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Performance of reverse osmosis and nanofiltration membranes in the fractionation and retention of patchouli essential oil
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Performance of reverse osmosis and nanofiltration membranes in the fractionation and retention of patchouli essential oil Adriana Donelian a , Patrícia F. de Oliveira a , Alírio E. Rodrigues b , Vera G. Mata b , Ricardo A.F. Machado a,∗ a Laboratório de Controle e Processos de Polimerizac¸ão, Departamento de Engenharia Química e Engenharia de Alimentos, Universidade Federal de Santa Catarina (UFSC), Campus Universitário, Trindade, P.O. Box: 476, Zip Code: 88010-970 Florianópolis, SC, Brazil b Laboratory of Separation and Reaction Engineering (LSRE), Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, Zip Code: 4200-465, Porto, Portugal
a r t i c l e
i n f o
Article history: Received 23 April 2015 Received in revised form 22 July 2015 Accepted 22 July 2015 Available online xxx Keywords: Patchouli Essential oil Membrane Supercritical carbon dioxide
a b s t r a c t Patchouli essential oil consists of over 24 different components. Patchoulol has been known for over a century as the most important component of this essential oil, being widely used in the perfumery and cosmetics industries. Recent research has demonstrated that another component of patchouli essential oil, ␣-bulnesene, has pharmaceutical properties, providing a decrease in thromboxane formation. In this study, three different membranes were evaluated in terms of their fractionation capability and retention of patchouli oil in supercritical media, aiming at the separation and concentration of the main oil components (patchoulol and ␣-bulnesene) and regeneration of CO2 . The membranes tested showed good resistance under the experimental conditions used, but did not show good fractionation and concentration of the patchouli oil components. The reverse osmosis membrane gave the highest oil retention (0.95) and lowest reduction in the permeate flux of the CO2 in the presence of the essential oil. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Patchouli oil is one of the important natural essential oils for the production of perfume and in medical applications [1–3]. It is obtained from the leaves of Pogostemon cablin (patchouli), a plant like many from the Lamiaceae family that accumulates large amounts of essential oil [4]. At present, patchouli oil is used in many fine fragrance products to provide a base and give lasting character, being one of the most valuable natural materials for the perfumery and cosmetic industries [4–6]. It is also listed as an approved substance for food flavoring by the FDA (Food and Drug Administration, USA) [7]. Patchouli oil contains bioactive compounds, which confer the plant anti-allergic and anti-bacterial activities on skin, as well as anti-oxidative and anti-inflammatory effects [8–12]. The color of patchouli essential oil is due mainly to the presence of substances commonly responsible for the color of oils of plant origin. These include chlorophyll (green) and the carotenoids (yellow and red).
∗ Corresponding author. E-mail address: [email protected] (R.A.F. Machado).
The composition of patchouli oil is distinct, consisting of over 24 different sesquiterpenes, in which patchoulol is the major constituent and, due to its fixative characteristic, it regulates the oil aroma [3,4]. Also, ␣-bulnesene is an important compound present in the oil which, in recent research, showed a potent inhibitory effect on platelet aggregation, reducing the risk of cardiovascular diseases [13]. Traditionally, patchouli oil is obtained by steam distillation from P. cablin leaves. This procedure, performed at a high temperature, can cause the degradation of thermally labile compounds [13,14]. However, recent researches carried out by Donelian et al. [15] have demonstrated that extraction with supercritical CO2 at 14 MPa and 40 ◦ C provided a yield of 5.07%, while steam distillation yielded 1.50%. In relation to the quality of essential oil, represented mainly by the concentration of patchoulol, the supercritical extraction yielded 31.39% of patchoulol in the oil, while steam distillation obtained only 19.4% yield. The use of supercritical CO2 for separation has been described in numerous publications [16,17]. However, this approach requires a considerable amount of energy to recycle the solvent to its original thermodynamic state for further processing. To avoid this, some researchers have studied the association of membrane separation with supercritical fluid extraction process with the aim of retaining the essential oil and regenerating the fluid, reducing compression
http://dx.doi.org/10.1016/j.supflu.2015.07.026 0896-8446/© 2015 Elsevier B.V. All rights reserved.
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costs [18–21], and also, when possible, of fractionating some components of the natural products in order to obtain a concentrated fraction of the main oil component. In order to isolate major compounds of patchouli oil, reports in published researches stand for the use of the host–guest inclusion method, using a host molecule to selectively recognize the guest molecule patchoulol, and of distillation combined with crystallization to isolate patchouli alcohol from patchouli oil [22,23]. For both of them the authors reported good separation results, recovering up to 40% of the patchouli alcohol. Su et al. [24] evaluated fractional distillation combined with crystallization as a method for the isolation of patchouli alcohol from patchouli oil, obtaining up to 52.9% of this compound. Zhang et al. [25] used high performance centrifugal partition chromatography (HPLCPC) in a preparative scale to separate patchouli alcohol, using a two-phase solvent system. The purity achieved was more than 98%, but it has the disadvantage of requiring the use of organic solvents. Sarmento et al. [18] evaluated the performance of three commercial reverse osmosis membranes: CG, AG and SG (Osmonics) in relation to the retention of lemongrass, orange and nutmeg essential oils at 12 MPa and 40 ◦ C. The oil retention was studied as a function of the transmembrane pressure difference (P) at values between 1.0 and 4.0 MPa and of the feed oil concentration (from 5 to 15% wt). The results demonstrated that the oil retention index was reduced with an increase in P, and significant variations according to the feed oil concentration were not observed. The best results were obtained with the SG membrane and a P value of 1.0 MPa, obtaining a retention index of up to 0.90 for all the essential oils tested, although these conditions gave the lowest CO2 permeate fluxes, indicating the occurrence of fouling. On analyzing the separation process with membranes for the regeneration of CO2 , using d-limonene as the solute, Carlson et al. [19] also found that the SG membrane, made