Presence Of Electrolyte Solutions Research Articles

Experimental measurement and thermodynamic modeling of dissociation conditions of hydrogen sulfide hydrate in the presence of electrolyte solutions

Understanding of hydrogen sulfide (H2S) hydrates phase equilibrium is important for sour gas production and transportation. In this study, hydrate dissociation conditions of H2S were measured in aqueous NaCl, KCl, MgCl2, NH4Cl, Na2SO4, and K2SO4 solutions at temperatures ranging from 273.4 to 298.8 K, pressures ranging from 1.13 to 21.90 bar, and weight percent of electrolyte ranging from 3.4 to 20.0 wt%. The experimental measurements were conducted in microcapillary silica tubes using an isothermal pressure search method. The dissociation enthalpies of H2S hydrate in electrolyte solutions were calculated by fitting the Clausius-Clapeyron equation to LHV (Liquid-Hydrate-Vapor) equilibrium curves. The result shows that the dissociation enthalpies of H2S hydrate in electrolyte solutions range from 57.7 to 71.5 kJ/mol. The inhibitory effect of six electrolytes on H2S hydrate formation is in the order of MgCl2 > NH4Cl > NaCl > KCl > Na2SO4 = K2SO4. Additionally, a thermodynamic model was developed to predict dissociation conditions of H2S hydrate in electrolyte solutions. The van der Waals-Platteeuw (vdW-P) model was used to describe the hydrate phase, and the liquid phase was modeled with the thermodynamic equation improved by Holder et al. The Duan-Moller-Weare-92 equation of state (DMW-92 EoS) and the Pitzer model were used to calculate fugacity and water activity, respectively. The average absolute deviations of pressure (AADP) indicate that the developed model can accurately predict the dissociation conditions of H2S hydrate for aqueous NaCl, KCl, Na2SO4, and K2SO4 solutions. Moreover, the valence band of hydroxyl group was used to characterize electrolytes effects on gas hydrate equilibrium conditions.

Modeling the equilibrium of two and three-phase systems including water, alcohol, and hydrocarbons with CPA EOS and its improvement for electrolytic systems by Debye-Huckel equation

Calculation of the phase equilibrium of hydrocarbons in the presence of electrolyte solutions is one of the most important and practical topics in chemical and petroleum engineering. The aim is to obtain an improved thermodynamic model that can predict the phase behavior of hydrocarbons along with electrolyte solution and alcohol with a good approximation. In this work, various equilibrium data published by previous researchers were collected, and then phase behavior of different systems including water, alcohol, and hydrocarbons was modeled using cubic plus association equation of state. Moreover, modified cubic plus association equation of state by Debye-Huckel equation was utilized for the prediction of the phase behavior of different systems containing salt. The results showed, for systems without electrolyte components, the cubic plus association equation of state predicts the phase behavior of these mixtures very well and the absolute average deviation value in these mixtures was between 1 and 10% for different systems. In recent decades, several equations of state have been proposed to predict the behavior of electrolyte mixture but, to the best of our knowledge, they did not consider all four components (hydrocarbon, water, alcohol, and salt) at the same time. In this research, an equation of state was presented to predict the phase behavior of systems that simultaneously contain hydrocarbons, water, alcohol, and salt in a mixture that considers both hydrogen bonds and ion interactions. The electrolytic cubic plus association equation is an equation that considers the effect of hydrogen bonds between different components as well as the effect of forces between existing ions. The results obtained for predicting electrolyte systems using the electrolytic cubic plus association equation showed that this equation can predict the phase behavior of these mixtures satisfactorily. The error value obtained for electrolytic systems and tangible components was between 1 and 12%.

Effect of Ion Type on the Interaction between Polar Model Oil and Mica Substrate: A Chemical Force Microscopy Study

Low salinity waterflooding is an effective approach to improving oil recovery, behind which the microscopic mechanisms have been debated over the past decade, and especially, the role of polar organic components of crude oil is almost ignored but proposed to dominate the adhesion force of oil-rock in specific cases. In this study, chemical force microscopy (CFM) was used to directly measure the adhesion forces between polar model oil and mineral surface in the presence of electrolyte solution with different ionic type and concentration. By the use of classic Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, the van der Waals and electrostatic forces were calculated, and it was found that there were some additional interactions, denoted as structural forces, playing an important part in the resultant forces. By the aid of extended DLVO (EDLVO) theory, the adhesion force of polar tip–substrate was found to increase in the order: Na⁺ < Ca²⁺ < Mg²⁺, and the low salinity effect (LSE) potential shows the opposite order, attributed to the ligand bridging and strong solvation of multivalent cations enhancing the electrostatic attraction of the tip–surface pair. In the case of sulfate ion as the anion, the adhesion force was smaller than that in the case of chloride ion because the SO₄²– ion can favor the formation of electrostatic repulsion between the tip and surface and accordingly enhance the LSE potential. On the basis of the experimental results, we propose a molecular interaction model between oil and solid substrate, which will provide an in-depth understanding of the effect of brine composition and concentration on oil detaching from a solid surface at the molecular level.

