Direct Contact Membrane Distillation Flux Research Articles

Investigation of performance and entropy generation rate of Direct Contact Membrane Distillation (DCMD) with Static Mixer (SM): 3D CFD study

This study investigated the performance of Direct Contact Membrane Distillation (DCMD) with a Static Mixer (DCMDSM) and compared it to conventional DCMD using 3D Computational Fluid Dynamics (CFD) under steady-state conditions. The permeate flux and total entropy generation rate (TEGR) were explored as functions of various parameters, including temperature differences between feed and permeate flow, inlet velocity, salt mass fraction, membrane porosity, membrane thermal conductivity, and membrane pore radius. The study revealed that the maximum permeate flux of DCMDSM was 79 % higher than DCMD. Additionally, the average TEGR of DCMDSM was 67 % lower than that of DCMD. Furthermore, increasing the inlet velocity led to higher permeate flux in both DCMD and DCMDSM. The results showed that the performance of the DCMDSM at lower velocities was better than at higher inlet velocities. Moreover, increasing the temperature difference between feed and permeate, salt mole fraction, and porosity showed similar effects on permeate flux for both DCMD and DCMDSM, with the permeate flux of DCMDSM consistently exhibiting 60 % higher permeate flux than DCMD across all parameter ranges. Finally, the analysis of membrane thermal conductivity indicated that higher thermal conductivity of the membrane resulted in better permeate flux for DCMDSM than DCMD. Additionally, the TEGR analysis revealed that it was minimized at lower temperature differences, higher inlet velocities, and lower membrane thermal conductivities for both DCMD and DCMDSM.

PVDF membranes for membrane distillation prepared by VIPS – A combined study of artificial water channel effectiveness and membrane performance prediction

Background A combined VIPS-NIPS technique was used to investigate the potential of self-supporting flat-sheet polyvinylidene fluoride (PVDF) membranes containing amphiphilic I-quartet Artificial Water Channels (AWC) for Direct Contact Membrane Distillation (DCMD). The AWC are formed in situ by self-assembly of HC6 molecules upon contact with water during membrane formation. Methods A Design of Experiment (DoE) was used to investigate the influence of various experimental parameters and their interactions on membrane performance, namely polymer and AWC concentrations in the dope solution, relative humidity and duration of the VIPS treatment. Pure water permeability (PWP), Liquid Entry Pressure (LEP) and DCMD flux were used to characterize membrane performance. A Response Surface Methodology (RSM) was used to evaluate the DoE results and a second order model was fitted. Based on the model predictions several multiple response-optimized (MRO) membranes were prepared. Results The performance improvement of the MRO membranes was 7.0 times for PWP (M-T4) and 3.3 times for MD flux (M-T3) over the average performance of the DoE membranes, while maintaining LEP of 1.9 bar and Salt rejection of 99.9%. In addition, hybrid PVDF/HC6 MRO membranes improved PWP by 3.2 times and MD flux by 1.6 times over pure PVDF MRO membranes. Conclusions DoE in conjunction with RSM enabled the prediction of membrane PWP, LEP and MD flux performance by varying the levels of the experimental parameters within predefined limits. The HC6 additive improves PWP and MD flux without loss of LEP or selectivity. HC6 promotes the formation of porous skin and asymmetric cross-sections with finger-like structures. Probably by affecting diffusion during phase separation due to its amphiphilic properties.

