Separation Of Multicomponent Mixtures Research Articles

Estimation of mixed-gas selectivity of membranes using the linear friction-based model

The development of analytical models for predicting the transport properties of membranes in the separation of multicomponent mixtures is highly relevant because (1) measurements of permeability and sorption of gas mixtures in membrane materials are laborious and time-consuming, and (2) estimation of transport properties based on pure gas measurements is desirable, however, rather unreliable and can lead to serious errors. In this paper, within the framework of the well-known frictional-coefficient formalism, we present nonlinear equations for the fluxes of gas mixture components through the membrane, which take into account the diffusional coupling of the fluxes compared to independent gas transport. As a result, an analytical equation for the mixed-gas selectivity was obtained. This equation has an implicit form, which is not quite convenient for practical application, since it has to be solved numerically. A simple explicit expression for mixed gas selectivity was derived using the so-called linear transport model, which is a linearized version of the original nonlinear flux equations. It is important to emphasize that a comparison of the linear model with the formally more rigorous nonlinear model showed only minor quantitative differences. The input parameters for the model are the single gas transport parameters. Testing the linear model using experimental data for the separation of hydrocarbons (n-butane/methane, n-butane/i-butane, propylene/propane) revealed an acceptable fit. A comparison of the model with recent experimental data on the separation of CO2-containing mixtures using microporous polymers is also presented. It is found that the calculated CO2/N2 mixed gas selectivity is in good agreement with the experimental data, while only a semi-quantitative agreement is observed for the CO2/CH4 separation. Besides, it is shown that the model developed for binary gas separation can be extended to ternary gas mixtures.

Optimization of multicomponent isotopes separation cascades parameters using improved grey wolf optimizer algorithm

The number of variables and design parameters in the multicomponent isotope separation cascades is considerable, and it is highly challenging to choose the best arrangement by obtaining the minimum interstage flow rate. Therefore, it is very important to develop a computational tool with high capability for calculating the cascade optimal parameters. The Improved Grey Wolf Algorithm, IGWO, is used in this study to develop an efficient code called the Isotopic Separation Real Code (ISRC-IGWO), which calculates the optimum parameters in the cascade for the separation of multicomponent mixtures. Investigations have been conducted in 4 separate tests to demonstrate this code's capability for computing the parameters with values close to the optimal conditions (in convergence to the near-optimal cascade). These evaluations have been carried out for both square and taper cascades, and different objective functions have been included in all tests. The findings show that ISRC-IGWO results are in agreement with optimal parameters calculation using other existing methods and IGWO is able to calculate cascade optimal parameters.

An MINLP formulation to identify thermodynamically-efficient distillation configurations

Designing configurations for separation of multicomponent mixtures by distillation is challenging because of (i) combinatorial explosion of the choice set, and (ii) nonconvex nature of the governing equations. This work proposes a novel Mixed Integer Nonlinear Program (MINLP) that is formulated to identify configurations that minimize the total exergy loss/maximize thermodynamic efficiency of the separation process. The formulation in its default form has several nonlinear nonconvex equations. We propose a model reformulation via a simple variable elimination technique to reduce the system of nonlinear equations to a single equation, which we refer to as the exergy constraint. We describe the properties of exergy constraints and exploit them in deriving additional valid cuts for the problem. Finally, we use the model for a case study concerning the recovery of Natural Gas Liquids (NGLs) from shale gas.

Chromatography in Catalysis

The main applications of gas chromatography for investigation of catalysts and catalytic processes are considered. The development of the sampling method as well as the microcatalytic and pulsed methods is described in historical aspect. The paper presents the advanced and promising directions of gas chromatographic studies, and the instruments providing efficient separation of multicomponent mixtures of substances with the control of complex catalytic reactions.

Small-Angle X-ray Scattering (SAXS) Measurements of APOBEC3G Provide Structural Basis for Binding of Single-Stranded DNA and Processivity.

