Asymmetry of ion transport in hybrid MF-4SC membranes with a gradient distribution of hydrated zirconia

Results of studies of the properties of hybrid MF-4SC membranes with a gradient distribution of hydrated zirconia nanoparticles through the thickness prepared by layer-by-layer casting from a polymer solution are described. The effect of the dopant concentration on the properties of the membranes is studied. At a low oxide concentration, the water uptake and ionic conductivity of the resulting samples increase compared to the original MF-4SC membrane. It is found that the diffusion permeability of HCl and NaCl solutions across these membranes exhibits an asymmetric behavior. It is shown that the diffusion permeability is higher in the case of diffusion of the solutions from the unmodified side of the membrane. The maximum asymmetry coefficient is obtained for a membrane containing 10% ZrO₂ in the modified layer for the diffusion of 0.1 M HCl solution (38%). The causes of the diffusion permeability asymmetry are discussed.     

Short Side Chain Aquivion Perfluorinated Sulfonated Proton-Conductive Membranes: Transport and Mechanical Properties

Data on the water uptake, proton conductivity, diffusion permeability, cation transport selectivity, and mechanical properties of short side chain Aquivion sulfonated perfluoropolymer membranes with an equivalent weight of 870 and 965 have been described. Properties of the membranes have been compared with those of a long side chain Nafion 212 membrane (equivalent weight of 1100). An increase in the equivalent weight leads to an increase in the sorption exchange capacity and water uptake of the membranes and a decrease in their proton conductivity. The conductivity of the Aquivion membrane with an equivalent weight of 870 is 1.4–1.5 times higher than that of the Nafion 212 membrane; it reaches 13.6 mS/cm in contact with water and 1.0 mS/cm at a relative humidity of 32% at 25°C. Diffusion permeability and cation transport selectivity exhibit a nonmonotonic dependence on the equivalent weight of the material. The lowest diffusion permeability, the highest Na⁺ cation transport selectivity (99.5%), and the best mechanical properties have been found for the Aquivion membrane with an equivalent weight of 965, which is characterized by the highest degree of crystallinity.     

Ion transport in hybrid membranes based on MF-4SC and silica surface-modified with proton acceptor groups

Methods for synthesizing hybrid MF-4SC membranes containing silica whose surface has been modified with proton acceptor amine-containing groups (3-aminopropyl- and 3-(2-imidazoline-1-yl)-propyl-) are proposed. The incorporation of surface-modified silica particles into the membrane matrix leads to a decrease in the water uptake and exchange capacity compared to a membrane containing pure SiO₂. The proton conductivity and diffusion permeability of NaCl and HCl solutions and the H⁺/Na⁺ ion interdiffusion are studied. The proton conductivity of the membranes containing surface-modified silica is higher than that of the parent membrane and the membrane containing pure SiO₂. It is shown that the surface modification of silica with 5 mol % of nitrogen-containing groups results in a decrease in the diffusion permeability and an improvement in the ion transport selectivity. This extraordinary change in the properties is caused by an increase in the size of the pores and the channels that connect them, along with a significant decrease in the free volume within the pores. At the same time, an increase in the amount of modifying groups to 10 mol % leads to a sharp acceleration of the diffusion permeability and interdiffusion processes because of the formation of through pores in the membrane matrix.     

Donnan-Potential Sensors Based on Zirconia-Modified Nafion Membranes Treated under Different Conditions for the Determination of Amino Acids with Several Nitrogen-Containing Groups

The effect of heat treatment at varying relative humidity and mechanical deformation on the properties of Nafion perfluorosulfonic cation-exchange membranes and Nafion-based hybrid materials containing hydrated zirconia nanoparticles has been studied. It has been shown that the treatment of the materials makes it possible to change their water uptake, ionic conductivity, and diffusion permeability over wide ranges. Variations in the water uptake and intrapore space volume of the membranes provided by their treatment and modification have led to a decrease in the sensitivity of DP-sensors (the analytical signal is the Donnan potential) to interfering hydroxonium cations in arginine and histidine solutions in 1.5?5 times. The material samples providing a high accuracy of determination of amino acid ions in a concentration range from 1.0 × 10^–4 to 1.0 × 10^–1 mol/L at pH < 7 have been selected.     

