Author : Chiara Giulia Laudani
Publisher :
ISBN 13 :
Total Pages : 222 pages
Book Rating : 4.:/5 (441 download)
Book Synopsis Immobilised lipase-mediated oleic acid esters and (R)-phenylethyl acetate syntheses in dense carbon dioxide: kinetics and thermodynamics by : Chiara Giulia Laudani
Download or read book Immobilised lipase-mediated oleic acid esters and (R)-phenylethyl acetate syntheses in dense carbon dioxide: kinetics and thermodynamics written by Chiara Giulia Laudani and published by . This book was released on 2007 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of enzymes in SCFs has bean growing over last two decades as chemists attempt to broaden the applications of biocatalysis. In addition to on going research in solvent-free systems, synthesis in SCFs can potentially offer new alternatives to enzyme-catalysed reactions. Continuing improvements in biocatalysts and a better understanding of biocatalysis assisted by SCFs are expected to greatly influence the production of fina chemicals. Historically emphasis has rested on performing biocatalysis in SC-CO2 in supercritical conditions of the whole reaction bulk. However, in the area of critical pressure, all CO2 density-dependent properties, such as the dielectric constant, refractive index, fugacity coefficient and solubility parameters, are strong function of pressure. Consequently, substrate/product solubility, solvation and mass transfer phenomena dramatically change at the critical point, leading to areaction performance dependence on pressure. The high sensitivity of solubility to pressure, particularly marked close to the critical point, makes the vapour-liquid phase equilibrium of the studied system very interesting to investigate. In this work, research efforts were aimed at developing selective methods for the production of polyfunctional molecules with high potential industrial applications by enzymatic reactions carried out in a liquid reaction bulk in subcritical conditions rich in dense CO2. In the first part of the PhD thesis, studies of the role of the solvent to investigate how the phase equilibrium triggers the reaction performance were carried out. Wax esters, chosen as model system to carry on a thermodynamic interpretation of the enzymatic esterification kinetics in denseCO2 as reaction medium, were successfully obtained from the esterification reaction between long-chain fatty alcohols and long-chain fattyacids over immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) in sub- and supercritical conditions of the whole reaction bulk. Firstly, complete and systematic screening and optimisation of the process parameters on the products final concentration and reaction rate in solvent-free system were developed. Secondly, the kinetics and thermodynamics correlation of the wax esters biocatalytic synthesis over Lipozyme RM IM by using dense CO2 as solvent medium in a batch stirred and in a continuous bench-scale plug-flow packed bed high-pressure reactors was investigated. Process conditions (pressure, temperature, stirrer speed, water content, substrates molar ratio, incubation time, solvent and substrates flow rates) were optimised. A complementary study of the model system substrates/CO2 vapour-liquid phase equilibria in two different apparatuses (a variable-volume view celi and a batch stirred reactor), using the synthetic and static-analytic methods was carried out. Kinetic observations on the pressure effect exhibited that liquid reaction mixture in subcritical conditions led to higher performance than when diluted in a single supercritical phase. A cogent physical explanation of the pressure effect on the reaction performance by exploiting thermodynamic arguments was put forward. The potential of developing enzymatic reactions in liquid rich in dense CO2 has bean explained on the basis of the high solubility of CO2 in substrates liquid mixture. On this basis, the strategy of performing biocatalysis in SC-CO2 in subcritical conditions of the whole reaction bulk is bound to find an increasing range of biotechnological applications for large-scala preparation. The outlook for exploitation of dense CO2 at lower pressures in developing new biotransformation schemes is very promising. Once a deep understanding of the biocatalysis in den se CO2 and of the pressure influence has bean acquired, in the second part of this research work an attempt to confirm these successful first results obtained by producing organic compounds with high added value by enzymatic reaction in dense CO2 was started. Research efforts were aimed to the production of enantiopure compounds by lipase-catalysed resolution in SC-CO2 combined with ILs, benefiting from the advantages of bothneoteric solvents properties. By combining SC-CO2 and ILs, an integral process of biocatalysis and separation can be developed since SC-CO2 is showing high ability to extract hydrophobic compounds from certain ILs, as it is high soluble in IL phase, while ILs are not measurably soluble in the SC-CO2. Sec-alcohols (Le. rac-1-phenylethanol) were chosen as model systems for the lipase-mediated kinetic resolution in dense CO2 combined with ILs by transesterification with vinyl acetate as acyl denar in the acyl transfer reaction over immobilised lipase B from Candida antarctica (NOVOZYM 435). Screening and optimization of several reaction parameters (pressure, stirrer speed, enzyme concentration, ionic liquid content, substrates molar ratio and incubation time) on the kinetic resolution of racemates of (+-)-1-phenylethanol in several ILs, dense CO2 and biphasic IL/SC-CO2 systems were developed in a high-pressure variable-volume view celI. This study has highlighted that by increasing the amount of the chiral catalyst, of the suitable solvent and of the acyl denar is a successful approach for the enzymatic kinetic resolution of racemates. The physical explanation of the pressure effect on the reaction performance by exploiting thermodynamic arguments put forward investigating the lipase-mediated wax esters synthesis in dense CO2 was validated. ILlSC-CO2 biphasic systems resulted excellent reaction media for enzyme-catalyzed resolution of racemic mixtures. On this basis, this PhD thesis is aimed to open new perspectives to develop integral green chemical processes by appropriate ILs/SC-CO2 biphasic systems because of the physical and chemical characteristics of these solvents and the enhanced catalytic properties of enzymes.