APOBEC3 enzymes are polynucleotide deaminases, converting cytosine to uracil on single-stranded DNA (ssDNA) and RNA as part of the innate immune response against viruses and retrotransposons. APOBEC3G is a two-domain protein that restricts HIV. Although X-ray single-crystal structures of individual catalytic domains of APOBEC3G with ssDNA as well as full-length APOBEC3G have been solved recently, there is little structural information available about ssDNA interaction with the full-length APOBEC3G or any other two-domain APOBEC3. Here, we investigated the solution-state structures of full-length APOBEC3G with and without a 40-mer modified ssDNA by small-angle X-ray scattering (SAXS), using size-exclusion chromatography (SEC) immediately prior to irradiation to effect partial separation of multi-component mixtures. To prevent cytosine deamination, the target 2′-deoxycytidine embedded in 40-mer ssDNA was replaced by 2′-deoxyzebularine, which is known to inhibit APOBEC3A, APOBEC3B and APOBEC3G when incorporated into short ssDNA oligomers. Full-length APOBEC3G without ssDNA comprised multiple multimeric species, of which tetramer was the most scattering species. The structure of the tetramer was elucidated. Dimeric interfaces significantly occlude the DNA-binding interface, whereas the tetrameric interface does not. This explains why dimers completely disappeared, and monomeric protein species became dominant, when ssDNA was added. Data analysis of the monomeric species revealed a full-length APOBEC3G–ssDNA complex that gives insight into the observed “jumping” behavior revealed in studies of enzyme processivity. This solution-state SAXS study provides the first structural model of ssDNA binding both domains of APOBEC3G and provides data to guide further structural and enzymatic work on APOBEC3–ssDNA complexes.

Membrane-Area Distribution and Order of Separation of Multicomponent Mixtures in Baromembrane Systems

Membrane-Area Distribution and Order of Separation of Multicomponent Mixtures in Baromembrane Systems

Features of distillation separation of multicomponent mixtures

Objectives. To improve the process of developing energy-efficient flowsheets for the distillation separation of multicomponent aqueous and organic mixtures based on a comprehensive study of the phase diagram structures, including those in the presence of additional selective substances.Methods. Thermodynamic-topological analysis of phase diagrams; modeling of phase equilibria in the AspenTech software package using the equations of local compositions: Non-Random Two Liquid and Wilson; computational experiment to determine the column parameters for separation flowsheets of model and real mixtures of various nature.Results. The fractionation conditions of the origin multicomponent mixture due to the use of sharp distillation, pre-splitting process, extractive distillation with individual and binary separating agents were revealed. The columns operation parameters and the energy consumption of the separation flowsheets ensuring the achievement of the required product quality with minimal energy consumption were determined.Conclusions. Using the original methods developed by the authors earlier and based on the generalization of the results obtained, new approaches to the synthesis of energy-efficient multicomponent mixtures separation flowsheets were proposed. The provisions that form the methodological basis for the development of flowsheets for the separation of multicomponent mixtures and supplement the standard flowsheet synthesis plan with new procedures were formulated.

Heuristic procedure for synthesis of separation system for multicomponent mixtures using fuzzy logic

In this study, the task is to develop a heuristic procedure for the synthesis of systems for the separation of multicomponent mixtures, which would take into account the uncertainty of the factors of the separation processes and the multivariance of the solution.
 The authors reviewed the current state of the existing methods for the separation of mixtures. Many works devoted to the synthesis of effective systems for the separation of multicomponent mixtures leave unsolved the problem of taking into account the uncertainty of many factors of the separation processes. In the presented work, it is proposed that a heuristic approach is applied using fuzzy logic.
 The proposed procedure is based on the choice of a separation sequence that takes into account the value of the separation coefficient and the difference in boiling points of two adjacent key components. The proposed strategy is based on an estimate of the likelihood of each rule for each possible separation. The search for solutions has five stages. First, the mixture to be separated and the available equipment are determined. After that, an ordered list of all separation options is drawn up with possible values of the economic costs of their implementation. Next, the mass load of possible separation is estimated and the separation with the minimum value of the separation ratio is selected. The heuristic is that the heavy separation is done last. And, at the last step, the most economical separation scheme is selected.
 The above strategy at the stage of quantitative assessment is subject to the value of the threshold S (boiling point difference). This point can be used to determine the quasi-optimal solutions to the problem of sequencing according to the rules of relaxation of separation. 
 For this fuzzy heuristic method for determining cost-effective separation sequences for mixtures, appropriate software has been developed. In addition, since the procedure uses the theory of fuzzy sets, the Fuzzy Logic Toolbox package of the Matlab was also used to solve the problem of synthesizing schemes for separating hydrocarbon mixtures. The proposed procedure was successfully tested in both software implementations using the example of separating a five-component mixture. 
 The main difference between the proposed approach and other approaches based on fuzzy logic for the synthesis of separation systems is the gradation of working rules and possible quantification of a set of rules, which eliminates conflicts between the rules.

