Fabrication Of PVDF Hydrophobic Composite Membranes Based On PDMS And ZIF-8/ZIF-L And Study On Its CO₂ Absorption Performance

As the most important greenhouse gas,the capture of CO2 brooks no delay.Membrane absorption CO2 technology is a coupling of membrane technology and chemical absorption technology.It features flexible operation,high CO2 capture efficiency,desirable energy consumption,and easy amplification.The hydrophobicity and anti-wetting ability of the membrane material are very important.Because in membrane absorption CO2 process,membranes are used to separate the gas and liquid phases,and once the membrane pores are wetted,the resistance to mass transfer of CO2 across the membrane will increase significantly,resulting in a decrease in the absorption efficiency of CO2.The CO2 gas permeability of the membrane material is also an important characteristic that affects the membrane absorption CO2 process.In this thesis,polyvinylidene fluoride(PVDF)was used as the substrate,based on the polydimethylsiloxane(PDMS)cross-linking system and ZIF-8/ZIF-L supported particle system,the PVDF composite membrane suitable for membrane absorption CO2 was prepared.The composite membrane has been fully characterized and experimentally tested.In this study,five types of PDMS crosslinking agents were selected,and five different PDMS-PVDF composite membranes were prepared by coating-curing methods;and then these composite membranes were fully characterized and experimentally tested.The effect of PDMS crosslinking agents on the performance of PDMS-PVDF composite membranes were explored.The results show that methyltriethoxysilane(MTES)is the best crosslinking agent for PDMS.The contact angle of the prepared PDMS-PVDF composite membrane is 108.4°,and its CO2 absorption flux is 1.61×10-3 mol m-2·s-1.To further enhance the hydrophobicity of the PDMS-PVDF composite membrane and improve the CO2 permeability decrease caused by the dense coating,ZIF-8 nanoparticles were introduced based on the above system,and the ZIF-8-PDMS-PVDF composite membrane was fabricated.The influence of the loading of ZIF-8 on the morphology and properties of the prepared membrane was explored.Under the best loading ratio of ZIF-8(20%),the contact angle of the composite membrane is 130.2°,and the absorption flux of CO2 is 2.83×10-3 mol·m-2·s-1.With the increase of ZIF-8 loading,the hydrophobicity of the prepared membrane was further enhanced,but it’s surface began to appear obvious agglomeration and cracks.The over-loading of ZIF-8 nanoparticles caused agglomeration and cracks on the surface of the composite membrane.To deal with these phenomena,this thesis introduced ZIF-L nanosheets to prepare defects-free PVDF composite membranes.By adjusting the loading ratio of ZIF-8 and ZIF-L,the ZIF-8-ZIF-L-PDMS-PVDF composite membrane with excellent hydrophobicity and CO2 gas permeability was successfully prepared.Under the best loading ratio of ZIF-8 and ZIF-L(30%and 10%),the contact angle of this composite membrane is 131.8°,and the absorption flux of CO2 is 2.99×10-3 mol·m-2·s-1.In the 10-day CO2 absorption experiment,the decrease in CO2 absorption flux was only 9.36%,which was much lower than the 49.21%of the original PVDF membrane,showing good operational stability.And in the AC impedance test,the anti-wetting performance of the ZIF-8-ZIF-L-PDMS-PVDF composite membrane is also significantly better than that of the ordinary PVDF membrane.