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Ultrasonic on Transesterification Reaction for Biodiesel Production

Definition

the effect of ultrasonic on the transesterification reaction of jatropha oil to biodiesel was studied in both homogeneous and heterogeneous catalyst systems. All reactions were operated at 9:1 methanol to oil ratio. In homogeneous catalyst system, the ultrasonic power of 1500 W and frequency of 20 kHz were applied to the mixture of hot oil (100oC) and methanol with 0.5% NaOH. The ultrasonic transesterification reaction time of 10, 20, and 30 sec were varied. It was found that at the 20 sec reaction time, biodiesel can be produced with high methyl ester content up to 98%. In case of heterogeneous catalyst system, firstly ultrasonic was used to mix together of oil and methanol, then the mixture was passed through the second step for fully transesterification reaction using K/Al2O3 as catalyst. Various parameters such as ultrasonic mixing time, reaction temperature and amount of catalyst were applied to find the optimum condition for the conversion of jatropha oil to biodiesel. It was found that the methyl ester content over 97% can be achieved from all condition. In addition, the contents of mono-, di-, triglycerides in biodiesel were analyzed and compared at different reaction conditions.

The conventional biodiesel production is known as method producing large amount of waste water. Therefore, a new process using heterogeneous catalyst has been developed for environmentfriendly and reduction of production cost. Several different heterogeneous basic catalysts have been proposed for transesterification reaction such as CaO, MgO, ZnO, and Na/γ-Al2O3 etc [3,7]. Normally, the reaction time of biodiesel production from homogeneous transesterification is around 30 min to 1 h depending on reaction temperature, FFA in oil, and amount of catalyst [8]. To shorten the reaction time, ultrasonic wave is one technique providing excellent mixing between the two phases. It will break down the liquid and form the cavitation bubbles resulting in the rising of mass transfer rate and acoustic streaming mixing

The system is equipped with convertor, horn, and reactor. The ultrasonic wave was generated from transducer in the convertor part and transmitted to the horn tip to cause the cavitations in the mixture of oil and methanol. Ultrasonic power and frequency were applied at 1500 W and 20 kHz, respectively into the reaction mixture of 9:1 methanol to oil molar ratio. In this experiment, the neutralized jatropha oil was used and its properties of density, viscosity, acid value, and free fatty acid were measured. For homogeneous transesterification system, a 100 mL of jatropha oil was heated at 100 oC and fed into the ultrasonic reactor to mix with the solution of 0.5 wt% NaOH catalyst in methanol. The ultrasonic reaction time was varied at 10, 20, and 30 sec.

In the heterogeneous transesterification system, ultrasonic was used to enhance the well mixing of jatropha oil and methanol before doing the reaction in the three-neck flask using K/Al2O3 as catalyst. Reaction temperature was controlled at 60oC with time of 0.5, 1, and 3 h. The ultrasonic mixing time was varied at 0, 10, 20, and 30 sec. Furthermore, three different amounts (3.3%, 5%, and 15%) of K/Al2O3 catalyst were used for the reaction. After reaction, glycerol was separated by gravitation and methyl ester was cleaned to remove the access alkali, methanol and water. Consequently, the purified methyl ester or biodiesel was measured for viscosity (Viscometer, Brookfield TC-200) and glyceride content was analyzed using Gas Chromatography . The free fatty acid methyl ester content was analyzed using Gas Chromatography.

In heterogeneous catalyst system, at first oil and methanol were mixed using ultrasound and then K/Al2O3 catalyst was added for the reaction. Table 3 shows the value of viscosity under the change of catalyst amount, ultrasonic mixing time, and reaction time. It was found that catalyst amount is more influential on reaction than ultrasonic mixing time and reaction time. Therefore, the amount of catalyst was fixed for the next study. By using 5% K/Al2O3 catalyst and 3h reaction time, the di- and tri-glyceride contents are remarkably decreased when the ultrasonic mixing time is increased from 5 to 20 sec. The longer ultrasonic mixing time than 20 sec will present less change of glyceride content in biodiesel.

 

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