Optimization of Supercritical Extraction of Linalyl Acetate from ...

Supercritical fluid extraction

Seyyed M. Ghoreishi1 Hossein Kamali1,2

Research Article

Hasan S. Ghaziaskar3 Ali A. Dadkhah1

Optimization of Supercritical Extraction of Linalyl Acetate from Lavender via Box-Behnken Design

1

2

3

Isfahan University of Technology, Department of Chemical Engineering, Isfahan, Iran. North Khorasan University of Medical Sciences, Research Center of Natural Products Safety and Medicinal Plants, Bojnurd, Iran. Isfahan University of Technology, Department of Chemistry, Isfahan, Iran.

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Essential oil was extracted from lavender using supercritical carbon dioxide by means of a newly developed periodic static-dynamic (PSD) procedure and the conventional semicontinuous (SC) technique. Applying GC-FID analysis in conjunction with Box-Behnken design, an optimum overall extraction yield (94.4 %) was obtained via PSD in contrast to 90 % for the SC method. The results indicate that supercritical fluid extraction is a viable technique for separation of constituents such as linalyl acetate, linalool, fenchone, and camphor for pharmaceutical and medicinal applications. Furthermore, a substantial reduction of energy consumption and solvent consumption is achieved with the developed PSD process compared to the conventional SC method. Keywords: Box-Behnken design, Lavender, Linalool, Linalyl acetate, Supercritical carbon dioxide, Supercritical fluid extraction

Supporting Information available online

1

Received: August 14, 2011; revised: December 22, 2011; accepted: January 25, 2012 DOI: 10.1002/ceat.201100429

Introduction

Due to the high-proportion usage of plant extracts in pharmaceutical and medical industries, theoretical and experimental research is required to produce the needed extracts. In this regard, the essential oil of lavender exhibits a broad spectrum of antiplatelet effects and is able to inhibit platelet aggregation induced by arachidonic acid, collagen, and the stable thromboxane receptor agonist U46619 without prohemorrhagic properties [1]. Linalyl acetate (36 % of lavender oil) seems to be the main active antiplatelet agent. Aroma inhalation of lavender essential oil or one of its main components, linalool, can significantly decrease symptoms associated with tension, anxiety, and stress and may also be applicable to the treatment of menopausal disorders [2]. Lavender essential oil demonstrates an interesting analgesic activity at doses devoid of sedative side effects [3]. Moreover, inhalation of the volatile fractions of lavender (0.1–0.2 mg mair–3) reduced the cholesterol content in the aorta and also atherosclerotic plaques [4], but had no effect on the content of cholesterol in blood. Allergic symptoms can also be suppressed by lavender oil [5]. A lavender-fragranced cleansing gel had a significant transient effect of improving

– Correspondence: Prof. S. M. Ghoreishi ([email protected]), Isfahan University of Technology, Department of Chemical Engineering, Isfahan 84156-83111, Iran.

Chem. Eng. Technol. 2012, 35, No. 9, 1641–1648

mood [6]. Even foot soaking in warm water containing lavender essential oil appeared to be effective for alleviating fatigue in terminally ill cancer patients [7]. The extraction of essential oil from flowers and leaves represents an attempt to isolate the desirable mixture while preserving the original composition with natural properties [8]. Unfortunately, the techniques usually adopted, such as steam distillation and solvent extraction, suffer from several limitations. The shortcomings of steam distillation are as follows: (i) It can cause degradation of thermolabile compounds and hydrolysis of water-sensitive materials, (ii) it can produce an incomplete collection of compounds responsible for the pharmaceutical properties, and (3) since steam distillation is based on the evaporation of volatile compounds induced by steam, thus, compounds with low vapor pressure are not completely extracted by this technique [9, 10]. In the extraction process using n-hexane, there are important economic, environmental, and safety problems. Vacuum distillation is needed to purify the extracted materials but complete separation is still not possible which is unacceptable for pharmaceutical applications. The toxic and flammability properties of the hydrocarbon solvent are major handicaps to its use [11]. Thus, research in developing a safer and more effective method for production of plant extracts for pharmaceutical and medicinal applications is needed. Supercritical fluids have proved to be effective solvents for applications in pharmaceutical, chemical, petrochemical, and environmental processes [11]. The extraction of natural products with supercritical fluids, especially with carbon dioxide

© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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S. M. Ghoreishi et al.

the internal standard for the GC-FID calibration analysis, respectively. Pure camphor (148075, 96 %, Aldrich), fenchone (46208, ≥ 99.5 %, Fluka), linalyl acetate (45980, ≥ 95 %, Fluka), and linalool (51782, ≥ 99 %, Fluka) were the standards for the four important constituents of lavender essential oil. Industrial-grade CO2 (≥ 99 %, Zamzam) was used as the supercritical fluid.

(CO2; nontoxic, nonflammable with a low critical temperature and a moderate critical pressure), has found numerous largescale applications in the food and perfume industries, including, e.g., decaffeination of coffee beans and extraction of bitter principles from hops, of essential and pungent principles from spices, of natural food colorants, and of essential oils for perfumery [12–14]. Owing to some inherent advantages of supercritical fluid extraction (SFE) over conventional liquid solvent extraction, the technology is also of interest for extraction of medicinal plants [15–17]. Ghoreishi and Sharifi [15] theoretically investigated supercritical CO2 extraction of mannitol from plane tree leaves. Numerous applications of analytical SFE to various herbs and natural product classes have been published [18–20]. Ghoreishi et al. [18] and Ghoreishi and Shahrestani [19] experimentally studied supercritical CO2 and subcritical water extraction of mannitol from olive leaves. Essential fatty acids such as c-linolenic acid were extracted from Echium amoenum (Boraginaceae) seed oil via supercritical CO2 [20]. Recently, a few studies were performed in regard to separation of essential oil from different types of lavender. Essential oil was extracted from Turkish lavender flowers [21, 22] and Italian lavender [23] using supercritical CO2. A new process design and operation for microwave-accelerated steam distillation of essential oils from Italian lavender was developed and compared with steam distillation [24]. A total of 85 components were identified in 2D GC-MS analyses of nine samples of Australian lavender essential oil using low-polarity and polar capillary columns [25]. The main objective of this study was to extract essential oil from Isfahan lavender flowers (Lavandula angustifolia) applying supercritical CO2 in a newly developed periodic static-dynamic (PSD) procedure and conventional semicontinuous (SC) method for the production of camphor, fenchone, linalyl acetate, and linalool used in the pharmaceutical and cosmetic industries. Moreover, in order to achieve the maximum extraction yield, the operating conditions of both methods were optimized via response surface design.

The SFE system presented in Fig. 1 was used for PSD and SC methods, operating in a temperature range of 298–523 K with a maximum pressure of 500 bar. The system is constructed such that any noncorrosive or corrosive fluid can be used as the supercritical fluid. The experimental setup for the supercritical extraction system is composed as follows: (1) CO2 cylinder (Zamzam), (2) molecular sieve column (Merck, molecular sieve 5A-K28751105148), (3) porous metal filter (Mott Metallurgical, 1003630-01-050), (4) cooler circulator (Sina), (5) pump head cooler, (6) HPLC pump (Jasco, PU-1580), (7, 8) valve (Shirvani), (9) three-way valve, (10) coil preheater, (11) injection valve (Rheodyne, 7000), (12) extraction column (Shirvani), (13) oven with PID temperature controller (Shimaz, maximum temperature 523 K), (14) valve (Shirvani), (15) back-pressure regulator (Tescom, 26-1762-24), (16) solute collection vessel, (17) double-pipe heat exchanger (Shirvani), and (18) cooler circulator (Sina).

