Biomass conversion systems providing integrated stabilization of a hydrolysate using a slurry catalyst following biomass pretreatment and methods for use thereof

Abstract

Digestion of cellulosic biomass solids to form a hydrolysate may be conducted with integrated catalytic reduction during digestion to transform soluble carbohydrates in the hydrolysate into a more stable reaction product. Such integrated catalytic reduction may be conducted using a slurry catalyst. Biomass conversion systems for performing integrated catalytic reduction can comprise: a hydrothermal digestion unit that contains a slurry catalyst capable of activating molecular hydrogen; an optional hydrogen feed line that is operatively connected to the hydrothermal digestion unit; a fluid circulation loop comprising the hydrothermal digestion unit and a catalytic reduction reactor unit, the catalytic reduction reactor unit also containing the slurry catalyst; a pretreatment digestion unit that is not part of the fluid circulation loop and does not contain the slurry catalyst; and a solids transport mechanism operatively connecting the pretreatment digestion unit to the hydrothermal digestion unit.

I claim: 
     
         1 . A biomass conversion system comprising:
 a hydrothermal digestion unit that contains a slurry catalyst capable of activating molecular hydrogen;   an optional hydrogen feed line that is operatively connected to the hydrothermal digestion unit;   a fluid circulation loop comprising the hydrothermal digestion unit and a catalytic reduction reactor unit, the catalytic reduction reactor unit also containing the slurry catalyst;   a pretreatment digestion unit that is not part of the fluid circulation loop and does not contain the slurry catalyst; and   a solids transport mechanism operatively connecting the pretreatment digestion unit to the hydrothermal digestion unit.   
     
     
         2 . The biomass conversion system of  claim 1 , wherein the solids transport mechanism operatively connects the bottom of the pretreatment digestion unit to the top of the hydrothermal digestion unit. 
     
     
         3 . The biomass conversion system of claim  0 , wherein the solids transport mechanism is capable of conveying a biomass pulp from the pretreatment digestion unit to the hydrothermal digestion unit while maintaining a pressurized state. 
     
     
         4 . The biomass conversion system of claim  0 , wherein the fluid circulation loop is configured to establish upward fluid flow in the hydrothermal digestion unit. 
     
     
         5 . The biomass conversion system of claim  0 , further comprising:
 a reaction product takeoff line in fluid communication with the fluid circulation loop, the reaction product takeoff line being located between the hydrothermal digestion unit and an outlet of the catalytic reduction reactor unit.   
     
     
         6 . The biomass conversion system of  claim 5 , further comprising:
 a solids separation mechanism that is operatively connected to the reaction product takeoff line.   
     
     
         7 . The biomass conversion system of claim  0 , wherein the slurry catalyst comprises a poison-tolerant catalyst. 
     
     
         8 . The biomass conversion system of claim  0 , wherein the slurry catalyst is regenerable through exposure to water having a temperature of at least 200° C. 
     
     
         9 . The biomass conversion system of claim  0 , wherein the slurry catalyst is operable to generate molecular hydrogen. 
     
     
         10 . The biomass conversion system of claim  0 , further comprising:
 a solids introduction mechanism that is operatively connected to the pretreatment digestion unit, the solids introduction mechanism comprising an atmospheric pressure zone and a pressure transition zone that cycles between atmospheric pressure and a higher pressure state.   
     
     
         11 . The biomass conversion system of claim  0 , further comprising:
 a solids introduction mechanism that is operatively connected to the hydrothermal digestion unit, the solids introduction mechanism comprising a pressure transition zone that cycles between a lower pressure state and a higher pressure state;
 wherein the pretreatment digestion unit is operatively connected to the hydrothermal digestion unit via the solids introduction mechanism. 
   
     
     
         12 . The biomass conversion system of claim  0 , wherein the fluid circulation loop is configured to establish upward fluid flow in the catalytic reduction reactor unit. 
     
     
         13 . A method comprising:
 providing cellulosic biomass solids in a pretreatment digestion unit;   heating the cellulosic biomass solids in the pretreatment digestion unit at a first temperature for a first time period, the first temperature and the first time period being sufficient to remove at least a portion of the hemicellulose and lignins from the cellulosic biomass solids, thereby producing a biomass pulp;   transferring at least a portion of the biomass pulp to a hydrothermal digestion unit that contains a slurry catalyst capable of activating molecular hydrogen;   heating the biomass pulp in the hydrothermal digestion unit at a second temperature for a second time period in the presence of molecular hydrogen while circulating the slurry catalyst therethrough, the second temperature and the second time period being sufficient to digest at least a portion of the cellulose, thereby forming a hydrolysate comprising soluble carbohydrates within a liquor phase;   at least partially transforming the soluble carbohydrates into a reaction product via a catalytic reduction reaction while the soluble carbohydrates are within the hydrothermal digestion unit; and   transferring at least a portion of the liquor phase to a catalytic reduction reactor unit that also contains the slurry catalyst, so as to further transform the soluble carbohydrates into the reaction product.   
     
     
         14 . The method of  claim 13 , further comprising:
 recirculating at least a portion of the liquor phase from the catalytic reduction reactor unit to the hydrothermal digestion unit.   
     
     
         15 . The method of  claim 14 , wherein the liquor phase is recirculated to the hydrothermal digestion unit at a recycle ratio of 2 or less. 
     
     
         16 . The method of  claim 14 , wherein the liquor phase is recirculated to the hydrothermal digestion unit such upward fluid flow is established therein. 
     
     
         17 . The method of  claim 13 , wherein, after heating to the second temperature and for the second time period, less than 10% of the cellulosic biomass solids, on a dry basis, remains undigested. 
     
     
         18 . The method of  claim 13 , wherein the second temperature is higher than the first temperature. 
     
     
         19 . The method of  claim 13 , wherein the liquor phase is transferred from the hydrothermal digestion unit to the catalytic reduction reactor unit such that the liquor phase flows upwardly in the catalytic reduction reactor unit. 
     
     
         20 . The method of  claim 13 , further comprising:
 removing the hemicellulose and lignins from the pretreatment digestion unit before transferring the biomass pulp to the hydrothermal digestion unit.   
     
     
         21 . The method of  claim 13 , further comprising:
 after further transforming the soluble carbohydrates into the reaction product, withdrawing a portion of the reaction product from the catalytic reduction reactor unit; and   converting the reaction product into a biofuel.   
     
     
         22 . The method of  claim 21 , further comprising:
 separating solids from the reaction product after withdrawing.   
     
     
         23 . The method of  claim 13 , wherein the slurry catalyst comprises a poison-tolerant catalyst. 
     
     
         24 . The method of  claim 13 , wherein the slurry catalyst is operable to generate molecular hydrogen.