Equilibrium Ratio Research Articles

K-value program for crude oil components at high pressures based on PVT laboratory data and genetic programming

Equilibrium ratios play a fundamental role in understanding the phase behavior of hydrocarbon mixtures. They are important in predicting compositional changes under varying temperatures and pressures in the reservoirs, surface separators, and production and transportation facilities. In particular, they are critical for reliable and successful compositional reservoir simulation. Several techniques are available in the literature to estimate the K-values. This paper presents a new model for predicting K values with genetic programming (GP). The new model is applied to multicomponent mixtures. In this paper, 732 high-pressure K-values obtained from PVT analysis of 17 crude oil and gas samples from a number of petroleum reservoirs in Arabian Gulf are used. Constant Volume Depletion (CVD) and Differential Liberation (DL) were conducted for these samples. Material balance techniques were used to extract the K-values of crude oil and gas components from the constant volume depletion and differential liberation tests for the oil and gas samples, respectively. These K-values were then used to build the model using the Discipulus software, a commercial Genetic Programming system, and the results of K-values were compared with the values obtained from published correlations. Comparisons of results show that the currently published correlations give poor estimates of K-values for all components, while the proposed new model improved significantly the average absolute deviation error for all components. The average absolute error between experimental and predicted K-values for the new model was 4.355% compared to 20.5% for the Almehaideb correlation, 76.1% for the Whitson and Torp correlation, 84.27% for the Wilson correlation, and 105.8 for the McWilliams correlation.

Latent Heat of Water Vapor of Rough Rice, Brown Rice, White Rice and Rice Husk

The latent heat of vaporization in rough rice, brown rice, white rice and rice hull was calculated by Clausius-Clapeyron equation, which does not require complex constraints as in Othmer method. Equilibrium relative humidity and ratio of the latent heat of vaporization with ln and ln were estimated with moisture contents ranging from 10% (d.b.) to 36% (d.b.) with 2% (d.b.) increment and temperatures ranging from to with increment. An empirical equation for calculating the latent heat of vaporization in rice was developed as a function of moisture content and temperature. The equation agreed well with the calculated results. The ratio for latent heat of vaporization were the greatest for white rice while they were similar among rough rice, brown rice and rice hull.

A Photochemical On–Off Switch for Tuning the Equilibrium Mixture of H2 Nuclear Spin Isomers as a Function of Temperature

The photochemical interconversion of the two allotropes of the hydrogen molecule [para-H(2) (pH(2)) and ortho-H(2) (oH(2))] incarcerated inside the fullerene C(70) (pH(2)@C(70) and oH(2)@C(70), respectively) is reported. Photoexcitation of H(2)@C(70) generates a fullerene triplet state that serves as a spin catalyst for pH(2)/oH(2) conversion. This method provides a means of changing the pH(2)/oH(2) ratio inside C(70) by simply irradiating H(2)@C(70) at different temperatures, since the equilibrium ratio is temperature-dependent and the electronic triplet state of the fullerene produced by absorption of the photon serves as an "on-off" spin catalyst. However, under comparable conditions, no photolytic pH(2)/oH(2) interconversion was observed for H(2)@C(60), which was rationalized by the significantly shorter triplet lifetime of H(2)@C(60) relative to H(2)@C(70).

Diffusive sampling of 25 volatile organic compounds in indoor air: Uptake rate determination and application in Flemish homes for the elderly

