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Equilibrium Solubility (equilibrium + solubility)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Modeling of polycyclic aromatic hydrocarbon SLE in aromatic solvents

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010
Thenmozhi Muthukumarasamy
Abstract Equilibrium solubilities of polycyclic aromatic hydrocarbon (PAH) solutes naphthalene, fluorene, acenaphthalene, fluoranthene, anthracene, phenanthrene, pyrene, chrysene and triphenylene in benzene and substituted benzene solvents are predicted using the Dortmund-AU model. The Dortmund-AU method performs better than the UNIFAC and modified UNIFAC (Dortmund) models when applied to PAH in benzene systems, but the accuracy of predictions deteriorates in the case of PAHs that have melting points greater than 380 K. Accounting for the heat capacity change on melting term makes considerable difference to the ideal solubility calculation in the case of higher-melting PAHs. A new term is added to the residual part of activity coefficient in the UNIFAC model to derive a modified empirical version. Application of this model to PAH solid,liquid equilibria is verified and the results are compared with those of Dortmund-AU model. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Miniaturization of Powder Dissolution Measurement and Estimation of Particle Size

CHEMISTRY & BIODIVERSITY, Issue 11 2009
Alex Avdeef
Abstract The objective was to investigate the applicability and limitations of an approach for estimating particle size from powder dissolution measurement using as little as 50,,g of sample in 1,ml of buffer solutions. The powder dissolution profiles of five sparingly-soluble drugs (hydrochlorothiazide, phenazopyridine hydrochloride, 2-naphthoic acid, indomethacin, and dipyridamole) were evaluated with a novel biexponential spherical particle equation and also the Wang,Flanagan spherical particle non-sink equation. The results were compared to particle sizing based on measured specific surface area by the Brunauer,Emmett,Teller (BET) method, and also based on Coulter counting. With the exception of hydrochlorothiazide, the model compounds indicated some agglomeration in the dissolution media. The dry-state specific surface area was larger than expected from either the Coulter method or the powder-dissolution data, especially for phenazopyridine hydrochloride. The particle radii estimated by the powder dissolution method ranged from 10 to 68,,m, with equilibrium solubilities spanning from 5,,g/ml (dipyridamole) to 911,,g/ml (hydrochlorothiazide). Powder dissolution data collected with the miniaturized apparatus can be used to determine particle size, with estimated values agreeing reasonably with those measured by the Coulter counter method. [source]

Analysis of supersaturation and nucleation in a moving solution droplet with flowing supercritical carbon dioxide

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2005
Mamata Mukhopadhyay
Abstract A supercritical antisolvent (SAS) process is employed for production of solid nanoparticles from atomized droplets of dilute solution in a flowing supercritical carbon dioxide (SC CO2) stream by attaining extremely high, very rapid, and uniform supersaturation. This is facilitated by a two-way mass transfer of CO2 and solvent, to and from the droplet respectively, rendering rapid reduction in equilibrium solubility of the solid solute in the ternary solution. The present work analyses the degree of supersaturation and nucleation kinetics in a single droplet of cholesterol solution in acetone during its flight in a flowing SC CO2 stream. Both temperature and composition are assumed to be uniform within the droplet, and their variations with time are calculated by balancing the heat and mass transfer fluxes to and from the droplet. The equilibrium solubility of cholesterol with CO2 dissolution has been predicted as being directly proportional to the Partial Molar Volume Fraction (PMVF) of acetone in the binary (CO2,acetone) system. The degree of supersaturation has been simulated up to the time required to attain almost zero cholesterol solubility in the droplet for evaluating the rate of nucleation and the size of the stable critical nuclei formed. The effects of process parameters have been analysed in the pressure range of 7.1,35.0 MPa, temperature range of 313,333 K, SC CO2 flow rate of 0.1136,1.136 mol s,1, the ratio of the volumetric flow rates of CO2 -to-solution in the range of 100,1000, and the initial mole fraction of cholesterol in acetone solution in the range of 0.0025,0.010. The results confirm an extremely high and rapid increase in degree of supersaturation, very high nucleation rates and stable critical nucleus diameter of the order of a nanometre. Copyright © 2005 Society of Chemical Industry [source]

Effect of die temperature on the morphology of microcellular foams

POLYMER ENGINEERING & SCIENCE, Issue 6 2003
Xiangmin Han
A study on the extrusion of microcellular polystyrene foams at different foaming temperatures was carried out using CO2 as the foaming agent. The contraction flow in the extrusion die was simulated with FLUENT computational fluid dynamics code at two temperatures (150°C and 175°C) to predict pressure and temperature profiles in the die. The location of nucleation onset was determined based on the pressure profile and equilibrium solubility. The relative importance of pressure and temperature in determining the nucleation rate was compared using calculations based on classical homogeneous nucleation theory. Experimentally, the effects of die temperature (i.e., the foaming temperature) on the pressure profile in the die, cell size, cell density, and cell morphology were investigated at different screw rotation speeds (10 , 30 rpm). Experimental results were compared with simulations to gain insight into the foaming process. Although the foaming temperature was found to be less significant than the pressure drop or the pressure drop rate in deciding the cell size and cell density, it affects the cell morphology dramatically. Open and closed cell structures can be generated by changing the foaming temperature. Microcellular foams of PS (with cell sizes smaller than 10 ,m and cell densities greater than 10 cells/cm3) are created experimentally when the die temperature is 160°C, the pressure drop through the die is greater than 16 MPa, and the pressure drop rate is higher than 109 Pa/sec. [source]