Predict Equilibrium Conditions Research Articles

Kinetics of the pulsed vacuum osmotic dehydration of green fig (Ficus carica L.)

The fig (Ficus carica L.) is a fruit native to the Mediterranean region. However, it has spread worldwide. Osmotic dehydration is used to reduce the moisture content in food, preserving its main characteristics. This study aimed to obtain the kinetics of the water loss, solid gain and water activity of green figs that were cut transversely and osmotically dehydrated in different sucrose solutions (40, 50 and 60 °Brix). The osmotic dehydration occurred at 40 °C, with a vacuum pulse of 74 mmHg in the first 5 min of the process in a total time of 240 min. The ratio of sample:solution was kept constant at 1:10 (weight/weight). Periodically, the samples were weighed to calculate the kinetics of water loss, solid gain, and water activity. The increase in the concentration of the sucrose solution from 40 to 60 °Brix promoted a percentage increase of water loss from 8.14 ± 0.80 to 12.80 ± 0.50%, of solid gain (0.89 ± 0.31 to 1.42 ± 0.70%), and the reduction of water activity (0.93 ± 0.02 to 0.91 ± 0.01). The mathematical models of Peleg and Azuara were tested for fitting the kinetics of water loss and solid gain. Both the mathematical models of Peleg and Azuara presented good fitness to the experimental data. However, the latter was more adequate (higher r2 and lower error), with predicted equilibrium conditions closer to the experimental values.

Equilibrium of tidal channels carrying nonuniform sand and interacting with the ocean

The complex interactions between flow hydrodynamics, sediment transport, geometry, and changes in base level control the morphodynamic evolution of tidal channels, inlets, and estuaries. Research on these complex settings have involved decades of field, laboratory, and modeling work. Studies on the one-dimensional morphodynamic of well-mixed, tide-dominated channels demonstrate that the evolution of a horizontal channel subject to tidal fluctuations at the ocean boundary is characterized by erosion in the ocean part of the channel and the formation of a landward migrating shoal that, depending on the channel length, may reach the landward boundary. When the shoal reaches the landward end of the domain, it is reflected and a beach forms as the flow and sediment transport reach conditions of equilibrium. At equilibrium, the elevation of the channel bed profile remains constant over a tidal cycle. Building on previous work, this study focuses on the poorly explored effects of nonuniformity of the sediment size distribution and of the interaction between tidal channel and longshore sediment transport on the equilibrium of tidal channels. The model is verified at laboratory scale, and it is then applied to predict equilibrium conditions with nonuniform sediment and without an imposed input of sediment from the ocean. Model results show that nonuniformity of the grain size distribution of the sediment increases the profile concavity. The equilibrium deposits tend to coarsen from the land to the ocean, and the sediment of the landward deposits presents an upward fining pattern. When the imposed input of sediment from the ocean is relatively small, the equilibrium profile presents a stable shoal at the oceanward part of the channel. In the case of a large input of sediment from the ocean, the channel gradually fills with sediment. The grain size distribution of these channel fill deposits coarsen in the oceanward and upward directions. The comparison between model results and field observations shows that the model can qualitatively capture some of the main features of tidal channels and can thus be of aid in coastal management and restoration with proper site-specific modifications.

Simulations and Laboratory Tests for Assessing Phosphorus Recovery Efficiency from Sewage Sludge

Phosphorus is a potential environmental pollutant, which could lead to the eutrophication of water bodies. For this reason, wastewater treatment plants worldwide are often designed and operated to eliminate phosphorous from effluents, at substantial cost. At the same time, phosphorus is an essential nutrient for agriculture and, consequently, human life. Data seem to suggest that the world will run out of phosphorus by around 2300, in the best case scenario, although even shorter estimates exist. This situation evokes the need for more efficient phosphorus recovery technologies, in order to meet current water quality requirements and—at the same time—critical future phosphorous needs. Chemical precipitation is the main process for achieving a phosphorus-containing mineral suitable for reuse as a fertilizer, where Struvite is an example of such a product. In this study chemical equilibrium of struvite precipitation was simulated using US Geological Survey (USGS)’ PHREEQC model, and results were compared to laboratory precipitation tests to evaluate struvite recovery efficiency under various conditions. pH had the most significant effect on the results and P recovery of >90% was achieved at pH = 9.5. Simulations indicated that struvite precipitation is affected by the presence of Amorphous Calcium Phosphate (ACP) and calcite in the final product of the process. The model showed great potential for predicting equilibrium conditions, and could be very helpful for future optimization of the process.

Prediction of the phase equilibria of methane hydrates using the direct phase coexistence methodology.

