Academic literature on the topic 'Polyamide composite membrane'

Polyamide thickness and roughness have been identified as critical properties that affect thin-film composite membrane performance for reverse osmosis. Conventional formation methodologies lack the ability to control these properties independently with high resolution or precision. An additive approach is presented that uses electrospraying to deposit monomers directly onto a substrate, where they react to form polyamide. The small droplet size coupled with low monomer concentrations result in polyamide films that are smoother and thinner than conventional polyamides, while the additive nature of the approach allows for control of thickness and roughness. Polyamide films are formed with a thickness that is controllable down to 4-nanometer increments and a roughness as low as 2 nanometers while still exhibiting good permselectivity relative to a commercial benchmarking membrane.

We modified TFC membranes via a series of chemical and surface reactions. A nascent polyamide (PA) active layer was prepared by interfacial polymerization and composited with GO nanosheets then reacted with CuCl₂·2H₂O. Finally, the composite membrane was treated with NH₄OH solutions.

Abstract Standardization of reverse osmosis (RO) membrane system allows transparency and accountability in performance benchmarking of different membrane elements, especially when a new product is introduced to the market. In the current study, we compared performance of three polyamide composite RO membranes (one from new entrant in the market, the other two are established manufacturers) for seawater desalination. Experimental work was conducted at a desalination plant in Egypt. The new membrane had higher permeate conductivity and lower salt rejection values than the two established products. Similar trend was observed as far as permeate flow was concerned.

The structure and composition of nanofillers have a significant influence on polyamide nanofiltration (NF) membranes. In this work, an asymmetric organic nanobowl containing a concave cavity was synthesized and incorporated into a polyamide layer to prepare thin film nanocomposite (TFN) membranes via an interfacial polymerization process. Benefiting from the hydrophilicity, hollow cavity and charge property of the compatible organic nanobowls, the separation performance of the developed TFN membrane was significantly improved. The corresponding water fluxes increased to 119.44 ± 5.56, 141.82 ± 3.24 and 130.27 ± 2.05 L/(m2·h) toward Na2SO4, MgCl2 and NaCl solutions, respectively, with higher rejections, compared with the control thin film composite (TFC) and commercial (CM) membranes. Besides this, the modified TFN membrane presented a satisfying purification performance toward tap water, municipal effluent and heavy metal wastewater. More importantly, a better antifouling property of the TFN membrane than TFC and CM membranes was achieved with the assistance of organic nanobowls. These results indicate that the separation performance of the TFN membrane can be elevated by the incorporation of organic nanobowls.

Interfacial polymerization of polyamide was conducted using hydrophobic and hydrophilic membrane support. The effects of monomer concentration were investigated, and the resulting thin-film composite membranes were tested for their performance in dye removal using different flow configurations. The results showed that a dense polyamide layer was successfully formed on the hydrophilic support, while a polyamide layer with a very loose structure was formed on the hydrophobic support. The polyamide layer became smoother and more hydrophilic as the concentration of trimesoyl chloride was increased, leading to increased permeate flux and reduced dye rejection. The highest sunset yellow rejection of 45.7% with a permeate flux of 4.9 L/m2.h was obtained when the polyamide layer was formed from trimesoyl chloride concentration of 0.05 w/v% (a high amine to acid chloride monomer ratio of 20) and the filtration was in cross-flow configuration.

