Liquid-liquid Systems Research Articles

Combined reaction and diffusion across the interface in reactive nonuniform liquid systems

A recently introduced theoretical framework is generalized to multicomponent reactive nonuniform systems. The modified and generalized Cahn-Hilliard equation is combined with a chemical kinetics model. Kinetic rate equations, which are formulated with activities rather than concentrations, are combined with non-Fickian diffusion driven by gradients in chemical potential. Based on the incompressible density gradient theory, which provides an expression for the Gibbs energy of a nonuniform system, a generalized method is developed to model the combined reaction and diffusion associated with reactive liquid-liquid systems. A set of partial differential equations describing the temporal evolution of the mole fractions of all the involved components in the bulk phases and the spatial and temporal evolution of the mole fractions in the interface has been derived. The obtained equations were used to investigate the dynamics of the interfacial properties of a ternary mixture with a simple chemical reaction. Special attention is given to reacting mixtures with reaction rates that are much smaller than diffusion rates. In particular, it was found that the mixture will remain in phase equilibrium upon reaction and that the interfacial chemical reaction will not affect the dynamics of the overall system, the latter being only affected by the bulk phase kinetics.

A polemic on the use of reversed-phase liquid chromatography to determine descriptors for the solvation parameter model

Revised descriptors for 74 varied compounds recommended for the characterization of reversed-phase silica columns using the solvation parameter model are assigned by the Solver method from experimental retention factors for calibrated gas-liquid and reversed-phase liquid chromatographic (RPLC) and biphasic liquid-liquid partition systems. These descriptors are taken as the best estimate of the true descriptor values and used to evaluate several RPLC systems as a single-technique approach for descriptor assignments. Various combinations of isocratic single column and multiple mobile phase compositions, multiple columns with a single mobile phase composition, and multiple columns and multiple mobile phase compositions are evaluated. A multiple column (Discovery HS C18 and HS F5, Fluophase-RP, and XBridge Shield RP18, Phenyl, and C18) with acetonitrile- and methanol-water mobile phases provided the best results with an absolute average deviation (AAD) of 0.043 for the electron lone pair interaction descriptor E, 0.047 for the dipole-type interaction descriptor S, 0.020 for the hydrogen-bond acid descriptor A, and 0.010 for the hydrogen-bond base descriptor B° for 46 varied compounds. These values compare favorably with the larger all columns and mobile phase composition RPLC dataset with the best estimate of the true descriptors, or all data set, with AAD = 0.026 for E, 0.044 for S, 0.027 for A, and 0.011 for B° for 74 varied compounds. The preferred RPLC systems for descriptor assignments contain columns identified as belonging to different selectivity groups that maximize the relative magnitude of the dipole-type contribution, s system constant, hydrogen-bond basicity, a system constant, and electron lone pair interactions, e system constant. RPLC systems are well suited to assigning the B° descriptor and, with proper system selection, the A and S descriptors. The E descriptor for compounds unavailable by calculation is more problematic and a few extreme values with an AAD > ± 0.1 were observed and can affect the reliability of the S descriptor assignments for these compounds. The likelihood of poor descriptor assignments using the Solver method can be identified by evaluating descriptor wells.

Chemical profiling of botanical extracts obtained in NADES systems using centrifugal partition chromatography combined with 13 C NMR dereplication-Hypericum perforatum as a case study.

Natural deep eutectic solvents (NADES) have emerged as interesting extractants to develop botanical ingredients. They are nontoxic and biodegradable, nonflammable, easy to prepare, and able to solubilize a wide range of molecules. However, NADES extracts remain difficult to analyze because the metabolites of interest stay highly diluted in the nonvolatile viscous NADES matrix. This study presents a robust analytical workflow for the chemical profiling of NADES extracts. It is applied to Hypericum perforatum aerial parts extracted with the neutral mixture fructose/glycerol/water (3/1/1, w/w/w), and compared to the chemical profiling of a classical dry methanol extract. Exploiting polarity differences between metabolites, the H. perforatum NADES extract was partitioned in a liquid-liquid solvent system to trap the hydrophilic NADES constituents in the lower phase. The upper phase, containing a diversity of secondary metabolites from H. perforatum, was fractionated by centrifugal partition chromatography. All fractions were chemically investigated using a 13 C NMR dereplication method which involves hierarchical clustering analysis of the whole NMR dataset, a natural metabolite database for metabolite identification, and 2D NMR analyses for validation. Liquid chromatography-mass spectrometry (LC-MS) analyses were also performed to complete the identification process. A range of 21 metabolites were unambiguously identified, including glycosylated flavonols, lactones, catechins, phenolic acids, lipids, and simple sugars, and 15 additional minor extract constituents were annotated by LC-MS based on exact mass measurements. The proposed identification process is rapid and nondestructive and provides good prospects to deeply characterize botanical extracts obtained in nonvolatile and viscous NADES systems.

