Review Fuel ethanol production: Process design trends and integration opportunities Carlos A. Cardona a, * ,O ´ scar J. Sa ´nchez a,b a Department of Chemical Engineering, National University of Colombia at Manizales, Cra. 27 No. 64-60 Of. F-505, Manizales, Caldas, Colombia b Department of Engineering, University of Caldas, Calle 65 No. 26-10, Manizales, Caldas, Colombia Received 12 July 2006; received in revised form 4 January 2007; accepted 4 January 2007 Available online 1 March 2007 Abstract Current fuel ethanol research and development deals with process engineering trends for improving biotechnological production of ethanol. In this work, the key role that process design plays during the development of cost-effective technologies is recognized through the analysis of major trends in process synthesis, modeling, simulation and optimization related to ethanol production. Main directions in techno-economical evaluation of fuel ethanol processes are described as well as some prospecting configurations. The most promising alternatives for compensating ethanol production costs by the generation of valuable co-products are analyzed. Opportunities for inte- gration of fuel ethanol production processes and their implications are underlined. Main ways of process intensification through reac- tion–reaction, reaction–separation and separation–separation processes are analyzed in the case of bioethanol production. Some examples of energy integration during ethanol production are also highlighted. Finally, some concluding considerations on current and future research tendencies in fuel ethanol production regarding process design and integration are presented. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Fuel ethanol; Process design; Process synthesis; Process integration; Co-products 1. Introduction Ethanol is one of the most important renewable fuels contributing to the reduction of negative environmental impacts generated by the worldwide utilization of fossil fuels. However, the production of ethanol is a complicated process. The transformation of such biological resources as energy-rich crops (like sugar cane or corn) or lignocellu- losic biomass requires the conditioning or pretreatment of the feedstocks for fermenting organisms to convert them into ethanol. Then, aqueous solutions of ethanol should be concentrated for obtaining hydrous ethanol. This product has to be dehydrated in order to be utilized as an oxygenate for gasoline, the trade form in which ethanol is mostly employed in the transportation sector. The complexity of this process partly explains why fuel ethanol has not played a leading role in comparison to cheaper oil derived fuels. Only in the last years due to rising environmental concerns and to the periodic crises in some of the larger oil exporting countries, has bioethanol become a viable and realistic alternative in the energy market. Therefore, the development of cost-effective technolo- gies for fuel ethanol production is a priority for many research centers, universities and private firms, and even for different governments. Due to the large amount of existing and not completely developed technologies for the production of ethanol (especially from lignocellulosic biomass), the application of process engineering tools is required. Process engineering applied to the production of fuel ethanol includes the design of new innovative pro- cess configurations aimed at reducing ethanol production costs. Through process design, product diversification for ethanol production processes can be achieved implying the improvement of their costs structure thanks to co-product 0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.01.002 * Corresponding author. Tel.: +57 6 8810000x50417; fax: +57 6 8810000x50193. E-mail address: ccardonaal@unal.edu.co (C.A. Cardona). Bioresource Technology 98 (2007) 2415–2457