2

2.4 PSD and SC SFE

Experimental

2.1 Materials Lavender flower samples, obtained from the Isfahan Agricultural Research Center, were dried at 313 K for a period of 60 min prior to extraction and weighing. This procedure was repeated until the weight of the samples became constant, which guaranteed zero water content. Since extraction kinetics in this study was controlled by the kernel particle size, an important sieving step was carried out to achieve a reproducible extraction yield in which the samples were passed through a sieve with mesh sizes of 20–30 (0.60–0.85 mm). The dried samples were kept within a sealed bag in a cold and dry place until they were used. Ethanol and n-hexanol (99.6 %, Merck) were utilized as the trap solvent for the collection of solute in the supercritical fluid and

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2.2

GC-FID Analysis

Chemical analysis and identification of different components such as camphor, fenchone, linalyl acetate, and linalool in the extracted essential oil were carried out using a gas chromatograph-flame ionization detector (GC-FID, Agilent Technologies, 6890N) equipped with a capillary column HP-5 (30 m length, 0.25 mm ID, 0.25 mm film thickness).

2.3 SFE Apparatus and Procedure

In order to increase the purity of CO2 (99.95 %; Zamzam), which is stored in a CO2 cylinder (1), it is passed through a

Figure 1. Schematic diagram of the supercritical extraction system.




column of molecular sieve beads (2) and metal porous filter (3). Then, it is cooled down to 273 K in a cooler circulator/ pump head cooler (4, 5), and subsequently charged by a feed pump (6). A valve (7) is placed at the effluent of the pump, and thus, the CO2 stream is easily controlled and saved properly for further use. CO2 is heated before entering the extraction column (12) by using a coil preheater (10) placed in an oven (13). After reaching the corresponding supercritical fluid conditions inside the extraction column, the static time is provided for the extraction process by closing the valve (14). After carrying out the static extraction, the dynamic extraction with constant volumetric flow rate of CO2 is started by opening the valve (14). At this stage, the system pressure is controlled and monitored by a back-pressure regulator (15) and a high-pressure pump. The stainless-steel extraction column (height 12.5 cm, ID 0.9 cm, OD 1.3 cm) (12) fitted with a porous metal filter at the inlet and outlet is manually charged with lavender flowers and glass beads (broken Pyrex laboratory glassware) with a mesh size of 20–30 at a ratio of 40–60 wt-%, respectively. First, CO2 is charged into the extraction column while the pump is set at the selected operating pressure, and the desired temperature is obtained via oven and preheater. After reaching the appropriate pressure and temperature in the column, the pump is turned off and isolated with a shut-off valve. Subsequently, a constant static extraction time is allowed for SCCO2 to dissolve the essential oil and then, by passing the CO2 at a constant flow rate, the dissolved oil via static and dynamic extraction is discharged from the column, cooled (258 K) via a 1-1 shell and tube heat exchanger (17, 18), trapped, and collected with 10 mL of ethanol in the collection vessel (16). The essential oil contained in the extracted samples was kept in the refrigerator for further GC-FID analysis. After each extraction procedure, the whole system is washed with ethanol and subsequently purged with CO2. The innovative PSD procedure developed in this study is composed of repeated staticdynamic extraction periods in which a static extraction with specific time was carried out, subsequently followed by a dynamic extraction with a constant extraction column average residence time of 2 min (constant CO2 volumetric flow rate of 2 mL min–1). In other words, a dynamic extraction is performed after every static extraction for several times, whereas the static and dynamic extraction is performed only once in the SC process compared to the PSD method.

2.5

Soxhlet Extraction

Besides SFE, traditional Soxhlet extraction was also carried out in a standard apparatus by the standard method [23] for 8 h with 50 mL of n-hexane. The total mass of four components in lavender flowers was experimentally determined by Soxhlet extraction being 80 % of the total mass of lavender flower samples.

2.6

Response Surface Design


time for the column during the dynamic extraction period using a constant flow rate (2.0 mL min–1). The three independent effective variables (temperature, pressure, and number of repetition×static time (tr×ts) on the dependent variables (response) of component and overall extraction yield (Yi, Yo) were investigated at three levels (–1, 0, and 1), utilizing the MINITAB software package according to the following equation: Yi or Yo = bo + R bjXi + R bjjXj2 + R bjkXjXk

(1)

Tab. 1 presents the chosen ranges for three independent variables at three levels. Table 1. Range of three independent variables in the PSD technique for the B-B method. Variables

–1

0

1

Temperature [K]

