Hydrogenation and polymer modification in supercritical fluids
The aim of this work was to investigate the applicability of using supercritical (sc) hydrofluorocarbons (HFCs) as alternative solvents for hydrogenation and polymer modification processes. Solubility studies in binary and ternary systems have been carried out using both dielectrometry and gravimetric techniques and results show that a range of unsaturated carboxylic acids (crotonic acid, 6-methoxy-1-tetralone, methylsuccinic acid, alpha-acetamido-cinnamic acid and itaconic acid) have a high degree of solubility in 1,1,1,2-tetrafluoroethane (HFC 134a). The solubility results were modelled successfully using the Peng-Robinson equation of state (PR EOS) and this model was used to devise a separation methodology for itaconic acid and methylsuccinic acid. It is suggested that HFC 134a can be used as both the reaction medium and the extracting solvent, which enables in-line separation of compounds during sc synthesis.;The homogeneous asymmetric hydrogenation of a range of unsaturated substrates (itaconic acid, dimethyl itaconate, alpha-acetamido-cinnamic acid and trans-2-methyl-2-penetenoic acid) has been studied using a rhodium/MonoPhos catalytic system. High yields and enantiomeric excesses (ee's) have been observed and this, coupled with the separation technique, provides an effective method of asymmetric reduction, which greatly enhances the commercial applicability of this technology.;The infusion of difluoromethane (HFC 32) into polystyrene (PS) and polyethylene (PE) has been characterised and the results have been compared to those obtained for carbon dioxide. Significant plasticization was observed in the polymeric materials and it was shown that manipulation of the experimental temperature, pressure and depressurisation rate could cause significant changes in the morphology of the samples.;It is concluded that sc HFCs are promising alternatives to conventional organic solvents and are useful for a variety of processes. These media have accessible critical constants, relatively high dielectric constant values and are able to facilitate the dissolution of polar solutes and rhodium based catalysts without the need for co-solvents or fluorinated ponytails. Furthermore, the investigation suggests that reactions carried out in the sc regime can allow facile reagent/product separation and it is logical to assume that a similar methodology can be applied to catalyst recovery.