Slippery for scaling resistance in membrane distillation: A novel porous micropillared superhydrophobic surface

Abstract

Scaling in membrane distillation (MD) is a key issue in desalination of concentrated saline water, where the interface property between the membrane and the feed become critical. In this paper, a new slippery mechanism was explored as an innovative concept to understand the scaling behavior in membrane distillation for a soluble salt, NaCl. The investigation was based on a novel design of a superhydrophobic polyvinylidene fluoride (PVDF) membrane with micro-pillar arrays (MP-PVDF) using a micromolding phase separation (µPS) method. The membrane showed a contact angle of 166.0 ± 2.3° and the sliding angle of 15.8 ± 3.3°. After CF4 plasma treatment, the resultant membrane (CF4-MP-PVDF) showed a reduced sliding angle of 3.0 o. In direct contact membrane distillation (DCMD), the CF4-MP-PVDF membrane illustrated excellent anti-scaling in concentrating saturated NaCl feed. Characterization of the used membranes showed that scaling due to NaCl crystals and possible membrane wetting occurred on the control PVDF and MP-PVDF membranes, but not on the CF4-MP-PVDF membrane. To understand this phenomenon, a "slippery" theory was introduced and correlated the sliding angle to the slippery surface of CF4-MP-PVDF and its anti-scaling property. This work provides a well-defined physical and theoretical platform for investigating scaling problems in membrane distillation and beyond.

Advanced Antiscaling Interfacial Materials toward Highly Efficient Heat Energy Transfer

“…After treating with CF 4 plasma, the prepared CF 4 –MP‐PVDF membrane showed a reduced sliding angle of 3.0°. This membrane further showed less scaling upon concentrating highly saline NaCl solution (25 wt%) by direct contact membrane distillation . On the contrary, both commercial PVDF (C‐PVDF) and MP‐PVDF membranes showed severe scaling and subsequent flux reduction.…”

“…Therefore, it is necessary to understand the membrane scaling behavior of inorganic salts (e.g., NaCl and CaSO 4 ). For instance, Xiao et al designed a superhydrophobic polyvinylidene fluoride membrane with micropillar arrays (MP‐PVDF) . Owing to their simultaneous phase separation during the coagulation, porous structures were clearly observed on the surface of MP‐PVDF.…”

A few-layer graphene for advanced composite PVDF membranes dedicated to water desalination: a comparative study

“…7c) against a ux of 12 L m À2 h À1 and a rejection rate of 99.90% estimated at 60 C for a porous superhydrophobic PVDF membrane micropillared with CF 4 (thickness ¼ 264 mm; porosity ¼ 79%). 74 To evaluate the effect of the lateral size of few-layer graphene, the ux-rejection values were compared taking into account the FLG-WJM and GPNs-UW membranes, 35 where both the membrane types were prepared via phase inversion and processed under the same working conditions. In this regard, it is quite important to stress that signicant changes in the ux take place due to the uid dynamics, unit conguration, driving forces, temperatures, and chemical compositions of the streams processed.…”

Mitigation of Membrane Wetting by Applying a Low Temperature Membrane Distillation

“…In both cases, wetting the pores caused by organic fouling can be limited by using surface-modified membranes. This concept was presented in several works, where membranes with additional thin layers were covered [ 12 , 13 , 14 , 15 ] or nanoparticles to membrane structure were added [ 4 , 16 ]. Unfortunately, long-term studies with intensive fouling and scaling have most often been omitted in these works.…”