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Membrane distillation has emerged as a promising technique for treating high-saline water. However, the process suffers from drawbacks such as wettability and fouling due to insufficient hydrophobicity of the membrane material. A practical approach for preparing hydrophobic membranes should involve improving surface roughness and chemistry manipulation. Herein, we explored chemical grafting of different functional groups viz. 1-(4-vinyl benzyl)azepane, N-(4-vinyl benzyl)decan-1-amine and 3-(triethoxysilyl)-N-(4-vinyl benzyl) propane-1-amine on polyvinylidene fluoride side chain to improve the hydrophobic characteristics and vacuum distillation performance (permeate flux and salt rejection). The successful grafting of hydrophobic functional groups on the polyvinylidene fluoride side chain was confirmed by spectral analysis such as 1H nuclear magnetic resonance, Attenuated total reflectance-Fourier transformation infrared spectroscopy, and X-ray photoelectron spectroscopy. The synthesised membranes were further characterised using morphology techniques (scanning electron microscopy, atomic force microscopy) for hydrophobicity (water contact angle, liquid entry pressure) and thermal and mechanical stability. The desalination performance of membranes was assessed by varying feed concentration (2–8 % NaCl) and feed temperature (30–75 °C). The 3-aminopropyltriethoxysilane grafted vinyl benzyl polyvinylidene fluoride membrane exhibited the highest flux (20.35 L m−2 h−1), salt rejection (99.99 %) at 4 % NaCl feed concentration and 60 °C feed temperature attributed to a well-arranged large number of pores and its hydrophobicity. The 3-aminopropyltriethoxysilane grafted membrane exhibited the highest anti-fouling characteristic. Further, high flux and salt rejection of the synthesised membranes for vacuum membrane distillation operation were compared to membranes reported in the literature, demonstrating its potential for high saline water desalination. [Display omitted] • Flat-sheet side chain chemical grafted PVDF membranes were prepared via NIPS. • Effect of feed concentration, and temperature; and anti-fouling characteristics of the membranes were studied. • M-APTES membrane exhibited the highest flux, salt rejection and anti-fouling characteristics. [ABSTRACT FROM AUTHOR]

One of the most water-intensive and environment polluting anthropogenic industries is the textile industry. Amongst textile dyes, methyl orange (MO) is an extensively used anionic azo dye that is toxic to the environment. In this study, the effect of various process parameters was studied for different operating conditions (mass flow rate, vacuum pressure, inlet feed temperature, dye concentration) to remove MO from synthetic wastewater in the vacuum membrane distillation (VMD) process. We determined the optimum conditions for operating variables using response surface methodology (RSM) and developed a regression model to describe permeate flux, dye rejection and specific energy consumption. The optimum operating parameters from the RSM study were bulk feed temperature: 70 °C, mass flowrate: 40 kg h−1, dye concentration: 60 mg l−1 and vacuum pressure: 720 mm Hg. For the optimized input process parameters, the experimentally observed values were permeate flux: 19.60 ± 1.03 l m−2 h−1, dye rejection: 99.80 ± 0.07%, and SEC: 2.04 ± 0.11 kW h m−3. Furthermore, for these optimized conditions, a 3D CFD model was developed to gain insight into the membrane module's thermal, velocity, and concentration field. The evaporation of feed at the membrane surface on the feed side and condensation of vapours at the membrane surface on the permeate side was captured in this model. The permeate flux profile and dye rejection for various cycles of VMD operation with intermittent washing were also performed to study the fouling behaviour of the membrane. The membrane's surface fouling was analyzed using SEM and FT-IR analysis. The SEM analysis of the fouled membrane indicated that the dye deposition was not severe due to high hydrophobicity, high liquid entry pressure, and high pore wetting resistance of the PTFE membrane. The FT-IR analysis showed that the fouled PTFE membrane sufficiently retained its initial structure and property. [Display omitted] [ABSTRACT FROM AUTHOR]