Tech Tuesday: Re-Thinking Recycling
I’ve talked about recycling before, and the various problems with how we currently do it, and the limitations of the materials, etc.; but let’s review:
- Paper: From virgin pulp until it’s done, we can recycle paper ~7 times, if we are lucky, and by the end, all we can really do with it is make paper egg cartons and drink trays1.
- Plastic: Plastic gets 2-3 turns through the system before it’s pointless to try again, and that is assuming we can identify and separate the various types.
- Ceramics: These don’t really recycle. Well, aside from glass, which isn’t really a ceramic, but some folks think it is. That isn’t to say they can’t be re-used2, but we generally can’t break ceramics down and turn them into new ceramics.
- Textiles: Plastic fibers have the same issue as plastics. Natural fibers can be re-used3, but we can’t really un-weave a bed sheet and spin it up as a new spool of thread. At least, no one bothers to that I am aware of.
- Metals: These can be recycled indefinitely. Seriously, melt it down and it’s good as new. The crystalline structure just reforms. About the only tricky part is making sure we know what alloy we are adding to the mix so we get the alloy we want out of the furnace.
So aside from metals (and obviously organic stuff that can be composted), it doesn’t appear that we have a lot of recycling we can actually do4.
Except, that’s not entirely true.
Paper is biodegradable. Burn it, pulp it into a slurry, compost it. Mother Nature will return it to the food chain. Think of it as full circle recycling. The paper comes from plants, and after composting it, it is returned to the plants. Same goes for natural textiles. So once we hit that 7th use, just send it back to the biosphere.
But what about plastics?
All plastics start out as a hydrocarbon, and then we chemically tease certain refined hydrocarbons into polymers through a catalytic process called polymerization. If the hydrocarbon of choice is petroleum, that process looks like this. One of the most common plastics in use today is polyethylene, which is a fancy word for two hydrogen atoms attached to one carbon atom and the carbon atoms are chained together with other CH2 molecules. That’s it, carbon and hydrogen (the definition of a hydrocarbon).
If the plastic is a bio-plastic or bio-polymer, one whose feedstock is cellulose or some other carbohydrate source (there’s that carbon – hydrogen combo again), the process is similar, but involves different catalysts, or employs bacteria, and the end results can be a bit different.
It’s important to keep in mind that not all bio-plastic is bio-degradable or compostable, so the feedstock does not make a specific plastic green. We could be making all of our plastic from agricultural by-products and still have the same problem we do today.
The key is those chains of molecules. They can be hard to break. Which isn’t a bad thing, since we do need materials that are lightweight and durable. But not every use of plastic needs to last decades. Food and drink containers, for example, or plastic bags, or other single use plastic products (Straws! Think of the sea turtles!). Hell, even cheap kids toys (you know, the kinds or toys you get from Happy Meals that your kids will forget about a week after they get them) doesn’t need to be capable of being an heirloom, not every toy is a Lego.
We can design the chains to break. They can be designed to break down in the presence of light, or water, or by bacteria. Often, those breaks just result in plastic particles that we hear about getting into our food and water supplies, basically just smaller and smaller chains of molecules. But if the plastic is designed to be truly bio-degradable, then it is converted to other hydrocarbons or atmospheric gases. Those gases, by the way, are usually carbon dioxide and methane (CH4), which are not desirable gases to release back into the atmosphere5. And, of course, if the chains are designed to break, the plastic will degrade over time, possibly very quickly, and we may want that plastic to hang around for a while before it’s used. Drink bottles and plastic bags may sit for years unused, so we’d want to be able to trigger things to degrade, which is tricky, which is another way to say, expensive.
So if plastics have a limited recycle life, what do we do?
Turns out, we can do something similar to what nature does with paper. We can pretty much run the polymerization process backwards, de-polymerization, and get the feedstock petroleum back. Then we can take that and run it through polymerization again to get virgin plastic once more. De-poly is not new, we’ve known how to do it since probably shortly after we figured out how to do polymerization. It’s just that it’s getting some fresh attention. It’s very important to note that de-polymerization doesn’t care much what kind of plastic it’s working with. You know the little recycling number on your yogurt cup? That number matters for simple recycling, but not so much to de-polymerization. We can even toss the various plastic foams (foam packing and insulation) in the mix.
Of course, de-polymerization takes heat, and pressure, and quite a bit of it. Not an outrageous amount, but a lot more than you need to simply melt plastic down and recycle it into something new. The required energy input strikes some people as a bad way to approach the problem, which I see as the perfect being the enemy of the good. We use massive amounts of energy to recycle metals, and de-polymerization happens at much lower temperatures. The trick is that unlike metal smelting, the de-poly process needs tight control, in that it has to all heat up at the same time, so you can’t just warm up a vat at the bottom. It’s not an insurmountable problem, just one that is tricky to scale (see, I used ‘tricky’ again, so you know what that means).
But it does fully break the polymer chains and reforms the base hydrocarbons.
Of course, those base hydrocarbons can also be reformed into fuels, which also irritates people who want the whole world to run on electrons harvested only from free-range, organic photo-voltaics and magnetic coils. For reasons…
Ideally, we’d all abandon single use plastics for compostables or paper, but that’s not going to happen. Plastics are here to stay, they are just too useful and convenient in a number of ways. And let’s all be honest, the current scheme of plastic recycling winds up with more plastic in landfills, or blowing on the wind, or in the water, than it does recycled into new stuff. Here we have a system that, if scaled up, can take all the plastic in your recycle bin, regardless of type, or common contamination, and fully recycle it. Less plastic in landfills, and, potentially, less petroleum extracted from the ground.
And I’m not being naive regarding the energy inputs or that the invisible hand of the market will make it all work in the way desired. It’s still too easy, relatively, to just pump more oil out of the ground. And still too easy to just toss plastic into a landfill. Such a system will probably require a subsidy or other regulatory approach to get it going. But we can’t keep pretending that we are recycling plastic, and unless there is a breakthrough in making plastics that can fully bio-degrade into harmless molecules on command, this is the best approach for recycling plastic.
- It’s called “Molded Pulp“, and we can also make packing material, plant pots, or even disposable bed pans – although those get incinerated, not recycled again
- Break it up and use it for land fill in place of gravel, or in concrete in place of gravel. There are other options as well, but ceramics are relatively safe to just dump, as even if the ceramic has something nasty in it, the ceramic composite will bind that something rather tightly. About the only danger is if you grind such things into a powder and breathe them in. Your lungs won’t thank you for that.
- Stuffing, insulation, whatever else you can do with chopped up cotton, linen, silk, and wool.
- Maybe if we develop nano-machines that can take things apart at the molecular level, we’ll be good, but for now…
- Now if you are composting those plastics in a bio-reactor and capturing those gases to feed a turbine…