chapter  4
32 Pages

Process Intensifi cation by Miniaturization

ByJoelle Aubin, Jean-Marc Commenge, Laurent Falk, Laurent Prat

Fine chemicals and pharmaceuticals industries produce high value-added molecules in discontinuous workshops, mainly comprised of stirred tanks. Whereas the synthesized products result from advanced chemical research, the corresponding production processes are based on poorly effi cient devices that may exhibit detrimental drawbacks with respect to the product quality, the environment (through excessive energy or solvent requirements), as well as process safety. The low performance of such equipment, and their accompanying high operating costs, is currently the basis of an awareness of the fi ne chemicals industry. This is particularly obvious for the production of intermediate products, for which the limitations induced by medium-size and large-size stirred tanks cause product losses by their low selectivity. Indeed, stirred vessels possess low thermal management capacities. For this reason, exothermic reactions are often performed in fed batch reactors or require appropriate dilution of the reactants. This can increase the amount of impurities and the need for additional downstream separation steps. The use of solvents is also detrimental for several reasons. Firstly, the use of solvents that cannot be fully refi ned and recycled induces direct and indirect environmental wastes. Secondly, additional separation units, as well as waste treatment and solvent recycling steps require large amounts of energy, and these expenses increase with the quantity of solvent involved in the process. Furthermore since the reaction rates are directly related to the concentration of reactants, the above-mentioned dilution contributes to a decrease in reaction rates. This results in an increase in the synthesis times, which induces an increase in the operating costs and the energy consumption, as well as a decrease in the productivity per unit volume. Finally, scale-up from the laboratory scale to the production scale is critical, especially for new added-value molecules. The use of

low-performance and diffi cultly scalable equipment lengthens the development steps before industrialization and the time to market. The corresponding costs can be particularly penalizing in the current context of strong economic competition.