Separation Of Multicomponent Mixtures Research Articles

Modeling-based optimization of the simultaneous enantiomeric separation of multicomponent mixtures of phenoxy acid herbicides using dual cyclodextrin systems by Capillary Electrophoresis

In this work, the Dubsky's model proposed for Capillary Electrophoresis (CE) enantioseparation systems with a mixture of chiral selectors was applied to the rapid optimization of the simultaneous enantiomeric separation of a multicomponent mixture of six phenoxy acid herbicides using a dual system of two cyclodextrins (CDs), (2-hydroxypropyl)-β-CD (HP-β-CD) and heptakis(2,3,6-tri-O-methyl)-β-CD (TM-β-CD). Simply by carrying out a small number of individual experiments separately with each CD, the Dubsky's model enabled to foresee the results that could be obtained for any possible combination of concentrations and relative proportion of both CDs in the mixture. Results obtained in this work demonstrated that the model was successful by improving the previous results experimentally obtained by the trial and error method for the simultaneous enantiomeric separation of the six phenoxy acid herbicides studied in this work. In fact, the separation was improved in terms of enantiomeric resolutions obtained (from 1.2 to 4.2 for concentrations of CDs of 4 mM HP-β-CD and 16 mM TM-β-CD) and by considerably reducing the time to optimize the separation conditions enabling to find, in a faster and efficient way, the most adequate proportion of both CDs and the concentration of each CD in the mixture to obtain baseline separation of the twelve enantiomers. Additionally, the apparent complexation constants between enantiomers and each CD were calculated. This is the first time that the above-mentioned model was applied to a multicomponent mixture of chiral compounds.

Gas Chromatography in Technology of High-Purity Noble Gases

The article presents the classification of the gas stream contaminant types in noble gas enrichment and purification units. For the safe and efficient system operation, it is necessary to choose the right method of multicomponent mixture separation and the optimal corresponding equipment operating parameters, also to offer a method to verify the absence of the undesirable contaminant in the gas stream. The methods to control the obtaining of required noble gas purity during cryogenic rectification are indicated. Application of various gas analysis methods is necessary to obtain high purity (up to 99.9999%) gases: gas chromatography, mass spectrometry, and their combination. The effect of the state of various components of a gas chromatograph on the analysis result are discussed. Recommendations are provided for noble gas analysis methodology, including the conditions for the determination of trace impurities. The article presents examples of practical application of gas chromatography to control the processes of noble gas enrichment and purification, using the example of production of pure xenon.

Direct Simulation of Ternary Mixture Separation in a ZIF‐8 Membrane at Molecular Scale

AbstractSeparation of H2 in a ZIF‐8 membrane from a syngas mixture composed of CO2, H2, and N2 at 300 K and 35 atm is simulated with the concentration gradient driven molecular dynamics (CGD‐MD) method. Steady‐state fluxes are computed to predict the H2 selectivity of the ZIF‐8 membrane using four different flexible force fields developed for ZIF‐8. The permselectivities predicted by the CGD‐MD method are compared with those obtained from the grand canonical Monte Carlo+equilibrium molecular dynamics (GCMC+EMD) approach, which is based on the solution‐diffusion model and widely used to predict permselectivities for mixture separations. The permselectivities obtained by using the CGD‐MD method accurately predict that ZIF‐8 is H2 selective over CO2 and N2. On the other hand, permselectivities predicted with the GCMC+EMD approach are found to be incorrect, that is, ZIF‐8 not selective for H2. The study suggests that a reliable non‐equilibrium molecular dynamics approach should be employed in order to obtain accurate predictions for the permselectivity of a membrane for a multicomponent mixture separation process which happens at moderate or high pressure conditions.

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.

Evaluation Criteria for Thermodynamic Efficiency during the Distillation Process

A thermodynamic analysis of the distillation process was carried out based on criteria determining the minimum amount of heat and work required for the process. The presented analysis makes comparing the effectiveness of various methods for the separation of multicomponent mixtures and establishing optimal conditions for implementation possible, within the chosen method.

Thermodynamic Approach to Substantiating the Work and Potential for Separation of Multicomponent Mixtures

Equations for calculating the thermodynamic work of separation are proposed and generalized.

