Single-component Data Research Articles

Testing the Accuracy of Correlations for Multicomponent Mass Transport of Adsorbed Gases in Metal−Organic Frameworks: Diffusion of H2/CH4 Mixtures in CuBTC

Mass transport of chemical mixtures in nanoporous materials is important in applications such as membrane separations, but measuring diffusion of mixtures experimentally is challenging. Methods that can predict multicomponent diffusion coefficients from single-component data can be extremely useful if these methods are known to be accurate. We present the first test of a method of this kind for molecules adsorbed in a metal-organic framework (MOF). Specifically, we examine the method proposed by Skoulidas, Sholl, and Krishna (SSK) ( Langmuir, 2003, 19, 7977) by comparing predictions made with this method to molecular simulations of mixture transport of H 2/CH 4 mixtures in CuBTC. These calculations provide the first direct information on mixture transport of any species in a MOF. The predictions of the SSK approach are in good agreement with our direct simulations of binary diffusion, suggesting that this approach may be a powerful one for examining multicomponent diffusion in MOFs. We also use our molecular simulation data to test the ideal adsorbed solution theory method for predicting binary adsorption isotherms and a method for predicting mixture self-diffusion coefficients.

Three Component Time-domain Electromagnetic Surveying: Modeling and Data Analysis

A comparative numerical modeling using single component (measuring the vertical component of the fleld, Hz) time-domain electromagnetic measurements (TEM) receiver and three component (measuring Hx, Hy and Hz) TEM receiver was undertaken. A forward mod- eling approach was used to compute the voltage response of half-space containing one or more conductive bodies excited by a bi-polar square waveform. Although this was a conductor scatter- ing, it was particularly useful as a practical use for the unexploded ordnance (UXO) detection. Unlike the single component data, results from the three component data are unambiguous as to the location and orientation of conductors. Measuring adding of the horizontal components of the secondary magnetic fleld leads to not only provide the best indication of target location, but also can be used to determine size, orientation, and characteristics of the targets, especially for the horizontal extending target. A three-component TEM fleld experiment at a well-documented wells site, NCU campus, were consistent with the efiects predicted by our theoretical modeling. As a result, the 3-component TEM survey is a must for the high resolution EM in the engineering purpose.

Examining the Accuracy of Ideal Adsorbed Solution Theory without Curve-Fitting Using Transition Matrix Monte Carlo Simulations

Ideal adsorbed solution theory (IAST) is a well-known approach to predicting multicomponent adsorption isotherms in microporous materials from experimental or simulation data for single-component adsorption. A limitation in practical applications of IAST is that useful calculations often require extrapolation of fitted single-component isotherms beyond the range for which data are available. We introduce a molecular simulation approach in which the intrinsic accuracy of IAST can be examined in a context that avoids any need to perform curve fitting with single-component data. Our approach is based on using transition matrix Monte Carlo to define single-component adsorption isotherms for arbitrary bulk-phase pressures from a single simulation. We apply our approach to several light gas mixtures in silica zeolites and a carbon nanotube to examine the intrinsic accuracy of IAST for these model systems.

A Methodology to Estimate Transport Diffusivities in 'Single-File' Permeation through Zeolite Membranes Using Molecular Simulations

To investigate the influence of ‘single-file’ diffusion on nonequilibrium transport phenomena inside zeolite nanopores, we calculated permeate velocities of guest species in AFI-type AlPO4-5 and MFI-type silicalite membranes, using a grand canonical ensemble molecular dynamics (GCMD) simulation. We chose as examples He/CH4 and CH4/SF6 mixtures through AlPO4-5, and CH4/CF4 mixtures through silicalite. In AlPO4-5 systems, He permeates much faster than CH4 in an He/CH4 mixture, whereas CH4 moves at nearly the same speed as SF6 in the CH4/SF6 mixture. In CH4/CF4 mixtures in silicalite, the permeate velocity of each component becomes close to each other, compared with that of pure gas. These results suggest that ‘single-file’ permeation occurs where one guest species cannot overtake the other inside nanopores under a concentration gradient, especially if at least one component has a molecular diameter similar to the host pore size. Moreover, the calculated separation factor for CH4/CF4 mixtures through silicalite showed a strong correlation with the permeate velocities of the guest species, suggesting the influence of ‘single-file’ permeation on the absolute values of the separation factor. Particularly, it is concluded that the decrease in CH4 permeate velocities directly leads to the decrease in the separation factors, compared with ideal separation factors. Finally, using these data from GCMD simulations and other molecular simulation techniques, we propose a methodology to predict transport diffusivities in binary mixtures. In this paper, the transport diffusivities of CH4/CF4 mixtures in silicalite were calculated based on Maxwell–Stefan (MS) theory. Further efforts to achieve the systematic estimation of these transport diffusivities will lead to the prediction of multicomponent separation factors using only single-component data.

