RETRACTED: Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics

RETRACTED: Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics

G Model ARTICLE IN PRESS JARMAP-86; No. of Pages 9 Journal of Applied Research on Medicinal and Aromatic Plants xxx (2016) xxx–xxx Contents lists ...

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G Model

ARTICLE IN PRESS

JARMAP-86; No. of Pages 9

Journal of Applied Research on Medicinal and Aromatic Plants xxx (2016) xxx–xxx

Contents lists available at ScienceDirect

Journal of Applied Research on Medicinal and Aromatic Plants journal homepage: www.elsevier.com/locate/jarmap

Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics Heri Septya Kusuma ∗ , Mahfud Mahfud Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia

a r t i c l e

i n f o

Article history: Received 24 August 2015 Received in revised form 6 August 2016 Accepted 13 August 2016 Available online xxx Keywords: Patchouli oil Pogostemon cablin Benth Microwave hydrodistillation Extraction Kinetics

a b s t r a c t In this study the extraction of essential oil from Pogostemon cablin Benth done by using microwave hydrodistillation. In the patchouli oil extraction with microwave hydrodistillation method is studied the effect of the size of the material (intact and chopped leaves) and the effect of the ratio of raw material to be extracted with a solvent to the yield of patchouli oil. Besides it also studied the effect of microwave power to the yield of patchouli oil and kinetics during the extraction process. Then, a microwave hydrodistillation model based on the assumption of a second-order mechanism was developed to predict the rate constant of extraction, the saturated extraction capacity and the initial extraction rate with various temperatures in two microwave powers, 400 and 600 W. Furthermore, the activation energies were determined as based on the second-order rate constants of extraction used for the model building. The values resulting from these calculations and experiments were compared and discussed. © 2016 Elsevier GmbH. All rights reserved.

1. Introduction Essential oils are also known as the etheric oils or oil fly (essential oil, volatile oil) produced by the plant. Essential oils can be obtained from the roots, stems, leaves, and flowers of plants. Essential oils have volatile properties at room temperature without decomposition, has a bitter taste (pungent taste), in accordance with the smell of aromatic plants, are generally soluble in organic solvents and insoluble in water. Essential oils are used in industry for the manufacture of cosmetics, perfumes, antiseptics, medicines, “flavoring agent” in food or beverages and cigarettes as well as mixing as aromatherapy. Pogostemon cablin (Lamiaceae) or patchouli is a bushy herb which is a member of the mint family and hails from Indonesia, Malaysia, and Philippines. This plant is indigenous to the Indonesia known as “nilam” or “dilem”. Patchouli (Pogostemon cablin Benth) is one of the plants that produce essential oils are quite important as Indonesian export commodities and foreign exchange accounted for approximately 60% of the total national exports of essential oils. Indonesia is the world’s largest supplier of patchouli oil with a contribution of 90%.

∗ Corresponding author. E-mail addresses: [email protected], [email protected] (H.S. Kusuma), [email protected] (M. Mahfud).

Patchouli oil is one of the most important base materials used in perfumery with its strong fixative property. Thus, the strongsmelling oil taken from the leaves is used in perfumes, incense, detergents, and hair conditioners. It has been used in some cultures to prevent diseases. Aside from providing alluring oriental notes, patchouli oil imparts tenacity to the perfume. Patchouli oil is equally indispensable in soaps, cosmetics, and incense (De Guzman et al., 1997). Patchouli is found in use in many famous perfumes such as Arpege, Tabu, Miss Dior, Opium, Paloma, Picasso, Ysatis and Angel (Singh et al., 2002). It should be noted that patchouli plants are the only commercial source of patchoulol and that cost-effective synthetic routes for enantiomerically pure patchoulol have yet to be developed (Deguerry et al., 2006) Some things that can be used as a solution to improve the qualitative and quantitative of patchouli oil, among others, is the process of patchouli cultivation, distillation techniques and equipment used, the treatment of raw materials, patchouli oil refining process as well as product packaging patchouli oil. There are several types of methods that can be done to separate or get patchouli oil, among others distillation, extraction and others. But today that is often used is distillation. In terms of distillation techniques are used, by using steam-hydro distillation method can be produced patchouli oil yield better than the conventional method using distilled water (hydro distillation). In addition, also required an optimal operating conditions and equipment design to obtain patchouli oil that has higher yield and good quality. But with that method takes a long

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Please cite this article in press as: Kusuma, H.S., Mahfud, M., Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics. J. Appl. Res. Med. Aromat. Plants (2016), http://dx.doi.org/10.1016/j.jarmap.2016.08.001