Modeling pore wetting in direct contact membrane distillation—effect of interfacial capillary pressure

In this study, we aimed to develop a model for computing direct contact membrane distillation (DCMD) performance, taking into account capillary pressure effects at the liquid–gas interface within membrane pores. We developed a simulation model to investigate how factors such as pore radius, feed/permeate temperature, pressure, and contact angle influenced the distance of liquid intrusion into the pore, the weight flow rate in a single pore, and the temperature at the liquid–gas interface. The model predicted that the permeation rate would decrease with an increase in the feed pressure when the permeate pressure was kept constant and also when the pressure difference between the feed and permeate was kept constant. It also predicted that the permeation rate would increase with an increase in the permeate pressure when the feed pressure was kept constant. The model also indicated that partial pore wetting would be enhanced with an increase in feed pressure when the pore size was as large as 1 μm but would diminish when the pore size was as small as 0.1 μm. According to the model, partial pore wetting diminished with a decrease in the permeate pressure. The model’s predictions were in line with the trends observed in the experimental DCMD flux data by many authors, particularly those regarding the effects of feed and permeate temperature and the effect of contact angle. The model’s predictions were compared with the experimental data recorded in the literature, validating the model’s accuracy.

Predicting and evaluating the performance of DCMD: The effect of non-ideal morphology and thermal conductivity of porous nanocomposite membranes

The aim of this work is to explore the effects of the factors affecting the thermal conductivity of the porous nanocomposite membranes and their performance in direct contact membrane distillation (DCMD). The thermal conductivity models were evaluated comprehensively for membrane material involving three-phases (filler particle, polymer and interface). Hashemifard-Matsuura-Fauzi (HMF) and Maxwell models were the most reliable models among three-phase and two-phase (nanocomposite material and pores) models, respectively. Thus, the thermal conductivity of the porous nanocomposite membrane was obtained by the combination of three-phase HMF and two-phase Maxwell model. Finally, the performances of PTFE/Silica aerogel (SiAG) and PTFE/CaCO3 porous nanocomposite membranes were disclosed by the heat and mass transfer model in a DCMD system in order to study the effects of particle loading, interlayer thickness and membrane porosity. It was concluded that both membrane thermal conductivity and the DCMD flux approach almost the same values at the high end of interface thickness, regardless of the thermal conductivity of the filler particle. In other words, the heat loss of the system can be controlled by tuning the interface thickness in order to achieve a high DCMD flux even by incorporating fillers with higher thermal conductivity rather than that of the pure polymer. In summary, our findings revealed that next to the membrane material and porosity, the type of the nanoparticle and interface thickness can be highlighted as the most important parameters for controlling membrane thermal conductivity and improving DCMD performance.

Scale Up and Validation of Novel Tri-Bore PVDF Hollow Fiber Membranes for Membrane Distillation Application in Desalination and Industrial Wastewater Recycling.

Novel tri-bore polyvinylidene difluoride (PVDF) hollow fiber membranes (TBHF) were scaled-up for fabrication on industrial-scale hollow fiber spinning equipment, with the objective of validating the membrane technology for membrane distillation (MD) applications in areas such as desalination, resource recovery, and zero liquid discharge. The membrane chemistry and spinning processes were adapted from a previously reported method and optimized to suit large-scale production processes with the objective of translating the technology from lab scale to pilot scale and eventual commercialization. The membrane process was successfully optimized in small 1.5 kg batches and scaled-up to 20 kg and 50 kg batch sizes with good reproducibility of membrane properties. The membranes were then assembled into 0.5-inch and 2-inch modules of different lengths and evaluated in direct contact membrane distillation (DCMD) mode, as well as vacuum membrane distillation (VMD) mode. The 0.5-inch modules had a permeate flux >10 L m−2 h−1, whereas the 2-inch module flux dropped significantly to <2 L m−2 h−1 according to testing with 3.5 wt.% NaCl feed. Several optimization trials were carried out to improve the DCMD and VMD flux to >5 L m−2 h−1, whereas the salt rejection consistently remained ≥99.9%.

