biomass. 
     
     
         3 . The method of  claim 2 , wherein the lignocellulosic biomass is selected from Napier grass, energy cane, sorghum, giant reed, sugar beet, switchgrass, bagasse, rice straw, miscanthus, switchgrass, wheat straw, wood, wood waste, paper, paper waste, agricultural waste, municipal waste, birchwood, oat spelt, corn stover, eucalyptus, willow, hybrid poplar, short-rotation woody crop, conifer softwood and crop residue. 
     
     
         4 . The method of  claim 1 , further comprising the step of concentrating a hydrolysate solution to produce said starting hydrolysate solution prior to said mixing step. 
     
     
         5 . A method of reducing the toxicity of a lignocellulosic hydrolysate towards a fermenting organism, comprising the step of mixing a starting lignocellulosic hydrolysate solution, said starting lignocellulosic hydrolysate solution comprising a mixture of fermentable sugars, furan aldehydes and aliphatic acids, with a magnesium base selected from magnesium hydroxide, magnesium carbonate and magnesium oxide for a period of time of at least 1 hour, at least 4 hours, at least 10 hours or at least 20 hours at a temperature between 40° C. and 70° C. and at a pH of between 6.5 and 8, thereby reducing the toxicity of the lignocellulosic hydrolysate. 
     
     
         6 . The method of  claim 5 , wherein the magnesium base is magnesium hydroxide. 
     
     
         7 . The method of  claim 5 , wherein the magnesium base is magnesium carbonate. 
     
     
         8 . The method of  claim 5 , wherein the magnesium base is magnesium oxide. 
     
     
         9 . The method of  claim 5 , wherein the mixing is carried out for a period of up to 4 hours. 
     
     
         10 . The method of  claim 5 , wherein the pH is in the range is between 7 and 8. 
     
     
         11 . The method of  claim 5 , wherein the temperature is between 40° C. and 70° C. 
     
     
         12 . The method of  claim 5 , wherein the temperature is between 40° C. and 55° C. 
     
     
         13 . The method of  claim 5 , wherein mixing the starting hydrolysate with the magnesium base is carried out in a batch reactor. 
     
     
         14 . The method of  claim 5 , wherein mixing the starting hydrolysate with the magnesium base is carried out in a continuous reactor. 
     
     
         15 . The method of  claim 14 , wherein the continuous reactor is a plug flow reactor (PFR). 
     
     
         16 . The method of  claim 15 , wherein the continuous reactor is a continuous stirred tank reactor (CSTR). 
     
     
         17 . A method of producing a fermentation product, comprising the step of culturing a fermenting microorganism in the presence of a detoxified hydrolysate solution produced by the method of  claim 1  under conditions in which ethanol is produced, thereby producing the fermentation product. 
     
     
         18 . The method of  claim 17 , farther comprising separating the fermentation product from the culture. 
     
     
         19 . The method of  claim 17 , wherein the fermenting organism includes one or more of  Escherichia coli, Zymomonas mobilis, Bacillus stearothermophilus, Saccharomyces cerevisiae, Clostridia thermocellum, Thermoanaerobacterium saccharolyticum,  and  Pichia stipitis.    
     
     
         20 . The method of  claim 17 , further comprising producing the detoxified hydrolysate prior to said culturing step. 
     
     
         21 . The method of  claim 17 , wherein the fermentation product is ethanol. 
     
     
         22 . A method for continuously reducing the quantity of toxins in a hydrolysate, comprising the steps of:
 (a) flowing a first continuous stream of the hydrolysate into a continuous reactor;   (b) flowing a second continuous stream of a magnesium base into the continuous reactor;   (c) mixing the hydrolysate with the magnesium base in the continuous reactor or a series of continuous reactors for a period of time sufficient to reduce the quantity of toxins in the hydrolysate; and   (d) flowing the hydrolysate out of the continuous reactor or the series of continuous reactors.   
     
     
         23 . The method of  claim 22 , wherein the magnesium base is selected from magnesium hydroxide, magnesium carbonate and magnesium oxide. 
     
     
         24 . The method of  claim 23 , wherein the magnesium base is magnesium hydroxide. 
     
     
         25 . The method of  claim 22 , wherein the reactor is a plug flow reactor (PFR). 
     
     
         26 . The method of  claim 22 , wherein the reactor is a continuous stirred tank reactor (CSTR). 
     
     
         27 . The method of  claim 22 , further comprising concentrating the hydrolysate prior to step (a). 
     
     
         28 . A method for continuously producing a fermentation product, comprising:
 (a) flowing a first continuous stream of a hydrolysate into a continuous reactor;   (b) flowing a second continuous stream of a magnesium base into the continuous reactor;   (c) mixing the hydrolysate with the magnesium base in the continuous reactor or a series of continuous reactors for a period of time sufficient to reduce the quantity of furan aldehydes in the hydrolysate;   (d) flowing the hydrolysate out of the continuous reactor or the series of continuous reactors;   (e) reducing the pH of the hydrolysate; and   (f) flowing the hydrolysate into a fermentation vessel containing a fermenting microorganism, thereby producing the fermentation product.   
     
     
         29 . The method of  claim 28 , wherein the magnesium base is selected from magnesium hydroxide, magnesium carbonate and magnesium oxide. 
     
     
         30 . The method of  claim 29 , wherein the magnesium base is magnesium hydroxide. 
     
     
         31 . The method of  claim 28 , wherein the reactor is a plug flow reactor (PFR). 
     
     
         32 . The method of  claim 28 , wherein the reactor is a continuous stirred tank reactor (CSTR). 
     
     
         33 . The method of  claim 28 , farther comprising concentrating the hydrolysate prior to step (a).