Life Cycle Assessment (LCA) and Multi-response Surface Methodology (MRS) to improve biodiesel production from used cooking oil

Abstract

Biodiesel is a fuel that is synthesized by a chemical transesterification process. Several input parameters influence the process. These includes the type and dosage of catalyst, methanol/oil molar ratio, process temperature, stirring time, and stirring speed. Yield, higher heating value and power consumption are usually the process output variables that are studied. Life cycle assessment (LCA) is a tool that is used to evaluate the consumption of energy, raw materials, waste and emissions on the impact of a product or process on the environment. This study seeks to minimize the power consumption, eutrophication and effect on climate change of biodiesel production from waste cooking oil when attempting to maximize its yield and higher heating value by the use of surface methodology (MRS) with desirability functions. Two optimization scenarios were considered in this study. The first one involved obtaining a biodiesel with a higher yield and greater heat also minimizing the dosage of catalyst, methanol/oil molar ratio and power consumption of the chemical process. In addition to the input and output variables considered in the first scenario, the second scenario sought to minimize eutrophication and the effect on climate change. A yield of 0.933 and 0.934, as well as a higher heating value of 43.57 MJ/kg and 43.50 MJ/kg were obtained for the first and second optimization scenarios, respectively. Also obtained were 313.45 E-06 kg PO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> eq. and 309.91 E-06 kg PO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> eq.; and 1873.47 E-05 kg CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> eq. and 1819.04 E-05 kg CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> eq., respectively, for the eutrophication and effect on climate change in the first and second optimization scenarios. An agreement between the experimental and predicted results demonstrates that MRS may be valid for optimizing the chemical process of biodiesel production, generating a biofuel with yield and higher heating value, while reducing the environmental impact.