Method for the continuous vapor phase acetylation of cellulose fiber

Claim 1

IN A PROCESS FOR THE CONTINUOUS VAPOR PHASE ACETYLATION OF DRY, CATALYST IMPREGNATED CELLULOSE FIBER WHEREIN THE FIBER IS CONTINUOUSLY MOVED ON A CONVEYING MEANS THROUGH AN ACETYLATING ZONE HAVING A FIBER INLET AND OUTLET, THE IMPROVEMENT WHICH COMPRISES FEEDING INTO THE PORTION OF SAID ACETYLATING ZONE ADJACENT SAID FIBER OUTLET, AN ACETYLATING VAPOR INITIALLY CONSISTING OF A MIXTURE OF 75 TO 95% BY VOLUME OF ACETIC ANHYDRIDE VAPOR AND FROM 25 TO 5% BY VOLUME OF ACETIC ACID VAPOR, ACETYLATING THE MOVING FIBER WITH SAID ACETYLATING VAPOR MOVING IN A DIRECTION GENERALLY COUNTERACTING TO THE MOVEMENT OF THE FIBER AND THE ACETYLATING VAPOR BECOMES PROGRESSIVELY MORE SPENT AND DILUTE IN ACETIC ANHYDRIDE AS IT MOVES TOWARD THE FIBER INLET PORTION OF SAID ACETYLATING ZONE, AND REMOVING THE SPENT ACETYLATING VAPOR ADJACENT SAID FIBER INLET.