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time to get good patchouli oil. Therefore, it is necessary to develop a new method that is microwave hydrodistillation which can speed up the process of distillation with a faster time and the availability of microwave that are easily obtained by the society (Kusuma and Mahfud, 2016). During the extraction and according to Fick’s law, the diffusion of the soluble components depends on the gradient of concentration existing between the solid phase (more concentrated) and the liquid phase (less concentrated). This gradient evolves to create an equilibrium between the two phases (Perry et al., 1997), then diffusion becomes negligible even when the contact time is infinitely long under the predetermined conditions. But, when the liquid phase is continuously renewed, the diffusion evolves until the solid phase has been worked out by the solvent. Matter transfer kinetics is studied in three theoretical stages: (i) putting the solid in contact with the solvent of extraction, which induces a distension of the particles and a solubilization of the compounds, (ii) solid scrubbing with transfer of solute by molecular diffusion from the inside of the solid phase, and (iii) diluting the solute diffused in the solvent to give the extract (Schwartzberg and Chao, 1982). Furthermore, hydrolysis of some water-insoluble compounds is often observed, which leads to additional molecules in the extract. Solidliquid extraction kinetics has already been studied (Adhikari et al., 2002; Seikova et al., 2004; Simeonov et al., 1999; Wongkittipong et al., 2004), and it has been generally observed that the extraction rate is rapid at the beginning of the process and slows down as equilibrium is approached. The purpose of this research is to study the process of patchouli oil extraction from patchouli leaves using a microwave hydrodistillation method. In this research studied the effect of several factors such as the treatment of plant materials (chopped and intact leaves) and the effect of the ratio of raw material to be extracted with a solvent to yield patchouli oil. Besides it also studied the effect of microwave power to the yield of patchouli oil and kinetics during the extraction process. Then methods for determining the initial extraction rate and the activation energy of essential oil extraction, based on a second-order extraction process were developed. The kinetic parameters were finally deduced to predict the amount of essential oil extracted, then the results of these calculations were compared and discussed with a view to optimize the extraction process. This study was necessary before developing and implementing a complete industrial process.

Fig. 1. Effect of particle size of patchouli leaves on yield of essential oil by various microwave power (solid to water ratio 1:20).

In the patchouli oil extraction using microwave hydrodistillation, distilled water (400 mL) and patchouli leaves (intact and chopped) were put in a series of round bottom flasks (1000 mL) to a ratio of solid to water of 1:5, 1:10 and 1:20 g mL−1 . The extraction was carried out for 60 min under different levels of effective microwave power (400 and 600 W). The extraction time shall be computed from the first drop out of the condenser. To study the kinetics of the extraction of patchouli oils, then the temperatures varied from 375 to 395 K for the microwave power 400 W and from 375 to 400 K for the microwave power 600 W. The different densities and their immiscibility required that the water and patchouli oil be separated from each other by separating funnel and the excess water be refluxed to the extraction vessel in order to provide uniform conditions of solid to water ratios for extraction. The patchouli oil was collected in amber vials, dried under anhydrous sodium sulfate and stored at 4 ◦ C. 2.3. Physical constants Specific gravity and refractive index of the essential oils extracted from the patchouli leaves were measured according to the method suggested by ISO 3757:2002(E). Specific gravity and refractive index was measured at 20 ◦ C. 2.4. Kinetic model

2. Materials and methods 2.1. Plant material Patchouli leaves were taken from Tulungagung, East Java, Indonesia in the form of dried intact leaves (4.69 ± 0.46 cm). For the treatment of chopped leaves, the leaves then were chop to a size around 1.02 ± 0.13 cm using a commercial grade blender (Arte Blender, BL-001) and stored at room temperature until required.

2.2. Microwave hydrodistillation procedure In employing microwave hydrodistillation, we used a domestic microwave oven (EMM-2007X, Electrolux, 20 L, maximum delivered power of 800 W) with wave frequency of 2450 MHz. The dimensions of the PTFE-coated cavity of the microwave oven were 46.1 cm × 28.0 cm × 37.3 cm. The microwave oven was modified by drilling a hole at the top. A round bottom flask with a capacity of 1000 mL was placed inside the oven and was connected to the three-way adapter and liebig condenser through the hole. Then, the hole was closed with PTFE to prevent any loss of the heat inside.

