Caltech Scientists Make Producing Plastics From CO2 More Efficient

For decades there has been this tantalizing idea being pitched of pulling CO2 out of the air and using the carbon molecules for something more useful, like making plastics. Although this is a fairly simple process, it is also remarkably inefficient. Recently Caltech researchers have managed to boost the efficiency somewhat with a new two-stage process involving electrocatalysis and thermocatalysis that gets a CO2 utilization of 14%, albeit with pure CO2 as input.

The experimental setup with the gas diffusion electrode (GDE) and the copolymerization steps. (Credit: Caltech)
The experimental setup with the gas diffusion electrode (GDE) and the copolymerization steps. (Credit: Caltech)

The full paper as published inĀ Angewandte Chemie International is sadly paywalled with no preprint available, but we can look at the Supplemental Information for some details. We can see for example the actual gas diffusion cell (GDE) starting on page 107 in which the copper and silver electrodes react with CO2 in a potassium bicarbonate (KHCO3) aqueous electrolyte, which produces carbon monoxide (CO) and ethylene (C2H4). These then react under influence of a palladium catalyst in the second step to form polyketones, which is already the typical way that these thermoplastics are created on an industrial scale.

The novelty here appears to be that the ethylene and CO are generated in the GDEs, which require only the input of CO2 and the potassium bicarbonate, with the CO2 recirculated for about an hour to build up high enough concentrations of CO and C2H4. Even so, the researchers note a disappointing final quality of the produced polyketones.

Considering that a big commercial outfit like Novomer that attempted something similar just filed for Chapter 11 bankruptcy protection, it seems right to be skeptical about producing plastics on an industrial scale, before even considering using atmospheric CO2 for this at less than 450 ppm.

Two-Dimensional Polymer Is A New Ultra-Strong Material

Plastics, by and large, are well-understood materials. Not as strong as most metals, but often much lighter, these man-made polymers have found innumerable applications that have revolutionized the way we live. The properties of plastics have been improved in many ways over the years, with composite materials like fiberglass and carbon fiber proving to have strength and lightness far beyond the simple properties of basic polymers alone.

However, a group of engineers at MIT have been working on a revolutionary type of polymer that promises greater strength then ever before while remaining remarkably light weight. It’s all down to the material’s two-dimensional molecular structure, something once thought to be prohibitively difficult in the world of polymer science.

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Tech In Plain Sight: Primitive Engineering Materials

It isn’t an uncommon science fiction trope for our hero to be in a situation where there is no technology. Maybe she’s back in the past or on a faraway planet. The Professor from Gilligan’s Island comes to mind, too. I’d bet the average Hacakday reader could do pretty well in that kind of situation, but there’s one thing that’s often overlooked: materials. Sure, you can build a radio. But can you make wire? Or metal plates for a capacitor? Or a speaker? We tend to overlook how many abstractions we use when we build. Even turning trees into lumber isn’t a totally obvious process.

People are by their very nature always looking for ways to use the things around them. Even 300,000 years ago, people would find rocks and use them as tools. It wasn’t long before they found that some rocks could shape other rocks to form useful shapes like axes. But the age of engineered materials is much younger. Whether clay, metal, glass, or more obviously plastics, these materials are significantly more useful than rocks tied to sticks, but making them in the first place is an engineering story all on its own.

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Plastics: PETG

You’d be hard-pressed to walk down nearly any aisle of a modern food store without coming across something made of plastic. From jars of peanut butter to bottles of soda, along with the trays that hold cookies firmly in place to prevent breakage or let a meal go directly from freezer to microwave, food is often in very close contact with a plastic that is specifically engineered for the job: polyethylene terephthalate, or PET.

For makers of non-food objects, PET and more importantly its derivative, PETG, also happen to have excellent properties that make them the superior choice for 3D-printing filament for some applications. Here’s a look at the chemistry of polyester resins, and how just one slight change can turn a synthetic fiber into a rather useful 3D-printing filament.

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