H. Inomata

Swelling behaviours of N-alkylacrylamide gels in water: effects of copolymerization and crosslinking density

N-isopropylacrylamide (NIPA)/N-n-propylacrylamide (NNPA) copolymer gels of various molar ratios were prepared by radical polymerization and the relationship between the swelling behaviour of the gels and the copolymerization ratio was studied experimentally. The effect of a crosslinking point on the swelling behaviour of the NIPA gels was investigated by preparing the gels with various crosslinking densities. The results of our experiments revealed that the transition temperatures of the NIPA/NNPA copolymer gels were changed in proportion to the monomer ratio used in copolymerization and that the crosslinking density strongly affected the swelling ratios but not the transition temperatures of the gels.

Phase Behavior and Reaction of Nylon 6/6 in Water at High Temperatures and Pressures

The phase behavior and reaction of nylon 6/6 in water were studied with a diamond anvil cell (DAC) technique and visual microscopy. Nylon 6/6 concentrations in water and cell temperatures were varied from 11 to 46% and from 264 to 425°C, respectively. The pressures studied ranged from 30 to 900 MPa. When an aqueous solution of 27% nylon 6/6 was rapidly heated (2.6°C/s) to 372°C at 30 MPa, the solution became homogeneous at 331°C. Upon cooling, the final pressure was 30 MPa and both particles and gas were observed. Analysis of the particles by Raman indicated decomposed nylon 6/6 solid. When an aqueous solution of 31% nylon 6/6 was rapidly heated (2.9°C/s) to 425°C at 58 MPa, the solution became homogeneous at 323°C. Upon cooling, the final pressure was 143 MPa, and, remarkably, only a second liquid precipitated and no gas or solids were observed. From the experiments, we concluded that the reaction pathways are completely different between the subcritical and supercritical water conditions. For the case of subcritical conditions, the final products were solid particles having a nylon character along with a considerable amount of gas. At supercritical water conditions, the final products were liquids having little nylon character and no gas. Experiments were performed at a constant temperature of 272°C at initial pressures ranging from 87 to 400 MPa. As the reaction proceeded, the pressure was measured at 30-s intervals. At average pressures less than 300 MPa, the nylon 6/6 samples melted and appeared to become homogeneous. At average pressures higher than 520 MPa, the nylon 6/6 samples remained heterogeneous. From these results, the rate of hydrolysis was concluded to increase with pressure. The reaction volume was found to be −21.1 cm3/mol, which can be explained by the overall formation of water-soluble products.

Energy analysis of supercritical carbon dioxide extraction processes

Abstract Supercritical fluids are being used to develop new extraction and cleaning systems. In this work, common cycles used in extraction cycles are analyzed in detail with respect to energy requirements and exergy losses. First, cycles that operate between the saturation region and supercritical region are considered. From the exergy analysis for pump cycles, it can be seen that there is an optimum extraction pressure that provides a minimum in exergy loss for a given extraction temperature and separation pressure. The minimum exergy losses are described by parametric equations in terms of extraction temperature, pressure and separation pressure. A similar set of equations is provided in terms of extraction temperature, density and separation pressure. Compressor cycles are also analyzed and it was found that selection between pump and compressor cycles can be made by determination of equal exergy loss points. These points are presented graphically and also in terms of parametric equations for extraction pressure or extraction density in terms of extraction temperature and separation pressure. Cycles that operate solely in the supercritical region were studied. The cycle proposed by de Swaan Arons (4th International Symposium on Supercritical Fluids, May 11–15, 1997, Japan) was found to provide very low exergy losses for a given change in extraction and separation density. It was also found that, while supercritical region cycles can provide lower exergy losses than cycles operating between the saturation and supercritical region, for some cases of high density difference, pump or compressor cycles can be competitive with the supercritical region cycles.

Vaporliquid equilibria for CO2/hydrocarbon mixtures at elevated temperatures and pressures

Vaporliquid equilibrium data were obtained for CO2/benzene/tetralin and CO2/n-decane/tetralin systems in the temperature range from 340 to 520 K at several pressures up to 15 MPa using a flow type apparatus and the binary CO2/benzene system at 343 – 414 K and 2.3 – 15.4 MPa. An attempt was made to predict the vaporliquid equilibria for the above ternary mixtures using new extended mixing rules and a corresponding states principle. Calculation results have shown that the experimental tie lines can be well predicted with the present method although the conjugate lines are not satisfactory.