of polyamide, gave the highest retention index, above 0.80 for an experimental period of 3 h. However, after the first 120 min, the permeate flux fell to zero, demonstrating that the high retention index was followed by an irreversible clogging of the membrane. However, it was verified that on alternating the feeding between CO2 + d-limoneno and pure CO2 , it was possible to achieve a retention index of over 0.94, but with low fluxes of CO2 . Hsu and Tan [26] used a reverse osmosis membrane made of polyamine (FilmTec FT-30) to remove ethanol from a mixture with water. Using scCO2 under pressure and temperature conditions slightly above the critical values the authors verified that the retention index of ethanol increased from 0.20 to 0.70, due to the formation of clusters of ethanol and CO2 . Sarmento [27] analyzed the behavior of different models of commercial nanofiltration and reverse osmosis membranes in relation to the retention and fractionation of polyphenol extracted from cocoa extract under supercritical conditions. The experiments were carried out at 12 MPa and 40 ◦ C, and the results showed that the nanofiltration membrane models DL, HL and NF gave the highest permeabilities with a retention index for polyphenol of over 0.90 when a P value of 1.0 MPa was applied. In relation to the fractionation of polyphenol, only the HL membrane showed a separation capacity, promoting a fraction in the permeate with no oligomers in the range between heptamers and decamers. Two nanofiltration membranes, TN and T, were investigated by Sarrade et al. [28] in the fractionation of triglycerides originated from fish oil and the purification of -carotene from either carrot oils or carrot seeds. The experiments were carried out at 31 MPa, 40 ◦ C and with a P value of 3 MPa, and the results showed that the TN membrane allowed a significant concentration of important triglycerides with a high molar mass (over 52 carbons) in the retentate and short-chain fatty acids in the permeate. In relation
to the purification of -carotene, the T membrane allowed a 2.4fold increase in the concentration of the pigment in the permeate stream. Therefore, the objective of this study was to evaluate the performance of three different commercial membranes in the separation of patchouli essential oil using supercritical CO2 , in order to promote the regeneration and recirculation of CO2 with a lower minimum pressure during the supercritical extraction, reducing the energy requirement for the solvent recompression [27]. The membranes were also assessed in relation to their capacity for the fractionation of patchouli oil, aiming at the separation and concentration of patchoulol with fixative properties, and ␣-bulnesene with pharmacological properties. 2. Experimental 2.1. Patchouli essential oil and membranes Patchouli essential oil was obtained by extraction with scCO2 at 10 MPa and 32 ◦ C. The pressure and temperature chosen were the best conditions identified by Donelian [29] under which to perform the patchouli essential oil extraction with scCO2 . For the extraction, patchouli leaves were collected from “Colônia Penal Agrícola” (Palhoc¸a, SC, Brazil). The extraction procedure is described in Donelian et al. [15]. Three different kinds of commercial membrane supplied by Dow Filmtec (USA) were studied. The membranes are described below: – Commercial membranes (maximum operation temperature: 45 ◦ C): • Nanofiltration membrane – model NF-90 – Thin polyamide film. • Nanofiltration membrane – model NF – Thin polypiperazine amide film. • Reverse osmosis membrane – model BW-30 – Thin polyamide film. 2.2. Equipment In this study, a membrane unit was designed and built from a supercritical extraction unit developed at the Laboratory of Separation and Reaction Engineering (LSRE). The equipment is schematically represented in Fig. 1. The experimental unit was constructed in stainless steel and designed to work up to 20 MPa. However, there is a security valve (VS ) regulated to lead the CO2 stream to the purge line if the pressure exceeds 19 MPa. The cylinder (1) supplies liquid CO2 (99.8% purity, Praxair, Portugal) to the surge tank (5). The pressurization of the system was accomplished through a high pressure pump (3) (Model MCPV 71, Haskel, USA) and the CO2 stream was cooled before entering the pump (3) in order to prevent cavitation inside the pump. The separation unit comprised two cells (6 and 7) constructed of stainless steel with a unit volume of 30 cm3 and arranged in series. The membrane to be tested was positioned in one cell (7), while the other cell (6) contained patchouli essential oil. The essential oil was placed together with glass beads to provide resistance in order to avoid a large quantity of oil from moving directly to the surface of the membrane. The membrane was placed over a perforated metal support, and the cells were sealed with poly(tetrafluorethylene) rings. The filtration area of the membrane was 3.14 cm2 and a cross flow regime was used during the experiments. The feed pressure in the cell was controlled through a downstream control valve (VR) (Model APR66, Veriflo, Parker Hannifin Corporation, USA) which allowed the pressure in the surge tank
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in order to verify the reversibility of the conditions and the occurrence of hysteresis.
Fig. 1. Experimental unit of supercritical process coupled with a membrane unit. (1) CO2 cylinder; (2) Cool Bath; (3) Pump; (4) Oven; (5) Surge tank; (6) Membrane Cell; (7) Essential oil Cell; (8) Backpressure regulator; (9) Thermostatic water bath; (10) Erlenmeyer flask; (11) Bubble flow meter; (M0 , M1 , M2 ) Manometer; (P1 ) (P2 ) Pressure transducers; (VM ) Micrometer valve; (VS ) Security valve; (VR ) Downstream control valve; (V0 , V1 , V2 , V3 , V4 , V5 ) On-off valves; (V6 , V7 , V8 ) Needle valves.
(5) to be reduced to the level required in the separation unit. The pressure at the exit of the valve VR was monitored through a pressure transducer (P1 ). The pressure on the permeate side of the membrane was controlled by a backpressure regulator (8) (Model 26-1762-24, Tescom, USA) and monitored by a pressure transducer (P2 ) (Model ECO-1, Wika, Germany). The temperature was maintained by a thermostatic water bath (9). During the fractionation experiments, the retentate CO2 flow was controlled manually through a micrometer valve (VM ) and was measured at the exit of the collector by a bubble flow meter (11) under room conditions. The extracts were collected separately in the retentate and permeate sides, at atmospheric pressure, in Erlenmeyer flasks (10) immersed in a cooling bath of ice and salt to minimize the loss of volatile fraction of the extract carried away with CO2 gas stream. 2.3. Membrane process procedure The working pressure of 10 MPa was chosen based on the best pressure conditions under which to obtain patchouli essential oil by supercritical extraction.