Unambiguous apparent conductivity for fixed-loop transient electromagnetic data

We derive an unambiguous apparent conductivity from total magnetic field TEM data for fixed-loop geometry. For single-component fixed-loop TEM measurements, apparent conductivity is either dual-valued or undefined. The ambiguity or non-existence is particularly evident for readings taken outside the transmitter loop, both for step and impulse response data. Therefore, computing apparent conductivity from single-component fixed-loop TEM data can be problematic, especially at intermediate delay times. However, if multi-component fixed-loop magnetic field data is available, an unambiguous apparent conductivity can be derived from |B (t )| at all times, except in the inductive limit. Impulse response measurements can be time-weighted and summed to yield “quasi-|B |” data. Apparent conductivity derived from quasi-|B | amplitudes is dual-valued, but usually only one of the alternatives is geologically plausible. Computing apparent conductivity from |B | or quasi-|B | amplitudes expedites generation of conductivity-depth sections from fixed-loop TEM. A field data example with multi-component SQUID data shows significant improvement in the conductivity-depth section when |B (t )| is transformed rather than the vertical component, Bz , alone; the lateral extent of a conductive target is under-estimated in the Bz CDI

Aqueous-phase adsorption of glycerol and propylene glycol onto activated carbon

Adsorption of reactant and product species can have a major effect on local pore concentrations in activated carbon-supported metal catalysts. Individual and combined adsorption of glycerol (GO) and propylene glycol (PG) onto activated carbon in aqueous solution is reported here at concentration ranges of 0.05–2.0M and temperatures from 25°C to 160°C. Langmuir and Freundlich isotherms are used to model the single component data, with the Langmuir model best describing results below 0.75M. The extended Langmuir model has been used to model the competitive adsorption system – model parameters determined from single component experiments accurately predict two component adsorption data over the temperature and concentration ranges studied. Propylene glycol adsorbs more strongly than GO onto the activated carbon supports studied, and also adsorbs to a somewhat greater extent compared to GO. This is attributed to the greater organic character of PG, which favors its selective adsorption onto the support material.

Understanding Macroscopic Diffusion of Adsorbed Molecules in Crystalline Nanoporous Materials via Atomistic Simulations

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Understanding Macroscopic Diffusion of Adsorbed Molecules in Crystalline Nanoporous Materials via Atomistic Simulations

The diffusion rates of molecules inside nanoporous materials lie at the heart of many large-scale industrial applications of these materials. Quantitatively describing this diffusion, particularly diffusion of chemical mixtures in situations leading to net mass transport, remains challenging. Molecular dynamics (MD) simulations can play an important complementary role to experiments in this area. This Account describes applications of MD to diffusion in nanoporous materials with a particular focus on macroscopic diffusion, that is, diffusion involving mass transport. These methods have made useful contributions to developing mixing theories for predicting multicomponent diffusion from single-component data and to screening new classes of materials for practical applications.

Adsorption of the enantiomers of 3-chloro-1-phenyl-propanol on silica-bonded chiral quinidine carbamate

The interactions of 3-chloro-1-phenyl-propanol with a quinidine carbamate-bonded chiral stationary phase under NPLC conditions were studied by measuring the adsorption isotherm data of its enantiomers by frontal analysis, modeling these data with a suitable isotherm model, and comparing the experimental overloaded elution band profiles with those calculated with this isotherm and the equilibrium dispersive model of liquid chromatography. The affinity energy distribution was calculated from the adsorption isotherm data. The results show that the surface of the adsorbent is heterogeneous and exhibits a bimodal adsorption energy distribution. This fact is interpreted in terms of the presence of two different types of adsorption sites on the stationary phase, nonselective and enantioselective sites. Albeit the bi-Langmuir isotherm model successfully accounts for the single-component data corresponding to both enantiomers, the competitive bi-Langmuir isotherm model does not allow an accurate prediction of the overloaded band profiles of the racemic mixture. Thermodynamic data are drawn for explanation. Some aspects of the retention mechanism are discussed in the light of the data obtained.

