Mole Fraction Of Component Research Articles

Variation of residence time with chain length for products in a slurry-phase Fischer–Tropsch reactor

The phrases “product accumulation” or “accumulated products” or “product holdup” have appeared in literature during the past several decades to qualitatively explain the experimental results for Fischer–Tropsch synthesis (FTS). This study develops an experimental method for a slurry reactor to evaluate the product accumulation inside the FT reactor by measuring the average residence time of products as a function of carbon number. The effect of accumulation of products on vapor–liquid equilibrium (VLE) in the reactor is also investigated. The results show that VLE is reached inside the FT reactor for components up to C17. Furthermore, the relationship between the mole fractions of components in the vapor and the liquid phase for lighter hydrocarbons, up to around C17, is adequately described by Raoult’s law. These results suggests that chain length–dependent solubility in the liquid phase is the predominant cause for chain length dependencies of secondary olefin reactions in FTS, and diffusion-limited removal of products is only significant for products with carbon number greater than 17.

Dissemination of units of mole fraction and mass concentration of gas components by means of first-grade working standards based on dynamic gas mixture generators

A comparison of static and dynamic methods of preparing gas mixtures is presented and requirements that working standards based on dynamic generators must satisfy are formulated. The basic sources of errors in the reproduction of mole fraction and mass concentration of components in gas mixtures are analyzed by a dynamic method and results from a study of methods of increasing the stability and precision of dynamic generators are presented. A new complex of first-grade working standards is described. Data of an experimental study of the metrological characteristics of dynamic generators based on the results gained from their use in international key comparisons are presented.

Thermodynamic analysis of the autothermal reforming of glycerol using supercritical water

Hydrogen can be produced by autothermal reforming of glycerol using supercritical water (SCW). With the aid of AspenPlus™, a systematic thermodynamic analysis of this process has been carried out by the total Gibbs free energy minimization method, which computes the equilibrium composition of synthesis gas (syngas). The predictive Soave-Redlich-Kwong equation of state (EOS) has been used as thermodynamic method in the simulation of the supercritical region. A sensitivity analysis has been conducted both for a pure glycerol feed and pretreated crude glycerol feed coming from biodiesel production. Simulations run so as to calculate the O 2 needed to enter the Gibbs reactor (reformer) for achieving the thermoneutral condition (no external heat to sustain the reformer operation is required). Thus, the effect of the main operating parameters (reforming temperature, water to glycerol mole ratio, glycerol purity in the feed of crude glycerol, oxygen to glycerol mole ratio and the inlet feed temperature) aimed to the hydrogen production has been investigated, by obtaining the mole fraction and molar flow-rate of components in syngas, as well as the hydrogen yield. By this way, the most thermodynamic favorable operating conditions at which glycerol may be converted into hydrogen by autothermal reforming using SCW have been identified. As a second part of the study, a conceptual design and an energy and exergy analysis of the overall process will be performed later.

Thermodynamic study of the supercritical water reforming of glycerol

Hydrogen can be produced by steam reforming, partial oxidation, autothermal, or aqueous-phase reforming processes using various noble metal based catalysts, but also by supercritical water (SCW) reforming. Using AspenPlus™, a systematic thermodynamic analysis of glycerol reforming using supercritical water has been carried out by the total Gibbs free energy minimization method, which computes the equilibrium composition of synthesis gas (syngas). The predictive Soave–Redlich–Kwong equation of state (EOS) has been used as thermodynamic method in the simulation of the supercritical region, after evaluating it against other EOS methods. A sensitivity analysis has been conducted on supercritical water reforming of pure and pretreated crude glycerol, as obtained from biodiesel production. The effect of the main operating parameters (temperature, concentration of glycerol feed, glycerol purity in the feed of crude glycerol, and pressure) aimed to the hydrogen production has been investigated in the reforming process, by obtaining the mole fraction and molar flow-rate of components in syngas, as well as the hydrogen yield. Selectivity to the different compounds has been also calculated. By this way, the thermodynamic favorable operating conditions at which glycerol may be converted into hydrogen by SCW reforming have been identified. The simulation results agree well with some few experimental data from the literature. This study is the first of a series addressed to glycerol reforming using SCW.