2.3.2. Patchouli essential oil fractionation and retention tests The temperature and P of the retention tests were chosen based on the results obtained during the characterization of the membrane with pure CO2 in order to minimize deviations from the optimum extraction conditions and the need to recompress CO2 . The cell (6) was loaded with patchouli essential oil to give an initial feed concentration of 10% wt. in relation to the CO2 that occupied the two cells at 10 MPa and 32 ◦ C. This concentration was set within the concentrations used for studies on the performance of membranes in the separation of scCO2 and essential oils [18,30]. Initially, the membrane used in the retention tests was characterized with pure CO2 at a P value of 1 MPa. The backpressure regulator (8) and the valve V7 were then closed, and the cell (6) contained the oil was pressurized by opening valves V4 and V5 , maintaining valve V6 closed. Once the working pressure was established in the cell (6), valve V6 was opened, placing the solubilized CO2 with the essential oil in contact with the membrane in the cell (7) and applying a P of 1 MPa via the backpressure regulator (8). At this moment, the fractionation and retention tests began. The retentate flux was maintained constant via valve V8 and the micrometer valve (VM ) in such a way that the relation between the permeate and retentate flows was around 2:1, avoiding the formation of a preferential pathway for the retentate. The collection and the quantification of the permeate and the retentate extracts were carried out during the process through collection and weighing in Erlenmeyer flasks (10). The concentration of essential oil in the permeate and retentate streams were determined based on the mass of the essential oil collected and on the mass of CO2 during the sampling period, calculated from the mass flux. The retention factor (˛) was calculated as one minus the ratio of the permeate essential oil concentration to the feed stream essential oil concentration. The experiments were performed until the essential oil concentration reached zero. At this time the feed of pure CO2 was interrupted by closing valves V4 and V7 , and maintaining the permeate and retentate fluxes until the system reached atmospheric pressure, with the aim of slowly depressurizing the cell (7). After the experiment, the cells, and also the tubing and valves through which the essential oil passed, were washed with isopropanol and purged with air. 2.4. Analytical procedure
2.3.1. Characterization of the membranes with pure supercritical CO2 During the membrane characterization tests with pure CO2 , the membrane cell (7) was isolated by closing valves V5 and V6 . For the pressurization of the separation unit, valves V6 , V8 and the backpressure regulator (8) were closed, while valve V7 was opened slowly, to promote equal pressurization on the two sides of the membrane at the beginning of the experiments. After the working pressure was established, a transmembrane pressure difference (P) was applied to the membrane by the backpressure regulator (8) on the permeate side. The feed pressure was maintained constant and the P values applied were 0.5, 1.0, 1.5, 2.0 and 2.5 MPa, to guarantee that the CO2 was under pressure conditions above its critical point (7.38 MPa, 31.4 ◦ C) on both sides of the membrane. For each P value applied, the CO2 flux on the permeate side was measured until a stationary flux was reached. The experiments were carried out at different temperatures (32 and 40 ◦ C) for each same membrane sample and using different samples of the same membrane. These temperatures were selected in order to maintain the CO2 in a supercritical state without surpassing the maximum temperature for operation of the commercial membranes (45 ◦ C). The pressure on the permeate side was varied gradually up to 2.5 MPa,
The structure of the membranes was investigated using scanning electron microscopy (Model XL-30, Philips, Netherlands). A cross-section of each membrane was analyzed by fracturing the sample with liquid nitrogen and coating it with a thin-gold film. The composition of the essential oil and the fractions obtained by the fractionation through different membranes was determined by separation and identification of the components in parallel using GC/FID and GC/MS, on a Varian CP-3800 instrument equipped with two split/splitless injectors, two CP-Wax 52CB bonded fused silica polar columns (50 m × 0.25 mm internal diameter, 0.2 m film thickness), a Varian FID-detector and a Varian Saturn 2000 MS iontrap mass spectrometer. The injection temperature was 240 ◦ C with a split rate of 1:50 for FID and 1:200 for MS. The oven temperature was programmed as isothermal at 50 ◦ C for 5 min, then increased from 50 to 200 ◦ C at a rate of 2 ◦ C/min and finally held isothermal for 40 min. The FID detector was maintained at 250 ◦ C. The carrier gas was helium at a flow rate of 1 mL/min, and the sample volume injected was 0.01 l of a solution containing 10% (w/w) of essential oil in ethanol. Due to the lack of standards available, it was not possible to identify all of the components present in the patchouli oil. Thus, the identification of the essential oil components was based
Please cite this article in press as: A. Donelian, et al., Performance of reverse osmosis and nanofiltration membranes in the fractionation and retention of patchouli essential oil, J. Supercrit. Fluids (2015), http://dx.doi.org/10.1016/j.supflu.2015.07.026
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Table 1 Pure CO2 flux (kg h−1 m−2 ) and standard deviation according to the P applied. P (MPa)
0.5 1.0 1.5 2.0 2.5
NF-90
NF
BW-30
Average flux
Standard deviation
Average flux
Standard deviation
Average flux
Standard deviation
43.17 104.23 177.15 247.33 318.99
2.07 2.02 8.34 20.94 40.27
55.53 132.46 239.18 351.17 499.44
4.97 20.23 28.29 12.73 23.79
36.94 73.76 108.62 152.15 205.51
0.75 3.32 1.42 5.35 7.67
on comparison of mass spectra obtained in the gas chromatography with the mass spectra available in the NIST 98 mass spectral library and in the literature [20] and the composition was expressed in percentage values calculated directly from the peak areas of the GC spectra. The alteration in the extract color was evaluated through the analysis of 1% wt. solutions of the extract in ethanol using a Shimadzu UV/VIS spectrophotometer (Model UV-1650PC) between the wavelengths of 190 and 1100 nm. 3. Results and discussion 3.1. Characterization of the membranes with pure supercritical CO2 On analyzing Fig. 2, which shows the pure CO2 flux through the NF-90 membrane as a function of the temperature and the P, it can be verified that during the decompression no hysteresis was observed, indicating the good reversibility of the NF-90 membrane after the compacting. The experiments carried with the other commercial membranes, NF and BW-30, also indicated the non-occurrence of hysteresis during the decompression. In Fig. 2 it can also be evidenced that the temperature has no influence in the permeate flux of CO2 for the NF-90 membrane. This analysis was conducted using different samples of the same membrane for each evaluated temperature. Fig. 3 shows the variation in the flux as a function of P and temperature using the same membrane sample for both temperatures. On analyzing Fig. 3, it can be observed that for all commercial membranes, the temperature, at the values studied (32 and 40 ◦ C), did not affect the flux of pure CO2 . Moreover, on comparing the pure CO2 flux as a function P, it can be noted that, for all membranes, as the P increases the difference between the fluxes also increases, due to the difference in the permeance of the membranes. Thus,
Fig. 2. Dependence of pure CO2 flux on the P applied for the NF-90 membrane during the compression and decompression, at different temperatures.
