Preparation And Propylene Dehumidification Performance Of Poly (Vinyl Alcohol)-silica Hybrid Membrane

Water content has to meet the strict requirement in propylene polymerization process in order to prevent catalyst poisoning. To meet the industrial demand, this study utilized the propylene/water vapor separation as model system and prepared two series of composite membranes with high dehumidification performance. The morphologies and physicochemical properties of the membranes were characterized by several analytical techniques such as scanning electron microscope (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and fourier transform infrared (FT-IR). The free volume characteristics of the membranes were investigated by positron annihilation lifetime spectroscopy (PALS).Based on the adhesion property of hyaluronic acid (HA), interfacial adhesion was enhanced and non-selective interface defects were eliminated via introducing HA as transition layer between poly(vinyl alcohol) (PVA) and silica. Water selective adsorption and diffusion velocity were improved due to the natural hydrophilicity of HA. PVA-(HA-silica) solution was prepared by blending the modified silica particles into PVA solution, and then PVA-(HA-silica)/PS was fabricated through dipping polysulfone (PS) hollow fibers into the as-prepared solution. Compared with the pristine PVA/PS membrane (permeance 215 GPU, separation factor 4720), this series of PVA-(HA-silica)/PS membranes dramatically improved the propylene dehumidification performance. When HA concentration was 0.2 wt.% and the HA-silica content was 4%, the permeance and separation factor of the composite membrane was 912 GPU and 9650, respectively.Inspired by the biomineralization process, (PVA-gelatin)-silica hybrid membrane was fabricated through gelatin-induced in situ synthesis of silica particles within PVA bulk. Sodium silicate as the silicon precursor was added into PVA-gelatin blending solution, and precipitated by gelatin and mediated by the polymeric phase. In the PVA-gelatin blend organic phase, gelatin acted as catalyst and templating agent to induce the nucleation and growth of silica particles, and PVA acted as membrane bulk to provide a confined space that inhibited the self-aggregation of silica particles. Hence, the silica particles were homogeneously distributed within the polymer matrix. Composite membranes with high dehumidification performance were prepared by coating PVA/gelatin-silica (separating layer) onto porous polysulfone (PS) hollow fibers (supporting layer). When the pH value of solution was 5.0 and silicate concentration was 30 mM, the permeance and separation factor of the composite membrane was 1500 GPU and 67511, respectively.Sorption experiment revealed that the mass transfer processes of water molecules in PVA-(HA-silica) and (PVA-gelatin)-silica membranes were governed by diffusion step. The effects of membrane fabricating conditions (silica content, solution pH value and silicon precursor concentration) and experimental parameters (temperature, pressure and flow rate) were systematically investigated as well. In view of the propylene deep dehumidification process, a proposal of coupling the membrane process with the traditional gas dehydration technology was presented on the basis of the hollow fiber composite membranes.