Sciencemadness Discussion Board - Pyrolyzing plastic waste: useful ?

Pyrolyzing plastic waste: useful ?

metalresearcher - 9-8-2021 at 02:34

I stumbled upon this article. I believe in Plastics Pyrolysis, but more as a means to create 'crude oil' from it as a precursor to new plastics, not as an energy source. As this article says, it costs more energy to process plastic waste and refine the 'crude oil' to a useable fuel than the obtained fuel delivers.

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

The last sentence is the most striking, which I totally agree:

The elephant in the room is capitalism and the throwaway culture that the present version of this economic system has created – ever demanding new markets, more sales, more consumption, and more waste.

The best way to beat plastic waste is not producing plastic packaging unless really necessary (i.e. medical products).
But IMHO it is better to pyrolyze plastic waste for new plastic durable products with its (preferable renewable) energy cost than dumping it into the landfill or incinerating it.
Currently, plastic is the worst recycled material, compared to steel, aluminum, paper and even concrete. Plastic waste from the UK sent to be 'recycled' is piling up in Hongkong and nothing happens with it.

https://www.youtube.com/watch?v=oRQLilXLAIU

What are your ideas ?

Belowzero - 9-8-2021 at 02:52

Quote:

The elephant in the room is capitalism and the throwaway culture that the present version of this economic system has created – ever demanding new markets, more sales, more consumption, and more waste.

We are supposed to leave politics at the door but this just is a slimy and nonsensical oversimplified argument from a typical academic socialist.
Any other system ever implemented is way more wasteful and harmful to the environment (USSR anyone?!..)
Never compared to anything aka the utopian standard.

Apart from the simpleton politics, recycling plastic is a very good idea, perhaps solar energy that isn't used and not being stored can be applied for such a purpose.
It is quite annoying how amost anything is packaged in plastic, worst being the single use bags.
Biodegradable is probably a much smarter route.

[Edited on 9-8-2021 by Belowzero]

Fyndium - 13-8-2021 at 10:53

Learn the concept of least bad option. Also, from achieving something, it is sometimes productive to move into damage control - whatever fails is not always total loss.

After that, the thing of pyrolyzing plastic into liquid hydrocarbons is a real and actual thing, and folks have used it to actually produce fuel for diesel engines and generators.

PVC can also be used to produce hydrochloric acid. I tested this and actually got a concentrated solution very quickly when the thermal decomposition took off. The reaction is autocatalytic once it takes off, so larger masses of PVC can cause issues if a runaway occurs. The smoke that pushed through, and the mess it left behind was a different concept. It also produces vinyl chloride, which is highly toxic, though, so severe caution should be taken.

[Edited on 13-8-2021 by Fyndium]

unionised - 14-8-2021 at 06:29

Quote: Originally posted by Belowzero

Quote:

The driving force of capitalism is "growth" and, on a finite planet, that's a problem.
No need to compare it to anything else.

Recycling is a better bet than biodegradation because the latter guarantees a waste of energy and materials.

Panache - 21-8-2021 at 02:17

I did my PhD I the late 90’s on pp film and that was within a mat eng department with a significant smattering of polymer academics. There was heaps of money around even back then for developing uses for the recycled polymers.
I had a note up on my fridge for ages
Recycling-An expensive but virtueous process that converts waste than nobody wants into materials that nobody wants. esp plastics
I think, if I can recall it only takes 1% ish pvc in a polyolefin (hope, pp etc) to render most of the materials useful properties completely compromised.
I recently went on a bit of a rant concerning the bag name polymers were getting around the world as misplaced, we should be criticising ourselves these things are too frequently dumped back into any natural environment I’ll equipped to deal with something although largely innocuous chemical it’s negative mechanical affects are wide ranging. Also as some of many additives compounded with polymers (in order to gain greater usefulness) have notorious affects and they leach out often.
We need look no further than ourselves to blame really. Capitalism sucks, socialism is great, conceptually, we have never really been able to get it to work. Perhaps if Cuba hadn’t tried to house missiles for the ussr socialism may have been successful there. Who knows.
I don’t think its anti capitalism to advocate stronger regulation. In fact those decrying industry regulation are absolute hypocrites often because in highly regulated industries (ie cannot get more regulated than criminalising a molecule) they pander to governments.
As always the solution is simple baby boomers fucked everything up. They continue to stymie real progress, kill them all!!

