Optimization of flat sheet hydrophobic membranes synthesis via supercritical CO2 induced phase inversion for direct contact membrane distillation by using response surface methodology (RSM)

• The hydrophobic membrane synthesis by supercritical CO2 induced phase inversion method.
• Ternary phase diagram was calculated theoretically for the nascent membrane in different conditions.
• Response surface method was employed to optimize the membrane.
• Optimized membrane was tested in membrane distillation process.

Flat-sheet hydrophobic polyvinylidene fluoride (PVDF) membrane was prepared by supercritical fluid induced phase inversion technique. The effects of initial polymer concentration, pressure, and temperature of supercritical fluid on the final membrane structures and surface hydrophobicity were investigated. The morphologies and hydrophobicities of PVDF micro porous membranes were analyzed by means of scanning electron microscopy (SEM) and contact angle (CA) measurement, respectively. The ternary theory phase diagram will evaluate the thermodynamic aspects of the membrane precipitation process for difference ScCO2 pressure and temperature. This phase diagram was constructed by theoretical calculation, based on Flory–Huggins solution theory. Response surface methodology (RSM) was used to optimize the characteristics of membrane structural by setting the parameters of membrane synthesis process (temperature, pressure and polymer concentration) to be used in direct contact membrane distillation (DCMD). Analysis of variance shows significant effects of each variable on the responses. The membrane is optimized under the following conditions: 14.76 wt.% PVDF concentration, 35 °C temperature and pressure of 10 MPa. The fabricated optimum membrane, compared to membrane prepared by conventional wet phase inversion method exhibited a better permeate flux.

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