Process for the production of methylhydroxyalkyl cellulose
A process of producing methylhydroxyalkyl cellulose (MHAC) is described and involves in a first step (a), (i) introducing cellulose and a suspension medium into an autoclave, the suspension medium comprising 20 wt. % to 50 wt. % of chloromethane, based on the total weight of the said suspension medium, and (ii) spraying the cellulose in the autoclave with an aqueous alkali metal hydroxide solution, thereby alkalizing the cellulose and reacting the cellulose with chloromethane. In a second step (b), hydroxyalkylating agent is optionally introduced into the autoclave at a temperature above 60° C. In a third step (c) alkali metal hydroxide is introduced into the autoclave in a hyperstoichiometric quantity of at least +0.1 mol eq., relative to the chloromethane utilised. In a fourth step (d), at least one hydroxyalkylating agent is optionally introduced into the autoclave at a temperature above 60° C., and the introduced hydroxyalkylating agent is allowed to react for at least 20 min. In a fifth step (e), additional chloromethane is introduced into the autoclave in a hyperstoichiometric quantity of at least +0.2 mol eq., relative to the total alkali metal hydroxide utilised up to this point. In a sixth step (f), additional alkali metal hydroxide is optionally introduced into the autoclave, and the reaction is allowed to continue at a temperature of from 60° C. to 110° C. Finally, the suspension medium is removed by means of distillation, thus forming a distillate comprising residual chloromethane, and the methylhydroxyalkyl cellulose is isolated. Optionally, the isolated methylhydroxyalkyl cellulose may be washed, and dried. The addition of hydroxyalkylating agent occurs in step (b) and/or step (d).
1 . A process of producing methylhydroxyalkyl cellulose (MHAC) comprising:
(a)
(i) introducing cellulose and a suspension medium into an autoclave, said suspension medium comprising 20 wt. % to 50 wt. % of chloromethane, based on the total weight of the said suspension medium, and
(ii) spraying the cellulose in said autoclave with an aqueous alkali metal hydroxide solution, thereby alkalizing the cellulose and reacting the cellulose with chloromethane;
(b) optionally introducing at least one hydroxyalkylating agent into said autoclave at a temperature above 60° C.;
(c) introducing alkali metal hydroxide into said autoclave in a hyperstoichiometric quantity of at least +0.1 mol eq., in relation to the chloromethane utilised;
(d) optionally introducing at least one hydroxyalkylating agent into said autoclave at a temperature above 60° C., and allowing the introduced hydroxyalkylating agent to react for at least 20 min;
(e) introducing chloromethane into said autoclave in a hyperstoichiometric quantity of at least +0.2 mol eq., in relation to the total alkali metal hydroxide utilised;
(f) optionally introducing alkali metal hydroxide into said autoclave, and allowing reaction to continue at a temperature of from 60° C. to 110° C.; and
(g)
(i) removing said suspension medium by distillation, thereby forming a distillate comprising residual chloromethane,
(ii) isolating the methylhydroxyalkyl cellulose, and
(iii) optionally washing, and drying the isolated methylhydroxyalkyl cellulose
wherein the hydroxyalkylating agent of step (d) is the same or different than the hydroxyalkylating agent of step (b), the alkali metal hydroxide is selected independently for each of steps (a), (c) and (f), and provided that addition of hydroxyalkylating agent occurs in at least one of step (b) and step (d).
2 . The process of claim 1 wherein the methylhydroxyalkyl cellulose is selected from the group consisting of methylhydroxyethyl cellulose (MHEC), methylhydroxypropyl cellulose (MHPC) and combinations thereof.
3 . The process of claim 1 wherein said suspension medium comprises dimethyl ether and 25 wt. % to 50 wt. % of chloromethane, based on the total weight of the suspension medium.
4 . The process of claim 1 wherein in step (a) said suspension medium is introduced into said autoclave in an amount of 1.5 to 4.0 parts per part of cellulose.
5 . The process of claim 1 wherein in step (c) the alkali metal hydroxide is a 35 to 60 wt. % aqueous solution of NaOH.
6 . The process of claim 1 wherein the hyperstoichiometric quantity of alkali metal hydroxide of step (c) is between +0.1 and +4.5 mol eq., in relation to the chloromethane utilised.
7 . The process of claim 1 wherein the hyperstoichiometric quantity of chloromethane of step (e) is between +0.4 and +4.0 mol eq., in relation to the total quantity of alkali metal hydroxide utilized.
8 . The process of claim 1 wherein the total quantity of hydroxyalkylating agent of steps (b) and (d) is from 0.02 to 5 mol eq. per AGU of the cellulose.
9 . The process of claim 1 wherein in step (c) and step (f) the alkali metal hydroxide is introduced into said autoclave at a rate of 0.01 to 0.4 mol eq. (per AGU of the cellulose) per minute.
10 . The process of claim 1 wherein in step (b) and step (d) the hydroxyalkylating agent is introduced into said autoclave at a rate of from 0.01 to 0.4 mol eq. (per AGU of the cellulose) per minute.