Sciencemadness Discussion Board - Plastics recycling: why not treat waste as crude oil ?

Plastics recycling: why not treat waste as crude oil ?

metalresearcher - 27-12-2019 at 00:45

Several articles appear in the media on plastic waste and it is so hard to dispose it off or recycle it.

https://www.smh.com.au/national/nsw/not-sure-what-can-and-ca...

Plastic is made from polymerized hydrocarbons, sometimes added chlorine (PVC) or fluorine (Teflon / PFAS).
When heated to 200-300 C, most will turn into a soup like hot crude oil and can be cracked to make new hydrocarbons to be processed.
When heated even more (500 or more C) it will decompose and the resulting gases can be processed to new hydrocarbons.

Am I too simplistic ?

I guess such a process is more expensive that making HCs from virgin crude oil.

What are your thoughts ?

12thealchemist - 27-12-2019 at 02:10

The problem is you have to put in a lot of heat and energy to convert the plastic to crude oil, and it's cheaper to get brand new crude oil than to back-convert plastic. The principle is sound - I've done it myself, and to great success, but it's very energy inefficient.
(Energy = gas, electricity, coal, etc.)

An answer, I suppose, is to use an incinerator for that which cannot be destructively distilled, and use the heat from that to thermolyse the remaining plastics.

B(a)P - 27-12-2019 at 02:19

IMHO the issue is the unquenchable desire for plastic products. If we burn the plastics more need to be made. We need to stop using them or develop technologies to properly recycle them.

madcedar - 27-12-2019 at 02:50

Quote: Originally posted by metalresearcher

Several articles appear in the media on plastic waste and it is so hard to dispose it off or recycle it.

https://www.smh.com.au/national/nsw/not-sure-what-can-and-ca...

Plastic is made from polymerized hydrocarbons, sometimes added chlorine (PVC) or fluorine (Teflon / PFAS).
When heated to 200-300 C, most will turn into a soup like hot crude oil and can be cracked to make new hydrocarbons to be processed.
When heated even more (500 or more C) it will decompose and the resulting gases can be processed to new hydrocarbons.

Am I too simplistic ?

I guess such a process is more expensive that making HCs from virgin crude oil.

What are your thoughts ?

I have wondered the same thing for years. It seems like a no brainer to crack the plastic down into petroleum products. Interestingly the article you link to mentions that plastic bags are the problem and yet the pie chart shows that beverage containers are >50% of the waste. The energy costs would be of no consequence given that the fuel for running the plant arrives by the truck load for the cost of just picking it up from the normal garbage runs, something that is already happening anyway. I assume the difficulties in the process is dealing with the metals, wood and garbage that inevitably ends up in the recycle waste. Those issues would be sorted out and equipment refined over time as experience grows.

Recycling

MadHatter - 27-12-2019 at 04:23

I live in Maine, 1 of 10 states that have refundable
deposits on plastic, glass and metal beverage
containers. We have redemption centers for people
to turn them in. The law prohibits containers from
from other states. Any plastic I can't turn in gets
burned along with any paper in the wood stove and
plastic burns hot. Despite this people still throw
cans and bottle on the side of the road. This is
pure laziness. I often take walks and bring a trash
bag with me and collect anything I find on the side
of the road. Their loss, my gain and environment is
a little cleaner for it despite some burning in the
wood stove. Burning is a way to "recover" some of
energy used to manufacture paper and plastic. It
returns heat and may save a few trees(and money).

[Edited on 2019/12/27 by MadHatter]

metalresearcher - 27-12-2019 at 05:12

Quote: Originally posted by MadHatter

I live in Maine, 1 of 10 states that have refundable
deposits on plastic, glass and metal beverage
containers. We have redemption centers for people
to turn them in. The law prohibits containers from
from other states. Any plastic I can't turn in gets
burned along with any paper in the wood stove and
plastic burns hot. Despite this people still throw
cans and bottle on the side of the road. This is
pure laziness. I often take walks and bring a trash
bag with me and collect anything I find on the side
of the road. Their loss, my gain and environment is
a little cleaner for it despite some burning in the
wood stove. Burning is a way to "recover" some of
energy used to manufacture paper and plastic. It
returns heat and may save a few trees(and money).

