Nonexchange Sorption Research Articles

Influence of temperature on non-exchange sorption of aromatic amino acids by anion exchanger AV-17-8

The equilibrium in thearomatic amino acid (tryptophan, phenylalanine, tyrosine and histidine) – anion exchanger AV-17-8 (Cl-) systems at different temperatures was investigated In order to identify the influence of both increased and decreased temperatures on the sorption equilibrium the temperature range was 277-343 K was studied. Sorption isotherms were obtained at 277, 293, and 343 K. The thermodynamic description of sorption systems was carried out using an approach based on the idea that the sorption process is stoichiometric. The integral and differential energy characteristics and the compensation effect between the enthalpy and entropy components for the studied sorption systems were calculated. A change in temperature led to a change in the physicochemical properties of the studied sorbates and sorbent. In the temperature range 277-243 K, the solvent content in the sorbent phase remained unchanged. A low solvent content at a temperature of 333 K and an increase in its amount at 343 K were experimentally established. It should be considered that at different temperatures the ionization constants of functional groups and the regions of existence of ionic forms of amino acids change, but the sorption mechanism does not change, since the recharging of amino acids did not occur. It was established that the process is exothermic for tryptophan and phenylalanine. With increasing temperature, the amount of sorbed substance decreased. The absorption energy was low due to the significant compensatory effect of enthalpy and entropy factors, the differential Gibbs energy was practically independent of temperature due to the stabilizing effect of hydrophobic forces in the sorbent phase. For the poorly soluble amino acid tyrosine, when the temperature increased from 277 to 293 K, a slight increase in sorption was observed, and with a further increase, a decrease to trace amounts was revealed. In the temperature range of 277-293 K, the sorption process was characterized by the formation of a supersaturated solution in the sorbent phase and was endothermic. The sorption of hydrophilic histidine increased with increasing temperature, which correlates with the solvent content in the sorbent phase, including low content at 333 K. The process of histidine sorption is endothermic, characterized by a strong dependence of the differential Gibbs energy on temperature and the absence of a compensation effect between the enthalpic and entropic components.

Selecting Reference States in Thermodynamic Descriptions of Non-Exchangeable Sorption

Selecting standard and reference states for a thermodynamic description of the non-exchange sorption of substances by ion exchangers is considered a stoichiometric process. It is shown that it is best to choose different reference states for free and sorption centers associated with the absorbed substance, since this allows calculations of the thermodynamic constants and energy characteristics of sorption. Results from calculating thermodynamic characteristics of sorption are presented and discussed for systems with the participation of amino acids (glycine and phenylalanine).

Nonexchange Sorption of Amino Acids on an AV-17 Anion Exchanger: Quantum-Chemical Simulation

The energy of interaction between various amino acids (glycine, alanine, and phenylalanine) and an AV-17 strongly basic anion exchanger in chloride and nitrate ionic forms under nonexchange absorption conditions is assessed by quantum chemistry calculations. We found that the amount of water in the starting fragments of sorption participants, the counterion of the anion exchanger, and the amino acid radical play an important role in energy and in the ratio of different intermolecular interactions (Coulomb, hydrophobic, and hydrogen bonds) to form ion-molecular structures in the ion-exchanger phase.

