Regina Santos

Modelling the extraction of essential oils with compressed carbon dioxide

Abstract Three models were used to describe the extraction of essential oils from oregano bracts using compressed carbon dioxide. They were developed on the basis of a plate-like geometry of the particles and were tested experimentally using various bract pre-treatments, pressures, temperatures and solvent flow rates. The two particle phase derived models applied, the Single Plate model (SP model) and the Simple Single Plate model (SSP model), differ only by the allowance or not for a film coefficient (kf) and have as the only adjustable parameter the matrix diffusivity (Dm). The third model, the Fluid Phase/Simple Single Plate model (FP/SSP model), considers both the particle mass balance and a detailed description of the fluid mass balance. In addition to the matrix diffusivity the FP/SSP model may require the adjustment of the fraction of oil leached by the solvent during the pressurisation procedure (f0). All models gave a good fit to the experimental data though the FP/SSP model gave the best fit. However, the matrix diffusivities found correlated very poorly with the estimated diffusivity of essential oils in carbon dioxide (D12), which indicates a complex intraparticle transport.

Disruption of glandular trichomes with compressed CO2: alternative matrix pre-treatment for CO2 extraction of essential oils

Abstract The disruption of essential oils glandular trichomes by contact with compressed carbon dioxide followed by rapid decompression was studied at isothermal condition (310 K). The pre- and post-expansion pressures, the exposure time to the pre-expansion pressure and the rate of decompression were all found to have a significant effect on the efficiency of the disruption process. The efficiency of the disruption process (percentage of glands disrupted during the fast decompression) was deduced from the results of subsequent extraction tests using compressed CO 2 under standard conditions. The damage to the glands was observed by SEM microscopy. The efficiency of the disruption process seems to be closely related to the amount of gas dissolved within the glands, the rate of decompression of the bed and the permeability of the glands. The experimental results revealed that for an exposure time of 60 min and a rate of decompression of 2 kg m −3 s −1 , the decompression from 70 barg to atmosphere led to a maximum efficiency of the disruption process. At these conditions, the improvement in the extractability of essential oils by compressed CO 2 was similar to that obtained by cryogenic comminution of the matrix and better than that obtained by ambient comminution. One advantage of the fast decompression treatment method is that it virtually eliminates the losses of essential oils observed in mechanical treatments. A further advantage is that it selectively liberates the essential oils with respect to higher molecular weight material. This results in a final extract with a higher content of essential oils.

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.

The structure of Pseudomonas fluorescens biofilms in contact with flowing systems

Using a specially designed flow system Pseudomonas fluorescens has been grown on the inside of glass tubes under carefully controlled conditions. Results show that films developed from water flowing at 0–5 m.s‐1 are less compact and thicker than with a water velocity of 2–5 m.s‐1. In the latter all the cells are aligned in the direction of flow whereas in the former the individual cells directly attached to the surface, are randomly distributed with groups of cells lying parallel to the tube axis.

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.

Non-biocidal Anti-fouling Coatings

The dry weight of fouling on raft panels coated with silicone elastomers (low energy surfaces) has been measured at two-monthly intervals for one year A flow cell is described for testing the adhesion of slimes to raft panels: Results on removal of slimes from silicone elastomers and formica are discussed

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.

Evaluation and modelling the utility of SCCO2 to support efficient lipase mediated esterification.

Supercritical fluids offer environmental advantages over chemical solvents, while providing enhanced separation and chemical selectivity. The use of supercritical fluids for the recovery of products from biomass and the transformation of selected molecules (to add value) was studied. Free fatty acids were bio-catalytically transformed to fatty acid esters using lipase within a supercritical fluid environment. A central composite rotatable design was used to evaluate the influence of operating conditions on the enzymatic esterification process and a response surface equation was optimized to identify the most favourable process conditions for maximum free fatty acid conversion. Based on the model equation the process conditions under which it was predicted a yield of 100% esters could be obtained were: pressure 200 bar, temperature 60 °C, ethanol concentration 2.0 M, enzyme concentration 11 wt.% and time 60 min. Experiments conducted under these conditions gave an ester yield of 94.3% (close to predicted results). The activity per unit mass of biocatalyst was found to be 1585 μmol/min/g(cat). The results support the use of supercritical fluids for process integration.

Extraction of useful components from herbs using supercritical CO2: Experimental findings and data modelling

Abstract Extraction of Thyme and Rosemary with CO 2 at 25 and 40°C and pressures up to 250 bar is described and the results modelled, Single Sphere Models being best. Good data fits were obtained for both herbs when effective diffusivities D e were fitted at each temperature and pressure but variations of D e with temperature and pressure were physically more convincing for Thyme.