Polycarbonate can be recycled using glycerol

A NEW chemical technique to recycle polycarbonate plastics using abundant and environmentally-friendly glycerol can recover up to 98% of the plastic’s monomer, bisphenol A (BPA), for reuse.

Polycarbonate plastics are difficult to recycle mechanically due to the low quality of the recovered material, while many chemical recycling processes use harsh reagents or conditions. Polycarbonate was discovered in 1898, and it is estimated that by the end of 2016 4.5m t of the plastic will have been produced, which creates a waste and recycling challenge. Deepak Pant, an associate professor at the Central University of Himachal Pradesh, India, says that his new recycling method is both green and economic.

Glycerol is a byproduct of biodiesel production, so is cheap and easy to obtain. Pant tested raw glycerol against analytical grade glycerol, using both to recycle scrap optical discs. The three-part process first involved pulverising the scrap discs into 2–3 mm pellets. The optical aluminium layer is removed by vibratory shaking – the heavier polycarbonate particles sink to the bottom.

The pulverised polycarbonate pellets then go through a digestion step. Pant mixed the pellets with glycerol, Na₂CO₃, a zinc oxide catalyst, and urea, which improves the yield of the desired BPA products and slows the breakdown of glycerol, making it reactive for longer. The mixture is heated to 120?C for 15 minutes and then to 170?C for 90 minutes. During the reaction the digested polymer further reacts in an alkoxylation process, giving the desired BPA monomer. After being cooled to room temperature, methanol is added. The mixture is then filtered to remove unreacted polymer, leaving a methanol solution of the BPA.

Pant achieved similar conversion rates using both crude glycerol and the pure glycerol. The carbon dioxide and ammonia produced as by-products can be easily removed by collecting them over water.

Pant will now look at scaling up the process.

Process Safety and Environmental Protection DOI: 10.1016/j.psep.2015.12.012