Liquid–liquid Displacement Porosimetry Research Articles

Study of novel Zn-MOF-II modified polymeric membrane in wastewater treatment containing oily waste and humic acid (NOM)

ABSTRACT The prime objective of the present work was to synthesise the polymeric membrane with Zn-MOF-II nanoparticles using the phase inversion method to purify oily wastewater and NOM. The dead-end filtration system was utilised to analyse the performance of fabricated membranes (without and with Zn-MOF-II), various feeds of 100 ppm concentration used, such as organic pollutants and oil effluent at 250 kPa and atmospheric temperature conditions. The following study involves the compaction factor, pure water flux, all mixed matrix membrane permeability, humic acid rejection, and oil–water emulsion rejection, contact angle, and liquid–liquid displacement porosimetry (LLDP). Scanning electron microscopy (SEM) and Fourier transforms infrared spectroscopy-attenuated total reflection (FTIR-ATR) goniometer were used to characterise the polymeric membranes. The FTIR-ATR spectra of the modified membrane exhibit a characteristic peak between 2,900 and 3,000 cm−1 associated with the presence of the –COOH group. The nanoparticles and polymer matrix were well compatible, as evidenced by SEM images of the polymeric membrane containing Zn-MOF-II nanoparticles. The maximum value of percentage rejection of oily wastewater (above 88.89%) and humic acid (above 86.88%) was obtained for the polymeric membrane containing Zn-MOF-II nanoparticles.

Automated Liquid-Liquid Displacement Porometry (LLDP) for the Non-Destructive Characterization of Ultrapure Water Purification Filtration Devices.

This scientific publication presents a novel modification of the liquid-liquid displacement porosimetry (LLDP) method, aiming for the non-destructive automated analysis of water purification membrane filtration devices in the microfiltration (MF) and ultrafiltration (UF) range. The technical adaptation of LLDP enables the direct in-line porosimetric analysis of commercial filtration devices, avoiding the filtration devices' destruction. Six commercially available filtration devices with polyethersulfone (PES) and polysulfone (PS) membranes were studied using an improved device developed by the IFTS, which was based on a commercial LLDP instrument. The filtration devices were evaluated in three different configurations: flat disks, hollow fibers, and pleated membranes. The results obtained using the proposed method were compared with other characterization techniques, including submicronic efficiency retention, image analysis of scanning electron microscopy (SEM), and gas-liquid displacement porosimetry (GLDP). The comparison of the results demonstrated that the proposed method accurately determined the porosimetric characteristics of the filters. It proved to be a precise technique for the non-destructive in-line evaluation of filter performance, as well as for periodic quality control and the fouling degree assessment of commercial filtration devices. This modified LLDP approach offers significant potential for the advanced characterization and quality assessment of water purification membrane filtration devices, contributing to improved understanding and optimization of their performance.

Creation of highly stable porous polyacrylonitrile membranes using infrared heating

Highly stable porous membranes made of commercial polyacrylonitrile (PAN) were developed for high pressure application in aprotic solvents. The membranes prepared by NIPS method from the casting solution with PAN concentration of 15 or 18 wt% in DMSO demonstrated good mechanical stability towards the transmembrane pressure of 30 bar and MWCO of 22 and 14.5 kg/mol, respectively; whereas the lower polymer concentration (12 wt%) led to collapsing of porous structure based on SEM data. By adjustment of treatment time and temperature, it was shown that the porous PAN membranes became insoluble in aprotic solvents such as DMSO, DMF, DMAc, and NMP after 5 min of infrared heating at 170 °C. The analysis of the data obtained by SEM, liquid-liquid displacement porosimetry, solvent filtration, and MWCO revealed that such IR treatment did not noticeably change the membrane structure and properties originally formed during the membrane casting. Replacement of conventional heating reported in the literature by IR heating allowed to reduce the treatment time from 6 h at 250 °C down to 5 min at 170 °C (estimated energy saving by a factor of 6.5). The mechanism of the transformation of PAN into insoluble form was proposed based on the data of FTIR analysis. The hypothesized role of adsorbed water molecules in accelerating cross-linking of PAN upon the near-IR heating was considered and discussed. IR treated PAN membranes can be employed as porous supports for solvent resistant nanofiltration membranes or directly as ultrafiltration membranes for non-aqueous applications.