Passive sampling of volatile organic compounds (VOCs) in air has received increasing attention in recent years. However, in order to use passive sampling as a reliable sampling technique a compound and sampler specific uptake rate is needed. Therefore, the scope of our study was threefold. First, uptake rates for 25 VOCs were determined under real indoor and outdoor conditions using axial-sampling tube-type samplers filled with Tenax TA, and active (pumped) sampling as a reference technique. Secondly, the mechanisms of passive sampling were investigated by comparing the experimentally determined uptake rates (0.13–0.46 ml min−1) to the ideal uptake rates, calculated based on Fick’s first law of diffusion and sampler geometry. Sampling efficiency SE, defined as the ratio between the experimental and ideal uptake rate, was introduced as a correction factor and showed that ideal uptake rates may underestimate VOC concentrations by a factor up to 4. This compound dependent SE is explained in terms of the partitioning coefficient K, i.e. the compound’s Tenax TA to air concentration equilibrium ratio. Compounds with a low K-value showed the most pronounced non-ideal sorptive behavior. Third, the experimentally determined uptake rates were used to determine VOC concentrations (between 12 and 311 μg m−3) in 6 homes for the elderly in Antwerp (Belgium). This study provides unique data for indoor air quality at care centers in Flanders.

Tissue Binding Affects the Kinetics of Theophylline Diffusion Through the Stratum Corneum Barrier Layer of Skin

New data sets on both (i) equilibrium theophylline (TH) partitioning/binding in stratum corneum and (ii) transient TH diffusion through human epidermis are explained by an extended partition-diffusion model with reversible binding. Data conform to a linear binding isotherm within the tested concentration range (0-2000 μg/mL) with an equilibrium ratio of bound-to-free solute of approximately 1.4. The permeability coefficient for TH is 4.86 × 10(-5) cm/h, and the lag time is 20.1 h. Binding occurs as a slow process, significantly affecting the kinetics of dermal penetration.

Curtin–Hammett and Steric Effects in HOBt Acylation Regiochemistry

While hydroxybenzotriazole is commonly used in a variety of bond-forming reactions, its acylation has been shown to produce a regiochemical (O vs N) mixture with complex kinetic behavior. Increased steric bulk on the electrophile favors formation of the oxygen-acylated product. Upon standing as a solid, the mixture can isomerize completely to the nitrogen adduct. An equilibrium ratio of regioisomers can be re-established in solution by adding either nucleophilic or electrophilic reagents, suggesting that the composition of the mixture is not significant to subsequent reactivity. Solvents can affect this regiochemical equilibrium through a Curtin-Hammett effect, where the shift in the tautomeric equilibrium of HOBt in polar solvents biases the reaction toward the oxygen adduct.

Genotype calling in tetraploid species from bi-allelic marker data using mixture models

BackgroundAutomated genotype calling in tetraploid species was until recently not possible, which hampered genetic analysis. Modern genotyping assays often produce two signals, one for each allele of a bi-allelic marker. While ample software is available to obtain genotypes (homozygous for either allele, or heterozygous) for diploid species from these signals, such software is not available for tetraploid species which may be scored as five alternative genotypes (aaaa, baaa, bbaa, bbba and bbbb; nulliplex to quadruplex).ResultsWe present a novel algorithm, implemented in the R package fitTetra, to assign genotypes for bi-allelic markers to tetraploid samples from genotyping assays that produce intensity signals for both alleles. The algorithm is based on the fitting of several mixture models with five components, one for each of the five possible genotypes. The models have different numbers of parameters specifying the relation between the five component means, and some of them impose a constraint on the mixing proportions to conform to Hardy-Weinberg equilibrium (HWE) ratios. The software rejects markers that do not allow a reliable genotyping for the majority of the samples, and it assigns a missing score to samples that cannot be scored into one of the five possible genotypes with sufficient confidence.ConclusionsWe have validated the software with data of a collection of 224 potato varieties assayed with an Illumina GoldenGate™ 384 SNP array and shown that all SNPs with informative ratio distributions are fitted. Almost all fitted models appear to be correct based on visual inspection and comparison with diploid samples. When the collection of potato varieties is analyzed as if it were a population, almost all markers seem to be in Hardy-Weinberg equilibrium. The R package fitTetra is freely available under the GNU Public License from http://www.plantbreeding.wur.nl/UK/software_fitTetra.html and as Additional files with this article.

