Study On Biodiesel Prepared By Hydrodynamic Cavitation Technology

Biodiesel is a sort of renewable fuel energy sources. Developing biodiesel industry is one of the effective ways to deal with energy crisis and environmental pollution today. High production cost is the biggest obstruction to the development of biodiesel industry in our country. This paper tries to develop a new-style, time and energy saving production technology for reducing the production cost of biodiesel.High temperature and pressure will be produced at the center point of bubbles when cavitation bubbles collapse in liquid during hydrodynamic cavitation process, accompanying with a series of cavitational effects. Because of its liberative energy and special environment, hydrodynamic cavitation can be used to intensify chemical reaction processes. Therefore, a hydrodynamic cavitation set-up was designed to intensify transesterification reaction process between rapeseed oil and methanol in this paper.The effects of inlet pressure of cavitation element, orifice plate, molar ratio of methanol to oil, reaction time, KOH amount and reaction temperature on transesterification were studied with the help of hydrodynamic cavitation. Orthogonality experiments indicate that the order of the impact factors is the molar ratio of methanol to oil > KOH amount > inlet pressure > reaction time, according to biodiesel yield. The effect of temperature on the yield was also investigated. The optimal reaction condition is 600 kPa inlet pressure, 6:1 molar ratio of methanol to oil, 1.0% KOH and 20 min. Under the optimal reaction condition, biodiesel yield more than 99% was obtained. The transesterification reaction time and yield obtained from hydrodynamic cavitation are better than that of mechanical stirring.In the present study, six kinds of orifice plates with different diameter and number of holes were used to investigate the effects of structure of orifice plates on the results of transesterification. Results shows that specific perimeter and cavitation number are the main parameters which affect the results of transesterification. If flow area is fixed on an orifice palte, many more number of holes but with smaller diameter is preferred.Futhermore, emulsification and intensification of hydrodynamic cavitation technology were considered. Hydrodynamic cavitation can emulsify oil and methanol system resulting in increasing the contact area greatly between the two phases of liquid, which lead to reaction process enhancement. Hydrodynamic cavitation is proved to be a time and energy saving method. Acoustic cavitation, which is similar to hydrodynamic cavitation, is applied to mix the oil and methanol system to make the two phases emulsify, and then particle size of emulsion drop is tested by laser particle size analyzer(Zetasizer 3000). Results indicate that the mean diameter of emulsion drop is 37.8 nm, and cavitation technology is an excellent process intensification method to emulsify oil and methanol system.The scale-up experiments indicate that the equipment of hydrodynamic cavitation is simple and reliable, and easier to be carried out in industry than other process intensification methods. The properties of the biodisel prepared from rapeseed oil are in accord with China biodiesel standard.