Various models of solid liquid extraction process have been desrcibed (Garkal et al., 2012; Muhammad et al., 2012). Muhammad et al. shows, in the study of the mechanisms and kinetics in the extraction process of essential oil from Citronella grass, that a model based on a second-order extraction kinetics was the most suitable model for an essential oil extraction process. It was then possible to build the kinetic models of an essential oil extraction using microwave hydrodistillation method and the extraction order and rate constant remained to be determined by experiments. 2.4.1. General equations Second-order mechanism model means that the extraction occurs in two simultaneous processes. The amount of extracted oil increases rapidly with time at the beginning and then decreases slowly with the time until the end of extraction process (Ho et al., 2005; Meizane and Kadi, 2008; Rabesiaka et al., 2007; Uhm and Yoon, 2011). The rate of dissolution for the essential oil contained in the solid to solution can be described by Eq. (1) dCt = k(CS − Ct )2 dt

(1)

Please cite this article in press as: Kusuma, H.S., Mahfud, M., Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics. J. Appl. Res. Med. Aromat. Plants (2016), http://dx.doi.org/10.1016/j.jarmap.2016.08.001

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Fig. 2. Effect of solid to water ratio on yield of essential oil by various particle size of patchouli leaves (microwave power 400 W).

where k is the second-order extraction rate constant (L g−1 min−1 ), CS the extraction capacity (concentration of essential oil at saturation in g L−1 ) and Ct is the concentration of Patchouli oil at any time t (min). By considering the initial and boundary conditions, t = 0 to t and Ct = 0 to Ct , the integrated rate law for a second-order extraction was obtained: Ct =

CS2 kt

(2)

1 + CS kt

By transforming Eq. (2), a linear form shown in Eq. (3) can be obtained and the extraction rate can be written as Eq. (4): t 1 t = + Ct CS kCS2

(3)

Ct 1 = t (1/kCS2 ) + (t/CS )

(4)

The initial extraction rate, h, as Ct/t when t approaches 0, can be defined as: h = kCS2

(5)

and, the concentration of essential oil at any time can be expressed after rearrangement as: Ct =

t (1/h) + (t/CS )

(6)

The initial extraction rate, h, the extraction capacity, CS , and the second-order extraction rate constant, k, can be determined experimentally from the slope and intercept by plotting t/Ct versus t. 2.4.2. Activation energy The kinetics described in the previous equations depends on the temperature according to the Arrhenius law defined by Eq. (7), k = k0 e(−Ea /RT )

(7)

The transformation of this equation allows to obtain a linear relationship between the second-order extraction rate constant and the reverse of temperature: ln k = ln k0 +

 −E  1 a R

T

(8)

where k is the extraction rate constant (L g−1 min−1 ), k0 the temperature-independent factor (L g−1 min−1 ), Ea the activation energy for the extraction (kJ mol−1 ), R the gas constant (8.314 J mol−1 K−1 ) and T is the absolute suspension temperature (K). As shown in the Arrhenius law, once k0 and k are known for an extraction, the activation energy Ea can be calculated.

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Fig. 3. Effect of microwave power on yield of essential oil by various particle size of patchouli leaves (solid to water ratio 1:20).

3. Results and discussion 3.1. Effect of size of the plant material The effect of particle size on the extraction yield was studied in the form of intact and chopped leaves. Based on this research can be seen that the yield of patchouli oil obtained from the chopped leaves is higher when compared with patchouli oil obtained from the intact leaves. Regarding this point, decreasing the particle size of leaves leads to a higher surface area, making extraction more efficient (Pourmortazavi and Hajimirsadeghi, 2007). The physical structure of the materials is of critical importance, as the extraction efficiency is related to the ability of the water vapor to diffuse within the materials. For that reason, the extraction conditions of the same group of essential oils may differ from one materials to another (Pourmortazavi and Hajimirsadeghi, 2007). Patchouli oil compounds are located inside the Pogostemon cablin Benth leaves structure in cell organelles. During the extraction process, the surface compounds are readily solubilized since they encounter little mass transfer resistance. On the contrary, extraction of essential oil involves a series of complex mass transfer mechanisms (Reverchon et al., 1995). Despite the lipophilic character of patchouli oil compounds, the water present in the Pogostemon cablin Benth leaves may interfere in the solute-water vapor interaction (particularly in the case of terpenoids, which are more polar than terpenes) and produces a decrease of extraction yield. For this reason, drying of the Pogostemon cablin Benth leaves is recommended. Generally, the plant material should not have water content higher than 12%; the presence of water can cause other undesirable effects, such as hydrolysis of compounds. Moreover, in order to attain an adequate contanct with the solvent, a pretreatment to produce cell disruption (comminuting, grinding, chopping) is critical. Then, the efficiency of the extraction process is improved by decreasing mass transfer resistance. Indeed, particle size greatly affects process duration. Particle size of Pogostemon cablin Benth leaves plays an important role in microwave hydrodistillation processes; if internal mass transfer resistances can be reduced, the extraction is controlled by equilibrium conditions, and thus short extraction times are required. Generally, decreasing particle size improves microwave hydrodistillation rate and yield. In the patchouli oil extraction using microwave hydrodistillation, the increase of patchouli oil yield in addition affected by the condition of extracted patchouli leaves, also influenced by the ratio of raw material to be extracted with a solvent and the used microwave power (Fig. 1).

