Extraction equilibria of penicillin G in four different types of organic solvent systems

Equilibrium experiments for physical and reactive extraction of penicillin G were carried out with varying pH, overall penicillin concentration and overall amine concentration in liquid–liquid extraction systems with four different types of organic solvents, i.e. amphiprotic solvent, hydrogen-bond donor solvent, hydrogen-bond acceptor solvent, and nonpolar organic solvent. Also, physical and reactive extraction equilibrium models were suggested to find the appropriate equilibrium model for each organic solvent type. By comparison between the experimental data and the calculated results from the extraction equilibrium models, the most probable physical and reactive extraction equilibrium models were determined. The physical extraction equilibrium models for all types of the organic solvents except for nonpolar organic solvent reflected solute–solvent interaction, while the reactive extraction equilibrium models were dependent on the organic solvent type.     

A neural network approach to predict activity coefficients

Artificial neural networks (ANNs) and a group‐contribution approach were used to develop an algorithm to predict activity coefficients for binary solutions. The Levenberg–Marquardt algorithm was used to train the ANN and to predict the parameters of the Margules equation. The ANN was trained using phase‐equilibrium database from DECHEMA. The selected systems include alcohols, phenols, aldehydes, ketones, and ethers. The trim mean based on 20% data elimination was selected as the best representation of the Margules‐equation parameters. The algorithm was validated with 121 VLE systems and results show that the ANN provides a relative improvement over the UNIFAC method.     

Enthalpy of absorption of CO2 with alkanolamine solutions predicted from reaction equilibrium constants

Differential enthalpies of absorption of CO₂ in aqueous solutions of 2-aminoethanol (MEA) and N-methyldiethanolamine were predicted from reaction equilibrium constants using the Gibbs-Helmholtz equation. Correlations for the reaction equilibrium constants and enthalpies of reaction found in the literature for each of the individual reactions taking place at CO₂ absorption were compared to experimental data, and from this, a set of equations was selected for the Deshmukh-Mather model in this work. The carbamate dissociation constant for MEA was fitted to experimental P_CO2 and ΔH_abs data. Heat contributions from each of the individual reactions taking place in the systems MEA+H₂O+CO₂ and MDEA+H₂O+CO₂ were calculated and presented as functions of loading and temperature. Predicted enthalpies of absorption agree well with the data from literature and with experimental data from this work. The calculation procedure described in this work may be used for the adjustment of reaction equilibrium constants by fitting the equilibrium model also to experimentally measured heats of absorption data in addition to P_CO2 data.     

VLE calculation of carbon dioxide+n-alkanes binary mixtures with MHV2 mixing rule

Vapor-liquid equilibria for binary and asymetric systems include carbon dioxide+C₁-C₈, C₁₀ are calculated by using the Peng-Robinson-Stryjek-Vera equation of state coupled with the modified MHV2 mixing rule. The modified UNIFAC model is used for determining activity coefficient and excess Gibbs free energy. Calculated equilibrium pressures and mole fractions in vapor phase are compared with the experimental data. The average absolute deviation percent (AAD%)s indicates that the error involved in the application of the MHV2 mixing rule by optimized q₁ and q₂ is less than WS and PRSK mixing rules in most cases.     

Melting temperature depression for low ether content polyether-polyester block copolymers with amide linkages

Melting behavior of a series of polyether-polyester block copolymers with low ether contents was studied. Significant melting-reorganization-remelting was suggested by means of differential scanning calorimetry. The equilibrium melting temperature of the copolymers was obtained by using the Hoffman-Weeks extrapolation. It has been found that the use of the on-set melting temperature for the Hoffman-Weeks plots is less reliable than the use of the corrected peak melting temperature. Copolymerization of polyetheramides with polyesters leads to a significant melting temperature suppression for the polyester crystal. We hypothesize that the locations of the junction points between blocks can be treated as chain ends for the crystallizable polyester blocks: the polyether-polyesters grow to form extended chain-like crystals with lamellar thickness limited by the polyester block length. For comparison, the nonlinear Hoffman-Weeks treatment, recently proposed by Marand, has also been applied to examine the behavior of melting temperature depression. Although the T _m ^o obtained from nonlinear extrapolation is much higher than the T _m ^o obtained from the Hoffman-Weeks extrapolation, similar trend regarding the composition dependence of T _m ^o have been found.     

