Kinetic and thermodynamic study of the transfer of anionic polyamidoamine dendrimers across two immiscible liquids

The kinetics and thermodynamics for the phase transfer of carboxyl-terminated polyamidoamine (PAMAM) dendrimers across the water/dichloroethane interface were analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. A three phase junction was employed by inserting a cylindrical gold electrode through the liquid–liquid interface. The reversible redox species decamethylferrocene (DMFc) was used in the organic phase in order to promote dendrimer transfer. It was found that the electrochemical behaviour of DMFc at the gold/dichloroethane interface depends on the generation and concentration of the dendrimer species in the aqueous phase. In addition, it was observed that the electrochemically driven transfer of these macromolecules corresponds to a quasi-reversible process. The data obtained from thermodynamic studies indicate that dendrimers are transferred between the two phases under study by an entropy controlled process.     

Interaction of acridine-calix[4]arene with DNA at the electrified liquid|liquid interface

The behaviour of an acridine-functionalised calix[4]arene at the interface between two immiscible electrolyte solutions (ITIES) is reported. Molecular modelling showed that the acridine-calix[4]arene has regions of significant net positive charge spread throughout the protonated acridine moieties, consistent with it being able to function as an anion ionophore. The presence of this compound in the organic phase facilitated the transfer of aqueous phase electrolyte ions. Upon addition of double stranded DNA to the aqueous phase, the transfer of electrolyte anions was diminished, due to DNA binding to the acridine moiety at the ITIES. The behaviour provides a basis for DNA hybridization detection using electrochemistry at the ITIES.     

Comparative analysis of the transfer of alkaline and alkaline-earth cations across the water/1,2-dichloroethane interface

The transfer of alkaline and alkaline-earth cations across the water/1,2-dichloroethane interface in presence of 1,10-phenanthroline (phen) in the organic phase was studied using cyclic voltammetry in a concentration range wide enough to cover the following experimental conditions: C_M2+(w) C_phen(o) and C_phen(o) C_M2+(w).

The results obtained (when C_M2+(w) C_phen(o)) were compared with the theoretical voltammetric criteria reported by Homolka1l] for facilitated transfer. It appears that the transfer of all these cations occurs via a facilitated mechanism. The stoichiometry of all complexes formed in the organic phase is also reported. The stability constants for Ca²⁺-phen and Sr²⁺-phen complexes were estimated and compared with the tendency observed in the transfer potentials of these cations.     

Penicillin G extraction by amberlite LA-2—a study of interfacial reaction kinetics by interfacial tension measurements

The concentration of reactants at an interface cannot be determined directly. The concentration at the interface has been estimated by measuring the interfacial tension at the interface between two immiscible solutions. An aqueous phase, de-ionised water containing penicillin G, and an organic phase containing amberlite LA-2 were used as a typical system to study the kinetics of interfacial reaction. The interfacial tension was measured by a spinning-drop tensiometer at 25 ± 0·1°C. The interfacial tension was found to correlate well with the concentrations of penicillin G, Amberlite, LA-2 and proton in each respective phase.     

Mass transfer of long chain fatty acids through liquid–liquid interface stabilized by porous membrane

Long chain fatty acids are usually undesirable contaminants in food oils and removal of these acids is an important task for the oil industry. In this paper the mechanism of transfer of fatty acids from liquid organic phase through flat porous membrane into water was investigated. The membrane pores initially were filled with the same organic solvent without fatty acid. It was demonstrated that the rates of transfer from octane into aqueous solution at pH 4 are inversely proportional to the distribution coefficients (K_d) and are mostly determined by diffusion in aqueous unstirred layers. Increase of pH of aqueous solutions from four to 12 results in a 20-fold increase of transfer rate for octanoic acid, and more than 1000-fold increase for oleic acid. Time lag values necessary for the kinetics of fatty acid transfer to reach the steady state were very small for the transfer from octane, but they were much higher in the case of viscous mineral oil. These last values were in good agreement with Barrer’s equation for diffusion through two unstirred layers. In both cases, there is no significant interface resistance for the transfer of relatively long chain fatty acids from organic solvent into water. Ion exchange processes take place in the aqueous phase and the thickness of the corresponding reaction layer decreases to zero at high pH. This final state is equivalent to the reaction, taking place at the interface. This method could be used for kinetic separation of short and long chain fatty acids at acidic pH and non-selective removal of different fatty acids into alkaline aqueous solutions. The membrane-based process does not need elevated temperature and probably is less energy consuming than distillation.     

