Four-channel catalytic micro-reactor based on alumina hollow fiber membrane for efficient catalytic oxidation of CO

The traditional automotive catalytic converter using commercial ceramic honeycomb carriers has many problems such as high back pressure,low engine efficiency,and high usage of precious metals.This study proposes a four-channel catalytic micro-reactor based on alumina hollow fiber membrane,which uses phase inversion method for structural molding and regulation.Due to the advantages of its carrier,it can achieve lower ignition temperature under low noble metal loading.With Pd/CeO_(2) at a loading rate of 2.3%(mass),the result showed that the reaction ignition temperature is even less than 160℃,which is more than 90℃ lower than the data of commercial ceramic substrates under similar catalyst loading and airspeed conditions.The technology in turn significantly reduces the energy consumption of the reaction.And stability tests were conducted under constant conditions for 1000 h,which proved that this catalytic converter has high catalytic efficiency and stability,providing prospects for the design of innovative catalytic converters in the future.

Fabrication of ZIF-8 membranes on dual-layer ZnO-PES/PES organic hollow fibers by in-situ crystallization

Compared to inorganic supports, polymeric supports can offer additional benefits, e.g., easier processing and cheaper. However, the organic surface has weak adhesion to the zeolitic imidazolate frameworks(ZIFs) membrane layer, which usually requires complex surface modification or seeding. Herein, we demonstrate that a dual-layer asymmetric polymer support prepared by a simple spinning process is a good candidate for the preparation of ZIF-8 membrane. The inner layer of the support is an organic hollow fiber(PES) with finger-like pores, and the outer layer is a ZnO-PES composite layer with finger-like pores also. The ZnO-PES composite layer is expected to contain uniform ZnO crystals in the polymer matrix, i.e., the ZnO particles in the skin layer of the support are not easy to fall off. Under the induction of ZnO particles in the outer layers, continuous ZIF-8 membranes can be prepared by single in-situ crystallization, showing good adhesion to the supports. The obtained ZIF-8 membranes show a H_(2) permeance of 8.7 × 10^(-8)mol·m^(-2)·s^(-1)·Pa^(-1) with a H_(2)/N_(2) ideal separation selectivity of 18.0. The design and preparation of this dual-layer polymer support is expected to promote the large-scale application of MOF membranes on polymer supports.

Effect of polytetrafluoroethylene hollow fiber microstructure on formaldehyde carbonylation performance in membrane contactor

Membrane contactor is regarded as a promising method for reaction and process intensification. The feasibility of formaldehyde carbonylation to synthesize glycolic acid using polytetrafluoroethylene(PTFE)membrane contactor has been proved in our previous study. In this paper, the effect of membrane microstructure on process performance was further investigated. Three porous PTFE hollow fibers with different pore sizes and one polydimethylsiloxane(PDMS)/PTFE composite membrane with dense layer were fabricated for comparison. The physical and chemical properties of four membranes, including chemical composition, morphology, contact angle, liquid entry pressure, thermodynamic analysis and gas permeability, were systemically characterized. Experiments of formaldehyde carbonylation under different reaction conditions were conducted. The results indicated that the yield of glycolic acid increased with decreasing pore size for porous membranes, which was due to the improvement of wetting behavior. The dense layer of PDMS in composite hollow fiber could effectively prevent the solvent from entering membrane pores, thus the membrane exhibited the best performance. At reaction temperature of 120℃ and operation pressure of 3.0 MPa, the yield of glycolic acid was always higher than 90% as the mass ratio of trioxane and phosphotungstic acid increased from 0.2:1 to 0.8:1. The highest turnover frequency was up to 26.37 mol·g^(-1)·h^(-1). This study provided a reference for the understanding and optimization of membrane contactors for the synthesis of glycolic acid using solvent with low surface tension.

Research of Oxidation Resistance of PVDF Hollow Fiber Membrane Used in Water Treatment

[Objective] The aim was to research the influences of different formulations on oxidation resistance of PVDF hollow fiber membrane.[Method]The immersion precipitation phase inversion method was employed to make casting solution with different formulations into hollow fiber membrane.The membrane was immersed in 1% NaClO solution for testing its performance changes.[Result]The membrane made by materials with bigger molecular weight had better oxidation resistance performance;the surfactant tween-80 could increase water flux,but lead to lower rupture intension;Pore-forming agent PEG400 do better than PVP in the oxidation resistance of membrane.[Conclusion]This study will provide a good idea for the development of the PVDF membrane with high oxidation resistance.

