Solvolysis Chemolysis

PET is manufactured in a two-step process. In the first step terephthalic acid (TPA) is esterified with ethylene glycol (EG) to form bis-2-hydroxyethylene terephthalate (BHET) and oligomers up to a molar mass of 2000 g/mol. Older plants use the transesterificafion of dimethylterephthalate (DMT) with EG, because for a long time it was difficult and 

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Solvolysis (chemolysis) is defined as a techniqne which obtains the raw materials, snch as TPA, DMT, EG monomers and oligomers as the reverse process of PET prodnction by saponification or transesterification with water, methanol or EG. For the process of PET production raw materials of high purity are obligatory. Polycondensation is not a chain reaction, but a step reaction. Impurities can stop the polycondensation at low molar masses, so high-purity standards are also reqnired for the solvolysis prodncts. The choice of process depends on the starting material and the demand for solvolysis prodncts. 

Heterogeneous process mainly involves chemolysis/solvolysis, and it uses chemical reagents or solvents for depolymerization of the polymer into monomers. It is a secondary recycling technique depending on the nature of polymers, a wide variety of solvents are used for the depolymerization process. Based on the nature of solvents, it is named as alcoholysis, methanolysis, glycolysis, etc. 

Homogeneous process involves chemolysis or solvolysis. Here, plastics are treated with some chemicals or solvents and are depolymerized to monomers. Based on the chemicals used, it is classified as hydrolysis, methanolysis, alcoholysis, glycolysis, etc. [26]. 

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