Adsorptive Separation Of Small Gas Molecules And Catalytic Degradation Of PET Plastic Over Several MOFs

Focusing on energy conservation,emission reduction and environmental protection,developing advanced energy-saving separation and catalytic technologies based on porous materials to realize efficient separation of small molecular gases and resource utilization of waste plastics,has great practical significance for the petrochemical industry to develop a green and low-carbon industry and achieve the strategic goal of"carbon neutrality".Focusing on this major demand of national development,this work mainly studies the adsorption performance on small molecule gases over several MOFs materials and explores the potential of MOFs materials applied in catalytic degradation and recycling of PET waste.It mainly involves the synthesis and modification of MOFs materials,and their performance for the capture of CO₂,the recovery of ethane and propane from natural gas,the separation of ethane and ethylene from cracked gas,and the catalytic degradation of PET plastic.This work belongs to the interdisciplinary fields of chemical engineering and material engineering.It is of great significance for the scientific research and practical applications.In this thesis,Gly@Cu-BTCs were synthesized and their enhanced separation performance toward CO₂/CH₄/N₂ and improved water vapor stability were studied.A series of Gly@Cu-BTCs were synthesized by grafting glycine to the secondary building units of the Cu-BTC.Gly_0.3@Cu-BTC exhibited a superior CO₂ capacity of 5.4 mmol/g at 298 K and 100 k Pa,and its adsorptive selectivity for the equimolar CO₂/CH₄ and CO₂/N₂ mixtures was separately up to8.53 and 59.38.DFT calculations revealed that the presence of glycine at Cu site protects it from water vapor attack sterically and thermodynamically,which is the origination of its improved stability against moisture,and simultaneously enhances the CO₂ selective adsorption of the material.In this thesis,Gly@Cu-BTC,Ala@Cu-BTC and GABA@Cu-BTC were prepared by grafting different amino acids to Cu-BTC.Compared Cu-BTC,all the modified materials exhibited higher C₂H₄,C₂H₆ and C₃H₈ adsorption capacities.At 298 K and 100 k Pa,Gly@Cu-BTC possessed high adsorption capacities reaching as high as 7.98 mmol/g,6.79 mmol/g and7.80 mmol/g separately for C₂H₄,C₂H₆ and C₃H₈,which are higher than most reported adsorbents.In addition,the selectivities of Gly@Cu-BTC toward C₂H₆/CH₄ and C₃H₈/CH₄were 13.3 and 173.5.while the selectivity toward C₂H₆/CH₄ was 3.7.Fixed-bed experiments showed that Gly@Cu-BTC could separate the CH₄/C₂H₆/C₃H₈ and C₂H₄/C₂H₆ mixtures completely at ambient conditions,and it also had excellent recycling stability.Computational simulations showed that Gly grafting onto unsaturated Cu site could improve the capacities of Gly@Cu-BTC for C₂H₆ and C₃H₈ due to the introduction of-COOH or-NH₂.In this thesis,the adsorption and separation performance of a zirconium-based material STA-26 for light hydrocarbons was studied.The STA-26 exhibited preferential adsorption of ethane,with the adsorption capacity of 4.22 mmol/g at 298 K and 100 k Pa,which was at a good level among most ethane-selective adsorbents.Also,the selectivity of STA-26 toward C₂H₆/C₂H₄ is 1.7,while the selectivities toward C₂H₆/CH₄ and C₃H₈/CH₄were 19.4 and 223.7,respectively.Fixed-bed breakthrough experiments confirmed that the C₂H₆/C₂H₄ and CH₄/C₂H₆/C₃H₈ mixtures could be separated by the fixed-bed of STA-26.Recycling breakthrough experiments showed that STA-26 had good recycliability.In this thesis,a zirconium-based MOF material UiO-66 was used to degrade the polyester plastics PET for the first time,and the reaction pathway was studied.The results showed that UiO-66 could effectively deconstruct PET into the monomers terephthalic acid and mono-methyl terephthalate in a solvent-free system with total yields of 98%under H₂ and 81%withut H₂ at 260℃.When the plastics systems with PET+PP or PET+PE were employed,UiO-66still catalyzed PET degradation effectively.Isotope labeling experiments suggested that this catalytic system engages in theβ-scission process as the major pathway while hydrogenolysis proceeds as a minor pathway.Compared to other traditional chemical degradation systems and hydrogenolysis catalysts,this system was solvent-free and the yields could reach reach international advanced level,demonstrating that UiO-66 has the potential to practical applications.In this thesis,the phase transition of UiO-66 during the PET degradation process for PET degradation were studied.Extensive structural characterization studies reveal that during the degradation process,UiO-66 undergoes an intriguing transformation into MIL-140A,which has the same linker and metal center as UiO-66.This was mainly attributed to the exchange between the ligand of UiO-66 and the reaction product TA during the catalytic degradation of PET.In addition,the linker exchange and phase transformation of the analogue UiO-66-F and UiO-66-NH₂,which had different functional groups in the linkers,are potentially rationalized by the different acid dissociation constant（p Ka）values of the linkers.The phase transition product MIL-140A also showed good catalytic activity toward PET degradation under 260℃and 1 atm H₂（total yield of 88%）,and MIL-140 exhibited better stability in the reaction.This work elucidated the phase transformation mechanism of UIO-66 in catalytic degradation of PET and provided a new idea for the preparation of high stability PET degradation catalyst.