Water Separation Efficiency Research Articles

Transition sandwich Janus membrane of cellulose acetate and polyurethane nanofibers for oil–water separation

Through sequential electrospinning, a sandwich Janus membrane (PU-(CA/PU)-CA) was constructed with hydrophobic polyurethane (PU) nanofiber membrane as the top layer, cellulose acetate/polyurethane (CA/PU) blend nanofiber membrane as the intermediate transition layer and hydrophilic cellulose acetate (CA) nanofiber membrane as the bottom layer. The effects of membrane structure, composition and thickness on the mechanical properties, permeability and separation ability of PU-(CA/PU)-CA nanofiber membrane were studied. The results show that the transition sandwich structure PU-(CA/PU)-CA membrane has good mechanical properties, high permeability and selective separation ability, and can realize the unidirectional transmission of water and efficient oil–water separation. When the membrane thickness is 80 μm, the hydraulic permeability is 3.4 ± 0.4 × 104 L/(m2 h bar), the oil–water separation efficiency reaches 99 ± 0.4%, and the tensile strength is 95.8% higher than that of the double-layer PU-CA membrane. The thermal stability and antifouling ability of PU-(CA/PU)-CA nanofiber membrane have also been improved, and the reusability is good. CA/PU transition interlayer improves the interfacial compatibility between CA and PU nanofiber membrane, enhances the performance of PU-(CA/PU)-CA nanofiber Janus membrane, and shows its application prospect in the field of separation and purification.Graphical abstract

Melamine resin-coated lignocellulose fibers with robust superhydrophobicity for highly effective oil/water separation

• Superhydrophobic strategies based on condensation and addition reactions. • Oil spill clean-up through selective absorption and active filtration processes. • The scalable manufacturing strategy is low-cost and environment-friendly. oil pollution incidents emerge in endlessly, threatening global ecological security and environmental sustainability. It is a consensus of current scientific research to develop environmentally friendly, sustainable and degradable materials for polluted water body restoration. Cellulose is one of the most attractive candidate materials due to its abundant reserves and all-green degradability. Herein, a technique used to modify lignocellulose fibers via the condensation and addition reactions is reported, and the modified lignocellulose fibers exhibit excellent superhydrophobic and degradation properties. The modification process consists of two main steps: 1) the in situ construction of micro-nano structures on the surface of lignocellulose fibers through the condensation reaction using melamine and formaldehyde; 2) using the addition reaction between the isothiocyanate compound with low surface energy and the amino groups of the melamine resin. The superhydrophobic isothiocyanate/melamine/formaldehyde (IMF) lignocellulose fibers are extremely repellent to water both in atmospheric conditions and underoil. It can separate various oil–water mixtures by absorption (with a high oil absorption capacity of > 1000 wt%) and gravity-driven filtration (with a separation efficiency of > 96%). The embedded superhydrophobicity in the IMF lignocellulose fibers remained unperturbed (with the water contact angle of > 150° and the oil–water separation efficiency of > 97%) even after repeating for 50 cycles. The presented strategy not only indicates a new direction for the comprehensive utilization of abundant lignocellulose fibers, but also proposes a promising way for the development of oil–water remediation technology.

Breaking of Emulsions with Chemical Additives: Using Surrogate Fluids to Develop a Novel Theoretical Framework and Its Application to Water-in-Crude Oil Emulsions.

