Abstract: Disclosed is a method of purification of utilized acetylation fluid recovered from a process of acetylating wood. The method involves subjecting the recovered acetylation fluid to cooling crystallization. By this method terpene and terpenoid impurities are removed, as well as other impurities. Disclosed is also a method of acetylating wood resulting in acetylated wood and utilized acetylation fluid comprising acetic acid, and purifying the utilized acetylation fluid by cooling crystallization.