Performances of biological aerated filter employing hollow fiber membrane segments of surface-improved poly(sulfone) as biofilm carriers

Using the surface of poly （sulfone） hollow fiber membrane segments as grafted layer, the hydrophilic acrylamide chain was grafted on by UV-photoinduced grafting polymerization. The gained improvement of surface wettability for the modified membrane was tested by measuring the contact-angle as well as FTIR spectra. Then correlation between the hydrophilic ability of support material and the biofilm adherence ability was demonstrated by comparing the pollutant removal rates from urban wastewater via two identical lab-scale up-flow biological aerated filters, one employed the surface wettability modified poly （sulfone） hollow fiber membrane segment as biofilm carder and the other employed unmodified membrane segment as biofilm carder. The experimental results showed that under the conditions of influent flux 5 L/h, hydraulic retention time 9 h and gas to liquid ratio （G/L） 10： 1, the removal rates of chemical oxygen demand （COD） and ammonium nitrogen （NH4^＋-N） for the modified packing filter and the unmodified packing filter was averaged at 83.64% and 96.25%, respectively, with the former filter being 5%-20% more than the latter. The effluent concentration of COD, NH4^＋-N and turbidity for the modified packing filter was 25.25 mg/L, 2 mg/L and 8 NTU, respectively. Moreover, the ammonium nitrogen removal performance of the filter packing the modified PSF was compared with the other bioreactor packing of an efficient floating medium. The biomass test indicated that the modified membrane matrixes provided better specific adhesion （3310-5653 mg TSS/L support）, which gave a mean of 1000 mg TSS/L more than the unmodified membrane did. In addition, the phenomenon of simultaneous denitrification on the inner surface of the support and nitrification on the outer surface was found in this work.

Effect of Diluent on the Morphology and Performance of IPP Hollow Fiber Microporous Membrane via Thermally Induced Phase Separation

Isotactic polypropylene （iPP） hollow fiber microporous membranes were prepared using thermally induced phase separation （TIPS） method. Di-n-butyl phthalate （DBP）, dioctyl phthalate （DOP）, and the mixed solvent were used as diluents. The effect of α （DOP mass fraction in diluent） on the morphology and performance of the hollow fiber was investigated. With increasing α, the morphology of the resulting hollow fiber changes from typical cellular structure to mixed structure, and then to typical particulate structure. As a result, the permeability of the hollow fiber increases sharply, and the mechanical properties of the hollow fiber decrease obviously. It is suggested that the morphology and performances of iPP hollow fiber microporous membrane can be controlled via adjusting the compatibility between iPP and diluent.

Effects of F127 on Properties of PVB/F127 Blend Hollow Fiber Membrane via Thermally Induced Phase Separation

Hydrophilic poly(vinyl butyral)(PVB) /Pluronic F127(F127) blend hollow fiber membranes were prepared via thermally induced phase separation(TIPS) ,and the effects of blend composition on the performance of hydrophilic PVB/F127 blend hollow fiber membrane were investigated.The addition of F127 to PVB/polyethylene glycol(PEG) system decreases the cloud point temperature,while the cloud point temperature increases slightly with the addition of F127 to 20%(by mass) PVB/F127/PEG200 system when the concentration of F127 is not higher than 5%(by mass) .Light scattering results show that the initial inter-phase periodic distance formed from the phase separation of 20%(by mass) PVB/F127/PEG200 system decreases with the addition of F127,so does the growth rate during cooling process.The blend hollow fiber membrane prepared at air-gap 5mm,of which the water permeability increases and the rejection changes little with the increase of F127 concentration.For the membrane prepared at zero air-gap,both water permeability and rejection of the PVB/F127 blend membrane are greater than those of PVB membrane,while the tensile strength changes little.Elementary analysis shows that most F127 in the polymer solution can firmly exist in the polymer matrix,increasing the hydrophilicity of the blend membrane prepared at air-gap of 5mm.

Structure and Properties of Polyurethane/Polyvinylidene Difluoride Blending Hollow Fiber

Utilization of polyvinylidene difluoride, PVDF, as the disperse phase and thermal plastic polyurethane, PU, as the continuous phase, the PU/PVDF blend hollow fiber membranes with the property of pressure-responsibility, PR, was prepared by melt.spinning. For these hollow fibers, the formation of the interracial micro-voids, IFM, and the spinablllty of the blend were analyzed. The pressm-e-responslblllty was studied by measuring the changing of pure water flux, PWF, with the pressure, and the influence of drawing and heat-setting on the structure and pressure-responsibility of the membranes were also discussed.

