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Science

New Chemical Process Can Convert Nearly a Quarter of All Plastic Waste Into Fuel (vice.com) 126

Posted by BeauHD from the promising-findings dept.
"Researchers at Purdue University have developed a new chemical process that they say can convert approximately one-quarter of the world's plastic waste into gasoline and diesel-like fuels," writes Slashdot reader dmoberhaus. Motherboard explains how it works: As detailed in a paper published this week in Sustainable Chemistry and Engineering, the chemists discovered a way to convert polypropylene -- a type of plastic commonly used in toys, medical devices, and product packaging like potato chip bags -- into gasoline and diesel-like fuel. The researchers said that this fuel is pure enough to be used as blendstock, a main component of fuel used in motorized vehicles. Polypropylene waste accounts for just under a quarter of the estimated 5 billion tons of plastic that have amassed in the world's landfills in the last 50 years.

To turn polypropylene into fuel, the researchers used supercritical water, a phase of water that demonstrates characteristics of both a liquid and a gas depending on the pressure and temperature conditions. Purdue chemist Linda Wang and her colleagues heated water to between 716 and 932 degrees Fahrenheit at pressures approximately 2300 times greater than the atmospheric pressure at sea level. When purified polypropylene waste was added to the supercritical water, it was converted into oil within in a few hours, depending on the temperature. At around 850 degrees Fahrenheit, the conversion time was lowered to under an hour. The byproducts of this process include gasoline and diesel-like oils. According to the researchers, their conversion process could be used to convert roughly 90 percent of the world's polypropylene waste each year into fuel.
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New Chemical Process Can Convert Nearly a Quarter of All Plastic Waste Into Fuel More

New Chemical Process Can Convert Nearly a Quarter of All Plastic Waste Into Fuel

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  • Plastic is literally fuel for the burner as it's almost always made out of petrochemicals. Why would you lose a massive amount of energy to make it a liquid fuel instead of a solid one?

    • Why would you lose a massive amount of energy to make it a liquid fuel instead of a solid one?

      Because cars don't burn solids.

      Oil is worth ten times as much as coal for the same energy content.

      • And hydrogen is worth ten times more. Sigh....

      • Re: (Score:2)

        by Luckyo ( 1726890 )

        We're living in a world of overabundance of liquid fuels across most of the world right now. Between shale boom in US and OPEC + Russia sitting at all time high production, prices are low.

        At the same time, burners burning various waste products are in high demand, and their fuel is in high demand as well.

      • Because cars don't burn solids.

        Cars shouldn't burn anything at all. A nice chemical reaction and an electric motor is all that's needed.

    • Have you ever smelled or breathed in the smoke that burning plastics give off? That's enough reason not to burn them.

      • Poor argument. Burning plastic at low temperature without sufficient oxygen makes a lot of dirty smoke, but most of that can be prevented in an industrial plant where you can do a much better combustion.

        • Re: (Score:2)

          by Luckyo ( 1726890 )

          Effectively all of it in modern burners. Not only do we have very fine levels of burn control, but we also have wide variety of exhaust filters.

  • So... (Score:5, Insightful)

    by Freischutz ( 4776131 ) on Friday February 08, 2019 @10:38PM (#58092906)
    So, they have discovered a method to convert millions of tons of plastic into fossil fuels that can be burned to release yet more sequestered carbon into the atmosphere. That's sure to solve our ongoing problem with carbon emissions causing climate change.

    • Re:So... (Score:4, Interesting)

      by ShanghaiBill ( 739463 ) on Friday February 08, 2019 @11:18PM (#58092998)

      The energy consumed would have been consumed anyway. So oil made from discarded plastic means we need to pump less oil from the ground.

      So there is no net additional release of carbon, and likely a net decrease since the plastic would eventually degrade and outgas in a landfill.

      • Re: (Score:3, Insightful)

        by Freischutz ( 4776131 )

        The energy consumed would have been consumed anyway. So oil made from discarded plastic means we need to pump less oil from the ground.

        So there is no net additional release of carbon, and likely a net decrease since the plastic would eventually degrade and outgas in a landfill.

        You are really struggling with the concept of carbon sequestration. The problem of plastic garbage is bad but the problem of releasing massive amounts of carbon into the atmosphere is worse. The whole point of mitigating climate change is to replace oil as a source of energy with energy sources that have a smaller carbon footprint. You sound like a heroin addict who thinks that switching to crystal meth will solve all his problems.

