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Energy spent recycling covered by resell value of said plastic?
by superpermutat0r 8y ago
Energy spent recycling covered by resell value of said plastic?
- TylerE 8y agoThe biggest problem is you can't _really_ recycle plastic. It would more accurately be called downcycling, as what you get out is of a much lower grade than what you put in. Contrast with aluminum where you get...aluminum back out.
- mirimir 8y agoTrue. But another perspective is that you're recycling petroleum. That is, we make plastic polymers: petroleum -> chemicals -> plastic polymers So why can't we use plastic polymers like petroleum? old plastic polymers -> chemicals -> new plastic polymers
- noobiemcfoob 8y agoAnd generate worse chemical waste than the plastic was to begin with
- mirimir 8y agoWhy any worse than waste from refining petroleum?
- pjc50 8y agoJust because we can go egg -> omelette does not imply omelette -> egg (Likely it can be done, but the energy involved will be a problem. Most polymerisation is exothermic, so reversing it requires energy input e.g. https://www.ewi.ca/reverse-polymerization.html https://www.ewi.ca/reverse-polymerization.html ) Some plastics can be recycled by simple melting - thermoplastics like ABS. Unfortunately they're often mixed with additives like flame retardants that cause problems.
- mirimir 8y agoUmmm, "omelette -> egg" is a lot harder "plastic -> plastic monomers". And really, if you want to convert omelettes to eggs, you just feed them to chickens. And eventually, you feed unmarketable chickens to pigs.
- Sileni 8y agoChemical reactions are typically driven by moving from a high potential energy state to a lower potential energy state. Polymers are incredibly stable because of their binding mechanisms. It takes a relatively large amount of energy to break down those bonds, and when you do, your end product is something far more stable than the original chemicals you started with. Which means it reacts less readily than the chemicals you started with. Take for example polyethylene, a product we can recycle relatively well. The first reaction gives polyethylene chains of length N. Because they're as long as a polyethylene chain can be, they're as strong as polyethylene can be, and have the best performance characteristics you can expect. Each time they're heated up to be remolded or have contaminants removed, and to a lesser extent just from use and contact with sunlight, some of those chains break. This creates more N/(2^x) length chains. This causes the plastic to get weaker over time. The energy cost to recombine those chains would consume more petroleum than simply creating new plastics, if it could be done at all.
- RandallBrown 8y agoSo it's "just" an energy problem? In a hypothetical future with 100% cheap renewable energy, we could recycle plastic over and over?
- nayuki 8y agoIf we have cheap/free energy, we could just synthesize hydrocarbons instead of digging them out of the ground. As an imperfect analogy, we used to mine fertilizers. Now we use energy to create ammonia directly from nitrogen in the air.
- mirimir 8y agoNo, we make ammonia from nitrogen and methane.
- s0rce 8y agoAssuming unlimited energy you could just take CO2 from the atmosphere and react it with hydrogen from water to synthesize all the hydrocarbon precursors you need to then make plastics. The plastics could be burned and you start over again.
- userbinator 8y agoI suspect this is the reason why something as seemingly trivial as colour is presenting such a huge obstacle to recycling --- the margins are already so low that no one really cares enough to solve the problem. (There is probably a lot of bureaucracy around the whole thing too, which is another impediment.) I believe that identifying what a substance is, is already nearly a solved problem (X-ray fluorescence spectrometers, etc.); it just costs too much to use it.