Intensification of absorption rate of carbon dioxide and ammonia in a simulated packed (Stephens–Morris) column using pulsed gas phase under optimized parametric conditions

BackgroundReducing gas emissions is a significant challenge in our ecosystem. Gas-liquid absorption is used in chemical industry to remove components from gas streams. Stephens–Morris tube, known for liquid-liquid and gas-liquid systems, has gained attention for gas absorption columns utilizing disc-shaped packing elements to improve mass transfer by creating tortuous flow path. MethodsThis investigation focuses on physical absorption of CO2 and NH3 in gas-liquid systems based on various process parameters vis. liquid flow rate (0.24–0.60 L/min), gas flow rate (6–60 L/min), pulsation frequency (0–9.06 Hz), pulsation amplitude (0–26 mm), effect of solute gas concentration (0–100 %), and effect of varying the number of discs in the disc column (15, 20, 25, 33). Response Surface Methodology (RSM) was used to predict maximum absorption efficiency under optimized conditions. Significant FindingsPulsation frequency and amplitude proportionally increased absorption coefficient, while liquid flow rate affected it differently in pulsed and unpulsed absorption. In gas film-controlled system, mass transfer coefficient was proportional to the gas flow rate. RSM yielded R2 of 0.975 while relative error and dwill was 0.097 and 0.96, respectively. Understanding system characteristics and operations at optimal pulsation frequencies and amplitudes can maximize absorption effectiveness, particularly for low-solubility gases dominated by liquid phase resistance.

Measurements, correlations and thermodynamic modeling of aqueous two-phase systems of polyvinylpyrrolidone (PVP) + sulfate/citrate salts

Aqueous two-phase systems (ATPS) can be described as an alternative to traditional liquid-liquid extraction systems, typically consisting of a polymer and a salt solution. An alternative polymer called polyvinylpyrrolidone (PVP) has emerged as a viable option for ATPS due to its low cost, stability, and potential. This study aimed to investigate the effect of the molecular weight of poly (vinylpyrrolidone) (PVP) (K17, K25, and K30) and the temperature (298.15, 303.15, and 308.15 K) in the system ATPSs composed of PVPs and sodium sulfate/potassium sulfate/tri sodium citrate. The tie-line data were determined by measuring the density (ρ) and refractive index (nD). Moreover, the phase compositions and plait point are investigated for different PVPs molecular weight, temperature, and salt type. In addition, the effect of these parameters on the binodal curve, tie-line length (TLL), and slope of tie line (STL) are analyzed in detail by comparing them with the literature data. The impact of the parameters on the binodal curves was investigated by utilizing the values of the effective excluded volume parameter (EEV) that were calculated from the LLE data. Furthermore, the binodal curves and the tie-line compositions were well-fitted by using some semi-empirical equations. The phase separation ability is enhanced with temperature and PVPs molecular weight. The modified UNIFAC-NRF is used to correlate the liquid-liquid equilibrium data of the studied systems and the optimized binary group interaction parameters were determined.

Coalescence Initiation in Liquid-Liquid Systems: A Stochastic Model.