    • If you want to sequester carbon, best first step is to stop digging up coal.

    • And not really discovered, as such. "Plastic pyrolysis" has been about for years, but no-one has made it economical on a scale suitable for handling the volumes of waste we produce.

    • So, they have discovered a method to convert millions of tons of plastic into fossil fuels that can be burned to release yet more sequestered carbon into the atmosphere. That's sure to solve our ongoing problem with carbon emissions causing climate change.

      Not exactly. The petrochemical industry is driven by the thirst for liquid fuels not solid plastics. Plastics are a byproduct of the oil and gas industry. If we can reuse plastic as a liquid fuel source then we would offset pumping yet more liquid out of the ground for burning, net emissions stay somewhat equal. What we do end up with is less plastic in the landfills.

      You can't solve global warming at the fuel production stage, you need to solve it at the consumption stage.

      • So, they have discovered a method to convert millions of tons of plastic into fossil fuels that can be burned to release yet more sequestered carbon into the atmosphere. That's sure to solve our ongoing problem with carbon emissions causing climate change.

        Not exactly. The petrochemical industry is driven by the thirst for liquid fuels not solid plastics. Plastics are a byproduct of the oil and gas industry. If we can reuse plastic as a liquid fuel source then we would offset pumping yet more liquid out of the ground for burning, net emissions stay somewhat equal. What we do end up with is less plastic in the landfills.

        You can't solve global warming at the fuel production stage, you need to solve it at the consumption stage.

        If somebody comes up with a more efficient and cost effective way to power your [whatever] just watch the fossil fuel industry go the way of buggy whip manufacturers. This is already happening, we are already sailing into a duck curve where electric will beat fossils on every level and no amount of conservatives hammering on about how fracking and using fossil fuels is patriotism can change that.

      • You can't solve global warming at the fuel production stage, you need to solve it at the consumption stage.

        I disagree. One problem is that there is no alternative to jet fuel right now to make things fly. Jet fuel is a mix of hydrocarbons but they don't have to be pumped out of the ground. We can synthesize them.

        The US Navy has been doing talks on their seawater-to-jetfuel process for years in the hope of getting more funding from Congress or private industry interested in developing the technology. They've done some very interesting demonstrations, and if their numbers are right then the economics look not

        • It's carbon neutral because it takes carbon that's in the water as dissolved CO2

          That's like saying burning oil and coal is carbon neutral because it takes carbon that is embedded in these resources which once were removed from the air. Sorry but your proposal is not only NOT carbon neutral it actually requires a shit ton of energy as well (reads expensive, and in scale likely causes carbon emissions).

          The only way you make something carbon neutral is to create a new carbon sink as your fuel source. e.g. Biomass isn't carbon neutral either if you don't plant new trees.

          • The only way you make something carbon neutral is to create a new carbon sink as your fuel source.

            The Navy process does this. Claiming otherwise is a basic fail of understanding the process. Go look it up.

            • I have looked it up. It's a great way of reducing reliance on oil, but it is not carbon neutral. Extracting CO2 from an existing sink, adding hydrogen, and then setting it on fire in a jet engine is not carbon neutral. You're taking CO2 dissolved in water and releasing it to the atmosphere.

              Unlike our ability to plant trees we have no ability to create new CO2 free water beyond the natural fresh supply cycle that exists. Ultimately the CO2 will be re-dissolved into the ocean, but not at any rate that makes t

    • If history is any indication, no one is going to do this. There is already a process for recycling ALL plastics into useful gases and liquids by cooking them under pressure, but nobody is using that either, because it's a PITA. 2300 bar is a shit-ton of pressure. For comparison, really serious diesel engine cylinder pressures only get up to about 180 bar. More importantly, supercritical water behaves itself even less than the normally-compressed stuff. It's not that the process doesn't work, it's just not l

      • Besides, if you could manage about twice that pressure, you can make diamonds. Now that's the way to sequester carbon.

      • I was going to post s.t. like this, but you beat me to it.

        Decades ago, I was Main Propulsion Assistant on a Guided Missile Destroyer. It was propelled by steam turbines, with steam at 1200 psi and 975 degrees (superheated). That's ~80 bar, and the steam was truly dangerous. A leak wouldn't scald you, it'd cut you in half. (I avoided that, as you may have surmised.) Some land-based boilers go higher than that, perhaps 3500 psi, or ~240 bar. For this plastic operation, they're talking nearly an order of

        • Oops, there was a mistake in the synopsis of the article here at /. The pressure the experiment used was 23 MPa =~ 3300 psi--NOT 2300 bar. Off by an order of magnitude. This is still a very high (and dangerous) pressure, but not as outlandish as it seemed.

