Synthesis of benzene from PET water bottles

Hello people,

today I present a very useful preparation, the synthesis of benzene from PET water bottles. The reaction employed is the pyrolysis of PET pieces with calcium hydroxide. The raw product is then purified by distillation. According to the reference [1], it proceeds through the initial PET hydrolysis to calcium terephthalate which then decarboxylate to benzene. Toluene, ethylbenzene, xylene and others are found as side-products.



Procedure

The synthesis is realized in a 11.4 l steel alcohol distiller re-adapted as reactor, purchased from eBay. PET bottles are cleaned and eventually dried, removed of label, cap, seal, also top and bottom part because too much hard, and cutted in pieces. Then 0.5 kg of PET pieces is mixed with 1.5 kg of calcium hydroxide ( PET:Ca(OH)2 1:3 ), introduced into reactor, pyrolysis started on a gas burner flame. The setup is in Figure.





The flame is open to maximum, the reactor bottom is red hot. Temperature of pyrolisate overcome 200 Celsius. Some fumes are collected initially, but then a yellow-green liquid pass through condenser along with water and wax. After a total of 2 hours, heating is interrupted, and everything let cool down to room temperature. Pyrolisate is separated from aqueous layer, extracted with 3x50 ml of water. Organic phase filtered through cotton plug to remove as much wax as possible. A yellow-green clear liquid is obtained which quickly turn brown; crude pyrolisate is 45 g ( 47 ml ), corresponding to 9% of the initial PET mass.

After collecting five batches, 250 ml of that is distilled simply in oil bath at 100 Celsius, discarding the fraction passing below 75 Celsius and collecting the one between 78-80 Celsius; 95 ml of very clear limpid benzene is obtained, d20 = 0.870 g/ml.



Discussion

Almost 100 ml of very pure benzene are collected from 2.5 kg of PET bottles. Reference report that from 1:5 PET:Ca(OH)2 ratio on, almost pure benzene is obtained, so theoretically the yield could increase much more.
Anyway, this experiment demonstrate that very valuable chemicals can be got from a trash material as water bottles. The reaction should not be seen only as a benzene synthesis but also the chemical recycling of PET bottles, which otherwise have to be done mechanically. The higher fractions can be recoverd as well, adding value to the experiments.

I think this reaction can be scaled up to become economically sustainable. Gas can be recovered and used to fuel the reaction itself, which furtherly decrease cost.

If biomethane is used as fuel, that add renewability to the process.

Reference

1. Chem. Lett. vol. 33, pp. 282-283, 2004

As usual, I thank you for the attention and remind you to watch the detailed procedure on my YT channel. Here you can find synthesis, purification, flammability test.

palico

Quote: Originally posted by dettoo456

Nice job. The yield is kind of shit considering the weight of PET required and natural gas but it’s definitely worth it if benzene is harder to get near you. You can also pyrolize HDPE & LDPE w/ alumina to yield long chain alkanes with potential use in gas engines. A smaller reaction vessel made out of steel and shoved into a kiln (or just a better insulated heat source) might be more economical and achieve higher yields as compared to the stove.

Quote: Originally posted by dettoo456

Moved from other thread: This paper (https://doi.org/10.1016/j.polymdegradstab.2022.109900) which describes PET pyrolysis to yield Paraldehyde, EG, and Benzoic Acid under fairly ‘weak’ conditions. Those conditions being atmospheric pressure, no catalyst or pH modifiers, and fairly fast (although they say slow) heating to only 400C. The whole process would only take 13 minutes apparently; 40C min−1 to 200C followed by 25C min−1 to 400C. They don’t state a dwell time at the 400C as far as I could tell, but in any case it wouldn’t be too difficult to replicate in theory. A yield of around 24g Paraldehyde, 10.5g Ethylene Glycol, & 4.6g Benzoic Acid are recovered as “oil” from 100g of PET. I’m looking to maybe try this procedure out in an Al paint pressure canister modified as a retort. Does anyone have any experience with a prep similar to this (that being PET pyrolysis at lower temps without any catalyst)?

Quote: Originally posted by Mateo_swe

Are this just for an intresting method of doing something with old PET bottles? There is an easy way of making benzene from sodium benzoate (food store) and NaOH (lye). Nilered has a video of the procedure. You just mix the benzoate and NaOH in an empty paint can, make a hole in the top and attach a condenser distillation setup. Then put a caming burner under the paint can and destill crude benzene. Do this outside. The crude benzene can then be re-distilled to obtain clear benzene. I tried this and it works very good.

Quote: Originally posted by palico

This method is much easier than sodium benzoate pyrolysis. You need two reactions, while here it is just one.