Hydrophobic Hollow Fiber Membrane Research Articles

Atmospheric water harvesting by osmotic distillation and direct contact membrane distillation using hydrophobic hollow fiber membranes

The use of a liquid desiccant air dehumidifier is an energy-efficient technology that can improve both indoor air temperature and humidity. However, the risk of concentrated liquid desiccant leakage into the air conditioning system during dehumidification can corrode the system, negatively impact indoor air quality, and potentially harm residents. To address this issue, this study investigates the effectiveness of osmotic distillation (OD) and direct contact membrane distillation (DCMD) for dehumidification and regeneration, respectively. The study analyzes the impact of inlet operating parameters, including liquid desiccant concentration, temperature, and flow rate, and air flow rate on the dehumidification performance and stability of the OD process. Calcium chloride was utilized as the liquid desiccant in this study. The results indicated that the dehumidification performance of the OD process improved with a higher desiccant concentration and lower desiccant temperature. However, the desiccant flow rate did not have a significant impact on dehumidification performance. Furthermore, the dehumidification performance decreased with a higher inlet air flow rate, but the moisture removal rate increased. The OD process demonstrated stable operation during the dehumidification process. DCMD was effective for desiccant regeneration, and no scaling occurred due to the deposition of calcium chloride crystals. However, the permeation flux of DCMD decreased as the feed concentration increased due to a decline in the feed vapour pressure and an increase in concentration polarization effect. In conclusion, the experimental results indicated that OD can effectively dehumidify humid air, while DCMD is a viable option for desiccant regeneration.

PVDF hydrophobic hollow fiber membrane modules for partial dealcoholization of red wine by osmotic distillation as a strategy to minimize the loss of aromas

Tempranillo red wines were partially dealcoholized (−3 v/v%) by osmotic distillation (OD) with membranes. First, polypropylene (PP) Liqui-Cel3M (3M) hollow fiber membrane modules were applied at 11 and 15 °C to study the effect of the removal of ethanol on the aroma of a certain wine. The influence of both temperatures was evaluated in terms of ethanol flux and aroma losses. Afterwards, two additional wines with different compositions were dealcoholized. The impact of the initial concentration of aromas on achieving a final product with an appealing aroma profile was studied, displaying the three wines a comparable aroma retention. Membrane OD was carried out with two additional hollow fiber membrane modules: another PP module (Zena) with a higher pore size, and a superhydrophobic PVDF module (Polymem). The latter gave rise to a partial dealcoholized wine with an aroma profile very similar to that of the pristine wine.

Iron Control in Liquid Effluents: Pseudo-Emulsion Based Hollow Fiber Membrane with Strip Dispersion Technology with Pseudo-Protic Ionic Liquid (RNH3+HSO4-) as Mobile Carrier.

The transport of iron(III) from aqueous solutions through pseudo-emulsion-based hollow fiber with strip dispersion (PEHFSD) was investigated using a microporous hydrophobic hollow fiber membrane module. The pseudo-protic ionic liquid RNH3HSO4- dissolved in Solvesso 100 was used as the carrier phase. This pseudo-protic ionic liquid was generated by the reaction of the primary amine Primene JMT (RNH2) with sulphuric acid. The aqueous feed phase (3000 cm3) containing iron(III) was passed through the tube side of the fiber, and the pseudo-emulsion phase of the carrier phase (400 cm3) and sulphuric acid (400 cm3) were circulated through the shell side in counter-current operational mode, using a single hollow fiber module for non-dispersive extraction and stripping. In the operation, the stripping solution (sulphuric acid) was dispersed into the organic membrane phase in a tank with a mixing arrangement (a four-blade impeller stirrer) designed to provide strip dispersion. This dispersed phase was continuously circulated from the tank to the membrane module in order to provide a constant supply of the organic solution to the fiber pores. Different hydrodynamic and chemical parameters, such as feed (75-400 cm3/min) and pseudo-emulsion phases (50-100 cm3/min) flows, sulphuric acid concentration in the feed and stripping phases (0.01-0.5 M and 0.5-3 M, respectively), metal concentration (0.01-1 g/L) in the feed phase, and PPILL concentration (0.027-0.81 M) in the carrier phase, were investigated. From the experimental data, different diffusional parameters were estimated, concluding that the resistance due to the feed phase was not the rate-controlling step of the overall iron(III) transport process. It was possible to concentrate iron(III) in the strip phase using this smart PEHFSD technology.