Wideband spectral matrix filtering for multicomponent sensors array

As multicomponent (3C or 4C) seismic acquisitions are now commonly used, specific processings for multicomponent data sets are required. The aim of this paper is to present a new wavefield filter for multicomponent seismic data. The proposed method is derived from a recent technique used for single component data, which takes into account the wideband characteristics of the signal. The multicomponent extended method incorporates the polarization information and processes the various components in a global way instead of treating them independently. The proposed method is based on the computation of a global spectral matrix which gathers all the frequential and component interactions. We prove that the eigenvalue decomposition of a reduced matrix issued from this global matrix enables an efficient separation in two complementary spaces: one contains the signal and the other, the noise. The results obtained on synthetic and real data are presented and compared with others methods in order to assess the performances of our algorithm.

Adsorption of Phenolic Compounds from Water on Activated Carbon: Prediction of Multicomponent Equilibrium Isotherms using Single-Component Data

Batch-type experiments were carried out to obtain equilibrium isotherms for the adsorption of phenol and m-cresol in aqueous solutions on activated carbon. Single solute systems, at 20 and 40∘C, were tested for Langmuir, Freundlich and Sips adsorption isotherms in the range of concentrations up to 200 mg/L. Equilibrium data were more closely followed by the Freundlich and Sips equations for all cases. Adsorption isotherms for bisolute systems at 20∘C, with two different initial concentrations of phenol and m-cresol, were predicted solely on the basis of single solute equilibrium parameters by using the equations of Butler and Ockrent and the IAS theory. The best agreement with the experimental loading values was afforded with the IAS theory based on Sips isotherm for pure compounds. However, this theory is found to be not able to predict with success the binary isotherms in this work where significant displacement of one solute by the other is observed. Chemical interactions in the adsorbed phase, estimated by a modified Butler–Ockrent model, can be responsible for this lack of success of the conventional IAS theory. The predictions based on the IAS theory are compared with the results of some empirical models.

Adsorption isotherm models for basic dye adsorption by peat in single and binary component systems

Colored effluents from textile industries are a problem in many rivers and waterways. Prediction of dye adsorption capacities is important in design considerations. The sorption of three basic dyes, namely Basic blue 3, Basic yellow 21, and Basic red 22, onto peat is reported. Equilibrium sorption isotherms have been measured for the three single-component systems. Equilibrium was achieved after 21 days. The experimental isotherm data were analyzed using Langmuir, Freundlich, Redlich-Peterson, Tempkin, and Toth isotherm equations. A detailed error analysis has been undertaken to investigate the effect of using different error criteria for the determination of the single-component isotherm parameters and hence obtain the best isotherm and isotherm parameters which describe the adsorption process. The linear transform model provided the highest R(2) regression coefficient with the Redlich-Peterson model. The Redlich-Peterson model also yielded the best fit to experimental data for all three dyes using the nonlinear error functions. An extended Langmuir model has been used to predict the isotherm data for the binary systems using the single component data. The correlation between theoretical and experimental data had only limited success due to competitive and interactive effects between the dyes and the dye-surface interactions.

Prediction of the band profiles of the mixtures of the 1-indanol enantiomers from data acquired with the single racemic mixture

The adsorption isotherm data of R- and S-1-indanol and of their racemic mixture on cellulose tribenzoate were measured by frontal analysis. These data were then fitted to the Langmuir, the Bilangmuir, the Toth, and the Langmuir–Freundlich isotherm models. The single component data fitted well to both the Bilangmuir and the Toth models. Combined with the lumped pore diffusion model (POR) of chromatography, these isotherms were used to calculate overloaded elution profiles of the pure enantiomers. The calculated and the experimental profiles agree excellently in all cases if the former are derived from the Bilangmuir model. The competitive experimental data also gave excellent agreement with the Bilangmuir model. The simultaneous fit of all the data, for the single components and the racemic mixture, gave again superior agreement with the bilangmuir model. The overloaded elution profiles of samples of the racemic mixture calculated with the Bilangmuir isotherm model combined with the POR model of chromatography gave results in very good agreement with the experimental band profiles of large samples of the racemic mixture. This confirms that in numerous cases the whole set of competitive isotherms of two enantiomers can be derived from the experimental data obtained only with the racemic mixture.

