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Plastic Pyrolysis is not a Solution

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This topic contains 3 replies, has 2 voices, and was last updated by  Stan 1 week ago.

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Frogfall frogfall

Plastic Pyrolysis is not a Solution

01/12/2019 at 23:18

Why pyrolysis and ‘plastic to fuels’ is not a solution to the plastics problem

https://www.lowimpact.org/pyrolysis-not-solution-plastics-problem/

Interesting post and thread on “lowimpact.org” website.

Wonder technology fixes such as pyrolysis for ‘plastic to fuels’ (1) and green energy from waste (EfW) are therefore offered up as the future solution. For, if such machines were capable of simply and sustainably converting plastic into fuel or energy, then citizens may feel encouraged to buy more and waste more, liberated from guilt with the knowledge that anything they saw and wanted could be purchased.

But this premise is inherently flawed. Pyrolysis of plastic can never be sustainable. In a recent academic journal, I detail why the concept is thermodynamically unproven, practically implausible, and environmentally unsound (2).

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warrior
02/12/2019 at 07:22
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Thanks for the link. Unfortunately the article goes off on a perpetual motion tangent. For waste, how do you compare inefficiency of pyrolysis to the plastic just being dumped into the ocean or burned in an open pit?

warrior
02/12/2019 at 23:59
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Yeah – I don’t think he’s doing himself any favours by talking about perpetual motion.

If his contention is that it takes 1000 kJ of fossil fuel burn to create 800 kJ worth of pyrolysed-plastic kerosine, then that would be a decent objection. That would not only be negative in energy terms – but when the 800 Kj of kerosine is eventually burnt, the total atmospheric carbon for that energy would be the equivalent of burning 1800 kJ worth of fossil fuel.

In fact, even if you got your 800 kJ worth of pyrolysed plastic kerosine by burning only 20 kJ worth of fossil fuel, you would still eventually send 1000 kJ worth of CO2 into the atmosphere.  But, either way, he doesn’t actually offer any numbers to back up his argument.

If this is supposed to be an argument in favour of EFW (energy from waste) plants – where the entire calorific value of the plastic is used to get electricity and heat – then why doesn’t he say so?  EFW also “disposes” of the waste plastic – and displaces an equivalent amount of fossil fuel use in power stations.  Of course it isn’t carbon neutral – as the plastic is fossil-derived in the first place.  So I guess it all depends on whether you want to instantly stop all energy from fossil-to-CO2 processes, or you are willing to accept EFW as a step in the right direction (like a heroin addict going onto a prescribed methadone programme).

Maybe he is advocating the “capture all the waste plastic and securely bury it” approach. This at least keeps the waste plastic out of the wider environment, I guess.

warrior
03/12/2019 at 20:53
1

The problem with plastic and fossil fuels is that they are really good solutions for what they were designed to do so eliminating them is not an easy engineering problem.

The shallow approach of some of the “plastic is bad” slogan type articles does not really help much. More useful would be to have a conversation about near term priorities. Perhaps the biggest concern is about plastic going in the ocean or the environment where it is exposed to sunlight and degrades. Next might be burning in an open pit. Pyrolysis or burning for energy in a properly designed furnace may be on the same level of concern as fossil fuels in general, at least additional resources were not used to get it out of the ground. Burial in a well designed landfill takes advantage of the general inertness of the plastics and in a sense puts the carbon back in the ground. The most preferred might be recycling, reuse, and avoidance but those are not realistic for 100% of the material.

So I think all of the solutions need to be compared to the reality that for a lot of countries Recycling really means send it to places like southeast asia where it is picked through and what is not useful is dumped or burned. In the western US we export over 400,000 tons of plastic. If even 20% is not useful or contaminated, and goes into the environment, then we are remote-dumping. Realizing that, I wonder if it wouldn’t be better to put the plastic in the trash and let it get buried in a regulated landfill.

So I think articles that warn against imperfect solutions need to compare them against the current reality

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