Polyvinylidene Fluoride Hollow Fiber Research Articles

Decreasing free fatty acid of crude palm oil with polyvinylidene fluoride hollow fiber membranes using a combination of chitosan and glutaraldehyde

Crude palm oil (CPO) has emerged as a significant commodity in the economic and social development of producer nations. However, the presence of free fatty acids (FFAs) results in decreased CPO quality. Due to many advantages, the PVDF hollow fiber membrane has a higher potential to remove FFA from CPO than other polymeric membranes, despite the fact that FFA rejection performance remains poor. To solve this issue, membrane surface modification has emerged as one of the potential options for increasing electrostatic contact between the membrane surface and the FFA, resulting in high efficiency FFA separation from CPO. In this investigation, the membrane surface was coated with chitosan (CS) as a coating agent and glutaraldehyde (GA) as a crosslinking agent. The findings of the characterization demonstrated that the presence of a CS/GA combination with a low CS weight on the membrane surface resulted in enhanced hydrophilicity, porosity, water flow, and surface roughness. Furthermore, as compared to the uncoated PVDF hollow fiber membrane, the performance of the CPO with PVDF/CS 0.5 hollow fiber membrane achieved a maximum result of FFA rejection of up to 14.99%. The use of a mixture of CS and GA on the PVDF membrane surface to improve FFA reduction has been shown to be a promising technique for scaling up membrane technology.

Preparation and assessment of polyvinylidene fluoride hollow fiber membrane for desalination by membrane distillation

Preparation and assessment of polyvinylidene fluoride hollow fiber membrane for desalination by membrane distillation

Desirable PVDF hollow fiber membrane engineered with synergism between small molecular weight additives for DCMD treating of a hypersaline brine

Developing membrane for brine waste reclamation via direct contact membrane distillation (DCMD) requires specially membrane characteristics engineering. Toward practical and scalable hydrophobic micromembrane with desirable properties, attaining energy-efficient and durability during hypersaline treatment remains a great challenge. Herein, polyvinylidene fluoride (PVDF) hollow fiber (HF) membranes were developed for particular use in DCMD for treating hypersaline (100,000 mg/L of NaCl solution) via adopting mixture of small molecular weight (MW) additives, including water, lithium chloride (LiCl), and ethylene glycol (EG). Engineered to suppress the limitation of single small MW additives only possessing a unique enhancement in the tailoring of specific properties for improving the partial DCMD performance, the research emphasis is placed on the synergistic effect between small molecular weight additives, resulting in a much-enhanced performance. The dope solution of PVDF/LiCl/H2O/N-Methyl-2-pyrrolidone (NMP) = 12/2/2/84 (wt%) spun HF membrane, P-L-W2, has been shown to reveal the most desirable membrane characteristics for DCMD, including comparable porosity (ε, 74.2 ± 0.4%), superior liquid entry pressure (LEP, 3.05 bar), and robust mechanical properties. The P-L-W2 membrane also exhibited enhanced water flux, energy efficiency, and anti-wetting ability in comparison with the neat PVDF HF membrane. With advantage of easy implement, the concept of adoption of additives mixture provides a novel platform to customize desirable PVDF HF membranes with enhanced DCMD performance.

Fabrication of a superhydrophobic mixed matrix PVDF-SiO2-HDTMS hollow fiber membrane for membrane contact carbon dioxide absorption

