Biodiesel Preparation By Tanseterification In Supercritical Methanol And Combustion Mechanisms

Biodiesel is a renewable, new environmentally friendly biomass fuel, which is a ideal substitute for petroleum diesel. In recent years, the competition in the field of new energy technology focuses on biodiesel. Biodiesel is made of methyl esters of fatty acids, produced by transesterification reaction of vegetable oil or animal fat with methanol. Biodiesel is superior to petroleum diesel in terms of sulfur content, flash point, aromatic content, biodegradability and other capabilities. Besides, biodiesel can be directly used in traditional engines without any modification, so it has a bright future.To overcome many shortcomings of biodiesel production process using traditional acid and alkaline catalysis methods, such as complex process, difficulties in separating the products. In this paper, the supercritical methanol transesterification reaction mechanisms and the factors influencing the process are studied. The combustion kinetics of biodiesel produced in different supercritical conditions is explored. It mainly concludes these contents as follows:The system of supercritical transesterification reaction is designed and set up. Three different kinds of biodiesels are separately produced using rapeseed oil, soybean oil and palm oil through supercritical transesterification reaction, and then theirs components are analyzed by gas chromatograph. In this paper, rapeseed oil is chosen as an example to study the factors affect conversion rate of the methyl esters, such as reaction temperature, reaction time, reaction pressure and the molar ratio of methanol to oil. And the optimal reaction conditions is obtained at the temperature of 300℃, pressure of 11MPa, molar ratio of 42:1 and reation time of 20 min. It is found that rapeseed oil can be completely converted to biodiesel within 20min at 300℃, which is much faster than that of 255℃. The conversion rate of methyl esters has been greatly improved when reaction pressure is increased from 9MPa to 11MPa. And increasing molar ratio of methanol to oil also results in increasing conversion rate. A model of transesterification reaction rate is established to get the transesterification reaction rate in different reaction conditions.The biodiesel combustion reaction mechanisms and affecting factors of tranesterification in supercritical methanol are studied. The results show that the ignition temperature of biodiesel from rapeseed oil, soybean oil and palm oil is 257.6℃, 240.4 and 238℃, respectively. The ignition temperature and activation energy decreases with increasing conversion rate of methyl esters. When the supercritical transesterification reaction temperature is increased from 255℃to 300℃, the conversion of methyl esters of the biodiesel produced within 20min increases from 13% to over 98%, the ignition temperature decreases from 331.4℃to 257.6℃, as well as the activation energy decreases from 143.6kJ/mol to 84.2kJ/mol. Supercritical transesterification reaction pressure and molar ratio of methanol to oil also affect the ignition temperature, activation energy and other kinetic parameters. At last, a model of biodiesel combustion kinetics is established to study the activation energy of different biodiesel, and obtained the law.