To improve the filtration performance and properties of organic solvent nanofiltration (OSN) membranes, we firstly introduce nanoporous silica (SiO2) particles into the polyamide (PA) active layer of polysulfone (PSf) membrane via an interfacial polymerization process. Results from the study revealed that introduction of SiO2 influenced the properties of PSf/PA-SiO2 composite membranes by changing the surface roughness and hydrophilicity. Moreover, results also indicated that nanoporous SiO2 modified membranes showed an improved performance of alcohols solvent permeance. The PSf/PA-SiO2 composite membrane modified by 0.025 wt % of SiO2 reached a permeance of 3.29 L m−2 h−1 bar−1 for methanol and 0.42 L m−2 h−1 bar−1 for ethanol, which were 20.0% and 13.5% higher than the control PSf membrane (permeance of 2.74 L m−2 h−1 bar−1 for methanol and 0.37 L m−2 h−1 bar−1 for ethanol). Conclusively, we demonstrated that the increase of membrane hydrophilicity and roughness were major factors contributing to the improved alcohols solvent permeance of the membranes.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009.
ENGLISH ABSTRACT: The aim of this study was to modify the surface of polyethersulfone (PES) ultrafiltration (UF) membranes to produce a more hydrophilic membrane by cross-linking poly(vinyl alcohol) (PVA) with sodium tetraborate (Na2B4O7.10H2O) (SB) on the surface. Key preparation factors were identified as PVA molecular weight, concentrations of the PVA and SB, cross-linking reaction time, number of coatings and the mode of coating. The effect of these factors on the membrane performance (salt retention and permeate flux) is discussed. These PVA-SB membranes typically had 11.46% retention and 413.30 L/m2.h flux for a feed containing 2000 ppm NaCl (0.45 MPa, 20°C, 45 – 50 L/h). The coating was shown to be uniform and stable by Fourier transform infrared spectroscopy (FT-IR) analyses. Coating significantly increased hydrophilicity and a maximum flux increase of 500 L/m2.h was reached. Measurements showed a reduced water contact angle and this confirmed the obvious enhancement of surface hydrophilicity. As a control, the role of the PVA base layer without cross-linking and the effects of its drying and heating on the water permeability of the PES-UF membrane were also studied, in order to ascertain maximum treatment conditions. Retention and permeate flux were determined (feed solution: 2000 ppm NaCl, applied pressure 0.45 MPa, 25°C, 45 – 50 L/h). It was found that the heating had the largest effect on the reduction of water permeability and therefore 50°C was the limit for treatment of this specific PES-UF membrane. Thin-film composite (TFC) membranes were prepared by an interfacial polymerization (IP) reaction between a polyfunctional amine and tri- or di-functional carboxylic chloride and then evaluated for their reverse osmosis (RO) performance. The salt retention of the PVA-SB membranes was improved when covering the cross-linked PVA gel sub-layer with a polyamide (PA) layer. However, the permeate flux decreased to below 30 L/m2.h (2000 ppm NaCl, 1 – 2 MPa, 20°C, 45 – 50 L/h). Two TFC membranes made from trimesoyl chloride (TMC) with m-phenylenediamine (MPD) or 2,6-diaminopyridine (DAP) exhibited retentions of 96.71% to 89.65% and fluxes of 10.93 to 27.91 L/m2.h, depending on the type of diamine used, when tested with a 2000 ppm NaCl solution (2 MPa, 25°C, 45 – 50 L/h). Two TFC membranes made from a n ew 2,5-furanoyl chloride (FC) with MPD or DAP exhibited retentions of 34.22% to 58.54% and fluxes of 49.21 to 25.80 L/m2.h, depending on the type of diamine used, when tested with a 2000 ppm NaCl solution (1 MPa, 25°C, 45 – 50 L/h). Novel PVA-SB-DAP-FC membranes made from the DAP with FC had the highest hydrophilicity value and exhibited >58.54% NaCl retention and 25.80 L/m2.h flux, and 75.08% MgSO4 retention and 34.75 L/m2.h flux, when tested with (2000 ppm feed, 1 MPa, 25°C, 45 – 50 L/h). The effect of the chemical structures of the different amines and carboxylic chlorides used on the RO performances of the TFC membranes prepared by two amines reacting with TMC or FC, on the surfaces of the modified asymmetric PES-UF membranes, was investigated. FT-IR and water contact angle determination were used to characterize the chemical structure, morphology and hydrophilicity of the PA layers of the composite membranes. The response surface methodology (RSM) was used to optimize the preparation conditions that had the largest effects on the RO performance of the PVA-SB-DAP-FC membranes. Good membrane performance could be realized particularly by manipulating three variables: DAP concentration, FC concentration and polymerization time (PT). The regression equation between the preparation variables and the performance of the composite membranes was established. Main effects, quadratic effects and interactions of these variables on the composite membrane performance were investigated. The membranes were characterized in terms of pure water permeation (PWP) rate, molecular weight cut off (MWCO), solute separation and flux. Mean pore size (μp) and standard deviation (σp) of the membranes were determined using solute transport data. The results revealed that PVA-SB membranes have almost the same pure water permeation that PES-UF membranes have. The MWCO of the PES-UF membranes decreased from 19,000 to 13,000 Daltons when the membrane was coated with PVA.
AFRIKAANSE OPSOMMING: Die doel van hierdie studie is die modifikasie van die oppervlakte van poliëtersulfoon ultrafiltrasie (PES-UF) membrane om meer hidrofiliese membrane te berei deur die kruisbinding van polivinielalkohol (PVA) met natriumtetraboraat ((Na2B4O7.10H2O) (NaB) op die membraanoppervlakte. Sleutelfaktore in die bereidingsproses is geïdentifiseer, naamlik: PVA molekulêre massa, PVA en NaB konsentrasies, kruisbindingsreaksietyd, die aantal bestrykingslae, en die manier waarop die bestrykingslae aangewend is. Die invloed van hierdie faktore op die membraanontsouting en vloed is ondersoek, en word hier bespreek. Hierdie PVA-NaB membrane het die volgende tipiese resultate getoon: 11.46% ontsouting en 413.30 L/m2.h vloed (Kondisies: 2000 dpm NaCl oplossing, 0.45 MPa toegepaste druk, 20 °C, vloeitempo 45–50 L/h). Die deklaag was uniform en stabiel, soos bepaal d.m.v. FTIR. Die aanwesigheid van die deklaag het die hidrofilisiteit verhoog en 'n maksimum vloed van 500 L/m2.h is behaal. Die waterkontakhoek is ook gemeet; 'n laer waarde het 'n verbetering in die hidrofilisiteit van die oppervlakte bevestig. Die rol van die PVA basislaag, sonder kruisbinding (kontrole), en die effek van uitdroging en verhitting hiervan, is ook bestudeer, om sodoende optimale behandelingskondisies te bepaal. Membraanontsouting en vloed is bepaal (Kondisies: 2000 dpm NaCl oplossing, 0.45 MPa toegepaste druk, 25 °C, vloeitempo 45–50 L/h). Verhitting het die grootste effek gehad op die afname in vloed. Daar is bevind dat 'n maksimum temperatuur van 50°C geskik is vir die behandeling van hierdie spesifieke PES-UF membraan. Dunfilmsaamgestelde (DFS) membrane is berei d.m.v. 'n tussenvlakpolimerisasiereaksie tussen 'n polifunksionele amien en 'n di- of tri-funksionele karbonielchloried, en daarna is die tru-osmose (TO) gedrag bepaal. Die ontsouting van die PVA-NaB membrane was hoër nadat die kruisgebinde PVA jel sub-laag met 'n poliamied (PA) laag bedek is. Die vloed het egter afgeneem, tot onder 30 L/m2.h (Kondisies: 2000 dpm NaCl oplossing, 1–2 MPa toegepaste druk, 20 °C, vloeitempo 45–50 L/h). Twee DFS membrane is berei met trimesoïelchloried (TMC), naamlik met m-fenieldiamien (MFD) of 2,6-diaminopiridien (DAP). Afhangend van die diamien wat gebruik is, is die volgende ontsoutingsresultate en vloede verkry: 96.71% tot 89.65% en 10.93 to 27.91 L/m2.h (Kondisies: 2 000 dpm NaCl oplossing, 2 MPa toegepaste druk, 25 °C, v loeitempo 45–50 L/h). Twee DFS membrane is ook berei met 'n nuwe verbinding, 2,5-furanoïelchloride (FC), en MFD of DAP. Afhangend van die diamien wat gebruik is is die volgende ontsoutingsresultate en vloede behaal: 34.22% tot 58.54% en 49.21 tot 25.80 L/m2.h (Kondisies: 2000 dpm NaCl oplossing, 1 MPa toegepaste druk, 25 °C, vloeitempo 45–50 L/h). Die PVA-NaB-DAP-FC membrane het die hoogste hidrofilisiteit getoon: 58.54% NaCl ontsouting en 25.80 L/m2.h vloed, en 75.08% MgSO4 ontsouting en 34.75 L/m2.h vloed (2000 ppm NaCl oplossing, 1 MPa toegepaste druk, 25 °C, vloeitempo 5–50 L/h). Die invloed van die chemiese struktuur van die verskillende diamiene en karboksielsuurchloriedes wat gebruik is in die bereiding van die DFC membrane op die oppervlakte van die gewysigde PES-UF membrane is in terme van TO ondersoek. FTIR en kontakhoekbepalings is gebruik om die chemiese struktuur, morfologie en hidrofilisiteit van die PA lae van die saamgestelde membrane te bepaal. Die eksperimentele oppervlakte ontwerp metode is gebruik om die bereidingskondisies vir die TO aanwending van die PVA-NaB-DAP-FC membrane te optimiseer. Goeie resultate is verkry deur die volgende veranderlikes te manipuleer: DAP en FC konsentrasies en die tydsduur van die polimerisasie. 'n Regressie-vergelyking tussen die bereidingsverandelikes en die funksionering van die saamgestelde membrane is bepaal. Die volgende is ook ondersoek vir hul effek op die funksionering van die saamgestelde membrane: hoof-effekte, vierkantseffekte, en interaksie tussen veranderlikes. Die eienskappe van die membrane wat bepaal is, is: deurlatingstempo van suiwer water (DSW), molekulêre massa-afsnypunt (MMAP), skeiding van opgeloste sout en vloed. Deurlating van opgeloste sout data is gebruik om gemiddelde poriegrootte (μp) en standaard afwyking (σp) van die membrane te bepaal. Resultate het getoon dat die PVA-NaB membrane amper dieselfde DSW gehad het as die PES-UF membrane. Die MMAP van die PES-UF membrane het afgeneem van 19,000 tot 13,000 Daltons na behandeling met PVA.