In order to obtain high performance polyvinylidene fluoride (PVDF) hollow fiber membrane for post combustion carbon dioxide (CO2) capture from flue gas by membrane contact absorption technology, a novel mixed matrix membrane fabrication process was proposed in this study. The mixed matrix PVDF-SiO2 (silicon dioxide)-HDTMS (hexadecyltrimethoxysilane) hollow fiber membranes fabricated via this process exhibit super-hydrophobicity on the outer surface and high mechanical strength. Among the membranes, the PVDF-SiO2(1.5)-HDTMS membrane exhibited the highest CO2 absorption performance, which was due to its excellent properties. It had water and diethanolamine (DEA, 1 mol/L) contact angles of 159.3° and 157.5°, respectively. Tensile strength, elongation at break, and LEPW (liquid entry pressure of water) of it were 3.2 × 106 Pa, 35.0%, and 9.0 × 105 Pa, respectively. The CO2 absorption flux of PVDF-SiO2(1.5)-HDTMS membrane attained 2.39 × 10−3 mol‧m−2‧s−1, which was 7.2% and 141.4% higher than that of the PVDF-HDTMS-1.5 and PVDF membranes, respectively. Moreover, CO2 absorption flux of the PVDF-SiO2(1.5)-HDTMS membrane decreased only 3% after twenty days of continuous operation. Highlighted by the outstanding performance in membrane contact CO2 absorption, the PVDF-SiO2(1.5)-HDTMS membrane shows great potential in the application of membrane contact absorption for post-combustion CO2 capture.

Seawater Desalination by Modified Membrane Distillation: Effect of Hydrophilic Surface Modifying Macromolecules Addition into PVDF Hollow Fiber Membrane.

Hollow fiber membranes of polyvinylidene fluoride (PVDF) were prepared by incorporating varying concentrations of hydrophilic surface-modifying macromolecules (LSMM) and a constant amount of polyethylene glycol (PEG) additives. The membranes were fabricated by the dry-wet spinning technique. The prepared hollow fiber membranes were dip-coated by hydrophobic surface-modifying macromolecules (BSMM) as the final step fabrication. The additives combination is aimed to produce hollow fiber membranes with high flux permeation and high salt rejection in the matter of seawater desalination application. This study prepares hollow fiber membranes from the formulation of 18 wt. % of PVDF mixed with 5 wt. % of PEG and 3, 4, and 5 wt. % of LSMM. The membranes are then dip-coated with 1 wt. % of BSMM. The effect of LSMM loading on hydrophobicity, morphology, average pore size, surface porosity, and membrane performance is investigated. Coating modification on LSMM membranes showed an increase in contact angle up to 57% of pure, unmodified PVDF/PEG membranes, which made the fabricated membranes at least passable when hydrophobicity was considered as one main characteristic. Furthermore, The PVDF/PEG/4LSMM-BSMM membrane exhibits 161 °C of melting point as characterized by the DSC. This value indicates an improvement of thermal behavior shows so as the fabricated membranes are desirable for membrane distillation operation conditions range. Based on the results, it can be concluded that PVDF/PEG membranes with the use of LSMM and BSMM combination could enhance the permeate flux up to 81.32 kg·m−2·h−1 at the maximum, with stable salt rejection around 99.9%, and these are found to be potential for seawater desalination application.

Impact of NaOCl ageing on reinforced PVDF hollow fiber membranes used in membrane bioreactor

Reinforced hollow fiber membranes are commercially available but its information is limited on open literature. Its notable mechanical properties due to the reinforced layer makes it suitable for membrane bioreactor (MBR) application. On the other hand, polyvinylidene fluoride (PVDF) is an increasingly popular material choice for membrane used in MBR due to its good chemical resistance against chlorine present in sodium hypochlorite (NaOCl), which is commonly used as a cleaning agent. The impact of NaOCl on the PVDF membrane characteristics was reported in literature, but little information is available about the membrane performance of the aged PVDF membrane caused by NaOCl in MBR operation. In this study, the membrane performance of a reinforced PVDF hollow fiber membranes after NaOCl ageing were investigated thoroughly in MBR operations. A series of characterization on virgin and fouled membranes with/without NaOCl exposure were carried out. The accelerated NaOCl ageing experiments revealed that reinforced hollow fiber membranes have notable mechanical strength, which is not significantly affected by NaOCl ageing as compared to their non-reinforced counterpart. Additionally, there was no significant effect on the membrane behaviours in MBR after the membranes were exposed to a 5000 ppm NaOCl solution at pH 7 for 48 h, which is equivalent to 246,000 ppm.hr (~6.1 years) NaOCl exposure using a normal dose of NaOCl for regular membrane cleaning. However, after 524,000 ppm.hr (~13.1 years) of NaOCl exposure, the membrane failed to perform and a sharp transmembrane pressure (TMP) increase during MBR operation was observed. The severe fouling of aged membranes was found to be attributed to the changes in hydrophobicity, pore size and the foulants left on the membrane despite cleaning. Even though the membrane was fouled quickly after 524,000 ppm.hr (~13.1 years) of NaOCl exposure, the permeate quality was not affected much as indicated by >90% removal for dissolved organic carbon (DOC) and soluble chemical oxygen demand (sCOD), which suggests that the reinforced PVDF hollow fiber membranes used in current study exhibit considerable chemical resistance against chlorine and can be used in the MBR system for a long period of operation.