          BTW, there are two links in the /. article. The first is too motherboard.vice.com, and that contains the incorrect figure of 2300 * atmospheric pressure. That's apparently where the 2300 bar figure in /. comes from. The other link is to an abstract w

    • No it is to keep it out of the land fills. Even if it is fuel neutral. The net is that it does not go into the ground. Maybe excess heat/steam can turn a steam turbine generator and make electricity.

  • Great idea! (Score:4, Funny)

    by Pollux ( 102520 ) <speter@@@tedata...net...eg> on Friday February 08, 2019 @10:42PM (#58092918) Journal

    Their conversion process could be used to convert roughly 90 percent of the world's polypropylene waste each year into fuel.

    Then we can put this fuel into our cars and burn, dumping all that carbon into the atmosphere, where it can no longer be any harm to our planet.

    Oh wait...

    • That fuel is already going into our cars. If we can avoid pulling more out of the ground where it belongs and converting it to plastic in a landfill or in the ocean, that's still a win for the environment. This doesn't prevent us from moving off of fossil fuels, but it would lessen, or more realistically stave off having to drill for more quite as fast. Plus the added benefit of finally having a real use for all that waste.

    • Their conversion process could be used to convert roughly 90 percent of the world's polypropylene waste each year into fuel.

      Then we can put this fuel into our cars and burn, dumping all that carbon into the atmosphere, where it can no longer be any harm to our planet.

      Oh wait...

      Great idea. That way we don't need to dig more oil out of the ground to put it in our cars where we will continue to burn at the same rate completely independently of this technology. Oh and we end up with less in our landfills.

  • Supercritical water (Score:3)

    by Livius ( 318358 ) on Friday February 08, 2019 @10:46PM (#58092928)

    At high enough pressures and temperatures, anything with carbon will turn into light hydrocarbons.

    But if it turns out that the math means this is practical, then this would be very cool.

    • Most likely it's a practical method to convert subsidies into salaries. Otherwise, the best method would be to just burn the stuff and make electricity or heat.

    • Anything with carbon? Great, let's start burning CO2!

      • Are you being sarcastic or are you clever enough that CO2 can be shift reacted to CO and then using Fischer Tropsch synthesis be hydrogenated into a hydrocarbon?

        The Germans used to do this with coal.

    • Well you're missing the "hydro" part in hydrocarbons but yes close enough ;-)

  • Nice (Score:2)

    by melted ( 227442 )

    So whatever plastic is currently capturing carbon, can return it right back into the atmosphere.

  • Not hard for pure hydrocarbon plastics (Score:4, Interesting)

    by joe_frisch ( 1366229 ) on Friday February 08, 2019 @10:55PM (#58092948)

    Plastics containing just H and C can probably be burned without much processing. The problem is that most recycled plastic is a mix of all sorts, including a lot of popular Cl containing plastics that are really nasty to burn.

    If there are sources of sufficiently pure hydrocarbon plastics (polyethylene, polypropylene and the like) and if this is more cost effective and energy effective than other methods, its fine. I expect the bigger problem is the initial purification. Maybe there is a solution to separating out the other plastics?

    • The problem is that most recycled plastic is a mix of all sorts, including a lot of popular Cl containing plastics that are really nasty to burn.

      I'm pretty sure that the job of safely burning plastics, including removing Cl at any point in the chain, is still easier than removing same Cl and turning the rest into a useful liquid fuel.

    • Yes and if these are pure hydrocarbon plastics, why go through all of this. Couldn't we just mix them with coal and burn them in existing facilities?

      • Couldn't we just mix them with coal and burn them in existing facilities?

        One little catch with your plan. How are you going to get subsidies that way ?

  • But let's talk about how energy intensive it is to get water into that supercritical state.

    Probably so expensive with current "green" technology that it would make more sense to just work on optimizing fossil fuel usage.

    Sure we could achieve this easily with nuclear power, but with dolts like Ocasia-Cortez running around trying to gut our nuclear industry it just ain't going to happen.

    Cool science, but not readily useful.

    • Nuclear power?

