**4. Fatty acid alkylesters production assisted by ultrasound**

Sound waves are the most common example of longitudinal waves. They travel through any material medium with a speed that depends on the properties of the medium. As the waves travel through air, the elements of air vibrate to produce changes in density and pressure along the direction of motion of the wave. If the source of the sound waves vibrates sinusoidally, the pressure variations are also sinusoidal (Serway and Jewett, 2004).

Sound waves are divided into three categories that cover different frequency ranges

(1) Audible waves lie within the range of sensitivity of the human ear. They can be generated in a variety of ways, such as by musical instruments, human voices, or loudspeakers. (2) Infrasonic waves have frequencies below the audible range. Elephants can use infrasonic waves to communicate with each other, even when separated by many kilometers. (3) Ultrasonic waves have frequencies above the audible range. You may have used a "silent" whistle to retrieve your dog. The ultrasonic sound it emits is easily heard by dogs, although humans cannot detect it at all. Ultrasonic waves are also used in medical imaging (Serway and Jewett, 2004).

Sonochemistry is a branch of chemical research dealing with the chemical effects and applications of ultrasonic waves, that is, sound with frequencies above 20 kHz that lie beyond the upper limit of human hearing. The development of ultrasound in organic synthesis began on 1930 when Richards and Loomis, 1927, applied ultrasound (100-500 KHz) in organic synthesis for determine the effect on the solubility of gases for first time. Developments were very slow, then Luche and Damiano, 1980, reported metal activation reactions using ultrasound probes. Thereafter, reaction systems using US to speed up chemical reactions have been developed.

on tallow), an RF heating for 5 min, and a methanol/tallow molar ratio of 9:1. Response surface methodology was employed to evaluate the influence of NaOH dose, RF heating time, and methanol/tallow ratio. The alkaline concentration showed the largest positive impact on the conversion rate. Similar fast conversion from canola oil to biodiesel was achieved in our previous work, indicating that RF heating, as an accelerating technique for

Fast transesterification of canola oil and methanol for biodiesel production was achieved using radio frequency (RF) heating. The conversion rate of oil to biodiesel reached 97.3% with RF heating for 3 min, a NaOH concentration (based on oil) of 1.0%, and a methanol/oil molar ratio of 9:1. A central composite design (CCD) and response surface methodology (RSM) were employed to evaluate the impact of RF heating time, NaOH concentration, and molar ratio of methanol to oil on conversion efficiency. Experimental results showed that the three factors all significantly affected the conversion rate. NaOH concentration had the largest influence, with the effect being more pronounced at lower (0.2-0.6%, based on weight of oil) concentration. No evident interaction among the three factors was observed. RF heating efficiency was primarily related to the amount of NaOH and methanol. The scale of the experiment was increased by five times (from 20 to 100 g oil per batch) without decrease of the conversion rate, indicating the scale-up potential of RF heating for biodiesel

Sound waves are the most common example of longitudinal waves. They travel through any material medium with a speed that depends on the properties of the medium. As the waves travel through air, the elements of air vibrate to produce changes in density and pressure along the direction of motion of the wave. If the source of the sound waves vibrates

(1) Audible waves lie within the range of sensitivity of the human ear. They can be generated in a variety of ways, such as by musical instruments, human voices, or loudspeakers. (2) Infrasonic waves have frequencies below the audible range. Elephants can use infrasonic waves to communicate with each other, even when separated by many kilometers. (3) Ultrasonic waves have frequencies above the audible range. You may have used a "silent" whistle to retrieve your dog. The ultrasonic sound it emits is easily heard by dogs, although humans cannot detect it at all. Ultrasonic waves are also used in medical

Sonochemistry is a branch of chemical research dealing with the chemical effects and applications of ultrasonic waves, that is, sound with frequencies above 20 kHz that lie beyond the upper limit of human hearing. The development of ultrasound in organic synthesis began on 1930 when Richards and Loomis, 1927, applied ultrasound (100-500 KHz) in organic synthesis for determine the effect on the solubility of gases for first time. Developments were very slow, then Luche and Damiano, 1980, reported metal activation reactions using ultrasound probes. Thereafter, reaction systems using US to speed up

sinusoidally, the pressure variations are also sinusoidal (Serway and Jewett, 2004). Sound waves are divided into three categories that cover different frequency ranges

biodiesel production, had a large applying area (Lui et al., 2011).

**3.3 Optimization production biodiesel under RF irradiation** 

**4. Fatty acid alkylesters production assisted by ultrasound** 

production (Lui et al., 2008).

imaging (Serway and Jewett, 2004).

chemical reactions have been developed.

