In a process for preparing an esterified cellulose ether a cellulose ether is esterified with (i) an aliphatic monocarboxylic acid anhydride or (ii) a dicarboxylic acid anhydride or (iii) a combination of an aliphatic monocarboxylic acid anhydride and a dicarboxylic acid anhydride in the presence of an alkali metal carboxylate and an aliphatic carboxylic acid, wherein the molar ratio [alkali metal carboxylate/anhydroglucose units of cellulose ether] is not more than [1.20/1] and the molar ratio [aliphatic carboxylic acid/anhydroglucose units of cellulose ether] is from [3.55/1] to [9.0/1].

In a process for preparing an esterified cellulose ether a cellulose ether is esterified with (i) an aliphatic monocarboxylic acid anhydride or (ii) a dicarboxylic acid anhydride or (iii) a combination of an aliphatic monocarboxylic acid anhydride and a dicarboxylic acid anhydride in the presence of an alkali metal carboxylate and an aliphatic carboxylic acid, wherein the molar ratio [alkali metal carboxylate/anhydroglucose units of cellulose ether] is not more than [1.20/1] and the molar ratio [aliphatic carboxylic acid/anhydroglucose units of cellulose ether] is from [3.55/1] to [9.0/1].

A process for producing a water-soluble cellulose derivative of a reduced content of water-insoluble particles comprises the steps of a) reacting cellulose with an alkaline material to produce alkali cellulose, b) reacting the produced alkali cellulose with one or more derivatizing agents to produce a water-soluble cellulose derivative, c) washing the produced cellulose derivative with an aqueous liquid once or several times to provide a moist cellulose derivative having a water content of 25 to 85 percent, based on the total weight of the moist cellulose derivative, d) subjecting the moist cellulose derivative to homogenization to form the moist cellulose derivative to a paste, and e) pressing the paste through a filter of a pore size of up to 200 m.

A process for producing a water-soluble cellulose derivative of a reduced content of water-insoluble particles comprises the steps of a) reacting cellulose with an alkaline material to produce alkali cellulose, b) reacting the produced alkali cellulose with one or more derivatizing agents to produce a water-soluble cellulose derivative, c) washing the produced cellulose derivative with an aqueous liquid once or several times to provide a moist cellulose derivative having a water content of 25 to 85 percent, based on the total weight of the moist cellulose derivative, d) subjecting the moist cellulose derivative to homogenization to form the moist cellulose derivative to a paste, and e) pressing the paste through a filter of a pore size of up to 200 m.

Provided are HPMCAS powder having high solubility when dissolved in a solvent and being capable of suppressing generation of undissolved materials; and a method for producing the powder. More specifically, provided is hypromellose acetate succinate powder having an average ratio of L to D of from 2.0 to 3.0, wherein L and D mean maximum and minimum diameters of each particle, respectively. Also provided is a method for producing a hypromellose acetate succinate, comprising the steps of: dissolving hypromellose powder in a solvent, esterifying the dissolved hypromellose with succinic anhydride and acetic anhydride in the presence of a catalyst to obtain a reaction mixture, and mixing the reaction mixture with water to precipitate hypromellose acetate succinate, wherein the reaction mixture just before being mixed with the water has a viscosity of from 100 to 200 Pa.Math.s.

Provided are HPMCAS powder having high solubility when dissolved in a solvent and being capable of suppressing generation of undissolved materials; and a method for producing the powder. More specifically, provided is hypromellose acetate succinate powder having an average ratio of L to D of from 2.0 to 3.0, wherein L and D mean maximum and minimum diameters of each particle, respectively. Also provided is a method for producing a hypromellose acetate succinate, comprising the steps of: dissolving hypromellose powder in a solvent, esterifying the dissolved hypromellose with succinic anhydride and acetic anhydride in the presence of a catalyst to obtain a reaction mixture, and mixing the reaction mixture with water to precipitate hypromellose acetate succinate, wherein the reaction mixture just before being mixed with the water has a viscosity of from 100 to 200 Pa.Math.s.

There is provided a method for producing hydroxypropyl methyl cellulose phthalate (HPMCP), including an esterification step of reacting hydroxypropyl methyl cellulose with a carboxybenzoylating agent in the presence of an aliphatic carboxylic acid in a kneader reactor equipped with two or more stirring blades rotating around their own axes and orbitally revolving, to obtain a reaction product solution containing HPMCP; a precipitation step of precipitating the HPMCP by mixing the reaction product solution with water to obtain a suspension of the precipitated HPMCP; and a washing and recovery step of washing the HPMCP in the suspension and recovering the washed HPMCP. Further, there is provided HPMCP having yellowness at 20 C. of 10.0 or less, as determined in a 10% by mass solution of the HPMCP in acetone.

Provided is a composition for hot melt extrusion including a drug and hypromellose acetate succinate (HPMCAS) having a hydroxypropoxy molar substitution of 0.40 or more and a mole ratio of an acetyl group to a succinyl group of less than 1.6. Further, provided is a method for producing a hot melt extrudate including the step of hot melt-extruding a composition for hot melt extrusion including a drug and hypromellose acetate succinate having a molar hydroxypropoxy substitution of 0.40 or more and a mole ratio of an acetyl group to a succinyl group of less than 1.6, at a hot melt temperature of not lower than a melting temperature of the hypromellose acetate succinate or of not lower than a temperature at which both the hypromellose acetate succinate and the drug are melted.

Provided is a composition for hot melt extrusion including a drug and hypromellose acetate succinate (HPMCAS) having a hydroxypropoxy molar substitution of 0.40 or more and a mole ratio of an acetyl group to a succinyl group of less than 1.6. Further, provided is a method for producing a hot melt extrudate including the step of hot melt-extruding a composition for hot melt extrusion including a drug and hypromellose acetate succinate having a molar hydroxypropoxy substitution of 0.40 or more and a mole ratio of an acetyl group to a succinyl group of less than 1.6, at a hot melt temperature of not lower than a melting temperature of the hypromellose acetate succinate or of not lower than a temperature at which both the hypromellose acetate succinate and the drug are melted.

A process for recovering an esterified cellulose ether from a reaction product mixture obtained from a reaction of (a) a cellulose ether with (b) an aliphatic monocarboxylic acid anhydride or a di- or tricarboxylic acid anhydride or a combination of an aliphatic monocarboxylic acid anhydride and a di- or tricarboxylic acid anhydride, comprises the steps of (i) contacting the reaction product mixture with an aqueous liquid and precipitating the esterified cellulose ether from the reaction product mixture, and (ii) isolating the precipitated esterified cellulose ether from the mixture obtained in step (i). Tackiness of the esterified cellulose ether can be reduced when a cellulose ether is added before or in step (i) to the reaction product mixture, to the aqueous liquid or a combination thereof.