We investigate the role of adding a water-soluble surfactant (Tween 20) that acts as a demulsifier on the stability of water-in-dodecane emulsions stabilized with Span 80. Performing bottle test experiments, we monitor the emulsion separation process. Initially, water droplets sediment fast (∼10 min) until they become closely packed and form the so-called dense packed layer (DPL). The presence of the DPL, a long-lived metastable high-water-fraction (70–90%) emulsion separating bulk oil and water layers, slows down significantly the kinetics (∼105 min) of water separation. Once the DPL is formed, the ratio of the volume of separated water to the total water amount is called as water separation efficiency. We assume that the emulsion stability is reached when the coverage of the emulsifier surfactant exceeds 80% and use the ideal solution approximation. From that, we rationalize the water separation efficiency and the minimum demulsifier concentration required to maximize it, in terms of the mean droplet size, the surfactant concentrations, the total water volume fraction, and the adsorption strength of the water-soluble surfactant. Model predictions and experimental findings are in excellent agreement. We further test the validity and robustness of our theoretical model, by applying it successfully to data found in the literature on water-in-crude oil emulsion systems. Ultimately, our results prove that the efficiency of a demulsifier agent to break a W/O emulsion strongly correlates to its adsorption strength at the W/O interface, providing a novel contribution to the selection guidelines of chemical demulsifiers.

Thermally Induced Silane Dehydrocoupling: Hydrophobic and Oleophilic Filter Paper Preparation for Water Separation and Removal from Organic Solvents.

Organic solvents with high purity are essential in various fields such as optical, electronic, pharmaceutical, and chemical areas to prevent low-quality products or undesired side-products. Constructing methods to remove impurities such as water residue in organic solvents has been a significant challenge. Within this article, we report for the first time a new method for the preparation of hydrophobic and oleophilic filter paper (named OCFP), based on thermally induced silane dehydrocoupling between cellulose-based filter paper and octadecylsilane. We comprehensively characterized OCFP using various characterization techniques (FTIR, XPS, XRD, and EDS). OCFP showed super-hydrophobic and oleophilic properties as well as remarkable water separation and removal efficiency (>93%) in various organic solvents with sustained reusability. In addition, the analytical results both before and after filtration of an NMR solvent using OCFP indicated that OCFP has an excellent solvent drying efficiency. This work presents a new strategy for the development of super-hydrophobic cellulose-based filter paper, which has great potential for solvent drying and water separation.

Fabrication of a durable coral-like superhydrophilic MgO coating on stainless steel mesh for efficient oil/water separation

A superhydrophilic/underwater superoleophobic MgO&SSM coating on SSM (stainless steel mesh) with micro-nano coral-like structure was fabricated by high-temperature treatment of SSM soaked with magnesium nitrate solution. This unique coral-like structure gives it a super high specific surface area and a large number of hydroxyl groups are exposed to the surface. The oil–water separation efficiency achieved 99.0% and the flux attained to 6195 L·m−2 h−1. And the oil–water separation efficiency was always as high as 98.0% after 10 times of repeated use. In addition, it could still maintain underwater superoleophobicity after immersing them in different pH solutions (pH, 5–12) or saturated NaCl solutions for a certain period of time. More importantly, it still maintained underwater superoleophobicity and shown excellent weather resistance after being treated at different temperatures for 2 h or after being exposed to ultraviolet rays at elevated temperatures for 6 h.

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Rational design of Janus nanofibrous membranes with novel under-oil superhydrophilic/superhydrophobic asymmetric wettability for water-in-diesel emulsion separation

Endowing nanofibrous membranes with special wettability has always been the dominant strategy to improve the separation performance for water-in-oil emulsions. In this work, a rational design of deacetylated cellulose acetate/polyvinylidene fluoride (dCA/PVDF) Janus nanofibrous membrane, with asymmetric wettability in either air, water or diesel environment, was developed via sequential electrospinning PVDF and CA membranes followed by alkali treatment. In the process of water-in-diesel emulsion separation, the under-diesel superhydrophilic dCA layer is able to capture the emulsified water and strengthens the demulsification ability of the Janus membrane, while the under-diesel superhydrophobic PVDF layer acts as a water barrier and further improves the separation ability. The Janus membrane therefore exhibited prominent separation performance not only for the water/diesel mixture (separation efficiency 99.98%) but also for the surfactant-stabilized water-in-diesel emulsion with l vol% water (separation efficiency 97.74%). Moreover, the Janus membrane maintained high separation efficiency over 96% after repeated use for 50 times or soaking in corrosive solutions for 24 h. The Janus dCA/PVDF nanofibrous membrane possesses competitive efficiency, reusability and acid/alkali resistance, making it a promising candidate as the separation membrane for the surfactant-stabilized water-in-diesel emulsion.