Сорбция гистидина ионообменниками различной природы

С целью сравнения сорбции полифункциональных веществ на ионообменниках различной природы исследовано поглощение гистидина гидрохлорида из водных растворов анионообменником АН-251 в хлоридной ионной форме, катионообменником КБ-4П-2 в натриевой ионной форме и полиам-фолите АНКБ-2 в солевой NaCl-форме. Установлено, что в первом случае протекает необменная сорб-ция за счет ион-дипольных взаимодействий между сорбционным центром «функциональная группа - противоион» и заряженной группой аминокислоты с участием молекул воды. На катионообменнике и полиамфолите протекает ионный обмен, поскольку в системе присутствует два сорта катионов Na+ и His+, величины которого, однако, невелики. В этих же системах протекает необменное поглощение за счет ион-дипольных взаимодействий противоположно заряженных структурных элементов с участием молекул расторителя, которые, могут протекать с противоионом любой природы, возникающим в си-стеме за счет ионного обмена.Установлено, что независимо от природы сорбента количество поглощенного гистидина при-близительно одинаково из-за дополнительных взаимодействий, протекающих в системе с участием сорбционных центров (в КБ-4П-2 и АНКБ-2) и малого набухания ионита (АН-251).Проведено термодинамическое описание исследуемых систем с использованием подходов, ос-нованных на представлении о стехиометричности закрепления вещества в сорбенте. Рассчитаны вели-чины коэффициентов равновесия, исправленных коэффициентов равновесия, коэффициентов активно-сти компонентов фазы сорбента, и термодинамических констант ионообменного и необменного равно-весия, а также дифференциальные энергии Гиббса, относящиеся к ионообменнику определенного со-става. В качестве состояния сравнения для обоих случаев выбирается состояние равновесия ионооб-менника в моноионной форме с водой.Установлено, что в процессе сорбции отклонение систем от состояния сравнения незначитель-ное, что связано с малым количеством поглощенного вещества по сравнению с количеством сорбцион-ных центров, термодинамические контанты равновесия близки к единице. Совместное протекание ион-ного обмена и необменной сорбции оказывает большее влияние на состояние сорбента по сравнению с необменной сорбцией в силу изменения ионной формы сорбента с минеральной на органическую

Investigation of the Nonexchange Sorption of Diverse Electrolytes by a Heterogeneous Sulfonic Cation-Exchange Membrane

The nonexchange sorption of diverse electrolytes by an MK-40 sulfonic cation-exchange membrane has been studied by conductometry without separating solution and membrane phases. The data of sorption experiments performed within the framework of the two-phase microheterogeneous model of an ion-exchange material have been used to find the Donnan constant for the MK-40 membrane in solutions of electrolytes, namely, HCl, NaOH, NaCl, MgCl2, CaCl2, and BaCl2. The concentration of an electrolyte sorbed by the membrane has been determined as depending on the nature and concentration of an equilibrium solution. Factors that have the most significant effect on the concentration of a sorbed electrolyte and the Donnan constant, such as the specific moisture capacity of the membrane and the nature and charge of counter- and coions, have been studied. The volume fractions of the gel and equilibrium solution phases have been determined by two methods, i.e., from the experimental data on the membrane specific conductivity in solutions of different natures and concentrations and from the data on the nonexchange sorption calculated within the microheterogeneous model of the membrane structure. It has been shown that the Donnan constant may be calculated for the MK-40 membrane in the salt solutions by a simplified method from the data on the sorption of an electrolyte of only one concentration, provided that the volume fractions of the conducting phases in the membrane are known.

Дифференцирующее действие растворителя при необменной сорбции аминокислот ионообменниками

При необменной сорбции ионообменниками веществ одной природы действующие силы являются одинаковыми, что осложняет разделение многокомпонентных смесей. Регулирование доминирующих взаимодействий в сорбционных системах с помощью изменения условий проведения процесса, позволит более эффективно разделять вещества без применения дополнительных электролитов. Известно, что растворитель играет важную роль во многих физико-химических процессах, особенно на границе раздела фаз, поэтому целью работы являлось выявление закономерностей необменной сорбции глицина и триптофана из водно-спиртовых растворов с различным соотношением компонентов в растворителе анионообменником АВ-17-2П (Сl). В работе использована простейшая аминокислота, не имеющая бокового радикала (глицин) и самая гидрофобная аминокислота (триптофан), а также высокоосновный анионообменник АВ-17-2П в Сl-форме, имеющий в качестве функциональных групп четвертичный азот. Исследованы свойства водно-спиртовых растворов аминокислот, анионообменника и равновесие необменной сорбции при различном содержании этилового спирта в составе растворителя (0, 25, 40, 50, 60, 75, 100 % по объему). Установлено, что свойства водноспиртовых растворов аминокислот (триптофана и глицина) и ионообменника АВ-17-2П (Сl) определяются соотношением воды и этилового спирта в составе растворителя, а также наличием полярных и гидрофобных частей в структуре объектов исследования. Изменение свойств сорбента и исследуемых сорбатов в зависимости от содержания органического компонента в растворе носит немонотонный характер: набухание анионообменника минимально при 75% alc, а растворимость триптофана имеет максимум при 40% alc, чего, однако, не наблюдается для глицина. Выявлено, что необменная сорбция аминокислот анионообменником АВ-17-2П из водно-спиртовых растворов также носит немонотонный характер в зависимости от содержания органического компонента в составе растворителя – наблюдается минимум сорбции триптофана и максимум сорбции глицина при сопоставимом содержании воды и спирта в составе растворителя. Различие в закономерностях сорбции исследуемых аминокислот определяется различием в их свойствах – полярностью глицина и гидрофобностью триптофана. Изменение состава растворителя позволяет регулировать сорбционные характеристики в системах анионообменник-аминокислота и более эффективно разделять смеси цвиттерлитов за счет дифференцирующего действия растворителя.

