Described is a process of preparing alkylhydroxyalkyl cellulose, e.g.,
methylhydroxypropyl cellulose (MHPC). The process includes: (a) alkylating cellulose
with an aqueous caustic solution containing from 1.5 to 5.5 equivalents of alkali
metal hydroxide, e.g., NaOH, per anhydroglucose unit (AGU) of said cellulose, in
the presence of a suspension agent, e.g., dimethyl ether, which contains alkyl
halide, e.g., methyl chloride, in an amount of from (equivalents of alkali metal
hydroxide per AGU minus 1.4) to (equivalents of alkali metal hydroxide per AGU
plus 0.8); (b) reacting the alkalised cellulose of step (a) with one or more alkylene
oxides, e.g., propylene oxide, at a temperature higher than 65 C., e.g.,
85 C.; (c) adding alkyl halide, to the product of step (b), in an amount
of at least the difference between (i) the equivalents of alkyl halide per AGU
in step a) and (ii) the equivalents of alkali metal hydroxide added per AGU in
step (a), provided that the amount of additionally added alkyl halide is at least
0.2 equivalents per AGU; and (d) isolating alkylhydroxyalkyl cellulose from the
reaction mixture of step (c). Optionally the isolated alkylhydroxyalkyl cellulose
may be purified.
