Recycling of Polymers Questions and Answers

Answer: C

Feedstock recycling of PET is carried out by hydrolysis.

Feedstock (chemical) recycling breaks a polymer back into its monomers or other chemicals. PET is a polyester, and its ester links can be cleaved by water (hydrolysis) to give terephthalic acid and ethylene glycol, which can be purified and repolymerized. Related routes are glycolysis and methanolysis.

Hydrogenation and dehydrogenation add or remove hydrogen and do not depolymerize a polyester. Ozonation attacks carbon-carbon double bonds, which PET's backbone lacks.

Answer: A

Polymer X is poly(ethylene terephthalate).

The product shown is bis(2-hydroxyethyl) terephthalate (BHET): a benzene ring carrying two ester groups in the para positions, each esterified with a 2-hydroxyethyl group. PET is the polyester of terephthalic acid and ethylene glycol, and glycolysis with excess ethylene glycol breaks its ester links by transesterification, returning exactly this monomer-like diester. BHET can be repolymerised to PET, which is why glycolysis is a standard chemical recycling route for bottles.

Polystyrene and ABS are addition polymers with all-carbon backbones and no ester groups to cleave, and PVC contains chlorine, which appears nowhere in the product.