C.P. Leo

Membranes with Great Hydrophobicity: A Review on Preparation and Characterization

Membranes are commonly designed with great hydrophilicity or hydrophobicity to promote or prohibit the transportation of water, respectively. There are vast applications of hydrophobic membranes such as filtration, gas separation, membrane gas absorption, pervaporation, membrane distillation and more that cannot be attained with hydrophilic membranes. However, the development of hydrophobic membranes was relatively slow in the past, as membrane technologists and researchers were more interested in reducing membrane hydrophobicity for permeability enhancement or fouling control in the aqueous separation. Thus, literature related to hydrophobic membranes has not been reviewed elsewhere. This review reported on the characterization and preparation methods for hydrophobic membranes. Hydrophobic ceramic membranes are commonly prepared by chemical modification. Besides using different types of chemicals, the membrane surface is roughened to enhance its hydrophobicity. For polymeric membranes, great hydrophobicity can be engineered using per-fluorinated polymers or phase immersion in a dual coagulation bath. Each technique has its advantages and weaknesses.

Model-based analysis of polymeric membranes performance in high pressure CO2 removal from natural gas

Penetrant-induced plasticization is known to be one of the main challenges of high-pressure membrane separation of CO2 from natural gas. Therefore, a procedure that integrates experimental and mathematical models was developed to analyze the performance of polymeric membranes for removal of CO2 at high feed pressure. A semi-empirical model for estimating plasticization pressure and permeability parameters at plasticization from permeation test data was proposed and tested on more than 90 polymeric membranes. Three model parameters (α1, α2 , and α3) were obtained and used to evaluate membrane performance in terms of plasticization pressure as well as permeability and productivity loss at plasticization pressure. Results from the analysis revealed that this set of parameters can be simply employed to evaluate membrane performance at high pressure.

Fouling mitigation in humic acid ultrafiltration using polysulfone/SAPO-34 mixed matrix membrane

Although ultrafiltration (UF) membranes are applicable in wastewater and water treatment, most UF membranes are hydrophobic and susceptible to severe fouling by natural organic matter. In this work, polysulfone (PSf) membrane was blended with silicaluminophosphate (SAPO) nanoparticles, SAPO-34, to study the effect of SAPO-34 incorporation in humic acid (HA) fouling mitigation. The casting solution was prepared by blending 5-20 wt% of SAPO-34 nanoparticles into the mixture of PSf, 1-methyl-2-pyrrolidinone and polyvinyl alcohol at 75 °C. All membrane samples were then prepared using the phase inversion method. Blending SAPO-34 zeolite into PSf membranes caused augmentation in surface hydrophilicity and pore size, leading to higher water permeation. In the HA filtration test, mixed matrix membranes (MMMs) with SAPO-34 zeolite showed reduced HA fouling initiated from pore blocking. The MMM with 20 wt% SAPO-34 loading exhibited the highest increment of water permeation (83%) and maintained about 75% of permeate flux after 2.5 h. However, the SAPO-34 fillers agglomerated in the PSf matrix and induced macrovoid formation on the membrane surface when excessive zeolite was added.

Potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus for aquaculture

Aquaculture activities in developing countries have raised deep concern about nutrient pollution, especially excess phosphorus in wastewater, which leads to eutrophication. NF, NF90, NF450 and XLE membranes were studied to forecast the potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus from aquaculture wastewater. Cross-sectional morphology, water contact angle, water permeability and zeta potential of these membranes were first examined. Membrane with higher porosity and greater hydrophilicity showed better permeability. Membrane samples also commonly exhibited high zeta potential value in the polyphosphate-rich solution. All the selected membranes removed more than 90% of polyphosphate from the concentrated feed (75 mg/L) at 12 bar. The separation performance of XLE membrane was well maintained at 94.6% even at low pressure. At low feed concentration, more than 70.0% of phosphorus rejection was achieved using XLE membrane. The formation of intermolecular bonds between polyphosphate and the acquired membranes probably had improved the removal of polyphosphate at high feed concentration. XLE membrane was further tested and its rejection of polyphosphate reduced with the decline of pH and the addition of ammonium nitrate.