Tyre Pyrolysis and the Circular Economy
- vicluca
- Sep 24
- 4 min read
Updated: Sep 26
Victor Luca
Published in The Beacon 21-Aug-22
Pyrolysis represents one environmentally-friendly way of dealing with end-of-life tires.
One of the research activities in which I was heavily involved from 2009 – 2019 was to find a solution for the disposal of radioactive spent ion exchange resins.
An ion exchange resin is typically encountered in a domestic setting as ½ mm polystyrene co-polymer beads, in other words plastic. Because of the chemical functionality incorporated into these polymer beads, they are able to efficiently adsorb impurities from contaminated water. For example you may find these materials in the water tank of espresso coffee machines to clean the water before it enters the machine and in point-of-use water filter systems.
Ion exchange resins are also used in nuclear power plants to clean reactor and spent fuel pool cooling water. Since the spent resin beads are highly radioactive they are extremely difficult to dispose of. One solution for the disposition of these polymers is to pyrolyze them and then send them to a special radioactive waste repository.
Municipal wastes are much easier to handle and dispose of. However, when you clean something you invariably also have to dirty something. For instance, in a domestic setting when washing your dishes the detergent-loaded water goes to the waste water pipe of your home, the dish cloth eventually ends up in a landfill and the plastic detergent bottle also has to be dealt with.
Pyrolysis is the process of decomposing materials by heating them in the absence of oxygen or in an oxygen-depleted atmosphere. This is how charcoal is made worldwide. Pyrolysis is therefore distinct from combustion which simply converts essentially all the carbon in the polymer to CO2 and other volatile green-house gases. When one pyrolyzes many polymers (plastics), three products are typically produced. A carbon powder, oil and some volatile gases.
Modern tires may look simple but they are, in fact, complex composite materials and can include natural rubber, synthetic rubber, steel, nylon, silica (derived from sand), polyester, carbon black and petroleum. Without these ancillary components your tires would last only a fraction of the time that they do at the moment.
We in New Zealand generate about 4.2 million waste tires per year. Whether you drive an internal combustion engine car or an electric vehicle, you will produce waste tires.
In NZ at the present time we are using waste tires as a fuel to heat cement kilns which operate at about 1400 oC. The tires supplement the coal that is used to power the kilns and as a result copious amounts of green-house gas emissions (CO2) are belched into the atmosphere. This is only half of the emissions that come from cement, the other half of the emissions come from the raw material lime, calcium carbonate, which is converted to CaO and CO2. Technical options are being explored for a solution to this half of the emissions equation.
Worldwide cement production represents a serious source of emissions, typically about 8% of global emissions. When tires are used as fuel in cement kilns they are completely combusted (burned) along with the other fossil fuels that are typically used. All of the carbon in the fuel and the tires ends up in the atmosphere. This is not what we are supposed be doing if we intend to continue to live on this planet.
There is absolutely no reason why hydrogen gas produced through renewable electricity can’t be used to heat cement kilns. Several major cement manufacturers in Europe are switching to the use of emissions-free hydrogen fuels to power cement kilns and also in steel making.
Instead, in NZ we are content to brag that we have found a use for waste tires. Yes, we have recovered energy from the tires. However, in getting rid of one waste (the tire) we have produced an even more insidious waste, the carbon dioxide emissions. Personally, I would rather put the tires into a landfill than the current practice of burning them. Of course there are alternatives for waste tire disposal such as re-use as some other product.
Frankly, rather than simply burning the tires in air to fire a cement kiln, it would be preferable to pyrolyze the tires to form the three valuable products shown in Figure 1.
The fuel oil could be used in farm machinery or to fire the pyrolysis plant and the carbon black is a valuable soil amendment. The metal wire can be recycled. The yield of carbon is at least 30% by weight which is quite a bit of the carbon. Carbon black is a valuable product which can be used as a soil amendment and/or as a feedstock for the manufacture of new tyres. In either case it is carbon that does not end up in the atmosphere.
These days, turn-key tire pyrolysis machines can be purchased at relatively low cost. I have just received very modest quote for a pyrolysis machine that can deal with every waste tire produced in this district. In this process the volume of waste tires is greatly reduced which is also a significant benefit.
Surely we can do better than just burning used tires and contributing to our per capita emissions. A regional end-of-life tyre pyrolysis facility would not just be good for the environment but would also contribute to our economy and create jobs.
Mayoral Forum Presentation
On 14-Aug-23 I presented to the Mayoral Forum on the possibility of setting up a regional end-of-life tyre pyrolysis facility. Below is my presentation.
Here is a link to the youtube recording:
Prior to the presentation I circulated what I referred to as White Paper on the subject.
The forum supported pursuing this initiative as part of the regional waste management strategy currently underway.
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