81. The lipase-catalyzed synthesis of fatty acid fructose esters in organic media and in supercritical carbon dioxideSaša Šabeder, Maja Leitgeb, Željko Knez, 2006, original scientific article Abstract: Sugar fatty acid esters are biodegradable surface active compounds in foodstuffs and cosmetics or pharmaceuticals. They have potential in replacing pollutant chemically synthesized surfactants. The enzymatic synthesis of fructose palmitate catalyzed by Candida antarctica B lipase was performed in different organic media in a batch react at atmospheric pressure. The influence of the organic solvent and temperature on the esterification was studied. Since supercritical carbon dioxide (SC CO2) has several advantages over organic solvents, such as high reaction rate, high mass transfer, non-toxicity, non flammability and low price, it was also chosen as a reaction medium for fructose palmitate production. The influence of temperature on immobilized lipase activity was studied at 10 MPa and the results were compared to the results obtained from reactions performed at atmospheric pressure under the same reaction conditions. The highest conversion (67%) was obtained after 24 hours of reaction in SC C02 at 80°C. A change of the particle size distribution and morphology of the untreated lipase and lipase treated with 2-methyl 2-butanol and SC C02 was observed.
This article was presented at 1st SEECChE, held in Belgrade, September 25-28, 2005
Keywords: chemical processing, high pressure technology, supercritical CO2, lipase catalyzed syntheses, esterification, fructose palmitate, biocatalysts, lipase, Candida antarctica B
Published in DKUM: 31.05.2012; Views: 2712; Downloads: 539
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82. Particle formation using supercritical fluids : a short reviewŽeljko Knez, 2006, review article Abstract: Particle formation and the design of solid particles and powdery composites with unique properties is at the moment one of major the developments of supercritical fluid (synonyms: dense gases, dense fluids, high pressure) applications. Conventional well-known processes for the particle-size redistribution of solid materials are crushing and grinding (which for some compounds are carried out at cryogenic temperatures), air micronization, sublimation, and recrystallization from solution. There are several problems associated with the above-mentioned processes. Some substances are unstable under conventional milling conditions, in recrysfallization processes the product is contaminated with solvent and waste solvent streams are produced. The application of supercritical fluids may overcome the drawbacks of conventional processes, and powders and composites with special characteristics can be produced. Several processes for the formation and design of solid particles using dense gases have been studied intensively. The unique thermodynamic and fluid-dynamic properties of supercritical fluids can also be used for the impregnation of solid particles, for the formation of solid powderous emulsions, particle coatings, e.g. for the formation of solids with unique properties for use in different applications. This review will focus on the fundamentals and on recent advances of particle formation and design processes using supercritical fluids on their applications and the technological advantages and disadvantages of various processes.
Keywords: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Published in DKUM: 31.05.2012; Views: 2888; Downloads: 198
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83. Kinetics of supercritical carbon dioxide extraction of borage and evening primrose seed oilPetra Kotnik, Mojca Škerget, Željko Knez, 2006, original scientific article Abstract: In the present work, high-pressure extraction of borage (Borago officinalis L.) and evening primrose (Oenothera biennis L.) seed oil, containing the valuable -linolenic acid (GLA), has been investigated. Extraction was performed with supercritical carbon dioxide on a semi-continuous flow apparatus at pressures of 200 and 300 bar, and at temperatures of 40 and 60 °C. A constant flow rate of carbon dioxide in the range from 0.17 to 0.20 kgžhwas maintained during extraction. The extraction yields obtained using dense CO2 were similar to those obtained with conventional extraction using hexane as solvent. The composition of extracted crude oil was determined by GCanalysis. The best results were obtained at 300 bar and 40 °C for both seed types extracted, where the quality of oil was highest with regard to GLA content. The evening primrose seed oil extracted with supercritical fluid extraction was particularly rich in unsaturated fatty acidsČ up to 89.7 wt-% of total free fatty acids in the oil. The dynamic behavior of the extraction runs was analyzed using two mathematical models for describing the constant rate period and the subsequent falling rate period. Based on the experimental data, external mass transfer coefficients, diffusion coefficients and diffusivity in solid phase were estimated. Results showed good agreement between calculated and experimental data.
Keywords: chemical processing, high pressure technology, supecritical CO2, seed oil extraction, evening primrose, borage, free fatty acids, kinetics, modeling
Published in DKUM: 31.05.2012; Views: 2348; Downloads: 115
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84. Electrohydraulic pressure control by a self-adjusting proportional derivative controllerDarko Lovrec, Friedrich Faber, 2006, original scientific article Abstract: The main characteristic of an electrohydraulic pump control system is the presence of an electrical signal path. It requires at least one sensor for the controlled value (in this case pressure), delivering feedback to be compared with the electrical or numerical reference in the controller. The additonal expense penalty for the sensor and the valve is offset by the advantage of flexibility in the structure and parameters of the controller in comparison to hydraulic - mechanical concepts. Thus, the transfer response can be adapted to demands, even in the operational state. Sophisticated control structures can be implemented easily in the form of computer or microcontroller programs. The layout of electrohydraulic pressure control discussed in this study includes the presented loading unit. The variable pump is designed to act together with a proportional valve having two metering edges. It is less expensive compared to the design with a synchronizing cylinder and four metering edges. However, only inferior static and dynamic performance can be expected. Hydraulic energy is supplied to the control valve directly from the output port of the pump - with the advantage of simple assembly, as there are no additional components required - but with the drawback that there is influence on the control loop`s properties at every change in the disturbance value or reference. The aim of the study presented in this paper is a more efficient and simple concept compared to other known methods for pressure control of the above mentioned pump including the dynamics of the distribution network, and also the characteristics of the hydraulic load with special focus on improvements in steady state and dynamic behaviour.
