Gary A. Leeke

Efficient batch and continuous flow Suzuki cross-coupling reactions under mild conditions, catalysed by polyurea-encapsulated palladium (II) acetate and tetra-n-butylammonium salts

Suzuki cross-coupling reactions are effected in both conventional organic solvents, under continuous flow conditions at 70 degree C, and in batch mode in supercritical carbon dioxide (scCO2), at temperatures as low as 40 degrees C in the presence of palladium(II) acetate microencapsulated in polyurea [PdEnCat] and tetra-n-butylammonium salts.

A Comparison of the use of FTIR spectroscopy with DSC in the characterisation of melting and crystallisation in polycaprolactone

The infrared spectrum of polycaprolactone has been recorded as a function of temperature in the range where melting and crystallisation of the polymer can occur. Examination of the carbonyl band of the spectra reveals a clear morphological sensitivity; heating the semi-crystalline polymer through the melting region results in a decrease in the intensity of the crystalline component of the carbonyl band. Accordingly, there was a subsequent increase in intensity of the crystalline carbonyl band on cooling. To enable comparison of these findings with a more conventional method of thermal analysis, similar experiments were conducted using a differential scanning calorimeter. The heated ATR accessory adopted for use in the FTIR spectrometer imposed significant limitations in the range of possible heating and cooling rates, but when these rates were carefully matched between FTIR and DSC, close correlation between the melting point and onset of re-crystallisation was observed. The results confirm that FTIR can be used as an alternative, if more laborious, way of investigating melting and re-crystallisation.

Continuous flow hydrolysis of sunflower oil for biodiesel.

Abstract Free fatty acids are an important intermediate for several industrial applications, particularly for production of biodiesel via methanolysis. The use of subcritical water as both solvent and reactant for the hydrolysis of vegetable oil to generate fatty acids has recently been proven to be a successful medium for hydrolysis without employing acid or alkali catalysts, while allowing for a simple process and high yield. Continuous flow hydrolysis of sunflower oil in subcritical water to obtain FFA was investigated in a tubular reactor at 10 to 20 MPa, 270 to 350°C and water/oil ratios of 80:20 and 50:50 v:v%. The rate of the hydrolysis was enhanced significantly by increasing reaction temperature end decreasing the water/oil ratio.

Particle seeding enhances interconnectivity in polymeric scaffolds foamed using supercritical CO2

Foaming using supercritical CO(2) is a well-known process for the production of polymeric scaffolds for tissue engineering. However, this method typically leads to scaffolds with low pore interconnectivity, resulting in insufficient mass transport and a heterogeneous distribution of cells. In this study, microparticulate silica was added to the polymer during processing and the effects of this particulate seeding on the interconnectivity of the pore structure and pore size distribution were investigated. Scaffolds comprising polylactide and a range of silica contents (0-50 wt.%) were produced by foaming with supercritical CO(2). Scaffold structure, pore size distributions and interconnectivity were assessed using X-ray computed microtomography. Interconnectivity was also determined through physical measurements. It was found that incorporation of increasing quantities of silica particles increased the interconnectivity of the scaffold pore structure. The pore size distribution was also reduced through the addition of silica, while total porosity was found to be largely independent of silica content. Physical measurements and those derived from X-ray computed microtomography were comparable. The conclusion drawn was that the architecture of foamed polymeric scaffolds can be advantageously manipulated through the incorporation of silica microparticles. The findings of this study further establish supercritical fluid foaming as an important tool in scaffold production and show how a previous limitation can be overcome.

Crystallisation control of paracetamol from ionic liquids

The crystallisation of Active Pharmaceutical Ingredients (API) from conventional organic solvents can yield undesirable crystal habits with poor physical properties that cause downstream processing problems. It has been proposed that ionic liquids (ILs) may offer an opportunity to perform controlled crystallisations from this media. Using paracetamol and the ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] and 1-hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF6] fundamental understanding of these systems was established by determining the Meta-stable Zone Width (MSZW) before completing a series of cooling crystallisations investigated across a temperature range between 20 °C and 90 °C. It has been shown that paracetamol can be crystallised from these systems to obtain the stable monoclinic form I and that the particle habit and size can be manipulated by changing the IL used, the solution concentration and the mechanism of crystal growth and in some cases crystal habits not commonly found from aqueous or organic solvents were produced. The results demonstrate that ILs may be a viable approach to manipulate crystal properties and should be explored more widely as a potential media for crystallisation of API.