A low frequency ultrasonic irradiation could be useful for transesterification of triglyceride with alcohol. Ultrasonication provides the mechanical energy for mixing and the required activation energy for initiating the transesterification reaction (Singh et al., 2007). Ultrasonication increases the chemical reaction speed and yield of the transesterification of vegetable oils and animal fats into biodiesel. Ultrasonic assisted transesterification method presents advantages such as shorter reaction time and less energy consumption than the conventional mechanical stirring method, efficient molar ratio of methanol to TG, and simplicity (Ji et al., 2006; Siatis et al., 2006).

Many researchers have tried to solve the mass-transfer limitation problem in biodiesel synthesis using ultrasonic cavitation and hydrodynamic cavitation. Cavitation has been shown to efficiently speed up the transesterification reaction because it simultaneously supplies heating as well as the stirring effect as a result of jet formation on bubble collapse. Cavitation is basically the formation, growth, and implosive collapse of gas or vapour filled microbubbles and can be induced acoustically (using ultrasound) or hydrodynamically in a body of liquid. The collapse of these bubbles lead to local transient high temperatures (g 5000 K) and pressures (g 1000 atm), resulting in the generation of highly reactive species, such as OH•, HO2•, and H• radicals in water. Cavitation effects also increase the mass and heat transfers in a medium and accelerate the reaction rates and yields (Mahamuni and Adewuyi, 2009).

Main factors that vary the yielding in the production of biodiesel using US are:

Effect of Ultrasonic Frequency on Biodiesel Yield. The frequency of the ultrasound has a significant effect on the cavitation process because it alters the critical size of the cavitation bubble, which in turn changes the intensity of the collapse of the cavitation bubbles.

Effect of Ultrasonic Power on Biodiesel Yield. It is well-known that as the ultrasonic power increases, the size of the cavitation bubbles increase leading to more intense collapse of bubble, which causes better emulsion formation of oil and methanol resulting into higher interfacial surface area for mass transfer and hence the higher biodiesel yield. The BD yield increased with increasing ultrasonic power from 150 to 450 W, but the ME content decreased at ultrasonic powers over 450 W. This is due to the decrease of the real irradiation time caused by the increase in the pulse interval required for tuning the temperature due to the extension of the irradiation power (Lee et al., 2011).

Effect of Catalyst Loading. As the amount of KOH increases, the concentration of methoxide anions, which are responsible for nucleophilic attack on the triglyceride molecules to produce biodiesel, also increase, resulting in higher biodiesel yield.

Effect of Oil/Methanol Molar Ratio. As oil and methanol are not miscible into each other, they form a heterogeneous reaction mixture and mass transfer between these two phases becomes important for the transesterification reaction. The presence of ultrasound can help increase the mass transfer between the two phases by the formation of a fine emulsion, which increases the interfacial area between the two phases. Ultrasound can also increase the mass transfer coefficient due to the presence of acoustic streaming and jet formations at the end of cavitation bubble collapse near the phase boundary between oil and methanol phases.

As shown in Fig. 2, the factors with more contribution to the production of biodiesel are ultrasonic power and catalyst loading, then oil/methanol molar ratio and finally, the frequency.

Alternative Methods for

**Oil Catalyst** 

the system is showed in Fig. 3.

Soybean NaOCH3 20g (30%

Chromobacterium viscosum

KOH First

Canola Soybean Corn

Jatropha Lipase

Palm CaO SrO BaO

Waste frying **Catalyst amount (%wt)** 

Soybean KOH 0.5 MeOH 1:6 611kHz, 139W,

Triolein KOH 1.0 MeOH 1:6 40kHz, 1200W,

Soybean Novozym 435 6.0 MeOH 1:6 40kHz, 500W

Jatropha Na/SiO2 3.0 MeOH 1:9 24kHz, 200W,

Palm KOH 20.0 MeOH Petroleum ether

stage 0.7 Second stage 0.3

Fish NaOC2H5 0.8 EtOH 35kHz,

Table 4. Ultrasound assisted transesterification

Coconut KOH 0.75 EtOH 24kHz, 200W,

KOH 1.0 MeOH 1:6 450W, 55C,

in MeOH) **Alcohol**

MeOH 1.6L:80g MeOH

5.0 MeOH 0.7s, 100W/m3,

3.0 MeOH 20kHz, 200W

MeOH 20kHz, 25C, 5min

**Oil to Alcohol molar ratio**

Fatty Acid Alkyl-Esters Production: Microwaves, Radio-Frequency and Ultrasound 281

consumption, by a two-step procedure: first a conventional heating under mechanical stirring (30 min at 45C), followed by ultrasound irradiation at the same temperature (35 min, 600 W, flow rate 55 mL/min). Our studies confirmed that high-throughput ultrasound applications definitively require flow reactors (Cintas et al., 2010). The detailed scheme of

