While I was working at a manufacturing company in Toronto, I often had lunch in quite a large conference room, equipped with many foldable chairs, tables, and my favourite, two leather love seats. I loved it as there was plenty of room for personal space due to everyone being afraid of everything all the time. Lots of room! This is where I met Bill, and this is where Bill introduced me – in few words – to the plastic-to-diesel recycling process. At first, I was skeptical… then I was confused… and over time, I realized how amazing of an idea it is.
My first searches on the web resulted in my finding a company called Cielo, based in Alberta. The photos I found made it look like the most complex and complicated process ever known to man. Really, it is quite an overwhelming impression. I can’t find the original photo, but I’ll show what I could find. I remember saying “Bill, your idea already exists!”. We discovered that their main issue wasn’t the depolymerization in itself, but rather the removing of the undesirable sulfur that slowed them down.
There were other companies I found, but nothing specifically for making fuel. Doing a search now will reveal more companies looking into this technology. I think it’s because of how it looks like under ESG metrics, but I can’t be certain. However, plastic waste (and waste in general) is quite a difficult topic to discuss, especially if you see how it’s managed in many third world countries. Boyan Slat (The Ocean Cleanup) showed how plastic materials break down over time into tiny microplastics, as well as his solution to solve the problem. There are many documentaries and analysis of microplastics in food and water, I digress.
Bill wants to make his own company in this field – he really wants to get government funding due to the monetary requirements of such a startup. Such a massively funded process would bring to its success a well-designed recycling process. People would be able to recycle and it would actually mean something.
I remember asking Bill this question many times. What kinds of plastics are no problem to turn into diesel? His response: #2, #4, and #5 plastics. The first two are multiples of 2, and the last, 5. Simple way to remember (for me). Now, how does this work? In a nutshell: Place in a steel container, suck all the air out, heat it up.
“Why take the air out?” I asked. “So that it doesn’t burn.” Was his reply. “How is the air removed?” He said to start heating from underneath, and the heat will push the air out, since hot air rises. I am not sure how sound this principle is, since there will still be some air left inside the container, right? Anyway, here is his machine taken out of storage during a surprise visit while he wasn’t there.
As this requires heat, this is a thermal depolymerization process; polymers are turned into a monomer or a mixture of monomers. It is an uncatalyzed reaction as there are no added chemicals or bio-agents; the only input is heat. This can be a chaotic process, giving rise to a mixture of volatile compounds (unless the plastics are of the correct category, and clean from contaminants) that have a higher heating value and can be burnt more efficiently.
As mentioned before, the plastics of focus are #2, #4, and #5. The presence of PVC can be a problem as it’s thermal depolymerization produces toxic HCl gas, which apart from being a slow and silent killer, clogs and corrodes equipment as well as the final product (diesel). I learned that plastic on copper wires is this kind of plastic, so trying to do copper recycling and fuel recovery at the same time would require a dichlorination system that would be expensive and add complexity to the system.
Another example of what would require more complexity is trying to depolymerize tires, as it would require a hydrodesulfurization system, due to the high sulfur content, which must be removed (now you see why Cielo may be having problems). We can’t be driving around burning diesel that has hydrogen chloride or sulfur in it now, can we! It’s real nasty and would probably not be very good for the engine. IDK ¯\_(ツ)_/¯
The primary plastics for depolymerization are polyethylene (PE[HD]/02, PE[LD]/04) and polypropylene (PP/05), which account for almost half of world-wide plastics production. They are pure hydrocarbons and thus, have a much higher conversion to fuel.
The recycling of other polymers like PFTE, Nylon 6, polystyrene (#06) and PMMA are more difficult and expensive. Even though they can undergo depolymerization to give their starting monomers, it is more expensive as it requires more energy and further sorting and filtering processes. The recycling of PET (#01) may also be a group to consider, as it contains a high quantity of resin and is a well understood thermoplastic.
Image thanks to Marcin Jozwiak from Pexels
The primary source of criticism is the fact that it requires a lot of heat, so it’s a very energy-consuming process. Thus, a serious balance of energy efficiency and conservation must be undertaken, compared to regular incineration. Large-scale operations are unequivocally more attractive because of vast increases in efficiency, due to economies of scale. Simultaneously, efficient and outside-of-the-box solutions to generating the energy required should also be explored for offsetting energy costs.
There are also cases where people in rural communities in Africa did this themselves, because although it may not be the most efficient process, it gave them diesel needed to power certain electro-mechanical devices that only run efficiently on diesel. Think of a truck or a generator. That being said, this device is intended to solve multiple problems at once: garbage and fuel. If a large-scale operation is not feasible, small-scale solutions are likely to win over, perhaps with additional outputs such as oil and gas. Some solutions are also intended for the making of construction material, rather than fuel (bricks). The question is then asked, is input material purity? If so, a recycling revolution really needs to take place so that something like this pulls through to the end.
Thanks for reading!