How to Convert 100% Of CO2 Into Ethylene

A team of researchers led by Meenesh Singh at University of Illinois Chicago (UIC) has discovered a way to convert 100% of carbon dioxide captured from industrial exhaust into ethylene, a key building block for plastic products.  While researchers have been exploring the possibility of converting carbon dioxide to ethylene for more than a decade, the UIC team’s approach is the first to achieve nearly 100% utilization of carbon dioxide to produce hydrocarbons. Their system uses electrolysis to transform captured carbon dioxide gas into high purity ethylene, with other carbon-based fuels and oxygen as byproducts.  

The process can convert up to 6 metric tons of carbon dioxide into 1 metric ton of ethylene, recycling almost all carbon dioxide captured. Because the system runs on electricity, the use of renewable energy can make the process carbon negative.  According to Singh, his team’s approach surpasses the net-zero carbon goal of other carbon capture and conversion technologies by actually reducing the total carbon dioxide output from industry.

It’s a net negative,” he said. “For every 1 ton of ethylene produced, you’re taking 6 tons of CO2 from point sources that otherwise would be released to the atmosphere.” 

Previous attempts at converting carbon dioxide into ethylene have relied on reactors that produce ethylene within the source carbon dioxide emission stream. In these cases, as little as 10% of COemissions typically converts to ethylene. The ethylene must later be separated from the carbon dioxide in an energy-intensive process often involving fossil fuels.   In UIC’s approach, an electric current is passed through a cell, half of which is filled with captured carbon dioxide, the other half with a water-based solution. An electrified catalyst draws charged hydrogen atoms from the water molecules into the other half of the unit separated by a membrane, where they combine with charged carbon atoms from the carbon dioxide molecules to form ethylene. 

Among manufactured chemicals worldwide, ethylene ranks third for carbon emissions after ammonia and cement. Ethylene is used not only to create plastic products for the packaging, agricultural and automotive industries, but also to produce chemicals used in antifreeze, medical sterilizers and vinyl siding for houses. Ethylene is usually made in a process called steam cracking that requires enormous amounts of heat. Cracking generates about 1.5 metric tons of carbon emissions per ton of ethylene created. On average, manufacturers produce around 160 million tons of ethylene each year, which results in more than 260 million tons of carbon dioxide emissions worldwide

In addition to ethylene, the UIC scientists were able to produce other carbon-rich products useful to industry with their electrolysis approach. They also achieved a very high solar energy conversion efficiency, converting 10% of energy from the solar panels directly to carbon product output. This is well above the state-of-the-art standard of 2%. For all the ethylene they produced, the solar energy conversion efficiency was around 4%, approximately the same rate as photosynthesis.
Their findings are published in Cell Reports Physical Science.


Robots Sort Recycling, Detect If An Object Is Paper, Metal Or Plastic.

Every year trash companies sift through an estimated 68 million tons of recycling, which is the weight equivalent of more than 30 million cars. A key step in the process happens on fast-moving conveyor belts, where workers have to sort items into categories like paper, plastic and glass. Such jobs are dull, dirty, and often unsafe, especially in facilities where workers also have to remove normal trash from the mix. With that in mind, a team led by researchers at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) has developed a robotic system that can detect if an object is paper, metal, or plastic.

The team’s “RoCycle” system includes a soft Teflon hand that uses tactile sensors on its fingertips to detect an object’s size and stiffness. Compatible with any robotic arm, RoCycle was found to be 85 percent accurate at detecting materials when stationary, and 63 percent accurate on an actual simulated conveyer belt. (Its most common error was identifying paper-covered metal tins as paper, which the team says would be improved by adding more sensors along the contact surface.)


Our robot’s sensorized skin provides haptic feedback that allows it to differentiate between a wide range of objects, from the rigid to the squishy,” says MIT Professor Daniela Rus, senior author on a related paper that will be presented in April at the IEEE International Conference on Soft Robotics (RoboSoft) in Seoul, South Korea. “Computer vision alone will not be able to solve the problem of giving machines human-like perception, so being able to use tactile input is of vital importance.”

A collaboration with Yale University, RoCycle directly demonstrates the limits of sight-based sorting: It can reliably distinguish between two visually similar Starbucks cups, one made of paper and one made of plastic, that would give vision systems trouble.



Invisible Plastic For Super Efficient Solar Panels

Antireflection (AR) coatings on plastics have a multitude of practical applications, including glare reduction on eyeglasses, computer monitors and the display on your smart-phone when outdoors. Now, researchers at Penn State have developed an AR coating that improves on existing coatings to the extent that it can make transparent plastics, such as Plexiglas, virtually invisible.

Plastic dome coated with a new antireflection coating (right), and uncoated dome (left)

This discovery came about as we were trying to make higher-efficiency solar panels,” said Chris Giebink, associate professor of electrical engineering, Penn State. “Our approach involved concentrating light onto small, high-efficiency solar cells using plastic lenses, and we needed to minimize their reflection loss.”

They needed an antireflection coating that worked well over the entire solar spectrum and at multiple angles as the sun crossed the sky. They also needed a coating that could stand up to weather over long periods of time outdoors. “We would have liked to find an off-the-shelf solution, but there wasn’t one that met our performance requirements,” he said. “So, we started looking for our own solution.”

That was a tall order. Although it is comparatively easy to make a coating that will eliminate reflection at a particular wavelength or in a particular direction, one that could fit all their criteria did not exist. For instance, eyeglass AR coatings are targeted to the narrow visible portion of the spectrum. But the solar spectrum is about five times as broad as the visible spectrum, so such a coating would not perform well for a concentrating solar cell system.

Reflections occur when light travels from one medium, such as air, into a second medium, in this case plastic. If the difference in their refractive index, which specifies how fast light travels in a particular material, is large — air has a refractive index of 1 and plastic 1.5 — then there will be a lot of reflection. The lowest index for a natural coating material such as magnesium fluoride or Teflon is about 1.3. The refractive index can be graded — slowly varied — between 1.3 and 1.5 by blending different materials, but the gap between 1.3 and 1 remains.

In a paper recently posted online ahead of print in the journal Nano Letters, Giebink and coauthors describe a new process to bridge the gap between Teflon and air. They used a sacrificial molecule to create nanoscale pores in evaporated Teflon, thereby creating a graded index Teflon-air film that fools light into seeing a smooth transition from 1 to 1.5, eliminating essentially all reflections.

The interesting thing about Teflon, which is a polymer, is when you heat it up in a crucible, the large polymer chains cleave into smaller fragments that are small enough to volatize and send up a vapor flux. When these land on a substrate they can repolymerize and form Teflon,” Giebink explained.


We’ve been interacting with a number of companies that are looking for improved antireflection coatings for plastic, and some of the applications have been surprising,” he said. “They range from eliminating glare from the plastic domes that protect security cameras to eliminating stray reflections inside virtual/augmented -reality headsets.”