> **Ultrasonic reaction condition**

26C, 30min

25C, 30min

(50%), 40C, 4h 0.5%v/v tertamyl alcohol/oil

21.5kHz,600W, 45C, 1h Flow 55mL/min

15min

30min

30min

Ethyl methyl ketone 47kHz, 340W, 60C, 2h

(50%), 65C, 60min

20kHz, 20C, 30min

7min

**Source of ultrasound** 

Multifrequency transducer UES300C sonochemist

Honda electronic cleaner

Ultrasonic bath KQ500DV Kunshan

3 transducer (21.5kHz)

Probe type VCX-

98 97 95

75.2 60

77.3 95.2 95.2

99

95 95

UP200S Hielscher ultrasonic Gmblt

600

UP200S Hielscher ultrasonic Gmblt

Water bath Bransonic cleaner

Transducer and probe

Bath Probe

UP200S Hielscher ultrasonic Gmblt

Horn transducer 81

**Ester conversion (%)** 

90 (Mahamuni and Adewuyi, 2009)

99 (Hanh et al., 2008)

90 (Cintas et al., 2010)

98.53 (Kumar et

84.5 (Kumar et

al., 2010a)

(Lee et al., 2011)

al., 2011)

(Boey et al., 2011)

(Mootabadi et al., 2010)

(Thanh et al., 2010)

(Armenta et al., 2007)

al., 2010b)

98 (Kumar et

96 (Yu et al., 2010)

**Ref** 

Fig. 2. Percentage contribution of the factors contributing to the production of biodiesel by ultrasound

#### **4.1 Esterification reactions assisted by ultrasound**

Not found reports of this methodology for the esterification reaction in the obtaining of biodiesel.

#### **4.2 Transesterification reactions assisted by ultrasound**

The works that use US in the transesterificatication reaction for the obtaining biodiesel use edible oils as soybean, triolein, palm, canola, fish and coconut. Also, use no edible oil as Jatropha, homogeneous basic catalysts as KOH, and heterogeneous basic catalysts as CaO, SrO, BaO, Na/SiO2 and Novozym435 enzymes and lipase. Table 8 shows the work carried out for bio-diesel production from various feedstocks under different conditions using ultrasound irradiation.

The equipments used are conformed by transducer, cleaner and probe used in batch processes. In recent years, chemistry in flowing systems has become more prominent as a method of carrying out chemical transformations, ranging in scale from microchemistry up to kilogram-scale processes. Compared to classic batch ultrasound reactors, flow reactors stand out for their greater efficiency and flexibility as well as lower energy consumption. Cintas et al., 2010, developed a new ultrasonic flow reactor, a pilot system well suited for reaction scale up. This was applied to the transesterification of soybean oil with methanol for biodiesel production. This reaction is mass-transfer-limited initially because the two reactants are immiscible with each other, then because the glycerol phase separates together with most of the catalyst (Na or K methoxide). In our reactor a mixture of oil (1.6 L), methanol and sodium methoxide 30% in methanol (wt/wt ratio 80:19.5:0.5, respectively) was fully transesterified at about 45 C in 1 h (21.5 kHz, 600 W, flow rate 55 mL/min). The same result could be achieved together with a considerable reduction in energy

Fig. 2. Percentage contribution of the factors contributing to the production of biodiesel by

Not found reports of this methodology for the esterification reaction in the obtaining of

The works that use US in the transesterificatication reaction for the obtaining biodiesel use edible oils as soybean, triolein, palm, canola, fish and coconut. Also, use no edible oil as Jatropha, homogeneous basic catalysts as KOH, and heterogeneous basic catalysts as CaO, SrO, BaO, Na/SiO2 and Novozym435 enzymes and lipase. Table 8 shows the work carried out for bio-diesel production from various feedstocks under different conditions using

The equipments used are conformed by transducer, cleaner and probe used in batch processes. In recent years, chemistry in flowing systems has become more prominent as a method of carrying out chemical transformations, ranging in scale from microchemistry up to kilogram-scale processes. Compared to classic batch ultrasound reactors, flow reactors stand out for their greater efficiency and flexibility as well as lower energy consumption. Cintas et al., 2010, developed a new ultrasonic flow reactor, a pilot system well suited for reaction scale up. This was applied to the transesterification of soybean oil with methanol for biodiesel production. This reaction is mass-transfer-limited initially because the two reactants are immiscible with each other, then because the glycerol phase separates together with most of the catalyst (Na or K methoxide). In our reactor a mixture of oil (1.6 L), methanol and sodium methoxide 30% in methanol (wt/wt ratio 80:19.5:0.5, respectively) was fully transesterified at about 45 C in 1 h (21.5 kHz, 600 W, flow rate 55 mL/min). The same result could be achieved together with a considerable reduction in energy

**4.1 Esterification reactions assisted by ultrasound** 

**4.2 Transesterification reactions assisted by ultrasound** 

ultrasound

biodiesel.

ultrasound irradiation.

consumption, by a two-step procedure: first a conventional heating under mechanical stirring (30 min at 45C), followed by ultrasound irradiation at the same temperature (35 min, 600 W, flow rate 55 mL/min). Our studies confirmed that high-throughput ultrasound applications definitively require flow reactors (Cintas et al., 2010). The detailed scheme of the system is showed in Fig. 3.


