Energy Generation from Thin Air : Is it Even Possible ?

Introduction

As we all know the need for energy is been increasing day by day in our world. As new appliances are bought by us in our homes, our daily energy expense has been increasing resulting in increasing need of energy generation which is directly connected to the increasing burning of fossil fuels ,resulting in growing pollution. This urgent need for an energy transition away from fossil fuels has led to the exploration of innovative technologies. Electrochemical CO₂ reduction is one of the promising approaches that could evolve the energy landscape by producing chemicals and fuels from CO₂, water, and renewable electricity.

Few Researchers from University of Cambridge have made a solar-driven reactor designed to convert captured CO₂ also known as Thin Air and plastic waste into eco-friendly fuels. During experimentation, carbon dioxide was converted into syngas, a pivotal precursor for sustainable liquid fuels. Simultaneously, plastic bottles underwent conversion into glycolic acid, a commonly utilized component in the cosmetics industry. Wait, let me explain the whole process.

The Way to Make Fuel from CO₂

Credits to Reference No. 3

So, this process also called as (MeOH) synthesis involves a two-step procedure where the energy and molecules collected from a fossil fuel or plastic, specifically methane (CH4), are transformed into MeOH (Methanol). In the first step, steam-methane reforming is employed to convert CH₄ into a mixture of H₂, CO, and a small percentage of CO₂. This synthesis gas undergoes a subsequent conversion to MeOH in the second step, operating at elevated temperatures (approximately 250°C) and pressures (50–100 bar). While the direct electrochemical creation of MeOH from CO₂ with high selectivities or current densities remains challenging, CO₂ and water electrolysers offer the potential to replace the steam-methane reforming step by producing CO and H₂ from CO₂ and H₂O. Essentially, the energy, carbon, and hydrogen content of CH₄ are substituted with solar energy, CO₂, and H₂O.

In the context of a purely solar-driven MeOH synthesis process, it is independent from the industrial inputs like CO₂ from cement or steel plants, the CO₂ and H₂O molecules must originate from feedstocks initially in equilibrium with the environment. A feasible feedstock in this scenario is water sourced from the environment and CO₂ from air at 400 ppm. To enable the operation of the CO₂ electrolyser, the initially dilute atmospheric CO₂ needs concentration. For the direct air capture (DAC) of CO₂, potassium hydroxide (KOH) is employed as a capture solvent, converting ambient CO₂ into carbonate upon contact. Subsequently, KOH and CO₂ are recovered through electrically driven bipolar membrane electrodialysis (BPMED). The recovered KOH is recirculated to the capture unit, while CO₂ remains in an aqueous electrolyte, pressurized to 50 bar in a KHCO₂ electrolyte before being fed to the CO₂ electrolyser. By using stoichiometric reaction and from various information collected ,the following equation is made :

Credits to Reference No.3

For more information refer, reference no. 3. While the reaction scheme and specific technologies outlined here serve to create a realistic air-to-barrel scenario, various alternate processes are possible. It may take time before a final, preferred combination of technologies is established. Nonetheless, this exercise enables an analysis of energy requirements and physical scales for each sub-process in a 10,000 ton/day plant.

Future of This Method

The motivation behind conducting the above-mentioned analysis is the exploration of how an air-to-barrel approach to CO₂ conversion can offer an initial evaluation of practical operating conditions and constraints for each step in the process. This holds particular significance for CO₂ electrolysers, which have yet to be thoroughly examined within an integrated system, despite their anticipated role in the energy transition. While the discussed case focuses on a specific set of technologies, it underscores the necessity for CO2 capture technology to seamlessly integrate with the CO2 conversion process. Additionally, if the CO2 conversion process does not yield a final product, it must integrate effectively with downstream processing.

A more comprehensive analysis in the future will reveal more further opportunities and upcoming expected limitations for solar fuel production utilizing CO₂ electrolysers as a conversion technology. This, in turn, will facilitate meaningful comparisons with alternative technologies such as reverse water-gas shift, direct CO₂ to MeOH heterogeneous catalysis, and solid-oxide CO₂ electrolysis.

In our specific scenario, the constraints of MeOH synthesis and the requirements for BPMED dictate that CO₂ electrolysis must be conducted at higher pressures than commonly reported in literature. Interestingly, the removal of CO₂ as a gas from the recovered capture solvent through depressurization or regeneration demands additional energy compared to utilizing the saturated solution directly. Also, this case study establishes new boundary conditions essential for industrial CO2 electroreduction, merging both fundamental and practical research within realistic conditions.

Conclusion

As technology advances, opportunities will emerge to optimize system efficiencies by substituting and refining different components. Nevertheless, the essential inlet and outlet conditions are relatively fixed. For instance, the prospect of CO₂ electroreduction in a gas-diffusion system instead of a pressurized aqueous system presents a notable possibility. Although removing gaseous CO₂ from BPMED incurs a specific energy cost, potentially justifying the use of amine-based DAC over alkaline capture, the gains in efficiency during the CO₂ reduction reaction may outweigh any additional energy requirements in the capture stage. However, unless the gas-diffusion system is pressurized, significant energy would be needed to compress CO and H₂ for the synthesis step, good offsetting gains in overall efficiency. Additionally, replacing the BPMED step with a thermally driven release of CO₂ from a capture solvent, utilizing waste heat, could enable the use of gas-diffusion layer configurations for CO₂ reduction while reducing the renewable electrical energy requirements of the overall unit.

This detailed air-to-barrel case example is anticipated to assist the CO₂ electroreduction community in evaluating relevant operating conditions crucial for scaling the technology practically. By considering these operating conditions and constraints, a new framework is provided to comprehend fundamental reaction phenomena and optimize catalyst, electrolyte, and reactor systems, serving as motivation to expedite the technology towards its ultimate goal. Envisaging the future energy and size requirements of CO2 electrolysers within a solar fuels process and comparing it to the current state of research allows for an assessment of when and how electrochemical CO2 reduction will contribute significantly to the imminent energy transition.

Reference : Finally, here I am giving credits to the websites and research paper which I got this information from especially the paper by Joule (reference no. 3). If you need any further information, please refer to the below articles and research papers :

1. https://bettersociety.net/fuel-from-air-cambridge.php
2. https://www.science.org/doi/full/10.1126/science.365.6457.964
3. Smith, W. A., Burdyny, T., Vermaas, D. A., & Geerlings, H. (2019). Pathways to industrial-scale fuel out of thin air from CO2 electrolysis. Joule, 3(8), 1822-1834.

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