A facile preparation of robust superhydrophilic and underwater superoleophobic copper foam for high efficiency and repeatable oil–water separation

Design of robust separation materials with superwettability for efficient oil–water separation is of great significance because of the serious problem of oil leakage. Herein, we have fabricated a superwetting material based on copper foam via chemical oxidation and hydrothermal method for oil–water separation. These modified copper foam with rough structure exhibit excellent superhydrophilicity and underwater superoleophobicity. Thus, it shows high oil–water separation efficiency (99%), excellent circulation and high‐flux (24,129 Lm−2 h−1). Meanwhile, the modified copper foam exhibits favorable durability and stability under extreme environment conditions, such as immersion tests in salt, different pH conditions, high temperature and mechanical abrasion tests. Therefore, the modified copper foam has the advantages of high separation efficiency and remarkable stability, and is promising material, which can be used for the treatment of industrial oily wastewater.

Robust super hydrophobic cotton fabrics functionalized with Ag and PDMS for effective antibacterial activity and efficient oil–water separation

The development of multifunctional super hydrophobic cotton materials for oil–water separation and biological activities has attracted significant research interest. In the present study, a robust, fluorine-free, durable and recyclable modified cotton fabric was created by graft polymerization and coating techniques. The surface was grafted with poly(glycidyl methacrylate) (PGMA), subsequently aminated with diethylenetriamine (DETA), and then immobilized with Ag to obtain CF@GMA@DETA(Ag). Moreover, Polydimethylsiloxane (PDMS) was coated on CF@GMA@DETA(Ag) for super hydrophobicity to obtain the modified cotton fabrics (CF@GMA@DETA(Ag)/PDMS). The water contact angle (WCA) reached 155° ± 1.5°. The modified cotton material had excellent oil–water separation efficiency. Meanwhile, the modified cotton material also has outstanding recyclability and stability. With Ag modification, the modified cotton material also showed impressive antibacterial properties. Furthermore, oil–water separation efficiency was generally higher than 97% in artificial seawater, which offers a possible application to separate oil and water in seawater. These properties render the as-prepared cotton fabric a promising material with potential applications.

Design and analysis of de-oiling coalescence hydrocyclone

ABSTRACT De-oiling hydrocyclones are extensively applied in oilfield wastewater purification for fluid separation, because of their efficient and rapid processing performance. However, it is difficult for a hydrocyclone to separate tiny oil droplets owing to the inadequate centrifugal force. A type of coalescence hydrocyclone (CHC) is designed based on the principle of centrifugal separation and hydraulic droplet collision coalescence. The structure, coalescence theory, and separation principle of the CHC are introduced. Based on the Euler–Euler method, the population balance model (PBM) is applied to a continuous equation to simulate the distributions of the velocities, oil volume fraction, and oil droplet size in the CHC. The simulation method is verified by conducting particle image velocimetry tests in a polymethyl methacrylate hydrocyclone. The results indicate that the CHC can improve the separation performance by enlarging the oil droplet size by collision coalescence before entering the hydrocyclone. The results of separation efficiency experiment indicate that the CHC can not only improve the oil–water separation efficiency but also clearly enhance the processing capability. The optimal inlet flow rate is 5.5 m3·h-1 and the split ratio is 25%. The feasibility of the structure design and the reliability of the separation performance are validated by experiments.

Preparation of the Temperature-Responsive Superhydrophobic Paper with High Stability.