Vent fluid chemistry of the Rainbow hydrothermal system (36°N, MAR): Phase equilibria and in situ pH controls on subseafloor alteration processes

The Rainbow hydrothermal field is located at 36°13.8′N–33°54.15′W at 2300 m depth on the western flank of a non-volcanic ridge between the South AMAR and AMAR segments of the Mid-Atlantic Ridge. The hydrothermal field consists of 10–15 active chimneys that emit high-temperature (∼365 °C) fluid. In July 2008, vent fluids were sampled during cruise KNOX18RR, providing a rich dataset that extends in time information on subseafloor chemical and physical processes controlling vent fluid chemistry at Rainbow. Data suggest that the Mg concentration of the hydrothermal end-member is not zero, but rather 1.5–2 mmol/kg. This surprising result may be caused by a combination of factors including moderately low dissolved silica, low pH, and elevated chloride of the hydrothermal fluid. Combining end-member Mg data with analogous data for dissolved Fe, Si, Al, Ca, and H 2, permits calculation of mineral saturation states for minerals thought appropriate for ultramafic-hosted hydrothermal systems at temperatures and pressures in keeping with constraints imposed by field observations. These data indicate that chlorite solid solution, talc, and magnetite achieve saturation in Rainbow vent fluid at a similar pH ( T,P ) (400 °C, 500 bar) of approximately 4.95, while higher pH values are indicated for serpentine, suggesting that serpentine may not coexist with the former assemblage at depth at Rainbow. The high Fe/Mg ratio of the Rainbow vent fluid notwithstanding, the mole fraction of clinochlore and chamosite components of chlorite solid solution at depth are predicted to be 0.78 and 0.22, respectively. In situ pH measurements made at Rainbow vents are in good agreement with pH ( T,P ) values estimated from mineral solubility calculations, when the in situ pH data are adjusted for temperature and pressure. Calculations further indicate that pH ( T,P ) and dissolved H 2 are extremely sensitive to changes in dissolved silica owing to constraints imposed by chlorite solid solution-fluid equilibria. Indeed, the predicted correlation between dissolved silica and H 2 defines a trend that is in good agreement with vent fluid data from Rainbow and other high-temperature ultramafic-hosted hydrothermal systems. We speculate that the moderate concentrations of dissolved silica in vent fluids from these systems result from hydrothermal alteration of plagioclase and olivine in the form of subsurface gabbroic intrusions, which, in turn are variably replaced by chlorite + magnetite + talc ± tremolite, with important implications for pH lowering, dissolved sulfide concentrations, and metal mobility.

The influence of medium on the stability of coordination compounds 4. The system In(tiron)−-NaC1O4-C2H5OHH2O

The stability constants of complex anion In(tiron)− in mixed solvents of ethanol-water with weight percentages of ethanol being 0,5,15,25,35 and 50 have been measured spectrophotometrically at 293 K, using NaClO4 as supporting electrolyte with ionic strength ranging from 0.1 to 3.3mol·dm−3. The thermodynamic stability constants of In(tiron)− in various mixed solvents have been obtained by a polynomial approximation equation based on Pitzer's theory. As a comparison, the traditional Debye-Huckel equation has also been used to treat the same data. The results show that this polynomial approximate method is obviously superior to the old one. It was discovered that there is a linear relation between the thermodynamic stability constants of In (tiron)− and the mole fraction of organic component in mixed solvents or the reciprocal of dielectric constants of mixed solvents. The medium effect and the standard free energy of transfer, ΔG°tr, for the coordination reaction: In3+ + tiron4- = In(tiron)− have also been discussed.

