توصيفگر ها :
گياه كلزا , استخراج فوق بحراني , بيوديزل , روش سطح پاسخ
چكيده انگليسي :
Due to the limitations of oil reserves, the increase in international price of fuels and environmental issues caused by using fossil fuels, the tendency towards alternative fuels such as biodiesel and bioethanol has raised. Biodiesel can be obtained from vegetable oils such as rapeseed oil. In the present study, two methods of soxhelet and supercritical fluid has been used for oil extraction, in order to be compared as final results. Two solvents of n-Hexane and Methanol have been used for achieving the most possible amount of oil in soxhelet extraction method. The obtained percentage of efficiency based on the dry weight of the seed for n-Hexane and Methanol, were respectively 47.86 and 51.12 percent. According to the desk research, in supercritical method, the parameters of the sample’s size, co-solvent’s amount and static timing were respectively considered 20-35 mesh, 1 milliliter of Ethanol and 30 minutes for all experiment. In this method, the parameters of pressure, temperature, flow rate and dynamic timing were considered as the effective parameters. Each of the mentioned parameters were considered as follows: pressure in the range of 100-200 bar, temperature in the range of 42-62° Celsius, flow rate in the range of 0.5-1.7 milliliter per minute and dynamic timing of 30-110 minutes. Then, using Response Surface Methodology, Central Composite Design and the software “Minitab”, 31 tests were selected randomly in order to find optimal amounts for obtaining the most possible amount of rapeseed oil. After performing all the tests, the maximum extraction of 55.98 was achieved in the pressure of 20 bar, temperature of 42° Celsius, flow rate of 1.15 milliliter per minute and dynamic timing of 40.51 minutes, using the model determined by the software. Due to the amounts “R2” and “R2_adj” which were respectively equal to 94.21 and 89.14 percent, the model determined by the software was approved. In the following stage, the soxhelet and supercritical oil, through transesterification process with the conditions of the molar ratio of 6 to 1 between methanol and the oil, 1 weight percent of the catalyst, 400 Watts of the ultrasonic device power and in 25 minutes were transformed into biodiesel and the efficiency amounts of 92.88 and 95.16 percent were obtained. Then, their physical features were determined based on ASTM standards and were compared to each other. For the biodiesel obtained through supercritical method, the density of 0.869 gram per cubic centimeters, viscosity of 4.33 square millimeter per second, flash temperature of 170° Celsius, cloud point of -2° Celsius, smoke point of 124° Celsius, acid number of 0.37 and 0.185 percent of free fatty acids were obtained; for the biodiesel obtained through soxhelet method, on the other hand, the density of 0.885 gram per cubic centimeter, viscosity of 4.74 square millimeter per second, flash temperature of 176° Celsius, cloud point of -1° Celsius, smoke point of 129° Celsius, acid number of 0.34 and 0.17 percent of free fatty acids were obtained. At the end, the fatty acids of the biodiesel obtained through supercritical method were recognized, in which the predominant fatty acid was “oleic acid”.
