How to Sequester Carbon by Turning It into Plastic
Is the Process Achievable at Scale?
Plastics, a ubiquitous, man-made element in the modern world, have been enormously beneficial to human society. Plastics are currently used for just about everything: food packaging, bicycle helmets, airbags in vehicles, cell phones, computers, roofing, insulation, and in sterile packaging in health care.
But plastics have also been identified as a driver of climate change because plastics production leads to greenhouse gas emissions.
The question emerges: Can plastics be produced in ways that do not worsen climate change?
Some people are likely to see plastics as a single substance without being aware of the different types of plastics. To achieve a common understanding of plastics, it is important to understand the distinctions.
Plastics (or polymers) is an umbrella term that includes hundreds of different types. Most people use just a handful of them, such as polyethylene terephthalate (PET), often used in food packaging and polyester fabric; high- and low-density polyethylene; polyvinyl chloride (PVC); polypropylene; and polystyrene (also known as Styrofoam).
It is important to note that PVC and polystyrene have already been found to have serious adverse side effects in that they can leach toxins into the environment throughout their entire lifecycle.
Another undesirable feature of plastic is that plastics are produced from fossil fuels. Plastic production is thus a major driver of man-made (anthropogenic) climate change.
One possible solution to reducing dependence on fossil fuels is to produce plastics directly from carbon dioxide (CO2), thereby helping to reduce the presence of CO2 in the atmosphere and counter climate change.
Conventional Plastic Production
Plastics are largely made from fossil fuels, such as oil and natural gas, or from plants (for bioplastics). These raw materials are refined into ethane or propane, which are then subjected to high levels of heat in a process called "cracking." Cracking converts them into monomers such as ethylene and propylene. These monomers are then combined with a catalyst to create a polymer "fluff" that looks like a powder. This powdered polymer is fed into an extruder where it is melted and run through a pipe where it forms a long tube as it cools. The tube is then cut into bits to form pellets, and the pellets are sent off to factories where they are made into products.
Bioplastics Are Not a Solution to Climate Change
Bioplastics may seem to be a viable alternative to the use of fossil fuels for producing plastic. There has been a lot of discussion about this in recent years, focusing on the use of bioplastics, such as polylactide (PLA) to produce things such as disposable cutlery made from potatoes or plastic bottles made from corn.
Bioplastics production, being an energy intensive process requiring the use of fertilizers, is not a viable alternative to conventional plastic production due to environmental impacts.
However, bioplastics are not actually a viable solution. For a start, they do not biodegrade easily and usually need to be fed into industrial composters in order to be processed or recycled. The production of bioplastics is also fairly energy intensive, and some bioplastics actually have a higher carbon footprint than ordinary plastics for this reason. Researchers at the University of Sheffield found that, with fertilizer costs, transport, and harvesting, bioplastics were the worst option, with their adverse impacts even exceeding those made from fossil fuels. Furthermore, the water and fertilizers used in producing bioplastics can contribute to the eutrophication and pollution of rivers and estuaries.
Utilizing CO2 for Plastic Production
In order to convert carbon dioxide (CO2) into plastics, two things are required—a large store of captured CO2 and a number of cleverly designed catalysts. A catalyst is a substance or chemical that causes a chemical reaction without itself being affected in any way. Many metals can be used as catalysts, but copper is particularly useful when trying to convert CO2 into plastic.
According to Prof. Peter Styring, Director of the UK Centre for Carbon Dioxide Utilization (CDUUK), most of the carbon currently available for potential plastic production comes from hydrogen production, but researchers are investigating the capture of industrial emissions as well. CDUUK has discovered how to make polyacrylamide (nylon) from CO2.
A number of research projects are currently underway at different locations around the world to develop the processes needed to convert CO2 into plastics. Given that around half the plastic in the world is currently made from ethylene, several of these projects are investigating how to make ethylene from CO2, which can then be turned into plastic.
At Rutgers University in New Jersey (US), scientists are using special electrocatalysts containing nickel and phosphorus in a process involving the combination of CO2 with water and electricity. This then produces complex carbon-containing molecules that can subsequently be used to produce plastics and other products, described by the research team as a form of "artificial photosynthesis."
Other research projects investigating the combination of CO2 with water and electricity, with copper as a catalyst, are underway at Swansea University’s Energy Safety Research Institute in Wales, and at the Ted Sargent Group at the University of Toronto.
The German company Covestro has designed a catalyst that could potentially allow CO2 to react with epoxides (a form of cyclic ether—an organic compound formed of ring-shaped molecules containing oxygen) to produce a family of chemicals called "polyether polycarbonate polyols." These substances can be used to make polyurethane, and Covestro plants in Germany are now producing mattresses using 20% captured carbon dioxide.
Research in plastic production from CO2, including the use of electrocatalysis, heterogeneous catalysis, and microbial fermentation, is underway.
In the UK, Econic is producing polyurethane from carbon dioxide and expects to be able to produce foam products, coatings, sealants, and elastomers ready for commercialization within two years.
The Centre for Sustainable Chemical Technologies at the University of Bath is hoping to produce polycarbonate by combining carbon dioxide with sugars, such as xylose.
In Germany, the research institute Fraunhofer has produced formic acid and methanol from carbon dioxide, subsequently converting them into the building blocks for the production of polymers and similar materials using fermentation through microorganisms, in particular methylotrophic bacteria and yeasts.
Two processes were employed. Heterogeneous chemical catalysis was used to convert CO2 to methanol, while electrochemistry was also used to produce formic acid from CO2. The methanol and formic acid can be used to build blocks for polymers and can also be used to "feed" other microorganisms to produce other products. In this project, the researchers introduced genes into the microbes to provide a blueprint for enzymes, a process known as metabolic engineering. The enzymes can subsequently be used as a catalyst.
In the US, the Department of Energy (DOE) Office of Fossil Energy and Carbon Management has also been involved in research in the production of plastic from CO2. In 2013, the agency announced it had funded the world’s first successful large-scale production of a polypropylene carbonate (PPC) polymer using waste CO2.
The project was actually carried out by Novomer Inc., in collaboration with Albemarle Corporation, using its manufacturing plant in Orangeburg, South Carolina. It tested the scale-up of Novomer’s catalyst technology and found that only minor modifications needed to be made to the company’s existing facilities to produce seven tons of polymer containing more than 40% CO2.
The Office of Fossil Energy is involved in other approaches to convert captured CO2 into products through its Carbon Capture and Storage program, managed by the National Energy Technology Laboratory. Novomer appears to be continuing this project, and
other companies are getting involved in this area of research as well, according to the website Packaging Europe.
Projected Impact of Plastic Production from CO2
The processes used by the research team at Fraunhofer can be implemented over a medium to long term, say ten years or so, although industry is under pressure to find other processes that can be implemented sooner. However, IDTechEx sees limited potential for this approach to reducing carbon emissions, even though it expects this sector to expand. The key requirement is the expansion of carbon capture infrastructure to feed such carbon utilization strategies with CO2.
These processes might not be as effective as the industry and some research organizations claim, however. Some environmental organizations warn that carbon capture and storage (CCS) remains unproven as a viable solution, and the projects in operation are ineffective and expensive. Should this turn out to be true, researchers will have to continue to seek new ways to cut emissions.
*Robin Whitlock is an England-based freelance journalist specializing in environmental issues, climate change, and renewable energy, with a variety of other professional interests including green transportation.