andy1988 - 21-8-2021 at 13:47

Here is an excellent article on plastic packaging. I didn't know of an approach to make cellophane moisture-proof prior to reading it, my expectation was that petrochemical-based films dominated market-share due to being much more moisture-proof, but looks like they dominate based on price:

Quote:

Cellophane dropped behind lower cost petrochemical-based films such as biaxially-oriented polyethylene terephthalate (BoPET) and biaxially oriented polypropylene (BOPP) in the 1980s and 1990s but it has made somewhat of a resurgence in recent times due to the fact it is biosourced, compostable, and biodegradable. Its sustainability record is clouded by its energy-intensive manufacturing process and potential negative impact of some of the chemicals used, but significant progress in recent years has been made by leading manufacturers in reducing their environmental footprint [1].

Yes I'm sure efficient recycling processes can be found for niche products, e.g. carpet. The problem is how the bean counters currently tally things. And I think changing how they tally things to include the ecosystem is they way to go [2][3].

Best not to get political, use more specific concepts than broad strokes on governance frameworks.

BromicAcid - 21-8-2021 at 14:30

Always avoid plastics where possible, should be a material of last resort not first attempt.

macckone - 21-8-2021 at 22:42

Many polymers can be derived from plants, some are primarily derived from plants.

PLA, rayon, cellophane, nitrocellulose are primarily derived from plants
Polyethylene is relatively easy to make from fermentable compounds. (sugars -> alcohol -> ethylene -> polyethylene).
PVC can also be made from ethylene.

There are biochemical paths to nylon and many other plastics.

So in short plastics can be made from renewable resources, it just currently costs more.

If it can be made from biological sources, then biodegradation is possible.
There are bacteria that eat polyethylene, pvc is more difficult for them to break down but it can be recycled.

And of course most plastics are flammable. Sweden burns most of their trash.

Plastic

MadHatter - 22-8-2021 at 20:23

Here where I live in Maine(USA) styrofoam food containers
and plastic straws are now verboten. Whether or not to
burn plastic ? It depends on many things. We have large
biomass electrical generation here already. I don't know if we
burn plastics as fuel.

Fantasma4500 - 19-9-2021 at 02:14

polyamide may under certain conditions (iirc 650*C+) produce HCN
PP/HDPE/LDPE may create "diesel"
polystyrene turns into styrene, useful as it can be oxidized into benzaldehyde over heated aluminium oxide catalyst with oxygen
melamine may be able to decompose into formaldehyde, actually certainly. if you ignite this plastic, you will smell formaldehyde. in the metal industry a white plastic is oftenly used for machining called "sustarin b" this also emits formaldehyde vapors when heated, iirc its close to melamine in composition

Amos - 19-9-2021 at 06:01

Quote: Originally posted by Belowzero

We are supposed to leave politics at the door but this just is a slimy and nonsensical oversimplified argument from a typical academic socialist.

Apart from the simpleton politics

The negativity in the original post was directed at wastefulness, whereas your negativity is directed at the poster and the "academic socialist" (this sounds shockingly anti-education by the way) whose article you certainly didn't even read, and uses unhelpful and unscientific language purely intended to insult. Not in any way an equal and warranted reaction. The knee-jerk assumption that any criticism of capitalism is somehow pro-Soviet is pretty "simpleton" too.

I'm hesitant to encourage simple pyrolysis as a primary means of plastics disposal because for many kinds of plastics, insidious and long-lived toxins like polychlorinated biphenyls and polycyclic aromatics are produced and must then be disposed of with even more care. I've not heard of accelerated decomposition (usually using bacteria or enzymes) posing this same problem but of course this is probably more expensive and can't be applied to all of the major plastics at this time. As renewable energy becomes cheaper and more widely available, I'd like to see more focus on UVC, ozone, or perhaps other chemical catalytic means that could be used to produce a consistent and useful byproduct of hydrocarbons or oxygenated derivatives. Or anything that avoids building LARGER, more difficult to process molecules as an unintended consequence.

