Performance And Preparation Of Novel Membranes For Desulfurziation Using Pervaporation

In order to enrich the variety of membrane material of desulfurization by pervaporation, by means of solubility parameter theory, polyether block amide (PEBAX) was chosen as membrane material for removing sulfur by pervaporation in this work and PEBAX/PVDF composite membrane was prepared by using PVDF UF membrane as the supporting layer. The results of thermogravimetry analysis and tensile testing indicated, respectively, fine mechanical property and thermorstability of PEBAX/PVDF composite membrane. The surface of membrane had no obvious defect from scanning electron microscope (SEM) and the combination between the separator layer and support layer was tight. It was found that the swelling degree of PEBAX homogeneous membrane increased with increase of thiophene content in feed and at200min the equilibrium reached from swelling experiment in the simulative gasoline composed of n-heptane and thiophene in the range concentration of400-1900μg·g-1, which explained the strong capacity of affinity between PEBAX material and thiophene. And the addition of hydrophobic PVDF supporting layer made that the swelling degree of PEBAX/PVDF composite membrane had a little enhancement compared with PEBAX homogeneous membrane. Pervaporation experiments were conducted to further investigate performance of PEBAX/PVDF composite membrane for removing sulfur. The consequence showed the total flux increased with the increasing temperature of feed, the separator factor decreased. When thiophene content in feed increased, the total flux, thiophene flux and n-heptane flux enhanced, but the separation factor reduced continuously. At30℃, the membrane exhibited optimum performance with the total flux of2.82kg·m-2·h-1and the corresponding separator factor of3.97for1000μg·g-1sulfur in feed.For further enhancing the performance of PEBAX membrane for desulfurization using pervaporation, mixed matrix membranes of polyether block amide (PEBAX) with activated carbon as the filler were prepared and used for removing sulfur in model gasoline composed of n-heptane and thiophene. The structure, internal morphology, thermal stability and crystallinity of the hybrid membranes were characterized by FTIR、SEM、TGA and XRD, respectively. It was found that there was no change in structure of PEBAX membrane before and after filling of activated carbon from the spectra of FTIR. The result from TGA indicated the incorporation of activated carbon in PEBAX membranes was helpful for improving thermal stability of PEBAX membrane. XRD results showed PEBAX membrane was amorphous and addition of activated carbon had no effect to crystal structure of PEBAX membrane. The uniformity dispersedness of activated carbon in PEBAX membrane and tight combination of separation layer and supporting layer were found from SEM. The swelling degree of mixed matrix membranes in model gasoline increased first and then decreased with the increase of activated carbon content. The membranes containing10%activated carbon exhibited the highest swelling degree. The effects of activated carbon content, feed temperature and sulfur content on desulfurization performance of the mixed matrix membranes with pervaporation were systematically investigated. Experimental results showed that higher content of sulfur content resulted in a higher total flux but a lower separation factor. By increasing the feed temperature, the total flux increased while separation factor decreased. Higher content of activated carbon in membranes restricted the mobility of polymer chains, which made the free volume to decrease so that the total flux decreased continuously. But the separation factor was suffered from the effect of both sorption and diffusion due to incorporation of activated carbon, hence, it increased first and then decreased with activated carbon increased. When the content of activated carbon in membrane reached10%, the membrane displayed the optimum desulfurization performance with the total flux of1.48kg·m-2·h-1and separation factor of4.69.In this work, in order to improve the mechanical strength and stability of PDMS membrane in gasoline, super-fine calcium carbonate and nano-fumed silica particles were chosen as the fillers and ethyl orthosilicate as cross-linker, by additional cross-linking for preparation of filled-PDMS membranes. The crosslinking status of membranes was characteristiced by FTIR between filled-membranes and homogeneous membrane. There was no any change in functional groups in membranes contrast to before and after filled the particles. The results of SEM showed the inorganic particles dispersed uniformly into the polymer. The results of tensile testing indicated incorporation of both fillers enhanced effectively the mechanical properties of PDMS membrane. The crosslinking densities of the membranes were calculated by Flory-Rehner formula for exploring the interaction between the PDMS and inorganic particles as well as the effect of inorganic particles content on crosslinking densities. The effects of polymer viscosity, crosslinking agent concentration, PDMS concentration, particle content, thiophene content in the simulative gasoline and temperature on the swelling degree were investigated by experiments, respectively. The results demonstrated the swelling degree of membranes decreased when the particles content and crosslinking agent concentration increased; but it increased with increase of polymer viscosity, the thiophene content and temperature; there was no obvious relationship between PDMS concentration and the swelling degree. The comprehensive properties of CaCO3-filled membrane were better than SiO2-filled membrane.