Please cite this article in press as: Kusuma, H.S., Mahfud, M., Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics. J. Appl. Res. Med. Aromat. Plants (2016), http://dx.doi.org/10.1016/j.jarmap.2016.08.001

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Table 1 Analysis of Variance (ANOVA) for patchouli oil yield. Source

Sum of Squares

Df

Mean Square

F-Ratio

P-Value

MAIN EFFECTS A:Microwave power B:Patchouli leaves size C:Solid to water ratio

0.414631 0.194005 0.0203414

1 1 2

0.414631 0.194005 0.0101707

64.00 29.94 1.57

0.0153 0.0318 0.3891

INTERACTIONS AB AC BC RESIDUAL TOTAL (CORRECTED)

0.00989576 0.0303724 0.00585916 0.0129579 0.688063

1 2 2 2 11

0.00989576 0.0151862 0.00292958 0.00647896

1.53 2.34 0.45

0.3420 0.2990 0.6886

Fig. 4. Second-order extraction kinetics of essential oil in microwave power 400 W from Pogostemon cablin Benth at various size of leaves and solid to water ratio.

3.2. Effect of solid to water ratio In this study, the extraction curves were obtained for different solid to water ratio (1:5-1:20, w/v). The results were plotted in Fig. 2 which show that much mass of patchouli leaves and the amount of essential oil that is obtained, not always positively correlated with increased of essential oil yield. In case of lower solid to water ratio, where amount of water is less, the plant material might have experienced the overheating or charring, resulting in the decreased rate and yield. For high water content, the heat could be wasted in heating up the water which might have reduced the efficiency of the process. Also, hydrolytic effect might have contributed to the lower yield. Generally, a higher solid to water ratio in extraction techniques can increase the recovery. Indeed, the extraction yield of target compounds is most likely dependent on how the ratio of solid to liquid is regulated (keeping the liquid volume or the solid mass constant) (Spigno and De Faveri, 2009). The solvent volume must be sufficient to ensure that the entire sample is immersed, so that the material can swell during extraction. However, in the microwave hydrodistillation, a lower solid to water ratio may give lower recoveries due to inadequate stirring of the solvent by microwaves and excessive swelling of the plant material. Moreover, a higher solvent volume requires higher power and more time to achieve the temperature required. Excessive solvent may also cause the dissolution of other undesirable compounds, lowering the extraction selectivity towards target compounds (Xiao et al., 2008). In this research, the solvent volume remains constant while the solid loading (Pogostemon cablin Benth leaves) changes. The yield of patchouli oil from Pogostemon cablin Benth leaves increased with decreasing ratio of solid to water from 1:10 to 1:20. The possible reasons for a lower extraction yield with a higher sample loading could be: (1) increasing the solid mass decreases the surface area available for solvent to penetrate plant materials and to solubilize

the target molecules (Ballard et al., 2010); (2) microwave energy is absorbed and dispersed by the larger amount of plant materials (Gao et al., 2007); (3) the incident microwave radiation per particle decreases with the increase of solid loading at a given power. This should give a relatively low dielectric heating effect, and thus a reduced effect of microwave radiation (Desai et al., 2010); (4) the absorption of microwave radiation by plant material near the surface of the vessel reduces the penetration depth of microwave radiation into the suspension (Ponne et al., 1996). Therefore the raw material in the interior part of vessel will not have the same level of microwave radiation. The influence of solid to water ratio on extraction yield may be associated with the temperature of plant sample–solvent mixture: if the solid mass is kept constant and the liquid volume is increased, the mixture temperature first increases and then decreases, and extraction yield exhibits a similar trend; if the liquid volume is maintained constant and the solid mass decreased, the temperature of the mixture is almost constant and the extraction yield increases gradually (Spigno and De Faveri, 2009). It may also be associated with properties of the target phytochemicals (e.g. thermostability), microwave-based extractor (with or without stirrer), solvent, and so on. Since the mechanism underlying the impact of solid to water ratio on microwave-assisted extraction remains unclear, further investigation is required (Zhang et al., 2011). Values of solid to water ratio frequently employed range from 1:50 to 1:10, but this ratio has to be adapted and optimized for each raw material. 3.3. Effect of microwave power The effect of heating rate on the extraction yield was determined for the different microwave power. Microwave power and temperature are related, because of the high power operation can raise the temperature above the boiling point of the solvent and produce an increase in the extraction yield results. Microwave power acts as a driving force to break up the structure of plant cell membranes, so that the essential oil can be diffused out and dissolved in a solvent. Therefore, increasing the microwave power will generally improve the extraction yield and result in shorter extraction time (Chan et al., 2011; Hu et al., 2008). Moreover, it is important to properly select the microwave power to minimize the time needed to reach the set temperature and avoid a “bumping” phenomenon in temperature during the extraction (Eskilsson and Björklund, 2000). From this research can be seen that the yield of patchouli oil obtained with microwave power 600 W is higher when compared with patchouli oil obtained with microwave power 400 W (Fig. 3). This is because the higher microwave power resulted the increase in temperature and the rate of extraction (evaporation) becomes faster. Microwave power and temperature are interrelated because high microwave power can bring up the temperature of the system. In this study, it can be seen that the greater used microwave power have resulted the higher operating temperature. The rise in temperature is a result of