Valorization and Potential Antimicrobial Use of Olive Mill Wastewater (OMW) from Italian Olive Oil Production.

The production of olive oil generates olive mill wastewater (OMW) which essentially derives from the processing, treatment and pressing of olives in mills. Traditional milling processes require a quantity of water varying between 40 and 120 L per quintal of pressed olives, generating a considerable amount of wastewater. It is thus necessary to reduce process water and enhance its use to implement the concept of a circular economy. To this end, our preliminary work was dedicated to water purification by means of suitable and efficient filtration systems. The microfiltered OMW was firstly concentrated through reverse osmosis. Then, an additional concentration step was carried out via vacuum membrane distillation using hydrophobic hollow fiber membranes. The application of the membrane-based processes allowed the recovery of a purified water and the concentration of valuable polyphenols in a smaller volume. The different fractions obtained from the purification have been tested for the determination of the antioxidant power (DPPH assay) and dosage of polyphenols (Folin–Ciocalteu assay) and were characterized using IR spectroscopy. All samples showed relevant antioxidant activity (percentage range: 10–80%) and total phenolic content in the 1.5–15 g GAE/L range. The obtained fractions were tested for their antimicrobial effect on numerous clinical isolates of Gram-positive and Gram-negative species, resistant and multi-resistant to current antibiotic drugs. OMW samples showed widespread activity against the considered (phyto)pathogens (MIC range 8–16 mg/mL) thus supporting the value of this waste material in the (phyto)pharmaceutical field.

Air bubbling assisted solar-driven submerged vacuum membrane distillation for aquaculture seawater desalination

Submerged vacuum membrane distillation (S-VMD) was proposed in this work to desalinate aquaculture seawater. In this S-VMD without feed-pumping system, the hydrophobic hollow fibre membranes are fully immersed in the feed tank with internal coil heated by solar evacuated tube collector. In this study, indoor test under steady-state condition was compared to the outdoor test under solar intensity variation. The system’s feasibility and practicality were investigated. In the daily outdoor performance test, the solar-powered S-VMD system obtained permeate flux at 2.1–5.2 kg/m2h, depending on the solar intensity profile. Air bubbling as enhanced flow promoter and anti-fouling technique was employed to overcome the polarizations at the membrane boundary layer. Compared to non-bubbling, the bubbling approach in the S-VMD system effectively achieved higher flux and fouling reduction with better permeate quality. It is suggested that the system can be applied in energy-deprived and space-constricted remote area, particularly marine aquaculture farm to produce clean water for coastal fishery communities.

Desorption characteristic of LiBr–H2O solution in hydrophobic hollow fiber membrane for absorption chiller

• A PTFE membrane module is used as a desorber in an absorption refrigeration system. • Water vapor transports through a hollow fiber membrane by Knudsen diffusion. • A concentration difference of about 0.4% is achieved with a tiny membrane desorber. The membrane-based desorber is considered a promising alternative to miniaturize the present generator in the absorption refrigeration system, owing to its large specific interfacial area, which is expected to reduce the required volume for the unit of cooling capacity of the system. The heat and mass transfer characteristics of a desorber consisting of a porous polytetrafluoroethylene hollow fiber membrane were evaluated by both experiment and simulation under practical working conditions. The Knudsen diffusion was verified by a gas permeability test prior to the water vapor desorption test. According to the desorption experiment results of the LiBr-H 2 O solution, a concentration difference of approximately 0.4% was achieved under the investigated conditions. The results also indicated that an increase in the solution flowrates leads to an increase in the water vapor desorption rate owing to the increase of sensible heat. The compared simulation and experimental results were consistent with an acceptable accuracy. This study provides a fundamental understanding of the heat and mass transfer of the membrane-based desorber, which benefits the design of the compact membrane-based absorption refrigeration systems.

