Experimental and CFD Study on the Role of Fluid Flow Pattern on Membrane Permeate Flux

This paper reports a study on the role of fluid flow pattern and dynamic pressure on the permeate flux through a micro filtration membrane in laboratory scale.For this purpose,a dead-end membrane cell equipped with a marine type impeller was used.The impeller was set to rotate in the clockwise and counter clockwise directions with the same angular velocities in order to illustrate the effect of rotation direction on permeate flux.Consequently, permeate fluxes were measured at various impeller rotational speeds.The computational fluid dynamics（CFD）predicted dynamic pressure was related to the fluxes obtained in the experiments.Using the CFD modeling,it is proven that the change in dynamic pressure upon the membrane surface has direct effect on the permeate flux.

Preparation and oxygen permeability of Bi_(26)Mo_(10)O_(69) porous layer modified ionic-electronic mixed conductor on air side

Bi26MO10O69 nanopowder was prepared by hydrothermal method and used as a surface modification material for oxygen separation membrane to enhance oxygen permeability. Thermal decomposition behavior and phase variation of the precursor were investigated by thermal analyzer （TG-DSC） and high-temperature X-ray diffraction （HT-XRD）. Bi26MO10O69 porous layer was coated on the air side of BaCo0.7Fe0.2Nb0.1O3-δ （BCFN） oxygen permeable membrane by dipping method. In the partial oxidation experiment of coke oven gas （COG）, the Bi26Mo10O69-coated BCFN membrane exhibits higher oxygen permeability and CH4 conversion than the uncoated BCFN membrane. When the thickness of BCFN membrane was 1 mm and the COG and air fluxes were 120 and 100 mL/min, the oxygen permeation flux reached 16.48 mL/（min.cm^2） at 875℃, which was 16.96% higher than the uncoated BCFN membrane. Therefore, Bi26MoloO69 porous layer on the air side will be promising modification coating on the oxygen permeability of BCFN membrane.

Effect of the Ultrasound Generated by Flat Plate Transducer Cleaning on Polluted Polyvinylidenefluoride Hollow Fiber Ultrafiltration Membrane

Polyvinylidenefluoride （PVDF） hollow fiber ultrafiltration membrane is frequently employed in water treatment. However, the fouling of ultrafiltration membranes affects the economic effectiveness of such process significantly. The ultrasound generated by flat plate transducer （UFPT） was used to clean the polluted PVDF ultrafiltration membrane with 2 g·L^-1 of citric acid aqueous solution in our study. The effects of UFPT intensity on the membrane surface were studied. The new membrane was easy to be polluted by the saturated CaCl2 solution. A synergistic effect of UFPT and 2 g·L^-1 citric acid aqueous solution could remove the foul of the membrane, and its flux could be recovered about 81%. The flux recovery of old membrane polluted was increased to 73.2% after 7 h soaking in citric acid aqueous solution, but its flux recovery without soaking was only increased to 56.2%.

Treatment of oil/water emulsion by polyethylene glycol ultrafiltration membrane

Polyethylene glycol(PEG) membranes with different molecular mass cut-offs were used to treat oil/water emulsion, and the effects of experimental conditions including pressure, temperature and different opera- ting modes on permeate flux and removal rate of chemical oxygen demand (COD_ Cr) were studied. The results show that the permeate flux of ultrafiltration membrane is influenced by pressure and temperature; practical pressure is chosen to be 0.30.7MPa for the PEG with molecular mass cut-offs of 8000 and 0.71.0 MPa for the PEG with molecular mass cut-offs of 2500; and the practical temperature is chosen to be 2532℃. Different operating modes of ultrafiltration also influence the permeate flux and removal rate of COD_ Cr. The ultrafiltration membrane of intermittent cross-flow operating mode is easier to be influenced by blocky polarization and contamination than that of sequential cross-flow operating mode. Removal rate of COD_ Cr in intermittent cross-flow and sequential cross-flow condition can be maintained at about 93%.

Transport Process of Isopropanol Aqueous Solution by Pervaporation

To study the transport process of isopropanol aqueous solution by pervaporation, the transport model of isopropanol and that of water at 323 K in polyvinyl alcohol(PVA) membrane were obtained in this paper. Theoretical predictions agreed well with the experimental results. The interactional parameter between water and PVA membrane is less than that between isopropanol and PVA membrane, which shows that water is preferentially dissolved in PVA membrane. The plasticizing coefficient and diffusion coefficient at infinite dilution of water are larger than those of isopropanol, which shows that the dissolution and permeation in PVA membrane of water are greater than those of isopropanol. Both the interactional parameter between water and isopropanol in the membrane and that in feed rise with the increase of isopropanol content in feed, which shows that the larger isopropanol content is, the higher selectivity of the membrane is and the more remarkable separation effect of pervaporation is.

