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Author = Valavi, Masood;
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Displaying Results 1 - 4 of 4 on page 1 of 1
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Crystallisation thermodynamics
(2017)
Valavi, Masood
Crystallisation thermodynamics
(2017)
Valavi, Masood
Abstract:
This study investigated two important thermodynamic parameters of crystallisation: the activity coefficient and solubility. The influence of composition and temperature on the activity coefficient was investigated to provide a better approximation of the driving force of crystallisation. It was found that the influence of temperature on the activity coefficient was generally much smaller than the influence of composition. Based on an analysis that was performed, a new estimation of the driving force was suggested. Since the driving force is also dependent on solubility, it is important to have an accurate estimation of solubility. Three models were used to calculate a solubility curve: “original NRTL-SAC”, “temperature-dependent NRTL-SAC” and “Pharma UNIFAC”. A comparison between the performances of these three models was presented. It was found that introducing a temperature-dependent binary interaction parameter to the original NRTL-SAC model could improve this model’s performance...
http://hdl.handle.net/10344/6117
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Improving estimates of the crystallization driving force: investigation into the dependence on temperature and composition of activity coefficients in solution
(2016)
Svärd, Michael; Valavi, Masood; Rasmuson, Åke C.
Improving estimates of the crystallization driving force: investigation into the dependence on temperature and composition of activity coefficients in solution
(2016)
Svärd, Michael; Valavi, Masood; Rasmuson, Åke C.
Abstract:
In this work the influence of temperature and composition on the activity coefficient in solution has been investigated, based on isothermal and isobaric vapor-liquid equilibrium data for 30 binary systems classified into four groups: water-organic, polar-polar, polar-nonpolar, and nonpolar-nonpolar systems. It is shown that under most conditions the temperature dependence of the activity coefficient is clearly weaker than the composition dependence. The analysis is extended to include solid-liquid solubility data of 15 binary systems of relatively large and complex organic molecules in organic solvents. Based on this, a novel approach to estimate the thermodynamic driving force of crystallization from solution is proposed. Rather than assuming that the activity coefficient ratio equals unity, it is shown that in most cases a more accurate assumption is to neglect only the temperature dependence of the activity coefficient. This allows the activity coefficient ratio to be estimated ...
http://hdl.handle.net/10344/7234
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Prediction of the solubility of medium-sized pharmaceutical compounds using a temperature-dependent NRTL-SAC model
(2016)
Valavi, Masood; Svärd, Michael; Rasmuson, Åke C.
Prediction of the solubility of medium-sized pharmaceutical compounds using a temperature-dependent NRTL-SAC model
(2016)
Valavi, Masood; Svärd, Michael; Rasmuson, Åke C.
Abstract:
In this work, the NRTL-SAC and the Pharma UNIFAC models are evaluated with respect to the capability of prediction of solid liquid equilibria of pharmaceutical compounds in organic solvents. The original NRTL-SAC model is extended through the introduction of temperature-dependent binary interaction parameters, and the two versions of the model are parametrized using vapor liquid equilibrium (VLE) data. The performance of the NRTL-SAC models for correlation and prediction of the solubility of eight medium-sized flexible pharmaceutical or pharmaceutically similar molecules in multiple pure, organic solvents is examined: risperidone, fenofibrate, fenoxycarb, tolbutamide, meglumine, butyl paraben, butamben, and salicylamide. The performance of the Pharma UNIFAC model is evaluated using data for six of these compounds. In general, it is found that introducing a dependence on temperature to the binary interaction parameters of the NRTL-SAC model can improve its capability for modeling and...
http://hdl.handle.net/10344/7235
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Thermodynamic stability analysis of tolbutamide polymorphs and solubility in organic solvents
(2016)
Svärd, Michael; Valavi, Masood; Khamar, Dikshitkumar; Kuhs, Manuel; Rasmuson, Åke C.
Thermodynamic stability analysis of tolbutamide polymorphs and solubility in organic solvents
(2016)
Svärd, Michael; Valavi, Masood; Khamar, Dikshitkumar; Kuhs, Manuel; Rasmuson, Åke C.
Abstract:
Melting temperatures and enthalpies of fusion have been determined by differential scanning calorimetry (DSC) for 2 polymorphs of the drug tolbutamide: FIH and FV. Heat capacities have been determined by temperature-modulated DSC for 4 polymorphs: FIL, FIH, FII, FV, and for the supercooled melt. The enthalpy of fusion of FII at its melting point has been estimated from the enthalpy of transition of FII into FIH through a thermodynamic cycle. Calorimetric data have been used to derive a quantitative polymorphic stability relationship between these 4 polymorphs, showing that FII is the stable polymorph below approximately 333 K, above which temperature FIH is the stable form up to its melting point. The relative stability of FV is well below the other polymorphs. The previously reported kinetic reversibility of the transformation between FIL and FIH has been verified using in situ Raman spectroscopy. The solid-liquid solubility of FII has been gravimetrically determined in 5 pure orga...
http://hdl.handle.net/10344/7230
Displaying Results 1 - 4 of 4 on page 1 of 1
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Journal article (3)
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2017 (1)
2016 (3)
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