In an article recently published in the journal ACS Energy Letters, researchers discussed the opportunities and challenges of CO2 to carbohydrate conversion.
Study: Challenges and Opportunities in Converting CO2 to Carbohydrates. ACS Energy Letters, 7, 3509-3523 (2022). https://pubs.acs.org/doi/10.1021/acsenergylett.2c01550 Image Credit: nexusby/Shutterstock.com
Since the industrial revolution, anthropogenic greenhouse gas (GHG) emissions have gradually increased, mostly due to the over-extraction and overuse of fossil fuels. As a result, the Earth's surface temperature has risen.
Fossil fuels will continue to play a large role as an energy source for decades, and it is not realistic to achieve 100% renewable energy immediately. Therefore, the development of carbon utilization, capture, and storage technologies that could remove tens of gigatons (Gt) of CO2 per year from the atmosphere and either use it or store it permanently is necessary to limit global warming.
While carbon capture and storage (CCS) in geological formations or the oceans would probably be necessary to stop global warming, there are serious concerns about feasibility, as well as issues with rising ocean acidity, leakage potential, and expense. CCS may not be as effective as using the captured CO2 to generate income.
CO2 can be directly used for a wide range of purposes or utilized as a renewable feedstock to create useful products. The overwhelming size of the task, both in terms of physical capability and expense, is the fundamental obstacle to carbon capture and utilization (CCU). The only two CCU uses that potentially scale to the required gigaton levels each year is the manufacturing of liquid fuel and synthetic food.
About the Study
In this study, the authors explored the several difficulties encountered with artificial carbohydrate synthesis from CO2 at a gigaton per year scale and also suggested the potential for scientific innovation to achieve the corresponding economically feasible synthesis. This study focused on the synthetic manufacture of carbohydrates from CO2 as a complement to or a replacement for industrial agriculture in the production of starch and sugar at gigaton-scales per year.
The team demonstrated that the artificial carbohydrate synthesis from CO2 could lessen the severe environmental effects of industrial agriculture and could also ease food and water shortages in developing countries. In case of a global agricultural catastrophe like climate change, massive volcanic eruptions, or nuclear winter, it might also be employed as a life and food support system in isolated bunkers to lower existential risk.
The researchers discussed the difficulties and possibilities of CO2 conversion to ingestible carbohydrates. Firstly, the difficulties and possibilities associated with the conversion of CO2 to formaldehyde, which was a crucial intermediary in many pathways from CO2 to carbohydrates, were determined. The opportunities and problems associated with the turning of formaldehyde into carbohydrates were covered. The conversion of carbohydrates to proteins was also explored.
The production of 1 Gt of synthetic carbohydrates requires roughly 14,000 TWh of electricity each year. In 2020, solar PVs generated 800 TWh and 136 TWh of renewable electricity, while wind power produced 1500 TWh. In fertilizer, between 50 and 70% of the nitrogen was lost by runoff, leaching volatilization, and denitrification.
From CO2 to protein, all further steps in the reaction network were at a high technology readiness level (TRL) of 8 or 9. Glycerol was considered to be safe for intake by humans in amounts up to 70% of their daily calorie demands. With 4310 kcal/kg, it had a high gross energy density. Depending on the physiological conditions, it could either be converted to glucose by gluconeogenesis or oxidized via glycolysis and produce 4310 kcal/kg of energy, CO2, and water.
About 35% of the world's crop production is used for animal feed, which could be made from synthetic cellulose. During the electrochemical reduction of CO2 in methanol electrolyte, a boron-doped diamond (BDD) electrode produced a high yield of formaldehyde with high Faradaic efficiency of 74%. By operating at a high temperature of 98 °C and a low formaldehyde conversion of 18%, a high selectivity to glucose could be obtained without creating branched-chain sugars.
The production of 1 Gt of synthetic carbohydrates from CO2 utilized around 8% of the total amount of energy consumed in the world in 2019, which was estimated to be over 170,000 TWh35.
In conclusion, this study elucidated that compared to the current biogenic approach to food production, artificial synthesis of edible carbohydrates from CO2 is a promising way to mitigate climate change from GHG emissions, reduce water pollution from nitrogen fertilizers, increase the planet's capacity for food production, and decrease food and water scarcities in developing countries. However, thermodynamics and the high level of stereospecificity necessary in the finished carbohydrate product made the synthesis of artificial carbohydrates from CO2 a substantial problem.
The authors mentioned that there are numerous chances for scientific innovation to get beyond these obstacles and make it feasible to synthesize artificial carbohydrates. They emphasized that it would take international cooperation amongst chemists, chemical engineers, biologists, and food engineers, among other fields, to reach this final aim at the gigaton per year scale required.
O’Brien, C. P., Watson, M. J., Dowling, A. W., Challenges and Opportunities in Converting CO2 to Carbohydrates. ACS Energy Letters, 7, 3509-3523 (2022). https://pubs.acs.org/doi/10.1021/acsenergylett.2c01550