PET depolymerisation in supercritical ethanol catalysed by [Bmim][BF4]

Abstract

Poly(ethylene terephthalate) (PET) was successfully depolymerised under supercritical ethanol. Robust conversion of 98 wt% from PET to diethylterephthalate (DET) was obtained by adding [Bmim][BF₄], as catalyst, accompanied by reduction of depolymerization time from ca. 6 h to 45 min. DET formation in the depolymerization process was characterized by HPLC, ¹H NMR, FTIR, TGA, DSC and SEM showing high purity and yield. The yields for different runs were determined by HPLC combined with interpolation from the standard/calibration curve. A 2³ factorial design was employed to evaluate the effect of different inputs such as (i) reaction time after supercritical condition, (ii) volume of ionic liquid (VIL) and (iii) amount of PET in the yield of DET. By the analysis of variance (ANOVA), including F-test and P-values, it was found that reaction time and amount of PET inputs correspond, respectively, to 44% and 23% of the evaluated response. Another positive aspect showed by the factorial design is that the amount of catalyst was not significant in the process, and the depolymerization can be conducted successfully since a small amount (this study used VIL ranging 0.15 to 0.35 mL) is present in the reaction media. The method proposed in this paper is advantageous over others, reported in the literature, due to the lower reaction time required for PET depolymerization and the higher DET yield.