Some theoretical considerations on preparative separation with orthogonal pressurised planar electrochromatography

In this work, separation of multicomponent mixtures containing components with the same and different electrophoretic mobility by using orthogonal pressurised planar electrochromatography is studied theoretically. Additionally, a simple way for determination of a maximum amount of mixture causing volume overload of flat/planar columns used in this technique is presented. In the next stage, effects of change in different parameters on process performance by simulation case studies are investigated. A comparative study of separation productivity of orthogonal pressurised planar electrochromatography with the continuous and periodic modes of mixture delivery and column chromatography is carried out.

Multiple Dividing‐Wall Columns – Current Status and Future Prospects

AbstractDividing‐wall columns are a well‐known and proven technology to separate a ternary mixture into pure products with significant savings in capital and operational costs compared to standard two‐column configurations. A consequent advancement are multiple dividing‐wall columns, which allow the separation of multicomponent mixtures in one column shell. However, due to their high complexity, no practical realization has been reported yet. This paper briefly discusses the current state of the art followed by a detailed description of a robust initialization of rigorous flow sheet simulations based on Vmin diagrams. With the data from the simulation a multi‐objective optimization can be performed. The knowledge from the simulations shall be used to build the first multiple dividing‐wall column worldwide.

Indirect Series of Falling Film Distillation Column to Process Synthetic Naphtha

The separation of multicomponent mixture by distillation is commonly accomplished by means of a sequence of columns and/or lateral withdrawals on a column. Desirable specifications for the product stream imply high energy consumption and operational costs due to the low thermodynamic efficiency associated with conventional distillation columns. For these reasons, unconventional technologies are proposed to promote separation, coupled with lower energy consumption. Within the context, the falling film distillation unit assisted by a biphasic thermosyphon provides such improvements. The objective of this study was to evaluate the separation of a multicomponent mixture (synthetic naphtha) in an indirect series of falling films columns. Tests were carried out at atmospheric condition considering the influence of feed flow, feed temperature and vapor chamber temperature. Experimental conditions were previously established from simulations in the Hysys® software, where the mixture was separated into a conventional steady state distillation unit. Results demonstrated that for the first, second and third columns of the series, enriched fractions of hexane obtained in the top stream were of 0.58, 0.72 and 0.82, on a mass basis, respectively. However, heavier compounds were identified in the top stream of the second column, nevertheless, these compounds correspond to less than 0.05 of the mass fraction. Even with a no complete separation, the energetic analysis of the global process shown there was a 12 % reduction in energy consumption of the falling film column compared to the simulated conventional column under the same conditions.

Evaluation of the Characteristics of Domestic Reverse-osmosis Modules for Organization of Circulating Water Supply for Small-tonnage Production

The possibilities of using domestic reverse-osmosis modules for the organization of circulating water supply and return to the cycle of the target product at low-tonnage chemical plants, as well as the application of these modules in self-contained dwellings, are considered. The selectivity of membranes was compared with the separation of aqueous solutions of multicomponent mixtures containing polar and nonpolar substances. The character of the dependences of the selectivity of membranes on the concentration of dissolved substances in the initial solution during the separation of multicomponent mixtures was studied. The possibility of achieving a clean water recovery ratio (the degree of closure of the circuit) is shown to be 96.5%. Schematic diagrams of circulating water supply systems intended for extraction of components lost with wastewater at small-scale industrial enterprises and for sewage treatment of sanitary-hygienic waters with the purpose of their further return to the production cycle, utilization or neutralization are proposed.

Understanding coupling effects in pervaporation of multi-component mixtures

Abstract The application of pervaporation for the separation of multicomponent mixtures may involve coupling effects among components and the membrane, which could increase or decrease the permeance of the target compound. In order to study and describe this phenomenon, mixtures of components present in two model reactions have been considered: the transesterification reaction between methyl acetate and butanol to produce methanol and butyl acetate, and the transesterification reaction between methanol and ethyl acetate to produce ethanol and methyl acetate. Both reactions are of utmost interest in the chemical industry and present high cost of separation due to the presence of azeotropic mixtures (i.e., methanol/methyl acetate; butanol/butyl acetate; ethanol/ethyl acetate). The separation performance of four commercial membranes (i.e., PERVAP 1255-30, PERVAP 4155-40, PERVAP 1255-50, PERVAP 4155-80) from Sulzer Chemtech, Switzerland, is evaluated. The effect of the feed concentration and the temperature on the separation performance was studied in terms of permeance and selectivity. Coupling effects were observed when the permeance of pure solvents was compared with that of the components in the mixture. The coupling effects were analyzed by the Hansen solubility approach and by the variation of activities within the membrane.

