Hydrated Limes in Carbon Capture?
Tanay N -
Your eyes do not deceive you. Don’t worry, I had the same reaction when I read about Hydrated Lime in carbon capture about a week and a half ago.
This past week was all about building my At-Home Direct Air Capture Unit (AHDAC). As I explained in my previous posts, CO2 needs to bind to a sorbent. I’m building AHDAC to promote environmental stewardship and show the general public that they too can take action to protect our planet. However, since the daily consumer does not have access to proper laboratory equipment, my options for sorbents are severely limited.
Well, after some research, I settled on Calcium hydroxide as the sorbent. The overall mechanism I’m harnessing is Ca(OH)2 + CO2 ↔ Ca(CO3) + H2O
Lime Research
How do limes fit into this picture? Turns out, we are not talking about the citrus fruit, but limestone! Limestone contains Ca(CO3) (Calcium carbonate), which thermally decomposes into CaO (Calcium oxide), also known as “quicklime.” When CaO reacts with water, it forms Calcium hydroxide or Ca(OH)2; in other words, water “hydrates” the lime.
As a result, 2 days ago, I embarked on a quest to Home Depot to find Hydrated Lime. Apparently, the closest they had was “Garden Lime.” This was not ideal, as Ca(CO3) made up 37% of the mass in the bag, which meant that if I used garden lime, my reactant (Calcium hydroxide) was not actually pure, and the product (Calcium carbonate) would exist before the reaction even happened. You can see how detrimental this could be for the experiment.
Fortunately, Ms. Holtzman lent me some pure Ca(OH)2 from her lab at school and also granted me permission to store the AHDAC in her lab. This was perfect, as I need to precisely weigh out the product of the reaction in the coming weeks. Transporting the unit to school and back could create mechanical disruption, heavily altering the experimental yields, so having it stay at school is great.
AHDAC Setup
Moreover, I had to buy an air pump and tubing from the aquarium section of Walmart. Seeing the materials I brought home, my mom firmly believed I had bought a fish. Much to her dismay, I had not; instead, I would be conducting carbon dioxide removal! (She was happy with this too).
The image below is the basic setup for the AHDAC. The small black module is the air pump, and the blue rectangular prism is the air stone. The larger container is used for easier transport.
Furthermore, water must be present within the closed reaction chamber to create a humid environment within the AHDAC (I’ll go more into why all these materials are needed in the next blog post).
While shopping for these materials, I also picked up some bagels and cream cheese. The cream cheese container can be stacked so that the Calcium hydroxide powder can safely sit dry, above the water line. You can see the “Cream Cheese setup” below.
I plan on adding more components to improve airflow and reaction potential in the following weeks, and I will attach more photos once completed. In my next blog post, I’ll go more into the specific intermediate chemical reactions happening behind the scenes to convert Calcium hydroxide into Calcium carbonate, how we can sustainably use Calcium Carbonate (the product of the reaction) in other applications, and why this specific setup is the most efficient.
In the meantime, I’ll work on eating the cream cheese so that I can actually use the containers, and I’ll read more into different tests I can conduct with my AHDAC. In the coming weeks, I’m ecstatic to learn more about the specific reaction mechanisms involved in DAC and work under Ms. Holtzman’s amazing guidance to securely conduct my experiments.
I know this was a lot of information, so feel free to ask any questions you have. I would also love to hear if you had any names for my AHDAC in the comments!
Thank you and I’ll see you next week!
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