Fabrication of High Performance PVDF Hollow Fiber Membrane Using Less Toxic Solvent at Different Additive Loading and Air Gap

Existing toxic solvents in the manufacturing of polymeric membranes have been raising concerns due to the risks of exposure to health and the environment. Furthermore, the lower tensile strength of the membrane renders these membranes unable to endure greater pressure during water treatment. To sustain a healthier ecosystem, fabrication of polyvinylidene fluoride (PVDF) hollow fiber membrane using a less toxic solvent, triethyl phosphate (TEP), with a lower molecular weight polyethylene glycol (PEG 400) (0–3 wt.%) additive were experimentally demonstrated via a phase inversion-based spinning technique at various air gap (10, 20 and 30 cm). Membrane with 2 wt.% of PEG 400 exhibited the desired ultrafiltration asymmetric morphology, while 3 wt.% PEG 400 resulting microfiltration. The surface roughness, porosity, and water flux performance increased as the loading of PEG 400 increased. The mechanical properties and contact angle of the fabricated membrane were influenced by the air gap where 20 cm indicate 2.91 MPa and 84.72°, respectively, leading to a stronger tensile and hydrophilicity surface. Lower toxicity TEP as a solvent helped in increasing the tensile properties of the membrane as well as producing an eco-friendly membrane towards creating a sustainable environment. The comprehensive investigation in this study may present a novel composition for the robust structure of polymeric hollow fiber membrane that is suitable in membrane technology.

Mechanically strong Janus tri-bore hollow fiber membranes with asymmetric pores for anti-wetting and anti-fouling membrane distillation

Wetting, fouling and mechanical robustness are three major challenges constraining the commercial applications of membrane distillation (MD). Herein, we have developed a robust Janus tri-bore hollow fiber membrane with anti-wetting/fouling resistance. The unique membrane was fabricated by an oxidant-induced deposition of polydopamine/polyethylenimine (PDA/PEI) and a subsequent grafting of sodium-functionalized carbon quantum dots (Na+-CQDs) on top of a hydrophobic tri-bore polyvinylidene fluoride (PVDF) hollow fiber membrane. The PDA/PEI deposition resulted in a nanoporous top layer, and the Na+-CQD grafting significantly enhanced the membrane surface hydrophilicity. In MD operations, the nanoporous PDA/PEI layer endowed the membrane with an excellent rejection to surfactants, thus reducing the wetting propensity, while the grafted Na+-CQDs facilitated the formation of a surface hydration layer, thereby mitigating the oil fouling. This study may expand the applications of mechanically robust tri-bore MD hollow fiber membranes to desalinate hypersaline and harsh wastewaters containing amphiphilic and hydrophobic contaminants.