318

323

328

Pressure [bar]

80

100

120

tr×ts [min]

24×5

12×10

8×15

For quantification of fenchone, linalool, camphor, and linalyl acetate contents in the extracted samples, the obtained area under the corresponding peaks in Fig. S3 (Supporting Information) were compared with the linear calibrations of Fig. S2. Finally, the component and overall extraction yields (Yi, Yo) were calculated using Figs. S1–S3 and the following Eqs. (2) and (3): Yi

mass of component i in extracted sample × 100 total mass of component i in lavender

Yo

(2)

mass of four components in extracted sample × 100 (3) total mass of four components in lavender

3

Results and Discussion

3.1

Optimization of PSD Operating Conditions

The obtained experimental results of 15 runs are summarized in Tab. 2. The results of the statistical analysis including the estimated regression coefficients, t-values, and p-values of overall extraction yield are listed in Tab. 3. Five second-order polynomial equations were determined by the B-B method for prediction of component and overall extraction yields as a function of independent variables: Yf

67114:9 414:834T10:005P 0:644T 2

Yl

A statistical experimental design based on the Box-Behnken (B-B) method [26] was planned with a fixed average residence

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20:898tr ts

0:034P2 0:794tr ts 2

68892:400 426:896T6:985P 27:669tr ts 0:644T 2 0:038P2 0:854tr ts 2


(4)

(5)

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Table 2. Responses of dependent variables using three levels-three factors B-B method to independent variables of the PSD technique. Exp.

T [K]

P [bar]

tr×ts

Yf

Yl

Yc

1

323

100

12×10

72.8

72.9

71.7

2

323

100

12×10

71.5

73.5

72.4

3

323

100

12×10

73.0

74.2

72.9

4

323

80

24×5

68.6

66.7

65.5

5

318

100

8×15

80.3

82.4

79.2

6

323

120

8×15

86.1

88.1

87.9

7

328

120

12×10

55.2

58.3

52.1

8

328

100

8×15

63.6

55.6

62.5

9

318

100

24×5

89.7

92.8

91.5

10

328

80

12×10

18.1

15.1

17.0

11

318

120

12×10

68.8

66.9

68.7

12

323

120

24×5

99.0

99.1

96.9

13

323

80

61.1

64.1

59.9

14

328

100

24×5

71.2

72.3

68.1

15

318

80

12×10

28.9

25.9

30.8

8×15

Table 3. Regression coefficients, -values and significance t-values for the model of PSD overall extraction yield estimated by Minitab software. Variables