In this paper, a method for preparing a high-stability superhydrophobic paper with temperature-induced wettability transition is proposed. First, a temperature-responsive superhydrophobic triblock polymer PHFMA–PTSPM–PNIPAAm was prepared by one-step polymerization of TSPM, HFMA, and NIPAAm in a mass ratio of 0.3:0.3:0.3, then a superhydrophobic paper with a good temperature response was successfully prepared by grafting amino-modified SiO2 with the polymer to modify the surface of the paper. A further study found that when the mass ratio of amino-modified SiO2 to polymer is 0.2, the coating has good superhydrophobicity and transparency. What is more, the prepared modified paper is in a superhydrophobic state when the temperature is higher than 32 °C, and is in a superhydrophilic state when it is lower than 32 °C, which can realize free conversion between superhydrophobic and superhydrophilic states. In addition, the superhydrophobic paper prepared by this method not only has high oil–water separation efficiency, and the superhydrophobic coating shows good stability and transparency, but also has low requirements of environmental conditions for preparation, relatively simple preparation process, and strong repeatability, and it has a very broad application prospect.

Superhydrophobic modification of the surface of cellulosic materials based on honeycomb-like zinc oxide structures and their application in oil–water separation

Honeycomb-like zinc oxide structures were prepared on the surface of cellulosic materials including cotton fabric fiber and filter paper fiber through plasma treatment followed by wet chemical reaction, the effect of plasma treatment is to increase the wettability and reactivity of cellulosic materials, so that the zinc oxide can nucleate and grow into a honeycomb-like structure on the cellulose fibers. The superhydrophobic surface was then obtained by modifying stearic acid on the zinc oxide structure. The microstructure, chemical composition and state, and wettability of the cellulosic materials were studied in detail. After the modification, the water contact angle and water sliding angle of the modified cotton fabric were 151° and 3.4°, respectively, and those of the modified filter paper is 154° and 4.5°, which indicates super-hydrophobicity. Due to the structural characteristics of zinc oxide-stearic acid structure, the superhydrophobic structure can maintain superhydrophobic performance in strong acidic or strong alkaline environments or after ultrasonic vibration treatment. Further, superhydrophobic modified cotton fabric and filter paper can be used for oil–water separation and adsorption of oil droplets in aqueous solution, and the oil–water separation efficiency is greater than 90%. This method of superhydrophobic modification of cellulosic materials has broad application prospects.

One-step environment-friendly process to design fire-resistant superhydrophobic carbon felts with excellent durability and oil–water separation performance

Nowadays, it has become an imminent challenge of developing a robust and efficient oil/organic solvent absorbing/releasing along with oil–water separating material. Herein, a simple and environment-friendly one-step immersion method is developed for fabricating superhydrophobic carbon felts with extraordinary properties. The as-prepared superhydrophobic carbon felts reveal outstanding durability and stability even exposed to various harsh environments, such as acid, base, salt, organic solvent, and UV light for quite long time. The superhydrophobic carbon felts exhibit excellent fire resistance, and the materials can stand at least 5 times of ethanol-soaking and burning without marked influencing on the superhydrophobicity. Meanwhile, the resultant materials reveal outstanding oil adsorption and oil–water separation performance. The superhydrophobic carbon felt can still absorb 7 times its own mass of cooking oil even after 10 extrusion cycles. Moreover, the oil–water separation efficiency can still reach 98.85% after 10 times of separation. Consequently, the materials can be used in oil/organic solvent collection and oil–water separation successfully. Therefore, the simple, environment-friendly, cost-effective fabrication method together with the extraordinary durability and stability, excellent and efficient performance will find its potential applications in industrial production and environmental remediation. A simple and environment-friendly one-step immersion method for fabricating superhydrophobic carbon felts is developed. The as-prepared superhydrophobic carbon felts reveal excellent fire resistance along with extraordinary durability and stability upon various harsh environments. Furthermore, the superhydrophobic carbon felts exhibit outstanding oil/organic solvent adsorption/releasing and oil–water separation performance.

