The alcoholysis reaction of polyethylene terephthalate (PET) and n-butanol to produce dibutyl terephthalate (DBTP) and ethylene glycol (EG) was investigated in the presence of a Bronsted-Lewis acidic ionic liquid (IL). It was found that a synergetic effect of Bronsted and Lewis acid sites enhanced the IL catalytic performance, and (3-sulfonic acid) propyltriethylammonium chlorozincinate [HO3S-(CH2)(3)-NEt3]Cl-ZnCl2 (molar fraction of ZnCl2 (x) was 0.67) was a good catalyst for the reaction. The conversion of PET was 100%, and the yields of DBTP and EG were 95.3% and 95.7% at 205 degrees C for 8 h, respectively. The reusability of IL was good and after it was used seven times, PET conversion and the yields of DBTP and EG did not significantly decrease. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1840-1844, 2013