The direct phase coexistence method is used for the determination of the three-phase coexistence line of sI methane hydrates. Molecular dynamics (MD) simulations are carried out in the isothermal-isobaric ensemble in order to determine the coexistence temperature (T3) at four different pressures, namely, 40, 100, 400, and 600 bar. Methane bubble formation that results in supersaturation of water with methane is generally avoided. The observed stochasticity of the hydrate growth and dissociation processes, which can be misleading in the determination of T3, is treated with long simulations in the range of 1000-4000 ns and a relatively large number of independent runs. Statistical averaging of 25 runs per pressure results in T3 predictions that are found to deviate systematically by approximately 3.5 K from the experimental values. This is in good agreement with the deviation of 3.15 K between the prediction of TIP4P/Ice water force field used and the experimental melting temperature of ice Ih. The current results offer the most consistent and accurate predictions from MD simulation for the determination of T3 of methane hydrates. Methane solubility values are also calculated at the predicted equilibrium conditions and are found in good agreement with continuum-scale models.

Thermodynamic model for predicting equilibrium conditions of clathrate hydrates of noble gases + light hydrocarbons: Combination of Van der Waals–Platteeuw model and sPC-SAFT EoS

In this communication, equilibrium conditions of clathrate hydrates containing mixtures of noble gases (Argon, Krypton and Xenon) and light hydrocarbons (C1–C3), which form structure I and II, are modeled. The thermodynamic model is based on the solid solution theory of Van der Waals–Platteeuw combined with the simplified Perturbed-Chain Statistical Association Fluid Theory equation of state (sPC-SAFT EoS). In dispersion term of sPC-SAFT EoS, the temperature dependent binary interaction parameters (kij) are adjusted; taking advantage of the well described (vapor+liquid) phase equilibria. Furthermore, the Kihara potential parameters are optimized based on the P–T data of pure hydrate former. Subsequently, these obtained parameters are used to predict the binary gas hydrate dissociation conditions. The equilibrium conditions of the binary gas hydrates predicted by this model agree well with experimental data (overall AAD P∼2.17).

Reduction of Chromium from Al2O3–CaO–SiO2–CrOX Slags by Carbon Dissolved in Liquid Iron

The goal of this work is to investigate the reduction of chromium from a quaternary slag by carbon dissolved in liquid steel. Laboratory scale experiments were conducted to study the reduction of chromium oxides in the slag by carbon dissolved in the melt. These experiments were made under different conditions of slag basicity and amount of added carbon. Thermodynamic calculations based on Double Sublattice model were applied using the commercial software Thermo-Calc, with the IRSID database. The results obtained showed good correlation with practical and calculated results, making it possible to predict equilibrium conditions of the system and to determine the activities of chromium oxides in the slag.

Mechanisms of the Different DNA Adduct Forming Potentials of the Urban Air Pollutants 2-Nitrobenzanthrone and Carcinogenic 3-Nitrobenzanthrone

2-Nitrobenzanthrone (2-NBA) has recently been detected in ambient air particulate matter. Its isomer 3-nitrobenzanthrone (3-NBA) is a potent mutagen and suspected human carcinogen identified in diesel exhaust. We compared the efficiencies of human enzymatic systems [hepatic microsomes and cytosols, NAD(P)H:quinone oxidoreductase 1 (NQO1), xanthine oxidase, NADPH:cytochrome P450 reductase, N,O-acetyltransferases, and sulfotransferases] and human primary hepatocytes to activate 2-NBA and its isomer 3-NBA to species forming DNA adducts. In contrast to 3-NBA, 2-NBA was not metabolized at detectable levels by the tested human enzymatic systems and enzymes expressed in human hepatocytes, and no DNA adducts detectable by (32)P-postlabeling were generated by 2-NBA. Even NQO1, the most efficient human enzyme to bioactive 3-NBA, did not activate 2-NBA. Molecular docking of 2-NBA and 3-NBA to the active site of NQO1 showed similar binding affinities; however, the binding orientation of 2-NBA does not favor the reduction of the nitro group. This was in line with the inhibition of 3-NBA-DNA adduct formation by 2-NBA, indicating that 2-NBA can compete with 3-NBA for binding to NQO1, thereby decreasing the metabolic activation of 3-NBA. In addition, the predicted equilibrium conditions favor a 3 orders of magnitude higher dissociation of N-OH-3-ABA in comparison to N-OH-2-ABA. These findings explain the very different genotoxicity, mutagenicity, and DNA adduct forming potential of the two compounds. Collectively, our results suggest that 2-NBA possesses a relatively lower risk to humans than 3-NBA.

