Published: January 25, 2011 r2011 American Chemical Society 2981 dx.doi.org/10.1021/ie101660q | Ind. Eng. Chem. Res. 2011, 50, 2981–2993 ARTICLE pubs.acs.org/IECR Incorporating Exergy Analysis and Inherent Safety Analysis for Sustainability Assessment of Biofuels Xiang Li, † Anand Zanwar, † Abhishek Jayswal, † Helen H. Lou,* ,† and Yinlun Huang ‡ † Dan F. Smith Department of Chemical Engineering, Lamar University, P.O. Box 10053, Beaumont, Texas 77710, United States ‡ Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, Michigan 48202, United States ABSTRACT: In the design of chemical/energy production systems, a major challenge is how to quantify the sustainability of the systems. Concerns on economic return and environmental impacts have been well received by researchers and practitioners. However, the irreversibility of the process has not been taken into consideration yet. Based on the first and second laws of thermodynamics, exergy analysis allows accounting for irreversibility in the process and provides a detailed mechanism for tracking the transformation of energy and chemicals. Sustainability assessment in the societal dimension is mostly a “soft” activity, as the aspects to be considered and the method of evaluation are frequently subjective. How to assess the societal impact of a process in the early design stage remains as a challenging issue. This paper will present a sustainability assessment method incorporating economic, environmental, efficiency, and societal concerns. The efficiency assessment is conducted through exergy analysis, while the societal concerns are measured by an enhanced inherent safety index method. In conjunction with a multicriteria decision-analysis method, this methodology will provide critical guidance to the designers. The efficacy of this methodology will be demonstrated through a case study on biodiesel production processes. The results show that the new heterogeneous catalyst process performs better than the traditional homogeneous process in every dimension. ’ INTRODUCTION Sustainability is a global issue for the long-term development of human society and ecosystem. The most widely known defini- tion is given by United Nation in 1987: “Sustainable develop- ment is development which meets the needs of the present with- out compromising the ability of future generations to meet their own needs.” 1 This combination of sustainability and develop- ment tries to reconcile economic growth with a new concern for environmental protection and societal issues. In chemical engineering, process systems engineering is always positioned to address the challenges of sustainability, especially in the early design stage. The consistent strictness of environmental regulations and continuing need to reduce costs have been chal- lenging the designers. In sustainable development, measuring the environmental and social impacts of an economic activity using specific and defined indicators is very important. The key question is how to assess sustainability and which indicators should be used. Current research on sustainability assessment are heading toward combining economic, ecological, and social indicators of sustain- ability. Different indices were proposed. 2-4 Many methodologies for process design assessment and selection have been guided generally by criteria integration, as reported by many researchers (Shah et al., 2003; Azapagic et al., 2006; Narayanan et al., 2007; Carvalho et al., 2008; Halim and Srinivasan, 2008; Sugiyama et al., 2008; Seay and Eden, 2009a,b; Othman et al., 2010). 5-13 In these works, the aspects of sustainability become an integral part of process design. The methodologies they developed have been used in the analysis and selection of design alternatives. These works have paved a way for a systematic assessment methodol- ogy. However, there are two issues that remain unsolved: (1) how to address the irreversibility/efficiency of the process and (2) how to address the societal performance of a process. In this work, the authors present a sustainability assessment methodol- ogy that addresses these two issues systematically in the early design stage. An overall flowchart is shown in Figure 1a to illus- trate the complete assessment process in this work. For practical consideration, this parallel assessment approach can only be used for up to two cases. If there are more than two design cases to be evaluated, the authors would recommend a series flowsheet, as shown in Figure 1b. In this approach, the economic performance will be considered first. The processes with unacceptable eco- nomic performance are eliminated from further consideration. The societal impacts are then evaluated followed by the assess- ment of the environmental dimensions, which include potential environmental impact and the efficiency of the process. This sequence is set because the designer needs to check the inbound safety issues first. If the inbound safety cannot be satisfied, the potential environmental impacts must be undesirable. The efficiency is checked last because there are strict regulations on safety and environmental issues, but no such regulations on effi- ciency. This series procedure improves the efficiency of screening by eliminating non viable processes at the early design stage. As shown in Figure 1, this research intends to investigate the sustainability of a chemical process from the following aspects: economic, environment, and society. The environmental dimen- sion encompasses two subcategories: potential environmental impact and efficiency. The efficiency assessment is conducted through exergy analysis, while the societal concerns are measured by an enhanced inherent safety index method. In conjunction Received: August 3, 2010 Accepted: December 6, 2010 Revised: December 3, 2010