Modeling and experimental validation of direct contact membrane distillation applied to synthetic dye solutions

AbstractBACKGROUNDIn order to protect water resources and reduce the harmful effects of releasing contaminated wastewater to the environment, the textile industry has increasingly demanded improved water reclamation technologies, such as membrane distillation. In this work, theoretical and experimental investigations were carried out to evaluate the behavior of the operational parameters of a direct contact membrane distillation (DCMD) setting with a commercial membrane applied to synthetic dye solutions, simulating textile wastewater from the fabric dyeing stage.RESULTSThe analytical model based on heat and mass transfer correlations specific to textile effluents implemented using Matlab® predicted the permeate flux with good agreement, with errors less than 10% when compared with the experimental values. There was a different trend for reactive and disperse dyes when input variables were changed. In general, increasing all variables led to an increase in permeate flux. An increase of 30 °C in the feed temperature increased by 2.0‐ to 2.3‐fold the permeate flux. Moreover, the simulation showed the influence of the permeate temperature and the membrane interface temperature on the permeate flux, which is not commonly achieved experimentally.CONCLUSIONSThe hybrid modeling supported by extensive experimental validation accurately predicted the permeate flux in DCMD to recover water from synthetic dye solutions containing reactive and disperse black dyes. DCMD is a promising technology for recovering textile wastewater containing these dyes, as it can use the waste heat from the hot effluent discharge. Therefore, this work can contribute towards the scaling up of DCMD, aiding in predicting and optimizing the operational variables. © 2020 Society of Chemical Industry (SCI)

In-situ construction of superhydrophobic PVDF membrane via NaCl-H2O induced polymer incipient gelation for membrane distillation

In-situ construction of superhydrophobic polyvinylidene fluoride (PVDF) membrane was prepared through nonsolvent induced phase inversion process for direct contact membrane distillation (DCMD). Saturated sodium chloride aqueous solution (NaCl-H2O) was added to the casting solution as a green phase inversion inducing agent. The variation of polymer crystal and the formation mechanism of micro-nano structure on membrane surface were studied. The results showed that NaCl crystals could act as nucleus for the pre-gelation and crystallization of PVDF chains. The “harsh” nonsolvent, water, accelerated the gelation process. When the optimum amount of NaCl-H2O was added, superhydrophobic membrane with lotus leaf like micro-nano spherical structure and interconnected channels was obtained. The pure water contact angle reached 155.3° with DCMD flux of 54.5 L/m2∙h, which was about 1.6 times for the membrane without NaCl-H2O addition. The stability was also improved owing to the superhydrophobic structure.

Study of the effective thickness of the water-intrudable hydrophilic layer in dual-layer hydrophilic-hydrophobic hollow fiber membranes for direct contact membrane distillation

Dual-layer hydrophilic-hydrophobic hollow fiber membrane is a promising membrane that simultaneously shows enhanced vapor transfer coefficient and inhibited conductive heat loss in direct contact membrane distillation (DCMD). The presence of an effective water-intrudable hydrophilic layer enables to reduce the vapor transportation distance and improve the water flux in DCMD. The aim of this study is to estimate the water-intrudable hydrophilic layer thickness in a dual-layer hydrophilic-hydrophobic hollow fiber membrane comprising a PVDF/PEG inner layer and a PVDF outer layer. The water-intrudable hydrophilic layer thickness was precisely measured by a dye solution permeation method under simulated DCMD conditions. The results showed that the water-intrudable hydrophilic layer thickness was highly determined by the pore size and effective porosity of the PVDF/PEG inner layer. The applied hydraulic pressure contributed significantly to the difference in the thickness of the water-intrudable hydrophilic layer. The membranes with higher thickness percentages of the water-intrudable hydrophilic layer exhibited simultaneously enhanced permeate water flux and energy efficiency in DCMD. This study offered a simple and reliable approach for the estimation of the effective thickness of the water-intrudable hydrophilic layer for the dual-layer hydrophilic-hydrophobic hollow fiber membrane that contributes substantially to the desalination performance enhancement in DCMD.

Macrovoid-Inhibited PVDF Hollow Fiber Membranes via Spinning Process Delay for Direct Contact Membrane Distillation.