Fluorine free TiO2/cyanate ester coated cotton fabric with low surface free energy and rough surface for durable oil–water separation

Low cost superhydrophobic cotton fabric was developed using TiO2/cyanate ester coating for the first time. The TiO2/cyanate ester coated cotton fabric displayed superhydrophobic behaviour with water contact angle of 158°, sliding contact angle of 8° and surface free energy of 18.0 mN/m2. Besides, the TiO2/cyanate ester coated cotton fabric also possesses excellent laundry durability as well as stability against acid, alkali salt solutions and mechanical abrasion. Consequently, the TiO2/cyanate ester coated cotton also delivered superior oil–water separation efficiency with different types of oil/water mixtures that includes engine oil/water, waste engine oil/water, petrol/water and diesel/water. The TiO2/cyanate ester coated cotton fabric shows separation efficiency as high as 98% with flux value of 7200 L/m2h for petrol/water mixture. Further, both cyanate ester and TiO2/cyanate ester coated cotton fabric delivers ultra-high UV-resistant ability with Ultraviolet Protection Factor value as high as 500 + . Hence, it is anticipated that the present approach of using cyanate ester can be widely explored further to construct multifunctional fabrics towards excellent self-cleaning as well as oil/water separation with UV and chemical robustness.

TiO2 encapsulated cross-linked polystyrene-polyacrylic acid membranes for waste oil-water separation

Special wetting polystyrene (PS) based superhydrophobic material has been investigated as a potential cost-effective and efficient oil-water separation membrane to remediate the oil spills. However, superhydrophobic properties of polystyrene based materials are susceptible to harsh physical or chemical conditions and their superhydrophobic properties can be diminished easily. To address the stability of polystyrene based superhydrophobic membranes, polystyrene was cross-linked with the acrylic acid (AA) either by ex-situ or in-situ polymerization on the TiO2 nanoparticles. Membranes fabricated either by ex-situ or in-situ polymerization of styrene-acrylic acid on the TiO2 nanoparticles exhibited enhanced oleophilic properties having the oil contact angles of ~ 0°. The water contact angles of different membranes varied in the range 141 ~155° demonstrating the variation of hydrophobic properties of different membranes fabricated by controlling the styrene-acrylic acid co-polymer coating method. Membranes fabricated with co-polymerized PS-polyacrylic acid(PAA)/TiO2 NPs can be used to separate for both highly viscous and light oils having exceptional oil-water separation efficiencies of ~99%. The in-situ co-polymerized PS-PAA/TiO2(NP) membranes separate high and low density oils from water with a separation efficiency of over ~99% with a flux of ~50,000–60,000 L m−2 h−1 under gravity driven process and a flux of ~7500–9000 L m−2 h−1 under antigravity driven process due to excellent oil-wetting properties. It was demonstrated that the oil–water separation efficiency, reusability, durability and hydrophobicity of the styrene-acrylic acid co-polymer coated TiO2 membranes can be enhanced by using appropriate membrane fabrication methods.

Preparation of biomimetic membrane with hierarchical structure and honeycombed through-hole for enhanced oil–water separation performance

Efficient oil–water separation plays a vital role in treating large amounts of industrial wastewater. However, current traditional separation methods are entwined with problems such as low efficiency and poor operability. Herein, we reported a nanofiber based on electrospinning and electrospray technology and spraying microspheres on the surface of a fiber mat for efficient oil–water separation. Owing to the electrostatic repulsion among the microspheres, the surface of the developed membrane had a honeycomb-like through-hole structure and super-high oil–water separation efficiency and oil flux. After 10 cycles, the membrane showed good separation efficiency and flux. This innovative work may provide a new idea and method for the design of biomimetic biopolymers, with broad application prospects in the field of oil–water separation.

