Hidenori Higashi

Solubilities and diffusion coefficients of high boiling compounds in supercritical carbon dioxide

Abstract A brief introduction of the data sources and the applications of correlation methods for the solubilities and diffusion coefficients of high-boiling compounds (mainly in solid state) in supercritical carbon dioxide are reviewed. Empirical equations, equations of state, solution models, and the Monte Carlo simulation for the calculation of solubilities in supercritical carbon dioxide are discussed. The application of empirical equation based on the Stokes–Einstein model, rough hard sphere theory, Schmidt number correlation, and molecular dynamics simulation for the calculation of diffusion coefficients in supercritical carbon dioxide at infinite dilution condition are reviewed. Further, the application of the Darken equation and the Leffler and Cullinan equation for the calculation of concentration dependence of diffusion coefficients in supercritical carbon dioxide is presented.

Correlation of diffusion coefficients for naphthalene and dimethylnaphthalene isomers in supercritical carbon dioxide

An equation proposed by Darken, including the thermodynamic factor and tracer diffusion coefficients of solvent and solute, was adopted to correlate the diffusion coefficients for naphthalene and dimethylnaphthalene (DMN) isomers in supercritical carbon dioxide and the correlated results were compared with the experimental data. IML equation of state with mixing rules and combining rules containing two adjustable interaction parameters were used for calculation of the thermodynamic factor. By using the interaction parameters adjusted to the solubility data, the concentration dependence of diffusion coefficients and their anomaly near the critical point of carbon dioxide can be quantitatively represented. In order to improve the reliability of experimental results, some re-measured diffusion coefficient data for naphthalene, 2,6- and 2,7-DMN at 308.2 K, and new data for naphthalene at 318.2 K and for 2,3-DMN at 308.2 K are presented.

Molecular dynamics simulation of diffusion coefficients of naphthalene and 2-naphthol in supercritical carbon dioxide

NVT ensemble molecular dynamics simulation has been applied to calculate the diffusion coefficients of naphthalene and 2-naphthol in supercritical carbon dioxide in the pressure range from 8 to 40 MPa under infinite dilution conditions. The Lennard-Jones (12-6) potential function was used as the intermolecular potential. The calculation results showed good agreement with the experimental values, by using the intermolecular interaction parameters between unlike molecules which were determined by Monte Carlo simulation to give good representation for the solubilities of naphthalene and 2-naphthol in supercritical carbon dioxide.

Diffusion coefficients of naphthalene and dimethylnaphthalene in supercritical carbon dioxide

Abstract A new experimental apparatus based on a pseudo-steady state solid dissolution method has been designed to measure the diffusion coefficients of supercritical carbon dioxide(1)-naphthalene(2) and supercritical carbon dioxide(1)-dimethylnaphthalene isomers(2) systems. The diffusion coefficients were measured at 308.2 K. In order to establish the validity of this method and the performance of the apparatus, the experimental results of the diffusion coefficients of naphthalene in supercritical carbon dioxide were compared with the literature data measured by other methods. The decrease of diffusion coefficient of naphthalene was observed near the critical point of carbon dioxide. The diffusion coefficients of 2,6-dimethylnaphthalene (2,6-DMN) and 2,7-dimethylnaphthalene (2,7-DMN) show almost the same values. The diffusion coefficients of these isomers are about 10% lower than those of naphthalene.

Development of a solution model to correlate solubilities of inorganic compounds in water vapor under high temperatures and pressures

Abstract A solution model, based on the regular solution theory coupled with Flory-Huggins entropy term, was developed for the calculation of solubilities of inorganic compounds in water vapor under high temperatures and pressures. The solubilities of sodium chloride (NaCl), potassium hydroxide (KOH), sodium sulfate (Na 2 SO 4 ), lead oxide (PbO), silicon oxide (SiO 2 ), lithium nitrate (LiNO 3 ), sodium nitrate (NaNO 3 ) and potassium nitrate (KNO 3 ) were correlated by optimizing internal energies and molar volumes of inorganic compounds which give their solubility parameters.

Calculation of diffusion coefficient for supercritical carbon dioxide and carbon dioxide+naphthalene system by molecular dynamics simulation using EPM2 model

NVT ensemble molecular dynamics (MD) simulation has been applied to calculate the self-diffusion coefficients of carbon dioxide and the tracer diffusion coefficients of naphthalene in supercritical carbon dioxide. The simulation was carried out in the pressure range from 8 to 40 MPa. The elementary physical model proposed by Harris and Yung was adopted for carbon dioxide and some approximation models were used for naphthalene. The systems of MD simulation for carbon dioxide consist of 256 particles. One naphthalene molecule was added for carbon dioxide+naphthalene system. The system can be assumed to be an infinite dilution condition for carbon dioxide+naphthalene system and the mutual diffusion coefficients are equal to the tracer diffusion coefficients of naphthalene. The self-diffusion coefficients of carbon dioxide and the tracer diffusion coefficients of naphthalene in supercritical carbon dioxide can be calculated by mean square displacement. The calculated results of diffusion coefficients showed good agreement with the experimental data without adjustable parameters.