Table 2 Average permeance of pure CO2 and coefficients of linear regression (R2 ) for each membrane.
Permeance (kg h−1 m−2 MPa−1 ) R2
NF-90
NF
BW-30
138.95 0.999
198.73 0.997
83.11 0.996
since the temperature, at the values studied, did not affect the permeate flux, the subsequent experiments were performed at 32 ◦ C, this being the best temperature for patchouli oil extraction [31]. The reproducibility and the permeability of each membrane were evaluated using the values calculated for the average pure CO2 flux and the standard deviation as a function of P based on the results obtained in the experiments carried out to evaluate the influence of temperature. The average flux and the standard deviations are shown in Table 1. It can be observed in Table 1 that the greatest variability was obtained with the NF membrane, followed by the NF-90 membrane, where the standard deviation increases as the P applied increases. These data were used to construct a graph of the flux of pure CO2 as a function of P (Fig. 4). Fig. 4 indicates a linear variation in the CO2 permeate mass flux with the P applied. This behavior was observed for all membranes except the NF membrane, where a non linearity was observed, probably due to the variation in the results as a consequence of the low reproducibility of this membrane, as well as the discrepancy in the value of the flux obtained at 2.5 MPa, attributable to the low mechanical resistance at this P value. Thus, the membrane permeance was calculated from the slope of lines in Fig. 4, neglecting the value obtained for the flux at 2.5 MPa in the case of the NF membrane. Table 2 shows the values for average permeance of the membranes in terms of pure CO2 .
Fig. 3. Flux of pure CO2 as a function of P and temperature for the same membrane sample (NF-90, NF and BW-30).
Please cite this article in press as: A. Donelian, et al., Performance of reverse osmosis and nanofiltration membranes in the fractionation and retention of patchouli essential oil, J. Supercrit. Fluids (2015), http://dx.doi.org/10.1016/j.supflu.2015.07.026
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Table 3 CO2 density for different pressure and temperature conditions employed (feed pressure: 10 MPa). Temperature (◦ C)
P (MPa)
CO2 density on the feed side (g/mL)
CO2 density on the permeate side (g/mL)
Density difference (g/mL)
32
0.5 1.0 1.5 2.0 2.5
0.750 0.750 0.750 0.750 0.750
0.735 0.717 0.692 0.652 0.377
0.015 0.033 0.058 0.098 0.373
40
0.5 1.0 1.5 2.0 2.5
0.628 0.628 0.628 0.628 0.628
0.578 0.484 0.357 0.278 0.231
0.050 0.144 0.271 0.350 0.397
Fig. 4. Dependence of pure CO2 flux on P applied for the membranes NF-90, NF and BW-30.
From Table 2 it can be noted that the permeance of the membranes in terms of pure CO2 follows the order: BW-30 < NF-90 < NF. Finally, comparing the linear regression coefficients, it can be concluded that the results obtained show an excellent fit, confirming the linear dependence of the permeate flux in relation to P.
3.1.1. Mass transfer mechanisms of the commercial membranes In order to determine the behavior of the pure CO2 permeation through the membrane a graph similar to that in Fig. 4 was constructed for each membrane. The graph was obtained using data on the stationary fluxes, the difference between the CO2 density on the feed side and that on the permeate side for each temperature and the P value applied in the experiments (Table 3). Fig. 5 shows the dependence of the CO2 permeate flux on the difference in the density of the solvent on the two sides of the NF-90 membrane. No relation between the CO2 permeate flux and the density gradient was found, since the behavior of the density gradient changed according to the temperature employed, and the flux was practically constant for the same P. This fact, allied to the linear relation between the flux and the P value and the insensitivity of the flux to the temperatures tested, indicates a predominantly convective behavior during the CO2 permeation through the NF-90 membrane [32], since the P is the driving force for the flux. The same behavior was observed for all of the commercial membranes tested, and indicated that the supercritical CO2 is able to plasticize the membranes. The swelling of the polymer chains facilitates the transport of the solvent, and this may explain the insensitivity of the CO2 flux to the temperature and, consequently, to the CO2 viscosity variations.
Fig. 5. Dependence of pure CO2 flux on the difference between densities on the feed and permeate sides for the NF-90 membrane at the two temperatures tested. Feed pressure: 10 MPa.
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ARTICLE IN PRESS A. Donelian et al. / J. of Supercritical Fluids xxx (2015) xxx–xxx Table 4 Retention index (RI) of the essential oil for different the membranes. Membrane
NF-90
NF
BW-30
RI
0.8472
0.9068
0.9509
Fig. 7. Retention index for patchouli essential oil during the separation process with NF-90, NF and BW-30 membranes.
Fig. 6. Average permeate and retentate fluxes during the fractionation of patchouli essential oil through membranes (a) NF-90, (b) NF and (c) BW-30. Conditions: 10 MPa, 32 ◦ C, P = 1.0 MPa and C0 = 10% wt.