Corrosion and lubricated sliding tribological behavior of Al-TiB2-nano Gr hybrid composites

Corrosion and lubricated sliding tribological behavior of Al-TiB2-nano Gr hybrid composites for varying wt% of reinforcements are studied. Composites fabricated in ultrasonic vibration assisted stir-cast method are characterized using optical micrographs and SEM images. Micro-hardness values of composites increases with incorporation of both TiB2 and nano-Gr bases while hardness decreases with addition of only nano-Gr phase. Corrosion characteristics are investigated using potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Corrosion resistance of composites is tailored from the parameters like corrosion potential, corrosion current, linear polarization resistance. Results show that corrosion potential shifts to negative direction with incorporation of reinforcing phases. Nano-Gr intensifies the corrosion of aluminum base matrix through hindering the corrosion path. Presence of TiB2 phase does not alter that effect of nano-Gr. Formation of protective film on the surface of Al-2.5TiB2-nano Gr composites is apprehended through impedance tests. The corroded surfaces are studied using SEM images and the morphologies reveal that localized corrosion occurs through formation of pit. Such localized corrosion is yielded by the formation of galvanic cell in between reinforcing phases (TiB2, nano-Gr) and base matrix in presence of electrolyte solution. Tribological characterization is performed under lubricated sliding. Composite surface does not react with the concerned lubricant. Without any change in the amount of solid lubricant (nano-Gr) or TiB2, wear and friction behavior of composites enhanced sufficiently in presence of liquid lubricant at contact surface compared to dry condition.

Energetic performances of FER-type zeolite in the presence of electrolyte solutions under high pressure

The influence of the synthesis procedure and therefore of the morphology (elongated crystals and plate-like crystals) and crystal size on the energetic performances of pure silica Ferrierite was studied by high pressure intrusion-extrusion of water and LiCl aqueous solutions (nonwetting liquid) at different concentrations. The results indicate that the morphology does affect neither the intrusion pressure nor the intruded volume. High intrusion pressure values were found (150, 189, 243 MPa for water, 5 M and 10 M LiCl aqueous solution, respectively) probably due to the channel pore system and to the small pore openings (8 and 10 MR) characteristic of this zeolite. A similar spring behavior of the “zeosil-nonwetting liquid” system is observed whatever the LiCl concentration. The zeolite samples were characterized by XRD, TG, 29Si solid-state NMR spectroscopy, N2 adsorption-desorption and SEM analysis before and after the intrusion-extrusion process.

Effect of wet-dry cycles on polymer treated bentonite in seawater: swelling ability, hydraulic conductivity and crack analysis

Waste disposal facilities are often isolated by clay liners in order to prevent pollutant migration into the ground. Bentonite is used as barrier material thanks to the low conductivity to water. However, the hydraulic performance may be impaired by contact with aggressive liquids due to cation exchange and highly concentrated solutions. Moreover, the combination of cation exchange and wet-dry cycles can further affect the efficiency of the bentonite as barrier material. This study was carried out to evaluate the effect of wet-dry cycles with seawater on untreated sodium bentonite and HYPER clay. HYPER clay is a polymer modified bentonite with enhanced performance in presence of electrolyte solutions. Bentonite and bentonite treated with 2% and 8% polymer by dry weight of the clay were evaluated for their swelling ability, self-healing capacity, crack formation and hydraulic conductivity by means of one-dimensional swell test, μCT scanning and hydraulic conductivity tests. The specimens were subjected to 6 wet-dry cycles for the swell tests and to 4cycles for the hydraulic conductivity tests. One-dimensional swell tests results showed that HYPER clay 8% had swollen the most and that its thickness after the 6th wet-dry cycle was comparable to the original thickness of untreated bentonite during its maximum swelling in deionised water. μCT analysis demonstrated the better self-healing capacity and the smaller volume of cracks of HYPER clay compared to untreated bentonite. Unlike the untreated clay, HYPER clays maintained low permeability to seawater throughout the wet-dry cycles.