A polyvinylidene fluoride (PVDF) hollow fiber membrane was fabricated through water-induced dope crystallization by allowing a facile spinning process delay (SPD) in the nonsolvent-induced phase separation (NIPS) process for direct contact membrane distillation (DCMD). The SPD was achieved by the addition of a small amount of water to the PVDF dope solution that was held in a closed container for a particular time. The crystalline property of the PVDF dope solution was investigated by differential scanning calorimetry. The obtained PVDF hollow fiber membranes were characterized with different techniques, including field emission scanning electron microscopy, X-ray diffraction, and the mechanical strength. Both the formation mechanism and properties were studied for the membranes with different SPD times. The results showed that macrovoid-inhibited PVDF membranes were obtained from 12 days of the SPD via the crystallization-dominated membrane formation process. The obtained membrane 4D-12 exhibited desirable membrane structure and properties for DCMD, which includes an improved liquid entry pressure of 2.25 bar, a surface water contact angle of 129°, a maximum pore size of 0.40 μm, and a mean pore size of 0.34 μm. The membrane 4D-12 possessed a twofold increase in both energy efficiency and permeate water flux in DCMD and stable permeate water flux and salt rejection through 224 h of continuous desalination operation. Compared to the commonly used approach by adding chemicals to the external coagulant, the SPD method provided a low-cost and environmentally friendly alternative to pursuing the macrovoid-free PVDF membranes for DCMD.

Anisotropic performance of a superhydrophobic polyvinyl difluoride membrane with corrugated pattern in direct contact membrane distillation

A novel surface-corrugated superhydrophobic polyvinylidene fluoride (PVDF) membrane (C-PVDF) was prepared for direct contact membrane distillation (DCMD) using a micromolding phase separation (μPS) method. The membrane showed a static contact angle of 159.0 ± 4.0°. However, dynamic measurements of the sliding angles revealed a lower value of 9.1 ± 0.8° when a water droplet slides in parallel to the ridge, and a higher value of 14.6 ± 1.6° if perpendicular to the ridge. This anisotropic property was also reflected in the DCMD fluxes for both feed of deionized water and 4.0 wt% NaCl solution: in case the feed flows in parallel to the ridge, a higher flux is resulted than it flows perpendicular to the ridge. Anisotropic MD performance cannot be explained by the Dusty-Gas model because the average characteristics of the membrane in the model are intrinsically the same for both flow modes. Instead, anisotropic wetting and sliding in the parallel and perpendicular orientation revealed that the MD performance has both thermodynamic and hydrodynamic origins.

Comparison of different mass transfer models for direct contact membrane distillation flux evaluation

Comparison of different mass transfer models for direct contact membrane distillation flux evaluation

One-step fabrication of isotropic poly(vinylidene fluoride) membranes for direct contact membrane distillation (DCMD)

Membrane distillation (MD) is a promising desalination process especially in small scale systems. However, the lack of commercial MD membranes severely impedes the industrialization. Although various approaches have been explored to develop high-performance membranes, the complicated processing procedures and high cost are two major obstacles to scale up the available membranes. In this study, a facile bottom-up method using water as coagulation bath was proposed to fabricate porous poly(vinylidene fluoride) (PVDF) membranes for direct contact membrane distillation (DCMD) in view of application in desalination. By covering a piece of non-woven substrate on the nascent film followed by immersion into a water bath, a skinless PVDF membrane with an isotropic structure was obtained. The SEM characterization confirmed the formation of a rough top surface and sponge-like granular membranes composed of spherulites. The water contact angles substantially increased from 71.7° for PVDF-N membrane to ca. 144° for bottom-up membranes. The DCMD flux of the bottom-up PVDF membrane was as high as 41.4 kg/(m2 h) with a polymer concentration of 15 wt%, when the feed and permeate temperatures were 70 °C and 20 °C, respectively. This facile, environmentally friendly approach provides the possibility of manufacturing large-scale high-performance MD membranes.