Please cite this article in press as: Kusuma, H.S., Mahfud, M., Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics. J. Appl. Res. Med. Aromat. Plants (2016), http://dx.doi.org/10.1016/j.jarmap.2016.08.001

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Fig. 5. Second-order extraction kinetics of essential oil in microwave power 600 W from Pogostemon cablin Benth at various size of leaves and solid to water ratio.

Fig. 6. Relationship between the absolute temperature and the second-order extraction rate constant k for extraction of essential oil from Pogostemon cablin Benth in microwave power 400 and 600 W.

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Fig. 8. Relationship between the initial extraction rate, ln h, and temperature, for extraction of essential oil from Pogostemon cablin Benth in microwave power 400 and 600 W.

Fig. 9. Relationship between the saturated extraction capacity, CS , and the temperature, for extraction of essential oil from Pogostemon cablin Benth in microwave power 400 and 600 W.

The degree of microwave absorption usually increases with the dielectric constant. A simple comparison between water and methanol shows that methanol has a lesser ability to obstruct the microwaves as they pass through but has a greater ability to dissipate the microwave energy into heat (dissipator factor of water, tan ␦ = 1.570.10−4 and dissipator factor of methanol, tan ␦ = 6.400.10−4 ) (Eskilsson and Björklund, 2000). The higher dielectric constant of water implies a significantly lower dissipation factor, which means that the system absorbs more microwave energy than it can dissipate (dielectric constant of water, ␧’ = 78.3 and dielectric constant of methanol, ␧’ = 32.6). This strong absorption provides an increase of the temperature inside the sample, leading to the rupture of cells by the in situ water. Therefore, it can increase the diffusivity of the target compound in the material (Jain et al., 2009). Fig. 7. Relationship between the temperature and the second-order extraction rate constant, ln k, for extraction of essential oil from Pogostemon cablin Benth in microwave power 400 and 600 W.

the ability of the material and solvent to absorb the energy of the microwaves. It is important to select a solvent with high extracting power and strong interaction with the material. Polar molecules and ionic solutions (typically acids) strongly absorb microwave energy because of the permanent dipole moment. On the other hand, when exposed to microwaves, nonpolar solvents such as hexane will not heat up.

3.4. Statistical analysis The effect of microwave power, patchouli leaves size, and solid to water ratio on extraction of essential oil from patchouli leaves was evaluated Analysis of Variance (ANOVA). The p-values in ANOVA were used as a tool to check the significance of each coefficient, which in turn may indicate the pattern of the interactions between the variables. The smaller was the value of p, the more significant was the corresponding coefficient. It can be seen from Table 1 that the linear coefficients (C) and cross product coefficients (AB, AC, BC) were not significant (p > 0.05). The other term coeffi-

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Fig. 10. Predictive model for extraction of essential oil from Pogostemon cablin Benth in microwave power 400 W at any extracting time and temperature.

Fig. 11. Predictive model for extraction of essential oil from Pogostemon cablin Benth in microwave power 600 W at any extracting time and temperature.

cient (A and B) was significant, with very small p values (p < 0.05). It indicated that microwave power and patchouli leaves size has important influence on extraction of essential oil from patchouli leaves.