Methane Hydrate Equilibrium and Formation Kinetics in the Presence of an Anionic Surfactant

This paper presents a new thermodynamic calculation procedure to predict gas hydrate equilibria in the presence of sodium dodecyl sulfate (SDS) micelles. This calculation procedure employs the Poisson−Boltzmann equation to determine the electrical potential and the water chemical potential change due to the presence of micelles. This water chemical potential change is incorporated into the Zele−Lee−Holder and Lee−Holder distortion model to predict equilibrium conditions of gas hydrates in the micelle solution. The prediction results agree with experimental results within an error of 5−20%. Both results show that the equilibrium dissociation pressures of methane hydrates at SDS concentrations ranging from 250 to 10 000 ppm are not much different from those in the absence of SDS. However, the initial formation rate of methane hydrates is greatly affected by SDS. One useful finding is that there is an optimal SDS concentration for the maximum initial formation rate.

Modelos Unitarios o colectivos? Perspectivas teóricas y evidencias preliminares provenientes de Perú

The document provides so me theoretical insights around collective models of household decision making and resource allocation. These models, in contrast with unitary ones, consider the consumption decisions of the family to be a result of a bargaining process and interaction between household members. The predicted equilibrium conditions tend to differ from the traditional approach of utility maximization. The focus is centered on two specific issues: the emergence ofthe pooling income hypothesis (which characterizes unitary models) and the efficiency hypothesis (which characterizes, within the collective framework, cooperative solutions). Using these insights, the article establishes preliminary tests for the collective approach, as against the unitary one, using data for Peru, and then investigates whether efficiency is achieved in consumption allocation. The results presented provide new insights about consumption behavior in Peru.

An activity model for multi-component ion exchange

Ion exchange resin is used extensively in the mineral processing industry to recover dissolved species form solution. These processes are usually modeled using a dual resistance model incorporating both external film diffusion and some form of intraparticle diffusivity. Although this type of model is tested and proven in many systems, certain assumptions relating to the model makes it impractical to apply to certain ion exchange operations, especially those involving multi-component ion exchange. This study addresses these short-comings by using a dual kinetic rate model which does not rely on accurately predicting equilibrium conditions. The model assumes that ion exchange takes place from a liquid layer surrounding the particle and that a single rate constant can be used to explain ion exchange kinetics from this ‘proximity’ layer. Furthermore, the concentration of a species in the bulk solution is influenced by the rate at which it is transported into the ‘proximity’ liquid layer. The model has been applied to various systems and proved to be extremely effective. Also, the model was able to describe reversible ion exchange.

A Method To Predict Equilibrium Conditions of Gas Hydrate Formation in Porous Media

A predictive model has been developed to determine the incipient hydrate formation conditions in porous media. The only additional information that is needed to determine the incipient hydrate formation conditions is the pore radius, surface energy per unit area, and wetting angle. It was found that the model performed well in predicting the experimental data of Handa and Stupin (J. Phys. Chem. 1992, 96, 8599).

Techniques for Estimating the Vapor‐Liquid Equilibrium of Sugar Solutions

AbstractA number of options for the mathematical prediction of sugar solution boiling points and corresponding equilibrium pressures and concentrations have been examined. Existing methods for this purpose have been found inadequate in that they can predict equilibrium conditions accurately only over a small concentration range, and usually only for pure sucrose solutions. Simple statistical techniques either fit such data poorly, or result in equations that are unreliable when extended beyond the concentrations or pressures over which the data were fit. In this work, general thermodynamically consistent equations have been applied to the prediction of boiling points of pure sucrose solutions, corn syrup, or mixtures of the two; valid over the entire concentration range of soluble solids, and at varying pressures.

A generalized model for predicting equilibrium conditions for gas hydrates

AbstractA modification of van der Waals and Platteeuw's (1959) hydrate equilibrium model which incorporates the effect of spherical asymmetry is developed. A corresponding states correlation is used to predict the deviation of Langmuir constants from ideal values. In this model the Kihara parameters obtained from hydrate equilibrium data agree well with those obtained from virial coefficient data.

Isotope and solvent effects of deuterium on aconitase

The activity of aconitase has been compared in H 2O and in 99% D 2O, with deuteriocitrate and deuterioisocitrate as well as the protiated substrates, citrate, isocitrate, and aconitate. The rates of all six interconversions were markedly inhibited by D 2O; the conversion of aconitate to citrate was affected much more than the conversion of aconitate to isocitrate. The values obtained for Michaelis constants and maximum velocities satisfactorily predict equilibrium conditions in H 2O and D 2O. Negligible isotope effects were observed with deuteriocitrate or deuterioisocitrate; this observation is consistent with the hypothesis that the first (and rate-limiting) step in the dehydration of these compounds is the rupture of the CO rather than the CH bond.