Reverse osmosis (RO) by polymeric membranes is known to be the most successful technology for brackish and seawater desalination processes. For the development of these polymeric RO membranes, two different techniques have been used: The phase inversion method for asymmetric membranes, such as cellulose acetate (CA) membrane and the interfacial polymerization for thin film composite (TFC) membranes. Polyamide composite membranes which are characterized by a thin film supported on a chemically different asymmetric porous membrane have become commercially successful for certain applications, especially for seawater desalination. Although TFC aromatic polyamide membrane has excellent characteristics and performance among other types of RO membranes, it suffers from some drawbacks such as biofouling and fouling caused by chemical foulant such as natural organic matter (NOM). The objective of this work is to present a new concept for the preparation of thin-film-composite (TFC) reverse osmosis (RO) membrane by interfacial polymerization on porous polysulfone (PS) support using novel additives. Hydrophi lic surface modifying macromolecules (LSMM) were synthesized both ex-situ by conventional method (cLSMM), and in-situ within the organic solvent of the TFC system (iLSMM). The effects of these LSMMs on the fouling of the TFC RO membranes used in the desalination processes were studied. Fourier transform infrared (FTIR) results indicated that both cLSMM and iLSMM were present in the active layer of the TFC membranes. Scanning electron microscopy (SEM) micrographs depicted that heterogeneity of the surface increases for TFC membranes compared to the control PS membrane, and that higher concentrations of LSMM provided smoother surface. Atomic force microscope (AFM) characteristic data presented that the surface roughness of the skin surface increases for TFC membranes compared to the control. The RO performance results showed that the addition of the cLSMM significantly decreased the salt rejection of the membrane and slightly reduced the flux, while in the case of the iLSMM, salt rejection was improved but the flux declined at different rates for different iLSMM concentrations. The membrane prepared by the iLSMM exhibited less flux decay over an extended operational period.