      Read this article, it seems to make a lot of sense and explains why nuclear power is not likely in the immediate or foreseeable future"

      https://www.popularmechanics.c... [popularmechanics.com]

      TLDR: Costs way too much, takes far too long to build. And NIMBY. Then there is that pesky unsolved waste issue...

  • In degrees celsius... (Score:4, Insightful)

    by Lanthanide ( 4982283 ) on Friday February 08, 2019 @11:29PM (#58093018)

    Scientific writing should always be in celsius, with farenheit in parentheses.

    between 716 and 932 degrees Fahrenheit = 380C to 500C. Looks like the author already took the perfectly workable celsius and obfuscated it by turning it into farenheit, which is stupid since no human would have an appreciation of what 716 farenheit is like compared to the normal temperature ranges they're familiar with anyway.

    around 850 farenheit = around 450C.

    • I'm not disagreeing with what you said, but the funny thing is I can "speak" and understand temperature fluently in Fahrenheit or Celsius from -40F/C to about 100C/212F, but outside of those boundaries I only can understand and get a grasp of how hot or cold something is only when the temperature is given in Fahrenheit. 380C-500C means nothing to me other than it's a number that is similar to the temperature on Venus or about twice as hot as the highest number on the dial of a kitchen stove, whereas when I

  • That's not the problem (Score:5, Insightful)

    by Solandri ( 704621 ) on Friday February 08, 2019 @11:52PM (#58093078)
    There are two classes of plastic trash.
    • Plastic thrown away in trash cans and as household garbage. These plastics end up in a landfill, meaning it's buried underground. Which happens to be where the petroleum to make the plastic originally came from. So it has zero net environmental impact (unless you plan to go digging up landfills).
    • Plastic thrown away on the streets, in the landscape, and in the water. These plastics mar the environment and cause all the problems we're hearing about (plastic in the oceans, microplastics in the food chain, animals being wrapped up and dying in plastic waste).

    Now, if they're going to convert plastic into fuel, which plastic do you think they're going to use? Obviously the former. Meaning (1) it will have zero effect on plastic pollution in the environment, and (2) you're just spending extra energy and money to convert petroleum byproducts into fuel, instead of just using new petroleum as fuel. You're just paying extra to swap carbon sequestered underground as plastics, for carbon sequestered underground as natural petroleum.

    Any solution to address environmental plastic pollution must address the non-collection problem. That means either enforcing proper disposal of plastic waste, designing plastic waste to degrade more quickly in the environment, or reducing the use of plastics entirely. This plastic to fuel idea does none of these things. The only thing it does is reduce the space taken up in landfills.

  • I remember my chemistry professor talking about how stupid it was to recycle plastics. He said we should just burn them for electricity instead of sorting, transporting, and otherwise expending all kinds of energy and effort in recycling. I'm guessing he brought this up in class because the city was debating a waste to energy plant and that burning plastics was part of that debate.

    What I'm wondering is where the energy would come from to reach these intense temperatures and pressures for this process. Not many things burn this hot. Would this be a kind of coal blast furnace like that used to make steel? That seems like a rather silly idea if the goal is to reduce the production of waste and CO2.

    There is a technology that can reach these temperatures. This technology also produces very little carbon, and theoretically none. That is the molten salt reactor, nuclear power. The US Navy is developing a technology much like this, only they use carbon sourced from CO2 dissolved in seawater. They want high temperature reactors too. Although the high pressures like this process uses might turn them off. They want to get away from the use of high pressure steam as that created inherent hazards to the crew on a ship. High temperatures are also a hazard but a ship at sea is surrounded by a huge heat sink, and any steam from that hot stuff meeting the water would be at atmospheric pressures.

    This plastic to fuel process is a nice idea but hardly new. I believe that gentlemen named Fischer and Tropsch developed this same process nearly a century ago in Germany. All they are doing is limiting the feedstock for the process to plastics, but the process would work on most any carbon based material.

    • Re: (Score:2)

      by piojo ( 995934 )

      What I'm wondering is where the energy would come from to reach these intense temperatures and pressures for this process. Not many things burn this hot. Would this be a kind of coal blast furnace like that used to make steel? That seems like a rather silly idea if the goal is to reduce the production of waste and CO2.

      The pressures are hard, yes. But the temperature is easy. Every flame I've heard of will reach that temperature (500C). Even a candle flame reaches 1000C.

      • To expand on this, it's ridiculously cheap and easy to build a propane or charcoal-fired crucible that will readily melt aluminum at temperatures substantially higher than what's needed here. As you point out, the difficulty is not the temperature, but in handling the required pressures.