Chemically Altering the Solubility and Durability of Dyes for Sensitized Solar Cells

By designing dyes with fluoroalkyl groups, the optical and electronic properties of the alkyl analogue were maintained while dramatically altering the solubility. Dyes, F-TABTA (8) and its masked derivative F-TABTSi (9), that enable them to be deposited under conventional organic solvent and scCO2 conditions, respectively, were developed. In liquid DSSC devices, the fluoroalkyl dye (F-TABTA, 8) performs slightly better than its alkyl analogue (D21L6, 10), and interestingly, it was found that the former device showed better stability over time. Deploying the silyl-masked precursor F-TABTSi (9), this dye was deposited onto TiO2 photoanodes from scCO2 in very short contact times (2.5 h), and ECEs of 7.70% were obtained that exceed the performance of the alkyl dye when deposited by conventional methods.

Modelling the disruption of essential oils glandular trichomes with compressed CO2

Abstract A theoretical model is proposed for the evaluation of the disruption efficiency of essential oils glandular trichomes (glands) with compressed CO 2 . The disruption of glands occurs during the fast decompression of the bed of herbaceous material. The glands are described as closed structures slightly permeable to CO 2 . When exposed to compressed CO 2 , the gas slowly penetrates the glands and dissolves in the intraglandular oil until the solubility limit is reached. During the fast decompression of the bed, the dissolved gas is desorbed from the oil phase and discharged to the bulk solvent. The inability of the glands to discharge the gas, at a rate dictated by the loss of solubility in the oil with the decompression of the bed, generates a pressure gradient across the glands that may lead to its rupture. In the present model, the excess pressure is described by an equation similar to Hagen–Poiseuilles formula for viscous flow due to a pressure gradient. The maximum pressure gradient across the glands during the fast decompression of the bed is then used to calculate the percentage of glands disrupted (efficiency of disruption) assuming a normal distribution of the bursting pressures of the glands. The model was applied to experimental results where the effects of pre- and post-expansion pressure, exposure time to pre-expansion pressure and the rate of decompression were investigated. Predictions of the model are also presented.

Modelling the extraction of soil contaminants with supercritical carbon dioxide.

Extractions of volatile organic compounds (VOCs) in contaminated soil from petroleum site were performed with supercritical carbon dioxide at different temperatures, pressures, extraction times, solvent flow rates, soil moisture contents and soil acidity. Three soil systems were investigated in order to compare the best parameters for extraction. A central composite rotatable design has been used to evaluate the influence of operation conditions on the extraction efficiency to generate model equations representing the types of soil. The results indicate that at least 70-80% of the initial amount of VOCs can be removed at moderate temperatures even at very high moisture content. Supercritical extraction is best suited to silt type soils which have a low adsorption capacity. VOCs recoveries from the artificial contaminated soil samples were higher in comparison with real contaminated soils. At moderate temperatures, the extraction efficiency for real soils is low because pollutants bind strongly to the soil.

Development of a rapid method to isolate polyhydroxyalkanoates from bacteria for screening studies

We describe a novel method of Polyhydroxyalkanoate (PHA) extraction using dimethyl sulphoxide (DMSO) for use in screening studies. Compared to conventional chloroform extraction, the DMSO method was shown to release comparable quantities of PHA from Cupriavidus necator cells, with comparable properties as determined using Fourier transform infrared spectroscopy and differential scanning calorimetry.

Comparison Between Compressed CO2 Extracts and Hydrodistilled Essential Oil

Abstract The yields and compositions of volatile concentrates and essential oils obtained from compressed CO2 extraction and hydrodistillation of a model herb, respectively, are compared. The experimental tests were undertaken on Origanum vulgare L. ssp. virens (Hoffm. et Link) letswaart using both intact and communited bracts. The yields and compositions obtained from the communited bract sizes compared well for both extraction techniques. This is an indication that degradation of the oil during the distillation process was minimal. However, when the intact bracts were used, the compressed CO2 extraction yield was significantly lower than that achieved by hydrodistillation. This stresses the need for an efficient pre-treatment step for the CO2 extraction of volatile concentrates.