Development of a methodology for the sustainability evaluation of biodiesel production from vegetable oil

Our work aims to extend the application field of a general framework for the evaluation of chemical continuous processes sustainability, i.e. Process Sustainability Prediction (PSP) Framework proposed by Fermeglia et al. [1], in order to perform a sustainability analysis of conventional processes of biotech industry, e.g. the biomass conversion to biofuel. The procedure proposed allows to choose the best operating parameters and inlet streams mass flow of the continuous process for the conversion of palm oil to biodiesel, employing a broad methodology that comprehends each aspect of sustainability, i.e. economy, environment and society. One indicator for each sustainability pillar has been adopted obtaining a global estimation of sustainability performances of process designs which will lead to the adoption of the most sustainable design among the different alternatives. The most relevant characteristics of our approach are the quickness of the sustainability evaluation as well as the opportunity of performing the analysis on a wide number of alternatives avoiding the need of new experimental data for each one. These benefits provided by our methodology give a considerable contribution to the wider context of sustainability assessment, reducing the number of possible alternatives to investigate using Life Cycle Assessment (LCA), a well-established but time-demanding methodology. The methodology proposed by Martins [2], based on four indicators, has been modified merging two indicators related to economic performances into a single one to reduce redundancy and considering the mass fraction of chemicals involved in the process instead of grouping them into quantity classes, aiming to avoid the imbalance generating by the adoption of various chemicals. The different process alternatives have been created performing a sensitivity analysis of the transformation process of palm oil into biodiesel [3] implemented in a process simulator (Aspen Plus), which includes transesterification, methanol recovery, water washing, fatty acid methyl ester (FAME) purification, catalyst removal and glycerol purification. Vegetable oil is the mixture of triglycerides (TG) as specified in [3], while the composition profile of palm oil feedstock is determined by Che Man[4]. The toxicity of compounds involved in the process has been estimated using quantum-mechanics property of molecular structures using COSMO-RS in order to calculate logKow, which is related to the hydro solubility of compounds and is adopted to evaluate whether a compound is more likely to reside in organic phase or in aquatic one. The scores obtained for each process alternative have been analysed using Data Envelopment Analyis (DEA) [6] in order to identify the optimal design and calculate the improvement needed for the others to become as efficient as the optimal one.