Continuous process for pretreating a ligno-cellulosic feedstock

Abstract

It is disclosed a continuous process for pre-treating a ligno-cellulosic feedstock. The ligno-cellulosic feedstock is introduced in a pressurized reactor vessel and subjected to a hydrothermal treatment with steam by inserting steam from at least a two steam streams having different temperatures. The ligno-cellulosic feedstock is then subjected to steam explosion. Preferably, at least a portion of the steam in the reactor is superheated steam and the superheated steam is located in a superheated zone which is in proximity of the outlet of the pressurized reactor vessel.

We claim: 
     
         1 . A continuous process for the pre-treatment of a ligno-cellulosic feedstock, comprising the steps of:
 a) introducing the ligno-cellulosic feedstock in a pressurized reactor vessel;   b) hydrothermally treating the ligno-cellulosic feedstock with steam at a reactor pressure, by inserting at least a first steam stream comprising a first steam and a second steam stream comprising a second steam in the pressurized reactor vessel, the first steam having a first steam temperature and the second steam having a second steam temperature, wherein the second steam temperature is greater than the first steam temperature; and   c) steam exploding the ligno-cellulosic feedstock.   
     
     
         2 . The process of  claim 1 , wherein the first steam stream is inserted into the pressurized reactor vessel through a first steam inlet or inlets and the second steam stream is inserted into the reactor vessel through a second steam inlet or inlets, wherein at least one second steam inlet has a distance from a feedstock outlet of the pressurized reactor vessel which is less than the distance from a feedstock inlet of the pressurized reactor vessel. 
     
     
         3 . The process of  claim 1 , wherein at least a portion of the steam in the pressurized reactor vessel is superheated steam. 
     
     
         4 . The process of  claim 3 , wherein the temperature of at least a portion of the superheated steam in the pressurized reactor vessel is at least 10° C. greater than the steam saturation temperature at the reactor pressure. 
     
     
         5 . The process of  claim 3 , wherein the superheated steam is included in a superheated zone of the pressurized reactor vessel, wherein the superheated zone has a volume which is less than a percent value selected from the group consisting of 50%, 30%, and 10% of the total volume of the pressurized reactor vessel. 
     
     
         6 . The process of  claim 5 , wherein the superheated zone is located in proximity of the feedstock outlet of the pressurized reactor vessel. 
     
     
         7 . The process of  claim 1 , wherein hydrothermally treating the ligno-cellulosic feedstock is conducted for a residence time which is a value in a range selected from the group consisting of from 1 minute to 30 minutes, from 2 minutes to 20 minutes, and from 3 minutes to 10 minutes. 
     
     
         8 . The process of  claim 1 , wherein the first steam temperature is in a range selected from the group consisting of from 170° C. to 230° C., from 175° C. to 210° C., and from 180° C. to 195° C. 
     
     
         9 . The process of  claim 8 , wherein the second steam temperature is greater than the first steam temperature by at least a value selected from the group consisting of 10° C., 30° C., 50° C., and 100° C. 
     
     
         10 . The process of  claim 8 , wherein the first steam and the second steam are saturated steam. 
     
     
         11 . The process of  claim 8 , wherein the second steam is superheated steam. 
     
     
         12 . The process of  claim 8 , wherein the reactor pressure is greater than a value selected from the group consisting of 13 bar, 15 bar, and 18 bar. 
     
     
         13 . The process of  claim 12 , wherein the first steam stream is inserted at a first steam pressure and the second steam stream is inserted at a second steam pressure, and the reactor pressure is at least a percent value selected from the group consisting of 60%, 80%, 90%, and 95% and less than 100% of the lower of the first steam pressure and the second steam pressure. 
     
     
         14 . The process of  claim 12 , wherein the reactor pressure is homogeneous. 
     
     
         15 . The process of  claim 8 , wherein the second steam stream has a mean flow which is greater than 0 and less than a percent value selected from the group consisting of 70%, 50%, 30%, 10% of a mean flow of the first steam stream and the second steam stream. 
     
     
         16 . The process of  claim 8 , wherein the total amount of steam per Kg of ligno-cellulosic feedstock on a dry basis introduced in the pressurized reactor vessel is in a range selected from the group consisting of from 0.2 Kg/Kg to 2 Kg/Kg, from 0.4 Kg/Kg to 1.5 Kg/Kg, and from 0.6 Kg/Kg to 1 Kg/Kg. 
     
     
         17 . The process of  claim 1 , wherein steam exploding the ligno-cellulosic feedstock comprises releasing a pressure applied to the feedstock through a blow line operatively connected to the feedstock outlet of the pressurized reactor vessel. 
     
     
         18 . The process of  claim 1 , wherein the ligno-cellulosic feedstock is introduced in the pressurized reactor vessel at a temperature which is in a range selected from the group consisting of from 20° C. to 100° C., from 40° C. to 95° C., and from 60° C. to 90° C. 
     
     
         19 . The process of  claim 18 , wherein the ligno-cellulosic feedstock introduced in the pressurized reactor vessel has a moisture content in a range of from 40% to 70% by weight of the ligno-cellulosic feedstock on a wet basis.