Waste PET recycling: glycolysis vs. hydrolysis

Abstract

Now, we are living in a world with a high level of economical development which asks higher quantities of raw materials with lower costs of production. This option is quite impossible to be reached if the source of raw materials will not be changed with a new concept: raw materials from waste. This is the case of polyethylene terephthalate (PET) which is obtained by the reaction of terephthalic acid and ethylene glycol, both compounds being derived from crude oil. A way to obtain PET for new applications is to recycle old PET by different chemical processes, as glycolysis and hydrolysis. This paper presents a comparative study of waste PET processing using glycolysis and hydrolysis as possible methods of chemical recycling. Both processes are carrying out in batch reactors, at almost the same temperature and using the same catalyst - Zn(CH3COO)2 . The differences are the solvent (glycol and water) and the pressure inside of the reactor which is 40 bar for hydrolysis and 1,2 bar for glycolysis. After a time of reaction of 2 hours the main product obtained in glycolysis process is bishydroxy-ethylene-terephthalate (BHET) and terephthalic acid for hydrolysis process. An economical evaluation regarding energy consumption, costs of chemicals and yield of final product could be very useful for the investors interested to develop an industrial process for chemical recycling process of waste PET.