Methods for Synthesizing Acylated Cellulose Through Instillation of an Acidic Catalyst
Instilling an acidic catalyst to a reaction mixture can be beneficial during the acylation of cellulose. Methods described herein can comprise preparing a reaction mixture comprising an acylating agent and cellulose, instilling a catalyst comprising an acid to the reaction mixture at an overall catalyst loading level of about 1% or less by weight of the cellulose, and reacting the cellulose with the acylating agent in the presence of the catalyst, thereby forming an acylated cellulose.
1 . A method comprising:
preparing a reaction mixture comprising an acylating agent and cellulose;
instilling a catalyst comprising an acid to the reaction mixture at an overall catalyst loading level of about 1% or less by weight of the cellulose; and
reacting the cellulose with the acylating agent in the presence of the catalyst, thereby forming an acylated cellulose.
2 . The method of claim 1 , wherein the catalyst comprises sulfuric acid and, optionally, phosphoric acid.
3 . The method of claim 1 , wherein the acylating agent comprises at least acetic anhydride and the acylated cellulose comprises acetylated cellulose.
4 . The method of claim 1 , wherein the catalyst is instilled portionwise to the reaction mixture while reacting takes place.
5 . The method of claim 1 , wherein the catalyst is instilled continuously to the reaction mixture while reacting takes place.
6 . The method of claim 1 , wherein at least some of the catalyst is instilled to the reaction mixture after a maximum exotherm of the reaction has been reached.
7 . The method of claim 6 , wherein up to about 5% of the catalyst is instilled to the reaction mixture after the maximum exotherm of the reaction has been reached.
8 . A method comprising:
preparing a reaction mixture comprising acetic anhydride, cellulose and a first portion of a catalyst comprising at least sulfuric acid;
instilling at least a second portion of the catalyst to the reaction mixture at an overall catalyst loading level of about 1% or less by weight of the cellulose; and
reacting the cellulose with the acetic anhydride in the presence of the catalyst, thereby forming an acetylated cellulose.
9 . The method of claim 8 , further comprising:
hydrolyzing the acetylated cellulose to remove a portion of the acetyl groups therefrom.
10 . The method of claim 8 , wherein the acetylated cellulose has improved filterability compared to an acetylated cellulose synthesized when the catalyst is added all at once.
11 . The method of claim 8 , wherein the second portion of the catalyst is instilled portionwise to the reaction mixture while reacting takes place.
12 . The method of claim 8 , wherein the second portion of the catalyst is instilled continuously to the reaction mixture while reacting takes place.
13 . The method of claim 8 , wherein at least some of the second portion of the catalyst is instilled to the reaction mixture after a maximum exotherm of the reaction has been reached.
14 . The method of claim 13 , wherein up to about 5% of the catalyst is instilled to the reaction mixture after the maximum exotherm of the reaction has been reached.
15 . The method of claim 8 , wherein the catalyst further comprises phosphoric acid.
16 . A method comprising:
preparing a reaction mixture comprising acetic anhydride and cellulose;
instilling a catalyst comprising at least sulfuric acid to the reaction mixture at an overall catalyst loading level of about 1% or less by weight of the cellulose, thereby forming a reaction product that comprises an acetylated cellulose; and
hydrolyzing a portion of the acetyl groups on the acetylated cellulose to produce an acetylated cellulose having a degree of substitution (DS) of about 2.5 or lower.
17 . The method of claim 16 , further comprising:
neutralizing at least a portion of the sulfuric acid prior to hydrolyzing.
18 . The method of claim 16 , wherein the cellulose comprises a non-dissolving grade cellulose.
19 . The method of claim 16 , wherein at least some of the catalyst is instilled to the reaction mixture after a maximum exotherm of the reaction has been reached.
20 . The method of claim 19 , wherein up to about 5% of the catalyst is instilled to the reaction mixture after the maximum exotherm of the reaction has been reached.
21 . The method of claim 16 , wherein the catalyst further comprises phosphoric acid.