1. Pressure stability of lipases and their use in different systemsMaja Leitgeb, Željko Knez, 2001, original scientific article Abstract: For the investigation of the solvent impact on the enzymes, lipases from different sources (Pseudomonas fluorescences, Rhizopus javanicus, Rhizopus niveus, Candida rugose and Porcine pancreas) were used. Stability and activity of these lipases in aqueous medium in supercritical $CO_2$ and liquid propane at 100 bar and 40°C were studied.
On the basis of previous results lipases were used for their application in two different systems. The application of the polysulphone membrane in the continuous stirred tank membrane reactor was studied on the model system of the hydrolysis of oleyl oleate in propane at high pressure. As a catalyst the Candida rugosa lipase was used. The next utilization of lipases was the use of on silica arerogel self-immobilized lipase from Porcine pancreas as catalyst for esterification reaction in near-critical propane at 40°C and 100 bar.
Keywords: chemical processing, supercritical fluids, lipases, enzyme stability, high pressure membrane reactor
Published in DKUM: 10.07.2015; Views: 1541; Downloads: 196
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2. Stability of proteinase from Carica papaya latex in dense gasesMaja Leitgeb, Mateja Primožič, Željko Knez, 2005, original scientific article Abstract: Proteinase from Carica papaya latex was tested on its thermal stability at atmospheric pressure and in supercritical carbon dioxide, near-critical propane and dimethyl-ether. In supercritical carbon dioxide at 300 bar thermalactivation of the examined proteinase was improved in the comparison toatmospheric pressure. In propane and dimethyl-ether (300 bar) activity of the examined proteinase decreased. Influence of compressionžexpansion cycles on residual activity of the same proteinase in supercritical carbon dioxide (300 bar and 50 °C) was studied, as well. Different ways of transition from supercritical to low-pressure-state were used which affected residual activityof the proteinase.Addition of water in the system increased activity of proteinase from C. papaya, which was incubated in supercritical carbon dioxide for 24 h. Optimum amount of water was found to be between 0.5 and 0.7 g/L.
Keywords: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Published in DKUM: 01.06.2012; Views: 2015; Downloads: 28
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3. Supercritical fluids as solvents for enzymatic reactionsMaja Leitgeb, Mateja Primožič, Željko Knez, 2007, review article Abstract: Enzymes may act in different solvent systems. Water as the solvent in vivo may be replaced partially or mostly with other solvents, such as micro-emulsions, organic solvents, reversed micelles, ionic liquids and supercritical fluids (SCFs).Several types of enzymatic reactions were performed in SCFs. Influence of SCFs on enzyme stability and activity is presented on different examples; on different reaction systems (hydrolysis, transesterification...) and on the use of non-immobilized (Subtilisin carlsberg, Aspergillus niger...) as well as immobilized enzymes. Several types of high-pressure enzymatic reactors (batch-, stirred-tank-, extractive semibatch-, recirculating batch-, semicontinuous flow-, continuous packed-bed-, and continuous-membrane reactors) have been used for the performance of enzymatic reactions. In the studies on stability of biocatalysts in a high-pressure batch-stirred tank reactor changes in biocatalysts activity due to pressurization/depressurization steps were observed. Interesting alternative to overcome this inconvenience is the use of the high-pressure continuous membrane reactors, where just single compression and expansion step is necessary.
Keywords: enzymatic reactions, supercritical carbon dioxide, high-pressure, enzyme stability, high-pressure reactors
Published in DKUM: 31.05.2012; Views: 3315; Downloads: 149
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4. 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: 160
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