In addition to the established carbon dioxide removal (CDR) technologies, there are many innovative approaches that are worth exploring. Here is a summary of 16 promising research directions and approaches that encompass a wide range of technological solutions related to CCS, CCU, and NCS. Some are included because of their novel ability to capture carbon, others because of their innovative incorporation of renewable energy or the utility of their end products.
Polymer membranes submerged in water
Due to their relatively low cost, facile fabrication, and straightforward scale-up, polymer membranes have been used as a practical alternative to traditional CCS gas separation processes in large-scale industrial applications for more than a decade (Bernardo, 2009). However, a new twist on this technology may significantly improve the efficiency of CCS. Researchers have found that submerging thermoplastic elastomeric membranes in water increases their ability to separate gas. According to research (Dai, 2019) submersion of sulfonated block polymer membranes in liquid water, followed by drying, provides a significant improvement in both CO2 permeability and CO2/N2 selectivity. This research suggests that submerging nanostructured membranes in water may constitute a promising candidate for more efficient gas separation technologies.
Low-temperature cerium oxide catalyst
A new approach using a cerium oxide catalyst at room temperature could offer a low-energy alternative to capture CO2. This negative emission technology does not require heat or high pressure and uses a liquid metal/electrolyte interface, which together with cerium nanoparticles turns CO2 into solid carbon (Esrafilzadeh et al, 2019).
Ultramicroporous carbon nanospheres
Chemical engineers at the University of Waterloo, have developed a low-cost CCS alternative using carbon nanospheres with abundant, uniform, and tunable ultramicroporosity. These nanospheres have excellent CO2 capture performances with extremely high capacities. The researchers have assembled facile guidelines that enable it to be engineered with abundant raw materials (sugar, molasses, rice husk, straws, or agar) and the carbon-saturated powder can be sequestered by burying it underground (Zang, 2019).
Researchers at Arizona State University’s Center for Negative Carbon Emissions are working on a cluster of artificial trees that use the wind to move air past chemical contactors instead of fans. This significantly reduces the energy required to remove carbon from the atmosphere. The trees’ “leaves” contain an ion exchange resin that has a high affinity for CO2 when dry. Once saturated with CO2, they are moved to an enclosed wet environment, where the gas is released and concentrated. A 12-column cluster of these devices is being built that will remove 1 ton of CO2 per day. Scaled versions of this technology could capture 3.8 million tons of CO2 annually for around $100 per ton. This approach reportedly has smaller water requirements and geographic footprint compared to land-based NETs. A forest of artificial trees would be capable of capturing as much CO2 as the Amazon rainforest, but it would be 500 times smaller (Wilcox, 2018).
Engineering researchers at the University of Toronto have developed a new electrochemical path for CCU. Their approach applies an electrolyzer (a device that uses electricity to drive a chemical reaction) that significantly reduces the cost of transforming carbon dioxide into products like plastics. This is a low-energy approach to capturing CO2 that forces air through an alkaline liquid solution. The CO2 is then dissolved in the liquid which forms carbonate. The researchers believe that their technology could significantly improve the economics of capturing and recycling carbon directly from the air (University of Toronto, 2019).
An application of electrogeochemistry at the University of California has a demonstrated ability to CO2 from the atmosphere. It works by breaking the chemical bonds in saline water to produce hydrogen and oxygen, which, in the presence of minerals, produces a highly reactive solution that can absorb CO2 from the atmosphere and turn it into bicarbonate (University of California, 2018).
Researchers at the University of Calgary’s Schulich School of Engineering have developed a method for turning CO2 (and methane) into solid carbon nanofibers using a metal catalyst. Compared to many other CCU applications carbon nanofibers are a useful high-demand byproduct. These nanofibers sell for about $100 per kilogram and they have multiple industrial uses that include making vehicles lighter and more efficient. These nanofibers could be used to replace the metal in cars and airplanes, wind turbines, battery manufacturing, and construction (Platt, 2019).
Researchers are developing enzymes (tiny proteins in cells that act as catalysts that convert one type of molecule into another) that can take carbon dioxide and convert it to other useful organic compounds. What makes this research noteworthy is the fact that enzyme systems are being created that can do this outside of living cells to simplify carbon fixation (Cho, 2018).
Marine-based renewable energy-powered platforms
A theoretical mobile application has been designed that extracts CO2 from seawater and uses renewable energy (photovoltaic solar cells) to turn it into synthetic fuel with no net CO2 emission. Carbon and hydrogen are catalytically reacted to yield liquid methanol fuel. This is scalable because it relies on existing technologies to recycle atmospheric CO2 into liquid fuel. The concept envisions the creation of marine-based artificial islands that can be implemented on a large scale. Because it is based at sea there is less concern about the space requirements of the impact on food production. Facilities would only be restricted by locations with wave heights below seven meters, places with a low probability for hurricanes, and where the water depth is less than 600 meters to ensure proper mooring. Such islands could be clustered together to form large-scale facilities. 70 of these artificial islands would make up a single facility that covers an area of around one kilometer squared (0.4 square miles). The researchers estimate that the output from 3.2 million floating islands would exceed the total global emissions from fossil fuels (Patterson et al. 2019).
