Reaction-reaction integration allows for the increase of process efficiency through the improvement of reaction processes. However, separation is the step where major costs are generated in the process industry. Therefore, reaction-separation integration could have the highest impact on the overall process in comparison with homogeneous integration of processes (reaction-reaction, separation-sep­aration; Cardona and Sanchez, 2007). The reaction-separation integration is a

TABLE 9.5

Integration of Reaction-Reaction Processes by Consolidated Bioprocessing (CBP) for Fuel Ethanol Production from Different feedstocks

particularly attractive alternative for the intensification of alcoholic fermentation processes. When ethanol is removed from the culture broth, its inhibition effect on growth rate is diminished or neutralized leading to a substantial improvement in the performance of ethanol-producing microorganisms. This improved perfor­mance can permit the increase of substrate conversion into ethanol. In particular, higher conversions make possible the utilization of concentrated culture media (with sugar content greater than 150 g/L) resulting in increased process produc­tivities. From an energy viewpoint, this type of integration allows the increase of ethanol concentration in the culture broth. This fact has a direct effect on distil­lation costs since more concentrated streams feeding the columns imply lower steam demands for the reboilers and, therefore, lower energy costs.

For these reasons, most of the proposed configurations using reaction-sepa­ration integration are related to the ethanol removal by different means including the coupling of different unit operations to the fermentation or the accomplish­ment of simultaneous processes for favoring the in situ removal of ethanol from culture broth.