3.2. Retention of patchouli essential oil by membrane separation The experiments on the fractionation and retention of patchouli oil were carried at 10 MPa, 32 ◦ C and with a P value of 1.0 MPa, since these were the best conditions identified during the membrane characterization. This P value was selected on the basis that on analyzing Fig. 4 it was observed that the difference between the fluxes of the membranes at this P was greater than that at a
P value of 0.5 MPa, which allows a better analysis of the distinct behavior of each membrane. Furthermore, at this low P value the need for recompression will be lower. Fig. 6 shows the permeate and retentate fluxes during the separation process using the NF-90, NF and BW-30 membranes. On analyzing the average flux of pure CO2 and the permeate flux during the separation process with the membranes, a lower flux is observed with the presence of the oil, particularly in the first 120 min, becoming closer to the flux of pure CO2 as the concentration of essential oil was reduced. Such a reduction in permeate mass flux in the presence of the essential oil may occur due the phenomenon of polarization at higher concentrations (reversible) or to the phenomenon of fouling (irreversible). In all the membranes the same behavior was observed, and the reduction in permeability in these experiments is attributable to polarization at higher concentrations, since this behavior was reversed with a reduction in the concentration of essential oil in the feed stream. However, using the BW-30 membrane (Fig. 6c) a lower reduction in the flux in the presence of the oil was observed (29.82%) when compared to the NF-90 (Fig. 6a) and NF (Fig. 6b) membranes, (33.78% and 41.67%, respectively). In relation to the retention index, it can be seen in Table 4 that the only retention index of the patchouli essential oil below 0.90 was obtained using the NF-90 membrane, making its application in the oil retention process unviable. This result has also been reported by Sarmento [27] who analyzed the commercial membranes NF-90, NF and BW-30 in the retention process of polyphenols from cocoa extract. On analyzing Fig. 7, a low retention index can be observed using the NF-90 membrane since the oil retention was significant only after the first 30 min. This behavior indicates that the oil retention occurred not only due to the characteristics of the membrane, but probably due to the effect of polarization at higher concentrations, where, due to the increase in the concentration of the solute retained at the surface of the membrane, an increase in the resistance to mass transfer occurred, leading to a reduction in the permeate flux and an increase in the retention index. However, using the NF membrane it was possible to achieve a good retention
Please cite this article in press as: A. Donelian, et al., Performance of reverse osmosis and nanofiltration membranes in the fractionation and retention of patchouli essential oil, J. Supercrit. Fluids (2015), http://dx.doi.org/10.1016/j.supflu.2015.07.026
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Table 5 Compositions of patchouli essential oil, permeate and retentate extracts obtained during the fractionation with the NF-90 membrane. Compounds identified
Peak area of the components (%) Oil
Permeate a
-Patchoulene ␣-Guaiene -Caryophyllene ␣-Patchoulene Seychellene ␥-Patchoulene ␣-Bulnesene Patchoulol
2.016 15.176 3.632 5.211 9.071 1.071 14.188 28.321
P1
– – – – – – – –
Retentate a
P2
– – – – – – – –
a
P3
– – – – – – – –
P4
a
2.794 18.446 4.549 6.003 10.681 1.228 14.675 23.619
– – – – – – – –
R1
R2
R3
R4
2.238 17.107 4.196 5.317 9.389 1.091 14.854 25.202
2.498 18.388 4.453 5.758 10.179 1.183 15.403 22.637
1.999 15.102 3.585 5.332 9.239 1.095 14.521 29.052
R2
R3
R4
2.447 18.428 4.481 5.465 9.735 1.116 15.067 21.627
2.400 18.163 4.333 5.570 9.853 1.137 15.358 22.995
2.022 15.381 3.601 5.375 9.320 1.104 14.690 28.394
R2
R3
R4
2.420 18.029 4.434 5.461 9.700 1.115 15.061 23.238
2.162 16.457 3.862 5.423 9.490 1.109 14.945 26.040
1.896 14.560 3.387 5.325 9.211 1.097 14.526 31.489
P1 and R1 → 0–30 min; P2 and R2 → 30–60 min; P3 and R3 → 60–90 min; P4 and R4 → 90–300 min. a Not possible to analyze chromatographically due to the low quantity of sample collected. Table 6 Compositions of patchouli essential oil, permeate and retentate extracts obtained during the fractionation with the NF membrane. Compounds identified
Peak area of the components (%) Oil
Permeate a
-Patchoulene ␣-Guaiene -Caryophyllene ␣-Patchoulene Seychellene ␥-Patchoulene ␣-Bulnesene Patchoulol
2.016 15.176 3.632 5.211 9.071 1.071 14.188 28.321
P1
– – – – – – – –
Retentate a
P2
– – – – – – – –
a
P3
– – – – – – – –
P4
a
2.380 16.868 4.028 5.672 9.969 1.165 14.449 25.063
– – – – – – – –
R1
P1 and R1 → 0–30 min; P2 and R2 → 30–60 min; P3 and R3 → 60–90 min; P4 and R4 → 90–300 min. a Not possible to analyze chromatographically due to the low quantity of sample collected. Table 7 Compositions of patchouli essential oil, permeate and retentate extracts obtained during the fractionation with the BW-30 membrane. Compounds identified
Peak area of the components (%) Oil
Permeate a
-Patchoulene ␣-Guaiene -Caryophyllene ␣-Patchoulene Seychellene ␥-Patchoulene ␣-Bulnesene Patchoulol
2.016 15.176 3.632 5.211 9.071 1.071 14.188 28.321
P1
– – – – – – – –
Retentate a
P2
– – – – – – – –
a
P3
– – – – – – – –
P4
a
2.809 18.083 4.375 6.318 11.214 1.323 13.937 22.037
– – – – – – – –
R1
P1 and R1 → 0–30 min; P2 and R2 → 30–60 min; P3 and R3 → 60–90 min; P4 and R4 → 90–300 min. a Not possible to analyze chromatographically due to the low quantity of sample collected.