The Soletair concept
A private company called Soletair is using carbon harvested from the air and renewable energy (photovoltaic or wind power) to make hydrogen. Using a catalytic synthesis these two elements are combined to make fuel or plastic. Using a multipurpose process that can be modified depending on the requirements, this approach can be adapted for a wide range of product applications (Soletair, n.d.).
CO2 as food
A California-based company by the name of Air Protein is using carbon to make nutritious foods, including meatless burgers and protein-enriched pasta. The technology involves taking carbon dioxide, oxygen, and nitrogen and combining it with water, renewable electricity, and a special class of microbes. The result is a flour that has the same nutritional profile of animal proteins and can be added to different recipes. The market for plant-based protein and meat alternatives could be as much as $85 billion by 2030. If successful, this sustainably produced food could use captured carbon to help feed the world while reducing emissions from land use and environmental impacts associated with traditional agriculture (Gallucci, 2019).
Mycelium soil sequestration
A company by the name of Hivemind has developed a biological carbon drawdown solution using a mycelium blend that sequesters CO2 in the soil. Their technology relies on photosynthesis instead of fossil fuels. It works as follows: CO2 is absorbed by plants, converted to carbon, and stored in a mycelium matrix in the soil. The company claims mycelium significantly increases the rate of capture of CO2 and storage of carbon in the soil. In the first pilot, 135 metric tons of CO2e were sequestered on a green roof, and over 200 tons in the meadow. They are working on the financing for a pilot project ordered by Shell Oil that would enable it to start to scale. The company’s CEO claims that HiveMind is the only biological carbon drawdown solution that is verified effective in the field at sequestering significant amounts of CO2. The developers claim that they can do this for $35 per ton of CO2. They are poised to scale and as of 2019, they claim to have some of the world’s top carbon emitters as clients. (CleanTecnica, 2019l Kelly, J. n.d.)
Vertical forests and living walls
Living walls and vertical forests may offer another approach to planting more carbon-sequestration vegetation that does not take up valuable space. Trees and plants that sequester CO2 are limited by suitable landmass and this leads to concerns that they can take away from land used for food production. In addition to sequestering carbon, this approach could also be used for food production. Vertical forests are already being deployed around the world in places like Italy, Switzerland, Indonesia, and China. A vertical forest in Nanjing is adorned with more than 1,100 trees and 2,500 cascading plants, absorbing 25 tons of CO2/year. There are also living walls in London and Paris and many other places around the world (Maude, 2017).
The Terraton Initiative
The goal of the Terraton Initiative is to use regenerative farming to remove and sequester 1 trillion metric tons of carbon from Earth’s atmosphere. Indigo Agriculture, an agricultural technology company based in Massachusetts, founded and runs the project. the Terraton Initiative will focus on improving farm profitability, environmental sustainability, and consumer health (Bezahler, 2019).
Trillion Trees initiative
Supported by the World Economic Forum, the Trillion Trees initiative is a collaboration between three of the world’s largest conservation organizations. The goal is to plant one trillion trees within a decade. The initiative is premised on a study that suggested that planting a trillion trees could capture more than a third of all the greenhouse gases humans have released since the industrial revolution (Bastin et al 2019).
Genetically modified phytoplankton
Genetically engineered phytoplankton (microalgae) may be able to turn CO2 into a storage-ready form of carbon (Singh & Dhar, 2019). This involves modifying the genes of phytoplankton in a way that makes them able to convert CO2 into a stable, sequestered form of carbon through photosynthesis. Those CO2-capturing organisms could then be spread throughout the oceans and the byproduct they make would sink to the ocean floor. Modifying the genes of phytoplankton would enable them to sequester carbon in areas of the global ocean that lack the nutrients needed for photosynthesis. This idea is based on a 2012 study in which researchers genetically engineered cyanobacteria to transform dissolved CO2 into HCO3. The HCO3 was taken up by the cyanobacteria and further fixed into biomass through photosynthesis (Chen, Liu, Chen, Cheng, Y.H. 2012).
While these approaches may offer promise, at present, most are hypothetical concepts that have not been tested outside of the lab. It is also important to point out that while these concepts warrant further investigation, most new technologies fail in the transition from the lab to the marketplace (Kintisch, 2014). However, this list suggests that in addition to the leading CDR technologies, there are a wide range of post-mitigation approaches that may contribute to efforts to draw down atmospheric carbon.
For references and more information go to CDR Resources. See also Glossary of Terminology Related to CDR.