Mechanisms for Direct Separation of Oil from Water with Hydrophobic Hollow Fiber Membrane Contactors

Oil–water separation in membranes traditionally involves the transfer of water through the membrane. Instead, this study presents the novel approach of permeating insoluble oil through a hydrophobi...

Porous Hydrophobic-Hydrophilic Composite Hollow Fiber and Flat Membranes Prepared by Plasma Polymerization for Direct Contact Membrane Distillation.

High water vapor flux at low brine temperatures without surface fouling is needed in membrane distillation-based desalination. Brine crossflow over surface-modified hydrophobic hollow fiber membranes (HFMs) yielded fouling-free operation with supersaturated solutions of scaling salts and their precipitates. Surface modification involved an ultrathin porous polyfluorosiloxane or polysiloxane coating deposited on the outside of porous polypropylene (PP) HFMs by plasma polymerization. The outside of hydrophilic MicroPES HFMs of polyethersulfone was also coated by an ultrathin coating of porous plasma-polymerized polyfluorosiloxane or polysiloxane rendering the surface hydrophobic. Direct contact membrane distillation-based desalination performances of these HFMs were determined and compared with porous PP-based HFMs. Salt concentrations of 1, 10, and 20 wt% were used. Leak rates were determined at low pressures. Surface and cross-sections of two kinds of coated HFMs were investigated by scanning electron microscopy. The HFMs based on water-wetted MicroPES substrate offered a very thin gas gap in the hydrophobic surface coating yielding a high flux of 26.4–27.6 kg/m2-h with 1 wt% feed brine at 70 °C. The fluxes of HFMs on porous PP substrates having a long vapor diffusion path were significantly lower. Coated HFM performances have been compared with flat hydrophilic membranes of polyvinylidene fluoride having a similar plasma-polymerized hydrophobic polyfluorosiloxane coating.

An Experimental Study PVDF and PSF Hollow Fiber Membranes for Chemical Absorption Carbon Dioxide

Poly (vinylidene fluoride) (PVDF) and poly-sulfone (PSF) polymer solutions were made at a concentration of 18% by weight of the polymer as a non-soluble additive of polymer solution in 1-methyl-2-pyrrolidone (NMP) solvent. PVDF and PSF hollow fiber membranes were fabricated via the wet phase-inversion process. Fabricated membranes were characterized in terms of gas permeability, wetting resistance, water contact angle and overall porosity. In order to study the structure of the membranes made, the scanning electron microscopy images of the model (TM3000, HITACHI, Japan) were used. The morphology study indicates that the PSF membrane shows an open cross-section structure with smaller pore sizes. However, the PVDF membrane illustrates a thick sponge-like structure. The fabricated PVDF membrane shows higher wetting resistance, surface porosity, water contact angle, and N2 permeability. The performance of the produced membranes was examined for the Absorption of carbon dioxide in a gas-liquid contactor membrane through the solution of mono-ethanolamine (MEA). The results show that CO2 absorption flux of the PVDF hollow fiber membrane is higher than PSF hollow fiber membrane. The maximum CO2 absorption flux of 8.10 × 10-3 (mole/m2 s) at the liquid phase flow rate of 300 ml/min for PVDF hollow fiber membrane was achieved and also the maximum CO2 absorption flux of 6.50 × 10-3 (mole/m2 s) at the liquid phase flow rate of 300 ml/min for PSF hollow fiber membrane was obtained. It can be concluded that a porous hydrophobic hollow fiber membrane with high surface porosity and high gas permeability can be a productive alternative for CO2 absorption through gas-liquid membrane contactors.