Chemistry and Origin of Enigmatic Monazite and Chevkinite/Perrierite in the Egyptian Black Beach Sand

AbstractThe content of monazite in the Egyptian black beach sand and coastal sand dunes is normally equal to or below 0.01 wt.%. The obtained high grade monazite concentrate includes three minor monazite groups in addition to major canary and lemon yellow coloured monazite: (i) the colourless to pinkish white coloured monazite; (ii) the opaque light to dark resinous, reddish brown and dark brown coloured monazite; and (iii) opaque yellowish red to brownish red coloured monazite grains group. These groups represent 3%, 4% and 2%, respectively, in the high grade monazite concentrate. A negligible amount of euhedral to subhedral black to brownish black chevkinite/perrierite mineral crystals was detected in the obtained monazite concentrate. The presence of these minor mineral groups affects the chemical composition of the obtained high grade monazite concentrate.The Ce2O3 is the main REE in the studied monazite. In the colourless‐pinkish monazite grains, the analyzed REE are the following, in order of abundance; Ce > La > Nd > Pr > Sm > Gd > Dy. UO2 ranges between 0.11 and 1.74 wt.%. The contents of Eu2O3 is under the limit of detection while ThO2 ranges between 3.99 and 8.58 wt.% with an average value of 5.57 wt.%. These grains are most probably igneous monazite from a highly differentiated granite.The resinous, brown monazite grains have lower Ce2O3 content (24.63 wt.%) and much lower La2O3 content (6.00 wt.%) but greater content of Eu2O3 (0.41 wt.%) than those of the colourless‐pinkish monazite. These monazites have the lowest contents of Th, U and Ca among the three groups. The resinous, brown monazites are most probably formed by metamorphism or alteration leading to leaching or replacement of pre‐existing minerals.The red monazite group has a lower average Ce2O3 content (25.28 wt.%) than the colourless‐pinkish variety (28.02 wt.%) but slightly greater than that of the resinous, brown ones. The red monazite group has the highest ThO2 and UO2 contents; 5.84 wt.% and 1.24 wt.%, respectively. It has the lowest monazite component mole fraction (0.75). The red monazite seems to have been formed by hydrothermal alteration of pre‐existing monazite and other mineral species bearing for Y, REE, Ca, Th and U.The two coupled substitution mechanisms: (Th, U)4++ Ca2+ 2REE3+, and (Th, U)4++ Si4+ REE3++ P5+, are obvious in the studied colourless‐pink monazite.

Prediction of the Selectivity Coefficient of Ionic Liquids in Liquid-Liquid Equilibrium Systems Using Artificial Neural Network and Excess Gibbs Free Energy Models

In this work, the selectivity coefficients of ionic liquids in liquid-liquid systems were correlated and predicted by the NRTL, UNIQUAC, and Wilson-NRF Gibbs free energy models and also by an artificial neural network system. The three thermodynamic models need six binary interaction parameters between solvent(1)-solvent(2), solvent(1)-ionic liquid, and solvent(2)-ionic liquid pairs in obtaining the selectivity of ionic liquid in liquid-liquid systems. Also, the selectivity coefficients of ionic liquids were modeled using an artificial neural network system. In the proposed neural network system, temperature, molecular weight of ionic liquid, molecular weight of solvents, and mole fractions of components (1) and (2) in the solvent-rich phase were considered as input data and the selectivity of ionic liquids in the liquid-liquid system was considered as output. The weights and biases were obtained using the quick propagation (QP) method. A total of 150 experimental data points were used for training and 30 experimental data for testing. The best network topology obtained was one neuron in a hidden layer with five nodes. The average absolute deviation percentages (AAD%) for the results obtained from the neural network system, the NRTL model, the UNIQUAC model, and the Wilson-NRF model are 0.0096, 0.0168, 0.0017, and 0.0178, respectively. Although the artificial neural network gave reasonably good results, the UNIQUAC model can more accurately predict the selectivity of ionic liquids in liquid-liquid equilibrium systems than the other models.

A universal method for calculating isobaric-isothermal sections of ternary system phase diagrams

A method for calculating and constructing isobaric-isothermal sections of ternary system phase diagrams with the use of convex hulls was developed. The method is based on the projection of the singularities of the lower part of the Gibbs energy convex hull onto the plane of component mole fractions followed by a geometric analysis of the properties of this projection. The method is applicable to a wide range of ternary systems, it can be used to find tie-line coordinates and determine the phase compositions of all the diagram regions. The quality of the suggested algorithm was estimated, and examples of the construction of several phase diagrams are given.

