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Journal of Cleaner Production
journal homepage: www.elsevier.com/locate/jclepro
Simulation and life cycle assessment of process design alternatives for biodiesel production from waste vegetable oils
Sérgio Morais a, b, *, Teresa M. Mata a, António A. Martins a, Gilberto A. Pinto c, Carlos A.V.Costa a
Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal REQUIMTE/Instituto Superior de Engenharia do Porto (ISEP), Rua Dr. António Bernardino de Almeida, 431 4200-072 Porto, Portugal c Departamento de Engenharia Química, Instituto Superior de Engenharia do Porto (ISEP), Rua Dr. António Bernardino de Almeida, 431 4200-072 Porto, Portugal
ar t i c l e i n f o
Article history: Received 17 July 2009 Received in revised form 13 March 2010 Accepted 25 April 2010 Available online 31 May 2010 Keywords: Biodiesel Waste vegetable oil Process design Process simulation Life cycle assessment (LCA) Alkali-catalyzed process Acid-catalyzed process Supercritical methanol process
a b s t r a c t
This study uses the process simulator ASPENPlusÒ and Life Cycle Assessment (LCA) to compare three process design alternatives for biodiesel production from waste vegetable oils that are: the conventional alkali-catalyzed process including a free fatty acids (FFAs) pre-treatment, the acid-catalyzed process, and the supercritical methanol process using propane as co-solvent. Results show that the supercritical methanol process using propane asco-solvent is the most environmentally favorable alternative. Its smaller steam consumption in comparison with the other process design alternatives leads to a lower contribution to the potential environmental impacts (PEI’s). The acid-catalyzed process generally shows the highest PEI’s, in particular due to the high energy requirements associated with methanol recovery operations. Ó 2010 ElsevierLtd. All rights reserved.
1. Introduction Some of the biodiesel advantages over petroleum diesel are extensively reported in literature (Sheehan et al., 1998; Nas and Berktay, 2007; Ma and Hanna, 1999; Srivastava and Prasad, 2000; Fukuda et al., 2001; Dorado et al., 2003; Knothe et al., 2003; Beer et al., 2002; Utlu and Kocak, 2008). Among others, it is derived from renewable resources, it isbiodegradable and with a higher ﬂash point (423 K) that makes it less volatile and safer during its transportation and handling. Moreover, biodiesel has a more favorable combustion emission proﬁle than diesel, such as lower emissions of carbon monoxide, particulate matter and unburned hydrocarbons. The high costs and limited availability of biodiesel feedstocks are however critical issues in thisindustry. The costs of vegetable oils can be up to 75% of the total manufacturing cost, which makes biodiesel production costs approximately 1.5 times higher than
those of diesel (Haas et al., 2002; Phan and Phan, 2008). For this reason, the use of waste vegetable oils can be an effective way of reducing production costs since it is 2e3 times cheaper than virgin vegetable oils (Phan and Phan,2008). In addition, it helps solving the environmental problems associated with disposal of the waste vegetable oils. The purpose of this study is to compare the potential environmental impacts of three process design alternatives for biodiesel production from waste vegetable oils, using process simulation and the life cycle assessment (LCA) methodology. The process design alternatives include: (1)the alkali-catalyzed process with free fatty acids (FFAs) pre-treatment, (2) the acid-catalyzed process, and (3) the supercritical methanol process using propane as co-solvent. These process design alternatives are simulated using the process simulator ASPEN PlusÒ in order to estimate the inventory data for the three process typologies, considering the same plant capacity and product purity...