[Edited on 9-19-2021 by Amos]

oceandeep67 - 11-12-2021 at 19:50

I appreciate people that care about the environment. I am just an average, skilled trade guy located in a 'ghetto' part of the U.S., but old enough to experience the effects of global warming. I am E.P.A. certified, so know a little about the subject. But just to an average person pyrolysis just feels like a bad approach. Couldn't plastics be recycled in a way to use as a raw material for (commercial) 3D printers to build condos, or micro homes for the poor?

Dr.Bob - 18-2-2022 at 07:27

The challenge (IMHO) is not big companies, as they simply supply what the consumer buys. The problem is that many people are lazy. I have seen people walk by a trash or recycling can ans throw stuff on the ground. Some of my neighbors sort and separate their waste well in to the various bins, but then I see a few who put clearly non-recyclable things in their blue bin as they are stupid, lazy or uneducated as to what goes where. The fact that no two places recycle the same things in the same manner does not help. We have towns near here that have entirely different lists of what is recycled, so you have different rules at home and work and friends houses. And businesses have a hard time convincing employees to do any better.

So I would advocate pushing to have most municipalities try to agree on one system of what is put where and then educate people on it well and if a certain place does not recycle say polystyrene, they still collect it and dispose of it, just to make the process the same everywhere. And better yet, put in more municipal incinerators to burn the remaining waste, along with a presort process that tries to remove any remaining items like metals/steel and glass that are easy to sort. But a well run incinerator with a scrubber is cleaner than most peoples home fireplaces in terms of pollution, and the power created could then replace electricity made from coal, oil and gas as well. Baltimore has done that for years, along with many other large cities and much of Europe. If we did that, along with building some new nuclear plants, we could make a serious dent in the CO2 emissions, along with the growing use of wind and solar. But again, the best solution is to stop wasting so much energy. It is much easier, more practical, cheaper, and more efficient to use less power, push efficiency, turn off lights, etc, and avoid using power than to capture CO2 and remove it.

Rainwater - 18-2-2022 at 08:05

Quote:

We are supposed to leave politics at the door but

Amen to that.

I would like to hear about the chemistry involved in refining this waste and converting it into reagents.
We might just solve the worldwide problem by focusing on the the solution.

khlor - 16-6-2022 at 20:29

Quote: Originally posted by macckone

If it can be made from biological sources, then biodegradation is possible.

Gentlemen, sorry that I'm late to the party, now with that out of the way... I disagree with this particular statement, while it is true that many plastics and many things can be made from bio available molecules or modified by bacteria, fungus or whatnot, not all that has been made from biomolecules or plants or biomaterials are biodegradables, take your polyethylene(PET, for short) example, it can be made from ethylene from ethanol, from sugars, but I hardly believe that PET is a biodegradable, though it can easily be recycled and with that being said,
well, politics... not big on that, find it important though, but I do not think it belongs on a thread like thins since I believe that we should all strive to solve technical problems despite politics IDK, I guess I'm going all science purist here...
I hope to have contributed for the discussion, as late as it seems, though.

j_sum1 - 16-6-2022 at 21:11

The sorting, separation and cleaning of polymer waste is always going to be problematic.

Where there exist waste streams of sufficient purity and volume, the reuse and recycling are viable. IMO. But there exists a multitude of situations where mixed polymers or mixtures of polymers or unlabelled packaging or unrecyclable additives are used. For example, the wrapper for a block of cheese may have as many as 7 different plastic layers bonded together which may render it non-recyclable even if it appears to be PE.

I see little problem with harnessing the energy content of waste polymers. High temperature incineration and electricity production in a modern plant is something that I think should be more common. Obviously very efficient waste-gas scrubbing is required. So also is responsible treatment and disposal of any resultant ash. But, as far as I can see, it is a better option than landfill, and a better electricity production option than burning of wood, which still happens quite a lot.

Jome - 16-6-2022 at 22:11

Quote: Originally posted by macckone

If it can be made from biological sources, then biodegradation is possible.

The two processes, where the precursor molecules originate from and whether or not the resulting product is biodegradable, are entirely unrelated.

We could make something non-biodegradable from natural sugars, and chemically synthesized sugars from petroleum if so desired. Biodegradability =/= "carbon sourcing".

CO2 capture seems semi-nonsensical, how could it possibly be made cheap enough to matter in a larger scale unless it is done by plants and their carbon is then "locked" into char used to improve soil quality? So, we should burn the plastic and bury the biocarbon, then work on some sustainable energy source and less single-use plastic, or perhaps new materials.