Coefficients b p-value

t-value

ob

–68183.5

0.001

–7.106

T

422.067

0.001

7.124

P

8.599

0.286

1.194

trts

–26.596

0.395

–0.930

T2

–0.656

0.001

–7.161

2

–0.038

0.001

–6.568

(trts)2

0.824

0.000

8.988

T×P

0.000

0.995

–0.007

Ttrts

0.034

0.714

0.387

Ptrts

–0.017

0.470

–0.781

P

Yc

67271:100 416:526T10:129P 0:648T 2 0:035P2 0:768tr ts 2

Yla

67001:000 413:3084T12:534P 0:640T 2 0:039P2 0:779tr ts 2

Yo

68183:500 422:067T8:599P 26:596tr ts 0:656T 2 0:038P2 0:824tr ts 2

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36:898tr ts

16:119tr ts

The analysis of variance (ANOVA) proves the suitability of the fitted models. The linear regression Yla Yo coefficient R2 for the extraction yield was calculated as 98.6 %, indi72.7 73.0 cating the good performance for the 73.3 74.7 developed model. R2 adjusted to the 74.0 75.2 extraction yield was calculated to be 95.9 %, i.e., the developed model 67.0 68.8 for prediction of the extraction 81.7 82.5 yield only differs by ± 4.1 % from the experimental data. Regarding 87.3 84.3 the statistical results (ANOVA) with 56.2 53.0 95 % confidence level, the effect of each term in the models could be 64.8 64.7 significant, provided that its p-value 92.0 90.9 is < 0.05. The ANOVA and error 16.1 18.1 values for the response surface model are given in Tab. 4. The lack67.7 69.0 of-fit or adequacy test is significant 98.8 99.3 at p-values < 0.05, demonstrating the adequacy of the selected quad62.4 59.2 ratic model. Tab. 4 presents the de71.6 72.9 gree of significance of different terms in the model from which, 27.5 29.6 based on the obtained results for the coefficients and p-values, it can be concluded that the linear (T, P, and trts), quadratic (T2, P2, and (trts)2), and interaction terms (TP, Ttrts, Ptrts) have strong, very strong, and weak effects on the overall extraction yield, respectively. It is imperative to realize that even though p-values are > 0.05 (Tab. 3) for the linear terms of P and (trts), due to the hierarchy rule in which the p-values are < 0.05 for the higher order (quadratic) of these two variables, the effect of linear terms must be considered in the model.

3.1.1 Effect of Supercritical Fluid Temperature and Pressure

(6)

(7)

(8)

Fig. 2 illustrates the effect of different operating temperatures and pressures of SC-CO2 on the overall extraction yield at constant tr×ts (8×15 min) and dynamic time (2 min). As temperature increases, two distinguished trends are observed in regard to the overall yield. In the range of 318–322 K, the yield increases with a mild slope until it reaches its maximum value (94.4 %), and a further increase up to 328 K causes a slight decrease in yield. These two different regions of yields can be attributed to retrograde solubility in which the counter effect of solute vapor pressure and supercritical fluid density are affecting the extraction yield. In other words, in the first region of increasing temperature, the solute vapor pressure enhancement overlaps the supercritical fluid density decrease up to 322 K where the maximum yield is obtained. At 322 K, the retrograde solubility is reached in which the effect of solute vapor pressure becomes equivalent to the effect of CO2 density and subsequently beyond that the effect of density decrease prevails vapor pressure enhancement. The effect of supercritical fluid pressure is also demonstrated in Fig. 2 for the operating range of 80–120 bar. Enhanced over-




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Table 4. ANOVA for the fit of the experimental data to the response surface. Source

Degree of freedom

Adjusted sum of squares

Adjusted mean squares

Regression

9

6593.90

732.66

Linear

3

1535.65

511.88

Square

3

3646.51

1215.50

Interaction

3

14.74

4.91

Residual error

5

96.90

19.38

Lack-of-fit

3

96.05

32.02

2

0.85

0.42

–

–

Pure error Total

14

for equilibration of the SC-CO2/solute system. In other words, 15 min static time in F-value p-value experiment no. 3 is sufficient for the system to reach its saturation solubility, whereas 5 and 10 min static times in ex37.81 0 periments no. 1 and 2 do not provide the 26.41 0.0002 saturation solubility of the solutes (fench62.72 0 one, linalool, camphor, and linalyl acetate) in SC-CO2. As indicated in Fig. 3, the high0.25 0.856 est yield (100 %) was obtained in run – – no. 1. In this regard, it should be noted that the overall extraction time of static plus 75.49 0.013 dynamic for experiment no. 1 is 168 min in – – contrast to 136 min for experiment no. 3. In conclusion, the optimum operating – – conditions for the newly developed extraction PSD technique are 110 bar, 322 K, and a periodic static time of 8×15 min at 2 min constant dynamic time in order to obtain 94.4 % overall yield. Tab. 5 summarizes the optimum operating conditions to obtain the maximum component extraction yields which are very similar to the corresponding optimum operating conditions for the overall yield.

Figure 2. Response surface of PSD overall extraction yield as a function of SC-CO2 temperature and pressure at tr×ts = 8×15 min.

all extraction yield is observed as the pressure is increased from 80 to 110 bar under which the maximum yield of 94.4 % is reached. A further increase in pressure has no significant effect on the yield. Beyond 110 bar, a very slight decrease in yield is observed which is expected due to the simultaneous counter effect of higher temperature which causes lower CO2 density with respect to density enhancement via pressure increase.