3.5. Kinetics of patchouli oil distillation Essential oil extraction comes in two successive stages: (i) first the driving force of the fresh solvent induces an important disso-

lution and scrubbing and most of the extraction takes place in that stage; (ii) then a much slower stage occurs with external diffusion of essential oil into the extract. These phenomena are typical of a second-order process and can be interpreted when analyzing the experimental results by plotting t/Ct versus time. The results of the analysis are, respectively, shown in Figs. 4 and 5. The agreement of the second-order extraction model with the experimental results confirms that the process of essential oil extraction by water medium works according to the model previ-

Please cite this article in press as: Kusuma, H.S., Mahfud, M., Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics. J. Appl. Res. Med. Aromat. Plants (2016), http://dx.doi.org/10.1016/j.jarmap.2016.08.001

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Table 2 Kinetic model of the second-order extraction of essential oil from Pogostemon cablin Benth in water. Power

Size of the plant material

400 Intact

Chopped 600 Intact

Chopped

Solid to water ratio

a (L g−1 )

Cs (g L−1 )

b (min L g−1 )

kexp (L g−1 min−1 )

h (g L−1 min−1 )

r2

1:20 1:10 1:5 1:20 1:10 1:5

0.910 0.471 0.216 0.813 0.450 0.230

1.098 2.124 4.621 1.230 2.225 4.352

15.471 8.001 3.677 6.066 3.353 1.714

0.054 0.028 0.013 0.109 0.060 0.031

0.065 0.125 0.272 0.165 0.298 0.583

0.967 0.967 0.967 0.993 0.993 0.993

1:20 1:10 1:5 1:20 1:10 1:5

0.813 0.432 0.209 0.737 0.369 0.199

1.231 2.317 4.789 1.357 2.708 5.028

12.152 6.454 3.123 5.497 2.755 1.484

0.054 0.029 0.014 0.099 0.050 0.027

0.082 0.155 0.320 0.182 0.363 0.674

0.974 0.974 0.974 0.993 0.993 0.993

Table 3 Experimental verifications of the points of the two models. Microwave power 400 W Temperature (K) Time (min) Ct exp (g L−1 ) Ct calc (g L−1 )

382 10 1.2741 0.9080

600 W 382 60 1.9785 1.8557

392 10 1.7121 2.1435

392 60 3.6015 3.5782

380 10 0.9285 0.8380

380 60 1.8548 1.8538

390 10 1.9190 1.8685

390 60 3.8333 3.7555

Table 4 Physical properties of patchouli oil extracted by microwave hydrodistillation method. Specific gravity (20 ◦ C) Power

Size of the plant material

400 Intact

Chopped 600 Intact

Chopped

Solid to water ratio 1:20 1:10 1:5 1:20 1:10 1:5

Refractive index (20 ◦ C)

ISO 3757:2002(E)

Experimental

0.9520–0.9750

0.9711 0.9734 0.9658 0.9665 0.9531 0.9574

1:20 1:10 1:5 1:20 1:10 1:5

ously described (Muhammad et al., 2012). Therefore, the saturated extraction capacity, Cs, the extraction rate constant, k, the initial extraction rate, h, and the coefficient of determination, r2 , are determined for various size of the plant material, solid to water ratio, and microwave power from the equation of linear curves given by Excel® software (y = aT + b, where y = t/Ct, a = 1/Cs, b = 1/kCs2 and T is temperature) from Figs. 4 and 5 (Table 2). As expected, the initial extraction rate, h, increased with temperature for two the microwave power studied, so did the extraction capacity (Cs) and the second-order rate constant k. Moreover, the extraction capacity in the microwave power 600 W was always superior to that the microwave power 400 W. It was also noticed that the initial extraction rate was faster with the microwave power 600 W than with 400 W. However, the rate constant was higher in the case of the microwave power 600 W than in that of the microwave power 400 W, for all size of the plant material and solid to water ratio, showing that cell penetration and diffusion are better in the microwave power 600 W (Fig. 6). By plotting the rate constant versus temperature, a linear relationship was obtained (Eq. (9)) with microwave power 400 W, whereas the evolution of the rate constant with temperature

ISO 3757:2002(E)

Experimental

1.5050–1.5150

1.5067 1.5107 1.5127 1.5117 1.5067 1.5127

0.9628 0.9735 0.9717 0.9707 0.9550 0.9704

1.5117 1.5057 1.5097 1.5077 1.5117 1.5127

followed a second-order polynomial increase (Eq. (10)) with microwave power 600 W. k400W = 0.0014T −0.4991(r2 = 0.921, RMSE = 0.012)

(9)

k600W = 0.0026T −0.9136(r2 = 0.967, RMSE = 0.011)

(10)

This is due to the rate constant is higher in microwave power 600 W than in microwave power 400 W. However, concentration at saturation is better in microwave power 400 W than in microwave power 600 W showing that the former is a better power for longer contact times. 3.5.1. Calculation of activation energy The linearized Arrhenius Eq. (8) obtained by plotting ln k versus 1/T (Fig. 7) shows that the rate constant increases with the increase in temperature. With this equation, activation energies may be calculated from the slopes and the values of temperature independent factors calculated from the intercept for the two microwave powers studied (Fig. 7). The relationships for the extractions in microwave power 400 W and in microwave power 600 W are, respectively, given by Eqs. (11) and (12): exp

 k400 w = 5.4789.107 exp

−68626.2502 8.314.T

 (r2 = 0.836, RMSE = 0.004)