IR Spectroscopic Study of the Mechanism of Phenylalanine Sorption from Aqueous Solutions by a Shaped Sulfonic Acid Cation-Exchange Membrane with a Styrene–Divinylbenzene Matrix

The mechanism of phenylalanine absorption by a shaped sulfonic acid cation-exchange membrane with a styrene-divinylbenzene matrix was studied by IR spectroscopy. An analysis of the results of the IR spectroscopic studies showed that the interaction in the sorbent–sorbate system is based on ion-exchange sorption via protonation with addition of the hydrogen counterion to the carboxyl group of amino acid and ion exchange with displacement of the hydrogen ion into the equilibrium solution. The occurrence of nonexchange sorption due to the additional interparticle interactions characteristic of the aromatic amino acid of phenylalanine was proven by sorbate association in the polymer material.

Thermodynamic Description of the Nonexchange Sorption of Substances by Ion Exchangers

Based on the stoichiometry of absorption, a thermodynamic approach is proposed for describing the nonexchange sorption of substances with ion exchangers from individual solutions and mixtures. This approach is applied to describe the absorption of amino acids using the sorption of tryptophan and hystidine with anion exchangers AV-17-2P in Cl form as an example. Integral and differential characteristics of nonexchange sorption in these systems are described.

Effect of counter- and co-ions on the structural transport parameters of sulfoacid cationite membranes

The diffusion permeability and specific electroconductivity of MK-40 sulfoacid cationite and Nafion 425 membranes are studied experimentally in NaOH, NaCl, and HCl solutions with various concentrations. The resulting concentration dependences of the electrodiffusion characteristics and data on the nonexchange sorption of the electrolytes are used to calculate the structural transport parameters of the membranes in terms of a two-phase conduction model. Analysis of a set of parameters, including the electroconductivity and diffusion permeability of the membrane gel phase, the volume fractions of the conductive phases, and a parameter that reflects their relative positions, the Donnan constant, and the diffusion coefficients of counter and co-ions in the membrane gel phase reveals the effect the nature of counter- and co-ions has on the electrodiffusion, structural, and sorption characteristics of sulfoacid cationite membranes with different types of structure.

Some thermodynamic peculiarities of the nonexchange sorption of phenylalanine on dissimilar anion exchangers

It is shown that the nonexchange sorption of phenylalanine on dissimilar anion exchangers occurs by the same mechanism, determined by the structure of the amino acid, while the absorbed amount of substance depends on the sorbent structure. It is established that the micelle formation and the phenylalanineanion exchanger sorption equilibrium depend on the amount and nature of functional groups in anion exchangers. It is shown that, in the systems under investigation, the nonexchange sorption constant is determined by the constant of phenylalanine micelle formation.

Activity coefficients of components of the sorbent phase in the nonexchange sorption of chloride-containing electrolytes on AN-31 low-basicity anion exchanger in the Cl form

Activity coefficients of components of the sorbent phase in the nonexchange sorption of chloride-containing electrolytes (hydrochloric acid and potassium, sodium, and magnesium chlorides) on AN-31 low-basicity anion exchanger in the Cl form are calculated and analyzed. Peculiarities of the sorption of the investigated electrolytes on the anion exchanger are discussed.

Equilibrium sorption of methionine on carboxyl cation exchangers from solutions of various acidities

The influence of the acidity of solutions of methionine on methionine interaction with KB-2 and KB-4 carboxyl cation exchangers in the protonated and deprotonated forms was studied by the calorimetric, sorption, and spectroscopic methods. It was found that nonexchange methionine absorption occurred from acid solutions, and mixed ion exchange and nonexchange sorption, from alkaline solutions. The enthalpies of sorption of methionine at various external solution pH values were determined.