Coalescence is a complex phenomenon leading to the merging of deformable particles of fluid. The complexity stems largely from the simultaneous occurrence of phenomena of a different nature (hydrodynamic, electrostatic, physicochemical) acting at different scales. The stochastic effects controlling the formation of the liquid bridge between two droplets of the same liquid, immersed in another nonmiscible liquid, are studied through a series of molecular dynamics simulations. The case of heptane droplets in water, relevant to solvent extraction, a key process of the circular economy, is considered. From this series of simulations, we have confirmed that the probability function of coalescence of two identical droplets in contact follows a Poisson distribution. We moreover propose a criterion for the initiation of coalescence based on nucleation theory. A complete description of the stochastic initiation of coalescence is hence provided, opening many perspectives for the simulation of coalescence in continuous approaches used in fluid mechanics and chemical engineering. The methodology can be generalized to droplets of different size and composition, immersed in gas, or to bubbles, i.e., to other physical problems whose kinetics is influenced by the molecular scale.

Microwave enhancement of extractions and reactions in Liquid-Liquid biphasic systems

Microwaves (MWs) are a powerful technology for electrifying chemical processing and can enable selective heating, which is impossible in conventional systems. This effect was recently ascribed to enhancing liquid–liquid reactive extractions in biomass derivative chemistry. Expanding upon prior research that showcased MW-induced temperature gradients and their optimization, this study delves into the impact of these gradients on extraction using a combination of experiments and simulations. The findings illustrate that the colder organic phase enforced by the MW heating leads to alterations in solute partitioning and phase behavior. Partitioning can be further tuned by adding salts or by carefully selecting solvents, as demonstrated via COSMO-RS calculations. The colder organic phase also leads to Rayleigh instabilities and active buoyancy-driven mixing. These effects, measured experimentally and simulated in COMSOL, can greatly enhance mass transfer rates in liquid–liquid systems. Under conditions reported in the literature, the MW enhancement to reactive extractions is minimal. Conditions that may lead to more impressive extractions and reactive extractions are suggested. Additionally, it's observed that temperature gradients retard byproduct formation.

Behaviour of Acoustically Levitated Drops in Mid-Water.

A low-impact acoustic levitation system has been developed to study immobilised single drops in liquid-liquid systems. The ability to observe liquid drops several millimetres in diameter for days enables fundamental research into a wide range of mechanisms. Non-invasive optical measurements with excellent optical accessibility are possible. This experimental work provides the basis for mass transfer studies, emphasizing the precise volume determination, signal noise, reproducibility, and the impact of the acoustic field on the drop and its surrounding environment. The setup can be effectively controlled and proves beneficial for research objectives provided that all liquid phases are entirely degassed, and there are no compressible voids present within the liquids. In addition to the precise, uniform, and reliable measurement conditions, we observed no acoustic streaming in the proximity of the drop and there was no significant vibration of the drop. Qualitative observations using rainbow schlieren deflectometry indicate that the nodal or anti-nodal planes of the standing waves can act as barriers to the dispersion of inhomogeneous dissolved substances in the continuous phase.

A continuous process in mixers-settlers for the removal/recovery of chromium in effluents from the tanning industry.

One of the main environmental issues caused by the tanning industry is given by the high concentration of chromium contained on its effluents. The removal of this pollutant has become a technological challenge. To solve this issue, this work proposes a continuous process based on mixers-settlers for the removal of the chromium present in effluents from the tanning industry. The process involves the use of liquid-liquid extraction systems. The study includes the development of isotherms for the removal and stripping, which are further represented through a mathematical model to determine the number of theoretical extraction stages and other operational variables. The results show that a better extraction is achieved in a system with two theoretical stages using Cyanex 272 as extractant, reaching more than 94% of removal of chromium with an extractant concentration of 0.32 mol/L. For stripping, sulfuric acid is used, obtaining a maximum recovery of 94%.

