Preparation Of Ni-MOFs/SBS Mixed Matrix Membranes And Its Application Of CH₄/N₂ Separation

Coal-bed methane（CBM）,an unconventional natural gas,is regarded as a potential energy resource because of its abundant storage worldwide.N₂ is regarded as the predominant impurity,and its removal is essential to achieve the efficient utilization of CBM.Due to their similar physicochemical properties of CH₄ and N₂（their molecular diameter and polarity）,membrane separation is the best method for efficient separation of CH₄/N₂.In this process,the polymer,as the main material of membrane separation,its separation is still restricted by the famous Robeson upper bound between permeability and selectivity,this is,it cannot have both excellent permeability and selectivity.The mixed matrix membrane（MMM）,which is the combination of polymeric materials and inorganic particles,has been introduced and offered the opportunity to break the reciprocal relationship between selectivity and permeability of Robeson trade-off or even surpass the upper bound trade-off line.MOFs show better compatibility with polymer matrices on account of the existence of their organic ligands.Therefore,the gas separation properties of CH₄/N₂ by preparing MOFs/polymer mixed matrix membranes are the main study in this thesis.In this paper,these two Ni-MOFs,[Ni₃（HCOO）₆]and Ni-MOF-74 as the inorganic fillers,were added into SBS1301 triblock copolymer matrix respectively and the THF as the solvent,a series of Ni-MOFs/SBS MMMs were prepared by mechanical blend and solution coating method.The effects of MOFs contents,temperature and pressure on the permeability and selectivity of single gas CH₄ and N₂ were investigated.Meanwhile,the gas permeation behavior was investigated by the measurement of the CH₄/N₂ gas mixture（CH₄/N₂:15/85 vol%and 50/50 vol%）.The specific research contents were as follows:1.[Ni₃（HCOO）₆]was synthesized using hydrothermal synthesis.By thecharacterization of XRD,FT-IR and SEM,the product was successfully synthesized.Using[Ni₃（HCOO）₆]fillers and SBS polymer substrate,a series of mixed matrix membranes were prepared.For the MMMs,the XRD peaks of[Ni₃（HCOO）₆]were observed in the patterns of MMMs,indicating that the skeleton structure of[Ni₃（HCOO）₆]was not destroyed.FT-IR further proved that characteristic peaks of both[Ni₃（HCOO）₆]and SBS could be identified in the FT-IR spectrum of MMMs.TGA analysis was carried out on the MMMs and the result showed that the thermal stability of MMMs had little effect with the addition of[Ni₃（HCOO）₆]fillers.SEM images confirmed that the[Ni₃（HCOO）₆]particles were uniformly dispersed in the SBS polymer matrix.For the single gas,at the[Ni₃（HCOO）₆]loading of 5 wt%,the CH₄ permeability reached the maximum value of 83.5 Barrer,being 108%higher compared with the permeability of the SBS membrane（38.6 Barrer）.With the increment of temperature,the permeability of CH₄ could reach 181.8 Barrer（1.0 atm,55℃）.As the pressure increased,the permeability of CH₄ decreased slightly.For the mixed gas of CH₄/N₂,it was measured that the[Ni₃（HCOO）₆]/SBS-5 sample exhibited an increasing for CH₄ permeability of 77.7 Barrer.2.A series of mixed matrix membranes were fabricated with Ni-MOF-74 as inorganic particles dispersed phase and SBS as organic phase.First of all,Ni-MOF-74 was analyzed by XRD,FT-IR,BET and SEM,demonstrating the successful synthesis.Then,the MMMs were investigated by XRD,FT-IR,SEM and TGA,the results showed that The structure of Ni-MOF-74 was not destroyed and dispersed uniformly in SBS matrix by means of mechanical blending method.For the single gas,the CH₄ permeability of Ni-MOF-74/SBS-15 sample reached the maximum value of 83.5 Barrer,which was 116%higher than that of the SBS membrane.The CH₄ permeability could further increase to 176.6 Barrer,with the increase in temperature to 55℃.For the CH₄/N₂ mixed gas（CH₄/N₂:50/50 vol%）,the Ni-MOF-74/SBS-15 sample exhibited increasing CH₄ permeability of 74.7 Barrer.