The Bombay Technologist

Glycolysis of Waste PET Using Zeolites as a Catalyst

Gaurav Mirlekar

Department of Oils Oleochemicals and Surfactant Technology

Balkrishna Kesarkar

Department of Polymer Engineering and Technology

Keywords: Polyester, Recycling, Monomers, Oligomers, Zeolites.

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Abstract

Polyethylene terephthalate (PET) bottle waste can be depolymerized using excess of ethylene glycol (EG) in the presence of zeolites, b-zeolite and Y-zeolite as transesterification catalyst. The glycolysis reaction can be carried out under reflux in excess of ethylene glycol for up to 8hrs. The product of glycolysis was mainly the virtual monomer, bis(2-hydroxyethyl) terephthalate (BHET) admixed with dimer as residue. The BHET obtained will be in pure crystalline form. Influence of the reaction time, PET: EG ratio, type, and concentration of catalyst on the yield of the glycolysis products were investigated. The yield of BHET monomer will be more than 60%, which is comparable with the conventionally used heavy metal catalysts such as zinc acetate and lead acetate. Melting point of zeolite is much greater than oligomer. So the oligomer+zeolite mixture can be separated by heating it to the melting point of oligomer followed by solid-liquid separation. This process of glycolysis of PET is economically viable and the catalysts are environment friendly.