碩士
中原大學
化學工程研究所
106
In this study, Polyamide(PA)/cellulose triacetate (CTA) composite nanofiltration membrane were fabricated through interfacial polymerization (IP) by using piperazine (PIP) and trimesoyl chloride (TMC) as monomer to form PA layer on to cellulose triacetate substrate. The effect of IP conditions, such as PIP concentration and TMC concentrations on the properties and performances of prepared membranes were investigated. Moreover, the effects of nanofiltration operation conditions, such as salt and dye type, feed concentration, feed temperature and operating pressure, on the nanofiltration performances were also discussed. In addition, the molecular weight cut-off (MWCO) and chorine resistance of prepared membranes were also tested. The resultant PA/CTA composite membranes were characterized by using attenuated total reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR), field-emission scanning electron microscope (FESEM), atomic force microscope (AFM), water contact angle and Zeta potential analyzer. The results showed that the PA/CTA composite membrane had the best nanofiltration performances when the PIP concentration and TMC concentration was 0.05 wt.% and 0.3 wt.%, respectively. A nanofiltration performances with 179 Lm-2h-1 pure water permeation flux at 6 kg/cm2 and 98% sodium sulfate rejection were obtained through the resultant PA/CTA composite membrane. The salt rejection followed the order of Na2SO4 > MgSO4 > NaCl > MgCl2. The prepared PA/CTA composite membrane in this study is a negatively charged nanofiltration membrane with a molecular weight cut-off of 600 g/mol for negative charge dye and a molecular weight cut-off of 1,600 g/mol for neutral solute polyethylene glycol (PEG). After treatment with 15,000 ppm sodium hypochlorite for 1 hour, the rejection of Brilliant Blue R dye by the prepared membrane is still above 99 %.