index for the patchouli oil (0.9068), the retention giving significant results from the first 30 min onwards, with a slight drop occurring only at the end of the separation process. This drop in the retention index was accompanied by a sharp increase in the quantity of oil permeated at the end of the process, which may be due to affinity between the polymer of the membrane and the compounds of the oil, promoting diffusion of the oil through the membrane during the fractionation process. Using the BW-30 membrane the best oil retention index (RI) was achieved (0.9509), again with significant retention being observed from the first 30 min onwards and a slight drop at the end of the separation process. However, this reduction in the retention index at the end of separation process was lower for the BW-30 membrane (9.0%) when compared with the NF membrane (12%). In relation to selectivity, on comparing the concentrations of the compounds in Tables 5–7, it can be verified that no membrane
had the capacity to totally separate compounds from the oil. However, using the NF and BW-30 membranes, which showed greater retention indexes, an increase in the concentration of patchoulol present in the retentate stream was verified over time. This may have occurred due to the kinetics of the separation process, since patchoulol is a polar compound, as well as the lack of affinity with the solvent meaning that a longer time is required for the compound to be solubilized and carried by the CO2 . Donelian [31] also observed, during the extraction of patchouli oil with scCO2 , that patchoulol was extracted in greater quantity at the end of the process. However, due to the higher retention index, the use of the BW-30 membrane promoted an increase of approximately 11% in the concentration of patchoulol present in the retentate R4 (obtained between 90 and 300 min) in relation to the concentration in the essential oil.
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Fig. 8. Photographs of the surface of the NF-90 membrane: (a) new sample; (b) sample after characterization with pure CO2 ; and (c) sample after the separation process with patchouli essential oil.
Fig. 9. Photographs of the surface of the nf membrane: (a) new sample; (b) sample after characterization with pure CO2 ; and (c) sample after the separation process with patchouli essential oil.
Fig. 10. Photographs of the surface of the BW-30 membrane: (a) new sample; (b) sample after characterization with pure CO2 ; and (c) sample after the separation process with patchouli essential oil.
Fig. 11. Photograph of cross section of each membrane.
3.3. Morphologic and structural analysis of the membranes Fig. 8 shows the photographs of the surface of the NF-90 membrane before and after the characterization with pure CO2 and retention tests.
In photographs (b) and (c), from Fig. 8, deformations can be observed on the surface of the membrane, caused by the perforated metal used to support the membrane during the separation process. Despite these deformations, the support did not damage the structure of the NF-90 membrane. Also, in the case of the new sample (a)
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Fig. 12. CO2 flux before and after the presence of the patchouli essential oil for each membrane evaluated.
it can be observed that the surface is not homogeneous, showing some scratches and marks, which explains the low reproducibility of the results. The photographs in Fig. 9 show that the surface profile of the NF membrane has the same characteristics as the NF-90 membrane. In Fig. 10 the photographs of the BW-30 membrane show that the surface of the new sample (a) was smoother and more homogeneous when compared to the surfaces of the NF-90 and NF membranes, which allows a higher reproducibility of results for this membrane. The photographs in Fig. 11 show the cross section of a new sample of each membrane and a thin layer of polyamide can be observed on the surface of the NF-90 membrane, responsible for the selectivity of the membrane, followed by a thicker layer which acts as a support, maintaining the structure of the membrane. For the NF membrane, the structure is the same as that of the NF90 membrane, but the thin layer on the surface, responsible for the selectivity, is comprised of the polymer polypiperazine amide instead of polyamide. Finally, for the BW-30 membrane the layer of polyamide on the surface is not as well defined as in the case of the nanofiltration membranes. However, the large apertures observed on the support facilitate the permeate flux, leading to less resistance. 3.4. Comparison between membranes The results presented in Table 4 and Fig. 12 show that although the permeate fluxes of the NF and BW-30 membranes in the presence of the oil were similar, the retention index obtained with the NF membrane was significantly lower when compared with the BW-30 membrane. Also, a lower reduction in the permeate flux of CO2 in the presence of the oil (29.82%) was obtained with the BW-30 membrane, maintaining a good permeate flux (53.03 kg h−1 m−2 ) and higher retention index (0.9509) in the separation process of the patchouli oil. Thus, the use of the BW-30 membrane promoted the best combination between retention index and permeate flux in the presence of the oil, allowing its use in the regeneration of CO2 with a minimal fall in pressure (1.0 MPa), aiming at the solvent recirculation in the supercritical extraction of patchouli essential oil. Another advantage of the separation process using membranes was a visible reduction in the greenish yellow color of the patchouli essential oil both in the permeate and retentate extracts for the
9
Fig. 13. Spectra for the solutions of 1.0% wt. of patchouli essential oil, permeate P4 , retentate R2 , retentate R3 and retentate R4 obtained using the BW-30 membrane. (For interpretation of the references to color in the text, the reader is referred to the web version of this article.)
process using the BW-30 membrane. In Fig. 13 the spectra for the patchouli essential oil, permeate and retentate extracts obtained using the BW-30 membrane are presented. In the oil spectrum the presence of peaks between the wavelengths of 400 and 500 nm was verified, which correspond to the blue region, and the wavelength of 675 nm (red region). However, between the wavelengths of 500 and 590 nm (green and yellow regions) the light absorption is almost zero and these bands are thus reflected leading to the greenish yellow color of the patchouli oil. On analyzing Fig. 13, it can be noted that the extracts are colorless since they do not show absorbance in the visible wavelength (above 400 nm). As the permeate and retentate showed the same change in the coloration, the dye was probably retained by the membrane. This color reduction was observed for all membranes, being the absorption of the dye by the amide group in the membranes the most likely explanation. This modification in the color of the oil is of great importance in the perfumery industry, since a yellow color can cause marks on clothes and hinder the development of perfumes with other colors.
4. Conclusions This study showed that besides promoting the retention of the patchouli essential oil (RI = 0.9509) with a good permeate flow, the use of the BW-30 membrane also allows the color of the oil to be retained, eliminating its greenish yellow coloration. In relation to the selective capacity, the use of the membranes did not promote the total separation of any component or the concentration of ␣bulnesene, and only in the process with the BW-30 membrane a significant increase in the patchoulol concentration occurred (11% in the retentate) in relation to the patchouli oil, mainly due to the process kinetics. Other aspects, such as an evaluation of the growing conditions of patchouli and the yield of essential oil should also be considered in future researches. Additionally, with the knowledge acquired from the process, as well as of the essential oil composition, it is possible to explore the development of specific membranes to enhance the separation process.
