Method for the acetylation of wood

Abstract

The present invention provides a method for the acetylation of wood comprising treating the wood with an acetylation medium under wood acetylation reaction conditions and drying the acetylated wood, wherein the drying comprises at least two steps, wherein the wood is first dried with a first drying medium and then with a second drying medium.

1 . A method for the acetylation of wood comprising treating the wood with an acetylation medium under wood acetylation reaction conditions and drying the acetylated wood, wherein the drying comprises at least two steps, wherein the wood is first dried with a first drying medium and then with a second drying medium. 
     
     
         2 . The method according to  claim 1 , wherein the first drying medium has a higher heat capacity than the second drying medium. 
     
     
         3 . The method according to  claim 1 , wherein the first drying medium comprises an acetylation medium vapour. 
     
     
         4 . The method according to  claim 1 , wherein the second drying medium is an inert gas, preferably nitrogen. 
     
     
         5 . The method according to  claim 1 , wherein the acetylation reaction conditions comprise a pressure of at least 1 barg. 
     
     
         6 . The method according to  claim 1 , wherein the drying in the first and/or the second step is carried out at a pressure lower than the acetylation reaction pressure. 
     
     
         7 . The method according to  claim 1 , wherein the acetylation medium comprises acetic acid, acetic anhydride or a mixture thereof. 
     
     
         8 . The method according to  claim 4 , wherein the acetylation medium comprises a mixture of acetic acid and acetic anhydride, preferably comprising at least 50 wt. %, more preferably at least 85 wt. % of acetic anhydride. 
     
     
         9 . The method according to  claim 1 , wherein the acetylation conditions comprise heating to a temperature in the range 160-190° C. 
     
     
         10 . The method according to  claim 1 , wherein the drying temperature in either one or both of the drying steps is in the range 150-190° C. 
     
     
         11 . The method according to  claim 1 , wherein in the first drying step the residence time is 5-25 min and, optionally, the gas to solid flow rate is 1-6 mass ratio. 
     
     
         12 . The method according to  claim 1 , wherein in the second drying step the residence time is 15-40 min and, optionally, the gas to solid flow rate is 0.7-5 mass ratio. 
     
     
         13 . The method according to  claim 1 , wherein the liquid content in the acetylated wood after acetylation and before drying is at least 55 wt. % on dry basis. 
     
     
         14 . The method according to  claim 1 , wherein the liquid content in the acetylated wood is reduced during the first drying step to at least 2-8 wt. % on dry basis and in the second drying step to max 0.5 wt. % on dry basis.