A Comparison Study of Brine Desalination using Direct Contact and Air Gap Membrane Distillation

Membrane distillation (MD) is a hopeful desalination technique for brine (salty) water. In this research, Direct Contact Membrane Distillation (DCMD) and Air Gap Membrane Distillation (AGMD) will be used. The sample used is from Shat Al –Arab water (TDS=2430 mg/l). A polyvinylidene fluoride (PVDF) flat sheet membrane was used as a flat sheet form with a plate and frame cell. Several parameters were studied, such as; operation time, feed temperature, permeate temperature, feed flow rate. The results showed that with time, the flux decreases because of the accumulated fouling and scaling on the membrane surface. Feed temperature and feed flow rate had a positive effect on the permeate flux, while permeate temperature had a reverse effect on permeate flux. It is noticeable that the flux in DCMD is greater than AGMD, at the same conditions. The flux in DCMD is 10.95LMH, and that in AGMD is 7.14 LMH. In AGMD, the air gap layer made a high resistance. Here the temperature transport reduces in the permeate side of AGMD due to the air gap resistance. The heat needed for AGMD is lower than DCMD, this leads to low permeate flux because the temperature difference between the two sides is very small, so the driving force (vapor pressure) is low. &#x0D;

Theoretical guidance for fabricating higher flux hydrophobic/hydrophilic dual-layer membranes for direct contact membrane distillation

In this study, a new simultaneous heat and mass transfer theoretical model of the membrane distillation process operating under direct contact membrane distillation (DCMD) mode has been developed for the hydrophobic/hydrophilic dual-layer composite membranes. Using the proposed model, a criterion parameter (β) was derived to determine whether the flux will be increased for the prepared hydrophobic/hydrophilic composite membranes. A flux ratio (γDL/SLM) of dual-layer to single-layer membrane was also developed to predict the DCMD flux performance of the composite membranes. To validate the theoretical model, three sets of dual-layer hydrophobic/hydrophilic composite membranes and single-layer hydrophobic membranes with defined total thicknesses (240 μm, 260 μm, and 285 μm) and different thickness ratios (δ/δo=3.69, 2.48 and 2.19) were purposefully fabricated using electrospinning technique. Theoretical modelling results were compared with the experimental data in terms of DCMD flux ratio. The experimental data of flux ratios for the three sets of fabricated membranes at 60 °C, γDL/SLE, are 2.75, 1.97 and 1.80, respectively, which fit well with the model prediction values (γDL/SLM= 2.96, 2.18, and 1.97) within high agreement level at a relative standard deviation of 9.6%. Furthermore, the flux ratio of DL2 to SL2 membranes (dual-layer and single-layer membranes with 260 μm total thicknesses and δ/δo=2.48 thickness ratio) at different feed inlet temperatures still maintain a high degree of consistency with model values. Overall, the results show the experimental data agree well with the theoretical model prediction for the flux ratio within relative standard deviation of 10.1%, thereby confirming the validity of the proposed model. Additionally, a critical value of the thickness ratio (χ) was calculatedχ=1+1β, this value could provide useful guidance to design a highly efficient hydrophobic/hydrophilic dual-layer composite membrane for DCMD applications in the future work.