Sorption of aliphatic amines by monocarboxycellulose from aqueous and water-ethanol solutions

The features of the sorption of hydrochlorides of lower aliphatic amines by monocarboxycellulose (MCC) from aqueous and water-ethanol solutions are studied. The ion exchange character of the sorption is shown by IR spectroscopy and potentiometry. It is found that the sorption of all studied salts of aliphatic amines by MCC from dilute aqueous and water-ethanol solutions is thermodynamically advantageous due to the great contribution of Coulomb interactions between cations and polyanions. The selectivity of sorption is predetermined by solvophobic (hydrophobic) interactions, which are thermodynamically disadvantageous at any compositions of the binary solvent due to the formation of dimeric associates of carboxyl groups in the phase of MCC, which hinder the contacts of hydrocarbon radicals of aliphatic amines with hydrophobic sites of the cellulose adsorbent matrix. At high concentrations of aliphatic amines in aqueous and water-ethanol solutions, the process of nonexchange sorption proceeds intensely through the hydrogen bonding between nitrogen atoms and hydroxyl groups of MCC.

Effect of basic chemical characteristics of soils on mobility of radionuclides in them

Interplay between the basic chemical characteristics of soils of the Belarussian Polessie and the tightness of fixation of Chernobyl-derived 137Cs and 90Sr in them is studied. The mobility of radionuclides in the soil proved to be controlled essentially by the soil type and organic matter content. In the investigated soils, nonexchange sorption of 137Cs and exchange sorption of 90Sr dominate.

The nonexchange sorption of histidine by low-basicity anion exchangers

The experimental data showed that the nonexchange absorption of histidine by AN-221, AN-251, AN-31, and EDE-10P anion exchangers in the HCl form depended on the structure of the anion exchanger. The activity coefficients of the components of the sorbent phase, thermodynamic equilibrium constants, and standard Gibbs energies of nonexchange sorption of histidine by the low-basicity anion exchangers were calculated and discussed.

Non-exchange sorption of electrolytes by ion exchangers: II. Sorption of sulfuric acid and lithium sulfate by Dowex 1×8 resin

Sorption of sulfuric acid and lithium sulfate by the sulfate form of ion exchanger Dowex 1×8 have been studied in the range of concentrations 0.025–2 M. The regularities observed were described with the help of mathematical and computer models similar to those used for description of sorption of HCl and HClO 4 in the previous communication [Soldatov et al. React. Funct. Polym. 60 (2004) 41]. The models account for the site sharing effect, Donnan distribution and dimerisation of hydrosulfate ion in the resinous phase. The main introduction in the sorption of sulfuric acid in the studied concentration range is done by conversion of sulfate to hydrosulfate counterion. Dimerisation of hydrosulfate and Donnan distribution becomes important at a concentration of the external H 2SO 4 solution above 1 M. Sorption of lithium sulfate is entirely controlled by the Donnan distribution.

Non-exchange sorption of electrolytes by ion exchangers: I. Sorption of hydrochloric and perchloric acids and their sodium salts by Dowex 1×8 resin

Sorption of hydrochloric and perchloric acids and their sodium salts was studied by Cl − and ClO 4 − forms of ion exchanger Dowex 1×8 in the concentration range of the external electrolyte 0.25–4 mol/l. Sorption of water and the total amount of the solution were also studied. Sorption of the acid appeared markedly higher than that of the respective salts. A mathematical modeling and computer simulation of the processes were performed. The overall sorption was represented as a superposition of the Donnan membrane distribution and formation associates type RAn · (AnKt) i · (H 2O) n in the homogeneous resin phase. The model expresses non-ideality of the resin phase in explicit form as formation of the above associates characterized by the constants of their formation. A good agreement between the experimental and calculated sorption in the whole concentration range was obtained in the assumption of two associates with i=1, 2 and n=1–3. The same factors control sorption of the acids and the salts and the difference in their behavior has a quantitative character. The main introduction into the overall sorption of the salts makes the Donnan distribution up to concentration of the external electrolyte 4 M, while the main part of the absorbed acids is contained in the associates.