An in silico environmental risk assessment of palm oil transesterification in supercritical ethanol as a tool to enhance sustainable biofuel production

Abstract

An in silico methodology was employed to assess the ecotoxicity of biofuels produced through the supercritical transesterification of palm oil with ethanol. The study correlated operating conditions (temperature and pressure) with variations in the composition of the resulting mixtures and their impact on key ecotoxicological factors, including molecular weight distribution, bioaccumulation factor (BCF), biodegradability, soil sorption coefficient (Log Koc), and octanol-air partition coefficient (Log Koa). Four biofuel samples were analyzed under distinct conditions: S1 (350 °C, 10.3 MPa), S2 (450 °C, 10.3 MPa), S3 (350 °C, 17.2 MPa), and S4 (450 °C, 17.2 MPa). Higher temperatures promoted thermal decomposition and polymerization, forming high-molecular-weight compounds, while increased pressure amplified this effect (up to 300 g·mol⁻¹ in S4). Ecotoxicological assessments revealed that S2 and S3 exhibited lower bioaccumulation potential (Log Kow < 3.5 in over 50 % of compounds) and high biodegradability, with more than 90 % degrading rapidly (BIOWIN 3 > 2.75). In contrast, S1 and S4 contained a higher proportion of compounds with elevated bioaccumulation potential and reduced biodegradability. Compared to commercial diesel (B8 blend), biofuels demonstrated a lower proportion of compounds with high soil adsorption potential (Log Koc > 4.5), reducing their environmental impact. Therefore, samples S2 and S3 stand out for their lower ecotoxicity and balanced composition of fatty acid ethyl esters (FAEE), which are less toxic than the fatty acid methyl esters (FAME) found in B8. This study emphasizes the significance of in silico evaluations in selecting emerging biofuels and mitigating their environmental impact.