Turning PLASTIC back into oil

A little basic chemistry to help this all make sense...

Pretty much all of thos stuff starts out as crude oil. Crude is a mixture of a whole bunch of different hydrocarbons, loose carbon, nitrogen, sulfur compounds and various other crud. The hydrocarbons are the useful bits, so lets take a look at those.

A hydrocarbon is a molecule containing carbon and hydrogen atoms in various structures. The simplest is Methane, or natural gas, which has one carbon and four hydrogen atoms. Structurally, it looks like this:



From there, the hydrocarbons get bigger and bigger. For example, Propane has three carbon atoms and 8 hydrogen atoms and looks like this:



As ther molecules get bigger their properties change in predictable ways. Hydrocarbon molecules are often refereed to by how many carbon atoms they have, so methane might be referred to as C1 (One carbon) and Propane as C3. As a hydrocarbon gets larger (a higher C number) it tends to become less volatile and less combustible. Gasoline is usually in the C5-C8 range (but has a bunch of other stuff mixed in). Kerosene is usually C6-C16 and diesel fuel is in the range of C8-C21. The more carbon atoms in a molecule, the more energy it provides, but the harder it is to get it to burn.

When we talk about plastics we are talking about polymers. These are long chain molecules that can contain thousands of carbon atoms. These polymers are put together from monomers which are a single building block. The simplest plastic is polyethylene, for which the monomer is ethylene. Ethylene has a formula of C2H4 and looks like this...



Notice how the molecule has two attachment points between the carbon atoms instead of just one. You can break that bond to create an "open" molecule that looks like this:



You can then stick a whole series of those "broken" molecules together in a chain or arbitrary length like this:




This is essentially the same as a standard hydrocarbon molecule, except the C number can be in the millions.

Different monomers are used to get different physical properties. For example, if you replace one of the hydrogens in ethylene with a chlorine atom you get a monomer that looks like this:



Stick a bunch of those together and you get this...



This is Polyvinyl Chloride or PVC

There is an almost unlimited number of variations to this process which produces the wide variety of plastics we see today.

To convert these plastics to gasoline requires cutting the molecules down to the size we need. Practically what is needed is heat and a catalyst to break the C-millions polymers to the C5-C8 range for gas. By changing the temprature and pressure under which the reaction is taking place we can change the size of the output molecules. This works great for polyethylene which is basically just one big hydrocarbon molecule, but with other plastics and their different chemistries you will get all sorts of different, and potentially nasty, compounds.

Actually, burning it in the backyard usually doesn't get hot enough to break the C-C bonds and so while the hydrogen burns off to produce water, the carbon tends to clump into something like graphite, which is the black solid stuff you see coming from the fire. With PVC or Teflon the halogen atoms (chlorine and fluorine respectively) bind with the extra hydrogen to form hydrochloric and hydrofluoric acids, both of which are nasty things to be breathing. Some of the carbon atoms which are separated can bind with nitrogen to form cyanide and nitrous oxide compounds which are also pretty toxic. Finally, the carbon soot is a smog contributor.

 

I understand that this is the first time that such a small pyrolysis plant has been made, potentially allowing every household to produce it's own diesel fuel.

However, as I've already said, I see a lots of legal problems related to that solution.
Besides the mentioned taxation issue, which is a big political and financial obstacle, there are other things, like:
- who guaranees the quality of the produced fuel? If you sip it in your car's tank, I'm sure it will automatically void any warranty which covers the engine.
- who guarantees that that the fuel or the residuals of it's production will not end up spilled in your backyard, or in some other place where it could contaminate the underground water?
- who guarantees that mr. Joe who has bought the apparatus is maintaining the plant correctly, and will not put in danger his house, or the neighborhood?
- etc.

 

If one of these things lets go it will at least take out the house and very possibly the entire neighborhood. What we are talking here is basically a back yard oil refinery.

This is a case of a technology that works great, but doesn't scale down very well.

 

Interesting. Thanks for the clarification, Daiquiri. Also, thanks for the organic chem refresher, Cthippo. Good to jog the memory, which is currently overloaded with various new things like boat building mumbo-jumbo.

Daiquiri - regarding taxation, does Italia have "on road" and "off road" fuel? In the States, we have to pay tax on all fuel used to power a vehicle on the road. If you put the same type of fuel in your boat, in your generator or in your tractor or small truck o the farm, you are not required to pay taxes on it.

This is where I see this type of small plant really working - for someone in a rural area that can make use of tax-free fuel.

 

I put on-road gas in my lawn mower because, guess what!, its hard to find an off-road gas station. What a rip!

 

I know what you mean, Hoyt.

I nearly always use on-road because I can find it. Out in rural areas, there are usually more sources of off-road.

I have even put on road diesel into by boats at times because it was cheaper than the charge at the marinas.

 

Yes, we do have it here. A so-called "de-fiscalized diesel" (admitted for agricultural and earth-moving machines, public transportation, power generation, commercial fishing and passenger-transportation boats etc.) is currently about half the price of the diesel for on-road use.
It is both a ridiculous and sad situation when it comes to fuel taxation in Italy. We still have some taxes tracing back to the pre-WWII monarchy.
Here comes the list of taxes incrementally introduced by italian government over the time... We have a tax for:

• the 1935 war in Abissynia (actual Ethiopia);
• the 1956 Suez crisis;
• the 1963 dam of Vajont disaster;
• the 1966 flooding of Florence;
• the 1968 earthquake in Belice;
• the 1976 earthquake in Friuli;
• the 1980 earthquake in Irpinia;
• the 1976 peacekeeping mission in Lebanon;
• the 1996 peacekeeping mission in Bosnia;
• etc.

Ammounting to a total of 0.25 Euro per liter of fuel. Always added, never revoked.
The final result is one of the highest energy costs (or perhaps the highest, I should check it out) in the EU.

 

some day you'll win that war in Abyssinia and the tax will be rescinded

 

I was already set to jump tchippy's ***, as usual but that was some nice cutting and pasting. Thx.

 

I doubt either of those will ever happen.

 

No thanks, I do my own writing

 

Wonder how far these guys got?

"Current Australian IPO Axiom Energy Limited has an interesting proposition for potential investors – the company will produce low sulphur diesel from waste plastics that until now could not be recycled and would otherwise end up as landfill. Axiom also plans to be the largest producer of biodiesel on the Australian Eastern seaboard. Currently, 88 per cent of the 1.5 million tonnes of plastic consumed in Australia annually is sent to landfill, this amount could convert to more than 1 billion litres of low sulphur diesel. For example, a simple ice-cream container, weighing just 68 grams can be converted into a diesel fuel which will power a VW Golf car with a diesel engine for approximately one mile."
http://www.gizmag.com/go/4534/

 

Reply by Marmot:
The most likely location for plastic to oil conversion devices is at existing landfills where the plastic is available. Those landfills produce great volumes of methane which (in the US at least) is collected and used to drive onsite diesel or gas turbine powerplants.

The energy in the landfill gas can power the conversion process.

http://www.gizmag.com/envion-plastic-waste-to-oil-generator/12902/

There are several pilot plants operating now and it looks like more operational plants are permitted and going online at landfills around the country. Time will tell if the technology is as economical or beneficial as its promoters claim. Personally, I believe they are on to something.

 

Wow! "I do my own" - what program did you use to model the molecules? Quite a bit of work making the alpha representation of the molecular models - thanks!

 

The images I borrowed from wikipedia, the text (typos and all ) is my own.