Analysis of NMR spectra in case of temperature‐dependent chemical exchange between two unequally populated sites

AbstractA new approach is introduced for analysis of nuclear magnetic resonance (NMR) spectra measured under conditions of asymmetric chemical exchange. It is based on a simultaneous least‐square fit of a due analytical formula to the experimental NMR spectrum. For this reason, we derived the analytical solution of Bloch‐McConnell equations describing the spectral lineshape in the case of the free induction decay and chemical exchange between two unequally populated sites. The obtained formula is shown to be in agreement with the one derived for continuous wave NMR experiments first published in fifties. On the other hand, typing errors were found in formulae presented in later monographs. Applicability of the approach to extensive NMR data was demonstrated on proton NMR spectra of a self‐complementary oligodeoxynucleotide d(GATGCATC) measured at various temperatures covering the duplex melting. The lineshape analysis of aromatic proton signals provided us the temperature dependence not only of the equilibrium ratio between duplexes and single strands, but also of the kinetics of duplex formation and dissociation, which is not obtainable for a sample in the state of thermodynamic equilibrium by other methods. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part A 38A: 117–127, 2011.

Isomerism of [64Cu-NOTA-Bn]-Labeled Radiotracers: Separation of Two Complex Isomers and Determination of Their Interconversion Energy Barrier Using Ion Pair Chromatography

The model complex [(64)Cu((S)-p-NH(2)-Bn-NOTA)](-) ([(64)Cu]1) was used to study the isomerism of [(64)Cu-NOTA-Bn]-labeled radiotracers. Two complex isomers [(64)Cu]1a and [(64)Cu]1b, which were formed at a ratio of 1:9 during the complexation of [(64)Cu]Cu(2+) with (S)-p-NH(2)-Bn-NOTA, were separated using ion pair chromatography. To study the interconversion, the nonradioactive complex isomers Cu1a and Cu1b were separated and thermally treated at 90 °C in both ammonium acetate solution and deionized water. A faster interconversion rate was observed for both isomers with lower concentrations of ammonium ions. At the end of reaction, the thermodynamic Cu1a to Cu1b equilibrium ratio was 6:94. The particular energy barriers of the interconversion for Cu1a and Cu1b were 130 kJ mol(-1) and 140 kJ mol(-1). Spectrophotometric measurements with Cu1a and Cu1b revealed two isomers adopting different geometrical configurations.

Effect of Batch Melting Temperature and Raw Material on Iron Redox State in Sodium Silicate Glasses

In this study, the redox state of iron in sodium silicate glasses was varied by changing the melting conditions, such as the melting temperature and particle size of iron oxide. The oxidation states of the iron ion were determined by wet chemical analysis and UV-Vis spectroscopy methods. Iron commonly exists as an equilibrium mixture of ferrous ions, Fe²?, and ferric ions Fe³?. In this study, sodium silicate glasses containing nanoparticles of iron oxide (0.5% ㏖) were prepared at various temperatures. Increase of temperature led to the transformation of ferric ions to ferrous ions, and the intensity of the ferrous peak in 1050 ㎚ increased. Nanoparticle iron oxide caused fewer ferrous ions to be formed and the Fe²?/Fe³? equilibrium ratio compared to that with micro-oxide iron powder was lower.

Vapor−Liquid Equilibrium Data for the Nitrogen + Dodecane System at Temperatures from (344 to 593) K and at Pressures up to 60 MPa

A static-analytical apparatus with visual sapphire windows and pneumatic capillary samplers has been used to obtain new vapor−liquid equilibrium data for the N2 + C12H26 system over the temperature range from (344 to 593) K and at pressures up to 60 MPa. Equilibrium phase compositions and vapor−liquid equilibrium ratios are reported. All of the measured vapor−liquid equilibrium data were subject to a thermodynamic consistency test of high-pressure vapor−liquid equilibrium data involving the calculation of the vapor-phase composition from the isothermal pressure liquid phase composition data. The consistency test showed that most of the data are thermodynamically consistent. The new results were compared with solubility data reported by other authors. The comparison showed that the vapor−liquid equilibrium data obtained in this study are in good agreement with those reported in the literature. The experimental data were modeled with the PR (Peng−Robinson) and PC-SAFT (perturbed-chain statistical associating fluid theory) equations of state by using one-fluid mixing rules and a single temperature-independent interaction parameter. Results of the modeling indicated that the PC-SAFT equation of state represents better the measured data of the N2 + C12H26 system over the whole temperature, pressure, and composition range studied.