Effect of Absorbents on NOx Removal through Polyvinylidene Fluoride (PVDF) Hollow Fiber Membrane Modules

NOx (NO and NO2) are air toxins that endanger life and represent a hazard to the environment, such as photochemical smog, global warming, acid rain, ozone depletion, and the occurrence of respiratory infections. Some technological strategies to diminish NOx emissions to meet regulations depend on two techniques: the dry process and the wet process. This study applies polyvinylidene fluoride (PVDF) hollow fiber membrane modules as a medium to remove NOx from solutions containing several absorbents such as hydrogen peroxide and nitric acid (H2O2-HNO3) solutions, sodium chlorite and sodium hydroxide (NaClO2-NaOH) solutions, and sodium chlorate and sodium hydroxide (NaClO3-NaOH) solutions. The experimental results showed that the oxidant’s strength influences NOx removal efficiency, where the absorbent solutions containing hydrogen peroxide had the highest removal efficiency as hydrogen peroxide is the most potent oxidant, followed by sodium chlorite and sodium chlorate. The three pairs of absorbents also gave a high NOx removal efficiency (above 90%), which means that all the absorbents used in the study are very potential to be used to diminish NOx via the wet process. NOx removal efficiency at the same feed gas flow rate increased as the number of fiber and absorbent concentrations is increased. However, NOx removal efficiency is reduced as the feed gas flow rate is increased at the same membrane module and absorbent concentration.

Modification of PVDF hollow fiber membrane by co-deposition of PDA/MPC-co-AEMA for membrane distillation application with anti-fouling and anti-scaling properties

In this study, a self-prepared polyvinylidene fluoride (PVDF) hollow fiber membrane with a hierarchical structure was used for facile modification by co-deposition of polydopamine (PDA) and poly(MPC-co-2-aminoethyl methacrylate hydrochloride) (MPC-co-AEMA) for application in direct contact membrane distillation (DCMD). The facile formation of the PDA/MPC-co-AEMA layer on the membrane outer surface drastically changed the chemical and physical properties of the membrane surface. Although the membrane became hydrophilic and smooth with a low porosity and small pore size, the bulk structure of the membrane remained almost intact. For a saline solution including protein and Ca2+ as organic fouling and scaling agents, the deposition of the hydrophilic PDA/MPC-co-AEMA layer on hydrophobic PVDF led to the alleviation of the membrane fouling and scaling during long-term DCMD application. Whereas the formation of a hydrated layer on the membrane surface avoided BSA fouling by avoiding hydrophobic–hydrophobic interactions, a combination of several chemo-physical properties of the modified membrane surface resulted in anti-scaling properties.

Nanoporous PVDF Hollow Fiber Employed Piezo-Tribo Nanogenerator for Effective Acoustic Harvesting.

Restricted by the inherent property of low power density, acoustic energy can hardly be effectively captured by conventional piezo- or triboelectric nanogenerators for powering miniature electronics. Herein, a novel piezo-tribo hybrid nanogenerator employing nanoporous polyvinylidene fluoride (PVDF) hollow fiber and polydimethylsiloxane (PDMS) valve, which can mimic the eardrum, has been advocated for efficient acoustic harvesting. The nanoporous, hollow, and valve structure design, together with the effective combination of piezo- and triboelectricity, make the nanoporous PVDF hollow fiber and PDMS valve based acoustic harvester (PHVAH) a promising candidate for acoustic-electric conversion. With an optimal output of 105.5 V and 16.7 μA and a power density of 0.92 W m-2 under the sound stimulation of 117.6 dB and 150 Hz, it can not only recognize audio signals but also convert the sound into electrical energy to light up seven LED bulbs in series. Exhibiting excellent durability and stability, the disruptive innovation proposed here is an effective method for hunting the ubiquitous sound energy in the environment, which provides great potential and impetus for using acoustic-electric conversion to power various low-power-consumption sensors.

