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- All Subjects: Sustainability
- All Subjects: Zeolites
MFI zeolite membranes were synthesized on α-alumina supports by secondary growth method. Novel positron annihilation spectroscopy (PAS) techniques were used to non-destructively characterize the pore structure of these membranes. PAS reveals a bimodal pore structure consisting of intracrystalline zeolitic micropores of ~0.6 nm in diameter and irregular intercrystalline micropores of 1.4 to 1.8 nm in size for the membranes. The template-free synthesized membrane exhibited a high permeance but a low selectivity in C3H6/C3H8 mixture separation.
CMS membranes were synthesized by coating/pyrolysis method on mesoporous γ-alumina support. Such supports allow coating of thin, high-quality polymer films and subsequent CMS membranes with no infiltration into support pores. The CMS membranes show strong molecular sieving effect, offering a high C3H6/C3H8 mixture selectivity of ~30. Reduction in membrane thickness from 500 nm to 300 nm causes an increase in C3H8 permeance and He/N2 selectivity, but a decrease in the permeance of He, N2 and C3H6 and C3H6/C3H8 selectivity. This can be explained by the thickness dependent chain mobility of the polymer film resulting in final carbon membrane of reduced pore size with different effects on transport of gas of different sizes, including possible closure of C3H6-accessible micropores.
CMS membranes demonstrate excellent C3H6/C3H8 separation performance over a wide range of feed pressure, composition and operation temperature. No plasticization was observed at a feed pressure up to 100 psi. The permeation and separation is mainly controlled by diffusion instead of adsorption. CMS membrane experienced a decline in permeance, and an increase in selectivity over time under on-stream C3H6/C3H8 separation. This aging behavior is due to the reduction in effective pore size and porosity caused by oxygen chemisorption and physical aging of the membrane structure.
In 2019, the World Health Organization stated that climate change and air pollution is the greatest growing threat to humanity. With a world population of close to 8 billion people, the rate of population growth continues to increase nearly 1.05% each year. As the world population grows, carbon dioxide emissions and climate change continue to accelerate. By observing increasing concentrations of greenhouse gas emissions in the atmosphere, scientists have correlated that the Earth’s temperature is increasing at an average rate of 0.13 degrees Fahrenheit each decade. In an effort to mitigate and slow climate change engineers across the globe have been eagerly seeking solutions to fight this problem. A new form of carbon dioxide mitigation technology that has begun to gain traction in the last decade is known as direct air capture (DAC). Direct air capture works by removing excess atmospheric carbon dioxide from the air and repurposing it. The major challenge faced with DAC is not capturing the carbon dioxide but finding a useful way to reuse the post-capture carbon dioxide. As part of my undergraduate requirements, I was tasked to address this issue and create my own unique design for a DAC system. The design was to have three major goals: be 100% self-sufficient, have net zero carbon emissions, and successfully repurpose excess carbon dioxide into a sustainable and viable product. Arizona was chosen for the location of the system due to the large availability of sunlight. Additionally, the design was to utilize a protein rich hydrogen oxidizing bacteria (HOB) known as Cupriavidus Necator. By attaching a bioreactor to the DAC system, excess carbon dioxide will be directly converted into a dense protein biomass that will be used as food supplements. In addition, my system was designed to produce 1 ton (roughly 907.185 kg) of protein in a year. Lastly, by utilizing solar energy and an atmospheric water generator, the system will produce its own water and achieve the goal of being 100% self-sufficient.