Superhydrophobic modification of cellulose sponge fabricated from discarded jute bags for oil water separation

Recent oil spills endanger the aquatic ecosystem besides huge loss of natural resources, hence require immediate attention. To develop economical solution for combating oil spills, discarded jute bags, with 60–65% cellulose were used to fabricate cellulose sponge using sol-gel method followed by freeze drying. The sponge surface was rendered superhydrophobic by dip coating with Tetraethyl-orthosilicate/Hexadecyltrimethoxy Silane (TEOS/HDTMS). The pristine and dip coated hydrophobic cellulose sponge (DHCS) were characterized for structure, morphology and hydrophobicity. FE-SEM confirmed the hydrophobic coating of TEOS/HDTMS on sponge surface, while superhydrophobicity was established with static contact angle of 151°. DHCS exhibited oil water separation efficiency of 98.5% and 97.2% and equilibrium adsorption efficiency of 35.55 g/g and 31.37 g/g for diesel oil and motor oil, respectively. The adsorption follow pseudo-second order kinetics with regression coefficients, R2 > 0.99. Equilibrium studies indicated that the Freundlich isotherm was best fit isotherm for oil water removal by DHCS. DHCS displayed significant recyclability with slight reduction of adsorption capacity to 85.2% for diesel oil and 82.5% for motor oil of its initial value after 10 cycles.

Effective oil-water mixture separation and photocatalytic dye decontamination through nickel-dimethylglyoxime microtubes coated superhydrophobic and superoleophilic films.

Oils and solvable organic pollutants in wastewater demand separations of the components along with efficient photocatalysis in water treatment. Herein, we report on a practical purification strategy by using the multifunctional nickel-dimethylglyoxime [Ni(DMG)2] microtubes to separate the liquid mixture and degrade organic pollutants. The self-assembled [Ni(DMG)2] tubes was synthesized by a facile co-precipitation method. The static contact angle of the film prepared by mixing [Ni(DMG)2] powder (1 : 2 wt%) into polydimethylsilicone (PDMS) to water can reach 161.3°, which can still remain superhydrophobic but oil-friendly under corrosion conditions. PDMS imparts good mechanical properties and serves as both the adhesive and hydrophobic material. PFOTS methanol solution contains a large number of low surface energy groups, which can reduce the surface free energy of [Ni(DMG)2] rough structure. The superhydrophobic rough surface prepared by hollow micron tubular [Ni(DMG)2] samples must have both low surface energy substance and hollow micron tubular morphology. Due to the unique wettability, oil and water were efficiently separated from the oil–water mixture through the films. The coated film itself is photocatalytic in degrading quinoline blue, rhodamine B, methyl orange and methylene blue. By using the film's multifunctionality, a practical wastewater treatment was realized via water–oil separation, followed by fast photocatalytic degradation of solvable dyes.

Demulsification of a Nigerian crude emulsion using ethoxylated-resoles and their xylene modified blends

Demulsification is a method used to reduce or disrupt the water - crude oil emulsion system without uttering the initial composition of the crude oil. This process is done by the introduction of chemicals called demulsifiers, which break the emulsion into aqueous and organic phases. In this study, the demulsifier formulated was the base-catalyzed phenol-formaldehyde resin known as the resoles, with the ratios of phenol to formaldehyde, varied between 1.0:1.2 and 1.0:2.0. The different samples of resoles where then ethoxylated to make them more hydrophilic using different weights (10, 15 & 20 g) of polyethylene glycol (PEG). Screening of the ethoxylated demulsifiers was done using the established bottle test procedure, at 70 °C, the concentration of 50 ppm, and 20 minutes of residence or separation time, in order to select the most effective demulsifier, based on the amount of water removed from the emulsion. The best chemical-demulsifier produced was the ethoxylated resole, which was then blended with xylene at varying percentages (0, 20, 40, 50, and 80 % weight/weight) and was further screened, using the bottle test method. From the analysis, it was obtained that the most effective ethoxylate-xylene demulsifier blend was sample DR3, and made of formaldehyde to phenol ratio of 1.8:1, 20 g of PEG 400 blended with 20 % xylene. The demulsifier gave a water separation efficiency of 85.7 %, compared with the commercial demulsifier, which yielded 72.7 %. The result indicates the practical significance of solvent modified demulsifiers for separating crude oil emulsions in the petroleum industries.

Separation Efficiency of Oil and Water from Oilfield Produced Water Using Cyclonic Flotation

Separation Efficiency of Oil and Water from Oilfield Produced Water Using Cyclonic Flotation