Ammonia recovery from human urine as liquid fertilizers in hollow fiber membrane contactor: Effects of permeate chemistry

The production of the existing nitrogen fertilizer is costly and less environmental-friendly. Various green technologies are currently emerging toward providing alternative options. In this study, a liquid/liquid hydrophobic hollow-fiber membrane contactor was employed at ambient temperature and natural urine pH ~ 9.7 to recover ammonium fertilizers from human urine. Results showed that permeate side chemistry was one of the major factors affecting the ammonia mass transfer. The study on the ammonia capturing performance of diluted sulfuric acid, phosphoric acid, nitric acid, and DI water confirmed that acid type, acid concentration, and permeate side operating pH were the most important parameters affecting the ammonia capturing tendency. Sulfuric acid was slightly better in capturing more ammonia than other acid types. The study also identified increasing acid concentration didn’t necessarily increase ammonia mining tendency because there was always one optimum concentration value at which maximum ammonia extraction was possible. The best permeate side operating pH to extract ammonia for fertilizer purposes was selected based on the dissociation equilibrium of different types of acids. Accordingly, the analysis showed that the membrane process has to be operated at pH > 3 for sulfuric acid, between 3.5 to 11.5 for phosphoric acid, and above 0.5 for nitric acid so as to produce their respective high-quality liquid ammonium sulfate, ammonium monophosphate/diphosphate, and ammonium nitrate fertilizer. Therefore, permeate side acid concentration, pH, and acid type has to always be critically optimized before starting the ammonia mining experiment.

Fabrication of a super hydrophobic polyvinylidene fluoride–hexadecyltrimethoxysilane hybrid membrane for carbon dioxide absorption in a membrane contactor

To obtain a super hydrophobic hollow fiber membrane for using in membrane contact absorption of carbon dioxide (CO2), hybrid polyvinylidene fluoride-hexadecyltrimethoxysilane (PVDF–HDTMS) membranes were fabricated via the non-solvent induced phase-inversion method with ammonia water as the non-solvent additive and dehydrofluorination reagent, and HDTMS as the hydrophobic modifier. The membranes exhibited super-hydrophobicity which was attributed to the formation of rough nanoscale microstructure and low surface free energy of the outer surface. The largest contact angle of water and diethanolamine (DEA) on the membrane outer surface attained 150°. Scanning electron microscopy images revealed that the membrane outer surfaces consisted of rough microscale hierarchical spherulitic particles with a nanoscale stereoscopic coralliform microstructure. Attenuated total reflectance–Fourier transform infrared spectroscopy of the membranes indicated that the HDTMS chains grafted in the PVDF were mainly located on the outer layer of the hollow fiber membranes. The membranes showed excellent CO2 mass transfer flux compared to our previously fabricated membrane with 8 wt % of phosphoric acid as the non-solvent additive in the dope (PVDF-PA-8). The membrane contactor with the membrane obtained by adding 1.5 wt% of HDTMS in the dope achieved the maximum CO2 mass transfer flux of 2.23 × 10−3 mol/m2s with the inlet gas (CO2/N2 = 19/81, v/v) at a flow rate of 20 mL/min and the absorbent liquid (1 mol/L DEA) at a flow rate of 50 mL/min. CO2 mass transfer flux of this membrane decreased by 17% after 17 days of operation and then remained stable.

NOx Removal from Air through Super Hydrophobic Hollow Fiber Membrane Contactors

NOx Removal from Air through Super Hydrophobic Hollow Fiber Membrane Contactors

Hollow fibre membrane-based liquid desiccant humidity control for controlled environment agriculture

Humidity control is an important factor affecting the overall sustainability, productivity, and energy efficiency of controlled environment agriculture. Liquid desiccants offer the potential for pinpoint control of humidity levels in controlled environments. In the present work, a dehumidification processes utilizing liquid desiccants pumped through the lumens of triple-bore PVDF hollow fibre membranes is implemented in a bench scale controlled environment agriculture system. Hydrophobic hollow fibre membranes were combined into an array and placed near the crops. Concentrated magnesium chloride liquid desiccant solution with a low vapour pressure was pumped through the hollow fibre lumens. The dehumidification permeance rate responded dynamically to the changing transpiration rate of the plants, as influenced by changes in environmental factors such as light, temperature, and vapour pressure. The dehumidification permeance rate increased from an average of 0.26–0.31 g m−2 h−1 Pa−1 as the velocity of the liquid desiccant through the hollow fibres increased from 0.023 to 0.081 m s−1. Humidity levels were targeted to be maintained within a range of 70–90% relative humidity at 23 °C. The membrane-based liquid desiccant system was demonstrated to successfully control humidity within a bench-scale controlled environment agricultural setup.