The synthesis and study of the transport properties of hybrid materials based on MF-4SK perfluorosulfonated cation-exchange membranes modified with ceria

Hybrid materials based on a MF-4SK perfluorosulfonated membrane and ceria nanoparticles are synthesized via the in situ method. The proton conductivity and diffusion permeability of the materials with respect to HCl and NaCl solutions are studied. It is shown that the modification of membranes makes it possible to increase their water uptake and leads to a significant increase in proton conductivity and a decrease in its activation energy.     

Ionic Conductivity of Ceria-Doped Ion Exchange Membranes on the Basis of Sulfonated Polynaphthaleneimide

Hybrid membrane materials on the basis of sulfonated polynaphthaleneimide doped with ceria have been synthesized, and their ionic conductivity has been investigated. The conditions for membrane synthesis with different dopant contents have been determined. Ceria doping leads to a decrease in the ionexchange capacity of membranes and an increase in their ion conductivity upon contact with water. After 7% ceria doping, the ionic conductivity of the initial membrane (1.9 × 10^?2 Ω^?1 cm^?1) increases up to 3.0 × 10^?2 Ω^?1 cm^?1.     

Percolation of composite poly(vinyltrimethylsilane) membranes with carbon nanotubes

Recent years have seen a flurry of activity in research on the use of nanoparticles to improve the properties of polymeric membranes. It is known that the change in the macroscopic properties of these hybrid materials is associated with the parameters of the cluster of incorporated nanoparticles. The percolation threshold is higher than 15 vol % for the spherical particles and decreases with the increasing aspect ratio of the embedded nanoparticles of another shape. The paper presents the results of study on the permeability of gases (N₂, O₂, CH₄ and C₃H₈) and a test liquid (ethanol) through hybrid membranes based on the glassy polymer poly(vinyltrimethylsilane) (PVTMS) with embedded multiwall carbon nanotubes (MWCNT) with a concentration of 0.3–3 wt %. It has been found that the permeability of gases and liquids alters at MWCNT concentrations above 0.4 wt %, which corresponds to the percolation threshold for the given particles as proved by calculations. In addition, the gas permeability coefficients measured indicate a change in the transport mechanism and selectivity of the membrane.     

A novel hybrid material based on polytrimethylsilylpropyne and hypercrosslinked polystyrene for membrane gas separation and thermopervaporation

To improve the membrane permeability and separation properties in gas separation processes and thermopervaporative (TPV) recovery of butanol from model fermentation mixtures, hybrid membranes based on polymers with an extremely high free fractional volume—polytrimethylsilylpropyne (PTMSP) and hypercrosslinked polystyrene (HCL-PS)—have been first prepared and experimentally studied. The composite membranes have been fabricated using the commercial sorbent Purolite Macronet MN-200 exhibiting high sorption capacity for organic solvents. It has been found that in the hybrid membranes, HCL-PS sorbent particles are nonuniformly distributed throughout the volume: they are located in the surface layer of the membrane. It has been shown that the introduction of a small amount of a modifying component (0.5–1.0 wt %) into the PTMSP matrix improves the time stability of transport properties and increase by a factor of 1.5–2 the permeability coefficients of the material to light gases (N₂, O₂, CO₂, CH₄) and butane vapor. It has been found that hybrid PTMSP/HCL-PS membranes have higher separation factors than those of PTMSP membranes in the TPV separation of a butanol/water binary mixture.     