Study on the Equilibria of the Complex Formation of Anionic Chelate of Zn(II) with Tridentate Ligand and the Cation of 3-(2-naphtyl)-2,5-diphenyl-2H-tetrazolium chloride

The equilibria of the complex formation between the anionic chelate of zinc(II) with the tridentate ligand of 4-(2-pyridylazo)-resorcinol (PAR) and the bulky organic tetrazolium cation of 3-(2-naphtyl)-2,5-diphenyl-2Htetrazolium chloride (TV) in the liquid-liquid extraction system Zn(II)‒PAR‒TV‒H2O‒2-methyl-1-propanol was studied by spectrophotometric method. The molar ratio of the reagents was determined by independent methods under the optimum condition for ion-association and for extraction. The validity of Beer’s law was checked and some analytical characteristics were calculated. The constants, describing the association process in aqueous phase and the extraction equilibria, were calculated. Based on this, a reaction scheme, a general formula and a structural formula of the complex were suggested. The zinc(II) cation is six coordinated with the tridentate ligand through the following atoms: the azo nitrogen, the pyridine nitrogen and the oxygen atom from the phenolic group, which is in ortho position relative to the azo group, each of them forming two five-membered chelate rings.

Experiments and CFD modelling of bubble formation at a lateral hole in a top-submerged nozzle

Top-submerged nozzles with lateral holes find applications as passive mixing devices in radiochemical/hazardous industries. We report the mechanism of bubble formation and detachment at a lateral hole in such a nozzle for the first time. Three distinct phases – a growth phase, an elongation phase and finally a rise/detachment phase – could be observed during bubble formation. Effect of gas flow rate, diameter of lateral hole (1, 2 and 3 mm) and physical properties of liquid-liquid system on bubble detachment time and bubble equivalent diameter are reported. Three different liquid-liquid systems (DM water, 2 N and 4 N nitric acid) have been considered. Bubble diameter first reduced, reached a minimum and then started to increase in an oscillatory manner with increase in air flow rate. Before the onset of oscillatory behaviour an increase in hole diameter was seen to reduce bubble diameter. Such a behaviour is typical to bubble formation at lateral hole and is not seen for top-submerged nozzles with central opening. A detailed analysis of the results was carried out and it was observed that inertial forces played a major role. The work also reports a fundamental criterion which must be achieved for onset of oscillations in bubble diameter with flow rate. We also report a 2D CFD model that can simulate bubble formation dynamics at a lateral hole. The model was validated qualitatively as well as quantitatively against the experimental data.

Liquid-liquid extraction of phenolic wastewater through a surface modified poly(vinylidene fluoride-co-hexafluoropropylene) hollow fiber membrane contactor and process optimization

BackgroundStrict environmental regulations have been recognized for phenolic wastewater treatment due to toxicity of the phenolic compounds. In this study, solvent extraction of a phenolic wastewater was investigated via a liquid-liquid membrane contactor system. MethodsPorous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were modified by coating an ultra-thin layer of hydrophobic surface modifying macromolecule (SMM). The membranes were characterized by various tests such as SEM-EDS, nitrogen permeation, overall porosity, contact angle and critical water entry pressure (CEPw). Significant findingsFrom SEM, an open structure with combination of finger-like and sponge-like structure was produced. The membrane exhibited high surface hydrophobicity (water contact angle of 109°) with good wetting resistance, overall porosity of 82% and mean pore size of 18 nm. From response surface methodology (RSM), the maximum phenol extraction flux of 2.02 × 10−3 kg/m2s was estimated by the model at the optimum process variables as phenol concentration of 448 mg/L, feed temperature of 42 °C, aqueous phase flowrate of 196 mL/min and organic phase flowrate of 117 mL/min. The coefficient of determination (R2) of 0.972 showed a close proximity between the model and the experimental data. The membrane showed a reasonable flux that can be a favorable alternative for industrial phenolic wastewater treatment.

Ultra-Low Viscosity and High Magnetic Susceptibility Magnetic Ionic Liquids Featuring Functionalized Diglycolic Acid Ester Rare-Earth and Transition Metal Chelates.