Competitive transfer of H+ and Al(III) ions facilitated by a Prometrine herbicide through a liquid/liquid interface

The transfer of aluminium(III) across the water/1,2-dichloroethane interface facilitated by the herbicide Prometrine (PROM) was investigated using cyclic voltammetry. In the presence of PROM in the organic phase, the transfer of Al(III) and H⁺ from the aqueous to the organic phase was observed and the competition between these two cations for the herbicide was analyzed at different pH values. At pH 4.50, it was possible to determine the formation of an Al(III):PROM complex in the organic phase, with a stoichiometry of 1:3 and a charge of 2⁺, indicating that the species in the complex with PROM is Al(OH)²⁺.     

Kinetic Basicities of Aqueous Binary Mixtures: A Surprisingly Good Linear Correlation with the Gas Phase Basicity of the Organic Cosolvent

A remarkably good correlation between the rate of proton transfer from excited protonated 1-aminopyrene and the gas phase basicities of the organic component in water: organic solvent binary mixtures has been found. We suggest that use of anilinium acids minimizes the effect of anion solvation and Coulomb interactions and enables the influence of the organic cosolvent on the proton transfer to be clearly observed. The model proposed is one in which the proton is always transferred to a water molecule and a concerted proton transfer to a water molecule solvated by the organic cosolvent also occurs. The cosolvent influence is then on this latter species via hydrogen bond interactions. The correlation holds in pure water but not in pure organic solvents where, clearly, the proton must be transferred to the organic molecule.     

Investigation of liquid–liquid interfacial electron transfer kinetics using multicenter ferrocenyl complexes

The redox behavior of two novel multicenter redox molecules (triferrocenylmethane and triferrocenylmethanol) has been studied in a thin film of nitrobenzene (NB) imposed between a graphite electrode and an aqueous electrolyte. The well separated three sets of redox peaks indicate strong intramolecular electronic communications between the three ferrocene centers in each molecule. They were adapted as model compounds for the study of electron transfer kinetics across the liquid/liquid interface with varied overall driving force using only one-type redox couples in the organic and aqueous phase, respectively. It has been shown that in both cases the dependence of interfacial electron transfer rate on the increased overall driving force across the nitrobenzene/water interface is not monotonic.     

Electron and ion transfer potentials of ferrocene and derivatives at a liquid-liquid interface

The electrochemistry of ferrocene, dimethyl ferrocene and decamethyl ferrocene at the interface of immiscible electrolytes has been investigated. The aqueous redox electrolyte was the hexacyanoferrate couple. It has been found that the study of the electron transfer reaction can be complicated by both the transfer of the ferricenium ion formed in the organic phase (1,2-dichloroethane) during oxidation, and by oxidation of the organic base electrolyte anion. However, by using a high concentration of aqueous electrolyte, the difference between ionic and electronic transfer potentials can be increased sufficiently to observe these two processes separately. Ionic transfer potentials of the ferricenium ion have been measured by preparing the corresponding FeCl⁻₄ salts. For decamethyl ferrocene, no electron transfer reaction could be observed at the liquid/liquid interface and it is proposed that this is due to distance effects, which become more marked for this more hydrophobic ferrocene derivative.     

Modeling of Facilitated Transport of Phenylalanine by Emulsion Liquid Membranes with Di(2-ethylhexyl)phosphoric Acid as a Carrier

ABSTRACT

A mathematical model is developed in this paper to simulate the facilitated transport of phenylalanine (Phe) in emulsion liquid membrane (ELM) systems with di(2-ethylhexyl)phosphoric acid as a carrier. The model takes into account the mass transfer in both the external aqueous phase and the organic membrane phase interfacial reaction as well as membrane breakage during agitation. The model is tested by comparing theoretical predications with experimental results using Phe extraction by ELM processes. It is found that the model is valid for simulating the facilitated transport of Phe with ELM under various experimental conditions.     