DEEP MIXING IN EVOLVED STARS. I. THE EFFECT OF REACTION RATE REVISIONS FROM C TO Al

We present computations of nucleosynthesis in low-mass red-giant-branch and asymptotic-giant-branch stars of Population I experiencing extended mixing. We adopt the updated version of the FRANEC evolutionary model, a new post-process code for non-convective mixing and the most recent revisions for solar abundances. In this framework, we discuss the effects of recent improvements in relevant reaction rates for proton captures on intermediate-mass nuclei (from carbon to aluminum). For each nucleus we briefly discuss the new choices and their motivations. The calculations are then performed on the basis of a parameterized circulation, where the effects of the new nuclear inputs are best compared to previous works. We find that the new rates (and notably the one for the 14N(p,g)15O reaction) imply considerable modifications in the composition of post-main sequence stars. In particular, the slight temperature changes due to the reduced efficiency of proton captures on 14N induce abundance variations at the first dredge up (especially for 17O, whose equilibrium ratio to 16O is very sensitive to the temperature). In this new scenario presolar oxide grains of AGB origin turn out to be produced almost exclusively by very-low mass stars (M<=1.5-1.7Msun), never becoming C-rich. The whole population of grains with 18O/16O below 0.0015 (the limit permitted by first dredge up) is now explained. Also, there is now no forbidden area for very low values of 17O/16O (below 0.0005), contrary to previous findings. A rather shallow type of transport seems to be sufficient for the CNO changes in RGB stages. Both thermohaline diffusion and magnetic-buoyancy-induced mixing might provide a suitable physical mechanism for this. Thermohaline mixing is in any case certainly inadequate to account for the production of 26Al on the AGB. Other transport mechanisms must therefore be at play.

Water desorption behavior of desiccant rotor under microwave irradiation

Microwave heating is expected to be a novel regeneration method of desiccant rotor in desiccant humidity conditioner, because it has advantages of direct and rapid heating of material. In this study, desorption experiments were conducted by using the practical desiccant rotor coated with zeolite in the microwave power ranging from 200 to 800 W and desiccant rotor length of 60–180 mm. As a result, both desorption ratio in a desorption equilibrium and initial desorption rate were found to increase linearly with microwave power. Concerning the effect of rotor length, it was found that initial desorption rate and desorption ratio at 600 s also increased with rotor length. However, experimental desorption ratio in a desorption equilibrium was much lower than estimated value, which was calculated on the basis of change in relative humidity involved by temperature increase of rotor, and the deviation increased with microwave power and rotor length. From the temperature measurement in the rotor, a noticeable temperature distribution was observed in the radial and axial directions of rotor even though water desorption attained an equilibrium state. Consequently, it was indicated that nonuniform heating of the rotor mainly caused decrease in desorption ratio. ► Water desorption of zeolite desiccant rotor was conducted with microwave heating. ► Initial desorption rate and equilibrium ratio rose linearly with microwave power. ► Initial desorption rate and equilibrium ratio increased with rotor length. ► Experimental desorption ratio was much lower than theoretically estimated value. ► A big temperature distribution existed in the radial and axial directions of rotor.