3.1.2 Effect of Periodic Static-Dynamic Extraction Time The response surface of overall extraction yield as a function of SC-CO2 temperature and periodic static-dynamic extraction time at 110 bar (optimum pressure) is illustrated in Fig. 3. Three sets of experimental runs in terms of trts were used: 24×5, 12×10, and 8×15 min. The periodic static-dynamic extraction time of 8×15 min was selected as the most appropriate condition in view of high yield (94.4 %), lower energy consumption for the pump and cooler circulator, lower solvent consumption (67 % and 33 % in contrast to runs no. 1 and 2, respectively), and easier solute recovery. Obviously, the effect of dynamic extraction is prevailing in experiments no. 1 and 2 and, therefore, not enough static extraction time is provided


Figure 3. Response surface of PSD overall extraction yield as a function of SC-CO2 temperature and periodic static-dynamic extraction time at 110 bar. Table 5. Overall and component yields under PSD optimum conditions. No.

Yield [%]

T [K]

P [bar]

tr×ts [min]

Yf

92.7

322

111

8×15

Yl

95.4

322

110

8×15

Yc

92.7

322

111

8×15

Yla

93.0

322

110

8×15

Yo

94.4

322

110

8×15

3.2 Optimization of SC Operating Conditions In order to optimize component and overall extraction yields (Yi, Yo) in the SC process, a statistical experimental design based on central composite design (CCD) [26] in conjunction


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with MINITAB software using five levels (–2, –1, 0, 1, 2) and four variables was planned with a fixed column average residence time (4 min) utilizing a constant flow rate (1.0 mL min–1). The effect of important independent variables on extraction yield such as dynamic time, static time, supercritical fluid pressure, and temperature, were investigated in the range of 80– 120 min, 10–30 min, 80–120 bar, and 313–333 K, respectively.

increasing pressure up to 112 bar due to the higher density, i.e., better interaction between solvent and matrix, solvation capabilities, and also a higher mass transfer driving force provide an appropriate medium for the leaching process to take place. Beyond 112 bar, saturation limitation occurs and thus, a constant trend of extraction is obtained up to 120 bar. 3.2.2 Effect of Extraction Time

3.2.1 Effect of Supercritical Fluid Temperature and Pressure Effects of variables on the overall yield of the SC method are illustrated in Figs. 4 and 5, and the final optimum results are provided in Tab. 6. The first variable is the temperature which has a direct effect on the physicochemical properties of CO2 (density, diffusion, viscosity, and surface tension) and the extracted compounds (solute vapor pressure). The effect of temperature on the extraction yield is depicted in Fig. 4. Enhancement of extraction yield is observed upon increasing the temperature in the range of 313–322 K, in which the higher solute solubility effect due to increased vapor pressure overlaps the effect of the solvent density decrease. Beyond 322 K, the retrograde solubility prevails and, therefore, the effect of density decrease overcomes the influence of increased vapor pressure of the solute. Thus, lower extraction yield is obtained in the range of 322–333 K. Fig. 4 also demonstrates the effect of pressure on the extraction yield in the range of 80– 120 bar. It is observed that the extraction yield is enhanced by

Figure 4. Response surface of SC overall extraction yield as a function of SC-CO2 temperature and pressure at ts = 22 min and td = 123 min. Table 6. Overall and component yields under SC optimum conditions. No.

Yield [%]

T [K]

P [bar]

td [min]

ts [min]

Yf

77.8

323

112

123

23

Yl

87.7

322

112

125

22

Yc

93.2

323

112

125

22

Yla

96.5

323

112

127

22

Yo

90.0

322

112

123

22

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It is important to optimize the contact of the supercritical fluid with the sample material in order to enhance the SFE efficiency. Variables influencing the solvent contact time with sample material include flow rate, SFE time, and SFE mode (static with no flow-through or dynamic with flow-through). The static extraction prior to dynamic extraction usually improves the solute recoveries in SFE. The effect of static and dynamic extraction times on the overall yield of the SC method is illustrated in Fig. 5. Samples were held in the static extraction mode in the range of 10–30 min, followed by a dynamic extraction in the range of 60–140 min at the constant flow rate of 1.0 mL min–1. The static extraction is increased up to 22 min and becomes constant in the range of 22–30 min. The observed extraction efficiency can be explained in terms of a higher mass transfer driving force up to 22 min. Using dynamic extraction, a higher mass transfer driving force at the beginning provides a suitable condition for extraction which continues up to 123 min. Thereafter, a constant mode of extraction is observed due to the very low essential oil concentration of the matrix.

