Comparing three options for biodiesel production from waste vegetable oil

Abstract

Biodiesel production is worthy of continued study and optimization of production procedures due to its environmentally beneficial attributes and its renewable nature. From a waste-management standpoint, production of biodiesel from used cooking oil is environmentally beneficial since it provides a cleaner way of disposing of these products than is typically the case. Biodiesel produced by base-catalyzed transesterification of vegetable oil is usually performed in batch reactors where the required energy is provided by heating accompanied by mechanical mixing. Using this technique, the best yield percentage was obtained using a methanol/oil molar ratio of 6:1, potassium hydroxide as the catalyst (1%), and 65°C temperature for one hour. Alternatively, ultrasonication can provide an effective way to attain the required mixing while providing the necessary activation energy. It was concluded that transesterification by low frequency ultrasound (20 kHz) offered a lot of advantages over the conventional classical procedure. It proved to be efficient (biodiesel yield up to 98-99%), as well as time and energy saving (dramatic reduction of reaction time to 5 min, compared to one hour or more using conventional batch reactor systems, and a remarkable reduction in static separation time to 25 min, compared to 8 hours). The third option studied was the application of microwave irradiation. The application of radio frequency microwave energy offered a fast, easy route to this valuable biofuel with advantages of enhancing the reaction rate and improving the separation process. The methodology allowed for the use of high FFA content feedstock, including used cooking oil, hence reducing the cost of production, which constitutes a major hurdle towards widespread commercialization of biodiesel.

Different techniques for the production of biodiesel from waste vegetable oil

“…Most investigators have observed an optimum reaction time around 1 h (Tomasevic and Siler-Marinkovic, 2003;Meng et al, 2008;Refaat et al, 2008 a). It was reported that excess reaction time does not increase the conversion but favors the backward reaction (hydrolysis of esters) which results in a reduction of product yield (Leung and Guo, 2006).…”

“…Refaat et al (2008 a) reported an optimum temperature of 65 °C, while Meng et al (2008) reported 50 °C as the optimum temperature (Fig. 7).…”

“…Ultrasonic irradiation also proved suitable for large-scale continuous processing of vegetable oils since relatively simple devices can be used to perform the reaction (Stavarache et al, 2007b). Refaat and El Sheltawy (2008) compared the use of ultrasonication for fast production of biodiesel from waste vegetable oil with the conventional basecatalyzed transesterification and concluded that transesterification by low frequency ultrasound (20 kHz) offered a lot of advantages over the conventional classical procedure. It proved to be efficient (biodiesel yield up to 98-99 %), as well as time and energy saving (dramatic reduction of reaction time to 5 min, compared to one hour or more using conventional batch reactor systems and remarkable reduction in static separation time to 25 min, compared to 8 h).…”

Production of Biodiesel from Waste Cooking Oil: A Review

“…The transesterification results clearly establish that there is considerable enhancement in reaction rates. This brings about considerable time saving as well as cost with 100% biodiesel yield by applying microwave irradiation for two minutes compared to one hour with the conventional technique, with adjusted temperature to 65 °C, a MeOH/oil molar ratio of 6:1and potassium hydroxide (1%) used as a catalyst has been studied [42,43] and showed that microwave-enhanced biodiesel is not, at least, inferior to that produced by the conventional technique.…”

Modeling of ultrasound assisted intensification of biodiesel production from neem (Azadirachta indica) oil using response surface methodology and artificial neural network

“…Ultrasound assisted transesterification gives the advantages of shorter reaction period and hence less energy consumption along with using an effective molar ratio of methanol to oil as compared to conventional mechanical stirring [6]. Ultrasound has been successfully employed to produce biodiesel from vegetable edible and non-edible oils are mostly used although oil-bearing materials such as seeds [7][8][9], rice bran [10], waste cooking oils [11][12][13][14], fish oils [15,16], animal fats [17] and sidestreaming products from edible oil production [18].…”