A Narrow Band-Based Multiscale Multigroup Full-Spectrum k-Distribution Method for Radiative Transfer in Nonhomogeneous Gas-Soot Mixtures

The full-spectrum k-distribution (FSK) approach has become a promising method for radiative heat transfer calculations in strongly nongray participating media, due to its ability to achieve high accuracy at a tiny fraction of the line-by-line (LBL) computational cost. However, inhomogeneities in temperature, total pressure, and component mole fractions severely challenge the accuracy of the FSK approach. The objective of this paper is to develop a narrow band-based hybrid FSK model that is accurate for radiation calculations in combustion systems containing both molecular gases and nongray particles such as soot with strong temperature and mole fraction inhomogeneities. This method combines the advantages of the multigroup FSK method for temperature inhomogeneities in a single species, and the modified multiscale FSK method for concentration inhomogeneities in gas-soot mixtures. In this new method, each species is considered as one scale; the absorption coefficients within each narrow band of every gas scale are divided into M exclusive spectral groups, depending on their temperature dependence. Accurate and compact narrow band multigroup databases are constructed for combustion gases such as CO2 and H2O. Sample calculations are performed for a 1D medium and also for a 2D axisymmetric combustion flame. The narrow band-based hybrid method is observed to accurately predict heat transfer from extremely inhomogeneous gas-soot mixtures with/without wall emission, yielding close-to-LBL accuracy.

Determination of Activity Coefficients of Semi-Volatile Organic Aerosols Using the Integrated Volume Method

We demonstrate the use of the Integrated Volume Method (IVM) to estimate activity coefficients of semi-volatile organic compounds pertinent to ambient/atmospheric aerosols in binary mixtures. We generate binary solution aerosols with different mole fractions of individual components; for each mixture, we measure total change in aerosol volume upon heating from 25 ○ C to 35 ○ C, with the aerosols being at equilibrium in both states. The change in aerosol volume, or in other words, the partitioning between the particle phase and the gas phase, is used to determine activity coefficients of the compounds as a function of their mole fraction in the mixture. We demonstrate this method using the following four model systems. System 1: adipic acid–pimelic acid, which illustrates polar organic–polar organic interactions. Non-ideal behavior was observed with activity coefficients around three at infinite dilution. System 2: adipic acid–dioctyl sebacate, which illustrates polar organic–non-polar organic interactions...

The laws of establishing stationary composition in a droplet condensing in a binary vapor–gas environment

It is shown that the mole fractions of components within a droplet growing in an atmosphere of two condensing gases and a carrier gas approach their stationary values with a power-law behavior in time on a large scale and with exponential behavior on a small scale for both diffusion-controlled and free-molecular regimes of isothermal condensation. The parameters of the power and the exponential laws are specified for each regime of binary condensation and are linked to the thermodynamic and kinetic characteristics of condensing vapors and to the stationary mole fractions of the components in a growing binary droplet. The stationary composition of the solution within the droplet is shown to be established at a comparatively small relative increase of the droplet radius. A relaxation equation for the droplet composition at arbitrary initial deviations of mole fractions from their stationary values has been solved, and the limitations on the initial deviations allowing monotonic establishment of stationary composition in solution within a growing droplet have been considered.

Thermodynamic properties of ethanol solution of chiral camphors and its derivatives

Enthalpies of mixing and the densities of ethanol solution of R- and S-enantiomers of camphor, 10-camphorsulfonamide, 10-camphorsulfonic acid, camphorquinone, and 10-camphorsulfonyl chloride have been measured for a wide range of mole fractions of heterochiral components at 298.15 K. Enthalpies of mixing were exothermic for all concentrations and heterochiral solutions were more stable than each of the homochiral solutions. Enthalpic stabilization of mixing of heterochiral solutions was increased with a decreasing concentration of all the camphor derivatives measured. The sequence of enthalpic stabilization on mixing was 10-camphorsulfonyl chloride, 10-camphorsulfonic acid, 10-camphorsulfonamide, camphor, and camphorquinone. Apparent molar volumes were determined and excess volumes of mixing of heterochiral solutions were small and negative. Enthalpic stabilizations were found to be dependent on dipole–dipole interaction between solutes and solvents.