Non-Destructive Characterization of Industrial Membrane Cartridges by Using Liquid-Liquid Displacement Porosimetry (LLDP).

This works aims to propose and demonstrate the accuracy of a novel method of characterization aimed for non-destructive analysis of microfiltration (MF) membrane cartridges. The method adapts conventional liquid–liquid displacement porosimetry (LLDP) for performing an in-line porosimetric analysis of the membrane cartridges, getting their pore size distributions (PSDs) and mean pore diameters (davg). Six commercial filtration cartridges featuring polyethersulfone (PES) pleated membranes were analyzed using a newly designed filtration rig, based on the liquid–liquid displacement porometer, developed at the Institut de la Filtration et des Techniques Séparatives (IFTS) and operated at constant flow. The experimental rig allows the direct and non-destructive characterization of the cartridge in its original presentation. Results have been compared with those obtained by using gas–liquid displacement porosimetry (GLDP) on small membrane coupons detached from such cartridges. The comparison allows us to conclude that the proposed method gives enough accuracy in the determination of porosimetric characteristics of the filters. This method can be used as a precise characterization technique for a non-destructive in-line study of filter performance and can be envisaged as useful to periodic quality or fouling control of the commercial cartridges.

Preparation and optimization of antifouling PPSU/PES/SiO2 nanocomposite ultrafiltration membranes by VIPS-NIPS technique

In this paper, the preparation of PPSU/PES/Nano silica composite ultrafiltration membranes by a combined vapor induced phase separation (VIPS) and non-solvent induced phase separation (NIPS) techniques were successfully investigated. For this purpose, the effect of VIPS time from 0 to 60s, the blending ratio of PPSU:PES from 0 to 100%, polymer concentration from 16 to 24wt.%, and SiO2 nanoparticles concentration from 0 to 5wt.% as an additive to dope solution on the performance and characteristics of ultrafiltration membranes were studied. As the number of parameters is high, the response surface methodology (RSM) was applied for designing the experiments for obtaining the optimum condition for the fabrication of a high flux ultrafiltration membrane. Liquid-liquid displacement porosimetry (LLDP), scanning electron microscope (SEM), pure water flux (PWF), and bovine serum albumin (BSA) retention were used for characterization of the fabricated membranes. The results are shown different trends for the effect of SiO2 nanoparticles concentration at the low and high polymer concentrations in dope solution. When the polymer concentration in the dope solution is low, the increase of SiO2 nanoparticles concentration resulted in lower fluxes, but at high polymer concentrations, the increase of the nanoparticles caused an increase in permeate flux. At optimum condition, the highest PWF of 76.65L/m².h (15.33L/m².h.bar), and a BSA retention of 82.01% was obtained.

Membrane characterization via evapoporometry (EP) and liquid-liquid displacement porosimetry (LLDP) techniques

To comparatively assess the Evapoporometry (EP) technique vis-à-vis the Liquid-Liquid Displacement Porosimetry (LLDP) technique, the pore size distributions, mean pore diameters (davg) and porosities of five polymeric (namely, nylon, PES, PTFE, PET and PVDF) and one inorganic (namely, alumina) UF/tight MF membranes were quantified by both techniques. For all the membranes, the pore size ranges were generally narrower and the pore size distributions had distinctive peaks for the LLDP technique. For the nylon, PES and PTFE membranes, the davg values obtained from the two techniques agreed well. However, for the PET and PVDF membranes, the differences were twofold due to the higher pressure needed for the LLDP tests. Specifically, for PET, the davg value obtained via EP was half that via LLDP, because the higher pressure compacted the lower mechanical strength polymer, leading to pore closure. On the other hand, for PVDF, due to the rubber nature, the higher pressure caused the pores to be stretched, leading to larger pores. As for the alumina membrane, because of the more ideal cylindrical pores, the d4-weighting of the LLDP measurement gave a greater davg value than that of the d2-weighting of the EP measurement. Also, porosity measurements were erroneous for LLDP if the active layer cannot be precisely quantified. With respect to MWCO, while EP does not explicitly quantify this, the LLDP generally over-estimated the values, because of the errors associated with the measurement of the first (largest) pores at the lowest pressures.