Structure,morphology, and transport characteristics of profiled bilayer membranes

A procedure for the fabrication of profiled cation-exchange bilayer membranes with the homogenized surface based on the commercial membrane MK-40 has been developed. The surface morphology and membrane microstructure have been studied by atomic-force microscopy, electron microscopy, and standard contact porosimetry. The concentration dependences of the electrical conductivity and diffusion permeability of the profiled and bilayer profiled membranes have been studied. It has been shown that the application of an MF-4SK film on the surface of the profiled membrane results in a decrease in its diffusion permeability and some increase in specific conductivity. Based on the data obtained, the transport and structure parameters have been calculated in terms of the microheterogeneous model to assess the influence of the modification on the properties of the support membrane. The current–voltage characteristics of the membranes have been measured in sodium chloride solutions, and it has been shown that profiling leads to an increase in the limiting current by 40%. The investigation of mass transfer of ions in the channels formed by the support and modified membranes has shown that under intense current regimes, the mass transfer coefficient through the profiled bilayer membrane is one and a half times that through the initial profiled membrane.     

Synthesis and study of hybrid materials based on Nafion membranes,hydrated silica,phosphotungstic acid,and its acid salts

The results of research of the properties of hybrid materials based on Nafion membranes, silica, phosphotungstic acid, and its acid salts (potassium, rubidium, and cesium) prepared by the in situ method has been described. Modification leads to an increase in the water content and a significant increase in the conductivity of the hybrid membranes, particularly at a low relative humidity. The materials containing slightly soluble acid salts of phosphotungstic heteropoly acid exhibit a lower conductivity than the material that contains the acid; however, the former are more stable. It has been found that the diffusion permeability of an HCl solution in Nafion + SiO₂ + M _x H_3?x PW₁₂O₄₀ systems is lower than in Nafion + SiO₂ and further decreases with increasing ionic radius of the cation. An explanation of the causes of these changes in the properties has been proposed.     

Characteristics of PD-sensors based on hybrid perfluorinated membranes in aqueous solutions of inorganic electrolytes and lysine

The characteristics of PD-sensors based on MF-4SC perfluorosulfonic cation-exchange membranes, particularly those containing surface-functionalized silica nanoparticles, in HCl, NaCl, KCl, CaCl₂, and lysine monohydrochloride solutions have been studied. It has been revealed that the degree of hydration of inorganic cations has a dominant effect on the magnitude of PD-sensor response in individual electrolyte solutions. It has been shown that the response and sensitivity of PD-sensors based on hybrid materials with respect to lysine cations increase with increasing concentration of amino groups grafted to SiO₂. This feature is attributed to an increase in the counterion concentration in the film owing to a decrease in the water uptake and enhancement of the interaction between the counterions and the functional groups (sulfo groups of membrane, amino groups of dopant) in membrane.     

Hybrid membranes based on polybenzimidazole and hydrated zirconia

Hybrid membranes based on polybenzimidazole and hydrated zirconia doped with phosphoric acid have been synthesized. The effect of synthesis conditions on the properties of the resulting materials has been studied. It has been shown that the modification of the membranes makes it possible to increase their proton conductivity. The introduction of hydrated zirconia decreases the amount of phosphoric acid leached out from the membrane exposed to water vapor. The diffusion permeability of composite membranes in solutions of various salts has been studied. Model tests of some samples under fuel cell operating conditions have been performed.     

Controlled template synthesis and properties of cobalt nanotubes

This study has been focused on the influence of the conditions of electrochemical template synthesis (i.e., potential difference and temperature of electrolyte solutions) on the structural and conductive properties of cobalt nanotubes. Polyethylene terephthalate track-etched membranes with a pore density of 1 × 10⁹ ions/cm² have been used as a template. Scanning electron microscopy, X-ray diffraction, and energy dispersive analysis have been used for a comprehensive elucidation of the dimensionality, chemical composition, and crystal structure of the synthesized samples. The optimum conditions for the synthesis of cobalt nanotubes with a minimum crystallographic anisotropy have been determined. It has been shown that controlling the synthesis conditions by changing electrolyte solution temperature and applied potential difference, one can vary the electrical and conductive properties of cobalt nanotube arrays, which have promising application in magnetic recording storage devices, high-precision magnetic field sensors, and optical devices.     