Figure 5. Response surface of SC overall extraction yield as a function of static and dynamic extraction time at 322 K and 110 bar.

According to the obtained results summarized in Tab. 6, the SC optimum operating conditions to achieve maximum overall extraction yield (90 %) for temperature, pressure, dynamic time, and static time were 322 K, 112 bar, 123 min, and 22 min, respectively. Moreover, the highest component extraction yield (wt-%) for fenchone, linalool, camphor, and linalyl acetate are found to be 77.8, 87.7, 93.2, and 96.5, respectively. These findings are compatible with the results of other studies [21–23]. For instance, the essential oil from Turkish laven-




der flowers was extracted using semicontinuous SC-CO2 in which extraction yields of 82.80 %, 39.85 %, and 58.17 % were reported under the optimum operating conditions for the overall, fenchone, and camphor, respectively [21, 22]. In another study, SC-CO2 extraction of Italian lavender flowers was performed at 90 bar and 321 K followed by a two-stage separation procedure conducted at 80 bar, 273 K, and 25 bar, 263 K, in the first and second separator, respectively [23]. The results revealed a maximum essential oil yield of 4.9 wt-%. Utilization of two techniques other than SC-CO2, such as microwave-accelerated steam distillation (MASD) and steam distillation (SD), for the extraction of essential oil from Italian lavender were reported [24]. MASD and SD component extraction yields of 47.82, 11.82, 10.74 and 46.85, 10.23, 11.90 wt-% were obtained for linalool, camphor, and linalyl acetate, respectively. Comparison of the obtained results in this study with the aforementioned previous researches indicates that the lavender flowers essential oil of this study is different in terms of the weight composition of four major constituents, namely, fenchone (8.08 %), linalool (47.76 %), camphor (12 %), and linalyl acetate (12.16 %). This indicates that essential oil extracted from lavender flowers contains up to 80 wt-% fenchone, linalool, camphor, and linalyl acetate. Furthermore, the obtained optimum overall extraction yield (94.42 %) via the newly developed PSD method is slightly higher than the yield obtained by the SC method performed in this study and by Adusoglu et al. [21], Akgün et al. [22], and Reverchon et al. [23]. Moreover, the new PSD method is superior in terms of the major saving of solvent and pump and cooler circulator energy consumption (74 %).

OD P T td ts Yi Yo Yf Yl Yc Yla

[cm] [bar] [K] [min] [min] [–] [–] [–] [–] [–] [–]

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outer diameter pressure temperature dynamic extraction time static extraction time component extraction yield overall extraction yield extraction yield of fenchone extraction yield of linalool extraction yield of camphor extraction yield of linalyl acetate

Greek symbols bo bj bjj bjk

[–] [–] [–] [–]

intercept linear coefficients squared coefficient interaction coefficient

Subscripts i o f l c la d s h

component overall fenchone linalool camphor linalyl acetate dynamic static hexanol

References 4

Conclusions

Experimental supercritical extraction of essential oil from Isfahan lavender flowers was carried out via a new PSD technique and conventional SC method. The results demonstrated that SC-CO2 extraction is a viable technique to be applied in pharmaceutical and cosmetic industries. Utilizing a response surface design to optimize the operating conditions revealed that maximum overall extraction yields of 94.4 % and 90 % can be achieved by PSD and SC procedure under optimum operating conditions. Comparison of the two methods demonstrated that the PSD method provides a slightly higher yield with major reduction in solvent and energy consumption.

Acknowledgment The financial support provided for this project by the Isfahan University of Technology (IUT) is gratefully acknowledged. The authors have declared no conflict of interest.

Symbols used As/Ah ID

[–] [cm]

surface of sample/surface of n-hexanol inner diameter


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