Preparation and characterization of an antifouling poly (phenyl sulfone) ultrafiltration membrane by vapor-induced phase separation technique

In this paper, anti-fouling poly (phenyl sulfone) ultrafiltration membranes were fabricated through the NIPS (V-0) and VIPS-NIPS (V-15 through V-60) technique. The effect of VIPS conditions on the structure and performance of the membranes has been investigated. Scanning electron microscopy (SEM) and liquid–liquid displacement porosimetry (LLDP) methods were used for membrane characterization. Pure water flux and BSA retention were also used for evaluation of separation performance of the fabricated membranes. The results revealed that by increasing VIPS time, pore size and permeate flux of the membranes were both increased except for V-30 membrane where both the pore size and PWF were decreased. BSA retention has an opposite behavior. By increasing VIPS time from 0 to 15 s, the PWF increased from 17.12 to 20.79 L/m2.h. At a VIPS time of 30 s, PWF reduced to 15.60 L/m2.h, and by further increase of VIPS time to 60 s, the flux increased to 37.69 L/m2.h. BSA retention showed a closer dependency to pore size of the membranes i.e. it decreased from 71.32% to 55.68% by increasing VIPS time from 0 to 15 s, then increased to 63.27% for V-30 membrane, and finally decreased to 52.69% at a VIPS of 60 s. It is noteworthy that the increase of VIPS time from 0 to 15 s leads to an increase in mean pore radius from 0.96 to 1.44 nm and then a decreases to 1.04 nm for a VIPS time of 30 s and finally to 1.39 nm with an increase of VIPS time to 60 s.

Mitigation of HA, BSA and oil/water emulsion fouling of PVDF Ultrafiltration Membranes by SiO2-g-PEGMA nanoparticles

In this work antifouling poly(vinylidene fluoride) (PVDF) ultrafiltration membranes were synthesized with direct blending of Poly(ethylene glycol) methyl ether methacrylate (PEGMA)-grafted SiO2 (SiO2-g-PEGMA) nanoparticles (NPs) in the casting solution by phase inversion method. Chemical structure of the SiO2-g-PEGMA NPs was analyzed by Fourier transform infrared (FTIR) spectroscopy. Effect of different wt.% of SiO2-g-PEGMA NPs on the structure and performance of prepared membranes were examined by Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy, Field emission scanning electron microscope (FESEM), Liquid–liquid displacement porosimetry (LLDP), pure water flux (PWF), hydraulic permeability, solute rejection study, water contact angle, water uptake, porosity and bovine serum albumin (BSA) adsorption. Modified membranes have higher solute rejection than plain PVDF membrane. Also, modified membrane with 0.5 wt% of SiO2-g-PEGMA NPs showed enhanced porosity, pore density, pore area, PWF and permeability. Water contact angle and amount of adsorbed BSA for the modified membrane with 1 wt.% of SiO2-g-PEGMA NPs were 50.7° and 0.05 mg/cm2 compared to 68.7° and 0.17 mg/cm2 respectively, for the plain membrane. Furthermore, antifouling property and rejection performance of modified PVDF membranes were investigated by humic acid (HA), BSA and oil-in-water (o/w) emulsion ultrafiltration experiment. It was observed from ultrafiltration study that the irreversible fouling and total fouling were decreased and achieved high flux recovery ratio for modified membrane.

Comparison of pore size distributions from dextran retention tests and liquid-liquid displacement porosimetry

Polyethersulfone (PES) UF retentive membranes developed to be used for virus retention have been characterized by dextran retention and liquid-liquid displacement porosimetry (LLDP). Results have been used to obtain the pore size distributions (PSD) of such membranes from both techniques.The comparison of pore size distributions obtained from both techniques suggests that PSD strongly correlates with retention capabilities and performance of the membrane, being LLDP a fast and reliable way to estimate MWCO of the analysed membranes. The method used here can be standardised to make it an accurate and convenient way to asses' possible applications for a given filter.