碩士
中原大學
化學工程研究所
97
To improve the permeation rate of polyamide (PA) membrane, a series of polyamide thin-film composite (TFC) membranes was prepared via interfacial polymerization of various water-soluble amines (DMDPA, NTEA, DETA) and various acyl chloride monomers (DEMDC, PC, TMC) on the surface of asymmetric cellulose acetate (CA) membranes. The PA/CA composite membranes were applied to the pervaporation separation of aqueous alcohol solutions. Attenuated total reflection infrared spectroscopy (ATR-FTIR), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize the chemical structures and morphologies of the polyamide active layers of the composite membranes. The affinity between the membrane and the feed solution was studied through contact angle measurement. The effects of the chemical structure of the monomers and the interfacial polymerization conditions, such as the monomer concentration of aqueous and organic solutions, the immersion time of aqueous solution, the polymerization time and organic solvents, on the pervaporation performance were investigated. In addition, the effects of the operation conditions of the pervaporation separation process, such as the operating pressure, the composition, the operating temperature, and the kind of the feed solution, on the pervaporation performance were also studied. It was found that the different chemical structures of the monomers, which caused different reactivities and sterical stabilizations, dominated the chemical structures and cross-linking degrees of the polyamide active layers of the composite membranes. The desirable monomers for interfacial polymerization were the amine monomer DETA and the acyl chloride TMC. From this study on the correlation between the chemical structure of polyamide layer and the pervaporation, it was found that the thickness of the polyamide active layer increased, the permeation rate decreased, and the water concentration in the permeate increased with a decrease in the viscosity of the organic solvent. To further understand the variation in the fine-structure of polyamide active layer of the composite membrane prepared via interfacial polymerization using different organic solvents, positron annihilation spectroscopy (PAS) coupled with a variable monoenergy slow positron beam (VMSPB) was utilized to detect the depth profile of the free volume and multilayer structure in the PA/CA composite membrane. The data obtained from PAS experiments were expected to correlate well with the pervaporation performance. It was found that the DETA-TMC/CA thin-film composite membranes prepared by immersing CA into 0.5 wt% aqueous DETA solution for 10s and then contacting it with 0.5 wt% TMC in iso-pentane organic solution for 5s had the best pervaporation performance of 90 wt% aqueous iso-propanol solution at 25 ℃, which was the permeation rate was about 780 g/m2h and the water concentration in the permeate was high than 99 wt%.

碩士
中原大學
化學工程研究所
106
In this study a polyamide (PA)/ polyethersulfone (PES) thin film tubular composite membrane was fabricated for nanofiltration. PES was chosen as the substrate polymer and the membrane formation of substrate was considered. The PA active layer was prepared by interfacial polymerization method and the effect of amine structures on nanofiltration performance were also studied. Finally, the PA layer was modified by post treatment for improve the nanofiltration performance and antifouling performance. Polyvinylpyrrolidone (PVP) was used as the membrane formation additive to improve the morphology and performance of PES substrate. The effect of PVP concentration on the membrane formation mechanism was studied by viscosity test, light transmittance experiment, optical microscopy and FE-SEM. Four kinds of commercial amines, piperazine (PIP),　ethylenediamine (EDA), triethylenetetramine (TETA) and pentaethylenehexamine (PEHA) were used to react with trimesoyl chloride (TMC) to form the PA active layer. The effect of amine monomer structures on the NF performance and morphology of prepared membrane were characterized by ATR-FTIR, XPS, AFM, SEM, Zeta potential and molecular weight cut off. Moreover, the PIP-TMC PA/ PES tubular membrane was modified with glutaraldehyde (GA) and polyethylene glycol (PEG) to improve the NF performance and antifouling performance. The results show that the membrane morphology become more bi-continuous structure as increasing PVP concentration. As added 30% PVP in PES dope solution, the membrane show the maximum pure water flux of 447 LMH under 6 bar. In the four kinds of TFC membranes fabricated with different amine, the PIP-TMC has the highest flux and rejection for sodium sulfonate solution, because it has loosest membrane structure and highest negative surface charge. After the membrane modified with GA and PEG, the flux and rejection for sodium sulfonate solution increase at the same time, due to the increase of membrane crosslinking degree and hydrophilicity.

碩士
中原大學
化學工程研究所
94
In order to improve the permeation rate of polyamide membrane, the polyamide thin-film composite membranes were prepared by interfacial polymerization of various diamines with trimesoyl chloride (TMC) onto the surface of the modified asymmetric polyacrylonitrile (mPAN) membrane for pervaporation separation of aqueous alcohol solution. Effect of diamine types, concentration of aqueous phase and organic phase, immersion time of aqueous phase, polymerization time, and concentration and temperature of feed on the pervaporation performances through polyamide/mPAN composite membranes were investigated. SEM, ATR-FTIR, water contact angle and AFM were used to characterize surface properties and morphologies of the polyamide active layers of the composite membranes. It was found that the structure of the polyamide active layer by interfacial polymerization near the support was denser, and that far away from the support was looser. For the EDA-TMC/mPAN composite membrane, the entire thickness of active layer increases with increasing the concentration of aqueous and organic phases, TMC, and the polymerization time, as resulted in increasing the permeation resistance. When the concentration of TMC solution increased up to 1 wt%, the hydrophilic property of the polyamide active layer increased. It was because that the unreacted -COCl groups of TMC were hydrolyzed to -COOH, as resulted in both highest permeate rate and water concentration in permeate for separation of 90 wt% aqueous isopropanol solution. In addition, it was also found that the increase of isopropanol concentration in feed resulted in decreasing the permeation rate and water concentration in permeate. While the permeation rate and water concentration in permeate increased with increasing the feed solution temperature. The polyamide/mPAN composite membrane prepared by immersing in 5 wt% aqueous EDA solution for 30min, and then contacting with 1 wt% TMC for 3min have the best pervaporation performance. For pervaporation separation of 90 wt% aqueous isopropanol solution at 70℃, that is, the permeation rate and water concentration in permeate are 350 g/m2-h and 96.5 wt% respectively.

