Modification and characterization of ultrafiltration membranes for treatment of produced water

Fabrication of a Self-Cleaning Surface via the Thermosensitive Copolymer Brush of P(NIPAAm-PEGMA)

Surface hydrophilicity and the inherent washing force are two crucial factors for constructing an underwater self-cleaning surface. Following this self-cleaning mechanism, we fabricated thermosensitive copolymer brushes of N-isopropylacrylamide (NIPAAm) and poly(ethylene glycol) methacrylate (PEGMA) on the polypropylene (PP) surface. Benefiting from the hydrophilic poly(ethylene glycol) (PEG) side chains, the copolymer brushes with the PEGMA content exceeding 5 mol % exhibited good surface hydrophilicity, whenever at temperatures below or above the lower critical solution temperatures (LCST). Hence their underwater oleophobicity was greatly improved with oil contact angles higher than 141° and oil adhesive forces lower than 20 μN. In addition, the sharp volume-phase transition feature was reserved in their copolymer backbones, as proved by the AFM result. Self-cleaning evaluation of the modified surfaces was performed by a simple temperature-change water cleaning method, after which only 0.2 wt % of oil residues remained on the brush surface of P(NIPAAm-5PEGMA) (with 5 mol % of PEGMA contents). The excellent self-cleaning capability is believed to be ascribed to its balanced surface features in hydrophilicity and the sharper volume-phase transition, when a hydrophilic surface can facilitate oil desorption and an intense conformation change of chain stretching and shrinking can offer the strong washing force to assist oil detachment. This study contributes to development of the underwater self-cleaning surface based on a hydrophilic surface with the chain motion.

Ceramic membrane fouling during ultrafiltration of oil/water emulsions: roles played by stabilization surfactants of oil droplets

Oil/water (O/W) emulsion stabilized by surfactants is the part of oily wastewater that is most difficult to handle. Ceramic membrane ultrafiltration presently is an ideal process to treat O/W emulsions. However, little is known about the fouling mechanism of the ceramic membrane during O/W emulsion treatment. This paper investigated how stabilization surfactants of O/W emulsions influence the irreversible fouling of ceramic membranes during ultrafiltration. An unexpected phenomenon observed was that irreversible fouling was much less when the charge of the stabilization surfactant of O/W emulsions is opposite to the membrane. The less ceramic membrane fouling in this case was proposed to be due to a synergetic steric effect and demulsification effect which prevented the penetration of oil droplets into membrane pores and led to less pore blockage. This proposed mechanism was supported by cross section images of fouled and virgin ceramic membranes taken with scanning electron microscopy, regression results of classical fouling models, and analysis of organic components rejected by the membrane. Furthermore, this mechanism was also verified by the existence of a steric effect and demulsification effect. Our finding suggests that ceramic membrane oppositely charged to the stabilization surfactant should be applied in ultrafiltration of O/W emulsions to alleviate irreversible membrane fouling. It could be a useful rule for ceramic membrane ultrafiltration of oily wastewater.

Probing the morphology and anti-organic fouling behaviour of a polyetherimide membrane modified with hydrophilic organic acids as additives

A polyetherimide based membrane was modified with various hydrophilic organic acids as additives. The results showed that the additives exhibited a remarkable improvement in the antifouling properties (FRR of 72%).

An intelligent superwetting PVDF membrane showing switchable transport performance for oil/water separation

A superamphiphilic poly(vinylidene fluoride) (PVDF) membrane with superoleophobicity under water and superhydrophobicity under oil is successfully prepared. Due to the switchable transport performance, the membrane is applicable to the separation of various oil-in-water and water-in-oil emulsions with a droplet size greater than 20 nm, and shows superior permeability and antifouling properties, as well as a high separation efficiency.

Development of high-productivity, strong cation-exchange adsorbers for protein capture by graft polymerization from membranes with different pore sizes

This paper describes the surface modification of macroporous membranes using ATRP (atom transfer radical polymerization) to create cation-exchange adsorbers with high protein binding capacity at high product throughput. The work is motivated by the need for a more economical and rapid capture step in downstream processing of protein therapeutics. Membranes with three reported nominal pore sizes (0.2, 0.45, 1.0 μm) were modified with poly(3-sulfopropyl methacrylate, potassium salt) tentacles, to create a high density of protein binding sites. A special formulation was used in which the monomer was protected by a crown ether to enable surface-initiated ATRP of this cationic polyelectrolyte. Success with modification was supported by chemical analysis using Fourier-transform infrared spectroscopy and indirectly by measurement of pure water flux as a function of polymerization time. Uniformity of modification within the membranes was visualized with confocal laser scanning microscopy. Static and dynamic binding capacities were measured using lysozyme protein to allow comparisons with reported performance data for commercial cation-exchange materials. Dynamic binding capacities were measured for flow rates ranging from 13 to 109 column volumes (CV)/min. Results show that this unique ATRP formulation can be used to fabricate cation-exchange membrane adsorbers with dynamic binding capacities as high as 70 mg/mL at a throughput of 100 CV/min and unprecedented productivity of 300 mg/mL/min.

Ceramic pore channels with inducted carbon nanotubes for removing oil from water

Water contaminated with tiny oil emulsions is costly and difficult to treat because of the colloidal stability and deformable nature of emulsified oil. This work utilizes carbon nanotubes (CNTs) in macro/mesopore channels of ceramic membrane to remove tiny oil droplets from water. The CNTs were implanted into the porous ceramic channels by means of chemical vapor deposition. Being hydrophobic in nature and possessing an interfacial curvature at nanoscale, CNTs enabled tiny oil emulsion in submicrometer and nano scales to be entrapped while permeating through the CNTs implanted pore channels. Optimizing the growth condition of the CNTs resulted in a uniform distribution of CNT grids, which allowed the development of lipophilic layers during filtration. These lipo-layers drastically enhanced the separation performance. The filtration capability of CNT-ceramic membrane was assessed by the purification of a dilute oil-in-water (o/w) emulsion containing ca. 210 ppm mineral oil 1600 ppm emulsifier, and a trace amount of dye, a proxy polluted water source. The best CNT-tailored ceramic membrane, prepared under the optimized CNT growth condition, claimed 100% oil rejection rate and a permeation flux of 0.6 L m(-2) min(-1), driven by a pressure drop of ca. 1 bar for 3 days on the basis of UV measurement. The CNT-sustained adsorption complements the size-exclusion mechanism in removing soluble oil.

Origin, separation and identification of environmental nanoparticles: a review

The biogeochemical and ecological impacts of environmental nanoparticles (ENPs) are some of the fastest growing areas of research today. However, efficient separation and collection of ENPs in natural systems remains difficult. This review article is focused on experimental investigation of separation and identification of ENPs, including nanoparticles with size fractions in the range of <2000, 450 to 2000, 100 to 450 and 1 to 100 nm. An automated ultrafiltration device (AUD) was used successfully to overcome the problem of efficiently collecting ENPs in large quantities in red soils. A significant amount of hematite nanoparticles was present on the surface coating of kaolinite nanoparticles and aggregated hematite nanoparticles overlapping the edge of a kaolinite flake in a size range of 5 to 8 nm. Synchrotron XRD technique is more straightforward and powerful than conventional XRD with oriented specimens and random powder methods for identifying nanoparticles, crystallinity, and particle size in red soils, particularly for the illite, kaolinite, goethite and hematite nanoparticles. The AUD apparatus can be employed to efficiently collect large quantities of soil and related ENPs for investigation of their structural characteristics and surface properties, which have significant impact on weathering reaction pathways, catalysis, the fate of vital elements and environmental pollutants, and ecosystem restoration.