Molecular dynamics and Monte Carlo simulations for the structure of the aqueous trimethylammonium chloride solution in the 0.2–1 molar range

Molecular dynamics and Monte Carlo simulations have been performed for characterizing the structure of the 0.2 and 1 molar aqueous trimethylammonium chloride solutions. Atomic charges were derived through the CHELPG and RESP fits to the molecular electrostatic potentials calculated for the cation in water at the IEF-PCM/B3LYP level using the 6-31G* and 6-311++G** basis sets. Maxima and minima of the calculated radial distribution functions were not sensitive to the four atomic charge sets. Simulated solution structures suggest non-negligible solute-solute interactions and remarkable inhomogeneity at both concentrations. This means that equilibrium ratios, derived for conformers/tautomers by means of ab initio calculations with the IEF-PCM continuum dielectric solvent model, should be corrected for free energy changes following solute association when compared to experimental data obtained for the 0.1-1 molar aqueous solutions.

Feasibility of Reactive Distillation for Ternary Systems with Azeotropic Mixtures: Decomposition Reaction

Systematic research on feasibility analysis for reactive distillation for ternary azeotropic systems has been conducted by Guo et al. [Guo, Z.; Chin, J.; Lee, J. W.; Feasibility of continuous reactive distillation with azeotropic mixtures. Ind. Eng. Chem. Res. 2004, 43, 3758−3769]. The analytical method they used was tray-by-tray calculations with difference point. There are two feasibility criteria, which are positive reaction extent is required on all trays and products can be reached by distillation or reactive distillation. In this work, we find that the feasibility analysis of reactive distillation using this method can be augmented by admitting the reverse reaction which can be compensated for by excess positive reaction on other trays. Two concepts that can accelerate the feasibility analysis are also shown. The first one is that the analysis of VLE vectors at the equilibrium line and the tray-by-tray calculation method with difference point are equivalent for determining the feasibility. Furthermore, the pinch point in the tray-by-tray calculation under chemical equilibrium and infinite reflux ratio is equivalent to a reactive azeotrope. The number of possibly feasible cases is increased by 21 from 27 to 48 out of all 113 possible ternary configurations. Nine of the 21 new cases are feasible regardless of the value of the equilibrium constant, and twelve cases may be feasible if the equilibrium constant is high enough. The result compares well with reactive distillation column simulations.

Activation of initiation factor 2 by ligands and mutations for rapid docking of ribosomal subunits

We previously identified mutations in the GTPase initiation factor 2 (IF2), located outside its tRNA-binding domain, compensating strongly (A-type) or weakly (B-type) for initiator tRNA formylation deficiency. We show here that rapid docking of 30S with 50S subunits in initiation of translation depends on switching 30S subunit-bound IF2 from its inactive to active form. Activation of wild-type IF2 requires GTP and formylated initiator tRNA (fMet-tRNA(i)). In contrast, extensive activation of A-type IF2 occurs with only GTP or with GDP and fMet-tRNA(i), implying a passive role for initiator tRNA as activator of IF2 in subunit docking. The theory of conditional switching of GTPases quantitatively accounts for all our experimental data. We find that GTP, GDP, fMet-tRNA(i) and A-type mutations multiplicatively increase the equilibrium ratio, K, between active and inactive forms of IF2 from a value of 4 × 10(-4) for wild-type apo-IF2 by factors of 300, 8, 80 and 20, respectively. Functional characterization of the A-type mutations provides keys to structural interpretation of conditional switching of IF2 and other multidomain GTPases.

Binding of [123I]iodobenzamide to the rat D2 receptor after challenge with various doses of methylphenidate: an in vivo imaging study with dedicated small animal SPECT