Influence of the pH on the Formation of the Catanionic n-Tetradecylammonium Cholate Surfactant Salt

The catanionic n-tetradecylammonium cholates, with the 1:1 and 1:2 cationic:anionic surfactant molar ratio, have been synthesized by reaction of tetradecylammonium chloride and sodium cholate. The stoichiometry of the compounds formed is strongly dependent on pH of the aqueous reaction solution. In the neutral and slightly acidic medium the isolated surfactant was detected as 1:1, at acidic medium (pH ≈ 3) as 1:2, while the cholic acid alone precipitated from the strong acidic solution (pH ≈ 2). The catanionic surfactants have been characterized by elemental and spectroscopic (IR, 1H, and 13C NMR) analyses, and microscopic observations. The mole fractions of individual components in precipitate present in the heterogeneous aqueous system have been determined as a function of pH. The data interpretation in the pH regions where two different kinds of precipitates coexist pointed to the complex equilibrium in the examined systems. The evaluation of the relevant equilibrium constants was solved by the nonlinear regression analysis. In the acidic region where cholic acid and 1:2 precipitate coexisted the equilibrium constants of dissolution were K 1 = 8.4 × 10−10 and K 4 = 3.7 × 10−27, respectively. In the region where 1:2 and 1:1 precipitate coexisted the equilibrium constant of dissolution of 1:1 tetradecylammonium cholate was K 2 = 4.2 × 10−20.

Can factor analysis be applied to spectra taken in binary solvent mixtures?

It is suggested that, in spite the logical inconsistencies, factor analysis can be applied in many cases to fluorescence and absorption spectra of dyes in binary solvent mixtures. Limits as to when this application will be successful are derived. This idea was applied to four different dyes in two different binary solvent mixtures and was generally found to generate smoother curves, plotting the contribution of one of the two contributing bands to the experimental spectrum vs. solvent component mole fraction, as compared to those that are generated when one uses the normally applied method of plotting maximum peak position vs. solvent component mole fraction.

Thermodynamic evaluation and optimization of the (LiF + NaF + KF + MgF 2 + CaF 2 + SrF 2) system

A complete critical evaluation of all available phase diagram and thermodynamic data has been performed for all condensed phases of the (LiF + NaF + KF + MgF 2 + CaF 2 + SrF 2) system, and optimized model parameters have been found. The (LiF + NaF + KF + MgF 2 + CaF 2) subsystem has been critically evaluated in a previous article. The model parameters obtained for the binary and ternary subsystems can be used to predict thermodynamic properties and phase equilibria for the multicomponent system. The Modified Quasichemical Model for short-range ordering was used for the molten salt phase, and the low-temperature and high-temperature (CaF 2 + SrF 2) solid solutions were modelled using a cationic substitutional model with an ideal entropy and an excess Gibbs free energy expressed as a polynomial in the component mole fractions. Finally, the (Li, Na, K)(Mg, Ca, Sr)F 3 perovskite phase was modelled using the Compound Energy Formalism.

Mixed micellization of anionic–nonionic surfactants in aqueous media: a physicochemical study with theoretical consideration

Mixed micellization of binary and ternary mixtures of anionic and nonionic surfactants, such as lithium dodecyl sulfate, polyoxyethylene(23)laurylether, and polyoxyethylene-tert-octylphenylether, is studied in aqueous solution using tensiometric, conductometric, and spectrophotometric methods. Although tensiometry and conductometry complement each other closely, the spectroscopic critical micellar concentration (cmc) is far from agreement with tensiometric study. Several parameters, e.g., cmc, degree of counterion binding, free energies of micellization, and interfacial adsorption, have been evaluated. Established theories of Clint, Rosen, Rubingh, Motomura, Georgiev, Maeda, and Blankschtein were applied to evaluate the mole fraction of different components in the self-aggregated phase, the interaction parameter, free energy contributions, and expected cmc.