Effect of Polyethylene glycol methyl ether blend Humic acid on poly (vinylidene fluoride-co-hexafluropropylene) PVDF-HFP membranes: pH responsiveness and antifouling behavior with optimization approach

Flat sheet asymmetric membranes were fabricated with homogeneous solution of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) using N-methyl-2-pyrrolidone (NMP) as solvent via phase inversion method. PEGME (Poly ethylene glycol methyl ether) (Mn 5000) blend Humic Acid (HA), of different mole ratio was used as additive. Characterization of the membranes was done by Field emission scanning electron microscope (FESEM), Fourier Transform Infrared (FTIR) spectroscopy, Atomic force microscopy (AFM) and Differential scanning calorimetry (DSC) studies. Liquid-liquid displacement porosimetry (LLDP) study evaluated the morphological parameters, average pore size and pore size distribution. Bovine serum albumin (BSA) (MW - 68,000 Da) was used to study the antifouling effect and pore blocking mechanism of the membranes. The pure water flux (PWF), solute rejection and flux recovery ratio drastically increases for the PEGME blended HA membranes whereas the water contact angle decreases significantly. The pH responsiveness character of the prepared membranes altered the hydraulic permeability and rejection % at different pH. Finally, optimization of the variables contributing towards the PWF and BSA rejection of the desired membrane was performed using Design expert software 9.0 TRIAL through ANOVA (analysis of variance) using the combination of response surface methodology (RSM) and central composite design (CCD).

Porosimetric characterization of polysulfone ultrafiltration membranes by image analysis and liquid–liquid displacement technique

Structural and surface properties of two commercial polysulfone ultrafiltration membranes have been evaluated by different techniques. Pore size distributions have been determined by Liquid–Liquid Displacement Porosimetry (LLDP) as well as by image analysis performed onto Field Emission Scanning Electron Microscopy (FESEM) images of the membrane surfaces. Fourier Transform Infrared Spectroscopy (FTIR) has been used to investigate membrane composition, and in particular, to obtain proper information on the presence of an additive within the membrane structure.Porosimetric results obtained by the two independent techniques compared reasonably well and the Molecular Weight Cut Off (MWCO) of the two membranes estimated from LLDP pore size distribution was found to be in good agreement with the nominal values given by manufacturers.

Fitting approach to liquid–liquid displacement porosimetry based on the log-normal pore size distribution

Liquid–liquid displacement porosimetry (LLDP) has been used to characterize several UF membranes in a wide range of molecular weight cut-offs (MWCO). A new method to convert porosimetric data into pore size distributions and related information has been developed based on assuming log-normal pore size distributions. The results of this are in good agreement with those from the customary data conversion algorithm (as derived by Grabar and Nikitine). The proposed method can also be used when a reduced number of experimental data points is available, leading to a significant reduction of data acquisition time needed to complete a reliable analysis.

Increase in hydrophilicity of polysulfone membrane using polyethylene glycol methyl ether

Flat sheet asymmetric polymeric membranes were prepared from homogeneous solution of polysulfone (PSF) by the phase inversion method using N-methyl-2-pyrrolidone (NMP) as solvents. Polyethylene glycol methyl ether (PEGME) of three different molecular weights (550Da, 2000Da and 5000Da) was used as the polymeric additive in the casting solution. The morphology and structure of the resulting membranes were observed by field emission scanning electron microscope (FESEM). The pore number, pore permeability and their distribution and average pore size of the membranes were determined by the liquid–liquid displacement porosimetry (LLDP) method. The permeation performances of the membranes were evaluated in terms of pure water flux (PWF), hydraulic permeability, and solute rejection, while hydrophilicity was evaluated in terms of porosity, equilibrium water content (EWC) and water contact angle. Solution of bovine serum albumin (BSA) of molecular weight 68,000Da was used to study the permeation performance of prepared membranes using a batch membrane cell of 350mL capacity. Results showed that with increase in molecular weight of PEGME, the pore number as well as pore area in membranes increased. Membranes with PEGME of higher molecular weights have higher PWF and higher hydraulic permeability due to high porosity. With increase in molecular weight of PEGME from 550 to 5000, the PWF increased from 17.5 to 227.8Lm−2h−1. Similarly, EWC increased from 59.7% for PEGME 550 to 70.8% for PEGME 5000 membranes. Contact angle was also decreased from 71° for PEGME 550 to 47° for PEGME 5000.

Liquid–liquid displacement porosimetry for the characterization of virus retentive membranes

Parvovirus retentive membranes made from polyethersulfone (PES) have been characterized by different techniques including dextran and phage retention. Results have been correlated with the pore size distributions of such membranes as obtained by liquid–liquid displacement porosimetry (LLDP). The results of LLDP concerning pore size distributions are proved to be consistent with those obtained by image analysis of SEM transversal sections and refer to the narrower pore section. Moreover, the maximum pore size determined by LLDP fairly correlates with the measured retention capabilities of the membranes. LLDP results suggest that the technique can be an accurate method for the determination of pore size characteristics of virus retentive membranes. This technique can be simplified to be even faster and straightforward by detecting only the maximum pore size of the membrane.