碩士
中原大學
化學工程研究所
99
To improve the pervaporation performance of polyamide membrane, a series of polyamide composite membranes were prepared by the interfacial polymerization of various diamine monomers (BATO,BAE and DOA) and acyl chloride monomers (tNDBC,　TPC and TMC) onto the surface of the asymmetric modified polyacrylonitrile (mPAN) membrane. These composite membrames were applied in the pervaporation separation of the aqueous tetrahydrofuran (THF) solution. Attenuated total reflection infrared spectroscopy (ATR-FTIR) and x-ray photoelectron spectroscopy (XPS) were used to characterize the chemical structures and compositions of the interfacially-polymerized layers of the composite membranes. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the surface and cross-sectional morphologies of the polyamide composite membranes. Further, the variable monoerergy slow positron beam (VMSPB) analyzer was used to examine the variations in the fine-structure in the different layer through the polyamide composite membrane. The data obtained from VMSPB analysis were expected to correlate well with the pervaporation performance It was found the different chemical structures of the monomers, which caused different sterical stabilizations, leaded to the difference in the reactivities between the monomers and the variation in the chemical structures of the polyamide active layers, in addition, the special functional groups in the molecular chain of the monomer also could influence the chemical structures and the chemical properties of the polyamide active layers. From the result of the VMSPB measurement, the composite membranes, which owned the different chemical structures in their polyamide active layers, had the variations in the free volume in the different layers through the polyamide composite membrane. The above results that we mentioned were highly consistent with the pervaporation performance. The effects of the hydrolysis time of the support membrane, the chemical structure of the monomer and the interfacial polymerization conditions, such as the monomer concentration of aqueous and organic solutions, the immersion time of aqueous diamine solution, the polymerization time, on the pervaporation performance were investigated. From the results of the pervaporation separation experiments, The most desirable conditions for the preparation of a polyamide composite membrane are as follows: The mPAN which is hydrolyzed using a 2M NaOH solution for 10 min is used as a support membrane. This support membrane is immersed in a 2 wt% aqueous BAE solution for 3 min. And then this membrane is contacted with a 1 wt% organic solution for 30 sec to carry out the interfacial polymerization. The resulting membrane is obtained and has the most desirable pervaporation performance of a 90 wt% aqueous THF solution, which is a permeation rate of about 1399 g/m2h and a water concentration in permeate higher than 99 wt%.

This research was undertaken to improve the understanding of structure-property-performance relationships in crosslinked polyamide (PA) thin-film composite (TFC) membranes as characterized by liquid and gas permeation studies. The ultrathin PA selective layer formed by interfacial polymerization between meta-phenylene diamine and trimesoyl chloride was confirmed to contain dense polymer matrix regions and defective regions in both dry and hydrated states. The first part of this research studied the effect of non-selective convection through defective regions on water flux and solute flux in pressure-assisted forward osmosis (PAFO). Through systematic comparison with cellulose triacetate (CTA) and PEBAX-coated PA-TFC membranes, the existence of defects in pristine, hydrated PA-TFC membranes was verified, and their effects were quantified by experimental and modeling methods. In the membrane orientation of selective layer facing the draw solution, water flux increases of up to 10-fold were observed to result from application of low hydraulic pressure (1.25 bar). Convective water flux through the defects was low (< 1% of total water flux for PA-TFC membranes) and of little consequence in practical FO or reverse osmosis (RO) applications. However, it effectively mitigated the concentration polarization in PAFO and therefore greatly increased the diffusive flux through the dense regions. The second part of this research characterized the structures of the PA material and the PA selective layer by gas adsorption and gas permeation measurements. Gas adsorption isotherms (N2 at 77K, CO2 at 273K) confirmed the microporous nature of PA in comparison with dense CTA and polysulfone materials. Gas permeation through the commercial PA-TFC membranes tested occurred primarily in the defective regions, resulting in Knudsen gas selectivity for various gas pairs. Applying a Nafion coating layer effectively plugged the defects and allowed gas permeation through the dense PA regions, which significantly decreased gas permeance and increased gas selectivity. Specifically, high He and H2 selectivity against CO2 suggests the potential applications of this membrane in He recovery and CO2 capture in pre-combustion. Finally, the dense PA matrix was modified with two types of novel nanofiller to improve desalination performance in RO. A series of dense, nano-sized (1-3 nm) polyhedral oligomeric silsesquioxanes (POSS) with different functional groups were systematically incorporated into the PA matrix by physical blending or chemical fixation. The free volume of the PA matrix increased with addition of POSS, leading to water flux increases of up to 67 %, while maintaining high NaCl rejections. The effects of adding microporous, hydrophobic zeolitic imidazolate framework-8 (ZIF-8) nanoparticles into PA are presented in the last chapter. A 162 % water flux increase was achieved without decreasing NaCl rejection. This interesting result can be attributed to a less crosslinked PA structure and to the intrinsic desalination properties of ZIF-8.