Theoretical Description of the Calorimetric Effects Accompanying the Mixed-Gas Adsorption Equilibria by Using the Ideal Adsorbed Solution Theory

The theoretical prediction of multicomponent adsorption equilibria from the single-component data is one of the most important problems in adsorption. The possibilities of the ideal adsorbed solution approach to study enthalpic effects accompanying the mixed-gas adsorption equilibria are presented. The obtained theoretical expressions for predicting isosteric heats of adsorption in a gas mixture are relatively simple and accurate. To predict phase diagrams and calorimetric effects in the mixed-gas adsorption, only the knowledge of single-gas adsorption isotherms and accompanying calorimetric effects is required.

Separation ofP- andSV-wavefields from multi-component seismic data in the domain

Multi-component seismic data contain richer information about the elastic parameters of the subsurface than do conventional single-component data. Separation of the compressional and shear wavefields from multi-component seismic data is crucial in estimating the subsurface elastic properties. We present a τ−p domain scheme to separate P- and SV-wavefields from multi-component seismic data observed at the free surface and ocean bottom. Based on plane-wave components with known horizontal slowness in τ−p domain, the whole P- and SV-wavefields are separated into the direction of observed P- and SV-wave oscillations, by rotation of the horizontal and vertical components respectively. The incident P- and SV-waves are extracted from the separated wavefields using plane wave partitions at the free surface and ocean bottom. The parameters used in the separation are the local seismic wave velocities and the density at the receiver location. Numerical tests on synthetic data for plane-layered models show good performance and accuracy of the scheme.

Analysis of Binary Transport Diffusivities and Self-Diffusivities in a Lattice Model for Silicalite

We have used dynamic Monte Carlo simulations to assess the self-diffusivities and transport diffusivities of binary mixtures in a lattice model for silicalite as functions of hopping rates, mixture composition, and total loading. We compute binary transport diffusivities using the Onsager formalism and subsequently discuss the binary Fickian and Maxwell−Stefan diffusivities. We have used our results to examine the accuracy of several approximations to mixture transport diffusivities that have been suggested previously. Our numerical data strongly support the observation that single-component Maxwell−Stefan diffusivities in this model exactly obey a mean-field expression. Our data also show that a relationship between the binary self-diffusivities and the binary Maxwell−Stefan diffusivities that was claimed by several authors to be exact is in fact only approximate. We have similarly examined several methods that have been proposed for predicting binary self-diffusivities from single-component data.

Single and Multicomponent Gas Phase Diffusion in a Porous Media: Modeling and Laboratory Measurements

