Carbon Capture Project

At my school, I am currently heading a club called LaunchX where we create science-based projects to positively impact our community. Most recently we created a small-scale carbon capture unit which relies on the process of mineralization.

Introduction

Mineralization is a natural process in which lime (calcium hydroxide - solid) in rock formations reacts with CO2 (gaseous) in the atmosphere to form calcium carbonate. 

Ca(OH)2  + CO2  →  CaCO3

This process takes millions and millions of years because reacting a gas with a solid is difficult due to an energy barrier between the two states. Our carbon capture machine uses the same methods, however humidity is increased to allow for intermediate steps to make the reaction faster. This is further explained in the Description and Explanation Section.

Setup Diagram

Description and Explanation

A raised platform was built inside a medium sized container. A filter paper with 5 grams of calcium hydroxide was placed on top of the platform. Water was filled inside the container up until the rim of the platform. To create humidity in the machine, an air pump pushes air from the atmosphere through a tube to an air stone which lies inside the container. This air stone is submerged in water so that when the air pump is connected to an outlet, the airstone releases bubbles in the water. Since atoms are always moving with energy,  water molecules on the surface of the bubbles are able to gain enough energy to transform from a liquid to water vapor inside the bubble. When these bubbles float to the surface of the water because of differences in density, the bubbles burst and water vapor is released into the air inside the carbon capture machine. The water vapor creates a thin water film on top of the calcium hydroxide. CO2 in the surrounding air can react to this water creating carbonic acid. Aqueous carbon acid can then more readily react with Ca(OH)2 to create CaCO3 where CO2 is successfully trapped. 

CO2 + H2O → H2CO3

Ca(OH)2 + H2CO3 → CaCO3 + 2H2O

Experimentation

A carbon dioxide and humidity sensor were placed inside the carbon capture unit to measure if humidity was sufficient enough and if carbon dioxide levels decreased in the unit. The air pump was turned on for 2 minutes reaching 1186 ppm of carbon dioxide. After this, carbon dioxide levels decreased, signaling that the chemical reaction was successfully taking place. We established that a chemical reaction with 5 grams of calcium hydroxide bears about 3 grams of calcium carbonate.

Conclusion

Although this carbon capture method works, it is not yet carbon neutral or carbon

negative. This is because manufacturing calcium hydroxide releases more carbon dioxide than the chemical reaction can remove from the atmosphere. However, if the calcium hydroxide is sourced from waste cement, this process can effectively decrease our carbon footprint. 

Pictures