4 ms·

From an economic perspective, the problem with pyrolysis waste-to-energy is that it takes more energy to use the process than it produces [1]. This is a proces

• InitialLastName 2y ago
  > I do not understand why organizations like Exxon-Mobil and the American Chemistry Council are promoting it. If they don't pretend there's a responsible way to dispose of plastic, someone might hold them responsible for the plastic waste they produce.
• dzdt 2y ago
  Organizations like Exxon-Mobil promote these fairy-tale schemes as a talking point to counter legislation that would restrict their unlimited production of fossil-fuel based plastics. Its the same scheme with carbon capture for coal-burning power plants. The technology doesn't and will never work as described, but talking up its potential gives an excuse not to regulate the polluting industry now.
• lenerdenator 2y ago
  > I do not understand why organizations like Exxon-Mobil and the American Chemistry Council are promoting it. Because if you start to look at plastics by what has to be done with them after they're consumed, they don't make sense as a common consumer product* anymore. And if they don't make sense as a common consumer product, then there's fewer people lining up to buy Exxon Mobil's plastic stocks, which are made of oil. Since Exxon Mobil is a company that exists to transfer value to shareholders via the extraction and processing of hydrocarbons, this is a problem. The ACC is made up of scientists and engineers that work for companies like Exxon Mobil. * common consumer product meaning that it's used in places for broad public use where alternatives such as aluminum or wood are viable, like beverage cans.
  • gs17 2y ago
    > use where alternatives such as aluminum or wood are viable, like beverage cans. I'm not sure if you meant it this way, but does wood actually get used in that niche? I'm imagining tiny barrels. I guess paper cups (or those big coffee things) are sort of that idea.
    • pantalaimon 2y ago
      I think GP was just taking aluminum cans as a single example. Another one would be wooden single-use cutlery is an alternative to plastic one.
    • hwillis 2y ago
      plastic packing peanuts vs paper stuffing, paper/plastic bags, blister packs vs cardboard boxes, paper-backed tape, paper/plastic plates, straws, etc
• frdsfctt 2y ago
  Thermodynamically combustion of pyrolysis products does not, cannot, use more energy than it produces. If it did, plastic would not burn. Plastic burns, hence pyrolysis is a net energy source. [1] That's not to say it makes sense. Myself, I'm in favor of a high temperature burn of plastic + scrubbers + insane taxes on halogenated polymers + insane deposits on fluorinated polymers -> to keep the flu stream clean. [1] pyrolysis itself is endothermic, clearly, since polymerization is extothermic. But the article you linked explicitly says burning pyrolysis by products which must, net, be exothernic An other way of looking at it is pyrolysis is a necessary first step for plastic combustion hence the cycle is net exo
  • samatman 2y ago
    You don't really need the insane taxes part, just an insistence that the plants are not allowed to emit halogens in the flue gas. The halogens are completely recoverable by bubbling them through an alkali mixture, doesn't matter what earth metals are used (some combination of sodium and calcium is cheapest), this will result in salts. You want to be a bit more careful about some metals, so that you don't have to precipitate them out of the salts to render them nontoxic. There are ways to preferentially bind the metals even in the gas phase, but it's best not to burn them to begin with, which isn't that hard because metals aren't found in high quantities in plastics to begin with, especially not the bad ones like cadmium and lead. Other than that, plastics are economically useful, but burying them is just delaying their release into the environment, which is not great. So burn them, and stop pretending they're useful for anything but fuel at the end of their service life. Pretty simple.
    • fuzzfactor 2y ago
      >bubbling them through an alkali mixture Which turns the liberated halogens back to salt automatically, in a very favorable reaction which is so strongly favored it is almost irreversible. Almost. But not if you carefully apply energy to the brine using an electrochemical process, especially one which has been improved for over a century after the patent expired, and you can't get much more efficient than that. Especially at the scale these operate at. These are not petrochemical plants since they were doing this before petrochemicals actually had plants. Crude oil wasn't even that popular yet. But who's going to need to do that, the spent alkali after scrubbing the halogens has no need for additional energy to be added. Unless you wanted to turn it back into full-strength alkali. Which wouldn't be cost-efective anyway, and nobody should be paying more than it's worth. Because there's planty of fresh material coming out of the caustic plants already. But you know how much energy it takes to produce that alkali originally from the virgin brine feedstock those plants use? More than it's worth. It a plain electrochemical reaction. No other raw materials needed. It's that "irreversable" reaction that's just a little too strong. So it takes a lot of energy to reverse. Kind of like trying to turn CO2 back into hydrocarbons. And if you want to try and capture CO2 from the atmosphere using alkali, fuggedaboutit. You're going to need a bigger caustic plant, and a lot more of them. There's a thing called material balance too, not just electrochemistry and thermodynamics at work.