Hydraulic conductivity and swelling ability of a polymer modified bentonite subjected to wet–dry cycles in seawater

The performance of clay liners may be impaired when in contact with aggressive solutions due to cation exchange. The efficiency of these liners can further deteriorate if cation exchange is combined with wet and dry cycles as a result of seasonal changes in temperature, rainfall and groundwater migration. The performance of untreated sodium bentonite is compared to the performance of a treated clay, HYPER clay, under wet and dry cycles, in seawater. HYPER clay is a polymer modified bentonite with enhanced performance in presence of electrolyte solutions. In this study, the bentonite is treated with 2% and 8% polymer by dry weight of clay. The swelling ability, self-healing capacity and permeability are investigated by means of swell index tests, one-dimensional swell tests in oedometer cells and hydraulic conductivity tests. The specimens were subjected to 6 wet–dry cycles in swell tests and to 4 cycles in hydraulic conductivity tests.The swell index tests showed that the swelling ability increased as the polymer content increased. Similar results were obtained from one-dimensional swell tests. The height of HYPER clay (8% polymer content) during the sixth wet–dry cycle was still considerably larger compared to the height of the untreated clay. The hydraulic conductivity of untreated sodium bentonite sharply increased within three cycles, while HYPER clay maintained its low permeability to seawater. During the fourth wet–dry cycle, the hydraulic conductivity of untreated bentonite was three orders of magnitude higher than HYPER clay 2%. Sodium bentonite was not able to heal cracks formed during drying, which constitute preferential flow paths for the solution.

Modeling of Lithium Ion Batteries Employing Grand Canonical Monte Carlo and Multiscale Simulation

In the current investigation modeling of two half cells (LiMn2O4 cathode and carbon anode) followed by modeling of the complete cell of the battery employing Grand Canonical Monte Carlo simulations to evaluate open circuit potential and energetic of the process involved had been carried out. Current model takes into account the effect of electrolyte and temperature variations on various battery parameters like open circuit potential, cell current, cell voltage and free energy of Li+ intercalation/deintercalation. Estimation of open circuit potential (OCV) of Lithium ion batteries becomes vital as it is a crucial parameter in (i) estimating diffusion coefficient of lithium in the electrode material during charge/discharge process, (ii) obtaining entropy of the reaction and internal energy calculations and (iii) understanding thermal runaway problems. The strong dependence of OCV with the state of charge (SOC) of the battery and temperature makes the prediction more difficult. To avoid computational tediousness, Grand Canonical Monte Carlo technique coupled with multiscale simulation is employed to predict experimental OCV of LiMn2O4 cathode material in the presence of electrolyte solution.

Failure modes in organic coatings studied by scanning acoustic microscopy

Scanning acoustic microscopy (SAM) has been found to be well suited to study physically and chemically induced changes and defects in polymer coatings exposed to corrosive environments. In this work, SAM was used to investigate sub-surface migration and blister formation in polymer coatings of different layer structure after exposure to a corrosive solution. Two model systems consisting of base coat and clear coat on steel substrates where studied. The time evolution of sub-surface migration fronts and blister initiation and their growth were investigated by analysing SAM images after different exposure times. Depending on the layer structure, it was possible to differentiate between transport of the electrolyte solution (i) through the coating and (ii) along the coating/substrate interface. Samples without clear coat typically showed randomly distributed blisters at the coating/substrate interface, irrespective of the location of initial defects. The random distribution of blisters is related to diffusion of the electrolyte solution through the coating layer followed by “nucleation” at weak spots of the substrate, at the interface between polymer and substrate or within the polymer. In contrast, samples with a clear coat acting as a diffusion barrier showed a sub-surface migration front of 2–4μm height, propagating along the coating/substrate interface, starting at initial defects. The linear propagation of this front cannot be explained by Fickian diffusion and is discussed in terms of an accelerated diffusion or crack growth kinetics. Since blistering started only at regions, where the migration front has already passed, the presence of electrolyte solution or water at the coating/substrate interface was found to be a prerequisite for the nucleation of blisters.

