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Design and Cost Evaluation of a Separation Process for a Multicomponent Mixture Using Dense CO2

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journal contribution
posted on 17.06.2009, 00:00 authored by Laura Álvarez, Ángel Martín, Germán Sanjuán, Lourdes Calvo
Simulations done on the separation of a multicomponent mixture exiting an enzymatic reactor using dense CO2 as solvent are presented. The enzymatic reaction was carried out in the liquid phase although the CO2 was introduced in supercritical state (80 bar and 40 °C). The purpose was to obtain α-methylbenzyl acetate, a fruity and floral aroma used in the food and cosmetic industries, from the corresponding alcohol and acetic anhydride. The separation of the effluent, consisting of five components (two products, the nonconverted reactants, and the solvent) was done in a series of countercurrent extraction columns where, again, CO2 was used as solvent. It was introduced at relatively low pressure (20 bar) since higher values lead to solubilization of all the components. The influence of the S/F ratio, the feed inlet position, the column dimensions and the use of reflux was analyzed for the separation of the main product with a model available from literature. The diameter of the column was estimated to avoid flooding. Then, the flow sheet of the integrated reaction−separation process with CO2 recycling was presented and discussed. Using an pressure−enthalpy diagram, the energy costs were deduced. The fixed costs were also guessed from previous experience. Using both items, the economical evaluation of the process was performed for a 5-d operation corresponding to the annual production of the aroma. The analysis showed that the process could be feasible after a fine optimization of the enzyme lifetime and reaction efficiency since the downstream separation was inexpensive. In order to make the process effectively profitable, applications would have to be found for the rest of the year (e.g., on the synthesis of other esters).

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