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1.
The development of a new process for gentle drying, micronisation and formulation of a high viscous biopoymer
Christian 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: 26.01.2011; Views: 2495; Downloads: 72
.pdf Full text (24,89 MB)

2.
Influence of temperature and pressure during PGSS[sup]TM micronization and storage time on degree of crystallinity and crystal forms of monostearate and tristearate
Zoran Mandžuka, Željko Knez, 2008, original scientific article

Abstract: For controlling the degree of crystallinity and crystal form during particle formation using supercritical fluids, knowledge of pressure influence on solid-liquid-gas (S-L-G) equilibrium and solubility data of the system is crucial. S-L-G equilibrium data were determined in pressure range from 50 to 600 bar for systems monostearate/CO2 and tristearate/CO2 using a high-pressure view cell. Results showed a temperature minimum for both systems.The solubilities of CO2 in liquid glycerides were high: maximum solubilities, which were determined at temperatures 70 and 90 °C and pressure range from 50 to 450 bar, were from 50 to 90 mol%. Physical characteristics of micronized monostearate and tristearate samples were studied in detail after micronization and after 3 months of storage at 20 °C.
Keywords: chemical processing, high pressure technology, supercritical fluids, micronization, fine particles, Particles from Gas Saturated Solution, degree of crystallinity
Published: 31.05.2012; Views: 2052; Downloads: 24
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Enzymatic reactions in dense gases
Željko Knez, 2009, review article

Abstract: The developments on applications of supercritical fluids as alternative solvents for biocatalytic processes that have taken place over the past two decades have been reviewed. An overview of process parameters influencing enzyme activity and stability, the influence of process parameters on reaction rates and productivity are presented. Applications of various types of reactors for enzymatic reaction in dense fluids, limitations of using enzymes as biocatalyst in supercritical fluids as well as future trends are presented. Main advantages of using dense gases as solvents for biocatalyzed reactions are the tunability of solvent properties and simple down stream processing features that can be readily combined with other unit operations. Although many enzymes are stable in supercritical fluids (SCFs) one should pay considerable attention to finding the correct reaction conditions for each substrate/enzyme/SCF system. One of the persistent problems is the instability and deactivation of enzymes under pressure and temperature. At present the most stable enzymes are hydrolases (lipases and esterases) for which pressure effect is lower than temperature deactivation.
Keywords: biocatalysis, supercritical fluids, enzyme bioreactors, heterogeneous biocatalysis
Published: 01.06.2012; Views: 1304; Downloads: 63
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5.
Phase equilibria in systems containing [alpha]-tocopherol and dense gas
Mojca Škerget, Petra Kotnik, Željko Knez, 2003, original scientific article

Abstract: Solubility of ▫$alpha$▫-tocopherol in CO2 and propane was determined at temperatures 303, 313, 333 and 353 K and over a pressure range from 79 to 286 bar for CO2 and 16 to 112 bar for propane. A static-analytic method was applied. The solubility of ▫$alpha$▫-tocopherol in dense CO2 under the conditions investigated was in the range of 0.2-17.0 mg/g CO2. The maximal solubilities of ▫$alpha$▫-tocopherol in propane were approximately up to ten times higher than in CO2 and were in the range from 38.9 to 171.9 mg/g propane. Phase equilibrium data for Milk Thistle seed oil in supercritical CO2 were determined at temperatures 313, 333 and 353 K and pressures ranging from 100 to 300 bar. The oil was previously additionally vitaminized and contained 1.9 wt.% of ▫$alpha$▫-tocopherol and 1.7 wt.% of free fatty acids (FFA). The solubility of oil in CO2 was in the range from 1.3 to 17.9 mg/g CO2. The distribution coefficients of ▫$alpha$▫-tocopherol and FFA between light and heavy phase were determined on a solvent free basis. The obtained separation factors increased with temperature and pressure to approximately 160-200 bar and decreased with a further increase of pressure.
Keywords: chemical processing, supercritical fluids, phase equilibria, separation factors, vitamin E, CO2, dense gases
Published: 01.06.2012; Views: 1017; Downloads: 18
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6.
Multifunctional composites by high-pressure spray processes
Eckhard Weidner, Marcus Petermann, Željko Knez, 2003, review article

Abstract: A series of spraying processes designed to generate powders and composites using supercritical fluids have been proposed in the past 15 years. In this review, thermo- and fluid-dynamic aspects and engineering principles are discussed and advantages of such technologies are demonstrated. These new techniques display convincing advantages, producing competitive high-quality products with tailor-made properties. Initial industrial applications have been achieved in the production of food products and fine-chemicals.
Keywords: chemical processing, high pressure technology, micronization, supercritical fluids, particles, powder generation, thermodynamics, fluid dynamics, PGSS
Published: 01.06.2012; Views: 1507; Downloads: 58
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7.
Particles formation and particle design using supercritical fluids
Željko Knez, Eckhard Weidner, 2003, review article