Modeling investigation of geometric size effect on pervaporation dehydration through scaled-up hollow fiber NaA zeolite membranes

A mass transfer model in consideration of multi-layer resistances through NaA zeolite membrane and lumen pressure drop in the permeate side was developed to describe pervaporation dehydration through scaled-up hollow fiber supported NaA zeolite membrane. It was found that the transfer resistance in the lumen of the permeate side is strongly related with geometric size of hollow fiber zeolite membrane, which could not he neglected. The effect of geometric size on pervaporation dehydration could be more significant under higher vacuum pressure in the permeate side. The transfer resistance in the lumen increases with the hollow fiber length but decreases with lumen diameter. The geometric structure could be optimized in terms of the ratio of lumen diameter to membrane length. A critical value of d1/L （Rc） to achieve high permeation flux was empirically correlated with extraction pressure in the permeate side. Typically, for a hollow fiber supported NaA zeolite membrane with length of 0.40 m, the lumen diameter should be larger than 2.0 mm under the extraction pressure of 1500 Pa.

Evaluation of diffusion in gel entrapment cell culture within hollow fibers

AIM: To investigate diffusion in mammalian cell culture by gel entrapment within hollow fibers. METHODS: Freshly isolated rat hepatocytes or human oral epidermoid carcinoma (KB) cells were entrapped in type I collagen solutions and statically cultured inside microporous and ultrafiltration hollow fibers. During the culture time collagen gel contraction, cell viability and specific function were assessed. Effective diffusion coefficients of glucose in cell-matrix gels were determined by lag time analysis in a diffusion cell. RESULTS: Significant gel contractions occurred in the collagen gels by entrapment of either viable hepatocytes or KB cells. And the gel contraction caused a significant reduction on effective diffusion coefficient of glucose. The cell viability assay of both hepatocytes and KB cells statically cultured in hollow fibers by collagen entrapment further confirmed the existence of the inhibited mass transfer by diffusion. Urea was secreted about 50% more by hepatocytes entrapped in hollow fibers with pore size of 0.1 μm than that in hollow fibers with MWCO of 100 ku. CONCLUSION: Cell-matrix gel and membrane pore size are the two factors relevant to the limited mass transfer by diffusion in such gel entrapment of mammalian cell culture.

STRUCTURE AND PROPERTIES OF COMPOSITE POLYURETHANE HOLLOW FIBER MEMBRANES

Composite polyurethane(PU)-SiO_2 hollow fiber membranes were successfully prepared via optimizing thetechnique of dry-jet wet spinning,and their pressure-responsibilities were confirmed by the relationships of pure water flux-transmembrane pressure(PWF-TP)for the first time.The origin for this phenomenon was analyzed on the basis of membranestructure and material characteristics.The effects of SiO_2 content on the structure and properties of membrane wereinvestigated.The experimental results indicated that SiO_2 in membrane created a great many interfacial micro-voids andplayed an important role in pressure-responsibility,PWF and rejection of membrane:with the increase of SiO_2 content,theability of membrane recovery weakened,PWF increased,and rejection decreased slightly.

Two-dimensional MXene hollow fiber membrane for divalent ions exclusion from water

Two-dimensional material membranes with fast transport channels and versatile chemical functionality are promising for molecular separation.Herein,for the first time,we reported design and engineering of two-dimensional Ti_(3)C_(2)Tx MXene(called transition metal carbides and nitrides)membranes supported on asymmetric polymeric hollow fiber substrate for water desalination.The membrane morphology,physicochemical properties and ions exclusion performance were systematically investigated.The results demonstrated that surface hydrophilicity and electrostatic repulsion and size sieving effect of interlayer channels synergistically endowed the MXene hollow fiber membrane with fast water permeation and efficient rejection of divalent ions during nanofiltration process.

