Life cycle assessment multi-objective optimization for eco-efficient biodiesel production using waste cooking oil

Abstract

In recent decades, fossil fuel consumption has increased exponentially despite limited resources, high cost, excessive air pollution and environmental degradation. This has contributed to an increasing recognition of biodiesel as an alternative combustible. This combustible is produced by a process of chemical transesterification. The study investigates modelling and optimal conditions for biodiesel production. It is based on five input process parameters that cause the greater environmental impact when employing used cooking oil. These input parameters are the methanol to oil molar ratio, catalyst dose, reaction temperature, reaction time and stirred speed. Biodiesel yield, high heating value and energy consumption also were considered to be output process variables, whereas global warming, acidification, human toxicity, terrestrial ecotoxicity and fresh water aquatic ecotoxicity were considered to be environmental impacts of the process. The effect on the environment of various input process parameters is often determined by life cycle assessment. Current paper provides a novel optimization of biodiesel production from waste cooking oil using multi-response surface methodology and life cycle assessment. It improves a new optimal sustainability production of biodiesel by combining the input process parameters, while minimizing the environmental impacts of the process. Four different optimization scenarios were proposed. The first scenario is one with a higher yield and higher heating value, but requires less catalyst and a lower methanol to oil molar ratio, as well as the power necessary for the chemical process. The second scenario attempts to minimize the environmental impact of the process on global warming, acidification, human toxicity, terrestrial ecotoxicity and fresh water aquatic ecotoxicity, while minimizing the methanol to oil molar ratio and the catalyst dose. In addition to considering the input process parameters and environmental impacts in the second scenario, the third scenario minimizes the power that the chemical process requires. Finally, the fourth scenario considered the same input process parameters and environmental impact as the third scenario in an effort to minimize the reaction time of the process. This fourth scenario was the one of least environmental impact in the production of biodiesel (global warming = 0.351768 kg CO2 eq.; human toxicity = 0.103402 kg 1.4-BD eq. and fresh water aquatic ecotoxicity = 0.027826 kg 1.4-BD eq.), in an efficient way ((η = 0.91374) while the calorific value of biodiesel obtained was high 42.466742 MJ/kg). The results enabled one to conclude that it is possible to optimize the chemical process in biodiesel production for a high yield and high heating value of that the biofuel, as well as a lower environmental impact.