metalresearcher
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Are plastics really difficult to recycle ?
Several sources (e.g. TheVerge.com) tell that plastic waste is difficult to recycle, which I can understand. Thousands of different plastics with
different color dyes in it allow it only to be downcycled, which means old clothing fibers or bottles can be recycled to street furniture or the like.
Not like metals or glass which can usually be recycled indefinitely without loss in quality.
But when heating *any* plastic to about 500 C, it decomposes into gaseous hydrocarbons which can be used to polymerize to virgin new plastics. But
that costs energy. And waht energy ? It can be heated electrically by renewable souces such as solar and wind, but part of the decomposition
hydrocarbons can be used as a fuel to heat it. Obviously, it won't cover all the required energy as it is a strongly endothermic process. So it is
actually a combination of incineration, where the energy is used to decompose another part of the plastic waste. Obviously, filtering for e.g. dioxins
or even HCl from PVC waste is required.
This is *not* a way to continue using disposable plastics, the root cause should be solved by using as few plastic packaging as possible, only when
hygiene (medical and food products) is required.
What are your ideas ?
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Johanson
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"What are your ideas?"
I looked into this a few years ago. I will share my conclusions:
1. You're right, it's really really hard to chemically-recycle plastic bottles out of a typical, municipal, mixed waste stream.
2. Not only is the chemistry hard (achieving purity, dealing with the other waste, producing unwanted byproducts, etc) but the economics are next to
impossible because you just simply can't transport enough tons of plastic waste cheaply and economically to your recycling facility to make it
pencil-out. It's a huge logistics/collecting/shipping nightmare.
3. At the time I was looking into it, there was just one large facility - somewhere in the L.A. area I don't remember - and it was losing money. If no
one is doing it, that's a pretty good sign it's difficulty, unfortunately.
4. It's really really cheap to just pump out nice, perfect, consumer plastic all day long from crude oil. Any chemical-recycling scheme has to at
least come close to matching those economics, or it's doomed. What bottling customer would pay a premium for no reason? Without economic feasibility,
any large-scale effort is impossible because you won't get financing
5. Some say the best way to "recycle" plastic waste is to incinerate it, use the heat to boil water, use the steam to turn a steam turbine, use the
steam turbine to rotate a generator, use the generator to power society. However, most large cities in the U.S. anyway have made it impossible to
permit trash incinerators. Large U.S. cities used to have municipal cogeneration plants that burned trash; not anymore.
6. I think the way forward is to somehow decompose the plastic and use it for something else. Forget about trying to make more plastic bottles out of
it.
Just my 25 cents worth
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markx
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I have to agree that plastic waste is hard to recycle in a reasonable way given the current background system and the way it operates. Plastic is a
very general term...not unlike metal alloy e.g. There are countless formulations with different properties and additives that make up the matter we
call plastic. These formulations are not easily separated from each other during recycling by physical properties and they tend to be contaminated.
This pretty much makes it impossible to produce anything that needs to conform to any critical standards regarding purity, constancy of strength or
dimensional stability, or composition from waste plastic mixes. Like bottles or bottle caps or pipe fittings that have to withstand a certain
pressure or have specific properties during the forming process. Only utterly uncritical stuff like garbage bags or puke bowls are eligible. Not to
mention that the production lines experience accelerated wear due to abrasive contamination within the waste plastic mix.
It is so much more favorable to "pay dues" to "institutions" who grant you the right to print a label on your product stating that a certain %tage of
your stuff is based on recycled plastic because "somebody else" is doing the recycling for the fee that you pay and to not touch the nightmare
yourself. In reality the used plastic is going to god knows where to be burned or dumped.
Exact science is a figment of imagination.......
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Twospoons
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Quote: Originally posted by metalresearcher  |
This is *not* a way to continue using disposable plastics, the root cause should be solved by using as few plastic packaging as possible, only when
hygiene (medical and food products) is required.
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This is the thing really : single use plastic packaging is the real issue. We need to return to using glass, metal and paper where possible, as these
are far easier to recycle or compost. Better still is reusable or refillable containers.