CO2/CH4 separation using inside coated thin film composite hollow fiber membranes prepared by interfacial polymerization

Carbon dioxide(CO_2) is greenhouse gas which originates primarily as a main combustion product of biogas and landfill gas. To separate this gas, an inside coated thin film composite(TFC) hollow fiber membrane was developed by interfacial polymerization between 1,3–cyclohexanebis–methylamine(CHMA) and trimesoyl chloride(TMC). ATR-FTIR, SEM and AFM were used to characterize the active thin layer formed inside the PSf hollow fiber. The separation behavior of the CHMA-TMC/PSf membrane was scrutinized by studying various effects like feed gas pressure and temperature. Furthermore, the influence of CHMA concentration and TMC concentration on membrane morphology and performance were investigated. As a result, it was found that mutually the CHMA concentration and TMC concentration play key roles in determining membrane morphology and performance. Moreover, the CHMA-TMC/PSf composite membrane showed good CO_2/CH_4 separation performance. For CO_2/CH_4 mixture gas(30/70 by volume) test, the membrane(PD1 prepared by CHMA 1.0% and TMC 0.5%) showed a CO_2 permeance of 25 GPU and the best CO_2/CH_4 selectivity of 28 at stage cut of 0.1. The high CO_2/CH_4 separation performance of CHMA-TMC/PSf thin film composite membrane was mostly accredited to the thin film thickness and the properties of binary amino groups.

Recovery of Copper Ions from Wastewater by Hollow Fiber Supported Emulsion Liquid Membrane

Recovery of copper ions from wastewater using a hollow fiber supported emulsion liquid membrane (HFSELM) was studied with LIX984N as carrier, kerosene as diluents, and sulfuric acid solution as stripping phase. Effects of compositions of feed and emulsion liquid phase, flow rates on both sides of membrane, and hollow fiber module parameters were investigated. The stability of the emulsion liquid phase without surfactant and the effect of buffer in the feed phase on the extraction rate were also evaluated. It is found that the stability of the emulsion phase without surfactant is poor. Higher flow velocity gives shorter residence time for the emulsion liquid phase on the tube side, reducing the effect of particle coalescence on the separation process. The extraction rate increases with the increase of feed phase pH, carrier concentration, hydrogen ion concentration in the stripping phase, and ef- fective hollow fiber area. The phase ratio in the emulsion liquid phase has a negative effect on extraction rate. The flow rates on both sides have little influence on the extraction performance of the HFSELM, while buffer addition in the feed solution improves the extraction efficiency.

Effects of Additives and Coagulant Temperature on Fabrication of High Performance PVDF/Pluronic F127 Blend Hollow Fiber Membranes via Nonsolvent Induced Phase Separation

Poly（vinylidene fluoride） （PVDF） has become one of the most popular materials for membrane preparation via nonsolvent induced phase separation （NIPS） process. In this study, an amphiphilic block copolymer, Pluronic F127, has been used as both a pore-former and a surface-modifier in the fabrication of PVDF hollow fibermembranes to enhance the membrane permeability and hydrophilicity. The effects of 2nd additive and coagulant temperature on the formation of PVDF/Pluronic F 127 membranes have also been investigated. The as-spun hollow fibers were characterized in terms of cross-sectional morphology, pure water permeation （PWP）, relative molecular mass cut-off （MWCO）, membrane chemistry, and hydrolphilicity. It was obsered that the addition of Pluronic F 127 significantly increased the PWP of as-spun fibers, while the membrane contact angle was reduced. However, the size of macrovoids in the membranes was undesirably large. The addition of a 2nd additive, including lithium chloride （LiC1） and water, or an increase in coagulant temperature was found to effectively suppress the macrovoid for- mation in the Pluronic-containing membranes. In addition, the use of LiC1 as a 2nd additive also further enhanced the PWP and hydrophilicity of the membranes, while the surface pore size became smaller. PVDF hollow fiber with a PWP as high as 2330 L·m-2·h-1·MPa-1, a MWCO of 53000 and＇a contact angle of 71 o was successfully fabricated with 3% （by mass） of Pluronic F127 and 3% （by mass） of LiC1 at a coagulant temperature of 25 ℃, which shows better performance as compared with most of PVDF hollow fiber membranes made by NIPS method.

Gas-initiation under UV and liquid-grafting polymerization on the surface of polysulfone hollow fiber ultrafiltration membrane by dynamic method

Using the inner-surface of polysulfone hollow fiber ultrafiltration membranes as grafted layer, the method of gas-initiation and liquid-polymerization has been studied, which aimed to adjust the diameter of the pores in the membranes. The degree of polymerization varied with the changes of the parameters, such as irradiation time, monomer concentration, temperature and time of polymerization and so on. The results indicated that using benzophenone(BP) which is in a gaseous condition as photo-initiator, acrylamide as graft monomer, the polyacrylamide chain was grafted on the surface of membranes. After the surface membrane being modified, the water flux and retention altered,and thus it can be seen that the diameter of the pores in the membrane was altered. These experiments contribute to finding a new way to produce the hollow fiber membrane with the small pore size and are extraordinarily worth developing and studying.

