Microwave assisted process

Generally, heating coils are used to heat the raw material in biodiesel production process. This treatment can be also done by microwave method. An alternative heating system "microwave irradiation" has been used in transesterification reactions in recent years. Microwaves are electromagnetic radiations which represent a nonionizing radiation that influences molecular motions such as ion migration or dipole rotations, but not altering the molecular structure (Fini & Breccia, 1999; Varma, 2001; Refaat et al., 2008). The frequencies of microwave range from 300 MHz to 30 GHz, generally frequency of 2.45 GHz is preferred in laboratory applications (Taylor et al., 2005). Microwave irradiation activates the smallest degree of variance of polar molecules and ions with the continuously changing magnetic field (Azcan& Danisman, 2007). The changing electrical field, which interacts with the molecular dipoles and charged ion, causes these molecules or ions to have a rapid rotation and heat is generated due to molecular friction (Azcan& Danisman, 2007; Saifuddin & Chua, 2004). The absorption of microwaves causes a very rapid increase of the temperature of reagents, solvents and products (Fini & Breccia, 1999).

Microwave process can be explained for the biodiesel production with transesterification reaction: the oil, methanol, and base catalyst contain both polar and ionic components. Microwaves activate the smallest degree of variance of polar molecules and ions, leading to molecular friction, and therefore the initiation of chemical reactions is possible (Nuechter et al., 2000). Because the energy interacts with the sample on a molecular level, very efficient and rapid heating can be obtained in microwave heating. Since the energy is interacting with the molecules at a very fast rate, the molecules do not have time to relax and the heat generated can be for short times and much greater than the overall recorded temperature of the bulk reaction mixture. There is instantaneous localized superheating in microwave heating and the bulk temperature may not be an accurate measure of the temperature at which the actual reaction is taking place (Barnard et al., 2007; Refaat et al., 2008).

When the reaction is carried out under microwaves, transesterification is efficiently accelerated in a short reaction time. As a result, a drastic reduction in the quantity of by­products and a short separation time are obtained (Saifuddin & Chua, 2004; Hernando et al., 2007) and high yields of highly pure products are reached within a short time (Nuechter et al., 2000). So, the cost of production also decreases and less by-products occurs by this method (Oner & Altun, 2009). Therefore, microwave heating compares very favorably over conventional methods, where heating can be relatively slow and inefficient because transferring energy into a sample depends upon convection currents and the thermal conductivity of the reaction mixture (Koopmans et al., 2006; Refaat et al., 2008). Microwave assisted transesterification process schematic diagram was presented in Figure 4.

There can be also a few drawbacks of microwave assisted biodiesel production, beside the great advantages. Microwave synthesis may not be easily scalable from laboratory small-scale synthesis to industrial production. The most significant limitation of the scale up of this technology is the penetration depth of microwave radiation into the absorbing materials, which is only a few centimeters, depending on their dielectric properties. The safety aspect is another drawback of microwave reactors in industry (Yoni & Aharon, 2008; Vyas et al., 2010). This survey of microwave assisted transformations is abstracted from the literature published from 2000 to 2011. And studies on microwave assisted method of transesterification reaction in the literature were summarized in Table 5. The biodiesel production have been studied by using microwave assisted method from different oils such as cottonseed oil (Azcan& Danisman, 2007), safflower seed oil ( Duz et al., 2011), rapeseed oil (Hernando et al., 2007; Geuens et al., 2008), soybean oil (Hernando et al., 2007; Hsiao et al., 2011; Terigar et al., 2010), corn oil (Majewski et al., 2009), macauba oil (Nogueira et al., 2010), waste frying palm oil (Lertsathapornsuk et al., 2008), micro algae oil (Patil et al., 2011), karanja oil (Venkatesh et al., 2011), jatropha oil (Shakinaz et al., 2010), yellow horn oil (Zhang et al., 2010), canola oil (Jin et al., 2011), camelina sativa oil (Patil et al., 2009), castor oil (Yuan et al., 2009), waste vegetable oils (Refaat et al., 2008), maize oil (Ozturk et al., 2010) and sunflower oil (Han et al., 2008; Kong et al., 2009).

image121

Fig. 4. Microwave assisted transesterification process shematic diagram

Raw

material

Catalyst

Catalyst

amount

(wt%)

Type of alcohol

Alcohol/ oil molar ratio

Microwawe

conditions

Reaction

time

Reaction

tempe­

rature

Performance

(%)

Ref.

Cotton seed oil

KOH

1.5

Methanol

6:1

21% of 1200 W

7 min

333 K

92.4 (yield)

Azcan&

Danisman,

2007

Safflower seed oil

NaOH

1

Methanol

10:1

300 W

6 min

333 K

98.4

(conversion)

Duz et al.,

2011

Rapeseed oil Soybean oil

NaOH

%1.3

Methanol

18:1 1.27 ml

300 W

1 min

60 °C

97

95 (yield)

Hernando et al., 2007

Corn oil Soybean oil

Diphenyla

mmonium

salts:

DPAMs

(Mesylate)

DPABs(Be

nzenesulfo

nate)

DPATs

(Tosylate)

DPAMs

DPABs

20 (molar) 10 (molar)

10 (molar) 10 9

Methanol

5 g

methenol / 2 g oil

20 min

150°C

100

96

100

92

97 (methyl ester yield)

Majewski et al., 2009

Raw

material

Catalyst

Catalyst

amount

(wt%)

Type of alcohol

Alcohol/ oil molar ratio

Microwawe

conditions

Reaction

time

Reaction

tempe­

rature

Performance

(%)

Ref.