Simulations of liquid chromatography using two-dimensional non-equilibrium lumped kinetic model with bi-Langmuir isotherm

A two-dimensional non-equilibrium and non-linear lumped kinetic model of liquid chromatography is formulated and numerically approximated to simulate the separation of multi-component mixtures in a packed fixed bed cylindrical column operating under isothermal conditions. The model equations incorporate the bi-Langmuir adsorption thermo-dynamics as well as the radial and axial variations of concentration. By introducing distinct regions of injection at the column inlet, radial concentration gradients are generated to intensify the effect of mass transfer rate in the radial-direction, inside the column. The mathematical model is developed by a system of non-linear convection-diffusion partial differential equations for mass balance in the mobile phase, coupled with differential equation for mass balance in the stationary phase and algebraic equations for adsorption isotherm. In this study, a high-resolution, semi-discrete, finite-volume technique is formulated and applied to gain the numerical solution of the governing non-linear-model equations. A few numerical case studies are performed to investigate the effects of the various critical parameters on the process performance. The developed numerical algorithm provide an efficacious mechanism for investigating the retention behavior, systematic monitoring and efficient operation of non-equilibrium, liquid chromatographic processes.

Simultaneous separation of ternary mixture using modified dual compression middle vessel batch distillation column: Control and dynamic optimization

BackgroundMultivessel batch distillation has been found to be an effective method for the separation of multi-component mixtures. In this article, an effort has been made to devise a fast middle vessel batch distillation column (MVBDC) for the ternary separation of an Ethanol/Propanol/Butanol mixture by the means of inducing vapor compression in the system. MethodsASPEN PLUS V12 has been used to generate the initial steady-state flowsheet of the process for equipment sizing. In contrast, ASPEN Dynamics was used to evaluate the performance of the batch distillation with various control structures and to perform a dynamic optimization on the proposed batch distillation column. MATLAB was used to identify single-input single-output transfer functions for more effective PID controller tuning. Significant FindingsThe proposed Middle vessel batch distillation was found to separate each component of the mixture to a purity of 99 mol% in 22 h (for the cascade control structures) and 21.73 h (for the temperature control structure). This was found to be significantly lesser than the batch time of a conventional batch distillation column (28.12 h), while the energy consumed by the proposed column was 3.4 MMkcal lesser than the energy consumed by the conventional column. Dynamic optimization further reduced the batch time by 14.4% while simultaneously reducing the energy consumed by 20.3%.

In Silico Multifactorial Modeling for Streamlined Development and Optimization of Two-Dimensional Liquid Chromatography.

Continued adoption of two-dimensional liquid chromatography (2D-LC) in industrial laboratories will depend on the development of approaches to make method development for 2D-LC more systematic, less tedious, and less reliant on user expertise. In this paper, we build on previous efforts in these directions by describing the use of multifactorial modeling software that can help streamline and simplify the method development process for 2D-LC. Specifically, we have focused on building retention models for second dimension (2D) separations involving variables including gradient time, temperature, organic modifier blending, and buffer concentration using LC simulator (ACD/Labs) software. Multifactorial retention modeling outcomes are illustrated as resolution map planes or cubes that enable straightforward location of 2D conditions that maximize resolution while minimizing analysis time. We also illustrate the practicality of this approach by identifying conditions that yield baseline separation of all compounds co-eluting from a first dimension (1D) separation using a single combination of 2D stationary phase and elution conditions. The multifactorial retention models were found to be very accurate for both the 1D and 2D separations, with differences between experimental and simulated retention times of less than 0.5%. Pharmaceutical applications of this approach for multiple heartcutting 2D-LC were demonstrated using IEC-IEC or achiral RPLC-chiral RPLC for 2D separations of multicomponent mixtures. The framework outlined here should help make 2D-LC method development more systematic and streamline development and optimization for a variety of 2D-LC applications in both industry and academia.

