Preparation of cellulose esters

Claim 1

IN A PROCESS FOR PRECIPITATING CELLULOSE ACETATE WHICH HAS BEEN PREPARED BY ACETYLATING CELLULOSE WITH A MIXTURE OF ACETIC ANHYDRIDE, ACETIC ACID, METHYLENE CHLORIDE AND ACETYLATION CATALYST, AFTER WHICH SAID CATALYST HAS BEEN NEUTRALIZED AND SAID CELLULOSE ACETATE IS IN SOLUTION IN A SOLVENT COMPRISING ESSENTIALLY ACETIC ACID AND METHYLENE CHLORIDE, SAID METHYLENE CHLORIDE BEING PRESENT IN AN AMOUNT SUBSTANTIALLY GREATER THA 30% BY WEIGHT OF SAID SOLUTION, THE IMPROVEMENT WHICH COMPRISES REMOVING METHYLENE CHLORIDE FROM THE CELLULOSE ACETATE SOLUTION BY DISTILLATION TO OBTAIN A RESIDUAL AMOUNT OF METHYLENE CHLORIDE IN SAID SOLUTION OF BETWEEN 5% AND 30% BY WEIGHT, SLOWLY INTRODUCING AN AQUEOUS PRECIPITANT OVER A PERIOD OF ABOUT 15 MINUTES TO THE RESULTING CELLULOSE ACETATE SOLUTION IN SAID ACETIC ACID AND SAID RESIDUAL METHYLENE CHLORIDE WITH AGITAION UNTIL AN AQUEOUS PRECIPITATION BATH COMPRISING BETWEEN ABOUT 20% AND ABOUT 40% BY WEIGHT OF ACETIC ACID IS FORMED AND THE CELLULOSE ACETATE PRECIPITATES FROM THE PRECIPITATION BATH THUS FORMED SUBSTANTIALLY ALL IN THE FORM OF SMALL DISKS AND SPHEROIDS HAVING SUBSTANTIALLY NO TENDENCY TO COALESCE, THEREAFTER REMOVING THE RESIDUAL METHYLENE CHLORIDE FROM THE PRECIPITATION BATH BY FURTHER DISTILLATION, AND RECOVERING THE PRECIPITATED CELLULOSE ACETATE FROM THE PRECIPITATION BATH AS A PRODUCT SUBSTANTIALLY FREE OF FINES, HAVING A BULK DENSITY BETWEEN ABOUT 0.4 AND 0.6 GRAM PER CC. AND CHARACTERIZED BY A UNIFORM INTERNAL PHYSICAL STRUCTURE, AT LEAST 95% OF SAID PRODUCT BEING RETAINED ON A 65-MESH SCREEN.