Fabrication and Characterization of Hydrophobic PVDF-based Hollow Fiber Membranes for Vacuum Membrane Distillation of Seawater and Desalination Brine

Fabrication of hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membranes was studied using Lithium chloride (LiCl) and polyethylene glycol (PEG) 35000 as non-solvent additives by dry-wet phase inversion process. Scanning Electron Microscopy revealed that LiCl addition made the finger-like voids become smaller and provided a sponge-like structure, in addition to increasing the membrane surface roughness to 42 nm, porosity to 83% and mean pore size to 5.75 nm with narrower pore size distribution. It also decreased Young's modulus to 63 MPa while, no significant improvement was observed in water contact angle (115.5o). During vacuum membrane distillation (VMD) of water, Mediterranean Sea water, Red Sea water and Red Sea brine, the PVDF membranes spun with LiCl achieved higher water permeation flux with values of 48, 32, 25 and 19 L/m2h, respectively. The flux-salinity relationship was represented by empirical correlations. The two membranes exhibited high salt rejection values (99.4%-99.8%) for the investigated saline solutions. These results suggest numerous interventions for membrane distillation within integrated desalination/salt recovery schemes or as a stand-alone facility with the combination of complementary appropriate thermal crystallization units. Two VMD/solar pond scenarios were investigated for dual production of water and salts.

The Functionalization Study of PVDF/TiO2 Hollow Fibre Membranes Under Vacuum Calcination Exposure

In this study, polyvinylidene fluoride (PVDF) hollow fibre membrane was modified by adding TiO2. TiO2 presence affects the membrane structure becomes more less hydrophobic which makes the membrane less fouling. Membranes were made via dry-wet spinning method and calcined under vacuum condition by furnace (100, 300, and 500 °C). Besides, PVDF-TiO2 uncalcined membrane were also prepared as comparison to investigated the effect of calcination on hollow fibre membrane’s functional groups. Fourier Transform Infrared (FT-IR) spectra indicated that all PVDF-TiO2 membranes have bands of OH in the TiO2 at ∼1600 cm−1. Peaks of α-phase PVDF crystals appeared at ∼876, ∼876, and ∼872 cm−1 for uncalcined, 100 and 300 °C, while for 500 °C the PVDF peak only shows at 874 cm−1. The peaks at ∼1200 cm−1 represent CF2 groups. Peaks at ∼1400 cm−1 assigned to CH2 groups, but it does not observed for 500 °C. Deconvolution by Fityk software that shows calcination using vacuum condition gives the compounds gradually decomposes. At high temperature calcination lead the CH2 peak extremely lost.

Study on the effect of air gap on physico-chemical and performance of PVDF hollow fibre membrane

Polyvinylidene fluoride (PVDF) was chosen in this study as the main material in fabricating membrane due to its excellent chemical resistance and good thermal stability. Combination of triethyl phosphate (TEP) with DMAc produce better structure of membrane which safer and provide high mechanical strength for membrane. Surface modified PVDF hollow fibre membrane (HFM) was prepared using dry-wet spinning technique by varying air gap namely 10 cm, 20 cm and 30 cm. The morphology was evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), mercury intrusion porosimetry (MIP), contact angle, tensile test and performing water flux testing. From the characterization data, PVDF HFM with 3 wt.% PEG 400, HFM 3-10 and HFM 3-20 referred as microfiltration membrane with pore size range 0.1-0.8 µm. While, HFM 3-30 act as ultrafiltration membrane with pore size ranging 0.01-0.1 µm. Experimental results revealed that by increasing the air gap from 10 cm to 30 cm, the porosity and finger-like length decreased due to the higher elongational stress that shift the pores from broad to narrow. Thus, PVDF HFM at 10 cm air gap, HFM 3-10 achieve the highest water flux due to the higher porosity, longer finger-like length and hydrophilicity achieved. The modified HFM at shorter air gap was found to be a promising membrane structure for excellence water performance and eco-friendly to environment.