Abstract: Major recent advances. Particle formation and design of solid particles and powdery composites with unique properties is at the moment a major developmentof supercritical fluids (synonymsČ dense gasses, dense fluids, highpressure) applications. This review will focus on recent advances and on fundamentals of these processes and their applications.
Keywords: chemical processing, high pressure technology, micronization, supercritical fluids, micro-particles, nano-particles, powder generation, crystallization, particles from gas saturated solutions
Published: 01.06.2012; Views: 2329; Downloads: 66
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8.
Estimation of solid solubilities in supercritical carbon dioxide: Peng-Robinson adjustable binary parameters in the near critical region
Mojca Škerget, Zorka Novak-Pintarič, Željko Knez, Zdravko Kravanja, 2002, original scientific article

Abstract: The density dependence of the binary parameters of the Peng-Robinson equation of state in near the critical region was examined. Published solubility data of eight compounds in pure CO2 have been fitted to the Peng-Robinson equation in combination with one and two parameters van der Waals mixing rules and in combination with the three parameter density dependent mixing rule of Mohamed and Holder. A systematic study has been done to determine the influence of different terms in the mixing rules. In order to obtain density dependence, binary parameters were calculated for each isotherm at particular experimental point separately in the way to equalise experimental and calculated solubility data. The system was formulated as an equation-oriented model and solved by means of a nonlinear programming optimisation algorithm. For all compounds the binary interaction parameters thus obtained were found to vary strongly with pressure in the range from 75 bar to approximately 150 bar, i.e. near the critical end point (CEP) of the low temperature branch of the three phase solid-liquid-gas (SLG) curve. At higher pressures, the parameter is practically independent on pressure. In general, for the systems investigated, kij increases linearly with increasing density and reaches a constant value at higher densities in the range from 700 to 800 kg/m3, depending on the system under investigation.
Keywords: solid liquid equilibria, equation of state, mixing rules, binary parameters, near critical region, nonlinear programming, thermodynamic model, supercritical fluids, CO2, solubility
Published: 01.06.2012; Views: 1376; Downloads: 69
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9.
HIGH PRESSURE PHASE EQUILIBRIUM OF THE BINARY SYSTEM TWEEN 80 AND CARBON DIOXIDE
Natalija Novak, 2014, undergraduate thesis

Abstract: In the frame of the diploma thesis we researched the phase equilibrium of the binary system Tween 80 and CO2. Equilibrium compositions of the system have been determined with a static analytical method at temperature 40, 60 and 80 °C and pressures up to 300 bar. The obtained data was plotted in isothermal diagrams where mass percentage is presented as a function of pressure. In this work also the viscosity of Tween 80 was determined in the temperature range between 20 and 80°C and shear rates up to 180 s-1. The measurements were obtained by using coaxial cylinder and compared with available literature data.
Keywords: supercritical fluids, phase equilibrium, carbon dioxide, Tween 80
Published: 22.04.2014; Views: 998; Downloads: 42
.pdf Full text (2,34 MB)

10.
“Thermodynamic and physical properties for high pressure process design”
Maša Knez Hrnčič, 2014, doctoral dissertation

Abstract: The thesis is comprised of three main categories. The first part of dissertation covers investigations of phase equilibria of compounds from natural materials in conventional and also non conventional supercritical fluids. In details, the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion) is investigated, quantitative and qualitative analyses to evaluate and identify compounds contained after performing preliminary extraction experiments from different natural tissues are presented. The impact of operating parameters (pre-treatment of the raw material with SFE; different extraction solvents: propane, CO2, non conventional SCFs; different extraction temperatures and pressures) on extraction kinetics is observed. Following substances were taken into consideration: vanillins, caffeine, carnosoic acid extract and lecithin. Second part of dissertation covers studies of phase equilibria of the systems bio oil/gas, which is crucial in biorefinery process design. In this part of dissertation, which covers studies of phase equilibria of binary and ternary systems, the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion) for binary system bio oil/supercritical fluid (bio oil/CO2) and (bio oil/H2) was studied. Additionally, phase behaviour of ternary systems of (bio oil/diesel/CO2) and (bio oil/tail water/CO2) under the impact of pressure and/or temperature is observed. These data are of a high importance for bio refineries as an important part of necessary sustainable development. In recent years, studies on biodiesel synthesis have focused on development of process intensification technologies to resolve some of these issues. Fundamental data to design fractionation process of components of bio oil are crucial for an efficient hydrogenation process of bio oil. In the third part of dissertation observation of phase equilibria and determination of the parameters like diffusion coefficient, density and viscosity for the systems polymer/CO2 at elevated pressures is investigated. An overview of different methods applied to determine the parameters like diffusion coefficient, density and viscosity of the systems polymer (PEG)/CO2 at elevated pressures is offered. Observation of phase equilibria of the binary system PEG/CO2, determination of the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion), determination of thermodynamically and physically properties of the system with new applicative methods and finally, comparison of the results obtained by different methods is provided. The interfacial tension (IFT) at the (PEG)/CO2 interface has been determined by using an experimental technique developed to study the interfacial interactions of the liquids in equilibrium with gas in a glass-windowed equilibrium cell by the means of Capillary Rise (CR) method. Advantages and disadvantages of methods that were applied are exposed and discussed.
Keywords: phase equilibria, natural materials, conventional and non conventional supercritical fluids, extraction, bio oil, data for biorefinery process design, systems polymer (PEG)/CO2, diffusion coefficient, density, viscosity, surface tension, Capillary Rise (CR) method.
Published: 28.10.2014; Views: 1389; Downloads: 221
.pdf Full text (4,46 MB)

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