[Edited on 17-6-2022 by Jome]

[Edited on 17-6-2022 by Jome]

khlor - 16-6-2022 at 22:48

Quote: Originally posted by Jome

CO2 capture seems semi-nonsensical, how could it possibly be made cheap enough to matter in a larger scale unless it is done by plants and their carbon is then "locked" into char used to improve soil quality? So, we should burn the plastic and bury the biocarbon, then work on some sustainable energy source and less single-use plastic, or perhaps new materials.

Reminds me of the plot of an anime where the world gone to hell and the economy was tied to how much carbon a country on corporation had, the carbon was stored in graphite ingots I think the name was shangre-la or something, it's been more ages since I watched it though the aspect of carbon economy stood with me for a while, since living in what was for the most part of this century a "third world country" and an "emerging economy" this crap was big deal then and kinda is now... crazy huh?

Bmoore55 - 17-6-2022 at 06:48

I worked with catalytic pyrolysis of biomass on an industrial scale and I have been running pyrolysis GCMS of polymers for almost a decade. Both are not an effective alternative because the crude products derived from the pyrolysis process A) destroy the reaction vessel and catalyst and B) are incredibly difficult to turn into a pure hydrocarbon product of any use. The best process I have seen in first an extraction of a sugar concentrate from biomass using supercritical water which can then be hydrotreated to produce a quality product. I admit, polymer pyrolysis is better than nothing, but it is not something that is currently very useful as an alternative to petroleum. If you want better use of petroleum then the world needs to work on building safe and reliable nuclear reactors as fast as humanly possible so we can stop burning up diesel and jet fuel for energy production.

Σldritch - 18-6-2022 at 02:14

I was just thinking of trying to get formaldehyde from broken my broken Keck clips. They are apparently often made from a plastic consisting of mostly POM. Not entirely sure how to do that though.

Perhaps you could even make DCM from POM plastic. The idea is to dry distill POM with Ferric Chloride. The Ferric Chloride should catalyse the degredation of POM being a lewis acid and then replace the oxygen with chloride groups allowing DCM to be distilled off in a similar wein to this reaction from Atomistry:

Quote:

Ferric chloride combines with ether to form a dark red, highly deliquescent solid of composition FeCl3.(C2H5)2O. It is soluble in water and alcohol, and at 100° C. decomposes quantitatively, yielding the oxychloride FeOCl: -

FeCl₃.(C₂H₅)₂O = 2 C₂H₅Cl + FeOCl

The reaction using POM should then be:

FeCl₃ + H₂CO = H₂CCl₂ + FeOCl

If this variant is quantitative too and you make your Ferric Chloride from Ferrous Chloride and Chlorine or get it from another cheap-ish source perhaps this would actually be a viable method to synthesize DCM.

As for the viability of recycling plastic: i could poke a million holes in the argument for and you could point out a million cases where i would be wrong but really what this boils down to is that nobody knows when plastic should be recycled or not. Why? That brings me to politics: we (the west) are not living "under" capitalism. If you doubt me, allow me to point out that Keynes, the father of "modern" economics was in fact a Communist:

Quote:

“the progressive reorganization of Society along the lines of Collectivist Socialism is both inevitable and desirable” - John Maynard Keynes, February 1911

Not to say everyone in the "elite" of the west is a Communist, it is just that they all want to steal from people us. Communism is effective in that goal, for obvious reasons, but im sure for many of them it is just a means to an end.

Chalo - 26-8-2022 at 18:02

Controlled Pyrolysis with an eye to recovering useful polymers, or oils that can be used as fuels, have endless problems that have been very well described in this thread especially by Bmoore55 (unless plastics can be sorted, without even small amounts of contaminating pvc getting into wrong batch; never going to happen, too many different plastics too intimately mixed). However, what about pyrolysing (anaerobic, electric heat) at high temperature all the way to synthesis gas (water, carbon monoxide, and hydrogen) as opposed to aerobic incineration to CO2 as commonly practiced now? Would not even need to separate plastic from cellulosic waste (wood, cardboard, etc). No complicated chemistry, electric generators have been run off syngas since wwii. At high enough temps no toxic or even mildly complex organic compounds survive.