(11)

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8

(r2 = 0.841, RMSE = 0.004)

(17)

This empirical equation represents the model for the evolution of essential oil concentration during extraction of Pogostemon calin Benth, for various temperatures at any time. The three dimensional representation of this equation is shown in Fig. 10. It indicates that the longer the extraction time and the higher temperature are, the higher the concentration is. For an extraction in microwave power 600 W, the relationship of Ct versus T and t can be obtained by substituting the values of h from Eq. (14) and CS from Eq. (16), in Eq. (6), which leads to: Ct =

t 7.0201.10

−15

exp(13167/T ) + (t/(0.2259T − 83.395))

2

(r 0.871, RMSE = 0.029) Fig. 12. Comparison between experimental and modelling concentration evolution for essential oil extraction in microwave power 400 W [r2 = 0.847, RMSE = 0.005] and 600 W [r2 = 0.827, RMSE = 0.027] at the same operating conditions (intact leaves, solid to water ratio 1:20, and temperature 375 K)Tables.

 k600 w = 3.7949.104 exp

−42083.8052 8.314.T

 (r2 = 0.935, RMSE = 0.006)

(12)

and the coefficients of determination are, respectively, 0.836 and 0.935. In both cases, the energies of activation are positive, showing that the extraction is an endothermic process. However, the activation energy of extraction is higher in microwave power 400 W (68.6263 kJ mol−1 ) than in microwave power 600 W (42.0838 kJ mol−1 ). Similarly, the temperature independent factor is higher in microwave power 400 W than in microwave power 600 W. All these remarks allow to consider that microwave power 600 W improves at once the extraction capacity (Cs) and the thermic balance (E400W > E600W) at the same time. The values of k calculated with Eqs. (11) and (12) were compared with the values of k obtained from the experimental results and the correlations were verified with an average error inferior to 2.3340%. 3.5.2. Modelling According to Eq. (5) k and h are only bound by the CS2 factor, therefore the relationships (13) and (14) were established by plotting ln h versus 1/T for both microwave powers and shown in Fig. 8.



h400 w = 8.1748.1017 exp

 h400 w = 1.4245.1014 exp

−16485 T −13167 T



(r2 = 0.992, RMSE = 0.015)

(13)

(r2 = 0.999, RMSE = 0.006)

(14)



The initial extraction rate is reached the same value in the two microwave powers at 383 K (110 ◦ C). At lower temperatures, h was better with microwave power 600 W and it was contrary at temperatures superior to 383 K. A relation between the concentration and time could still be established by plotting the concentration at saturation, CS versus temperature. The curves shown in Fig. 9 lead to the corresponding equations, respectively, for microwave power 400 W and microwave power 600 W. C S = 0.1786T −65.88(r2 = 0.996, RMSE = 0.085)

(15)

C S = 0.2259T −83.395(r2 = 0.979, RMSE = 0.268)

(16)

These relations have nearly same and show that the concentration at saturation increases with temperature at the same rate in the two microwave powers. By combining Eqs. (6), (13) and (15), the equation describing the evolution of Ct versus time and temperature with microwave power 400 W, can be written as Eq. (17): Ct =

t 1.2233.10−18 exp(16485/T ) + (t/(0.1786T − 65.88))

(18)

As in the case of microwave power 600 W, this empirical Eq. (18) represents the evolution model of essential oil concentration during its extraction from Pogostemon calin Benth in microwave power 600 W for various temperatures at any time. The three-dimensional plot of this equation is shown in Fig. 11 and points out the same trends. Essential oil extraction yields are better in this microwave power as contact time and temperature are high. The models represented by Eqs. (17) and (18) were compared with the experimental results, and are shown in Fig. 12 for microwave power 400 and 600 W, respectively. A good fitting between experimental and calculated data was obtained for the two models showing the validity of the relationships. Moreover, as other experiments were carried out for other temperatures and contact times in both solvents, Table 3 compares the experimental and calculated results to show that the agreement is globally good as average errors are inferior to 2.2343%. For further experiments under the same conditions of size of the plant material and solid to water ratio, Eqs. (17) and (18) could be used to determine the amount of essential oil likely to be extracted from Pogostemon cablin Benth, respectively, in microwave power 400 and 600 W, at any time and any temperature. 3.6. Evaluation of physical properties Physical properties (specific gravity and refractive index) of patchouli oil are shown in Table 4. For comparison purpose, standard properties obtained from ISO 3757:2002(E) are also shown in the same Table. The specific gravity and refractive index of essential oils obtained from patchouli leaves within the ranges specified by ISO. Therefore, considering physical properties of the extracted essential oils, three process factor on microwave hydrodistillation does not introduce any problems to the essential oils extracted from patchouli leaves. 4. Conclusions In this study, we have shown that the kinetics of the extraction of essential oil from Patchouli leaves (Pogostemon cablin Benth) with microwave power 400 and 600 W is based on a pseudo secondorder model. Consequently, it can be said that the mechanism of the essential oil extraction proceeds in two steps: a fast dissolution of essential oil followed by a slow diffusion of solute from the solid particles. The extraction rate constant, the saturated capacity of the extraction and the initial extraction rate can be predicted with this second-order model as functions of the temperature and of the composition of the solvents. In accordance to an endothermic process, the yield of essential oil is found to increase with temperature, for both the microwave powers studied. The activation energies