An NMR study of a water-methanol solution sorbed in MF-4SK sulfonated cation-exchange membranes

Concentration dependences of self-diffusion coefficients (SDCs), self-diffusion activation energies for water and methanol, and chemical shifts of the protons of the hydroxyl groups δ_OH simultaneously in an external water-methanol solution and the solution sorbed in MF-4SK membranes have been studied by NMR. It has been revealed that the SDC of pure methanol and pure water sorbed in an MF-4SK membrane is 3–5 times lower than that outside the membrane. It has been found that, in the presence of a small amount of methanol, the SDC of water in the membrane is 1.5–2 times higher than the SDC of pure sorbed water. At a solution concentration of 0.1–0.5 mole fraction, the SDC values of water and methanol in the membrane vary only slightly and are about 6 × 10^?6 and 4 × 10^?6 cm²/s, respectively. It has been determined that the δOH value in the membrane is 100–200 Hz higher than that in the external solution. The observed increase in δ_OH and decrease in SDC in the membrane suggest that the state of the solution in the MF-4SK sulfonated cation-exchange membrane has significantly changed compared to the external solution. The effect of the implanted carbon phase (CP) on the SDC of water and methanol and δOH of the solution sorbed in the MF-4SK membranes containing the CP has been studied. It has been revealed that at a methanol mole fraction of up to 0.5, the introduction of 23 wt % CP decreases the SDC of the solution components by no more than 10–20%. At a methanol mole fraction of 0.25–0.5, the self-diffusion activation energies for methanol and water in the external and membrane solutions decrease by 5–7 kJ/mol.     

Ceramic microfiltration membranes based on natural silica

The physicochemical features of preparation of macroporous ceramics and multilayer ceramic materials based on natural silica—quartz sand—from the Republic of Belarus, Qatar, Saudi Arabia, Mongolia, Azerbaijan, Turkmenistan, and Vietnam have been studied. It has been shown that the properties and structure of macroporous ceramic substrates are mostly determined by the phase composition of the natural sand and its quartz content. Membrane layers on the macroporous ceramic surface have been formed by the deposition of a suspension of fine natural silica in an aqueous solution of an aluminosilicate binder. The resulting microfiltration membranes with an average pore size of 3–5 μm, an air permeability coefficient of 10^–12–10^–13 m², a water permeability of 10–50 m³/(m² h bar), and a tensile strength of up to 10 bar are promising for wide practical use in the microfiltration of liquid media.     

Fabrication of high-performance PVA/PAN composite pervaporation membranes crosslinked by PMDA for wastewater desalination

The pyromellitic dianhydride(PMDA) crosslinked poly(vinyl alcohol)(PVA) was coated on top of the PAN ultrafiltration membrane to form a PVA/PAN composite PV membranes for wastewater desalination. The composite membranes have high application value in industrial wastewater treatment. By varying the membrane fabrication parameters including the weight percent(wt%) of the PMDA, the crosslink temperature and duration, membrane with the best desalination performance was obtained. The composite membrane with a 2-lm-thick PVA selective layer containing 20 wt% of PMDA and being crosslinked at 100 °C for 2 h showed the highest Na Cl rejection of 99.98% with a water flux of 32.26 L/(m~2 h)at 70 °C using the 35,000 ppm Na Cl aqueous solution as feed. FTIR spectroscopy, wide-angle X-ray diffraction, thermogravimetric analysis and scanning electron microscope have been used to characterize the structures and properties of both the crosslinked PVA dense films and PVA/PAN composite membranes. The effects of the concentrations of PMDA,the crosslinking time and temperature to the membrane water contact angle, swelling degree, salt rejection and water flux were systematically studied.     

Porous hollow fiber membranes with varying hydrophobic–hydrophilic surface properties for gas–liquid membrane contactors

In relation to the demand for asymmetric porous hollow fiber membranes to be used in gas–liquid membrane contactors designed for operation in organic media, polysulfone membranes of this type have been prepared and subsequently modified to impart oleophobic properties to their surface. The structure and properties of the membranes have been characterized using various techniques, such as optical and scanning electron microscopy, and by measuring contact angles and the permeability of helium, carbon dioxide, and hexane. The surface properties of the membranes have been modified by etching with a mixture of hydrogen peroxide and sulfuric acid or coating with a perfluorinated acrylic copolymer. In the latter case, modified membrane samples have shown a significant reduction in wettability with both water and organic liquids. The hexane permeability data indicate the absence of hexane flow through the membrane modified with perfluorinated acrylic copolymer until a gauge pressure of about 1 atm. The results of the study lead to the conclusion that these membranes can find use in gas–liquid membrane contactors, e.g., for the removal of dissolved gases from liquid hydrocarbons.     

