Vaporizing Plastics Recycles Them Into Nothing But Gas, Researchers Find (arstechnica.com) 32
Polypropylene and polyethylene plastics "can be recycled," reports Ars Technica. But as "polyolefin" polymers, "the process can be difficult and often produces large quantities of the greenhouse gas methane.
"Now, researchers at the University of California, Berkeley have come up with a method of recycling these polymers that uses catalysts that easily break their bonds, converting them into propylene and isobutylene, which are gasses at room temperature. Those gasses can then be recycled into new plastics..." [T]he previous catalysts were expensive metals that did not remain pure long enough to convert all of the plastic into gas. Using sodium on alumina followed by tungsten oxide on silica proved much more economical and effective, even though the high temperatures required for the reaction added a bit to the cost. In both plastics, exposure to sodium on alumina broke each polymer chain into shorter polymer chains and created breakable carbon-carbon double bonds at the ends. The chains continued to break over and over.
Both then underwent a second process known as olefin metathesis. They were exposed to a stream of ethylene gas flowing into a reaction chamber while being introduced to tungsten oxide on silica, which resulted in the breakage of the carbon-carbon bonds. The reaction breaks all the carbon-carbon bonds in polyethylene and polypropylene, with the carbon atoms released during the breaking of these bonds ending up attached to molecules of ethylene... The entire chain is catalyzed until polyethylene is fully converted to propylene, and polypropylene is converted to a mixture of propylene and isobutylene. This method has high selectivity — meaning it produces a large amount of the desired product.
That means propylene derived from polyethylene, and both propylene and isobutylene derived from polypropylene. Both of these chemicals are in high demand, since propylene is an important raw material for the chemical industry, while isobutylene is a frequently used monomer in many different polymers, including synthetic rubber and a gasoline additive.
"Because plastics are often mixed at recycling centers, the researchers wanted to see what would happen if polypropylene and polyethylene underwent isomerizing ethenolysis together," the article adds. "The reaction was successful, converting the mixture into propylene and isobutylene, with slightly more propylene than isobutylene." The reaction worked, even if there were contaminants from other plastics. And "When the research team increased the scale of the experiment, it produced the same yield, which looks promising for the future...."
The researchers hope this some day could reduce the demand for chemicals derived from fossil fuels.
Thanks to Slashdot reader echo123 for sharing the article.
"Now, researchers at the University of California, Berkeley have come up with a method of recycling these polymers that uses catalysts that easily break their bonds, converting them into propylene and isobutylene, which are gasses at room temperature. Those gasses can then be recycled into new plastics..." [T]he previous catalysts were expensive metals that did not remain pure long enough to convert all of the plastic into gas. Using sodium on alumina followed by tungsten oxide on silica proved much more economical and effective, even though the high temperatures required for the reaction added a bit to the cost. In both plastics, exposure to sodium on alumina broke each polymer chain into shorter polymer chains and created breakable carbon-carbon double bonds at the ends. The chains continued to break over and over.
Both then underwent a second process known as olefin metathesis. They were exposed to a stream of ethylene gas flowing into a reaction chamber while being introduced to tungsten oxide on silica, which resulted in the breakage of the carbon-carbon bonds. The reaction breaks all the carbon-carbon bonds in polyethylene and polypropylene, with the carbon atoms released during the breaking of these bonds ending up attached to molecules of ethylene... The entire chain is catalyzed until polyethylene is fully converted to propylene, and polypropylene is converted to a mixture of propylene and isobutylene. This method has high selectivity — meaning it produces a large amount of the desired product.
That means propylene derived from polyethylene, and both propylene and isobutylene derived from polypropylene. Both of these chemicals are in high demand, since propylene is an important raw material for the chemical industry, while isobutylene is a frequently used monomer in many different polymers, including synthetic rubber and a gasoline additive.
"Because plastics are often mixed at recycling centers, the researchers wanted to see what would happen if polypropylene and polyethylene underwent isomerizing ethenolysis together," the article adds. "The reaction was successful, converting the mixture into propylene and isobutylene, with slightly more propylene than isobutylene." The reaction worked, even if there were contaminants from other plastics. And "When the research team increased the scale of the experiment, it produced the same yield, which looks promising for the future...."
The researchers hope this some day could reduce the demand for chemicals derived from fossil fuels.
Thanks to Slashdot reader echo123 for sharing the article.
That title (Score:5, Funny)
"Turning something into gas turns it into gas!"
Presumably what they really meant to say was that vaporizing plastics successfully breaks them down into non-plastic molecules.
It's not as short, but being brief is pointless if you sacrifice necessary accuracy.
Re: That title (Score:2)
How much energy do you need for it to be useful is also interesting.
Re: That title (Score:5, Interesting)
Plastics are very stable molecules, which is why when they 'break down' they tend to just break down into tinier bits that are still plastic. From that I infer that it takes a lot of energy to break them apart properly.
The cost of this recycling should be built into plastics as a tax at the point of manufacture, because externalizing the cost into ubiquitous global pollution is not the same as the cost actually going away.
Re: (Score:1)
Cool story, bro. Are you new to the way the world works? Companies will just manufacture their plastics in some third world shithole that doesn't tax them because they want those sweet, sweeeeet jobs.
Not saying that you are wrong, but attitudes like yours are one reason for why we make less progress than we could.
Re: (Score:2)
There are more solutions than taxing that could be used, like stopping the oil company lobbying powers that probably push the government to purposefully make things less efficient in general.
Recycling local plastics is probably cheaper than drilling new oil, doing all the massive pipeline of chemical processing, shipping it overseas...