Where I live single use plastic shopping bags are now history. Bring your own reusable bags, or buy a paper bag. This has stopped millions of bags
heading to landfill annually.
Helicopter: "helico" -> spiral, "pter" -> with wings
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BromicAcid
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I always buy glass given the chance, less chemical leaching, less funky tastes. About as recyclable as you can get. In most circles though when I
bring that up someone will counter immediately with "Have you ever fallen with a glass bottle in your hand?" Of course I have, and lived to tell
about it but I do understand there is risk to going with glass.
Some plastics are cheaper to recycle than others. That's one of the hurdles. We used to have to sort plastics by type locally but about five years
ago they went to single stream recycling because people complained. It's my understanding that single stream recycling really puts the nail in the
coffin for trying to recycle plastics because it adds yet another step in a arduous process.
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j_sum1
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There are enormous quantities of polymer waste that end up being exported to (predominantly) South East Asian countries for recycling. And then not
being recycled. We have created financial incentive for this kind of thing by taxing or charging for recycling at source. The value reclaimed in the
recycled material is insufficient to cover the collection, transportation and processing costs required. In other words, recycling plastics generally
does not pay.
Added to the difficulty is that the recycled product is limited in its uses. We demand high quality for anything that comes into contact with food.
And anything that is highly engineered demands consistent properties that cannot be guaranteed with recycled polymers. And so, either high demands are
placed on sorting used plastics, or virgin plastics are used: often at lower cost.
My thoughts are that we would be better served to reclaim the energy within the materials than to attempt to reclaim the material itself. We would
save on sorting and transportation. We would process material locally, which has numerous positive spin offs. And we would eliminate the problems
caused by inconsistent and inferior product output. We do have the technology to do this cleanly. I really don't know why we are not doing it more
often.
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Texium
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Frustratingly, my city doesn’t accept glass in its single stream recycling program. As I understand it, this is the case for many cities in the US,
largely due to the lower demand for glass recycling and the scarcity of recycling plants. Recently, my city starting offering the privilege of glass
recycling as a separate program for $8/month. For comparison, my existing trash and recycling service is only $10/month, so I would be almost doubling
my bill just to be able to recycle glass. I’m pretty sure it has to get shipped to another state.
The plastic recycling is stupidly restrictive too. They only accept PETE and HDPE, and moreover, items must be bottle or jug-shaped. Plastic tubs or
jars are anathema for some reason, even if they are PETE or HDPE. I keep a secondary recycling bin for all of the other plastics, which I drop off
once every couple months at a different local recycling plant that accepts them. I have no clue what they actually do with them.
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mayko
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One cool idea I've seen recently is projects like this one, where plastic bottles are processed into 3D printing filament on a DIY scale:
https://www.dezeen.com/2022/05/26/polyformer-reiten-cheng-re...
al-khemie is not a terrorist organization
"Chemicals, chemicals... I need chemicals!" - George Hayduke
"Wubbalubba dub-dub!" - Rick Sanchez
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clearly_not_atara
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| Quote: | | It's really really cheap to just pump out nice, perfect, consumer plastic all day long from crude oil. Any chemical-recycling scheme has to at least
come close to matching those economics, or it's doomed. What bottling customer would pay a premium for no reason? |
Basically this. A plastic bag weighs about five grams. That's less than half a cent worth of crude oil. Or two seconds worth of labor at US federal
minimum wage, which most people believe is too low. Automated trash sorting is very hard. Oil refining is very advanced. And then consider that people
throw stuff covered in food into recycling containers and it ends up full of mold and bugs. You're not sorting that for half a cent per item. It's not
going to happen.
In theory waste plastic could be processed via the water-gas shift reaction:
n H2O + (CH2)n >> 2n H2 + n CO
which produces hydrogen that can be applied to fertilizer, steel, jet fuel, etc.