Table 4. Ultrasound assisted transesterification

Alternative Methods for

with these technologies.

0003-021X

8904

5401, ISSN 0960-8524

**6. References** 

Fatty Acid Alkyl-Esters Production: Microwaves, Radio-Frequency and Ultrasound 283

The development of additives that improve the properties of biodiesel would allow an improvement in cold flow properties for biodiesel from oils as palm, which can be obtained

Efforts must concentrate on developing these technologies at pilot and industrial levels,

Armenta, R.E.; Vinatoru, M.; Burja, A.M.; Kralovec, J.A.; Barrow, C.J. (2007) Fish Oil

Azcan, N. & Danisman, A. Microwave assisted transesterification of rapeseed oil. Fuel,

Bandow, H. (2010) A two-step continuous ultrasound assisted production of biodiesel fuel

Barnard, T.M.; Leadbeater, N.E.; Boucher, M.B.; Stencel, L.M. & Wilhite, B.A.(2007)

Boey, P.L; Ganesan, S.; Maniam, G.P. & Ali, D.M.H. (2011) Ultrasound aided in situ

Cintas, P.; Mantegna, S.; Calcio, E. & Cravotto, G. (2010) A new pilot flow reactor for high-

Sonochemistry, Vol.17, No.3, (March 2010), pp. 555–559. ISSN: 1350-4177 Duz, M.Z.; Saydut, A. & Ozturk, G. (2011) Alkali catalyzed transesterification of safflower

Fangrui, Ma.; & Milford, A. (1999) Biodiesel Production: a Review. Bioresource Technology,

Gedye, R.; Smith, F.; Westaway K.; Ali, H.; Baldisera, L.; Laberge, L. & Rousell, J. (1986) The

Geuens, J.; Kremsner, J.M.; Nebel, B.A.; Schober, S.; Dommisse, R.A.; Mittelbach, M.;

Giguere, R.J.; Bray, T.L.; Duncan, S.M. & Majetich, G. (1986) Application of commercial

Vol.87, No. 10-11, (August 2008), pp.1781–1788. ISSN: 0016-2361

Fuels, Vol.21, No.3, pp.1777-1781, ISSN: 0887-0624

No.3, (March 2011), pp.308–313, ISSN: 0378-3820

pp.279–82, ISSN: 0040-4039

ISSN: 0040-4039

Vol.70, No.1, (October 1999), pp. 1-15, ISSN 0960-8524

Energy & Fuels, Vol.22, No.1, pp.643–645, ISSN: 0887-0624

Transesterification of Fish Oil to Produce Fatty Acid Ethyl Esters Using Ultrasonic Energy. J Am Oil Chem Soc, Vol.84, No.11, (November 2007), pp.1045–1052 ISSN

from waste cooking oils: A practical and economical approach to produce high quality biodiesel fuel. Bioresource Technology, Vol.101, No.14, (July 2010), pp.5394–

Continuous-Flow Preparation of Biodiesel Using Microwave Heating. Energy &

transesterification of crude palm oil adsorbed on spent bleaching clay. Energy Conversion and Management, Vol.52, No.5, (May 2011), pp.2081–2084, ISSN: 0196-

intensity ultrasound irradiation. Application to the synthesis of biodiesel. Ultrasonics Sonochemistry, Vol.17, No.6 (August 2010) 985–989. ISSN: 1350-4177 Dharmendra Kumar, Gajendra Kumar, Poonam, C.P. Singh. (2010) Fast, easy ethanolysis of

coconut oil for biodiesel production assisted by ultrasonication. Ultrasonics

seed oil assisted by microwave irradiation. Fuel Processing Technology, Vol.92,

use of microwave ovens for rapid organic synthesis. Tetrahedron Lett, Vol.27, No.3,

Tavernier, S.; Kappe, O.; & Maes, B. (2008) Microwave-Assisted Catalyst-Free Transesterification of Triglycerides with 1-Butanol under Supercritical Conditions.

microwave ovens to organic synthesis. Tetrahedron Lett, Vol.27, No.41, pp.4945–58,

with continuous processes, low energy consumption, economic and insurance.

Fig. 3. Detailed scheme of the system for biodiesel production (Cintas et al., 2010).