Re: That title (Score:2)
Re: (Score:2)
I can't tell from the summary if they really get rid of the plastic, or if there's a non-negligible amount of microplastics in the resulting gas.
Re:That title (Score:5, Informative)
The summary says it turns the plastics into propylene and isobutylene -- the monomers from which we produce polypropylene and butyl rubber.
Polypropylene accounts for about 20% of all worldwide plastic production. Since it has many applications in common with polyethylene, it probably could be more. Polypropylene produced by this process would both be both recycled *and* from an engineering standpoint, virgin plastic. Butyl rubber is roughly 98% isobutylene. It's used for inner tubes, tires, gaskets, medical devices, sporting goods and so on. While not quite as common as styrene-butadiene synthetic rubber, it can replace it in numerous applications.
If this process can be economically scaled, it could take a lot of plastic out of the waste stream. If similar processes yielding ethylene could similarly be developed and scaled, then recycling could actually make a significant environmental difference -- at present it's largely greenwashing. Of course those are a lot of "ifs".
Re: That title (Score:2)
Re: That title (Score:1)
Re: (Score:2)
Using the correct terminology, vaporizing polymers successfully breaks them down into monomers.
The real news is finding better catalysts to do it. As TFA points out we always knew how to decompose polymers, but the catalysts kept fouling.
Interesting (Score:3)
I see that this is interesting, but I'm a bit concerned about chlorine and flourine that's common in some plastics as well as biological and metal contamination.
I can see that some biological contamination actually could contribute and be recycled and that metal probably separates relatively easy. But halogen gases can be tough to separate out.
Re: (Score:2)
Well, this process won't release elemental fluorine, but it may result in small molecules with fluorine attached. Probably the same for chlorine. Fluorine is too reactive to stick around, and chlorine if pretty reactive, to. I expect that chlorine would end up a HCl, but I suppose there might be an oxygen and maybe a carbon or so in there. (They don't seem to be doing this in a vacuum.) (OTOH, there's hot sodium in the first stage, so it might yield NaCl.)
I do not call this "recycling" (Score:2)
Re: (Score:2)
Implicit in the term recycling is an energy/effort/cost savings over just making a product from scratch. This "recycling" process requires more energy than simply making plastic from petrochemicals.
Citation Needed. Please show your full calculation for energy of both.
And when you're done I'll criticise you again. Your definition of recycling is arbitrary. At no point has recycling ever been defined as something that requires energy effort *OR* cost savings over making a product from scratch, to say nothing of the fact that your sentence implies you need all of them. Recycling is purely defined as turning waste into a usable product. The goal of recycling has always been to reduce the use an original r
Re:I do not call this "recycling" (Score:5, Informative)
Re: (Score:3)
And a sanitation system takes more energy than just shitting in the street. But we rather prefer it. (There are lots of things in use that are more dangerous than ethylene at 320C.)
Parts of your argument are definitely correct. Every factual statement you made MAY be correct, as I'm no expert in that area. But your conclusions don't follow. This is part of a sanitation system, if it produces salable end products, that's a side benefit.
Re: (Score:2)
There is absolutely no way this can be done at less energy that simply making more plastic.
Irrelevant. We can't just keep making infinite amounts of plastic. We don't have infinite supplies of raw materials. We can't just go grab everything we need from another planet or something. Recycling will only get more and more necessary.
Re: I do not call this "recycling" (Score:2)
Re: (Score:3)
To ensure we have enough capacity at all times, we will have a lot of excess renewable generation most of the time. Gluts will be predictable 48 hours in advance with weather forecasting.
Technologies that can make use of energy when available, like electric heating to recycle plastics into gasses, will be a nice way of stabilizing energy prices by consuming energy when there is more than the rest of the grid needs. In exchange such operations will get preferential pricing, making stuff like recycling and de
Re: (Score:3)
>Implicit in the term recycling is an energy/effort/cost savings over just making a product from scratch.
I'm sure industry sees it that way, but that is because they've externalized the expense of dealing with the waste.
That's why we should be taxing them for the cost of the environmental cleanup at point of manufacture. If their products are still marketable at the required prices, recycling before the product is broken down and dispersed into the environment will be worth the rebate.
Re: (Score:2)
OK, but you'll need import taxes on plastics imported from places that don't require externalities be included in the price.
Re: (Score:2)
Absolutely. Level playing field.
Re: (Score:2)
Implicit in the term recycling is an energy/effort/cost savings over just making a product from scratch.
No. Recycling has never been about an energy, effort, or cost savings. Recycling only means "converting waste material into reusable materials". Just because most businesses only recycle if there is financial incentive to do so, doesn't mean recycling has to be that way. Recycling should be mandated and forced, regardless of whether or not it costs more. If the businesses can't handle it, they don't deserve to keep operating anyway.
Re: (Score:2)
> Who would pay to build a money-losing, energy-hungry chemical plant like this?
Let the market handle it and then stupid money-losing schemes won't occur regularly.
Maybe Microsoft will have to excess power from Three Mile Island and they can recycle plastics during off hours.
Leave room for creative solutions.
Today's title (Score:2)
brought to you by the department of redundancy department.
Re: (Score:2)
Not necessarily. There are plenty of vaporization processes that leave behind solid by-products. More information is added to the context by saying "nothing but gas"
Acme (Score:3)
Where have I seen this tech before?
https://external-content.duckd... [duckduckgo.com]
Thermal depolymerization (Score:1)
Once energy is free and plentiful (Score:2)