[Edited on 04-20-1969 by clearly_not_atara]
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Jenks
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Manual sorting adds a lot of cost, but a lot could be automatically sorted if legislation required recyclable items to be tagged in some way, such as
by adding an RFID chip, bar code or fluorescent marker to specific kinds of items to get something of the separation cost-effectiveness we get with
ferrous metals. And the priority should be with the more common items, like plastic bottles, or items with a larger mass of plastic per item, or with
plastics that are particularly amenable to recycling if they can be obtained pure and clean, like PET. Legislation is also needed to level the playing
field a little, shifting a little of the profit from making disposable products to incentivize the use of recyclable materials and subsidize the
purchase of the resulting products, since business isn't going to factor the cost to the environment and public health into their products on their
own.
As far as reuse, I love glass too for water storage, but I wonder if polypropylene leaches so much after it is reused many times. It hates UV exposure
though and disintegrates. For my part, aside from recycling I try to reuse plastic bags and cups and plastic and glass jars and bottles as much as
possible.
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Rainwater
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All those extra bells and whistles, are impractical
One time use plastics should be phased out, period.
And bigger government is never the answer.
One of the companies I contract for is trying to get legislation passed for them to use a biodegradable polymer with most the same properties as pet,
for their food related, 1 time use products. But the fda has been saying no for years.
It use to be unbroken glass bottles come with a core charge for returning them, Cans too.
You could pick them up off the road of you needed quick cash.
It boils down to humans being lazy. Cats to
[Edited on 29-4-2023 by Rainwater]
"You can't do that" - challenge accepted
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Texium
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| Quote: Originally posted by Rainwater | One time use plastics should be phased out, period.
And bigger government is never the answer.
One of the companies I contract for is trying to get legislation passed for them to use a biodegradable polymer with most the same properties as pet,
for their food related, 1 time use products. But the fda has been saying no for years. |
At the risk of
verging into politics, have you considered that it may not be “bigger government” that is the problem, but the fact that there are three petroleum
lobbyists in congress for every legislator?
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Twospoons
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A quick search on Phys.Org shows some of the research that is ongoing into plastic recycling. Some interesting ideas and results there.
Helicopter: "helico" -> spiral, "pter" -> with wings
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clearly_not_atara
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| Quote: | | And the priority should be with the more common items, like plastic bottles, or items with a larger mass of plastic per item |
Recycling heavy plastic items could probably work fine. But it would require us to discard the popular imagination that recycling is something you do
every week.
On the other hand, commercial composting actually works, but people were burned by the recycling industry so uptake has been slow. See also: the
decline in the PV industry in Spain after the government cut a subsidy in 2013.
[Edited on 04-20-1969 by clearly_not_atara]
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Rainwater
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To address the OP.
Pyrolysis will crack the bonds but consumes a lot of energy.
Steam cracking at high pressure works to but same problem as pyrolysis
Without a new catalytic to break the C-C bonds, efficently recycling plastic is limited to reforming the material.
Mis matching plastics and contaminates limits molding techniques that will effectively work.
Short of door mats, clothing, and large objects this limits profitable of the process.
I think its past the point of recycling efforts.
large scale cleanup efforts work, but until the rate of production is less than the rate of disposal, it will only get worse
"You can't do that" - challenge accepted
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Rainwater
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https://youtu.be/Z-HHbU0zoXk
Good old bee worms.
Who would have thought that a pest we use pesticides on would be a pathway to a solution to the plastic problem. We've got to be the dumbest species
on the planet.
What other organisms produce polymers?
Spiders recycle their own silk
Bayberry bushes have a thick wax on their fruit. And lipids love attacking them.
"You can't do that" - challenge accepted
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B(a)P
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The human condition is the issue. I once did a survey on waste management practices for a local government area experiencing a large amount of
waste/recycling cross contamination that was causing them huge contractual penalties with their waste contractor and terrible environmental outcomes.
We did both surveys of waste composition in each stream from key areas as well as interviews representatives from the addresses where we audited their
waste disposal habits.
Key outcomes:
- when multiple dwellings shared a waste disposal receptacle the sorting of waste from recyclables was by far the worst.
- households in lower socio-economic areas were more likely to have the perception that waste from recyclables sorting should happen at the waste
facility not at the household.
- commercial addresses performed poorly in the separation of waste from recyclables.
- cross contamination of the waste and recyclable stream was at a level where the recyclable stream could not be recycled without significant
reprocessing at the waste facility, which is extremely labour intensive.
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