博士
中原大學
化學工程研究所
99
In this research, a polyamide composite membrane was fabricated, and its free volume size and distribution and variation in the multilayer structure and chemical composition were probed using a variable monoenergy slow positron beam (VMSPB) to understand the relationship between the membrane separation performance and free volume. The experimental plan for this research is divided into four parts: (1) solving the charging effect in an insulating composite membrane during positron annihilation spectroscopic (PAS) experiments to improve the measurement sensitivity and efficiency; (2) verifying the membrane growth direction by means of positron annihilation spectroscopy from the point of view of free volume; (3) developing a positron analytical technique that can measure a membrane maintained in the wet condition by means of the membrane’s protective layer of SiOxCyHz on the vacuum side; and (4) setting up a two-dimensional age-momentum correlation (2D-AMOC) technique that can separate momentum spectroscopy from the original one-dimensional positron annihilation lifetime spectroscopy and that can quantitatively obtain the relationship between chemical composition and free volume variation at each layer in a composite membrane by means of the relationship between momentum and annihilation lifetime based on conducting an annihilation lifetime analysis for a specific momentum range (3 or 2 annihilation). The data obtained from the first part of the experimental plan indicated that use of the platinum sputtering technique resulted in a uniform deposition of platinum particles on the insulating polymeric membrane surface. An extremely thin layer (~ 1 nm) of deposited platinum could effectively remove the charging effect associated with the accumulation of positron in the membrane surface, leading to uninterrupted measurements using a VMSPB operating at high vacuum conditions. In the second part of the experiments considered in this research, positron annihilation spectroscopy, based on the concept of free volume, was used to verifying the membrane growth direction of the interfacially polymerized polyamide layer that began to form the moment the organic and aqueous phases contacted each other. This selective layer, once formed, would hinder the diffusion of the aqueous monomer solution toward the organic phase. Hence, over time, the structure of the polyamide layer formed tended to become loose. When the polyamide composite membrane was applied for the pervaporation separation of an aqueous alcohol solution, the permeate water concentration was shown to increase with the polyamide layer thickness. The pervaporation performance and the change in the structure of the composite membrane were correlated with the findings from the positron annihilation spectral analysis. The third part of this research experimental plan is about devising means to maintain a membrane in the wet condition, despite the operation of a VMSPB at a high vacuum (10-8 torr). The challenge of using a VMSPB to measure the correct free volume in a composite membrane wetted by a feed solution was addressed by integrating a plasma deposition technique, with which a protective SiOxCyHz layer was deposited on the surface of a polyamide composite membrane. Such a nondestructive way enabled simulating the condition of a pervaporation membrane kept in direct contact with a liquid environment, thereby making it possible to measure the free volume in the different layers of a composite membrane in the wet state. Results indicated that different feed solutions had varying degrees of swelling effect, and the extent of the membrane swelling due to the feed solution was demonstrated to be in the following order: isopropanol ＞ 70 wt% isopropanol/water solution ＞ water. Compared to a modified polyacrylonitrile (mPAN) substrate, the polyamide layer was found to be comparatively denser and less swollen. The fourth and last part of experiments for this research was conducted to obtain data by means of the 2D-AMOC technique developed to define the relationship between momentum and ortho-positronium (o-Ps) annihilation lifetime, which was determined by doing an annihilation lifetime analysis for a specific momentum range. The free volume radius in the polyamide layer was found to be 2.1-3.4 Å and in the nano-scale range of 36-196 Å in the region after the polyamide layer. Combined with transmission electron microscopy (TEM), findings indicated that the polyamide layer was shown to be composed of a continuous dense structure and that the region after the polyamide layer was descriptive of a discontinuous nano-scale hole structure. A two-detector coincidence Doppler broadening of annihilation radiation (2D-DBAR) was used to investigate the effect of the chemical composition of each layer in the composite membrane on the free volume. This research would provide a complete understanding of the microstructure variation in an ultrathin composite membrane. In regard to the membrane pervaporation performance, this research would also provide an understanding of the principle of pervaporation rate and the mechanism of pervaporation separation transport. Both of this understanding would then furnish significant information about the areas of membrane structure design and membrane performance prediction.

