The Science of Pyrolysis
Pyrolysis of plastic (or thermal depolymerisation) is the breakdown of plastic back to its crude oil origin and is one way of processing plastic waste to take it out of the environment and make it into something useful.
Plastics are materials composed of long chains hydrocarbon based units which have been derived from crude oil. The simplest example of this is the polymerisation of ethylene/ethene (C2H4) to form polyethylene (C2H4)n. Polyethylene is a common material for plastic carrier bags.
Pyrolysis is the reversal of this process. The process occurs at high temperature without oxygen, in the presence of water vapour and a catalyst. Pyrolysis doesn't break all the bonds evenly to produce the ethylene monomers as before but occurs stochastically to produce a distribution of hydrocarbon products of differing atomic chain lengths.
This video describes the pyrolysis process from plastic to fuel well:
Application of Pyrolysis in Ukraine
You may be thinking pyrolysis of plastic is all well and good but doesn't really solving the plastic waste issue because all we are producing is hydrocarbons which will be burnt releasing CO2 into the atmosphere. And you would be correct that this solution is not perfect but for these reasons we believe it is very much worth still pursuing in Ukraine:
Pyrolysis removes stagnant waste plastic from the environment which is not degrading and causing much damage to wildlife for example.
Pyrolysis makes use of the energy held in plastic. Hydrocarbons are fundamental to the operation of our world and perhaps more so in Ukraine where the options to switch to a green solutions is far more economically out of reach for most. Every litre of pyrolysis fuel produced is a litre less of fresh crude oil demand.
As Christians we believe it is good for people to work to provide for themselves and that we are called to care for the Earth God has put us in. This project, in creating jobs and processing plastic waste (even to this not so perfect extent) allows us to practically demonstrate the values God cares about.
And linked to this, the Pyrolysis project for us as Christians is ultimately a means to an end of seeing more people in our community in Ukraine come to know and follow Jesus Christ. The project helps us to get to know far more people than we would otherwise giving us an opportunity to share the hope we have in a God who loves them deeply and fully.
Ukraine has a lot of plastic waste just like many countries around the world and much of it is held in plastic dump sites such as in this photo:
Our processing of this waste by pyrolysis in Kaharlyk currently operates as follows:
1) The plastic is received as large compact chunks from the waste processing centre. It is stripped and the big stray pieces of cardboard and other non-plastic is removed. The waste is shredded and then sent through the sieve to ensure only the small enough pieces of plastic proceed. The remaining plastic is reshredded until the flakes of plastic pass through the sieve.
2) The shredded plastic is then sent to the washer to remove the dirt.
3) It is then sent into the pyrolysis unit which is a cuboid furnace where the plastic passes through it six times in screw augers. This is where it breaks down at 450C in the presence of a catalyst.
4) Almost all of the fuel product is vapour upon exiting the pyrolysis unit. This passes through the heat exchanger cooling column which condenses the vapour to liquid and separate it from the gas.
5) The gas product is fed back into the furnace such that the unit powers itself and the liquid is collected and released into storage at the bottom of the cooling column.
Some photos to illustrate the process are shown below:
Development Plans during the Gap Year
Wayne started with an experiment pyrolysis unit on a table with the current unit being his 4th generation with a projected capacity of processing 200kg/hour of plastic. Long term, we are looking to be able to design a unit which will fit in a 40ft shipping container so it can be transported and deployed with ease. The following steps will be the focus of the work on the Pyrolysis project during my gap year:
1) The first step is to eliminate the bottlenecks in the supply chain which block a seamless process from waste plastic to fuel so that it can start generating some income. The most prominent problem currently is the production of wax where the plastic has not broken down sufficiently.
2) Then the fuel requires improvement in its quality. This is because the liquid product is a mixture of lots of different hydrocarbon chain lengths which limits its use. If we can build a fractional distiller, then we can separate the fuel into its constituent parts.
3) Finally, there are also health and safety concerns since these are not regulated in Ukraine. It will be necessary to see where simple but effective health and safety measures can be implemented to be able to prevent and mitigate accidents where possible.
If you have read this and are inspired and/or have relevant expertise you would like to share, please do get in touch here. We would also be delighted to welcome you for a short visit if you who would like to see the project first hand.