科研之友
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摘要
The factors influencing the stability of a catalyst are crucial information for the catalytic processes. The main objective of this work was to evaluate the activity of the enzyme Lipozyme 435 in processes with supercritical carbon dioxide (SC-CO2) as reaction medium. The effects of temperature (40-60 degrees C), pressure (10-20 MPa), exposure time (1-6h) and depressurization steps (1-3) on the activity of the enzyme were evaluated. The kinetic data of inactivation and thermodynamic parameters were also determined. Infrared spectroscopy (FT-IR) analyses and field scanning electron microscopy (FESEM) were carried out to investigate the structure of Lipozyme 435. The results showed that the activity of Lipozyme 435 decreased with the increase of pressure, temperature, exposure time and the number of pressurization/depressurization cycles. The thermodynamic parameters showed the stability of the immobilized lipase under the tested conditions, and the kinetic data of inactivation revealed a half-life of 11 h for the lipase exposed to SC-CO2 (40 degrees C/10 MPa) for 1 h. FT-IR analyses suggested a change in the secondary structure of the immobilized lipase, considering the first amide band, while the FESEM images did not present morphological alterations on the macroporous anionic resin used as a support for the enzyme that could affect its activity. The study of the esterification of oleic acid with methanol showed that high yields (Y, glg x h) and esterification rates (X, %) can be obtained under certain process conditions (I 0 MPa and 40 degrees C). Moreover the esterification percentage in supercritical CO2 was 67% higher than in n-hexane medium.
- 出版日期2016-1