Quantitative evaluation of sebum lipid components with nuclear magnetic resonance

A NMR spectroscopic method is described that enables the quantitation of specific lipid classes and components, independent of fatty acid composition. We demonstrate this method for measuring cholesterol, squalene, and pools of sterol esters, wax esters (WEs), and triglyceride (TG) components in sebum and meibum. When 600 MHz NMR equipment is used in conjunction with highly sensitive cryogenically cooled probes, this method has adequate sensitivity, and for some applications, advantages over commonly used HPLC-evaporative light-scattering detection and mass spectrometry-based approaches. This method is shown to be useful for preclinical and clinical monitoring of the efficacy of sebum-reducing agents in animals and humans. In Syrian hamsters, 3% topical flutamide and 20 mg/kg oral isotretinoin reduced sterol esters by 18.7% and 30.0%, respectively, and reduced WEs by 32.9% and 31.8%, respectively, as measured in a punch biopsy of the ear. In a 72 patient clinical methodology study, the assay delivered reproducible and noninvasive measurements of WEs, cholesteryl esters, TGs, and squalene from Sebutape skin blots. The quantitative results of sebum analysis obtained by the NMR method correlate well with those obtained with HPLC-based approaches. This approach may be broadly applicable to cases in which fatty acid-independent quantification of lipid classes is desired.

Comparison between two different hemichromes of hemoglobins (HbA and HbS) induced by n-dodecyl trimethylammonium bromide: Chemometric study

The interaction of n-dodecyl trimethylammonium bromide (DTAB) with oxyhemoglobin A and oxyhemoglobin S is investigated using UV–visible absorption spectra and chemometric resolution techniques. Oxyhemoglobins (A and S) induced to partial oxidized form (ferrihemoglobin) by DTAB and finally transform to fully oxidized hemichrome. Hemichrome mole fractions of HbS are more than HbA because of more hydrophobic interaction of DTAB–HbS in second set of binding site relative to DTAB–HbA. The visible spectra between 500 and 650 nm are used for identifying the present components in solution because each species of hemoglobin has a specific spectrum in this region. The number of components and mole fraction of mentioned species were determined by employing chemometric resolution techniques. Subspace comparison was used for determination of the number of components in each concentration of hemoglobin and DTAB. After the determination of components, multivariate curve resolution-alternating least square (MCR-ALS) by initial estimates of spectral profiles and proper constraints, was used to resolve the data matrix into pure concentration and spectral profiles. The results show that both number and mole fraction of components which were formed during hemoglobin (HbA and HbS) oxidation by DTAB were initial hemoglobin concentrations independent. Furthermore, in average the mole fraction of hemichrome of HbS is 14.4% more than HbA. On the other hand, the mole fraction of HbA ferrihemoglobin is 15.6% higher than HbS averagely.

Pseudocomponent Delumping for Multiphase Systems with Waxy Solid Phase Precipitation

Modeling of wax precipitation from hydrocarbon mixtures requires extended compositional data for the heavy fractions; as a result, the number of components in the mixture is usually large and phase equilibrium calculations are computationally expensive and may be prohibitive. A lumping procedure which reduces the dimensionality of phase equilibrium calculations without affecting the location of solid phase transitions is used. By lumping into pseudocomponents, some information on mixture behavior is lost; this information is recovered by a delumping (inverse lumping) procedure. Delumping acts as an interface between simulation tools and results involving different fluid representation levels. The key in the delumping procedure is to relate equilibrium constants of the detailed fluid to some quantities evaluated from lumped fluid flash results. A general form of a two-parameter cubic equations of state is used for vapor and liquid phases, and heavy components are assumed to precipitate in a single solid solution. The proposed lumping/delumping procedures are successfully tested for two synthetic mixtures and a typical reservoir fluid (gas-condensate). Very good agreement is obtained between phase distributions and component mole fractions of detailed and delumped systems. This is the first time that a delumping procedure is proposed for multiphase systems with solid phase precipitation.