On the importance of equilibrium in studies on the transport of hydrogen in metals

In this paper, specific properties of the metal-hydrogen systems, M-H's, and bulk metal-hydrogen solids, MH_n's, are reviewed, with an emphasis of problems related to reaching the equilibrium and its confinements. In MH_n's the chemical potential of interstitial H species is determined both by its concentration and the self-stress of the metal matrix, these being in a feedback relation. Consequently, the transport of hydrogen in metals is non-Fickian. This imposes special requirements on the studies of this transport. For determining its kinetic parameters, not only should the experiments be initiated at equilibrium in the system under study, as in the case of studies of Fickian transport, but the experiments themselves must also be performed close to equilibrium. Accordingly, the recently proposed transfer function spectroscopy at quasi-equilibrium has to be considered as the only technique making possible a reliable estimation of the kinetic parameters of this transport: not only the diffusion coefficient of hydrogen, but also the bulk elastic modulus of MH_n. The properties of various transfer functions are compared and the usefulness of specimens of different shapes are discussed.     

The GRAINS thermodynamic and kinetic code for modeling nebular condensation

The GRAINS thermodynamic and kinetic code for modeling condensation and grain growth in the solar nebula is described. The code calculates CWPI-type (Condensation With Partial Isolation) equilibrium partitioning of 33 chemical elements among 242 gaseous and 520 condensed phases, and growth in the nebula of metal and olivine grains by condensation from the nebular gas accompanied by diffusional redistribution of major and trace elements in those grains. Several examples of the GRAINS application to cosmochemical problems are briefly discussed.     

Drift-free magnetic equilibrium reconstruction using the response to plasma position modulation

Inductive magnetic sensors are widely used for plasma equilibrium reconstruction and control. However, their measurements involve electronic integration and can therefore experience drift leading to inaccurate plasma positioning. For this reason, we have studied an original drift-free approach to estimate the plasma equilibrium. The principle of this correction is based on modulation of the plasma position and current at three independent frequencies and analysing the modulated magnetic signals to provide additional estimation on the equilibrium. Using a plasma model based on current wires, the accuracy of such a method is assessed for Tore Supra in terms of the signal to noise ratio. The plasma position is recovered within a precision of 5 mm for a signal to noise ratio better than 80 dB. Applying our approach to dedicated experiments performed on the Tore Supra tokamak, we confirm the quality of the result and find that we can estimate the radial and vertical positions of the plasma to 1 mm with a one standard deviation confidence interval.     

DESORPTION ISOTHERMS AND DRYING CHARACTERISTICS OF SHRIMP IN SUPERHEATED STEAM AND HOT AIR

Desorption isotherms for shrimp were determined at the temperatures of 50, 60, 70 and 80°C. Amongst the moisture equilibrium predictions between the BET and GAB models, the latter has a better predictable capability. The GAB parameters are correlated with the temperatures by the Arrhenius expression. Drying characteristics of shrimp in drying media at the temperature range of 120-180°C for superheated steam and of 70-140°C for hot air have been examined. Drying rate and effective diffusion coefficient are used to quantify quantitatively the difference between the superheated steam and the hot air dryings. The temperature is more important effect on drying rate and effective diffusion coefficient in the superheated steam than in the hot air. Inversion temperature exists between 140 and 150°C. Comparing to the hot air, the shrimp dried by the superheated steam shows a lower degree of shrimp shrinkage. In addition, product colours are slightly different to those from the commercial sources.     

Canonical form and mathematical interpretation of electrolyte solution systems

We describe a canonical form of electrolyte solution systems for the mathematical interpretation of solidliquid equilibrium. The canonical form is obtained from the analysis of the algebraic structure of electrolyte solution systems and the Karush-Kuhn-Tucker (KKT) conditions for the minimization of the total Gibbs free energy. As a result, the mathematical role of solid species in the solid-liquid equilibrium problem is explained as a Lagrange multiplier of a sort of the linearly constrained optimization problem. This finding will add to the development of an efficient numerical algorithm for the simulation of electrolyte solution systems. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.