Flowsheets of multicomponent multiphase systems separation and material balance calculation features

The applicability of a method for determining the number of free variables required to solve the balance task for flowsheets with a Florentine vessel or decanter during the separation of multicomponent mixtures has been considered. The rule and algorithm that allows one to determine the number of the free variables schemes with recycles have been formulated and proposed.

Choline chloride based deep eutectic solvents as extraction media for separation of n-hexane–ethanol mixture

Two different choline chloride based deep eutectic solvents (DES) were tested for the separation of azeotropic mixture of n-hexane and ethanol via liquid-liquid extraction. The simplest mixtures of choline chloride with dibasic acids: oxalic (DES1) or malonic (DES2) with molar ratio 1:1 were used. The selected DESs were characterized by differential scanning calorimetry (DSC). Extraction experiments were conducted with pseudo-ternary mixtures n-hexane–ethanol–DES. Tie-lines were obtained at temperatures 293.15 K, 313.15 K and atmospheric pressure. The extraction performance of DES was characterized with solute distribution coefficients and values of selectively for ethanol. It has been shown that the most successful component for the separation of a mixture of n-hexane-ethanol is water. It was found that DES1 is more effective then DES2 for extraction of ethanol. The higher efficiency of separation of DES as compared to conventional ionic liquids (IL) makes it possible to consider them as an alternative promising solution in the separation of multicomponent mixtures. Experimental data was fitted using the nonrandom two liquids (NRTL) model.

Developing a technique for improving the efficiency of iterative methods for the calculation of the multicomponent rectification process

Studies of the technological base of mobile control over the processes of rectification are based on determining the concentration and temperature profiles of the installation in the established regime at different coordinates of the point of application of controlling influence. A problem of the calculation of static characteristics of the process is in the iterative determination of such concentrations of components in the bottoms so that the bidirectional calculations, based on them, and carried out to the control section of a rectifying column, make it possible to obtain identical results. The θ-method is the effective technique for the provision of convergence of such calculations. However, when calculating multi-plate rectifying columns with several feeding inputs, in which the separation of multicomponent mixtures occurs, it is necessary to use a simple procedure for the reduction in time spent searching for the solution. The problem of reducing the necessary number of iterations is solved by the exponentiation of coefficient θ, which is determined by the introduced tuning parameter of the algorithm. The extreme dependence of the number of iterations on this exponent is proven. Performed calculations of the column for separating the multicomponent product of the MTBE synthesis proved that the proposed modification of the θ-method of convergence of iterative calculations of the operating modes of rectifying columns makes it possible to reduce the time, necessary for the search for the solution, by 50 %. In this case, it is not necessary to obtain high quality of initial approximations of compositions of the separation products. The method is characterized by high stability and workability in a wide range of change in the input magnitudes.

DISTILLATION OF BINARY TWO-PHASE MIXTURES WITH VARIOUS PHYSICO-CHEMICAL PROPERTIES: NORMAL MODE AND DEVIATIONS FROM IT

In this article, the normal continuous mode of distillation is considered using an example of binary two-phase mixture distillation. In practice, there are often deviations from the normal mode. It has been proved that the deviation leads to an increase in energy consumption for the ongoing process. In the industry, columns separating binary mixtures are normally the finishing apparatuses in the flow-sheet separation of multicomponent mixtures, which are obtained in the reactor as a result of main reactions as well as by-reactions. The distillation of binary mixtures is relatively simpler than that of multicomponent mixtures. In this regard, the fundamental parts of monographs especially in the thirties-forties of the last century started with the study of binary mixtures, although multicomponent mixtures were the main focus. The aim of analyzing this complex and the highly energy-intensive process is to facilitate the choice of a mathematical model for the process and the determination on its basis variance. Variance is a set of independent variables that allow calculation of a process only after taking into account the number of independent equations related to these variables. A case of deviation from the normal distillation regime where an under-heated liquid enters the column feed has been revised. This leads to an increase in energy consumption during distillation. Key indicators of the normal regime relative to the level of feed and the temperature of the liquid are shown in the text.

