Alcoholysis of poly(ethylene terephthalate) to produce dioctyl terephthalate with sub- and super-critical isooctyl alcohol

The alcoholysis of poly(ethylene terephthalate) (PET) to produce dioctyl terephthalate (DOTP) was studied using sub- and super-critical isooctyl alcohol (2-EH). In situ transformation of PET in 2-EH up to 643 K was observed with hydrothermal diamond anvil cell (HDAC). The result shows that PET begins to melt at about 513 K, and then quickly degrades to dissolve in 2-EH. But with longer time and higher temperature, new crystal solid presents which maintains stability up to the highest temperature of 643 K. The main liquid product of alcoholysis is DOTP and the DOTP is an important intermediate product which will decompose to produce crystal solid of terephthalic acid (TPA). As for the super-critical 2-EH, although the degradation rate of PET is very fast, the decomposition of DOTP is also very fast, thus, the sub-critical alcoholysis is advantageous to obtain DOTP. The optimal alcoholysis of PET to obtain DOTP are as follows: reaction temperature 573 K, weight ratio of 2-EH/PET 4 and reaction time 3 h, and the degradation rate of PET is 100% and the yield of DOTP is 97%. The DOTP is very easy to separate and purify only with SiO2 column chromatograph after removal of water-soluble components and 2-EH.