[Edited on 2019/12/27 by MadHatter]

Weird that they don't accept foreign (i.e. interstate) containers. That should be ruled federally.

Plastic in the woodstove ??? That is a very bad idea, toxic fumes may expel from your chimney and it will damage your flue as well and increase the risk of a flue fire and when that occurs and the insurance knows you burn plastic, they may not pay you.

Rather write your local council how they can better handle plastic waste.

andy1988 - 27-12-2019 at 08:50

Quote: Originally posted by metalresearcher

When heated to 200-300 C, most will turn into a soup like hot crude oil and can be cracked to make new hydrocarbons to be processed.
When heated even more (500 or more C) it will decompose and the resulting gases can be processed to new hydrocarbons.

Here is a recent line of research you can read on that, 850C.

The problem I see convincing municipalities in my area to recycle is that they don't want to pay anything more than what it costs to ship it to the dump. They imagine innovators and the "free market" will somehow satisfy their demand, and if not, they don't care. Even if you develop a great process, good luck getting financing for equipment under those constraints. Then again I suppose the new material produced might be worth it?

[Edited on 27-12-2019 by andy1988]

mysteriusbhoice - 30-12-2019 at 03:46

better off incinerating the plastic in a special furnace to produce electricity directly, thats already a thing!!

rockyit98 - 30-12-2019 at 05:53

the true meaning of the three arrows.

for me it's reduce reuse hoard till it's recycling day.

stoichiometric_steve - 31-12-2019 at 06:33

There is already a process called "Hydrothermal Carbonisation" that was adapted and patented for plastics.

pneumatician - 25-3-2020 at 10:27

https://www.youtube.com/results?search_query=japanese+plasti...

another for recicle tires producind excess electricity...

human ego and avarice my friend.

RogueRose - 25-3-2020 at 11:40

I was reading some things about what to do with mixed plastic waste, like highly degraded plastic bags (heavy duty 1-2 ton tote bags and such) and other plastics that crumble after exposure to UV, as it's really bad to recycle it, and a suggestion was to use to to generate H2 similar to water-gas generation that makes H2 and CO IIRC. Heating the plastic to where it vaporizes w/o O2 and running the gas through hot charcoal or coal and it supposedly breaks it down into a high quality stream of H2 and probably CO and CO2. IDK if the H2 can be separated out and the CO used to heat the plastic, but that would be a good use I would think.

As for the mention of tires, I've seen a number of good uses and one that has been used for some time is in the production of lime/CaO or cement as it needs a lot of heat and tires burn very hot. The problem is that there is significant SO2 emissions from this. Another use for tires that I've seen is using it in paved roads where saftey, low noise or high longevity is a high priority. The rubber is used in the top layer and it greatly reduces stopping distances, increases grip on tires (going around turns and such) even while wet, it also allows for much more quiet running of vehicles on roads. Finally, it supposedly can allow the surface to last up to 2-3x longer than a standard asphalt finish, IDK how thick/deep it needs to be or what % is needed to be added, but all of these seem to be pretty nice features of using chipped or powdered recycled tires. It can also be used as the complete surface of a road or driveway where they do tar and chipping (different than being mixed into the asphalt), and again it supposedly has the features I mentioned above.

Panache - 14-4-2020 at 03:46

Recycling
An expensive but virtuous process that turns waste that nobody wants into raw materials that nobody wants.
Are there thermal lava flows anywhere predictable enough to use as a heat source for the cracking?
The Germans and the Japanese have blast furnaces utilising pellets of compressed polyolefins, heated to red heat as carbon source. Unsure of how economical they are but sound theory.
I've always thought we should bail up the polymer waste into huge cubes and build a replica great pyramid of Giza...sure would create some jobs and tourism for the town building it in addition to the revenue for accepting the waste.
I worked on recycled polyethylene back in the 90's it's exceedingly difficult. You need such little contaminant for everything to go to shit. Makes ok railway sleepers for use in constructing piers.