Acknowledgements The authors wish to thank CAPES (Brazil) and GRICES (Portugal) for their financial support to this study.
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Performance of reverse osmosis and nanofiltration membranes in the fractionation and retention of patchouli essential oil Adriana Donelian a , Patrícia F. de Oliveira a , Alírio E. Rodrigues b , Vera G. Mata b , Ricardo A.F. Machado a,∗ a Laboratório de Controle e Processos de Polimerizac¸ão, Departamento de Engenharia Química e Engenharia de Alimentos, Universidade Federal de Santa Catarina (UFSC), Campus Universitário, Trindade, P.O. Box: 476, Zip Code: 88010-970 Florianópolis, SC, Brazil b Laboratory of Separation and Reaction Engineering (LSRE), Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, Zip Code: 4200-465, Porto, Portugal
a r t i c l e
i n f o
Article history: Received 23 April 2015 Received in revised form 22 July 2015 Accepted 22 July 2015 Available online xxx Keywords: Patchouli Essential oil Membrane Supercritical carbon dioxide
a b s t r a c t Patchouli essential oil consists of over 24 different components. Patchoulol has been known for over a century as the most important component of this essential oil, being widely used in the perfumery and cosmetics industries. Recent research has demonstrated that another component of patchouli essential oil, ␣-bulnesene, has pharmaceutical properties, providing a decrease in thromboxane formation. In this study, three different membranes were evaluated in terms of their fractionation capability and retention of patchouli oil in supercritical media, aiming at the separation and concentration of the main oil components (patchoulol and ␣-bulnesene) and regeneration of CO2 . The membranes tested showed good resistance under the experimental conditions used, but did not show good fractionation and concentration of the patchouli oil components. The reverse osmosis membrane gave the highest oil retention (0.95) and lowest reduction in the permeate flux of the CO2 in the presence of the essential oil. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Patchouli oil is one of the important natural essential oils for the production of perfume and in medical applications [1–3]. It is obtained from the leaves of Pogostemon cablin (patchouli), a plant like many from the Lamiaceae family that accumulates large amounts of essential oil [4]. At present, patchouli oil is used in many fine fragrance products to provide a base and give lasting character, being one of the most valuable natural materials for the perfumery and cosmetic industries [4–6]. It is also listed as an approved substance for food flavoring by the FDA (Food and Drug Administration, USA) [7]. Patchouli oil contains bioactive compounds, which confer the plant anti-allergic and anti-bacterial activities on skin, as well as anti-oxidative and anti-inflammatory effects [8–12]. The color of patchouli essential oil is due mainly to the presence of substances commonly responsible for the color of oils of plant origin. These include chlorophyll (green) and the carotenoids (yellow and red).
∗ Corresponding author. E-mail address: [email protected] (R.A.F. Machado).
The composition of patchouli oil is distinct, consisting of over 24 different sesquiterpenes, in which patchoulol is the major constituent and, due to its fixative characteristic, it regulates the oil aroma [3,4]. Also, ␣-bulnesene is an important compound present in the oil which, in recent research, showed a potent inhibitory effect on platelet aggregation, reducing the risk of cardiovascular diseases [13]. Traditionally, patchouli oil is obtained by steam distillation from P. cablin leaves. This procedure, performed at a high temperature, can cause the degradation of thermally labile compounds [13,14]. However, recent researches carried out by Donelian et al. [15] have demonstrated that extraction with supercritical CO2 at 14 MPa and 40 ◦ C provided a yield of 5.07%, while steam distillation yielded 1.50%. In relation to the quality of essential oil, represented mainly by the concentration of patchoulol, the supercritical extraction yielded 31.39% of patchoulol in the oil, while steam distillation obtained only 19.4% yield. The use of supercritical CO2 for separation has been described in numerous publications [16,17]. However, this approach requires a considerable amount of energy to recycle the solvent to its original thermodynamic state for further processing. To avoid this, some researchers have studied the association of membrane separation with supercritical fluid extraction process with the aim of retaining the essential oil and regenerating the fluid, reducing compression
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costs [18–21], and also, when possible, of fractionating some components of the natural products in order to obtain a concentrated fraction of the main oil component. In order to isolate major compounds of patchouli oil, reports in published researches stand for the use of the host–guest inclusion method, using a host molecule to selectively recognize the guest molecule patchoulol, and of distillation combined with crystallization to isolate patchouli alcohol from patchouli oil [22,23]. For both of them the authors reported good separation results, recovering up to 40% of the patchouli alcohol. Su et al. [24] evaluated fractional distillation combined with crystallization as a method for the isolation of patchouli alcohol from patchouli oil, obtaining up to 52.9% of this compound. Zhang et al. [25] used high performance centrifugal partition chromatography (HPLCPC) in a preparative scale to separate patchouli alcohol, using a two-phase solvent system. The purity achieved was more than 98%, but it has the disadvantage of requiring the use of organic solvents. Sarmento et al. [18] evaluated the performance of three commercial reverse osmosis membranes: CG, AG and SG (Osmonics) in relation to the retention of lemongrass, orange and nutmeg essential oils at 12 MPa and 40 ◦ C. The oil retention was studied as a function of the transmembrane pressure difference (P) at values between 1.0 and 4.0 MPa and of the feed oil concentration (from 5 to 15% wt). The results demonstrated that the oil retention index was reduced with an increase in P, and significant variations according to the feed oil concentration were not observed. The best results were obtained with the SG membrane and a P value of 1.0 MPa, obtaining a retention index of up to 0.90 for all the essential oils tested, although these conditions gave the lowest CO2 permeate fluxes, indicating the occurrence of fouling. On analyzing the separation process with membranes for the regeneration of CO2 , using d-limonene as the solute, Carlson et al. [19] also found that