Mixed-matrix membranes and high surface area carbons (HSACs) are promising methods for cost-effective gas separation, which is important for reducing the emission of greenhouse gases into the atmosphere. We tested the pressure dependence of permeability and selectivity for a triblock copolymer membrane loaded with 0, 5, 10, 20, or 30 wt.-% hollow carbon spheres. We found that the permeability of the membrane increased with pressure, while the selectivity of the membranes remained fairly constant. We used a scanning electron microscope to evaluate the membranes before and after the permeability/selectivity testing, which revealed some changes in the appearance of the membranes. We synthesized our HSACs by hydrothermally carbonizing samples of three carbonated beverages, Mello Yello®, Mtn Dew®, and Push® Orange Soda, at 200 ºC, and then further heat treating the resultant carbon powder at 1000 ºC in a tube furnace. These powders had surface areas between 300 and 820 m²/g. Gravimetric adsorption tests showed CO2 uptake between 10 and 13 mass-% and selectivity values around 10. Elemental analysis showed our samples to be ≥90% carbon, with trace amounts of heteroatoms such as oxygen or sulfur. We investigated the properties of carbon powders prepared with an artificial sweetener by adding Splenda® to samples of Diet Pepsi®, Diet Mtn Dew®, and water, which we then carbonized and analyzed by a similar method. We were able to show that these powders had some properties that were advantageous for CO2 adsorption. We have shown through our research that there can be many approaches to gas separations including the use of mixed-matrix membranes and the use of high surface area carbon powders.
Zoe Mann, ’17