Application of Submerged Ultrafiltration in Pretreatment of Flue Gas Desulfurization Wastewater

Nowadays,the zero liquid discharge of flue gas desulfurization(FGD)wastewater from coal-fired units has attracted the attention of all countries in the world.The pretreatment methods generally have the problems of high operation cost,small treatment capacity,and poor flexibility.However,the membrane method can avoid the above problems.In the current research,it has not been found that someone directly uses submerged ultrafiltration to pretreat FGD wastewater.Therefore,this paper innovatively proposed to directly use ceramic ultrafiltration membrane to treat FGD wastewater,which can ensure effluent quality and improve the flexibility of the pretreatment system.In this paper,the performance of submerged ultrafiltration membrane for the filtration of FGD wastewater from a power plant was studied to optimize the filtration performance and improve the effluent quality.The effects of operating parameters such as membrane permeate flux,aeration rate and filtration/backwashing time combination on the membrane performance were studied.The results showed that when the filtration/backwashing time combination was 15 min/30 s,with the increased in permeate flux from 55 L/(m2·h)to 100 L/(m2·h),the steady transmembrane pressure(TMP)increased from 39 kPa to 70 kPa,and the fouling rate increased significantly from 4.5 kPa/h to 7.3 kPa/h;When the aeration rate increased from 10 m3/(m2·h)to 30 m3/(m2·h),the membrane pollution was much reduced.Excessive aeration rate cannot further alleviate the membrane pollution,but also brought greater energy consumption;Increasing backwashing time can effectively inhibit the formation of gel layer on the surface of the membrane and prolong the initial stage of low-pressure operation;The rejection of suspended solids(SS)and turbidity of the equipment studied in this paper can reach more than 99%under various working conditions,which can satisfy the water quality requirements of the subsequent steps.The submerged ultrafiltration membrane was suitable for the pretreatment of FGD wastewater because it can ensure the quality of permeate under the premise of long-term operation.

Dynamic Membrane for Cross-flow Micro-filtration in Treating Activated Sludge

Mixed liquid of activated sludge (AS) were micro-filtrated by dynamic membrane (DM) made of 6000 mesh kaolin. The results illustrated that the permeate quality and flux with DM filtration were superior to that with direct filtration in treating AS. The experiments of membrane washing showed that DM could abate the internal fouling of membranes efficiently, and the permeate flux of renewed membrane reached 90% of that of new membranes. The denser the mixed liquid suspended solids (MLSS) were, the lower the permeate flux was. Increasing of both flow velocity over the membrane surface and trans-membrane pressure (TMP) could lead to some enhancement of permeate flux, while the former approach could be carried out more economically. The feasibility of application of the DM to membrane bioreactor (MBR) has been ascertained.

Mixed-conducting perovskite-type Sr_xBi_(1-X)FeO_(3-δ)oxygen-permeating membranes

SrxBi1-xFeO3- (SBF) series mixed conductors were synthesized using Standard ceramic method. The properties of such materials were characterized by XRD, O2-TPD techniques. Ab-normal crystal phenomena were found and explained and correlated with the oxygen permeation results. By analysis of the critical radius (rc), the degree of openness of the lattice (Fv) and the average metal-oxygen bonding energy of the perovskite lattice (ABE), it was proposed that the oxygen permeation flux is determined mainly by the oxygen diffusion rate in bulk when 1-x≤0.5, and by the concentration of oxygen vacancy when 1-x≥ 0.5. The stability of Sr0.5Bi0.5FeO3- was also investigated, and the high stability of it was attributed to the stable BO6 octahedra.

Superhydrophobicity-improved Ethanol-Water Separation

Efficient separation of biofuels from fermentation broths vis pervaporation plays an important role in addressing the global challenges,such as developing renewable energy.Great efforts have been continuously devoted in the past decades to developing high-performance pervaporation membranes.A recent report published in Science by Zhao et al.showed that a superhydrophobic surface could contribute significantly to improving the pervaporation separation of ethanol-water mixture,which will generate broad interest for the new design of separation membranes.

Hydrophobic polyethersulfone porous membranes for membrane distillation

Membrane distillation （MD） is a thermal, vapor-driven transportation process through micro porous hydrophobic membranes that is increasingly being applied to seawater and brine desalination processes. Two types of hydrophobic microporous polyethersulfone fiat sheet membranes, namely, annealed polyethersulfone and a polyethersulfone/tetraethoxysilane （PES/TEOS） blend were prepared by a phase inversion process. The membranes were characterized and their performances were investigated using the vacuum membrane distillation of an aqueous NaCI solution. The performances of the prepared membranes were also compared with two commercially available hydrophobic membranes, polyte- trafluorethylene and polyvinylidene fluoride. The influence of operational parameters such as feed temperature （25-65 ℃）, permeate vacuum pressure （200 800 mbar）, feed flow rate （8-22 mL/s） and feed salt concentration （3000 to 35000 mg/L） on the MD permeation flux were investigated for the four membranes. The hydrophobic PES/TEOS membrane had the highest salt rejection （99.7%） and permeate flux （86 kg/（m^2 -h）） at 65 ℃, with a feed of 7000 ppm and a pressure of 200 mbar.