A Proposed Thermodynamic Model for Gas Hydrate Equilibrium in Electrolyte Solutions

In this work, the thermodynamic stability of gas hydrates is investigated in the presence of electrolyte solutions. The proposed model is based on the Van der Waals–Platteeuw model for gas hydrate equilibrium, and the Pitzer and Mayorga model is employed to calculate the water activity in the electrolyte solutions. Available values for the Pitzer model parameters are usually adjusted using experimental data at 25°C, which is usually higher than the gas hydrate formation temperature. In order to eliminate this problem, those adjustable parameters are re-optimized using experimental data from the literature at the lowest temperature. In the case of mixed electrolyte solutions and without using any adjustable parameters, a mixing rule is proposed to estimate the water activity. The new mixing rule is based on the ionic strength of the mixture and estimates the mixture water activity by using properties of the single electrolytes that constitute the mixture. The results show the proposed model can calculate hydrate equilibrium conditions with good accuracy, especially at low concentrations, which is the case for most industrial applications.

Mapping of cavitational activity in high frequency sonochemical reactor

In the present work, distribution of cavitational activity in high frequency sonochemical reactor has been quantified with the help of different mapping techniques based on experimental investigations and theoretical analysis. In experimental investigations, amount of iodine liberation at different locations has been quantified whereas quantification of cavitational activity using theoretical analysis is based on the solution of space dependent part of the wave equation with the help of COMSOL Multi-physics software. The effect of frequencies of irradiation with and without presence of electrolyte solution (NaCl) to intensify the cavitational activity has been investigated in order to understand behavior of cavitation phenomena. The analysis presented in the work helps in identifying the regions with maximum cavitational intensity so as to obtain maximum efficacy for the desired physical or chemical transformations.

High‐performance separation of small inorganic anions on a methacrylate‐based polymer monolith grafted with [2(methacryloyloxy)ethyl] trimethylammonium chloride

A glycidyl methacrylate-co-ethylene dimethacrylate monolith in capillary format (100 microm/id) has been grafted with chains of poly([2(methacryloyloxy)ethyl] trimethylammonium chloride (poly-META) and applied to the ion-chromatographic separation of selected inorganic anions. Grafting chains of META onto the generic monolithic scaffold resulted in a monolith with 'electrolyte responsive flow permeability', which manifested as increased permeability in the presence of electrolyte solutions. Using an eluent of 2 mM sodium benzoate and on-column contactless conductivity detection, a test mixture of six common anions was isocratically separated and detected within 12 min, with the first four anions baseline resolved within a retention time window of 3.2 min. Retention time precision was < or = 1.2% for all anions tested. Separation efficiencies of 15,000 N/m were achieved for fluoride at 1 microL/min, with column efficiencies up to 29,500 N/m obtained at a lower flow rate of 100 nL/min. Furthermore, repeatability of the column modification procedure using photografting methods was acceptable, with retention times between replicate columns matching within 9%.

Electrokinetic and rheological properties of Na-bentonite in some electrolyte solutions

Electrokinetic and rheological properties of Na-bentonite suspensions were investigated in the presence of various electrolyte solutions including LiCl, NaCl, KCl, NH 4Cl, NaClO 4, CH 3COONa, NaNO 3, Na 2SO 4, Na 3PO 4, CuCl 2, MnCl 2, CaCl 2, BaCl 2, NiCl 2 and AlCl 3. It was found that divalent cations (Cu 2+, Mn 2+, Ca 2+, Ba 2+ and Ni 2+) and trivalent cation (Al 3+) were potential determining cations for the Na-bentonite suspensions. Trivalent cation, Al 3+, changed the surface charge of Na-bentonite from negative to positive. The zeta potential measurements showed that monovalent counter-cations and mono-, di- and tri-valent anions were indifferent ions for the Na-bentonite suspensions. The plastic viscosity and the Bingham yield stress values of the Na-bentonite suspensions were also determined in the presence of electrolyte solutions.

Behaviour of a cobalt spinel ultrafiltration membrane during salt filtration with different ionic strengths

The characterisation of the surface charge of a cobalt spinel ultrafiltration membrane was investigated in the presence of electrolyte solutions by means of streaming potential measurements. The selectivity of a membrane towards different salts depends on the electrostatic interactions between the species in solution and the charge of the membrane surface. Firstly, the values of the streaming potential coefficient were measured during the filtration of NaCl, CaCl 2, Na 2SO 4 and CaSO 4 as a function of pH and ionic strength. The iso-electric point was determined for each electrolyte. Secondly, the rejection rates of the electrolytes were measured by ionic chromatography. The rejection was explained by a correlation with the surface charge of the membrane.