Liquid membranes a moving film apparatus for measurement of mass transfer in emulsions,and its application to active transport of phosphate ions

A new apparatus to measure mass transfer in emulsion is described. It consists in a cylindrical rod of “Teflon” surrounded by a flowing film of a water-in-oil emulsion in a column filled with an aqueous solution. It allows easy and precise measurement of the interfacial area between the solution and the emulsion. In the conditions of the experiments, mass transfer resistance can be assumed to be mainly in a diffusional layer of the organic phase of the emulsion.Data of the rate of active transport of phosphate ions through the organic phase of a water-in-oil emulsion using Aliquat 336 as carrier and montanide 80 as surfactant are obtained.A simple diffusion model, assuming fast exchange reaction at the interfaces and control of the kinetics by the diffusion through a very thin layer of the organic phase, gives a good representation of the kinetics of transfer and explains its dependence on carrier and surfactant concentrations in good agreement with experimental results.     

EXTRACTION OF NICKEL FROM AQUEOUS SULFATE SOLUTION INTO BIS(2,2,4-TRIMETHYLPENTYL)PHOSPHINIC ACID,CYANEX 272TM -EQUILIBRIUM AND KINETIC STUDIES

ABSTRACT

Equilibrium and kinetic studies have been carried out on the extraction of nickel from sulfate solutions using bis(2,2,4 trimethylpentyl) phosphinic acid HDTMPP, “Cyanex 272tm”- It was found that nickel extraction in HDTMPP was favored by the presence of sodium in the organic phase and that equilibrium nickel concentration could be written in terms of the pre-equilibrated extractant concentration

Kinetic studies were carried out using the rising drop method, reaction orders were determined with respect to the aqueous phase nickel concentration, Ni²⁺, the aqueous phase sodium concentration, Na ⁺ the pH, the organic phase dimer concentration ------ and the organic phase sodium salt concentration ---- In addition, it was found that the extraction kinetics could be explained in terms of an aqueous phase interfacial reaction accompanied by diffusion through the interface. Mass transfer coefficient values were determined indicating extraction rates for metal extraction into HDTMPP were the same order of magnitude as those found for HDEHP.     

Extraction Kinetics of Organic Acids with Tri-n-octylphosphine Oxide

The extraction kinetics of organic acids with tri-n-octylphosphine oxide (TOPO) was investigated to determine the extraction mechanism. It was found that the species were in equilibrium at the interface and the extraction rate was limited by the mass transfer, except for crotonic acid. In crotonic acid, the observed rates were analysed by considering the film diffusion of the acid and the reaction between the acid and TOPO in organic solution.     

Interpretation of the Extraction Mechanism of the Purex and Thorex Processes from Kinetics Data

Abstract

The rate of transfer of species between phases in solvent extraction is expected to be controlled by chemical reaction kinetics, diffusion, or a combination of these steps. Transfer kinetics data for uranium(VI), thorium(IV), and zirconium(IV) indicate that the chemical reaction is the rate-controlling step for most dispersed systems. The evidence for this conclusion is: (1) the transfer rate constants for the extraction of uranium were the same for Lewis cell, single drop, and Kenics mixer tests; (2) the forward transfer rate constants increase with increasing TBP concentration (the viscosity of the organic phase also increases) in all cases; (3) the reverse transfer rate varies dramatically with changes in nitrate concentration in the aqueous phase (same phase viscosities); and (4) the difference in the activation energies of the forward and reverse reactions for uranium(VI) transfer is equal to the heat of reaction of uranium with TBP. A proposed mechanism for the solvent extraction kinetics which is consistent with the experimental results includes the formation or decomposition of a charged interfacial complex as the rate-controlling step and equilibration of the interfacial complex with the bulk organic complex as the rapid step.     