Molecular dynamics simulation of fluorination effect for solvation of trifluoromethylbenzoic acid isomers in supercritical carbon dioxide

A molecular dynamics (MD) simulation was applied to carbon dioxide+trifluoromethylbenzoic acid isomer and carbon dioxide+methylbenzoic acid isomer systems to investigate the interactions between carbon dioxide and the solutes. The pair correlation functions between the carbon dioxide and trifluoromethyl group or methyl group in the solutes were calculated to study the fluorination effect of solvation. As a result, it was found that the interactions between carbon dioxide and trifluoromethyl group in trifluoromethylbenzoic acid isomers were stronger than those between carbon dioxide and the methyl group in methylbenzoic acid isomers. The simulation results had the same tendency as the experimental solubility enhancements and coincided with the trend of the interaction parameters of the Peng-Robinson equation of state that were determined from the solubility data.

Concentration dependence of diffusion coefficients for supercritical carbon dioxide + naphthalene system

The concentration dependence of diffusion coefficients for naphthalene in supercritical carbon dioxide at 308.2 K was measured by a pseudo steady-state solid dissolution method. The experimental diffusion coefficients were compared with the calculated results by the Darken equation including a thermodynamic factor and tracer diffusion coefficients of supercritical carbon dioxide and naphthalene. The thermodynamic factor in the Darken equation was determined by using several cubic equations of state. The calculated results by the Darken equation represent the concentration dependence of the experimental diffusion coefficients.

Effect of Nucleation Temperature on Detecting Molecular Ions and Charged Nanoparticles with a Diethylene Glycol-Based Particle Size Magnifier

The classical nucleation theory predicts that a decrease in nucleation temperature under a constant saturation ratio increases the energy barrier for homogeneous nucleation to occur; therefore lower nucleation temperature would allow higher saturation ratio inside a condensation particle counter (CPC) while suppressing homogenous nucleation of working fluid vapor below a threshold value. On the other hand, the classical theory also predicts that a decrease in nucleation temperature increases the energy barrier for heterogeneous nucleation to occur, which potentially increases the minimum detectable size of CPC. Accordingly, it is important to investigate experimentally whether higher super-saturation under lower nucleation temperature decreases the minimum detectable size or not. Minimum detectable sizes of a diethylene glycol (DEG)-based nanoparticle size magnifier (nano-PSM) developed by Ito et al. (Ito, E., Seto, T., Otani, Y., and Sakurai, H. [2011]. Aerosol Sci. Technol. 45:1250–1259) were investigated at three different nucleation temperatures. Mobility standard molecular ions and mobility-classified silver nanoparticles were used as test aerosol particles. The vapor flux exiting from the evaporator in nano-PSM is accurately controlled using a syringe pump. The temperature of the mixing region and condenser in the nano-PSM is controlled at adiabatic mixing temperature, which we call its nucleation temperature. When the nucleation temperature was set at 16.7, 25.0, and 33.3°C, the minimum detectable mobility diameter values, which were defined at 50% value of counting efficiency curve, were 2.2, 2.9, and 3.0 nm, respectively, indicating that lower nucleation temperature is favorable for detecting smaller sized particles using DEG-based PSM or CPCs. Copyright 2015 American Association for Aerosol Research

Centrifugal Filter for Aerosol Collection

Air filters collect particles by the mechanical collection mechanisms, namely, inertia, interception, gravitational settling, and Brownian diffusion. There exists the most penetrating particle size (MPPS) in submicron size range for which none of the collection mechanisms work effectively. In this study, we propose a new type of filter named as “centrifugal filter,” which collects aerosol particles by centrifugal force together with the conventional mechanical collection mechanisms. The centrifugal filter proposed in the present work may be rotated by a motor or compressed air. Air passes through the filter in the axial direction of filter rotation. The filter rotates so does the air embedded in the filter, and therefore centrifugal force exerts on particles. In addition to the mechanical collection mechanisms, small migration of particles due to the centrifugal force enhanced the collection efficiency of submicron particles significantly without increasing the pressure drop. The performance tests of centrifugal filter were conducted by changing the fiber diameter, the air flow velocity and the rotation speed. We found that the collection efficiency of filter is enhanced significantly by rotating the filter without increasing the pressure drop and that the filter efficiency is well predicted by the conventional filtration theory accounting for the centrifugal force. Copyright 2015 American Association for Aerosol Research