A performance comparison of cyclopentyl methyl ether (CPME) and hexane solvents in oil extraction from sewage sludge for biodiesel production; RSM optimization

Abstract

A comparative study of oil extraction from secondary dry sludge was performed via Reflux and Folch methods by cyclopentyl methyl ether (CPME) and hexane as green and organic solvents, respectively. Response surface methodology based on Box-Behnken design (RSM-BBD) was utilized to optimize and predict the impact of influential factors, including sludge amount (4–6 g), the volume of solvent (12–16 mL), and extraction time (2–6 h). The maximum oil extraction efficiency was 8.078 % and 4.076 % under the optimal conditions: 5.15 g, 16 mL, 2 h for CPME, and 4.22 g, 11 mL, 2 h for hexane. The raw sludge was characterized by FESEM and XRF analyses, while the extracted oil characteristics were determined by GC-Mass and FTIR methods. As a result, the Folch method by CPME solvent was a more efficient way to extract oil from sewage sludge. Finally, biodiesel was produced via the transesterification double-step process (TDSP) using NaOH/Clinoptilolite-Fe3O4 magnetic catalyst. The production efficiency of biodiesel from the oil extracted by CPME and hexane is 6.94 % and 4.1 %, respectively. The maximum yield of biodiesel production was6.94 % under the optimum reaction conditions: methanol to oil molar ratio of 10:1, catalyst weight of 0.45 wt%, and reaction time of 2.5 h with the help of the electrolysis method.