An Introduction to Carbon Capture

Estimated Reading Time: 7 minutes

TL;DR

Carbon capture systems extract carbon dioxide from the air. In our subscriber issue, we learned about some of the startups working on developing direct air capture technology. In today’s issue, we learn about the science underpinning carbon capture and discuss a few avenues for achieving more efficient carbon capture.

A Brief Overview of the Science of Carbon Capture

CO2 scrubbers are devices that capture carbon from either the atmosphere or from industrial emissions and put it to other uses. As the diagram below illustrates, captured carbon can be sequestered in the ground, used for enhanced oil recovery or used to manufacture useful byproducts.

A diagram representing steps that can be taken with captured carbon. The CO2 can be sequestered into geological formations, used for enhanced oil recovery, or converted into byproducts (source).

Carbon dioxide scrubbers can be implemented by a number of different technologies. As the diagram below illustrates, membrane gas separation uses the physical property that gases of different weight diffuse differently to separate constituents of air with different molecular weights.

An example of a membrane gas separation cartridge which separates air into oxygen and nitrogen. Membrane gas separators use synthetic membranes made of polymers or ceramics to separate gases based by weight; lighter gases diffuse more easily than heavier gases which can be used to separate gases (source).

Other techniques include using special materials which can absorb CO2 (source), using solvents such as sodium hydroxide which react with CO2 to produce byproducts, using metal organic frameworks) that adsorb CO2, and calcium looping. One challenge with carbon capture technologies is that other emission byproducts can be introduced into the atmosphere as a result. Considerable research will be required to achieve scalable, cheap, safe carbon capture.

These tradeoffs suggest that low-tech methods to capture carbon such as planting trees could play a useful role. Reforestation has the powerful advantage of being cheap and easy to implement but has natural limits on the amounts of carbon that can be removed from the atmosphere. In addition, as global warming continues, devastating events like the 2020 California Wildfires could potentially release large amounts of the carbon captured by trees back into the atmosphere along with further pollutants. Careful forest husbandry is required to manage forests without creating undue fire hazards.

A natural method of removing carbon dioxide is to plant trees. However, trees can only remove so much carbon dioxide from the atmosphere. In addition, wildfires can release captured carbon back into the atmosphere (source).

Trees have their limitations as carbon sequestration devices since they can only sequester so much carbon. Scientists have suggested that as DAC scrubbing technology improves, it may be feasible to construct a network of artificial trees which remove CO2 from the atmosphere in a distributed fashion. Today’s DAC scrubbers rely on complex chemistry which typically requires large industrial setups, but future DAC scrubbers could rely on bioengineered solutions which allow for distributed implementation of carbon capturing.

Direct air capture scrubbers require multiple reactions to remove carbon from air. Improving the efficiency of carbon capture is of high global interest but will require considerable R&D investment (source).

Sequestration Methods

Geological sequestration attempts to store carbon directly in geological formations. Captured CO2 from scrubbers would have to be transferred to safe locations for storage through a network of pipelines that transfer captured CO2 from extraction spots to storage spots as the diagram below shows. One major challenge with transport pipelines is that CO2 can suddenly leak from the pipeline. Large releases of carbon dioxide can lead to death by asphyxiation (source). In addition, geologically sequestered CO2 can leak from sequestration sites over time. Carbon storage in geological formations likely poses some of the same challenges as nuclear fuel storage, albeit with a considerably less dangerous byproduct. Greater research will be required to understand the long term geological effects of storage and the geological stability of formations.

An illustration of the carbon sequestration process. Specialized plants could capture carbon dioxide, which is compressed then transferred through pipelines to a geological injection size which stores CO2 within the earth (source).

Another potential method might be to use bioengineering to create microbial organisms that can fix the carbon (source). Microbial processing holds out the promise of producing useful byproducts without lower geological risk, but will require considerable additional research to become feasible.

Discussion

Carbon capturing technologies will require decades of continued research before they are feasible to deploy at scale. Improved simulation techniques could play a role in accelerating the design of improved scrubbers (source1, source2).

Highlights for the Week

• Interesting twist from Tesla. Could be promising for Ethereum, the 2nd largest cryptocurrency project.

Elon Musk @elonmusk

Tesla & Bitcoin

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Deep Into the Forest is a newsletter by Deep Forest Sciences, Inc. We’re a deep tech R&D company specializing in the use of AI for deep tech development. We do technical consulting and joint development partnerships with deep tech firms. Get in touch with us at partnerships@deepforestsci.com! We’re always welcome to new ideas!

Credits

Author: Bharath Ramsundar, Ph.D.
Editor: Sandya Subramanian