Magnetic ionic liquids (MILs) comprise a subcategory of ionic liquids (ILs) and contain a paramagnetic metal center allowing them to be readily manipulated by an external magnetic field. While MILs are popularly employed as solvents in catalysis, separations, and organic synthesis, most low viscosity combinations possess a hydrophilic character that limits their use in aqueous matrices. To date, no study has reported the synthesis and characterization of hydrophobic MILs with viscosities similar to those of hydrophilic MILs and organic solvents while simultaneously exhibiting enhanced magnetic and thermal properties. In this study, diglycolic acid esters are employed as ligands to chelate with paramagnetic metals to produce cations that are paired with metal chelates composed of hexafluoroacetylacetonate ligands to form MILs incorporating multiple metal centers in the cation and anion. Viscosity values below 31.6 cP were obtained for these solvents, the lowest ever reported for hydrophobic MILs. Solubilities in nonpolar solvents such as benzene were observed to be as high as 50% (w/v) MIL-to-solvent ratio while being insoluble in water at concentrations as low as 0.01% (w/v). Effective paramagnetic moment values for these solvents ranged from 5.33 to 15.56 Bohr magnetons (μB), with mixed metal MILs containing multiple lanthanides in the anion generally offering higher magnetic susceptibilities. MILs composed of ligands containing octyl substituents were found to possess thermal stabilities up to 190 °C. The synthetic strategies explored in this study exploit the highly tunable nature of the employed cation and anion pairs to design versatile ultra-low viscosity magnetoactive solvents that possess tremendous potential and applicability in liquid-liquid separation systems, catalysis, and microfluidics where the mechanical movement of the solvent can be easily facilitated using electromagnets.

Characterization of a solid-supported aqueous biphasic system for the sorption of dyes from aqueous solution

An aqueous biphasic system (ABS) comprising solutions of ammonium sulfate and polyethylene glycol-2000 (PEG-2000) in which the latter is supported on a porous polymeric substrate (Amberlite XAD-16) has been characterized by examining its performance in the removal of dyes from aqueous solution. Comparison of its behavior to that of a commercial sorbent (ABEC) consisting of a polyethylene glycol covalently bound to a polymer support indicates that the capacity, uptake kinetics, and efficiency of the supported ABS are comparable or superior to that of the ABEC resin. In addition, results obtained at various PEG-2000 concentrations and with PEGs of a range of molecular weights demonstrate that in contrast to ABEC resin, the behavior of a supported ABS can be readily “tuned” to provide the desired dye retention. The relative retention of various dyes is not generally predictable from their behavior in an analogous liquid-liquid system, however, the apparent result of synergistic effects between the XAD-16 support and the PEG phase.

Reinforcement learning based hybrid bond-order coarse-grained interatomic potentials for exploring mesoscale aggregation in liquid-liquid mixtures.

Exploring mesoscopic physical phenomena has always been a challenge for brute-force all-atom molecular dynamics simulations. Although recent advances in computing hardware have improved the accessible length scales, reaching mesoscopic timescales is still a significant bottleneck. Coarse-graining of all-atom models allows robust investigation of mesoscale physics with a reduced spatial and temporal resolution but preserves desired structural features of molecules, unlike continuum-based methods. Here, we present a hybrid bond-order coarse-grained forcefield (HyCG) for modeling mesoscale aggregation phenomena in liquid-liquid mixtures. The intuitive hybrid functional form of the potential offers interpretability to our model, unlike many machine learning based interatomic potentials. We parameterize the potential with the continuous action Monte Carlo Tree Search (cMCTS) algorithm, a reinforcement learning (RL) based global optimizing scheme, using training data from all-atom simulations. The resulting RL-HyCG correctly describes mesoscale critical fluctuations in binary liquid-liquid extraction systems. cMCTS, the RL algorithm, accurately captures the mean behavior of various geometrical properties of the molecule of interest, which were excluded from the training set. The developed potential model along with the RL-based training workflow could be applied to explore a variety of other mesoscale physical phenomena that are typically inaccessible to all-atom molecular dynamics simulations.

СПОСОБЫ ПОЛУЧЕНИЯ ХОЛИНХЛОРИДА

The conditions and parameters of industrial methods for the production of choline chloride are analyzed. The synthesis of high purity choline chloride with a yield close to theoretical is carried out at moderate pressures, temperatures of 30-100 °C in gas-liquid, liquid-liquid systems

Microbial pigments: Eco-friendly extraction techniques and some industrial applications