Mass recovery characteristics of hydrophobic hollow fiber membrane-based refrigerant mass exchangers in vapor absorption refrigeration systems

In thermally-driven vapor absorption refrigeration systems, a solution heat exchanger performs the heat recovery to elevate the thermal performance. This study focuses on the use of the hydrophobic hollow fiber membrane (HFM) for mass recovery of water vapor between two streams of lithium bromide (LiBr) solution across the HFM layers. We propose two configurations of the HFM-based refrigerant mass exchangers (HFM-RME): direct-contact and vacuum operating modes. A theoretical analysis explores the characteristics of the mass recovery processes based on simultaneous heat and mass transfer. Because the driving force of the water vapor mass recovery across the HFM layers is due to the difference in vapor pressures between the two streams of the LiBr solution, a larger temperature difference leads to higher mass recovery of the water vapor. In the direct-contact operating mode, the two streams of LiBr solution flow in direct contact across the HFM layers. The conduction heat transfer across the HFM layers reduces the solution temperatures along the length of the HFMs; as a result, it deteriorates the mass recovery of the water vapor. However, in the vacuum operating mode, the two streams of LiBr solution flow through each HFM, and the water vapor occupies the shell side at vacuum condition. The water vapor diffuses through the shell side, as the temperature difference between the LiBr solutions is given. The conduction heat transfer is neglected, and the solution temperature difference is adequately maintained along the HFM length, compared with the direct-contact operating mode. Therefore, the mass transfer of the water vapor, is enhanced by introducing the vacuum operating mode. The present work provides a comprehensive understanding of the heat and mass transfer characteristics in the proposed HFM-RMEs.

Wastewater treatment and microbial community dynamics in a sequencing batch reactor operating under photosynthetic aeration

A sequencing batch bioreactor (SBR) treating municipal wastewater was photosynthetically aerated using microalgae cultivated in a photobioreactor (PBR). Symbiotic interactions and CO2/O2 exchange were established between activated sludge in the SBR and microalgae in the PBR through hydrophobic hollow fiber membranes. Photosynthetic aeration enhanced COD removal in the SBR from 52.2% (without external aeration) to 90.3%, whereas N-NH4+ and P-PO43- removal increased by 63.5% and 90.4%, respectively. The SBR performance under photosynthetic aeration was comparable to that under mechanical aeration. However, no nitrification was observed in the SBR, indicating oxygen limitation and poor growth condition for nitrifiers. In the PBR, there was a rapid increase in biomass concentration and it stabilized at 3.0 g/L after 22 days of operation. High nitrogen demand in the PBR indicated the steady flow of inorganic carbon from the SBR through the membranes. Prolonged oxygen limitation and massive sludge attachment on the membranes resulted in low suspended sludge concentration in the SBR. Microbial community analysis indicated gradual enrichment of facultative and strictly anaerobic microorganisms in the SBR. These results highlight the potential of microalgae in lowering the cost of wastewater aeration and underline the challenges in sustaining symbiotic gas exchange during long-term.

N2O absorption through super hydrophobic hollow fiber membrane contactor

Dinitrogen monoxide (N2O) is mainly produced in Horticulture and farming activities, industrial processes and combustion of fossil fuels. N2O is one of the harmful emissions and its global warming potential is 310 times greater than CO2 on a molecular basis. This research aims to absorb N2O from its mixture with air through super hydrophobic hollow membrane contactor using a mixture of 0.5M HNO3 and 0.5 wt % H2O2 solutions as absorbent. In the experiment, the feed gas flowed through the shell side of the contactor, while absorbent solution flowed through the lumen fibers. Experimental results show that the amount of N2O absorbed and N2O absorption efficiency increased with the absorbent flow rate and the number of fibers in the contactor resulting from the increase in the turbulence and surface area for gas–liquid contact, respectively. The overall mass transfer coefficient and the flux increased with the absorbent flow rate due to the decrease of the mass transfer resistance in the liquid phase. However, the overall mass transfer coefficient and the flux decreased with the number of fibers in the contactor due to the decrease of the absorbent flow rate in a single fiber. The amount of N2O absorbed and the flux increased but the N2O absorption efficiency decreased with increasing the feed gas cross flow rate. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 362–366, 2019