      • The pressures are hard, yes. But the temperature is easy. Every flame I've heard of will reach that temperature (500C). Even a candle flame reaches 1000C.

        But how can they get to these temperatures without burning anything? The goal, so it seems, is to avoid carbon going into the atmosphere.

        I assume electric heat can get hot enough but then there is still the question on where to get the energy. Any heat engine that converts boiling water to steam for turning a turbine would be quite wasteful use of that heat if the electricity is then just run to an electric heater. If there is something that is hot enough to begin with then the inefficient process of con

        • Re: (Score:2)

          by piojo ( 995934 )

          The rule of thumb is that hydrocarbons contain around 9 kcal of energy per gram. One kcal is enough to raise a gram of water by a thousand degrees, and almost every other substance is heated more easily than water (specific heat being around 1/4 to 1/2 that of water). PP has a specific heat of 0.46 calorie per gram degree. If my math is correct, burning one gram of plastic (not necessarily PP) could heat a little over 5 grams of PP to the needed temperatures.

    • You shouldn't need high temperature or pressure to burn these in a trash-to-smoke power plant. (I think the fancy term now is "co-generation" but I'm a bit behind on the latest buzz words). If you burn *just* plastic, you may need to be creative but if you mix it with other things that burn easily (such as paperboard), it should all just burn and generate heat. If not just add something that burns hotter to the mix. If you can *separate* the plastic, I suggested in a previous post just to mix it with yo
    • https://en.wikipedia.org/wiki/... [wikipedia.org]

      Produces energy and gets rid of nasty byproducts.

  • 2300 bar (atm) LOL (Score:3)

    by joe_n_bloe ( 244407 ) on Saturday February 09, 2019 @01:39AM (#58093284) Homepage

    That would be interesting.

    The abstract, though, says: "supercritical water at 380–500 C and 23 MPa" which is 230 bar, which is still a respectable pressure (3300 psi) but the sort of "reasonable" pressure encountered in modern steam turbine power generation, etc.

    • It would be interesting but not exactly a huge problem. These kinds of pressures were used around the WWII days by the Germans to liquefy coal into hydrocarbons. It makes for some very interesting vessel designs.

  • Why? (Score:1)

    by Anonymous Coward

    > estimated 5 billion tons of plastic that have amassed in the world's landfills

    Plastic is lighter than water and water weights 1 ton per 1 cubic meter. So, ideally packed 5,000,000,000 tons of plastic would fit into 5 cubic kilometers, e.g. 5 km x 10 km x 100 m landfill. I don't see a problem. It looks like a very good way to keep carbon from atmosphere.

  • Holy fuck people...

    From the linked journal:
    temperature: 450 C
    pressure: 23 Mpa

    It is not 2300 bar, it's 230 bar.

    Standard propane burns at 1980 C in air and thats the same pressure as a scuba tank. So temperature and pressure are easy to achieve. This can reduce solid plastics waste and potentially reduce the consuption of crude oil.

    And maybe we can stop dumping plastics in the ocean and killing all the damned sea life.

    Oh yeah, stop burning plastics. The extraneous chemicals in there are going to kill you a

  • Wonder want happens to non-PP plastics that are in the mix? It's the waste sorting that costs.

    There are plenty of locations with waste heat that could co-power a process like this for low incremental cost. So those bleating about 100% efficiency are walking the wrong road.

  • Turning what is otherwise waste into something *useful* is definitely a plus.

    Ferret

  • Another something into fuel (Score:3)

    by p51d007 ( 656414 ) on Saturday February 09, 2019 @01:00PM (#58094926)
    How many more will there be? Turning CORN into fuel was a wasteful enterprise, that benefits only the "farm industry". Many other things can be turned into fuel.

  • What throughput in this process ?

    How many energy do they consume to transform back these plastics ?

    Woudn't be better to directly use this energy for the final usage ?

  • One way or another, the solution to all plastic waste is to blow it out of tail pipes hither and yon.

  • All the electricity they put in to convert the plastic in a fuel, probably doesn't return 10% from the fuel so created. It would be more efficient to use the electricity directly to do the things we normally would do, such as charge the battery in an electric vehicle. Also, you can use plastic directly as plastic to do plastic things -- like making reusable shopping bags -- at probably 1/1000 the energy requirement of making fuel from the same material.

    No. This has nothing to do with finding a use for plast

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