A team of advanced materials chemistry researchers led by Dr. Geoffrey Ozin of U of T’s Department of Chemistry have made a significant breakthrough in using light to convert carbon and carbon dioxide to carbon monoxide.
In an article published in Energy and Environmental Science entitled Carbon photochemistry: towards a solar reverse Boudouard refinery†, Ozin’s team showcases an alternative to carbon-intensive methods of producing industrial carbon monoxide.
Carbon monoxide and carbon dioxide are both hazards to human health, with rising carbon dioxide concentrations in our atmosphere increasing the existential threat of climate change induced by global warming. Paradoxically, both gases are also vital elements of large-scale production of commodity chemicals and fuels.
In the chemical sector, for example, carbon monoxide serves as feedstock for the synthesis of acetic and methanol, pharmaceuticals, fragrance, and polymers. Carbon monoxide is used in the food industry for the packaging of fresh meat products such as fish and beef, and to acidify carbonized beverages. Its uses are wide-ranging, from refining or removing rust from metals to serving as a key component of infrared lasers.
Creating carbon monoxide for such applications has usually been done via thermally powered processes involving the gasification of coal, and partial oxidation of natural gas. These methods of production have big carbon footprints and significant toxic by-products, in a gigantic industry: the global CO2 market size in 2022 was USD $84.2 billion and is projected to grow to USD $141.9 billion by 2031.
In nature, the carbon cycle maintains a delicate equilibrium between CO2 in atmospheric, terrestrial, and oceanographic sources and sinks. Rather than burning fossil fuels to generate CO, the greener approach pioneered by Ozin’s team uses light for the production process, combining this process with the emerging practice of using CO2 as chemical feedstock.
The source of carbon to enable this conversion process can be natural, the paper shows. It may also come from fossil emission sources as well as air using specialized capture, storage and release technologies, or biochar made by slow burning of agricultural biomass.
The UofT team uses a light-powered reaction that employs this captured CO2, converting it to CO in ways that are less energetically and chemically intensive than the same reaction driven by heat.
“The CO generated photochemically by this means can justifiably called green,” Ozin said, going on to explain that the vision of the solar fuels group in the Chemistry Department at UofT is to gradually convert the chemical and petrochemical industries from an addiction on legacy fossil resources and fossil power to more eco-friendly processes, ones enabled by waste carbon dioxide and carbon, employing processes driven by light in solar refineries.
"By this means, it should prove feasible to decarbonize the generation of commodity chemicals and fuels, motivated by the desire to ameliorate greenhouse gas-induced climate change and global warming."
Previous attempts at eco-friendly carbon monoxide production utilized thermal steam-gasification of fossil fuels, biomass, and/or waste materials—super-heating the necessary feedstock with steam to produce the carbon monoxide. However, thermal steam gasification generates a large carbon footprint and can be hampered by issues like ash melting, and tar contamination. It requires injections of pure oxygen and produces combustion-related contaminants like dioxins and furans.
Ozin’s team is instead pioneering photochemistry methods that can be carried out at room temperature while generating fewer contaminants.
Green CO generation will continue to become more economically viable contingent on advancements in the efficiency of photoreactors, battery performance, solar concentration optics, and light emitting diodes. Improvements in these technologies will bring down the costs to make the minimum selling price of CO, until it is competitive with thermochemical and electrochemical technologies currently used as production methods.
Transitioning the production of carbon monoxide from processes that burn fossil fuel into production powered by renewable energy and using unwanted atmospheric CO2 and waste forms of carbon offers the prospect of creating green sector jobs while reducing the environmental footprint of producing this paradoxically toxic and yet crucial industrial chemical.
Note: The Ozin Group acknowledges and appreciates Hydrofuel Incorporated for sponsorship of this research.