Study On Preparation And Aromatics/aliphatics Separation Of Tublar MOFs Hybrid Membrane

Aromatic/aliphatic mixtures separation is important but challenging process in refining and petrochemical industries and pervaporation has potential application prospect. Therefore, the development of new membrane materials is the one of the problems to be solved. Organic/inorganic hybrid membranes have been considered to be the promising materials for pervaporation. However, the compatibility and dispersion of traditional inorganic particles in organic polymers are still remain to be improved. Metal organic framework?MOFs? have received the widespread attention because of its diversity of topology structures constituted with various organic ligands and inorganic metals. Owing to the tailorable pore properties, high surface areas and incorporation of both inorganic and organic entities in MOFs, they are proposed to be ideal candidates to fabricate nanohybrid membranes in terms of their excellent compatibility with polymer matrix. MOFs materials were employed as facilitated transport particles and the application of MOFs in aromatic facilitated transport assembly pervaporation membranes was researched in this study. After choosing different types of MOFs as hybrid particles, tubular MOFs/polymer hybrid membranes were prepared successfully with different membrane forming methods in aromatic/aliphatic separation.Firstly, MOF-based Cu₃?BTC?₂/PVA?BTC = benzene-1,3,5-tricarboxylate, PVA = poly?vinyl alcohol?? nanohybrid membranes were fabricated on a ceramic tubular substrate by using a pressure-driven assembly method. The morphology and structure of the resulting membranes were characterized by scanning electron microscope?SEM?, energy dispersive X-ray spectrometer?EDX?, powder X-ray diffraction?XRD? and thermal gravity analysis?TGA?. The Cu₃?BTC?₂/PVA membranes were then used in separating 50 wt.% toluene/n-heptane mixtures through pervaporation. The effects of PVA concentration, Cu₃?BTC?₂ loading feed composition, and operating temperature on membrane performances were explored. The results indicated that the separation factor and permeate flux of optimized Cu₃?BTC?₂/PVA membranes were improved to 17.9 and 133 g/?m2h?, respectively. Furthermore, the relationship between the microstructure and separation performance of the hybrid membrane was investigated. The separation principle was supposed to be that enhanced affinity between toluene and the membrane through incorporating Cu₃?BTC?₂ particles, improving separation performances.Based on the previous experiments, formate Co?HCOO?₂ was choosen as hybrid particle because its unique superiority such as mild synthesis conditions and low cost. To our best knowledge, transition metal Co²⁺ was proposed to use as the facilitated transport carriers in the formation of the membrane for separating aromatic/aliphatic mixtures. The aromatic could donate lone electron pair and transition metal ions possess empty d orbit as receptor. Therefore, the transition metal ions could complex with aromatic compounds, but have little or no reactivity with aliphatic compounds. Co?HCOO?₂ with different sizes were synthesized through solvothermal methods, and then doped with poly?ether-block-amide??PEBA?. The hybrids were deposited on the outer surface of tubular ceramic substrate by a dynamic pressure-driven assembly method. The morphologies and structures of the Co?HCOO?₂ particles and Co?HCOO?₂/PEBA membranes were characterized by SEM, EDX, TGA, positron annihilation lifetime spectrometer?PALS?, dynamic light scattering?DLS? and nanoindentation. The membranes were then used in separating aromatic/aliphatic mixtures through pervaporation. When toluene content in feed solution was 10 wt.%, the permeate flux of the membrane was 771 g/?m2·h? with a separation factor of 5.1. The relationship between the microstructure and separation performance of the hybrid membrane was investigated by modern analytical tools. Free volume of PEBA membrane and Co?HCOO?₂/PEBA nanohybrid membrane was characterized with positron annihilation lifetime spectroscopy?PALS?. Furthermore, the mechanical property of Co?HCOO?₂/PEBA hybrid membrane was studied by the nanoindentation. Due to the immobilization effect of the Co?HCOO?₂ for Co²⁺, the membrane showed stable separation performance in 30 h.