Several years ago I wrote a blog on the topic of burning plastics – in a controllable fashion – as opposed just to dumping it somewhere. The act of burning plastics – or lest talking  about it has got a “trigger” effect on many people. That is understandable, but a little discussion helps clear the air. 

I still think that there is nothing principally wrong with burning the right kinds of plastics. That is how develop nations deal with this mixed unusable feedstock. It is called Waste-to-Energy and Copenhagen turned one of the most modern installations of its kind into an icon! 

Burning plastic, as well as any other organic substance, still produces CO2. Whereas uncontrollable burning releases only emissions. Controlled burning enables to harvest the energy of combustion into useful work. Whether it is for heating or electricity generation purposes. 

Any use of waste plastics is better than littering! I stand behind this fully.  

Despite many efforts of, waste still ends up washed out on beaches or collects in the middle of the oceans, there seems to be more plastic ending up in the environment every year. As the humanity’s life standard grows, so does the consumption of plastic. The problem is that plastic waste does not have any use for remote communities, and since no collection is present, it just gets dumped. The problem of ocean pollution begins on the land. There is the place to take care of it and solve it at its source. 

How to deal with plastics?

Plastics are made of crude oil. This black liquid extracted from the earth’s crust undergoes a huge amount of processing, before becoming plastic. When the highly purified feedstocks – such as ethylene, are polymerized in reactors, into materials that are solid at room temperature, polyethylene. This world’s most popular polymer type gets used everywhere, from packaging bags and bottles, to wire insulation, pipes and numerous consumer products. 

Annually, more than 300 million tons of plastics are produced. A tiny fraction gets re-cycled into its original state – real recycling. Most of it gets dumped or burned or down-cycled, since there are no economic alternatives. 

Why are plastics so uneconomical to recycle?

In short: cheap virgin materials,mixed sources, presence of additives, dirty and irregular collected waste. 

Virgin polymers are really cheap – polyethylene pellets cost less than a US dollar per kilogram.  For this price, you get pure, clean pelletized material, that is ready to use in an plastic injection molding, or en extrusion machine. On the other hand, used plastic, for example from a food wrapper, contains ink, rest of the food it wrapped and some dust. It is also likely that two wrappers, although similar, will be of a different grade and will contain different additives. If you want to re-use it, you first sort it, grind it down, wash it, then dry, melt, filter, vacuum distil and eventually,  mix with virgin material, since the material has degraded on the way. In this way, you produce a product with a slightly inferior quality, than the virgin product – both optically (colour) and mechanically (strength) and hygiene. It is a hard sell to a customer.  The real problem with recycling is getting qualitative feedstock. I gave an example with polyethylene. There is no bin for polyethylene. There is, if you are lucky, a bin for packaging. This includes PET, Polypropylene, PLA et cetera. Sorting this rich mix is technologically or labour demanding. 

If you manage to get hands on pre-sorted polyethylene, there are ways to turn it into something useful. There are, however, not many companies, able to do that. This Austrian one, is an example of a successful business. 

This is the best you can do with plastic waste in theory. In practice, building up such processes is technologically demanding and costly and requires large amounts of pre-sorted feedstock and high tech heavy machinery to turn it into something useful. It can therefore successfully work only in densely inhibited industrialized places. It will not work in remote areas. 

 What are the other options? 

Re-cycling means finding a use for the plastic, while keeping its mechanical properties. Ideally, you return in to the same application as you collected it from. 

There is down-cycling, which means finding an application in a lower value area, here, mixed granulated plastic gets re-formed into products, where the optical quality is not of high importance – such as Gardening tiles, speed bumps, traffic sign bases et cetera.

 These tiles are also made of Down-cycled plastic. The manufacturer did not disclose its composition, but it is likely PE, PP or PVC. 

Down cycling is less cost-demanding than re-cycling. Equally, the quality of the entry ingredients can be lower, for example in terms of the colour. The 

reality is that very little plastic actually gets recycled. Most activities labelled as recycling are in fact down-cycling. 

