What is the best process to do so (pyrolysis, gasification,or any other process)?
What is the yield per ton of waste?
Yes, the technology is called pyrolysis. The yield depends on your feedstock and you have a number of products not only oil -->diesel. Plastic is a collective noun and cover very different materials (the long carbon chain is the common element). Plastic waste can be very different depending on the source (e.g. municipal, developed country; the industrial waste individually need to be analyzed), so yield cannot be defined.
Your products are:
- oil --> diesel (after upgrading). ~170-300 kg/t of plastic waste (but your yield can be very different),
- heat energy,
- pyrolysis gas and solid parts --> electricity.
- chemicals,
- ash.
Another thought, to reuse the plastic the best to separate first. No reason to handle them together. The sorting makes all kind of reusing effort more beneficial. Speedy machines are available what can assort shredded plastic based on density and color.
any thermal degradation process can break polymers by beta scission, i.e. breaking the second to terminal position carbon-carbon link and progressing to smaller molecules, along with condensation of these into coke. Depending on severity it can be conducted to most severe case to ethylene and coke and to more modest to very unsaturated hydrocarbon fuels.
It can be performed with the process of Pyrolysis, through which the application of heat in a oxygen less controlled chamber breaks down long chain hydrocarbon into short chain subtances, like diesel, coke etc.
As mentioned above, the process you are looking for is called pyrolysis. Pyrolysis is an established process, you can buy turn key equipment for this application. The characteristic of the product will vary greatly depending on the feed. The recovery of usable oil tend to be low (in my experience around 2-5% (liter/kg)) as significant portions of the feed tends to either be converted to non-condensable gases or solid carbon. Some thing you may want to consider: the presence of oxygen during the start is usually unavoidable outside of laboratory conditions, but the presence of oxygen in any stage will significantly decrease your usable yield. The upside is the non-condesable gases are rich in hydrocarbons and can be used to fuel the later stages of the process. If you do not plan to use the off gases as fuel, you may want to consider installing a burn tower.
Polyalkenes (PE, PP, etc) will yield yield clear, waxy oil similar to petrol or light fraction diesel, these do tend to form waxes at temperatures below 26 C. Polyaromatics (synthetic rubber, etc) tend to produce very aromatic oils similar to middle and heavy fraction fuel oils, these tend to form waxes at relative high temperatures (based on experience I've seen wax formation above 30 C). Consider those two things if you're planning to store the product for a signifcant (more than a month) amount of time.
Additionally, oils produced by polyaromatics are heavy in benzene bearing compounds and as such proper safety and storage measures must be done.
Edit:
Sorry I forgot to mention this above, halogenated polymers of any sort will form dioxins and furans during pyrolysis. Segregation of the feed material is highly recommended.
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