Direct precipitation method for producing extrusion-grade cellulose acetate powder and resulting product

Claim 1

Method for preparing cellulose acetate powder from an acid dope containing from about 6% to about 15% by weight cellulose acetate ester, the acid dope comprising about 60 to about 100 percent aqueous acetic acid solution and a cellulose acetate ester dissolved in the solution and having an acetyl content of about 38 to about 41 weight percent; the method comprising: (a) mixing in the dope about 0.25 to about 5.0 parts per part of cellulose acetate ester of a water immiscible coagulating agent having a boiling point less than 150° C. (302° F.) to form a mixture; (b) precipitating from the mixture the cellulose acetate ester in about 25% to about 35% aqueous acid at a temperature of about 65° C. (149° F.) to about 95° C. (203° F.) by adding at a rate slow enough to prevent localized precipitation about 5% to about 12% aqueous acetic acid solution that is preheated to the same temperature as the acid dope while vigorously agitating the mixture sufficiently to keep large coagulate particles apart into smaller coagulate particles of a size that will pass through a 45 mesh screen so as to form a liquid powder slurry; (c) aging the liquid powder slurry for about 15 minutes in about 25% to about 35% aqueous acetic acid; (d) removing the coagulating agent from the liquid powder slurry down to about 1% or less by weight of the liquid powder slurry and at a temperature of about 65° C. to about 95° C.; (e) removing liquid from the liquid powder slurry remaining after step (d) to obtain a wet powder of coagulate particles; (f) washing the wet powder with water to remove the residual acetic acid; and drying the powder at a temperature of about 65° C. to about 95° C. to remove the water.