Process integration is gaining more and more interest due to the advantages related to its application in the case of bioethanol production: reduction of energy costs, decrease in the size and number of process units, and intensification of the biological and downstream processes, among others. For instance, the combina­tion in a same unit of the enzymatic hydrolysis and the microbial transformation leads to the reduction of the negative effect due to the inhibition of the enzymes by the product of the reaction catalyzed by them. This corresponds to an integra­tion of the reaction-reaction type.

In general, reaction-reaction integration has been proposed for the integra­tion of different biological transformations taking place during ethanol produc­tion (Cardona and Sanchez, 2007). This type of integration mainly includes the combination of the enzymatic reactions for hydrolysis of starch or cellulose with the microbial conversion of formed sugars into ethyl alcohol. There exist different possibilities for reaction-reaction integration during production of ethanol from starch (Figure 9.1) and lignocellulosic biomass (Figure 9.2).

Considering as the starting point the nonintegrated separate hydrolysis and fer­mentation (SHF) process, several cases of reaction-reaction integration may be analyzed for ethanol production from both starchy and lignocellulosic materials.