Measurement of vapor-liquid equilibria at elevated temperatures and pressures using a flow type apparatus

Abstract Vapor-liquid equilibrium data were obtained for CO 2 -n-heptane, CO 2 -n-decane, CO 2 -trans-decalin, CO 2 -tetralin, CO 2 -quinoline, benzene-tetralin and benzene-quinoline systems in the temperature range from 340 to 710 K at several pressures up to 25 MPa. A flow-type apparatus was developed and used for vapor-liquid equilibrium measurements in order to reduce the residence time of heat sensitive substances at high temperatures. The operation of the present apparatus was easy and improved by employing an overflow type self-control system equipped with a back pressure regulator. The reliability of this experimental apparatus and procedure was proven since the vapor-liquid equilibrium data for the CO 2 -n-heptane system were in good agreement with literature data and the vapor and liquid phase compositions were independent of the sample flow rate within the range of flow rate employed. Measured data were correlated using equations of state and mixing rules based on the corresponding state principle.

Measurement and prediction of phase equilibria for the CO2-ethanol-water system

Abstract In relation to the concentration of ethanol solution from fermentation using near- or super-critical CO 2 extraction, vapor-liquid equilibria for the CO 2 -Ethanol-Water system were measured at 9.6, 17.2, 19.6, 25.0 and 32.0 °C up to 9 MPa in the wide range of ethanol concentration, including very dilute region (0.1–5wt%), where no data have been reported. A flow type apparatus equipped with a back pressure regulator was adopted for measurements in order to maintain the feed composition. From our experimental results, we concluded that, 1. 1) There are certain T and P conditions which give a maximum separation factor. 2. 2) In the low concentration region of ethanol, the distribution coefficient of ethanol is about 213 of the value in the higher ethanol concentration region. The measured data were compared with the results predicted by Patel-Teja equation and Group-Contribution equations of state (GC-EOS).

Application of liquid crystal theory to the estimation of mesophase pitch phase-transition behavior

The molecular field treatment developed for analysis of phase equilibria of meson-nonmesogen liquid crystal mixtures was applied to a quantitative description of the phase transition behavior of mesophase pitches, which were prepared by mixing a benzene-soluble fraction with a benzene-insoluble fraction of coal-tar pitch. The result showed that such a simplified theoretical treatment can be used to describe a phase diagram for a mesophase pitch.

Measurement of osmotic pressure in aqueous solutions of poly(ethylene glycol) and poly(N-isopropylacrylamide)

Abstract Nagahama K., Inomata H. and Saito S., 1994. Measurement of osmotic pressure in aqueous solutions of poly(ethylene glycol) and poly( N -isopropylacrylamide). Fluid Phase Equilibria , 96: 203-214 The osmotic pressure of aqueous solutions of poly(ethylene glycol) (PEG) and poly( N -isopropylacrylamide) (PNIPA) was measured over the temperature range from 5 to 35°C at concentrations from 0.5 to 2.5 wt.%. It was found that the mixing enthalpy Δ h and mixing entropy Δ s of water, which were determined from the temperature dependence of the osmotic pressure, were negative and that the magnitude of δ h was slightly larger than that of TΔs . This indicated that the dissolution of the polymers in water was dominated by enthalpy or intermolecular interaction. The existence of local structure in the solution was revealed by a negative entropy. Virial coefficients were determined from the concentration dependence of the osmotic pressure. The second virial coefficient of PEG aqueous solution increased linearly with a decrease in temperature, while that of PNIPA aqueous solution had a maximum around 15°C, and suggested the existence of two θ temperatures. The third virial coefficient of PNIPA aqueous solution increased at lower temperatures. The osmotic pressure data were correlated with the lattice model proposed by Prange et al. (Prange M.M., Hooper H.H. and Prausnitz J.M., 1989. AIChE J., 35: 803).

New equation of state based on the significant structure model

Abstract A new non-cubic equation of state based on molecular thermodynamics has been developed by considering cell theory and forming the potential energy of a system from the volumetric average of the van der Waals type and the 15-6 Mie type potential energies. The proposed equation has four constants and requires knowledge of the critical temperature, the critical pressure, the critical volume, the excluded volume and an additional parameter to characterize any given fluid. The new equation yields good agreement with experimental saturation properties of 29 non-polar and 16 polar substances from reduced temperatures of 0.5 to the critical temperature. The new equation exactly fits the critical point, generally gives better predictions of liquid volumes than, and predictions of vapor pressures and heats of vaporization equally as good as commonly used cubic equations, and yet only requires two fitting parameters.

The significant structure model equation of state extended to mixtures

Abstract Our previously proposed equation of state has been extended to mixtures. The new mixing rule requires only one binary parameter and combines two types of mixing rules: a classical mixing rule for the infinitely dilute density region, and a local mole fraction mixing rule for the no free volume region. The new mixing rule yields good agreement with experimental PVT properties of polar binary systems which contain CO 2 , H 2 O, MeOH and EtOH.