Subsurface vapor migration of volatile chemicals may impact ambient and indoor air quality, increasing the importance to investigate the fate and transport of these chemicals. This project involved both modeling and experimental work to study the vapor phase transport behavior of single, binary, and tertiary component systems present in the gas phase. The experimental phase resulted in the development of a diffusion cell for measuring vapor phase transport. Three organic compounds (toluene, cumene, and isooctane) common to petroleum-based products were selected. The objective of this research project was to evaluate how the rate of a component diffusing alone in a stagnant gas mixture compares to the rate of the same component when diffusing in the presence of multiple diffusing species. The equipment was first validated by measuring the unobstructed gas phase diffusion fluxes for each organic compound. The diffusion coefficients were then calculated from the experimentally measured diffusive fluxes using Fick's Law at 20 and 25°C and compared to the respective literature values. The experimental/literature (E/L) ratio was calculated for toluene, cumene, and isooctane. The range of the average E/L ratio for the single component data sets is 0.93 to 1.05. The validation data provided the baseline for extending the research to multicomponent data. The multi-component systems research was characterized as either binary systems or a three-component system. The binary systems were either isooctane/tolu-ene or isooctane/cumene. The three-component system consisted of a mixture of all three compounds. For both temperatures and all compounds the flux rate decreased for any single component due to the dilution effect by incorporation into a mixture. Applying Fick's Law to calculate the effective diffusion coefficient for each compound that corresponded to the resulting concentration gradient by the mixture, an enhancement in the diffusive flux of each individual species was observed. This enhancement can be explained by a compositional coupling of each component to all others which results in a total vapor phase mass flux comprised of both diffusive and pseudo-advective mass transport. This pseudo-advective component is attributed to simultaneous diffusion of other species in the presence of the one of interest. Since this research project incorporated a mixture of toluene and cumene present in a background carrier solvent of isooctane, by calculating the ratios Dexp(3-component)/ Dexp(2-component) and Dexp(2-compo-nent)/Dexp(single component), an estimate is obtained of the enhancement effect due to the advective component of simultaneously diffusing chemicals. The diffusivity ratios for the three-component system compared to the dual component system ranged from 0.8 to 3.7. The diffusivity ratios for individual compounds were for 1.5-3.7 cumene, 0.8-1.2 for toluene, and 1.0-1.2 for isooctane. The diffusivity ratios for the dual component system to the single component systems ranged from 0.8 to 4.0. The range of diffusivity ratios for individual compounds were for 2.0-4.0 for cumene, 0.8-1.6 for toluene, and 1.1-1.4 for isooctane. A ratio greater than 1.0 indicated an enhancement effect on the molecular diffusion rate due to the presence of one or more additional diffusing chemical species present. The majority of fate and transport models are based on single component behavior modeled by Fick's Law using the pure gas phase diffusion coefficient. The enhancement of the individual diffusive flux in a multicomponent mixture observed in this study and accounted for by pseudo-advec-tive mass transport results in an under-prediction of the actual multicomponent diffusive fluxes. It is recommended that a more rigorous diffusion equation such as the Stefan-Maxwell equation be considered for incorporation into vapor phase transport models when modeling multicomponent/ contaminant systems.

Some Results for Reflux Condensation of Hydrocarbon Vapour Mixtures

This paper presents some data for condensation of pure and mixed vapours from a new reflux condenser research facility at NEL. The facility contains a single tube test condenser and a dump condenser to allow partial condensation in the test condenser. Single component data for condensation of iso-octane are well predicted using a correction to the Nusselt theory for gravity-controlled condensation for the effects of waves and turbulence. Some initial data for condensation of mixtures of pentane and iso-octane are compared with the predictions of a Colburn and Drew model. The basic Colburn-Drew model gave good agreement with the measured overall heat transfer coefficient, but underestimated the vapour composition and temperature changes. Improved agreement with the data could be obtained by enhancing the diffusive heat and mass transfer coefficients to allow for the relative velocity of the liquid and vapour phases and for the effects of waves on the condensate film. However, the measured separation of the components was still significantly greater than predicted.

Adsorption of Guest Molecules in Zeolitic Materials: Computational Aspects

Recent progress in the computation of thermodynamic properties of guest molecules in zeolites, using classical molecular simulation techniques, is reviewed. It is shown that grand canonical Monte Carlo simulations, using statistical biaising for studying large anisotropic molecules, together with an appropriate guest−guest force field, may provide a reasonably accurate prediction of single component and binary mixture adsorption data for systems such as normal and branched alkanes, benzene, alkyl benzene isomers and halocarbon molecules in a variety of aluminosilicate hosts. The Monte Carlo algorithms used to obtain reliable thermodynamics data (adsorption isotherms and heats) are discussed as well as the newly developed semiempirical force fields, which allow a better transferability of the potential parameters from one guest/host system to another.

Use of a mathematical model for prediction of the performance of the simultaneous biosorption of Cr(VI) and Fe(III) on Rhizopus arrhizus in a semi-batch reactor

The simultaneous biosorption of Cr(VI) and Fe(III) ions in single component and binary systems has been studied using Rhizopus arrhizus, a filamentous fungus, in a semi-batch reactor. The mono-component equilibrium data have been analysed using the Langmuir model. For the prediction of the performance of the reactor for mono- and bicomponent biosorption of Cr(VI) and Fe(III) ions, a mathematical model based on mass balances for liquid and solid phases has been used. The forward and backward rate constants, K 1 and K 2, have been calculated in the case of single metal biosorption and then used for modelling of the multi-component biosorption in the semi-batch reactor. The proposed model was shown to correlate well with single and bicomponent adsorption data. The capacity of Cr(VI) in the binary systems is greater than that of Fe(III), in agreement with the single component data.