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> 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 chemi
by Sileni 8y ago
> 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.
Sure, you could theoretically break down most plastics to CO2 and the like. They're a lower energy state than most plastics. The question is why expend the energy to get something we have a huge surplus of. You're not going to be able to get volatiles such as methane or ethylene out of that process efficiently, because it's a higher energy state than the plastics. Tar sands and the like are a mixture of volatiles and heavier compounds; they're not a homogeneous compound the way most plastics are. The compounds going into a thermal cracking system, such as decane, are actually higher in total energy content than the products, such as heptane. They're just more difficult to work with, and as such less valuable economically.
Really, if you're not satisfied with the previous explanation you're going to have to look into an entry level organic chemistry textbook to understand it.
- mirimir 8y agoWell: Tsuji et al. (2003) Thermal cracking of oils from waste plastics https://sci-hub.tw/10.1007/s10163-003-0090-x https://sci-hub.tw/10.1007/s10163-003-0090-x Walendziewski (2005) Continuous flow cracking of waste https://sci-hub.tw/10.1016/j.fuproc.2004.12.004 https://sci-hub.tw/10.1016/j.fuproc.2004.12.004 Das and Pandey (2007) Pyrolysis and catalytic cracking of municipal plastic waste for recovery of gasoline range hydrocarbons https://core.ac.uk/download/pdf/53188820.pdf https://core.ac.uk/download/pdf/53188820.pdf
- Sileni 8y agoLike I said in the first response, if you're willing to throw a huge excess of energy at the problem, sure. Calculate out the energy expenditure on any of those reactions. You're talking about burning thousands of times more hydrocarbons than are being recovered. It's a bit like saying you don't need to worry about algorithmic efficiency with a big enough computer.
- mirimir 8y agoSo they're just doing it as an exercise, I guess. What then? Just landfill it? Recycling mixed plastics is nontrivial. And old-school incineration is a nightmare of toxics emissions.
- imtringued 8y agoWhat's wrong with landfills? The petroleum was taken from the ground now the plastic returns to where it came from. Unless Recycling is economical, it will release additional CO2 into the atmosphere.