Social and environmental impacts of replacing transesterification agent in soybean biodiesel production: Multi-criteria and principal component analyses

Abstract

The use of renewable feedstocks for biodiesel production makes it an attractive large-scale alternative to fossil diesel. Nevertheless, traditional routes employ methanol as transesterification agent, a fossil based chemical. To improve renewability, governmental policies and subsidies have arisen to promote substitution of methanol. In the Brazilian soybean biodiesel scenario, the objective of this work is to compare the methylic and ethylic production routes, and unveil whether ethanol-based biodiesel has potential to be more sustainable. The comparison is supported by: (i) Construction of the fatty acid methyl ester and fatty acid ethyl ester soybean biodiesel production chains; (ii) Assemblage of the respective inventory matrices to quantify energy and material flows; and (iii) Application of Multi-criteria Analysis and Principal Component Analysis for data interpretation and identification of the most relevant factors affecting sustainability. Focus is on the social and environmental aspects of sustainability. Contrarily to common belief, fatty acid methyl ester, although more environmentally impacting in the step of methanol production, is shown to be generally more sustainable than the ethylic counterpart, which shows a heavy burden in the social dimension, more severe conditions of the transesterification process and extra transport demand, as demonstrated by the multi-criteria analysis, which combines quantitative indicators with ad hoc principles of green process design to provide a criticality matrix and a one-dimensional index, the Sustainability Degree. Principal Component Analysis, on the other hand, indicates average wage, water intensity and carbon intensity as the top influential indicators, out scaling energy consumption. A low compliance to the original objectives of increasing sustainability by substituting fatty acid ethyl ester for fatty acid methyl ester is observed and the importance of the social dimension is thoroughly evidenced.