Plastic supply: elastic demand?

24 Jan 21 | Re: The obstacles to reducing plastic production | Link-U-Post

We've all seen the alarming environmental consequences of plastic waste, so we all should agree that we want to use less of it. But is that even possible? My understanding is that plastic is made from the fractions of crude oil that are less valuable as fuel. In other words, it's a by-product. On that understanding, so long as there's a demand for petrol, the other fractions of oil are going to have to be used for something, so less demand for plastic might result in a lower price but wouldn't do much to reduce supply.

This matters particularly because plastic recycling seems quite dubious. Even assuming that all the plastic you send for recycling actually gets recycled, and not shipped round the world for two years before being thrown into a pond in Malaysia, it will degrade during the process and can't be sent round the loop indefinitely, so recycling only delays the inevitable. A hundred tons of polyethylene that are manufactured are a hundred tons that will one day end up in landfill (or the ocean, or my back garden) whether it takes a week to get there or whether it gets recycled for ten years first. A similar point can be made about reusable plastic items: no matter how treasured your plastic plates are, you aren't going to keep them for all eternity so eventually they will become waste even if your heirs use them for generations before that happens. As soon as any plastic is manufactured it is destined to become rubbish eventually.

Therefore, there are only two ways to deal with the plastic problem properly:

find some way to break it down when it inevitably gets thrown away - I've heard of solutions involving specialised bacteria, which would be wonderful news, or maybe some process could reswizzle it into a material that would biodegrade after use, or maybe it could be burnt and carbon-captured or something.
manufacture less plastic in the first place.

The first solution seems vital to research but quite a long way off - let's cross our fingers. In the meantime, is the second solution economically plausible or not? I'm going to look at the five most commonly used polymers and see whether they actually are by-products, as I vaguely believe they are, and if so, what else might be done instead with whatever they are made from. According to Creative Mechanisms the five most common plastics are polyethylene terephthalate (PETE), polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP) and polystyrene (PS). Good, that more or tallies with what would probably spring to mind for most people. Let's take a look at them. (As well as Creative Mechanisms, a great site, I'm getting some of this from Wikipedia so the usual caveats apply - maybe this is all bunk planted by internet anarchists.)

PETE

PETE is known as polyester when used for clothes but also makes see-through plastic bottles and other things. It's made from ethylene glycol and terephthalic acid. Ethylene glycol comes from ethylene (ethene), or else from carbon monoxide. Carbon monoxide gets produced mainly by burning coal, but ethylene comes from crude oil - it's made by cracking larger hydrocarbons such as naphtha and gasoil. As for terephthalic acid, it is produced from p-Xylene, which comes from naphtha.

If demand for PETE were to drop, the petrochemical industry would presumably have a lot of naphtha on its hands. Other uses of naphtha are as lighter fuel, camping fuel, and to dilute crude oil to make it runnier so that it can be moved about. It doesn't seem like those applications have a lot of latent demand so I think that in the event of a naphtha glut, industry would either continue to produce plastic with it and sell it at lower prices, or else find some use for burning it all for fuel.

As for carbon monoxide, it apparently has various industrial uses so presumably the coal plants would turn to those, assuming they didn't just release it all into the environment. This question is of limited interest to the environmentally minded since everyone already agrees we want to burn less coal.

PE

Plastic bags, detergent bottles, wheelie bins, artificial hips. This is an easy one. Polyethylene is made from ethylene, which as we've already seen is mainly made from naptha. Reduced PE use would therefore add to the naphtha glut resulting from our abandonment of PETE.

PVC

Used for pipes and your dad's trousers, PVC is made out of chloroethene (ethylene with a big fat chlorine atom plonked onto it). Unsurprisingly it is made out of ethylene, which to reiterate, comes from naphtha. The chlorine apparently comes from brine, so it isn't a by-product: we would just leave it in the sea.

PP

Polypropylene is used for packaging and car parts and has cornered the market in living hinges, ie the bendy bit of a sauce bottle lid, which apparently is a very specialised application. It's made from propylene (propene), which also comes from that wonder substance naphtha.

PS

Polystyrene is used to make squeaky packaging that goes everywhere as well as vessels, cases, pots, tubs and cups. It's made from a rather extravagent molecule called styrene, which is produced from ethylbenzene. Ethylbenzene is derived from unicorn sweat and also occurs naturally in petroleum, where almost all of it is used to make plastic. Small amounts of it are also used for an assortment of things including synthetic rubber, paints and pesticides. However those account for well under one percent of ethylbenzene use so if there was a glut of it then it might test the limits of human ingenuity to find what to do with it.

Conclusion

It seems that a big drop in plastic consumption would lead to a great deal of naphtha knocking around without much purpose, and smaller but still significant quantities of ethylbenzene. It doesn't seem like the other known uses of these sexy liquids would ever be able to account for the total amount produced, so I would foresee that barring a worldwide government ban, plastic would continue to be produced and offloaded to whoever would buy it.

Therefore, a better approach to the plastic problem might be to reduce demand for the intrinsically valuable products of crude oil, chiefly petrol. We should continue to research ways to deal with plastic at the end of its life cycle, and to dispose of the plastic that we use as responsibly as we can, but I would advise anyone campaigning to reduce plastic consumption to pivot towards campaigning for green energy and reduced energy use. Nobody is drilling up crude just to get naphtha, so if demand for fuel oil drops then the naphtha stays in the ground along with it and the plastic problem goes away. Finding uses for naphtha that aren't environmentally nasty would also be worth doing.

Posted by MR BOERHAAVE at 15:30

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