A universal transportation model for reverse osmosis systems

This paper presents a new transport model for reverse osmosis (RO) systems, which combines irreversible thermodynamics, together with solution-diffusion theory. The simplifications adopted by the classical theory for solution-diffusion mechanisms have been found to be quite lacking when it comes to predicting the separation of multicomponent mixtures. The presented model accounts for multicomponent computations through the application of thermodynamic property models, as a means to predict the various interactions amongst the species that are present in solution. The developed transport model is relatively easy to implement, and can be utilized alongside existing equipment and thermodynamic property models. The applicability of the model presented in this paper has been tested on three different case studies, including a case that investigates single component behavior and a case that investigates multicomponent behavior The proposed model shows very good agreement with experimental results.

Optimal design of cyclones in series for the separation of multicomponent mixtures of Portland cement

A nonlinear programming problem was developed for the separation and classification of Portland cement particles into different fractions through the optimal design of two cyclones classifier in series. The equations and restrictions considered included the global mass balances, the equations for the geometric design of the cyclones, the equations for the efficiency calculation, the operating limitations of the process and the pressure drops of the equipment. The results show that an increase on the particles cut size led to a greater dimensions cyclone, as expected. Moreover, fractional efficiencies obtained increase with the reduction of the cut size. The solids load effect is also evaluated, reductions of the solids feed by 50% of its maximum value does not result in a remarkably decrease of efficiencies values. The proposed model has provided useful information and constitutes a starting point for a better understanding of the overall separation process of multi-component Portland cement mixtures. It is a valuable tool for the correct design of this type of separators, given its versatility to optimize under different operating conditions and with different materials.

On the relationship between non-mixing cascade and a cascade with constant partial cuts for separation of multi-component mixtures

Understanding the relationship between the quasi-ideal cascade (QIC) and the matched abundance ratio cascade (MARC) is very helpful in analysis and research of the separation cascade mechanism as well as practical applications of the cascade theory. For different values of separation factors and separation condition, the relationship between QIC and MARC is investigated. It is determined that they belong to different types of cascades. Only when the separation factor is constant and the separation process is symmetrical, both cascades become equivalent. It follows that in practice these two types of cascades should be considered separately when searching the optimal cascade with its best separation performance.

Approximate shock layer solutions for the separation of multicomponent mixtures with different axial dispersion or mass transfer coefficients

In this paper new approximate shock layer solutions for the separation of mixtures with different axial dispersion or mass transfer coefficients are presented and analyzed. These solutions are useful for understanding the dynamics of this kind of separation processes including fixed bed and countercurrent adsorption as well as distillation processes. Further, they can be used for model reduction using so called wave models.

Optimization of a Square Cascade of Centrifuges for Separation of Multicomponent Mixtures of Stable Isotopes

A method of optimizing the parameters of a three-stream square cascade for separation of multicomponent mixtures of stable isotopes under specified external conditions is proposed. It is based on a combination of a check calculation of the parameters of the cascade based on the separation factor approximation and a numerical search for the values of the external flows which are required to secure a specified external concentration. It is shown that this method can be used to calculate the optimal parameters of a square cascade for separating mixtures with a different number of components.

Principles of Operation of a Rotating Wall Mass Analyzer for Preparative Mass Spectrometry.

In this contribution, we describe the principles of operation of a rotating wall mass analyzer (RWMA), a mass-dispersive device for preparative mass spectrometry. Ions of different m/z are spatially separated by RWMA and deposited onto ring-shaped areas of distinct radii on a surface. We use a combination of an analytical equation for predicting the radius of the deposition ring and SIMION simulations to understand how to optimize the experimental conditions for the separation of multicomponent mixtures. The results of these simulations are compared with the experimental data. We introduce a universal mass calibration procedure, based on a series of polyacrylamide ions, which is subsequently used to predict the deposition radii of unknown analytes. The calibration is independent of the polarity, kinetic energy, and charge state of the ion as demonstrated by assigning m/z values of different analytes including multiply charged ubiquitin ions. We demonstrate that mass resolution of the RWMA is affected by the width and kinetic energy distribution of the ion beam. The best mass resolution obtained in this study is m/Δm = ∼20. Preparative mass spectrometry using RWMA provides the advantages of simplicity, compactness, and low fabrication cost, which are particularly promising for the development of miniaturized instrumentation. The results presented in this work can be readily adapted to preparative separation of a variety of charged species of interest to the broad scientific community.

