Paul Meenan

Crystallisation of paracetamol (acetaminophen) in the presence of structurally related substances

Paracetamol was crystallised from aqueous solutions containing various concentrations of structurally related compounds. Crystal shape was characterised by image analysis and the additive concentration incorporated into the crystals determined by HPLC. The crystal structure of pure acetaminophen displays a hydrogen bonded network, from which is derived a mechanistic interpretation of the abilities of additive molecules to influence crystal growth. This structural approach was used to explain the observed additive uptake, the morphological changes, and the previously reported inhibition of nucleation.

The influence of impurities and solvents on crystallization

Publisher Summary This chapter reviews the fundamentals of impurity incorporation, solvent interaction, and solution thermodynamics. The advent of sophisticated molecular modeling tools coupled with the increasingly accurate means to determine crystal structure has led to a greater understanding of crystal surfaces, and consequently, of crystal surface impurity and crystal surface-solvent interactions. As crystallization is essentially a molecular recognition process that occurs on a grand scale, impurity and solvent influences can be rationalized in terms of intermolecular interactions. Because of the requirement of high-purity crystalline products, an understanding of the effects of solvents on purification is also necessary. The solvent can influence the separation efficiency through its effect on crystallization kinetics, solution thermodynamics, and crystal interface structure. The mass transport processes at the crystal-liquid interface play a central role in crystallization. The influence of solvent and impurities on the structure and growth rates of faces is discussed in the chapter, along with its effect on the incorporation of impurities. The solvent-solute-impurities interactions in solution interact with the interface during the crystallization process. With appropriate thermodynamic analysis, it is proved that these interactions ultimately affect crystallization as a purification process.

The influence of spray drying conditions on the particle properties of recrystallized burkeite (Na2CO3·(Na2SO4)2)

Abstract The influences of preparation conditions on the particle properties of spray dried slurries of the double salt burkeite (Na 2 CO 3 · (Na 2 SO 4 ) 2 ) are examined to define particle size and porosity for maximal uptake of detergent components. Use of X-ray powder diffraction and energy dispersive elemental analysis showed that in the process burkeite was the only salt formed. The structure of the pores within particles, formed by the spaces between the crystals, was characterized by mercury intrusion. Typically, a pore volume of 0.5 ml g −1 was obtained, in which more than half of the volume was in pores less than 0.5 μm. The particle porosity was rather insensitive to variation in the size of the atomizing nozzle. However, the rate of drying, which was controlled by changing the air inlet flow rate, was found to be an important parameter. The pore volume was found to increase significantly with reduction in drying rate. The observation is interpreted in terms of established models for the drying of slurry droplets.

Deriving empirical potentials for molecular ionic materials

Abstract The procedure for deriving interatomic potentials for molecular ionic materials, using empirical fitting procedures, is described. Potentials are obtained for carbonates, phosphates and perchlorates, and used to calculate crystal and lattice properties which are compared with available experimental data.

Determination of a transferable interatomic potential for alkali-metal perchlorates and its application to morphological modelling

The development of an interatomic potential for alkali-metal perchlorates is presented. The potential is fitted to orthorhombic sodium perchlorate and transferred to the perchlorates of caesium, potassium and rubidium. The derived potential data provide a consistent fit to the known crystal structures and elastic constants. Transferability of the potential to the cubic phase of sodium perchlorate leads to a poorer match to experimental data, which perhaps reflects the fact that this phase only stabilises at a high temperature. Unrelaxed and relaxed surface and attachment energies for the low-index crystal planes are calculated for potassium perchlorate, from which crystal morphologies are predicted. The simulations provide a good match to experimental growth morphologies using the Hartman–Perdok attachment energy model, but a poorer one using the more classical Gibbs–Wulff surface-energy model. Potential growth mechanisms, based on these observations, are discussed.

The influence of batch processing on the particulate properties of burkeite (Na2CO3(Na2So4)2)

Studies of the particle porosity as a function of residence time associated with the crystallization of high surface area burkeite (Na2C03(Na2SO4)2) agglomerates revealed no evidence for Ostwald ripening. However, a significant increase in particle porosity was observed following milling, reflecting particle breakdown and the consequent exposure of more particle surface to the liquid phase. The action of spray drying was found to reverse this trend with the particulates so formed exhibiting a much lower porosity, reflecting the blocking of surface pores by recrystallized material.

A transferable interatomic potential for alkali chlorates and bromates

Interatomic potential parameters obtained via empirical fitting techniques provide good agreement between predicted and experimentally derived structural parameters for a range of alkali chlorate and bromate salts, as well as a double chlorate/bromate salt. Examination of the transfer of these parameters to modelling the structural properties of the divalent salt strontium chlorate provided a reasonable, albeit poorer, reproduction of the experimental data. Calculated elastic constants for all materials are provided.

Potential fitting to molecular ionic materials

Abstract The development of an interatomic potential for alkali perchlorates and phosphates is presented. The potentials are fitted to sodium perchlorate (space group, Cmcm) and calcium phosphate and are transferred to another phase of sodium perchlorate (space group, F 43m) and also the perchlorates of caesium, potassium and rubidium and to the phosphates of strontium and magnesium. The calculated structure and elastic constants are compared with experimental data.