Please cite this article in press as: Kusuma, H.S., Mahfud, M., Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics. J. Appl. Res. Med. Aromat. Plants (2016), http://dx.doi.org/10.1016/j.jarmap.2016.08.001

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determined from the Arrhenius equation and second-order rate constant show that extraction of essential oil requires less energy in microwave power 600 W because its extraction kinetics is lower in it than in microwave power 400 W. Using a model based on the assumption of a second-order extraction, a three-dimensional predictive model was established to measure the capacity of extraction at any time and any temperature of extraction for each of the two microwave powers studied in already described conditions of size of the plant material and solid to water ratio. The calculated values obtained from these models can represent well the experimental results showing its reliability. These results will now be used for other investigations within the framework of essential oil extraction from Pogostemon cablin Benth; the power of the microwave in particular requires further studies. As a matter of fact, the essential oil extraction of Pogostemon cablin Benth is currently industrially performed with boiling water. The results obtained in this study showed that addition of microwave power allowed to increase the yield of essential oil while working at lower temperatures. References Adhikari, B., Howes, H., Bhandari, B.R., Yamamoto, S., Truong, V., 2002. Application of a simplified method based on regular regime approach to determine the effective moisture diffusivity of mixture of low molecular weight sugars and maltodextrin during desorption. Journal of Food Engineering 54, 157–165. De Guzman, C.C., Villanueva, M.A., Torres, R.C., Regros, R.A., Cosico, W.C., Aragones, E.G., 1997. Production and Processing of Citronella, Patchouli, and Ilang-ilang. Department of Science and Technology, Philippines, pp. 135–185. Deguerry, F., Pastore, L., Wu, S., Clark, A., Chappell, J., Schalk, M., 2006. The diverse sesquiterpene profile of patchouli, Pogostemon cablin, is correlated with limited number of sesquiterpene synthases. Archives of Biochemistry and Biophysics 454, 123–126. Garkal, D.J., Taralkar, S.V., Kulkarni, P., Jagtap, S., Nagawade, A., 2012. Kinetic model for extraction of eugenol from leaves of Ocimum sanctum Linn (Tulsi). International Journal of Pharmaceutical Applications 3 (1), 267–270. Ho, Y.S., Oumarou, H.A.H., Fauduet, H., Porte, C., 2005. Kinetics and model building of leaching of water-soluble compounds of Tilia sapwood. Separation and Purification Technology 45, 169–173. Kusuma, H.S., Mahfud, M., 2016. Microwave-assisted hydrodistillation for extraction of essential oil from patchouli (Pogostemon cablin) leaves. Periodica Polytechnica Chemical Engineering 60, 1–11. Muhammad, H.H., Hasfalina, C.M., Hismamuddin, J., Zurina, Z.A., 2012. Optimization and kinetics of essential oil extraction from citronella grass by ohmic heated hydro distillation. International Journal of Chemical Engineering and Applications 3 (3), 173–177. Perry, R., Green, D.W., Maloney, J.O., 1997. Perry’s Chemical Engineers’ Handbook, 7th ed. McGraw-Hill, New York. Schwartzberg, H.G., Chao, R.Y., 1982. Solute diffusivities in leaching processes. Food Technology 73, 73–86. Seikova, I., Simeonov, E., Ivanova, E., 2004. Protein leaching from tomato seed-experimental kinetics and prediction of effective diffusivity. Journal of Food Engineering 61, 165–171.

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Please cite this article in press as: Kusuma, H.S., Mahfud, M., Microwave hydrodistillation for extraction of essential oil from Pogostemon cablin Benth: Analysis and modelling of extraction kinetics. J. Appl. Res. Med. Aromat. Plants (2016), http://dx.doi.org/10.1016/j.jarmap.2016.08.001