Carbon Capture & Storage with Magnesium-Promoted Rapidly Nucleated Hydrates

Carbon Capture & Storage with Magnesium-Promoted Rapidly Nucleated Hydrates
M. Bandara, A. Mardon

1 Undergraduate Engineering Student, McMaster University Hamilton, Canada bandarm@mcmaster.ca
2 Faculty of Graduate Studies & Research University of Alberta Edmonton, Canada mardon@ualberta.ca 

Abstract—Researchers at the University of Texas at Austin have discovered a method to catalyze the nucleation of carbon dioxide hydrates at 3000 times the rate they typically occur. This discovery opens a door to the possibility of storing carbon dioxide in a solid form under the ocean floor. Removing carbon from the atmosphere can reverse the effects of global warming and benefit society, the economy, and the environment. 

Index Terms—Carbon capture, CCS, chemistry, climate change, CO2 hydrates, global warming, magnesium, magnesium oxide, nucleation

I. GREENHOUSE GASES & GLOBAL WARMING
GREENHOUSE gases are climate forcers that trap heat in the atmosphere. These gases cause global warming through the greenhouse effect [1].  

 Carbon dioxide (CO2) is largely produced by the burning of fossil fuels like coal, natural gas and oil. Other sources include burning solid waste, burning organic material and chemical reactions used in manufacturing (e.g. cement production). 

 Fig. 1. 2019 U.S. CO2 Emissions by Source [2]

 36.44 billion metric tons of carbon dioxide were emitted globally in 2019 [3]. The gas is naturally sequestered by the biological carbon cycle [2]. Carbon dioxide makes up 80% of greenhouse gas emissions in the United States [2]. 

 
Fig. 2. U.S. Greenhouse Gas Emissions 2019 [3]

 Atmosphere levels of carbon dioxide have risen from under 320 ppm to around 420 ppm since 1960 [4].
 

Fig. 3. Atmospheric CO2 (1960-2021) [4]

 The effects of global warming can be acute but are devastating in the long term. Global warming increases droughts, heatwaves, hurricanes, and severe weather. Sea levels inevitably rise, air pollution increases, and wildlife extinction accelerates [5][6]. The Annual Greenhouse Gas Index (AGGI) measures the atmosphere’s capacity to trap heat based on the presence of greenhouse gases. The AGGI has continuously increased for decades [7].

Fig. 4. Annual Greenhouse Gas Index [7]

II. EXISTING SOLUTIONS
Carbon dioxide is naturally removed from the atmosphere by forests and oceans. Tress sequester CO2 through the process of photosynthesis. Oceans act as a carbon sink when microscopic marine algae like phytoplankton absorb CO2. 

Carbon dioxide can also be manually removed from the atmosphere with chemicals. Bioenergy with Carbon Capture and Storage (BECCS) is a process where emissions are captured before they reach the atmosphere and are stored underground. Chemical scrubbing captures carbon dioxide directly from the atmosphere through chemical processes but it is costly and energy intensive. Carbon mineralization converts the gas into a solid form. Carbon mineralization is an extremely slow process [8]. These techniques are imperfect and have major downsides associated with them.   
III. CARBON DIOXIDE HYDRATES
Hydrates are produced when carbon dioxide and water are mixed at high pressures to a form a snow-like crystalline substance. The reaction process typically takes hours or days to initiate. Researchers at the University of Texas at Austin finds that adding magnesium to the reaction accelerators the process by a factor of 3000. This is the fastest hydrate formation pace ever documented at under 1 minute [9].

 
Fig. 5. Formation of Hydrates on an Mg plate [9]

The potential of hydrates is promising in the fight against global warming. Large scale underwater reactors can allow billions of tons of greenhouse gas to be stored under the ocean floor. This means that billions of tons of carbon dioxide can be removed from the atmosphere and safely stored [10]. Removing carbon from the atmosphere brings the world one step closer to net negative emissions. 

IV. SOCIAL, ECONOMIC, ENVIRONMENTAL & ETHICAL IMPACTS
   The social impact of this technology will be a positive outlook on climate change efforts. In the long term, reducing global warming will minimize health issues, food insecurity, water security, and the loss of housing. This will avoid future conflicts over resources [11]. 
   Building infrastructure boosts the economy and creates jobs, however implementing this technology is costly at a large scale. In the long-term removing greenhouse gases can lower the cost of food, energy, insurance (climate caused damage), and minimize inflation [12]. 

The environmental impact of net negative carbon emissions is vast. Rain and temperature patterns will become more predictable, sever weather events will decrease, the sea levels will steady, the air will be cleaner, and wildlife extinction will slow down [5][6]. In contrast the environmental impacts of underwater carbon dioxide reactors are minimal. Leaks of carbon dioxide, water, or the hydrate they form will have no environmental impacts as they are already naturally occurring in those environments. Magnesium also has minimal environmental impacts if leaked underwater [9]. While magnesium is destructive to the environment, very little magnesium is consumed by the reaction as the hydrates form on its surface [13]. 

It may be viewed as unfair if a handful of nations fund projects like this because they benefit the whole world. Dividing the costs throughout developed nations through international treaties will create an incentive for governments to use tax dollars to build expensive infrastructure. Developing nations are the most impacted by climate change, so international projects allow world leaders to support these countries. While burying hydrates is safe, questions regarding the short- and long-term impacts will surely rise. Some people believe that humans should not interfere with the climate while many others believe it is the responsibility of this generation to make the world a better place for future generations by any means necessary. It is important to discuss these ethical topics when undertaking impactful projects like this. 

V. CONCLUSION
 Magnesium-promoted rapid nucleation of carbon dioxide hydrates holds great potential in the race to reach global net negative carbon emissions. Although further refinement of the process is required, the breakthrough of magnesium as a catalyst may revolutionize chemical carbon dioxide removal.

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