3D printed spacers for organic fouling mitigation in membrane distillation

3D printing offers the flexibility to achieve favorable spacer geometrical modification. The role of 3D printed spacers for organic fouling mitigation in direct contact membrane distillation (DCMD) is evaluated. Compared to a commercial spacer, the design of 3D printed triply periodic minimal surfaces spacers (Gyroid and tCLP) - varying filament thickness and smaller hydraulic diameter enhanced DCMD fluxes by 50–65%. The highest DCMD flux was obtained with the 3D tCLP spacer due to its specific geometrical design feature. However, its design characteristics resulted in higher channel pressure drop compared to 3D Gyroid spacer. Moreover, 3D Gyroid spacer exhibited superior fouling mitigation (lower membrane organic mass deposition and reversible membrane hydrophobicity with humic acid solution), attributed to its tortuous design that repelled foulants. 3D Gyroid spacer was effective in achieving high water recovery (85%) while maintaining good quality distillate (10–15 μS/cm, 99% ion rejection) in DCMD with wastewater concentrate that contained high organics, mixed with inorganics. In MD, high organic contents minimally affected MD fluxes but reduced membrane hydrophobicity. Repeated DCMD cycles showed that organic pre-treatment as well as cleaning-in-place of membrane and spacer are essential for achieving high recovery rate while maintaining a stable long-term DCMD operation with wastewater concentrate.

3-[[3-(Triethoxysilyl)-propyl] amino] propane-1-sulfonic acid zwitterion grafted polyvinylidene fluoride antifouling membranes for concentrating greywater in direct contact membrane distillation

Direct contact membrane distillation (DCMD) is attractive for wastewater reuse where low-grade heat is highly abundant, but membrane fouling is of critical concerns. In this work, a zwitterion surface-grafted composite polyvinylidene fluoride membrane (PVDF-T) was introduced for DCMD treatment of greywater, a lightly polluted wastewater. Surface grafting was achieved by hydroxylation of a pristine PVDF membrane followed by silanization with the zwitterionomer 3-[[3-(triethoxysilyl)-propyl] amino] propane-1-sulfonic acid (TPAPS). The resulting composite PVDF-T membrane showed a significantly reduced water contact angle but nearly the same liquid entry pressure (LEP) indicating that silanization took place mostly at the surface, and the porous matrix remained hydrophobic. Elemental analysis confirmed that the TPAPS surface grafting was successful. Gas permeability tests indicated increased transport resistance, indicating the extra resistance imposed the zwitterionic modification. In concentrating the synthetic greywater, the PVDF-T membrane exhibited much more stable DCMD flux and constant permeate conductivity than the virgin PVDF membrane. Visual and scanning electron microscopy analysis after MD experiments showed that the PVDF-T membrane was fouled less than the pristine membrane. Improvement in surface hydrophilicity, electronegative charge and steric hindrance were ascribed as the main factors for the fouling resistance of a surface grafted zwitterionic composite PVDF membrane.

Sustainable operation of membrane distillation for hypersaline applications: Roles of brine salinity, membrane permeability and hydrodynamics

This study aims to explore the role of brine salinity in achieving sustainable operation of membrane distillation (MD), particularly in hypersaline applications where highly concentrated or saturated solutions are treated. Given the state-of-the-art MD modeling work mainly focused on the mass and heat transfer phenomena for dilute systems, our simulation work predicts the trends of permeation flux in direct contact MD (DCMD) with elevated feed concentrations up to saturation, by a newly-developed exponential decay function. Also, a semi-empirical equation of the solute transport coefficient Sherwood number (Sh) is derived as Sh = (α1ωF + α2) ReβSc0.33, which for the first time incorporates the influence of feed concentration into the concentration polarization calculation in MD. Numerical analysis on the supersaturation ratio, concentration factor and concentration polarization effect showed that low to modest membrane permeability, reasonably high feed temperature and modest hydrodynamics (500 < Re < 2000) may help to prevent supersaturation and potentially reduce membrane scaling in hypersaline applications.