The effect of various doses of methylphenidate on the binding of [(123)I]iodobenzamide ([(123)I]IBZM) to the rat D(2) receptor was assessed using small animal SPECT. D(2) receptor binding was measured at baseline and after pretreatment with various doses of methylphenidate. For baseline and methylphenidate challenge, striatal equilibrium ratios (V(3)″) were computed as an estimation of the binding potential. After methylphenidate, striatal V(3)″ was 1.61 ± 0.61 (mean ± SD; 0.3mg/kg), 0.91 ± 0.44 (3mg/kg), 1.01 ± 0.44 (10mg/kg), 0.91 ± 0.34 (30mg/kg) and 0.99 ± 0.51 (60mg/kg). Baseline values amounted to 1.73 ± 0.48, 1.32 ± 0.35, 1.50 ± 0.27, 1.82 ± 0.55 and 1.66 ± 0.41, respectively. Differences between baseline and methylphenidate were significant for the doses 3, 10, 30 and 60mg/kg, whereas no significant difference was obtained for 0.3mg/kg methylphenidate. Between-group differences of percentage reduction of D(2) receptor binding were only significant for the groups pretreated with 0.3 and 30mg/kg methylphenidate, respectively. Methylphenidate between 0.3 and 60mg/kg decreased D(2) receptor binding with a maximum reduction after 30mg/kg. As no between-group differences were evident between the groups pretreated with 3, 10, 30 and 60mg/kg, it may be inferred that doses ≥ 3mg/kg were sufficient to induce maximum dopamine concentration in the synaptic cleft. Further investigations are needed in order to clarify whether the variation between subjects can be accounted for by different synaptic mechanisms at the presynaptic binding site.

A new reduction method for phase equilibrium calculations

Phase equilibrium calculations require the most important computational effort in many process simulators and in reservoir compositional simulations. In this work, a new reduction method for phase equilibrium calculations is proposed. A new set of independent variables (and the related set of error equations) is introduced, based on the observation that, under certain conditions, the equilibrium ratios can be related only to some component properties (elements of the reduction matrix) and to equation of state parameters. The new formulation leads to simpler expressions of the elements of the Jacobian matrix. Some important features are presented, and an interesting and useful link with classical flash calculation methods is revealed. The reliability and efficiency of the proposed method are tested on several synthetic and reservoir hydrocarbon mixtures. The proposed method proves to be robust and it performs in all cases better than previous reduction methods. Finally, it is discussed how the new set of independent variables can be used for a variety of phase equilibrium calculations.

Diastereoisomeric β-ethyl aspartate–cobalt(III) complexes: Λ(+)578- and Δ(−)578-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato]cobalt(III) bis(perchlorate) monohydrate

The structures of the diastereoisomers Λ(+)(578)-, (I), and Δ(-)(578)-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato-κ(2)N,O(1)]cobalt(III) bis(perchlorate) monohydrate, (II), both [Co(C(6)H(10)N(2)O(4))(C(2)H(8)N(2))(2)](ClO(4))(2)·H(2)O, are compared. In both structures, the ester group of the amino acid side chain is engaged only in intramolecular hydrogen bonding to coordinated amine groups. This interaction is stronger in (I) and correlates with previously observed diastereoisomeric equilibrium ratios for related metal complex systems in aqueous media. The two perchlorate anions of (II) are located on twofold axes. Both perchlorates in (I) and one of the perchlorates in (II) are affected by disorder. Both structures exhibit extensive three-dimensional hydrogen-bonding networks.

Hydrogen Exchange Equilibria in Glutathione Radicals: Rate Constants

The reduction of oxidized glutathione GSSG by hydrated electrons and hydrogen atoms to form GSSG•− is quantitative. The radical anion dissociates into GS• and GS−, and the S-centered radical subsequently abstracts a hydrogen intramolecularly. We observe sequential development of UV absorbance signatures that indicate the formation of both α- and β-carbon-centered radicals. From experiments performed at pH 2 and pH 11.8, we determined forward and reverse rate constants for the overall equilibrium between sulfur-centered and carbon-centered radicals: kforward = 3·105 s−1, kreverse = 7·105 s−1, and K = 0.4. Furthermore, on the basis of the differences between the kinetics traces at 240 and 280 nm, we estimate that α- and β-carbon-centered radicals are formed at a surprising ratio of 1:3. The ratios found at pH 2 also apply to pH 7, with the conclusion that the equilibrium ratio of S-centered:β-centered:α-centered radicals is, very approximately, 8:3:1. The formation of carbon-centered radicals could lead to irreversible damage in proteins via the formation of carbon−carbon bonds or backbone fragmentation.