A new approach in modelling phase equilibria and gas solubility in electrolyte solutions and its applications to gas hydrates

This paper presents a new predictive model for phase equilibria and gas solubility calculations in the presence of electrolyte solutions. It treats salts as pseudo-components in an equation of state (EoS) by defining the critical properties and acentric factor for each salt. The water–salt, gas–salt and salt–salt binary interaction parameters (BIP) have been determined by using available experimental data on freezing point depression and boiling point elevation as well as gas solubility and salt solubility data in saline solutions. The methodology has been applied in modelling sodium chloride, potassium chloride and their mixtures, as well as solubility of methane and carbon dioxide in aqueous single and mixed electrolyte solutions. The developed model is capable of accurately predicting the phase behaviour, gas hydrate stability zone and potential salt precipitation in single and mixed electrolyte solutions. The model predictions are compared with available independent experimental data, including hydrate inhibition characteristics of single and mixed electrolyte solutions, and good agreement is demonstrated.

A Laboratory Apparatus to Measure Chemico-Osmotic Efficiency Coefficients for Clay Soils

Abstract A laboratory apparatus for measuring the chemico-osmotic efficiency coefficient, ω, for clay soils in the presence of electrolyte solutions is described. A chemico-osmotic experiment is conducted by establishing and maintaining a constant difference in electrolyte concentration across a soil specimen while preventing the flow of solution through the specimen. The chemico-osmotic efficiency coefficient is derived from a measured pressure difference induced across the specimen in response to the applied concentration difference. The effective diffusion coefficient (D*) and retardation factor (Rd) of the electrolytes (solutes) also can be determined simultaneously by measuring the diffusive solute mass flux through the specimen until steady-state diffusion is achieved. Experimental results using specimens of a geosynthetic clay liner subjected to potassium chloride solutions indicate that the measurement of ω may be affected by soil-solution interactions, as well as by changes in the induced chemico-osmotic pressure difference due to solute diffusion. As a result, ω should be evaluated using the induced pressure difference at steady state. The time required to achieve a steady-state response in induced pressure difference is related to the time required to achieve steady-state diffusion of all solutes, and may be affected by the circulation rate at the specimen boundaries. The circulation rate should be sufficiently rapid to minimize changes in the boundary concentrations due to diffusion, but sufficiently slow to allow measurement of solute mass flux at the lower concentration boundary for evaluating D* and Rd.

Effects of polydiallyldimethyl ammonium chloride coagulant on formation of chlorinated by products in drinking water

The objectives of this research work was to evaluate the reduction of THM precursors by cationic p-DADMAC and determine the correlations between the chlorine demand and trihalomethane formation in the presence of electrolyte solutions and ambient light. The chlorine demand was found to be significantly reduced provided that the H 2SO 4 electrolyte was fed to the sample solutions. The amount of CHCl 3 formation was also decreased when the Na 2SO 4 electrolyte was introduced in spite of the levels of light intensity. The p-DADMAC can not only effectively remove the turbidity but also reduce the formation of CHCl 3. The optimum dosage of p-DADMAC for reducing the turbidity TOC and CHCl 3 in the humic acid and source water samples was determined and depended upon the nature of organics.

A STUDY OF PROVENTION FOR CONTACT CORROSION OF LIGHT METALS

When light metals contact with other metals, for instance steel, it eroded especially in the presence of electrolytic solution, such as NaCl.Aluminum alloy (52S) panels are worn with steel bands with or without various coating or insulating pastes, and submerged into a aqueous solution containing 5.85%NaCl, 0.3%H2O2.In untreated (direct contact and bare) panels, aluminum panels generals gas bubbles and considerably eroded, but steel band not so eroded. When insulating cloth tape (cloth painted with paste consists of polybutene, paraffine, boiled oil, gilsonite and zinc chromate etc.) Placed between aluminum alloy and steel, the corrosion rectrogressed. Steel band eroded and aluminum alloy not affected. After the submerge over 1 month, significant lowering in tensile strength of aluminum alloy not founded.When panels are coated with various coatings, (zinc chromate primer, wash-primer, vinyl resin primer) showed good resistance.Between insulating paste, polybutene-boiled oil-zinc chromate type showed best results, and in coatings, vinyl type primer was best and wash primer-zinc chromate primer (synthetic resin vehicle) was the second.It is interesting what then metals are contact directly, erosion occured at aluminum panel and produce white precipitate, aluminum hydroxide, and when metals are insulated by paste, erosion occured at steel and produce reddish ferric precipitate.