Waste frying oil

NaOH

1

Methanol

6:1

600 W

5 min

64°C

93.36 (methyl ester content)

Yucel et al.,

2010

Macauba oil

Novozyme

435

Lipozyme

IM

2.5

5

Ethanol

Ethanol

9:1 9:1

15 min 5 min

30°C

40°C

45.2

35.8

(conversion)

Nogueira et al., 2010

Waste frying palm oil

NaOH

3

Ethanol

12:1

800 W

30 s

97

(conversion)

Lertsathaporn suk et al.,

2008

Rapeseed oil

KOH

NaOH

1

1

Methanol

Methanol

6:1 6:1

67 % of 1200 W

5min

3min

323 K 313 K

93.7

92.7 (yield)

Azcan & Danisman,

2008

Soybean oil

nano CaO (heterogen eous catalyst)

3

Methanol

7:1

60 min

338 K

96.6

(conversion)

Hsiao et al., 2011

Soybean oil Oleic acid

sulfated

zirconia

5

Methanol

20:1

20 min

60 °C

90

(conversion)

Kim et al.,

2011

Dry micro algae

KOH

2

Methanol

9:1

800 W

6 min

80.13

(conversion)

Patil et al.,

2011

Crude karanja oil

KOH

1.33

Methanol

%33.4

(w/w)

180 W

150 s

89.9

(conversion)

Venkatesh et al., 2011

Jatropha oil

KOH

1.50

Methanol

7.5:1

2 min

65°C

97.4

(conversion)

Shakinaz et al., 2010

Crude palm oil

KOH

1.50

Ethanol

8.5:1

70 W

5 min

70°C

85 (yield) 98.1

(conversion)

Suppalakpany a et al., 2010

Yellow horn oil

Heteropol

yacid

(HPA)

1

Methanol

12:1

500 W

10 min

60°C

96.22

(FAMEs)

Zhang et al.,

2010

Soybean oil

NaOH

1

Methanol

6:1

900 W

1 min

303 K

97.7

(conversion)

Hsiao et al., 2011

Canola oil

ZnO/La2O

2CO3

(heterogen

eous

catalyst)

< 1

Methanol

1:1 (w/w)

< 5 min

<100°C

> 95 (yield)

Jin et al., 2011

Camelina sativa oil

Heterogen eous metal oxide catalysts (BaO, SiO)

1.5

2

Methanol

9:1

800 W

94

80 (FAME yield)

Patil et al.,

2009

Castor bean oil

Al2O3 / 50% KOH SiO2 / 50% H2SO4 SiO2 / 30% H2SO4

1

1

1

Methanol

Methanol

Ethanol

1:6 1:6 1:6

40 W

40 W 220 W

5 min 30 min 25 min

95

95

95

(conversion)

Perin et al.,

2008

Castor oil

H2SO4 / C

5

Methanol

1:12

200 W

60 min

338 K

94 (yield)

Yuan et al.,

2009

Triolein

KOH

NaOH

5

Methanol

1:6

25 W

1 min

323 K

98

(conversion)

Leadbeater &

Stencel, 2006

Raw

material

Catalyst

Catalyst

amount

(wt%)

Type of alcohol

Alcohol/ oil molar ratio

Microwawe

conditions

Reaction

time

Reaction

tempe­

rature

Performance

(%)

Ref.

Frying oil

NaOH

0.5

Ethanol

1:6

50% of 750 W

4 min

60°C

87

(conversion)

Saifuddin &

Chua, 2004

Rapeseed oil

Supercritica l 1-butanol

2.5:1

4 hour

80 bar

310°C

91 (fatty acid buthyl ester conversion)

Geuens et al.,

2008

Domestic

waste

vegetable oil Restaurant waste

vegetable oil Neat vegetable virgin

sunflower oil

KOH

1

Methanol

6:1

500 W

1 h

65°C

95.79

94.51

96.15 (biodies el yield)

Refaat et al., 2008

Safflower seed oil

NaOH

1

Methanol

10:1

300 W

16 min

60°C

98.4 (methyl ester content)

Duz et al.,

2011

Soybean oil

NaOH

1

Methanol

6:1

600 W (Ultrasonic)

900 W

(Microwave)

1 min

2 min

333 K

97.7

(conversion)

Hsiao et al., 2010

Maize oil

NaOH

1.5

Methanol

10:1

98

(conversion)

Ozturk et al.,

2010

Soybean oil Rice bran oil

NaOH

0.6

Ethanol

5:1

10 min

73°C

73°C

99.25

99.34 (FAME yield)

Terigar et al., 2010

Jatropha curcas

NaOH

4

Methanol

30:1

7 min

328 K

86.3

(conversion)

Yaakob et al., 2008

Sunflower oil

H2SO4

0.05

Methanol

10:1

400W

45 min-

96.2

(conversion)

Han et al.,

2008

Sunflower oil

DO2/SO4

0.02

Methanol

12:1

300W

-25 min

94.3 (biodiesel yield)

Kong et al., 2009

Table 5. Microwave assisted method studies of transesterification reaction in the literature

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