Process for the continuous production of cellulose esters

Claim 1

A CONTINUOUS PROCESS FOR THE ESTERIFICATION OF CELLULOSE WHICH COMPRISES THE FOLLOWING PROCESS STEPS: DEFIBERING CELLULOSE IN 15 TO 30 TIMES ITS DRY WEIGHT OF WATER; REMOVING WATER FROM THE DEFIBERED CELLULOSE UNTIL IT IS IMPREGNATED BY AN AMOUNT OF WATER OF FROM 0.6 TO 2.5 TIMES THE DRY WEIGHT OF THE CELLULOSE; SUSPENDING THE RESULTING WATER IMPREGNATED CELLULOSE IN 30 TO 200 TIMES ITS DRY WEIGHT OF AQUEOUS LOWER CARBOXYLIC ACID, SAID AQUEOUS LOWER CARBOXYLIC ACID BEING A SOLVENT FOR THE CELLULOSE ESTER BEING MANUFACTURED AND HAVING A CONCENTRATION OF FROM 50 TO 80%; REMOVING AQUEOUS CARBOXYLIC ACID FROM THE RESULTING SUSPENSION UNTIL THE CELLULOSE IS IMPREGNATED BY AN AMOUNT OF AQUEOUS CARBOXYLIC ACID OF FROM 1.5 TO 4 TIMES THE DRY WEIGHT OF THE CELLULOSE; DISPLACING THE REMAINDER OF THE WATER FROM THE RESULTING ACID IMPREGNATED CELLULOSE BY MEANS OF AT MOST 3 TIMES THE DRY WEIGHT OF THE CELLULOSE OF THE SAID LOWER CARBOXYLIC ACID WHEREBY CELLULOSE IMPREGNATED WITH SUBSTANTIALLY ANHYDROUS ACID RESULTS TOGETHER WITH AQUEOUS LOWER CARBOXYLIC ACID; WITH THE PROVISO THAT THE SUSPENSION OF THE SAID WATER IMPREGNATED CELLULOSE IS EFFECTED WITH THE ENTIRE AMOUNT OF THE AQUEOUS LOWER CARBOXYLIC ACID RESULTING FROM THE SAID DISPLACEMENT OPERATION AND AN AMOUNT OF THE AQUEOUS LOWER CARBOXYLIC ACID RESULTING FROM THE SAID REMOVAL OPERATION SUCH THAT THE TOTAL WEIGHT OF AQUEOUS LOWER CARBOXYLIC ACID PER UNIT OF TIME USED FOR THE SAID SUSPENSION OPERATION REMAINS CONSTANT; ESTERIFYING THE SAID CELLULOSE IMPREGNATED WITH SUBSTANTIALLY ANHYDROUS LOWER CARBOXYLIC ACID RESULTING FROM THE SAID DISPLACEMENT OPERATION WITH A MIXTURE OF A LOWER CARBOXYLIC ACID ANHYDRIDE, AN ESTERIFICATION CATALYST AND A SOLVENT FOR THE CELLULOSE ESTER BEING MANUFACTURED; AND STOPPING THE ESTERIFICATION OPERATION USING REMAINING AQUEOUS LOWER CARBOXYLIC ACID RESULTING FROM THE SAID REMOVAL OPERATION, WHICH ACID HAS NOT BEEN USED FOR THE SAID SUSPENSION OPERATION.