Some aspects of multidimensional chromatographic techniques coupled with mass spectrometry applied for the separation of multicomponent mixtures of pesticides

Summary For very complex multicomponent mixtures, it is preferable to use different variants of multidimensional (planar) chromatography. In multidimensional separations, the modes of planar chromatography commonly applied are comprehensive 2D planar chromatography on mono and bilayers, coupled-layer chromatography, combination of multidimensional planar chromatographic (MDPC) techniques, and also hyphenated methods. Different multidimensional (planar) chromatography techniques and hyphenated methods may be alternative modes for separation and identification of pesticides in environmental analysis, especially after coupling with modern detection techniques. Proper identification and quantita tive analysis of the analytes are possible through the use of sensitive detection techniques such as high-resolution mass spectrometry (HRMS).

The driving force as key element to evaluate the pervaporation performance of multicomponent mixtures

Pervaporation presents an efficient alternative to other high energy demanding technologies, such as distillation, in the separation of challenging mixtures in the chemical industry (e.g., azeotropic mixtures). In this work, the transesterification reaction between butanol and methyl acetate to produce methanol and butyl acetate is considered as case of study of an equilibrium-limited reaction. The objective is to emphasize the importance of a prior evaluation of the driving force of each compound in order to determine when pervaporation is an appropriate technique to perform the separation of multicomponent mixtures. Three commercial membranes from PolyAn GmbH (Germany) and two membranes from Sulzer Chemtech (Switzerland), selected from a previous study, are used for the separation of equimolar mixtures of methanol–methyl acetate–butanol–butyl acetate, at 30, 40 and 50°C (±2°C). Results show that all the studied membranes present a preference for the permeance of butanol, reaching permeances of butanol until 140,000 GPU. However, methanol and methyl acetate are the compounds with a higher driving force due to their higher volatility, leading to higher concentration in the permeate and preferential separation instead of butanol. Thus, the study of permeances/permeabilities and selectivities is required but not sufficient to evaluate the real performance of pervaporation. The driving force has to be evaluated, and membranes that enhance the effect of the driving force by permeating the species with the highest driving force should be preferably selected. Then, pervaporation is used under conditions of maximum performance.

Influence of heat transfer across the wall of dividing wall columns on energy demand

The implementation of a vertical dividing wall (DW) into a distillation column is a well‐known concept which can result in considerable energy savings for the separation of multicomponent mixtures. It is commonly known that heat streams across the DW, which are present due to temperature differences between both sides, may either increase or decrease the energy demand for a certain separation task. However, no work has been published so far which explains the maximum influence on energy demand. This article derives the maximum extent to which the minimum energy demand for a given column design can change due to heat transfer across the DW. Additionally, it is illustrated how energy‐efficient column operation can be assured even if the total amount of transferred heat is unknown. These results show that the phenomenon of heat transfer across the DW can be handled very well with a suitable control strategy. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1648–1662, 2015

Multicomponent Separation Efficiency of an Optimal Cascade with Prescribed Target Isotope Concentration

The particularities of optimization of cascades for the separation of multicomponent mixtures of isotopes according to the criterion of minimum total feed flow of the steps are examined. It is shown on the basis of a computational experiment that optimal cascades have high efficiency indices, which is expressed in the fact that the efficiency and separative power utilization indices are close to 100%. These cascades can be calculated for any concentration of the target isotope. They are mixing cascades with respect to the absolute and relative concentration of the components. However, in most cases it is possible to find a close to optimal R cascade which will differ little in terms of the total flow and concentration of all components.

Solvent Extraction and Separation of Gallium(III) using Hexaacetato Calix(6)Arene

Gallium(III) was extracted at pH 3.5 by equilibrating eight min with 10 mL of 0.0001 M acetyl derivative of calix(6)arene in xylene. Gallium(III) was stripped quantitatively with 0.1 N hydrochloric acid and determined spectrophotometrically with 0.01% PAR at 510 nm. The nature of the extracted species was determined from the log-log plots and its stoichiometry was confirmed by numerical treatment to experimental data. The IR analysis of Ga(III) loaded organic phase was also studied. The conformational change of reagent during complex formation was studied from the 1H NMR treatment. The temperature dependence of the extraction equilibrium and metal loading capacity of the reagent was also evaluated. The proposed method was successfully applied for the extraction and separation of multicomponent mixtures, synthetic mixtures, and binary and ternary separation of gallium from the associated elements. The results obtained were reproducible and accurate.