Improving membrane distillation performance: Morphology optimization of hollow fiber membranes with selected non-solvent in dope solution

Abstract

This study aimed at improving membrane distillation (MD) performance by mixing various nonsolvents (NSs) in polymer dope solutions. The effect of each NS on the inner structure and surface morphology of hollow fiber (HF) membrane was investigated. Membrane morphology is manipulated by controlling liquid-liquid (L-L) and solid-liquid (S-L) demixing time, which is a function of the viscosity and water affinity of dope solutions. Consequently, the addition of NSs altered membrane morphology by affecting the diffusion rate during NS induced phase separation (NIPS) process. The performance results showed that the dope solution composed of 11/71.2/17.8 wt.% polyvinylidene fluoride (PVDF)/ triethyl phosphate (TEP)/toluene produced the most promising HF membrane for MD.The optimal membrane demonstrated a unique bicontinuous structure with increased porosity and mean pore size. The addition of toluene as NS in dope solutions enhanced crystallization process, which increased the Young's modulus of membrane but slightly decreased its maximum tensile strength at break. The optimal PVDF HF membrane demonstrated a steady flux of 18.9 LMH at 60 °C/20 °C of feed/permeate temperatures and a salt rejection of 99.99 % when tested for 72 h. The results suggest that incorporation of toluene as a NS into PVDF dope solutions can increase permeation performance in MD by enhancing the morphology of HF membranes.

Double layer PVDF blends PVDF‐HFP membrane with modified ZnO nanoparticles for direct contact membrane distillation (DCMD)

“…It was observed the morphology of all the membranes (membrane B, DB, and D) was sponge‐like throughout the membrane. This was because of the ethanol‐induced phase inversion, where slow solvent‐non solvent exchange during the phase inversion process 28,29 . Besides, the presence of PVDF‐HFP in membrane B and membrane DB also resulted in delayed demixing due to the HFP content that favors spongy like formation 11,30 …”

“…This was because of the ethanol-induced phase inversion, where slow solvent-non solvent exchange during the phase inversion process. 28,29 Besides, the presence of PVDF-HFP in membrane B and membrane DB also resulted in delayed demixing due to the HFP content that favors spongy like formation. 11,30 Based on the cross-sectional image in Figure 7a, it clearly showed differences in the top and bottom layers Abbreviations: R a , mean roughness; R q , standard deviation of the height value.…”

3D printing for membrane separation, desalination and water treatment

“…Majority of the membranes used are made of polymers but ceramic membranes are also utilized. Conventional polymeric membrane fabrication techniques include phase inversion [69], hollow fiber spinning [70], stretching, and extrusion. Increasing number of studies have also focused on the electrospinning technique for various desalination and water treatment applications [71][72][73].…”

Nanoscale zero-valent iron (nZVI) immobilization onto graphene oxide (GO)-incorporated electrospun polyvinylidene fluoride (PVDF) nanofiber membrane for groundwater remediation via gravity-driven membrane filtration

“…Each sample was first applied with N2 gas to measure the gas permeability. A sessile drop method utilizing Theta Lite 100 (Attension, Sweden) with built-in software was used to analyses the contact angles of all the membranes (Yao et al, 2019). A water droplet around 5 µl was released from a needle tip onto the membrane surface.…”