 

Even downcycling demands a well built infrastructure and machinery to re-process sorted and collected mater

ial of sufficient quality and in large quantities. Before such material is processed

, it must be dried, melted, filtered and pelletized to be fed into injection molding machines.  Otherwise, it is not economically viable.

So what is the next worse thing you can do with plastics? 

Pyrolysis – turning solids back to gases and liquids. 

In this process, also termed – chemical recycling- (I do not like this name, since it’s misleading), mixed feedstocks of polymers are heated to progressively higher temperatures in reactors, in the absence of air. As plastic gets hotter, it will start to melt. Beyond 250 C, some plastics start to break up into smaller blocks – a process called thermal depolymerization. These blocks are gaseous or liquid at room temperature and in properties, they are similar to crude oil or its components – petrol or diesel. The plastic pyrolysis oil (PPO) can get combusted. It can be blended into diesel and utilized as a fuel for power generators. 

Burning makes the climate crisis worse! 

One of the main arguments against using plastics as an energy source is that this only further exacerbates the climate crisis. This can be somewhat debunked by a back of the envelope calculation.  The total annual production of plastics is 300 million tons. If we simplify plastics to -CH2- (Polyethylene repeating unit), the worst case scenario, the full amount of plastics would contain 257 million tons of pure carbon (C = 12 grams/mol, H2 = 2gram/mol ) (300Mt/14*12 = 257Mt). If this carbon got perfectly combusted, it would produce CO2 = about 950 million tons of CO2 (molar weight 44g/mol), just shy of 1 Gt. Annual global CO2 production assigned to human activity was 38Gt in 2022. Emissions of burning all this plastic would be between Japan and Germany. 

Fortunately, most plastic does not have to get thrown away every year. It becomes embedded in many of our structures – pipes, cables, cars, building materials etc. 

The main problem to target is the small amounts of packaging, maybe several per-cent that causes major pollution of the land and sea. 

Pyrolysis might not be the favorite solution, but I view it as an appropriate solution. One, which takes the less than beautiful reality of the world into account.  Moreover, this turns waste plastic into something with a value, so it won’t end up as litter so quickly. Fossil fuels are there to stay for declades to come, especially in decentralized applications, where generators will provide power to remote communities. 

It is exactly these communities that struggle with waste management. Whether it is Asia, or Africa, this is the appropriate solution. 

Building a pyrolyzer is principally a simple. Almost DIY friendly. 

 

There are also more professional ways to build pyrolyzers, like this Indian company has demonstrated.

In the case of pyrolysis, it is possible to build a cheap device in simple conditions. Since the products of the pyrolysis are highly flammable and gases and liquids are formed, there is inherent danger of explosion and fire. Utmost care must be taken and preferably also safety designed into the equipment. 

Burning better than littering? 

The next option of disposing of low-value mixed and dirty plastics is, like suggested in the previous blog, burning them. But not burning to get rid of them, but to turn the energy present in the chemical bonds into useful work.  Again, the main reason being to prevent plastic being thrown out into the environment.   

 

The reality is that people will have a demand for heat. In remote areas, heat for cooking and heating is sourced from fossil sources, coal, oil or gas and from renewable sources – wood or charcoal. Wood is not always a good renewable source, we need trees to keep growing not just to capture CO2, but primarily, to prevent soil erosion and maintain biodiversity. Charcoal, although one of the most widespread, is also a very wasteful way of utilizing wood. In the charring process, about 90% of the stored energy is lost. Producing charcoal in the traditional way also leads to heavy smoke emissions. 

Complete and efficient combustion of plastics is a safe, efficient and appropriate way of disposing of them. In order to reach the right temperatures, it should always be done in a closed stove and not by itself, but it should have some other, porous materials present, such as wood, to wick the molten plastics. This energy should always be utilized for some purpose. Nothing, no plastics or organic matter should be burned, just to get rid of it. This is the worst you can do. Or do you think, that burning these rice straw in the open fire is in any way beneficial to the environment, seeing how much smoke it produces?