It is essential to provide the most appropriate bioethanol production conditions. In this way, a considerable amount of energy will be saved. In the present study, three types of sugars, including sugarcane juice, sugarcane, and sugar beet molasses were chosen as raw materials. The fermentation was carried out at three different reaction times (24, 48, 72 h) and three temperature levels (25, 30, 35 °C). Experimental samples were chosen based on the Box-Behnken Design (BBD). To evaluate the effect of fermentation factors (time, temp, ST) on responses (density, viscosity, FP, ON, and BIOC) based on the BBD design, the total number of experiments was 17 runs, including four central points and 13 factorial points. Afterward, the bioethanol concentration (BIOC) and its physical properties, including viscosity, density, flash point (FP), and octane number (ON), were optimized based on the operating conditions. The response surface methodology (RSM) was performed to find the best fermentation conditions in which the bioethanol physical properties reach the optimal values. The results indicated that the optimal conditions for input variables were reported for sugar beet molasses, after 72 h, at 35 °C, and the corresponding responses were 12.8 g/l for the BIOC, 2.28 mPa.s for viscosity, 0.9767 g/cm3 for density, 28.52 °C for the FP, and 95.41 for the ON. The high values of R2 and low error rate showed that the RSM could successfully optimize the responses. The present work suggests a less expensive and less time-consuming approach that is helpful for fuel production plants.

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