Characterisation of polymeric UF membranes by liquid–liquid displacement porosimetry

Two series of commercial polymeric (regenerated cellulose and polyethersulfone) membranes made by Millipore ® have been characterized, obtaining their pore size distribution by liquid–liquid displacement porosimetry (LLDP). A fully automated porosimeter designed by us has been used in the determination of pore size distributions. Results show a good accuracy and reproducibility of LLDP measurements. Binary and ternary liquid mixtures have been used to wet and penetrate into the membrane pores when performing LLDP leading to quite similar results when an effective surface tension is assigned for the ternary mixture. The use of different liquid mixtures and soaking conditions allowed to assure a proper wetting of the membrane pores without damaging the membrane structure during the analysis.

Analysis of cleaning protocols in ceramic membranes by liquid–liquid displacement porosimetry

Membrane technology has experienced an important development in the last years, being more and more employed as an alternative to conventional separation processes. However, the investment due to purchase and replacement of membranes in industrial plants is still a very significant cost. Therefore, it is necessary to analyze the variables that determine the operating lifetime of the membranes. In this research work, the structural changes that take place in ceramic membranes as a consequence of chemical cleaning were evaluated. As a case study, milk ultrafiltration process was selected since this is a typical and well-established application in the food industry, in particular, in cheese making. Three cleaning protocols with increasing aggressiveness were tested, namely basic, basic plus acid and basic plus acid plus disinfectant. At the end of the operational cycles, the changes in permeability, pore distribution and mean pore radius occurred in the membrane active layer for each protocol were analyzed by liquid–liquid displacement porosimetry (LLDP). The results obtained indicate that the membrane after alkaline + acid + oxidant cleaning presented a total number of pores and porosity values higher than the others, while the cleaning protocol less effective was the alkaline one.

Pore size distribution of ceramic UF membranes by liquid–liquid displacement porosimetry

Commercial ceramic tubular membranes made by Tami ® have been characterized by several techniques. Their pore size distributions (PSD) have been obtained by liquid–liquid displacement porosimetry (LLDP). Computerized image analysis (CIA) of SEM pictures has been used to get information on the width of the active layer of the studied membranes. These values of thickness have helped to evaluate the porosity of the membranes and to get representative radii from measurements of the permeability to several gases and liquids. A fully automated porosimeter designed by us has been used in the determination of pore size distributions. Results show a good accuracy and reproducibility of LLDP measurements. Binary and ternary liquid mixtures have been used to wet and penetrate into the membrane pores when performing LLDP leading to quite similar results when an effective surface tension is assigned for the ternary mixture. This procedure can be used to calibrate the technique to be extended to thick ultrafiltration and even to nanofiltration membranes.

Comparison of liquid–liquid displacement porosimetry and scanning electron microscopy image analysis to characterise ultrafiltration track-etched membranes

Liquid–liquid displacement porosimetry (LLDP) has been used to analyse very regular track-etched polymeric membranes in the ultrafiltration (UF) range, with a nominal pore diameter of 50 nm. A fully automated porosimeter has been used in the evaluation of pore size distributions and results have been compared with image analysis performed on scanning electron micrographs (SEM–CIA) of the membranes. Comparison gives a nice agreement between both results (mean pore radius of 23.6 nm for LLDP results and 24.0 nm for SEM–CIA performed on the same samples used for LLDP). A not so satisfactory agreement is obtained for other indirectly evaluated parameters as porosity (means of 1.4 and 2.1%) or the mean total number of pores (19.6×10 12 pores/m 2, from LLDP and 11.1×10 12 pores/m 2 for SEM–CIA). These results show that LLDP measurements have good accuracy and reproducibility and that the analysing fluid mixtures used do not significantly modify neither the chemical nature nor the structure of the membrane material used. Of course, ulterior research should be made in order to elucidate the influence of solvents and other parameters of the LLDP analysis. Membranes so regular as track-etched UF ones could be used as appropriate standards to refine the technical parameters for LLDP.