Polymers pyrolisys - how it works?

[Gloyn]

Hi,

I was browsing the Internet and I found a thread about polymers pyrolysis:

http://www.energeticforum.com/renewable-energy/7040-how-turn-plastic-waste-into-diesel-fuel-cheaply.html

Guy there states, that just due to temperature of about 400C polymer chains are being broken into shorter chains and he obtains hydrocarbons from diesel fuel range (10-15 carbons in chain). My question is: how is that possible, as all papers that I've read until now states, that not only high temperature is required, but also pressure of ~12MPa at least for successful decomposition of polymers. What chemical reactions are involved? It would be awesome if someone could give a short description of what happens (from a point of view of a chemist) to those polymers in the device from the link.

 

[jbsteele]

The type of pyrolysis being discussed in the thread is Thermal Cracking. In this process, polymers are heated to temperatures between 300-600°C and the molecules break apart into smaller molecules. This is also known as thermal depolymerization. The key factor during thermal cracking is the heat, which causes a chain reaction in which the bonds between the polymer molecules are broken, forming smaller molecules called monomers. Monomers such as ethylene, propylene and butene can then be further processed into useful products like diesel fuel. The pressure used in the device from the link is not necessary for thermal cracking, as the high temperatures alone are enough to break down the polymer molecules. However, pressure may be used to increase the yield of the desired products. In general, the chemical reactions involved in thermal cracking involve breaking the C-C and C-H bonds in the polymer molecules, which releases energy and creates smaller molecules. These molecules can then be further processed into fuels or other useful products.