Currently, due to population growth and industrial expansion, the consumption of fossil fuels is continuously increasing. On the other hand, the limited resources of these fuels and the environmental pollution they cause have pro‎mp‎ted researchers to consider producing alternative fuels from plant sources. The eucalyptus plant has gained attention because of its high cineole content in its leaves and its extensive applications in the medical, food, wood, and paper industries. In addition to its various applications, this plant can also be used as a source for biodiesel production due to the high oil content in its leaves. The conventional method of oil extraction uses solvents; however, extraction using supercritical fluids, especially supercritical carbon dioxide, has become a focus of interest. In this study, response surface methodology and central composite design were employed to design experiments un-der different operational conditions. The impact of four variables, including temperature, pressure, flow rate of supercritical carbon dioxide, and dynamic time, was investigated on the yield and recovery rate of oil extraction within the ranges of 35 to 75 degrees Celsius, 15 to 35 megapascals, 0.8 to 2.2 milliliters per minute, and 40 to 160 minutes, respectively. For biodiesel production, the transesterification method was used along with the oil extracted by solvent that had the highest extraction yield. The results obtained from the extraction process and the transesterification method, including extraction yield, oil recovery percentage, and biodiesel yield (the total methyl esters of fatty acids), were presented. The experiments showed that the extraction model had a coefficient of determination of 95.27 and an adjusted coefficient of determination of 91.12, indicating a good fit. The findings revealed that with an increase in pressure and dynamic time, the amount of oil extracted increases. This increase is attributed to the rise in the density of the supercritical fluid at high pressures and the in-creased driving force due to fresh solvent flow and longer dynamic time. However, with further increases in pressure and dynamic time, the slope of the extraction percentage decreases; this is because increased pressure may reduce permeability and mass transfer coefficient, and with longer time, the amount of oil available in the sample decreases, leading to lower extraction. Increasing the temperature up to about 55 to 60 degrees Celsius causes an increase in the oil extraction percentage, as the vapor pressure of the solute components increases, meaning that the solubility of the solute in supercritical carbon dioxide in-creases. However, with further temperature increases, the oil extraction percentage decreases due to the reduction in solvent density and consequently the solubility of supercritical carbon dioxide. It is also anticipated that increasing the flow rate up to about 1.7 milliliters per minute will increase the oil recovery percentage due to a reduction in the mass transfer boundary layer thickness around solid particles. However, with further increases in flow rate, the oil recovery percentage will decrease due to reduced residence time and insufficient contact of the solvent with the solid. The response surface method identified the optimal operational conditions for oil extraction at a temperature of 57.5 degrees Celsius, pressure of 35 mega-pascals, flow rate of 1.7 milliliters per minute, and dynamic time of 160 minutes, calculating the optimal extraction yield to be 13.12%, which correlates well with the laboratory results of 11.32%. Finally, the yield of biodiesel obtained from the oil produced under the optimal ex-traction conditions reached 88.2%.

علي اكبر دادخواه

محسن محمدي , حميد زيلوئي