Superhydrophobic or Hydrophilic Porous Metallic/Ceramic Tubular Membranes for Continuous Separations of Biodiesel–Water W/O and O/W Emulsions

Abstract

This paper reports the effective surface effect of porous inorganic membranes on improving the emulsion separations (i.e., perm-selective extraction of either oil phase or aqueous phase from the emulsions). A novel tubular form of superwetting, porous, stainless steel/ceramic membranes were demonstrated for enabling continuous separations of oil–water emulsions, extracting either oil phase or aqueous phase from the flowing emulsions. The superhydrophobic membranes consist of macroporous (4 μm) stainless-steel SS434 tube with inner wall surface modified with superhydrophobicity (>150° contact angle) via perfluoro-silane grafting functionalization. The (super)­hydrophilic membranes consist of 4-μm porous stainless-steel SS434 tube without/with inner wall coated with nanoporous alumina (6 nm average pore size), the surface of which was further modified with superhydrophilicity via Hydrophil-S solution deposition. With the cross-flow membrane filtration setup, the surface-engineered tubular membranes were studied for perm-selective extraction of aqueous or oil phase from oil–water emulsions (water-in-oil W/O and oil-in-water O/W) that are relevant to a real industrial biodiesel (FAME) production process. The superhydrophobic membrane (4 μm pore size) has demonstrated capability of extracting nearly 100% pure oil while rejecting water phase when either W/O or O/W emulsions were tested as feed. The superhydrophobic membrane showed distinct advantage of 2-orders-of-magnitude-higher flux extraction of oil at 100 times higher “break-through” pressures. On the other hand, the super/hydrophilic nanoporous membranes (6 nm) have shown selective water permeation (separation factor up to 35) when biodiesel-relevant W/O emulsions were tested. Finally, the membrane function is discussed from the perspective of improving industrial biodiesel processing yield by overcoming equilibrium limitations during the biodiesel formation reactions. Future work on in situ reaction–separation experiments are envisioned.

Droplet Dynamics and Freezing Delay on Nanoporous Microstructured Surfaces at Condensing Environment

“…Varanasi et al showed rare-earth oxide ceramics materials promoted dropwise condensation, repelling water droplets and sustaining hydrophobicity even after exposure to harsh environments [55]. Other ceramic membranes grafted and coated by perfluorosilane showed promising results [56][57][58][59]. In condensate condition, self-cleaning of superhydrophobic surfaces by self-propelled droplet jumping and sweeping have also been demonstrated by several studies [30,32,[60][61][62].…”

Hydrodynamic and Performance Evaluation of a Porous Ceramic Membrane Module Used on the Water–Oil Separation Process: An Investigation by CFD

“…Membrane separation processes can be classified into four categories according to the pore size: microfiltration, ultrafiltration, nanofiltration, and reverse osmosis [ 24 , 25 , 26 ]. The pore size of the membrane determines the filtration properties of water/oil emulsions, which can also vary, depending on the concentration of the oil in the emulsion and, consequently, on the size of the oil drop [ 13 , 27 ].…”

Aggregation‐induced demulsification triggered by the hydrophilic fabric for the separation of highly emulsified oil droplets from water

“…[16] By retrieving the kinds of literatures in this field, [17][18][19][20][21] it was found that the materials in the form of the membrane were promising for the separation of different emulsions, especially those with hierarchical structures consisting of fibre and nanoparticles/features, such as stainless steel mesh coated with ZnO nanowires, [22] cotton fibres with roughened morphology in nano-scale, [23] ceramic membrane coated with Al 2 O 3 nanoparticles. [24] While much progress has been made in this field, restrictive factors like the cost, availability of raw materials as well as complicated preparation process, were remained more or less for the scaleup production of the material.…”