Hello, I am currently working on my undergraduate thesis called "Chemical Recycling of Waste Polyethylene Terephthalate (PET) Bottles: Production of Ethylene Glycol via Mild Alkaline Methanolysis"

PET is composed of two polymers: terephthalic acid (TPA) or dimethylterephthalate (DMT) + ethylene glycol (EG).

There are three parts to my experimentation. First is the depolymerization reaction in which I react 0.5 g of PET powder, 5 g of sodium carbonate, 50 mL of methanol and 3.33 g of benzalkonium chloride pure (catalyst). Second, is the isolation and purification of EG. And third, is the characterization of the obtained EG.

I am currently having problems with the second part. My method is to add activated carbon (around 2g) to remove the catalyst, filter it, add strong acid to precipitate TPA, then it will be heated until the solids clump together and then it will be filtered again. The filtrate will then undergo simple distillation to isolate water, methanol, and any possible EG formed. Then it will undergo rotary evaporation to isolate EG. Then it will undergo characterization tests to check if EG really was obtained.

The problem is, my solution will not precipitate TPA upon the addition of a strong acid. A study that focuses more on the isolation of TPA used a benzalkonium chloride (20%) solution. When I attempted to use that for my trials, I found that it could precipitate TPA.

The difference is in our catalysts. Mine is pure and his is 20%.

Do you think that I am not adding enough activated carbon to remove most of the catalyst and therefore TPA will not precipitate?

Thank you for reading.