Since ancient times, natural coloring agents have been produced from plants, insects, animals, and ores. Although they have a dangerous impact on mammals and the environment, synthetic dyes replace natural colors because of their limited availability throughout the year; instability in light, heat, and pH; increased global demand; and low water solubility. Therefore, pigments from microbial sources are considered the best alternatives to natural pigments. The potential of microbial pigments for easy mass production, diversified coloring properties, and inexpensive production is now receiving the attention of researchers and industries. Most industrial extraction processes are based on traditional liquid-liquid systems that use organic solvents for the extraction of pigments. The environmental pollution generated by these chemicals has become a central issue in societal and political decisions. This has led to a growing demand for efficient eco- friendly extraction technologies. In the last two decades, significant advances have been made in the green chemistry of pigment extraction and separation techniques. Methods such as ultrasound-assisted extraction, microwave-assisted extraction, pressurized liquid extraction, enzyme-assisted extraction, and more recently, ionic liquid-assisted extraction have been developed. This review summarizes the methods for the simple and eco -friendly extraction of microbial pigments for applications in the food and textile sectors.

Intensification of esterification reaction microbubble mediated reactive distillation

The current study is based on the microbubble mediated reactive distillation by converting conventional homogeneous liquid-liquid system into a heterogeneous vapour-liquid system. Microbubbles owing to their higher surface area to volume ratio provides better mass transfer as well increasing the conversion and rate of reaction. To prove the hypothesis, production of methyl acetate was investigated because of its industrial importance. The experimental plan was designed using Response Surface Methodology (RSM). It allowed analysing the effects of operational parameters simultaneously. The kinetics investigation demonstrated that the esterification reaction occurs, indeed, on the vapour liquid interface at the skin/surface of the bubble and follows pseudo-first order kinetics. The maximum conversion of the process was found to be 91% in 20 min which is significantly higher than any previous study. Furthermore, RSM and Gated Recurrent Unit (GRU) were employed to develop models to analyse the correlations among parameters and to predict the responses. The GRU produced higher R2 = 0.9981 as compared to R2 = 0.9715 produced by RSM. The results depict that GRU model is more robust and reliable than Response Surface Methodology for parameter interaction study and response prediction.

Measuring liquid-liquid volume composition in transparent tubing using a linear CMOS sensor

Recent advances in milli- and microscale fluidics have led to the miniaturization of liquid-liquid extraction systems. Carryover is a primary mode of failure in these systems, where unwanted liquid appears at the outlet of the opposite phase. Active monitoring of carryover is key to realizing automation and deployment of such fluidic technologies. In this paper, we present an inexpensive sensor and simple methods of analysis to quantify carryover. The sensor measures the volume composition of immiscible liquids using off-the-shelf tubing, a LED light source, a linear CMOS sensor, and shadowgraphy. Beam4 optical modeling is included to provide insight into this sensor's optical behavior. We report measurements of single and two-phase flows and explore average pixel ratio (signal:background) and menisci counting analyses. As an added benefit, we use average pixel ratio to identify bulk liquids and their constituents, specifically toluene, water, and 0–50 wt% sucrose in water.

Drop size distribution in batch stirred tank at high organic to aqueous phase ratios

Hydrodynamic studies were carried out at high organic to aqueous (O/A) phase ratios in a liquid-liquid batch stirred tank. Minimum mixing speed for complete dispersion, Sauter mean diameter, and drop size distribution have been measured with Rushton turbine and pitched blade turbine for three different liquid-liquid systems. Experiments have been performed at various impeller speeds and organic-to-aqueous phase ratios. Minimum mixing speed for complete dispersion (Nmin) was measured by visual observation as well as by sample withdrawal technique. Surfactant stabilization technique has been used to measure the drop size. Minimum mixing speed was found to be strongly dependent on impeller type and organic-to-aqueous phase ratios. About 10–40% decrease in minimum mixing speed was observed when organic to aqueous phase ratio was increased from 10 to 50. Sauter mean diameter was significantly affected by impeller speed, physical properties of the liquid systems, and dispersed phase holdup. Experimental drop size distributions were fitted with the log-normal distribution. Empirical correlations have been developed to predict minimum mixing speed and Sauter mean diameter at various operating conditions. Absolute Average Relative Error for the prediction of minimum mixing speed and Sauter mean diameter using developed correlations were found to be 18.45% and 11.06%, respectively.