Oceans as tools for capturing carbon
Oceans are a massive carbon sponge, absorbing a quarter of global CO2 emissions. That makes them a powerful tool to fight climate change. A company called Equatic is testing a bold idea to remove carbon dioxide from the atmosphere: pull it directly out of the ocean. The company is piloting this idea with a barge in Los Angeles that removes 100 kg of CO2 from seawater every day.
The direct ocean capture process
Captura’s process works like a large desalination plant. It continuously draws in seawater, separating 1% of it to turn into concentrated brine, which the company runs through a patented electrolysis machine. Electrolysis, a process used across various industries, including desalination, sends water through a series of electrified membranes. Each membrane separates different molecules in the water, forming acidic and alkaline solutions. The acid is added to the remaining ocean water, where it triggers a reaction with bicarbonate ions, causing CO2 to come out as bubbles. The company then adds the alkali to the water to neutralize it before releasing it.
The X-Prize and its influence on carbon capture
Companies like Equatic and Captura have emerged in part thanks to the X-Prize competitions, international contests that reward innovative solutions to global problems. These prizes are effective because they incentivize research and development in key areas, such as carbon capture, and attract the attention of investors and the general public. The X-Prize has been a driving force behind many technological advances and has helped accelerate progress in areas such as carbon capture, global health, and space exploration.
Advantages and disadvantages of direct ocean capture
Compared with air capture, direct ocean capture (DOC) is less explored territory. But Equatic, Captura, and others are trying to demonstrate the concept’s viability with support from the Chan Zuckerberg Initiative, the Gates Foundation, oil and gas companies, and the Advanced Research Projects Agency–Energy (ARPA-E). Pulling carbon from ocean water, where it is present at a concentration 150 times higher than in the atmosphere, is more efficient than air capture.
Alternative direct ocean capture technologies
Meanwhile, at MIT, chemical engineering professor T. Alan Hatton, mechanical engineering professor Kripa Varanasi, and their colleagues have devised a DOC technology that minimizes the use of membranes, making it even simpler and cheaper than electrolysis. The “reactive flow” system sends water through two electrochemical cells in tandem. In the first cell, a bismuth electrode releases protons that separate CO2 from the water’s carbonates and bicarbonates, while a silver chloride electrode releases chloride ions to balance the charge.
Environmental considerations
As companies and investors push ahead with DOC projects, environmental organizations are urging caution. It will be important for ocean carbon removal technologies to advance responsibly and “not endanger the health of ocean ecosystems or those who depend on them.” The climate crisis is so clear and severe that we need ocean-based carbon removal. But there are natural, proven ways to do it, such as conserving and restoring seagrass meadows or growing seaweed. Electrochemical DOC technologies simply have too many unknowns to spend limited research budgets on, given the limited time we have.
This blog post was inspired by Prachi Patel’s article “Using The Oceans To Help Capture Carbon,” published in IEEE Spectrum. https://spectrum.ieee.org/direct-ocean-carbon-capture
ChatGTP helped me with the writing and with a good part of the summary. Here’s the conversation behind its creation. GPT-4 + Webpilot plugin https://chat.openai.com/share/5931adec-3d6b-4c91-add2-bdb045696cb2