Elaboration of composite hollow fiber membranes with selective layer from poly[1-(trimethylsylil)1-propyne] for regeneration of aqueous alkanolamine solutions

The results of research on elaboration of the hollow fiber composite membranes for regeneration of aqueous solutions of alkanolamines in membrane gas-liquid contactor are presented in this work. Asymmetric polysulfone (PSF) hollow fiber UF membranes were used as a porous support, poly[1-(trimethylsylil)-1-propyne] (PTMSP) was employed as a diffusion layer. The influence of PSF hollow fiber casting conditions on hydraulic permeability was studied. Samples of composite membranes were obtained with a defectfree layer of PTMSP and carbon dioxide permeance of 0.26 m³ (STP) (m² h bar)^?1. It was revealed by SEM that the thickness of the PTMSP separation layer is 2.5 microns, where in X-ray spectrometry analysis data and calculations according to resistance-in-series model discovered that the selective layer penetration depth to the pores of the support was 1.4 microns. Calculation by resistance-in-series model showed that 98.6% of resistance to the gas transport is attributed to PTMSP, partially intruded in the pores of the support. Chemical stability of materials which comprise composite membrane makes promising their using for regeneration of aqueous solutions of alkanolamines (pH > 11) from carbon dioxide at a temperature of 100°C and a pressure drop of 10 bar in the membrane gas-liquid contactors.     

Hydrochloric acid diffusion coefficients at acid-fracturing conditions

The reaction of a 15% HCl solution with Indiana Limestone was investigated at 93 °C and 34.5 MPa using an annular flow reactor that was erected vertically. The laminar flow conditions were such that both free and forced convections contributed to the overall mass-transfer rate. The experimental results correlated well with theory when the forced and free convections were in the same direction (assisting flow) and when free-convection mass transfer dominated the mass-transfer process. Deviation from theory, however, occurred when free convection was in the opposite direction to forced convection (opposing flow). Correlating the experimental results with theory provided a method for the determination of the effective diffusion coefficient of HCl at the high temperature, pressure and acid concentrations encountered in acid-fracturing treatments. An HCl effective diffusion coefficient of 5.25 × 10⁻⁵ cm²/s was found from correlating the present experimental results with theory.Recent trend in designing acid-fracturing treatments is to use computer models to predict and optimize the etched length of the created fracture. The accuracy and reliability of such computer model predictions depend heavily on the accuracy of the values used for physical parameters such as reaction rate and diffusion coefficient of HCl. The annular flow reactor and the correlations discussed here provide a way to obtain reaction rates and diffusion coefficients at practical conditions for use in computer models and design of acid-fracturing treatments.     

镇北长8油藏缓速酸冲压酸化增注技术研究及应用

针对镇北油田长8注水井注水压力高且逐年上升,欠注严重,酸化增注效果差且有效期短的问题,提出了缓速酸冲压酸化工艺。运用水力冲压产生微裂缝,再用缓速酸进行酸化。根据区块的物性和储层伤害因素的分析,优选出了缓速酸的酸液体系为8%(w)HCl+3%(w)HF+1%(w)HBF_4+3%(w)HEDP+3%(w)H_3PO_4+1%(w)聚环氧琥珀酸钠+1%(w)聚乙二醇。该酸液体系1 h溶蚀率为25.02%,8 h溶蚀率为35.31%;Ca~(2+)抑制率为87.76%,Mg~(2+)抑制率为88.87%,Fe~(3+)抑制率为86.88%,沉淀抑制性明显优于目前在用酸化体系;岩心驱替实验也表明该酸液体系能明显改善地层的渗透率。在室内研究的基础上进行现场试验3井次,平均注水压力下降了3.9 MPa,日增注51 m~3,有效期已达到270天,取得了较好的降压增注效果。