1. Estimation of solid solubilities in supercritical carbon dioxide: Peng-Robinson adjustable binary parameters in the near critical regionMojca Škerget, Zorka Novak-Pintarič, Željko Knez, Zdravko Kravanja, 2002, original scientific article Abstract: The density dependence of the binary parameters of the Peng-Robinson equation of state in near the critical region was examined. Published solubility data of eight compounds in pure CO2 have been fitted to the Peng-Robinson equation in combination with one and two parameters van der Waals mixing rules and in combination with the three parameter density dependent mixing rule of Mohamed and Holder. A systematic study has been done to determine the influence of different terms in the mixing rules. In order to obtain density dependence, binary parameters were calculated for each isotherm at particular experimental point separately in the way to equalise experimental and calculated solubility data. The system was formulated as an equation-oriented model and solved by means of a nonlinear programming optimisation algorithm. For all compounds the binary interaction parameters thus obtained were found to vary strongly with pressure in the range from 75 bar to approximately 150 bar, i.e. near the critical end point (CEP) of the low temperature branch of the three phase solid-liquid-gas (SLG) curve. At higher pressures, the parameter is practically independent on pressure. In general, for the systems investigated, kij increases linearly with increasing density and reaches a constant value at higher densities in the range from 700 to 800 kg/m3, depending on the system under investigation.
Keywords: solid liquid equilibria, equation of state, mixing rules, binary parameters, near critical region, nonlinear programming, thermodynamic model, supercritical fluids, CO2, solubility
Published in DKUM: 01.06.2012; Views: 2331; Downloads: 120
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2. Phase equilibira of permethrin and dicofol with carbon dioxidePetra Kotnik, Amra Perva, Mojca Škerget, Željko Knez, 2005, original scientific article Abstract: The solubilities of pesticides (permethrin and dicofol) in CO2 were measured by a static-analytic method at pressures ranging from 10.0 MPa to 25.0 MPa andtemperatures of 293.2 K, 303.2 K, and 313.2 K. Due to the nonconventional shape of some solubility isotherms, solid-liquid transitions of pesticides under pressure of CO2 were determined using a modified capillary method. Sincethe solubilities depend on solvent density, the experimental binary solid-fluid equilibrium data were correlated as a function of solvent density by two different models.
Keywords: chemical processing, high pressure technology, CO2, pesticides, phase equilibria, solubility
Published in DKUM: 01.06.2012; Views: 2097; Downloads: 36
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3. Measurement of CO2 solubility and diffusivity in poly(L-lactide) and poly(D,L-lactide-co-glycolide) by magnetic suspension balanceElena Markočič, Mojca Škerget, Željko Knez, 2008, original scientific article Abstract: The solubility of supercritical carbon dioxide (scCO2) in poly(l-lactide) and poly(d,l-lactide-co-glycolide) at different temperatures (308, 313 and 323 K) and pressures (10-30 MPa) was measured using a magnetic suspension balance. The solubility data were also used for estimating the binary diffusion coefficients. The results show a good solubility of CO2 in both polymers: up to 43% in poly(l-lactide) and 30% in poly(d,l-lactide-co-glycolide). The diffusion coefficients have high values, which verify the liquid-like solvating properties of scCO2. The diffusion coefficient depends on the quantity of gas already absorbed by the polymer; its values decrease with increasing gas concentration.
Keywords: SC CO2, solubility, diffusivity, magnetic suspension balance
Published in DKUM: 31.05.2012; Views: 1892; Downloads: 107
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4. Phase equilibria of vanillins in compressed gasesŽeljko Knez, Mojca Škerget, Amra Perva, 2007, original scientific article Abstract: Solid-liquid phase transitions of vanillin, ethylvanillin, o-vanillin and o-ethylvanillin in compressed hydrocarbons (isobutane and propane), fluorinated hydrocarbons (R23, R134a and R236fa) and sulphur hexafluoride (SF6) were determined with a modified capillary method in a pressure range between 0.1 and 31.0 MPa. Equilibrium solubilities of vanillins in compressed fluorinated hydrocarbons were determined at temperatures 313.2 and 333.2 K and over a pressure range between 1.1 and 26.0 MPa with a static-analytic method. Experimental solubility data were correlated by a density-based Chrastil model. Results showed that phase equilibria of vanillins in investigated compressed gases are influenced by the type of alchoxy group (methoxy or ethoxy) and the position of OH group (ortho or para), bound to the aromatic ring of solute, as well as the molecular structure of the gas. Three phase SLG curves in p,T-projections mainly exhibited temperature minimums and negative slopes dp/dT, with a maximum melting point depression between 9 and 21 K; all systems with SF6 exhibited a continuous positive slope dp/dT of approximately 4.5 MPa/K. SLG curves with a temperature maximum at low pressure were observed for systems of o-vanillins with R23. Solubilities of o-vanillins in R23 and R236fa were higher in comparison with p-vanillins, whereas, in the case of R134a, the solubilities were influenced by the alchoxy group bound on aromatic ring: vanillin and o-vanillin with methoxy group are more soluble than vanillins with ethoxy group (ethylvanillin and o-ethylvanillin). The highest solubility of all four vanillins was observed in R236fa.
Keywords: solid-liquid-gas equilibria, melting point depression, solubility, vanilin isomers, hydrocarbons, fluorinated hydrocarbons, SF6
Published in DKUM: 31.05.2012; Views: 2120; Downloads: 94
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