气液并流吸收近界面浓度分布不稳定性实时观测

气液自由界面附近的瞬时浓度分布信息对于理解相际传质动力学很重要。利用激光全息干涉测量系统分别对乙醇、甲醇并流吸收CO2过程中液相内近界面的摩尔分数分布进行了实时观测。研究表明,水平槽道内气液流动传质过程中液相内的不稳定性现象是普遍存在的。它主要包括界面湍动和周期性脉冲爆发2种形式。当传质达到稳态时近界面CO2摩尔分数的分布结果表明,流场内存在着微弱的摩尔分数波动。吸收体系的性质和流速直接影响传质推动力的大小,从而决定摩尔分数波动的强度及深度。     

Mass transfer enhancement of acetic acid across a plane kerosene/water interface by an electric field

The intensification of mass transfer of acetic acid from kerosene into water across a plane interface by the application of an electric field normal to the interface is investigated. The application of an electric field affects mainly mass transport through the bulk of the organic phase rather than the interface. In the range (5–30) × 10⁴ V/m the mass transfer coefficient changes from 8 × 10^?6 to 2 × 10^?5 m/s. A model based on the movement of electric charges in the organic phase indicates that a Sherwood-Grashof correlation for free convection only is also suitable for the electrically driven process if the Grashof number is modified to take into account the effect of the electric field on the movement of the electric charges.     

Kinetic study of the hydrolysis of two formate esters held in a single organic drop

The rising drop technique was used to study the kinetics of the alkaline hydrolysis of two formate esters; n-butylformate and iso-amylformate in toluene formed the organic phase, whilst aqueous sodium hydroxide was used as the continuous phase. The effects of ester and alkali concentrations on the rate of the hydrolysis were studied. The order of the reaction was found to change with respect to the concentration of both reactants. Cetyltrimethylammoniumbromide (CTAB) was used as a possible catalyst for this liquid–liquid hydrolysis. When CTAB was added to the aqueous phase, enhancement of reaction was observed, whilst its addition to the organic phase caused inhibition of the hydrolysis. It is suggested that the enhancement of the reaction is due to the interaction of micelles in proximity to the interface while the inhibition is probably due to chemical blocking of the interface by adsorbed molecules of ionized CTAB.     

Investigation of the kinetics of ion and assisted ion transfer by the technique of ac impedance of the micro-ities

The microhole and micropipette tip-supported interface between two immiscible electrolyte solutions (ITIES) were used to study the kinetics of ion and assisted ion transfer reactions, respectively, using the technique of ac impedance. The ion transfer reaction studied was that of tetramethylammonium transfer between water and 1,2-dichloroethane (1,2-DCE). The assisted ion transfer process investigated was that of potassium, facilitated by dibenzo-18-crown-6, between the same solvents. In each case, the standard apparent rate constant, k⁰, was demonstrated to be a quantity which is inaccessible to measurement by electrochemical means. Both reactions were illustrated to be controlled by the diffusion of the participating species only.     

Dynamic interfacial tension minima in finite systems

A physical model is presented to explain the dramatic interfacial tension minima that may sometimes occur during the equilibration of a surface-active solute between two liquid phases. The effects of bulk phase mass transfer resistances, interfacial sorption kinetics, and finite phase volumes are included. Adsorption and desorption barriers are treated both by linear and Langmuir kinetics. Dynamic interfacial tension minima are predicted whenever the solute mass transfer resistance is higher and/or a large desorption barrier exists in the phase towards which transfer is occurring. Experimental dynamic tension minima for acidic organic phases contacting an alkaline aqueous phase can be rationalized by the existence of desorption barriers. The relevance of such tension minima to interfacial turbulence, spontaneous emulsification, and enhanced oil recovery is discussed.     

相转移催化元素硫歧化反应的动力学

在45—70℃、氢氧离子浓度为0.02—0.14mol/l范围内研究了四氯乙烯/水体系中氢氧化四丁铵相转移催化元素硫歧化反应初始阶段的动力学.实验得到表观速度表达式:R_(?)a=k~(?)[Q~+]_(aq)[OH~-]_(aq)[S]_(org)~(1/2),并导得表观活化能为79kJ/mol.用液液体系伴有快速化学反应的传质模型成功地解释了本体系动力学.推测了元素硫的歧化反应机理,从动力学上提出了本体系相转移催化的证据.