Ki-Pung Yoo

An approximate nonrandom lattice theory of fluids: General derivation and application to pure fluids

Abstract A new equation of state was derived based on the nonrandom lattice fluid theory. By expanding the Helmholtz free energy from the full Guggenheim combinatory with vacant sites around the reference athermal solution an approximate and explicit form was obtained. The model was tested for its applicability and parameters for 211 pure fluids were presented. It was found that the model describes quantitatively the P-σ-T property above critical point the saturated density, the vapor pressure, and the heat of vaporization of various molecularly complex fluids with only two temperature dependent molecular parameters for each pure fluid. The structure of the formalism for pure fluids can be readily extended to multicomponent mixtures.

An Approximate Nonrandom Lattice Theory of Fluids: Mixtures

Abstract A new approximate nonrandom lattice fluid model was derived and applied to pure fluids in the previous paper[You et al., 1993a] in which an explicit expression for thermodynamic properties were obtained by expanding Helmholtz free energy and the nonrandomness factor around the reference athermal solution. In this work, the model was extended to mixtures and applied to density to equilibria of vapor-liquid vapor-solid and liquid-liquid phases to multiphase equilibria including UCST behaviors and to heat of mixing for nonpolar/nonpolar nonpolar/polar and polar/polar binary mixtures of simple and complex molecules. With two parameters for pure components and one binary interaction energy parameter results obtained to date demonstrated that the mixture theory is quantitatively applicable to a wide range of temperature pressure and density.

Supercritical fluid extraction and liquid chromatographic-electrospray mass spectrometric analysis of stevioside fromStevia rebaudiana leaves

SummaryOptimal conditions were developed for the HPLC-ESI-MS and supercritical fluid extraction of stevioside fromStevia rebaudiana leaves. In the HPLC-ESI-MS of this compound, the negative ion mode showed higher sensitivity than both UV and the positive ion mode. In developing an alternative extraction method for stevioside using SFE, the effect of temperature, pressure, and percentage of modifier was evaluated on the extraction yield. Although sufficient extractability was not obtained by pure CO2 under any conditions of temperature and pressure, the addition of a modifier dramatically improved the extraction yield of stevioside, making it comparable to organic solvent extraction. Among the modifiers evaluated, the mixture of methanol and water showed greater extraction efficiency than the others. The extraction yield by CO2-methanol-water (80:16:4) was found to be 150% of conventional organic extraction. In addition to improving the extraction yield, SFE obviously provided a higher purity of stevioside in the final extract.

A nonrandom lattice fluid hydrogen bonding theory for phase equilibria of associating systems

Abstract The Veytsman statistics for hydrogen bonding (HB) contribution is combined with the nonrandom lattice fluid (NLF) model developed recently by the present authors. The physical contribution is characterized by two temperature dependent molecular parameters representing molecular size and interaction energy for a pure fluid, and a binary interaction parameter for a binary mixture. The chemical part is represented by internal energy and entropy of HB. The resulting NLF-HB equation of state was applied to describe thermodynamic properties of pure fluids and phase equilibrium of mixtures. The results for alkane–alcohol mixtures showed significant improvements over those of the NLF EOS (equation of state) and HM (hole quasichemical group-contribution) model.

MODELING OF SOYBEAN OIL BED EXTRACTION WITH SUPERCRITICAL CARBON DIOXIDE

Dry-milled soybeans are extracted with supercritical carbon dioxide at pressures 270 to 375 atm, temperature 50 to 70‡C, solvent flow rates 0.025 to 0016 cm/sec as a linear velocity in the bed-at supercritical state, and three types of soybean particle size in the range 0.05 to 0.2828 cm.Under these conditions, extraction rates of soybean oil from solid substrates in a fixed bed (1.1 mm I.D. x 200 mm Height) have been determined.The extraction rates were constant during the initial extraction period where the film resistance controls the rates, and then, the rales shifted to time-dependent diffusion controlling mass transfer mode. To correlate these features, mass transfer calculations were carried our for the constant rate period and the subsequent unsteady mass transfer rate period, respectively.

Development and Current Status of the Korea Thermophysical Properties Databank (KDB)

Physical property data, phase equilibrium data, and predictive models are essential parts of process design and operation. With the support of the Ministry of Commerce, Industry and Energy (MOCIE) of Korea, four universities collaborated to develop a thermophysical property databank and to obtain experimental data. In this paper topics related to the development and use of the thermophysical properties and phase equilibrium database are discussed. The databank contains about 4000 pure components and 5000 phase equilibrium data sets. Most of the data were collected along with the experimental uncertainties. Various estimation methods and thermodynamic models were included to calculate properties and phase equilibria. Data can be searched for with a stand-alone program or using an Internet web site. The current status and future prospects of the KDB (Korean Thermophysical Properties Databank) are discussed.

Distortions in Z-scan spectroscopy

The sample imperfection induced distortions in the closed Z-scan curve are analyzed. It is found that both the magnitudes of the peak and valley transmittances and the shape of the curve are distorted significantly by the inhomogeneous thickness, the nonuniform nonlinearity, and the curved surfaces of the sample. The results suggest that the I-scan method is a more practical choice for the measurement of the third-order nonlinear susceptibility of an inhomogeneous sample.

Strategies for supercritical fluid extraction of hyoscyamine and scopolamine salts using basified modifiers.

The supercritical fluid extraction behaviors of hyoscyamine and scopolamine were investigated and found to be highly dependent upon the chemical nature of the compounds. Free bases of hyoscyamine and scopolamine were freely soluble in supercritical CO2 with increasing temperature and pressure; however, the salts of these alkaloids were not soluble under any experimental conditions. It was found that alkaline modifiers such as methanol basified with diethylamine could enhance the solubilities and extraction yields of these alkaloids from plant matrices as compared to other modifiers.

Measurement of activities of solvents in binary polymer solutions

Abstract Vapor liquid equilibrium data of nine binary solvent+polymer systems were measured by a vacuum electro-microbalance cell. Tested solvents were n -heptane, n -octane, n -nonane, methanol, ethanol, n -propanol and water. Polymers were poly (dimethylsiloxane, M n : 26,000), poly (propylene oxide, M n : 2000) and poly (ethylene glycol, M n : 600). Data obtained in the present study together with existing literature data were correlated by UNIQUAC model. Reliability of the experimental apparatus and the data was discussed.

Modeling of supercritical-fluid phase-equilibria using a new nonrandom lattice-fluid theory

Abstract Experimental data for equilibrium solubility of biochemical substances such as stearic acid, oleic acid, triolein, and tristearin in supercritical carbon dioxide are measured. The experimental data and others in the literature are modeled by a newly formulated nonrandom lattice-fluid theory equation-of-state. The model is rigorously tested for its applicability to model supercritical-fluid phase-equilibria using a single binary interaction parameter for systems containing molecules of arbitrary size and shape of SCF-liquid equilibria for 27 binary systems, SCF-solid equilibria for 16 binary systems, SCF-polymer equilibria for 4 systems, and of 6 ternary mixtures for a wide range of temperature and pressure.