A N-doped Cobalt@graphitized carbon material derived from ZIF-67 assisted polyvinylidene fluoride hollow fiber membrane for supercapacitors

In this work, a porous nanostructure active carbon material (N-doped Co@graphitized carbon) for supercapacitor is prepared from a ZIF-67 assisted polyvinylidene fluoride (PVDF) hollow fiber membrane by a simple anaerobic calcination method at a relative low temperature (600 °C). The addition of ZIF-67 can prevent the porous structure of PVDF hollow fiber membranes from collapsing during the calcination process, meanwhile the PVDF membranes can also prevent the Co particles derived from ZIF-67 aggregating together. At the same time, the doped N can increase the conductivity and wettability of the carbon material and generate pseudocapacitance effect. Furthermore, the obtained unique Co@C core@shell structure can improve the electrochemical activity of the carbon material. Under the synergistic effects of the above factors, the prepared active material delivers a specific capacitance of 652 F g−1 at 1 A g−1. Even at 10 A g−1, it still remains 97.1% retention rate after 20,000 cycles.

PTFE-assisted immobilization of Pluronic F127 in PVDF hollow fiber membranes with enhanced hydrophilicity through nonsolvent-thermally induced phase separation method

The use of amphiphilic copolymer Pluronic F127 as an additive has shown effectiveness in fabricating polyethersulfone (PES) membranes with excellent antifouling properties due to its roles in enhancing pore structure and surface hydrophilicity. However, F127 was found to be unstable in polyvinylidene fluoride (PVDF) membranes as its hydrophilic modifying function was deactivated over time. In present work, we developed a novel approach to immobilize F127 in PVDF hollow fiber membranes using polytetrafluoroethylene (PTFE) particles as a binding agent through the combined nonsolvent and thermally induced phase separation (N-TIPS) method. The results suggest that the hydrophobic segment of F127 could adsorb firmly onto PTFE with the hydrophilic segments protruding outwards. The dual-functions of F127 were observed in pore formation and surface hydrophilization for PVDF membranes. The water contact angle of PVDF/PTFE/F127 membranes decreased from 102 ± 4° to 76 ± 3° compared with membranes without additives. The resultant membranes possess a pure water permeability (PWP) of 869 ± 39 L m−2h−1bar−1 with a mean pore size of 0.09 ± 0.01 μm and an outstanding tensile strength of 7.0 ± 0.3 MPa, suggesting the potential of N-TIPS method for tuning the membrane pore structure and hydrophilicity by using multifunctional additives.

Improved Desalination Performance of Polyvinylidene Fluoride Hollow Fiber Membranes by the Intermediate Role of Surfactants

AbstractPolymer hollow fiber membranes (HFMs) are the core or base membranes of various membrane processes (e.g., ultrafiltration and membrane distillation). Preparing polymer HFMs with higher water flux helps improve the efficiency of the membrane processes. Using pore‐forming additives is the commonly used and efficient method to improve the water flux. The current dilemma is that the conventional methods that increase the amounts or the molecular weight of the additives to improve the water flux usually lead to the decrease in membrane mechanical strength. Herein, different from the conventional research strategy, increasing the surfactant surface activity (SA) is first found to deeply promote the core of nonsolvent‐induced phase separation (NIPS) that of the mutual diffusion between water and dopes. As a result, this method distinctly improves the surface porosity (from 0.8% to 9.7%) and optimizes the pore size distribution of polyvinylidene fluoride (PVDF) HFMs. Benefit from these, the water flux of ultrafiltration (3.1‐fold increase, maximally) and direct contact membrane distillation (2.3‐fold increase, maximally) are increased greatly. Moreover, the mechanical strength is not negatively affected due to the additive amount of small molecule surfactants is constant and small (2.0 wt%).