Simulation of nonisothermal reactive liquid chromatography using two‐dimensional lumped kinetic model

AbstractA nonisothermal two‐dimensional lumped kinetic model of reactive liquid chromatography is formulated and applied to simulate the separation of multicomponent mixtures in a fixed‐bed cylindrical column operating under nonisothermal condition. The axial and radial variations of concentration and temperature as well as reversibility of the chemical reactions are incorporated in the model equations. The model comprises a system of convection‐diffusion‐reaction partial differential equations coupled with algebraic and differential equations. Due to the nonlinearity of adsorption and reaction kinetics, it is required to apply an accurate numerical scheme for solving the model equations. In this study, an efficient and accurate high‐resolution flux‐limiting finite‐volume scheme is proposed to solve the model equations. A number of stoichiometrical reactions are numerically simulated to determine the level of coupling between the temperature and concentration profiles. Moreover, the effects of various critical parameters on the process performance are examined. The results obtained are beneficial for understanding reaction and separation processes inside a liquid chromatographic reactor and to improve its performance.

TECHNOLOGY OF CYCLIC DISTILLATION IN ALCOHOL PRODUCTION

Alternate changing of the steaming periods and liquid overflow allows to intensify mass transfer between liquid and steam and to reduce the specific consumption of heating steam in the process of separation of multicomponent mixtures. Known methods and models have not found widespread practical use due to the lack of mass transfer in the steam period, fluctuations in steam pressure in the collector, the complexity of constructive solutions to ensure cyclic mode, etc. The authors propose a technology for rectification, which involves the cyclic motion of the liquid without interrupting of the supply of heating steam and the construction of a rectification column for its implementation. The purpose of the work was to research the effectiveness of the proposed technology in the process of rectification of alcohol-containing fractions and to establish the specific flow rate of steam in the impurity concentration column. To ensure a cyclic mode, the column was equipped with movable liquid transfer devices connected to actuating mechanismes, which acted according to the controller program, and perforated (scale-shaped) trays. The primary task was to determine the hydrodynamic mode of operation of the contact devices - the lower and upper the critical vapor velocity of at which the liquid is retained on the plates and there is its entrainment. It is established that the vapor velocity in the free section of the column can reach 1.2 m/s or more, and in the openings of the scales must exceed the first critical velocity of 6.5-7.5 m/s. The weeping of the tray occurs at the vapor velocity in the holes of 1.5-1 m/s. The investigations were carried out in the production conditions of the Chudniv branch of SE “Zhytomyr liquor producer ”. It is experimentally proved that in the process of rectification of alcohol-containing fractions, the main impurities are removed completely, the degree of extraction of higher fusel alcohols is increased by 38%, methanol - by 15.6 %, the multiplicity of concentration of the main impurities is increased by 25 %, the higher alcohols - by 40 %, methanol – by 34 %, acrolein – by 36 %. The costs of heating steam are reduced by 30 % compared to typical installations and do not exceed 13 kg/dal of absolute alcohol introduced with feed. Exempted from the key impurities the bottom liquid of the impurity concentration column should be used for hydroselection in the purifying column.

ZIF filled PDMS mixed matrix membranes for separation of solvent vapors from nitrogen

The efficiency of chemical processes can be improved by recovering high value volatile organic compounds (VOCs). For this purpose PDMS based mixed matrix membranes were prepared by using ZIF-7, ZIF-8, ZIF-67, ZIF-71 and ZIF-L as filler for VOC removal from permanent gases. Membranes were characterized by separating pure or mixed solvent vapors of methanol (MeOH), ethanol (EtOH), isopropanol (IPA), n-propanol (PrOH) and ethyl acetate (EtAc) from nitrogen. The total VOC permeability and VOC/N2 selectivity increased with the incorporation of ZIF-L and ZIF-71, while other ZIFs had limited influence on the separation performance of membranes. ZIF-L (20% wt.)/PDMS membrane exhibited total VOC permeability of 9874 Barrer and VOC/N2 selectivity of 45 in the separation of ethanol and IPA vapor from nitrogen in a mixture with molar composition of EtOH:IPA:N2 = 10:10:980. Those values were higher than the permeability and selectivity of pure PDMS by 60 and 33%, respectively. ZIF-L filled PDMS membrane was also used for the separation of multicomponent mixtures and showed total VOC permeability of 10215 Barrer and VOC/N2 selectivity of 72 in the separation of ethanol, isopropanol, ethyl acetate and water vapor mixture from nitrogen. A method was also proposed to compare the separation performance of membranes with each other and with the performance of membranes reported in the literature based on the dew point temperature of membrane streams.