Effect of Feed Gas Flow Rate on CO2 Absorption through Super Hydrophobic Hollow Fiber membrane Contactor

Carbon dioxide is pollutant in natural gas that could reduce the heating value of the natural gas and cause problem in transportation due to corrosive to the pipeline. This study aims to evaluate the effects of feed gas flow rate on CO2 absorption through super hydrophobic hollow fiber contactor. Polyethyleneglycol-300 (PEG-300) solution was used as absorbent in this study, whilst the feed gas used in the experiment was a mixture of 30% CO2 and 70% CH4. There are three super hydrophobic hollow fiber contactors sized 6 cm and 25 cm in diameter and length used in this study, which consists of 1000, 3000 and 5000 fibers, respectively. The super hydrophobic fiber membrane used is polypropylene-based with outer and inner diameter of about 525 and 235 μm, respectively. In the experiments, the feed gas was sent through the shell side of the membrane contactor, whilst the absorbent solution was pumped through the lumen fibers. The experimental results showed that the mass transfer coefficient, flux, absorption efficiency for CO2-N2 system and CO2 loading increased with the feed gas flow rate, but the absorption efficiency for CO2-N2 system decreased. The mass transfer coefficient and the flux, at the same feed gas flow rate, decreased with the number of fibers in the membrane contactor, but the CO2 absorption efficiency and the CO2 loading increased.

Effects of Absorbent Flow Rate on Co2 Absorption through a Super Hydrophobic Hollow Fiber Membrane Contactor

Effects of Absorbent Flow Rate on Co2 Absorption through a Super Hydrophobic Hollow Fiber Membrane Contactor

Comparison of fouling behaviors of hydrophobic microporous membranes in pressure- and temperature-driven separation processes

Hydrophobic hollow fiber membranes were systematically investigated in two different operation modes including microfiltration (MF) and membrane distillation (MD). Using synthetic feed waters containing model foulants, wastewater secondary effluent, and seawater, the differences in fouling behaviors and its reversibility for the membranes between MF and MD operation modes were compared. Our results demonstrate that fouling patterns in MF were completely different from those in MD. The rates of flux decline were higher in MF than in MD in most cases. No flux declines were observed by model foulants such as alginate, humic acid, and kaolin in MD although thick foulant layers were observed by SEM analysis. This can be attributed to the difference in water transport mechanisms between MF and MD. It was found that the flux decline due to the foulants in the wastewater was more reversible in MD than in MF and could be recovered not only by chemical cleaning but also by physical cleaning.

Fabrication and characterization of affordable hydrophobic ceramic hollow fibre membrane for contacting processes

Affordable hydrophobic hollow fibre membranes were prepared using kaolin and alumina based ceramic powders via a combined phase inversion and sintering technique, followed by a grafting with fluoroalkylsilane (FAS). The crux of the matter in this paper is to study the changes in the properties of the hollow fibre membranes (gas permeation, mechanical strength, pore size, porosity, tortuosity, morphology, and contact angle) by the addition of alumina (Al2O3) to the pure kaolin with mono or multiparticle sizes. By varying the overall loading and particle size of alumina addition, different morphologies of the membranes were obtained due to the differences in the path lengths during phase inversion process for each solvent and nonsolvent exchange. The successful grafting with FAS was evidenced by the increase in contact angle from nearly equal to zero degree before grafting to 140° after grafting. Kaolin–alumina-4, one of the hollow fibres fabricated in this work, achieved a mean pore size of 0.25 μm with the bending strength of 96.4 MPa and high nitrogen permeance of 2.3×10-5 mol·m-2·Pa-1·s-1, which makes the hollow fibre most suitable for the membrane contactor application.