Controlling the inner surface pore and spherulite structures of PVDF hollow fiber membranes in thermally induced phase separation using triple-orifice spinneret for membrane distillation

In this study, we controlled the inner surface structures of polyvinylidene fluoride (PVDF) hollow fiber membranes via a thermally induced phase separation process using a triple-orifice spinneret for direct-contact membrane distillation (DCMD). The coextrusion of propylene carbonate (PC) through the outermost channel of the spinneret led to porous outer surfaces with similar pore sizes and spherulitic structures for all the PVDF hollow fiber membranes. In the innermost channel, the extrusion of solvents having different compatibilities with PVDF and the diluent (PC) as the bore liquids controlled the inner surface pore sizes and spherulite structures, and the effects of these inner surface structures on the DCMD performance were investigated in detail. Increasing the compatibility of the bore liquids toward the diluent led to an increase in the inner surface pore size because of the formation of loose, isolated spherulites, which remarkably enhanced the water vapor permeability from 4 to 8.3 L m−2 h−1, while reducing the membrane hydrophobicity, liquid entry pressure, and salt rejection. When increasing the bore liquid compatibility with the polymer, the surface pore size decreased because of the tight spherulite contact, enhancing membrane salt rejection and wetting resistance. Given the significance of bore liquid compatibility with the diluent and the polymer in controlling the inner surface structures, a useful guideline is presented for selecting the appropriate bore liquids to prepare hollow fiber membranes with the desired inner surface structures for high MD performance.

Removal of high concentration Congo red by hydrophobic PVDF hollow fiber composite membrane coated with a loose and porous ZIF-71PVDF layer through vacuum membrane distillation

Although membrane distillation (MD) technology has the outstanding advantages of almost 100% solute retention and mild operation conditions, its further development is limited by low permeate flux. In order to solve the problem, the improvement of membrane hydrophobicity becomes one of the effective solutions. In this study, a loose and porous hydrophobic zeolitic imidazolate frameworks-71 (ZIF-71)/polyvinylidene fluoride (PVDF) coating layer was composited on the outside surface of PVDF hollow fiber support membrane by the dilute solution coating to enhance membrane hydrophobicity. The prepared hollow fiber composite (HFC) membranes were employed to remove high concentration Congo red (CR) through VMD. The effects of different operation conditions including the dye concentration, feed temperature, vacuum pressure and feed flow rate on CR rejection and permeate water flux were investigated. In the variation range of operating conditions, all the CR rejection of the PVDF HFC membranes shows a slight change and remains above 99.9%. Under the optimal operation conditions including dye concentration 600 mg·L−1, vacuum pressure 31.325 kPa, feed temperature 60°C and feed flow rate 50 L·h−1, HFC membrane exhibit a permeate water flux of 13.15 kg·m−2·h−1. HFC membrane suffers dye fouling during the continuous dye filtration for 100 h. The fouling mechanism was proposed and a combined cleaning way including forward washing, back flushing and chemical desorption has been proved to be effective in recovering membrane water flux.

Evaluation of membrane-based air pre-dehumidification for a capillary radiant air conditioning system

The polyvinylidene fluoride hollow fibre membrane air dehumidification tests were carried out between the liquid desiccant solutions and the wet air. Three liquid desiccant solutions of LiBr solution (50%), LiCl solution (35%) and CaCl2 solution (40%) were tested under different wet air conditions. The results showed that all the membrane dehumidification processes were stable. The air moisture content in the outlet of the membrane was maintained as 6.5 g/kg (da)–8.2 g/kg (da) when the air moisture content in the inlet of the membrane was operated from 17.1 g/kg (da) to 32.4 g/kg (da). The dehumidification amount of LiBr solution (50%) and LiCl solution (35%) was more productive. On this basis, a membrane-based air pre-dehumidification process for the capillary radiant air conditioning system was built. Since the ideal dew point temperature range of the indoor air is below 14–17°C according to the cold supply water, all the air moisture content at the membrane outlet is much lower than that of the ideal dew point temperature range, which means non-condensing occurs in the capillary tube surface. The membrane-based air pre-dehumidification process can easily form an adaptive regulation process of humidity with the capillary radiant air conditioning system under different environmental parameters.