PVDF/magnetite blend membranes for enhanced flux and salt rejection in membrane distillation

This study reports on the enhancement of direct contact membrane distillation (DCMD) performance by incorporating magnetite nanoparticles (NP) in polyvinylidene fluoride (PVDF) membranes to render the membrane bulk hydrophilic while maintaining a hydrophobic top surface. Hansen solubility parameters (HSP) were first calculated to assess the affinity/compatibility of NP with the polymer, dope solution and aqueous feed. Extensive characterizations were done to elucidate the structural and physiochemical properties of the blend membranes. Energy dispersive spectrometry (EDS) analyses confirmed the uniform distribution of NP within the membrane matrix. Contact angle values showed that the NP did not compromise the hydrophobicity of the membrane top layer. The blend membrane had a 92% higher water uptake value, compared to the pristine sample, indicating the high hydrophilicity of the membrane bulk. Blend membrane also showed higher (ca. 36%) DCMD flux, due to their hydrophilic sub-layer, without compromising the salt rejection. Leaching tests were conducted using both water and concentrated acid to confirm the presence of nanoparticles and to demonstrate the membrane stability in aqueous medium.

Effect of Casting Conditions on SMM Blended Polyethersulfone Hydro–Phobic/–Philic Composite Membranes: Characteristics and Desalination Performance in Membrane Distillation

This study aims at further improvement and development of the novel hydro–phobic/–philic composite membranes which are made specifically for membrane distillation (MD). This was attempted by studying the effect of the casting conditions during the membrane preparation process by the phase inversion method. Two variables were chosen to study, which are the evaporation time before gelation and the gelation path temperature. Some of the membranes were allowed to evaporate at room temperature for 2 or 3 minutes to study the effect of evaporation time. The temperature of the gelation path was varied to 4°C, 20°C or 60°C in order to study the gelation path temperature effect. The prepared membranes were characterized using gas permeation test, measurement of the liquid entry pressure of water (LEPw), X–ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy (AFM). The effects of the casting conditions on the membrane morphology were identified, which enabled us to link the membrane morphology to the membrane performance. The membranes were then tested for desalination of 0.5 M NaCl solution by direct contact membrane distillation (DCMD) and the results were compared to commercial polytetraflouroethylene (PTFE) membrane. It was found that the membrane which was prepared with no evaporation time produced better flux than those with evaporation time. Regarding the gelation path temperature; the membrane prepared with gelation path temperature of 4°C was better than those prepared with gelation path temperature of 20 or 60°C. It should be emphasized that the DCMD flux of the membranes prepared with no evaporation time or with a gelation path temperature of 4°C was superior to the commercial one. Furthermore, all the prepared membranes were tested successfully for the desalination application. In other words, no NaCl was detected in the permeate.

Fabrication of a super-hydrophobic polyvinylidene fluoride hollow fiber membrane using a particle coating process

Membranes with outstanding anti-wetting property are essential for membrane distillation (MD) applications. In this work, a hydrophobization treatment for porous polyvinylidene fluoride (PVDF) hollow fiber membranes using an etching method combined with an ultrafiltration coating process was developed to achieve this desired property. PVDF particle was subjected to an etching process to coarsen its surface. Etched PVDF particles were subsequently dispersed in a dispersant with a specific PVDF-dissolving capacity and then coated onto the PVDF hollow fiber membrane surface via ultrafiltration to construct a super-hydrophobic surface with a micro/nanostructure. After this process, the super-hydrophobic PVDF hollow fiber membrane with the surface contact angle of 163.8°was obtained, and the coating layer on the membrane surface was exceedingly stable. Moreover, the membrane pores were not blocked by the coating layer. The optimal etching conditions for the PVDF particles were as follows: solubility parameter of the etchant, 25.6 (J/cm3)1/2; etching time, 60min at 25°C. A super-hydrophobic surface with a stable particles coated layer is achieved in an optimal coating condition (solubility parameter of the dispersant, 25.87 (J/cm3)1/2; PVDF particles coated, 18.0g/m2). The direct contact membrane distillation (DCMD) experiments showed that after the surface modification process, the hydrophobicity of the membrane was significantly enhanced. In addition, the anti-wetting property of the membrane improved, the time for membrane to be wetted through the channel increased from 40 to 180min, the pure water DCMD flux increased from 26.0 to 29.9kgm−2h−1, and the critical wetting depth increased from 19.5 to 35.7µm.