(591a) Development of a Group Contribution Method to Predict Sublimation Enthalpies of Solids Constituted by Aromatic and/or Polycyclic Aliphatic Rings. Application for Solid-Vapour Equilibria

Over the last few years, significant research has been conducted with regard to particle formation using supercritical fluid technologies. Non-solvent particles with controlled particle size distribution can be produced by using these environmentally friendly processes. As a consequence, different industries, such as the pharmaceutical, can take advantage of these techniques for different purposes.

Solubility of the solid in the supercritical fluid is crucial to determine which supercritical fluid technique must be used. Isofugacity criterion, together with cubic equations of state, is the most used approach to fit and estimate these equilibrium data. Nevertheless, different solid properties should be known before starting this estimation.

One of those properties is the sublimation pressure. As a matter of fact, different works indicate that a bad choice of the method to calculate this pressure might yield high deviations in the outcome. Clausius-Clapeyron equation can be used for instance to calculate that pressure. However, it is required the knowledge of the sublimation enthalpy. Therefore, a consistent group contribution method to estimate this enthalpy, based only on the molecular structure of the compound, can speed up this calculation process.

A group contribution method to estimate the sublimation enthalpy of any solid constituted by aromatic and/or polycyclic aliphatic rings is proposed in this work. Pharmaceuticals are usually constituted by this type of “chemical” rings. A training set of sublimation enthalpies was built by using literature (90% of the values) or calculated (estimated from experimental solubility) data.

Sublimation pressure of the naphthalene will be calculated with our method, and subsequently the solid-vapour equilibrium of the system CO₂-naphthalene at high pressure will be determined.

Sublimation enthalpies for this type of solids were predicted with our group contribution method with an average absolute relative deviation of less than 9%. Moreover, equilibria data CO₂-naphthalene at high pressure were fitted with Peng-Robinson equation of state with an average absolute relative deviation of less than 15%.

These results highlight that this group contribution method can be applied to calculate sublimation enthalpies of any pharmaceutical, with the aim of using the obtaining value for fitting or predicting solid-vapour equilibria at high pressure.