Methane Adsorption Performance On Metal-Organic Framework And Improvement Of Water Stability

Natural gas is more and more highly valued by countries all over the world because of its advantages:abundant reserves,convenient storage and transportation,clean and environmental,high thermal efficiency.Adsorption natural gas technology is a research hotspot in the field of natural gas storage.Due to large specific surface area,adjusted pore volume and structure,metal-organic frameworks are ideal materials for absorbing and storing natural gas.In this paper,metal-organic frameworks with higher methane adsorption were synthesized,and the water stability of Zn（bdc）（ted）₀.5 was improved by surface carbonization.HKUST-1 was synthesized by solvothermal method.The methane adsorption capacity of HKUST-1 with different metal ions loaded or organic acids modified was investigated.With a molar ratio n(Cu²⁺):n（K⁺）of 10:1 loading K+,the methane adsorption of K-HKUST-1 increased from 10.96 mmol/g to 11.75 mmol/g.HKUST-1 synthesied with molar ratio n（HNO₃）:n（H₃BTC）of 5:1,had the best modification effect.The methane adsorption increased to 11.95 mmol/g.The specific surface area increased from 1499 m²/g to 1933 m²/g.Zn（bdc）（ted）₀.5 was synthesized by solvothermal method.The optimized synthesis conditions were as follows:n（Zn（NO₃）₂·6H₂O）:n（H₂BDC）:n（ted）:n（DMF）=1.5:1:2.5:200,the crystallization temperature of 120℃,the crystallization time of 48h.The methane adsorption of Zn（bdc）（ted）₀.5 was 15.6 mmol/g in 25℃ 3.5MPa.The specific surface area is 1270 m²/g,and the pore volume is 0.72 cm³/g.The methane adsorption of Zn（bdc）（ted）₀.5 exposed to air at 25℃ and a relative humidity of 37%for 5 days decreased significantly to 6.0 mmol/g.Obvious cracks and cavities on the surface of the crystal appeared.The surface hydrophobicity of Zn（bdc）（ted）₀.5 carbonized was significantly improved.The Zn（bdc）（ted）₀.5 carbonized had a Water Contact Angle improvement from 38.2° to 144.2° and an unchanged methane adsorption.After exposed to humid air for 5 days,the methane adsorption decreased less than 1 mmol/g.Carbonization is mainly to reduce the interfacial tension of the crystal surface through high temperature,transform the organic ligands on the crystal surface into an amorphous carbon layer,and good hydrophobic properties were obtained.The water stability of Zn（bdc）（ted）₀.5 was significantly improved.Adsorption isotherm of methane in Zn（bdc）（ted）₀.5 could be well described by Langmuir-Freundich model.At 3.5MPa,the adsorption heat of methane in Zn（bdc）（ted）₀.5 was 14.03 kJ/mol.The diffusion behavior of methane in Zn（bdc）（ted）₀.5 was simulated with the molecular dynamics method.The maximum self-diffusion coefficient of methane in Zn（bdc）（ted）₀.5 was 7.48 × 10^-9m²/s.