Keywords: automatic control engineering, electrohydraulic systems, pressure control, self-adjusting proportional controller
Published in DKUM: 31.05.2012; Views: 2291; Downloads: 145
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85. Laminar flow of a shear-thickening fluid in a 90° pipe bendJure Marn, Primož Ternik, 2006, original scientific article Abstract: The non-Newtonian fluid flow in a sharp 90 curved pipe is studied numerically to obtain the pressure loss coefficient prompted by disagreement between the existing empirical correlations and results obtained by computer codes. This disagreement results from presumption of fully developed flow throughout the curvature (correlations) while the actual flow is partially developed for the Newtonian and sharp 90 curved bend non-Newtonian flows, and fully developed for slightly bent 90 curvature non-Newtonian flow. The Quadratic model is employed to accommodate the shear-thickening behavior of an electrostatic ash and water mixture. Numerical results are obtained for different values of Reynolds number. Finally, results for local pressure loss coefficient are compared with values obtained for the Power law rheological model.
Keywords: shear-thickening fluid, fluid dynamics, rheological model, pipe bend flow, numerical modelling, pressure losses
Published in DKUM: 30.05.2012; Views: 1995; Downloads: 91
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86. Preparation of enantiomers using high pressure technologiesPaul Thorey, 2010, dissertation Abstract: The study of two different methods of obtaining chiral alcohols is proposed herein.
The requirement of the relatively new paradigm of green chemistry associated with clean
technologies such as biocatalysis or non-conventional solvents, dense gases, was
focused at. Indeed, the two methods of production of chiral alcohols were:
- the conversion of acetophenone into (R)-1-phenylethanol in dense gases
catalysed by Lactobacillus brevis alcohol dehydrogenase and its
coenzyme, NADP/H;
- the resolution of (±)-trans-1,2-cyclohexanediol by cocrystal formation with
tartaric acid followed by supercritical extraction.
In both cases high enantiopurities were achieved (ee>99%).
Keywords: High-pressure technologies, enantiomers, green chemistry, R-1-phenylethanol, Lactobacillus brevis, alcohol dehydrogenase, NADP, liquid propane, enzyme deactivation, resolution, trans-1, 2-cyclohexanediol, tartaric acid, cocrystal, supercritical carbon dioxide, extraction, X-ray diffraction, differential scanning calorimetry
Published in DKUM: 02.02.2011; Views: 3053; Downloads: 159
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87. The development of a new process for gentle drying, micronisation and formulation of a high viscous biopoymerChristian Reibe, 2011, dissertation Abstract: Biopolymers are characterised by their biodegradable behaviour in certain environments. Especially the development of natural biopolymers from renewable resources is gathering increasing interest in the scientific as well as in the industrial sectors . Since Biopolymers may be tailored to specific requirements, the encapsulation of pharmaceutical compounds or flavours in biopolymers would open wide avenues for the production of controlled- release systems. Most common mechanical pulverisation processes are milling and grinding. With these processes it is not possible to produce specific morphologies like foams or hollow spheres, but always splintered edges. Encapsulation is carried out by common precipitation techniques.
Gelatine, as a widely applied biopolymer, represents one example of those substances of large interest, but it is difficult to process. Especially gelatines with high molecular mass are difficult or almost impossible to be pulverized by spray drying techniques, due to their high viscosity.
In the frame of this research work, an integrated high-pressure spraying, drying and pulverization process for high viscous gelatine was developed, based on a combination of the water removing effects "Evaporation" and "Gas-solubility". The resulting products were dry, free-flowing gelatine powders, still exhibiting high molecular masses. Due to the new, gentle method of processing, a completely new gelatine product with unique properties was obtained. Even the encapsulation of edible oil in high ratios was found to be possible with this new process. The characterisation was carried out by standard methods for gelatine on the one hand side, and standard procedures for characterising powders on the other hand side.
The developed process was patented under the identifier "WO 002009135601 A1".
Keywords: High Pressure Process, Supercritical Fluids, High molecular mass Gelatine, Micronisation, CO-2 - spray drying, Encapsulation, Gelatine Powder
Published in DKUM: 26.01.2011; Views: 3525; Downloads: 269
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88. Modifikacija pralnega stroja glede porabe vode : diplomsko deloUroš Ljubojević, 2008, undergraduate thesis Keywords: pralni stroj, doziranje vode, poraba vode, hidrostat, eng, washing machine, laundry machine, water filling, water consumption, pressure switch
Published in DKUM: 04.02.2009; Views: 3116; Downloads: 436
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