Synergistic action of non-solvent induced phase separation in preparation of poly(vinyl butyral) hollow fiber membrane via thermally induced phase separation

A systematic study of air gap distance effects on the structure and properties of poly(vinyl butyral)hollow fiber membrane via thermally induced phase separation(TIPS)has been carried out.The results show that the hollow fiber membrane prepared at air gap zero has no skin layer; the pore size near the outer surface is larger than that near the inner surface; and the special pore channel-like structure near the outer surface is formed,which is quite different with the typical sponge-like structure caused by TIPS and the finger-like structure caused by non-solvent induced phase separation(NIPS),because of the synergistic action of non-solvent induced phase separation at air gap zero.The pore size gradually decreases from outer surface layer to the intermediate layer,but increases gradually from intermediate layer to the inner surface layer.With the increase of air gap distance,the pore size near the outer surface gets smaller and a dense skin layer is formed,and the pore size gradually increases from the outer surface layer to the inner surface layer.Water permeability of the hollow fiber membrane decreases with air gap distance,the water permeability decreases sharply from 45.50×10-7 to 4.52×10-7 m3/(m2·s·kPa)as air gap increases from 0 to 10 mm at take-up speed of 0.236 m/s,further decreases from 4.52×10-7 to 1.00×10-8 m3/(m2·s·kPa)as the air gap increases from 10 to 40 mm.Both the breaking strength and the elongation increase with the increase of air gap distance.The breaking strength increases from 2.25 MPa to 4.19 MPa and the elongation increases from 33.9% to 132.6% as air gap increases from 0 mm to 40 mm at take-up speed 0.236 m/s.

PDMS/ZIF-8 coating polymeric hollow fiber substrate for alcohol permselective pervaporation membranes

In order to develop high performance composite membranes for alcohol permselective pervaporation(PV),poly(dimethylsiloxane)/ZIF-8(PDMS/ZIF-8)coated polymeric hollow fiber membranes were studied in this research.First,PDMS was used for the active layer,and Torlon?,PVDF,Ultem?,and Matrimid?with different porosity were used as support layer for fabrication of hollow fiber composite membranes.The performance of the membranes varied with different hollow fiber substrates was investigated.Pure gas permeance of the hollow fiber was tested to investigate the pore size of all fibers.The effect of support layer on the mass transfer in hydrophobic PV composite membrane was investigated.The results show that proper porosity and pore diameter of the support are demanded to minimize the Knudsen effect.Based on the result,ZIF-8 was introduced to prepare more selective separation layer,in order to improve the PV performance.The PDMS/ZIF-8/Torlon?membrane had a separation factor of 8.9 and a total flux of 847 g·m-2·h-1.This hollow fiber PDMS/ZIF-8/Torlon?composite membrane has a great potential in the industrial application.

MORPHOLOGIES AND GAS SEPARATION PROPERTIES OF MELT-SPUN ASYMMETRIC POLY(4-METHYL-1-PENTENE)HOLLOW FIBER MEMBRANES

Poly(4-methyl-1-pentene) (PMP) hollow fiber membranes were prepared by the melt-spun and cold-stretch(MSCS) method. Scanning electronic microscopy (SEM) was used to characterize the section and surface structures of themembranes with special asymmetric structure. The preliminary results of gas permeation measurements indicated that the resultant hollow fiber membranes have the potential ability for oxygen/nitrogen separation.

Transport Study of Cu （Ⅱ） Through Hollow Fiber Supported Liquid Membrane

The transport of Cu(II)from aqueous solutions containing buffer media through hollow fiber supported liquid membrane(HFSLM)using di(2-ethylhexyl)phosphoric acid(D2EHPA)dissolved in kerosene as membrane phase and hydrochloric acid as striping phase was investigated.A set of factors were studied,including tube side velocity,shell side velocity,pH of the feed phase,Cu(II)concentration in the feed phase,buffer media concentration and D2EHPA concentration in the membrane phase.Experimental results indicate that the mass transfer coefficient increases with increasing both carrier concentration in the organic phase and flow rates on the tube side and shell side,and decreases with increasing initial Cu(II)concentration in the feed phase.With increasing pH value and acetate concentration in the feed phase,the mass transfer coefficient reaches a maximum value then decreases.The optimal operating conditions are obtained at pH value of 4.44 and 0.1 mol·L -1 acetic ion concentration in feed phase,and carrier volume fraction of around 10%in kerosene as organic phase.A mathematical model of the transport mechanism through HFSLM is developed.The modeled results agree well with the experimental ones.