(566c) A Porous Copper Metal Organic Framework with Highly Nucleophilic Amine Links for CO2 Gas Separation from Biogas

The rising interest in using biogas as an energy fuel has lower the consumption of fossil fuel and inclines the environment toward sustainability. Despite having low CO₂ emissions during the combustion of biogas, it still involves a significant challenge to overcome. Biogas consist of ~ 40% of CO₂ depending upon the substrate and conditions of the digester used during production [1]. This CO₂ is the major undesirable component for the energy recovery of the biogas as it lowers the calorific value of the fuel. Adsorption driven materials have set a benchmark intensively in CO₂ separation in the biogas upgrading process [2,3]. Wide variety of adsorbents have been studied for their separation performances and energy consumption to procure efficient, energy-saving and environmentally benign separation processes [4]. MOFs (Metal-organic framework) are an emerging class of porous materials, which has gained enormous attention in the past two decades and has a widespread potential application in gas separation and purification technology. MOFs outstand the other porous material due to their unique properties such as high surface area, tunable pore size and easy tailoring of chemical functionalities.

A new copper MOF was synthesized using facile solvothermal synthesis and resulted in a cuboid-shaped, 300-500 nm size particles. The resultant MOF showed the carbon dioxide uptake capacity of 1.8 mmol/g at 293 K and 1 bar. Furthermore, when the temperature was decreased up to 273 K and at 1 bar, 16 % increase in volumetric uptake was observed. The MOF displayed type I isotherm with permanent porosity and no hysteresis. The N₂ adsorption isotherm was recorded at 77 K and revealed BET surface area of 756 m²/g with a pore volume of 0.27 cm³/g calculated using density functional theory. The gravimetric high-pressure adsorption was carried out for both CO₂ and CH₄ gases at 10 bar. The Cu-MOF showed 215 % higher uptake of CO₂ than CH₄ at 10 bar and 293 K. The CO₂ binding energy of the adsorbent was evaluated by calculating isosteric heat of adsorption (Q_st) by interpolation approach from the temperature-dependent isotherms using Van’t Hoff’s equation and resulted in a significant low value,18 kJ/mole, which describes that the low energy is required to regenerate the MOF in desorption cycles and hence reduces the energy consumption. To investigate the CO₂ separation performance, the Cu-MOF powders were structured into hierarchical strong pellets and further used in pressure swing adsorption (PSA) equipment for breakthrough adsorption and desorption cycles. Kinetic study of the pellets was carried by further simulating the breakthrough data to obtain mass transfer coefficient and diffusivities value.

References

[1] I Angelidaki, L Treu, P Tsapekos, G Luo, S Campanaro, H Wenzel, et al., Biogas upgrading and utilization: Current status and perspectives, Biotechnology Advances. 36 (2018) 452-466.

[2] S Chaemchuen, NA Kabir, K Zhou, F Verpoort. Metal-organic frameworks for upgrading biogas via CO2 adsorption to biogas green energy, Chem.Soc.Rev. 42 (2013) 9304-9332.

[3] B Yuan, X Wu, Y Chen, J Huang, H Luo, S Deng. Adsorption of CO2, CH4, and N2 on Ordered mesoporous carbon: Approach for greenhouse gases capture and biogas upgrading, Environ.Sci.Technol. 47 (2013) 5474-5480.

[4] K Zhou, S Chaemchuen, F Verpoort. Alternative materials in technologies for Biogas upgrading via CO 2 capture, Renewable Sustainable Energy Rev. 79 (2017) 1414-1441.