碩士
中原大學
化學工程研究所
98
To improve the permeation rate of polyamide (PA) membrane, a series of polyamide thin-film composite (TFC) membranes was prepared via interfacial polymerization of various water-soluble amine monomers (HA, DAPE and DAPL) and various acyl chloride monomers (SCC and tNBDC) on the surface of asymmetric modified polyacrylonitrile (mPAN) membranes. The PA/mPAN composite membranes were applied to the pervaporation separation of aqueous alcohol solutions. Attenuated total reflection infrared spectroscopy (ATR-FTIR), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize the chemical structures and morphologies of the polyamide active layers of the composite membranes. The water contact angle measurement and the atomic force microscopy (AFM) were used to characterize the surface hydrophilicity and surface roughness of the composite membranes. The effect of the chemical structure of the monomers and the interfacial polymerization conditions, such as the monomer concentration of aqueous and organic solutions, the immersion time of aqueous solution, the polymerization time on the pervaporation performance were investigated. In addition, the influences of the membrane swelling on the changes of membrane fine-structure and pervaporation performance were systematically analyzed by positron annihilation spectroscopy (PAS) and molecular dynamics (MD) simulation. From the result of PAS analysis, the swollen polyamide active layer showed a large o-Ps lifetime than the dry active layer, and the PAS analysis at wet state was consistent with the pervaporation performance of the polyamide TFC membranes. The theoretical analysis by the MD simulation technique was showed that the side chain fluctuation of tNBDC would be improved more obviously than that in the SCC membrane after swollen, which led to from the more effective free volume in the wet tNBDC membrane. It was found that the DAPL-SCC/mPAN thin-film composite membranes prepared by immersing mPAN into 0.1 wt% aqueous DAPL solution for 60 sec and then contacting it with 0.5 wt% SCC in toluene organic solution for 15 sec showed the best pervaporation performance of 90 wt% ethanol aqueous solution at 25oC, the permeation rate was about 590 g/m2h and the water concentration in permeate was about 96.7 wt%.

Reverse osmosis (RO) is considered as the most widely utilized technique worldwide for water treatment. However, the commercial thin-film composite (TFC) membranes, which are normally made of polyamide (PA) through interfacial polymerization (IP), still experience certain major issues in performance and fabrication. The spin assisted layer-by-layer (SA-LbL) technique was established for overcoming some drawbacks with commercially available PA membranes. Also, recent investigations have recognized the nanoparticle inclusion into the selective layer as a powerful technique for improving the membrane efficiency. Hence, two different methodologies are presented here to improve the membrane performance, i.e., (1) SA-LbL technique to fabricate TFC membrane by the deposition of alternate ultrathin layers of different polyelectrolytes on polysulfone (PSF) commercial ultrafiltration membrane and (2) the nanoclay incorporation into the membranes during IP process to develop TFC membrane. Two types of nanoclays, cloisite (CS)-15A and montmorillonite (MNT), were incorporated to enhance the separation efficiency. This SA-LbL is an innovative method for the RO membrane manufacture, and has not been described earlier to the best of our knowledge. In addition, this work validated for the first time, the efficiency of the two nanoclays at the PA selective layer in the RO membrane. The membrane performance was evaluated using sodium chloride solution in a cross-flow permeation-testing cell for salt rejection and water flux. The results show significant improvement in water flux and salt rejection. The permeation test of 120 bilayers of poly (allylaminehydrochloride)/poly (vinylsulfate) on PSF substrate showed water flux of 37 L/ (m2.h) and salt rejection of 53%, for a 2000-ppm salt solution feed. The highest water flux of 40 L/m2.h with 80% salt rejection, relative to the control membrane was obtained for the membranes containing nanoclays at 25oC temperature, 40.0 bar pressure and 2000 ppm feed concentration. Thus, our study demonstrated that these TFC membranes are promising, and these novel fabrication techniques are great tool to manufacture the RO membrane.