the SG membrane, made of polyamide, gave the highest retention index, above 0.80 for an experimental period of 3 h. However, after the first 120 min, the permeate flux fell to zero, demonstrating that the high retention index was followed by an irreversible clogging of the membrane. However, it was verified that on alternating the feeding between CO2 + d-limoneno and pure CO2 , it was possible to achieve a retention index of over 0.94, but with low fluxes of CO2 . Hsu and Tan [26] used a reverse osmosis membrane made of polyamine (FilmTec FT-30) to remove ethanol from a mixture with water. Using scCO2 under pressure and temperature conditions slightly above the critical values the authors verified that the retention index of ethanol increased from 0.20 to 0.70, due to the formation of clusters of ethanol and CO2 . Sarmento [27] analyzed the behavior of different models of commercial nanofiltration and reverse osmosis membranes in relation to the retention and fractionation of polyphenol extracted from cocoa extract under supercritical conditions. The experiments were carried out at 12 MPa and 40 ◦ C, and the results showed that the nanofiltration membrane models DL, HL and NF gave the highest permeabilities with a retention index for polyphenol of over 0.90 when a P value of 1.0 MPa was applied. In relation to the fractionation of polyphenol, only the HL membrane showed a separation capacity, promoting a fraction in the permeate with no oligomers in the range between heptamers and decamers. Two nanofiltration membranes, TN and T, were investigated by Sarrade et al. [28] in the fractionation of triglycerides originated from fish oil and the purification of -carotene from either carrot oils or carrot seeds. The experiments were carried out at 31 MPa, 40 ◦ C and with a P value of 3 MPa, and the results showed that the TN membrane allowed a significant concentration of important triglycerides with a high molar mass (over 52 carbons) in the retentate and short-chain fatty acids in the permeate. In relation
to the purification of -carotene, the T membrane allowed a 2.4fold increase in the concentration of the pigment in the permeate stream. Therefore, the objective of this study was to evaluate the performance of three different commercial membranes in the separation of patchouli essential oil using supercritical CO2 , in order to promote the regeneration and recirculation of CO2 with a lower minimum pressure during the supercritical extraction, reducing the energy requirement for the solvent recompression [27]. The membranes were also assessed in relation to their capacity for the fractionation of patchouli oil, aiming at the separation and concentration of patchoulol with fixative properties, and ␣-bulnesene with pharmacological properties. 2. Experimental 2.1. Patchouli essential oil and membranes Patchouli essential oil was obtained by extraction with scCO2 at 10 MPa and 32 ◦ C. The pressure and temperature chosen were the best conditions identified by Donelian [29] under which to perform the patchouli essential oil extraction with scCO2 . For the extraction, patchouli leaves were collected from “Colônia Penal Agrícola” (Palhoc¸a, SC, Brazil). The extraction procedure is described in Donelian et al. [15]. Three different kinds of commercial membrane supplied by Dow Filmtec (USA) were studied. The membranes are described below: – Commercial membranes (maximum operation temperature: 45 ◦ C): • Nanofiltration membrane – model NF-90 – Thin polyamide film. • Nanofiltration membrane – model NF – Thin polypiperazine amide film. • Reverse osmosis membrane – model BW-30 – Thin polyamide film. 2.2. Equipment In this study, a membrane unit was designed and built from a supercritical extraction unit developed at the Laboratory of Separation and Reaction Engineering (LSRE). The equipment is schematically represented in Fig. 1. The experimental unit was constructed in stainless steel and designed to work up to 20 MPa. However, there is a security valve (VS ) regulated to lead the CO2 stream to the purge line if the pressure exceeds 19 MPa. The cylinder (1) supplies liquid CO2 (99.8% purity, Praxair, Portugal) to the surge tank (5). The pressurization of the system was accomplished through a high pressure pump (3) (Model MCPV 71, Haskel, USA) and the CO2 stream was cooled before entering the pump (3) in order to prevent cavitation inside the pump. The separation unit comprised two cells (6 and 7) constructed of stainless steel with a unit volume of 30 cm3 and arranged in series. The membrane to be tested was positioned in one cell (7), while the other cell (6) contained patchouli essential oil. The essential oil was placed together with glass beads to provide resistance in order to avoid a large quantity of oil from moving directly to the surface of the membrane. The membrane was placed over a perforated metal support, and the cells were sealed with poly(tetrafluorethylene) rings. The filtration area of the membrane was 3.14 cm2 and a cross flow regime was used during the experiments. The feed pressure in the cell was controlled through a downstream control valve (VR) (Model APR66, Veriflo, Parker Hannifin Corporation, USA) which allowed the pressure in the surge tank
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in order to verify the reversibility of the conditions and the occurrence of hysteresis.
Fig. 1. Experimental unit of supercritical process coupled with a membrane unit. (1) CO2 cylinder; (2) Cool Bath; (3) Pump; (4) Oven; (5) Surge tank; (6) Membrane Cell; (7) Essential oil Cell; (8) Backpressure regulator; (9) Thermostatic water bath; (10) Erlenmeyer flask; (11) Bubble flow meter; (M0 , M1 , M2 ) Manometer; (P1 ) (P2 ) Pressure transducers; (VM ) Micrometer valve; (VS ) Security valve; (VR ) Downstream control valve; (V0 , V1 , V2 , V3 , V4 , V5 ) On-off valves; (V6 , V7 , V8 ) Needle valves.
(5) to be reduced to the level required in the separation unit. The pressure at the exit of the valve VR was monitored through a pressure transducer (P1 ). The pressure on the permeate side of the membrane was controlled by a backpressure regulator (8) (Model 26-1762-24, Tescom, USA) and monitored by a pressure transducer (P2 ) (Model ECO-1, Wika, Germany). The temperature was maintained by a thermostatic water bath (9). During the fractionation experiments, the retentate CO2 flow was controlled manually through a micrometer valve (VM ) and was measured at the exit of the collector by a bubble flow meter (11) under room conditions. The extracts were collected separately in the retentate and permeate sides, at atmospheric pressure, in Erlenmeyer flasks (10) immersed in a cooling bath of ice and salt to minimize the loss of volatile fraction of the extract carried away with CO2 gas stream. 2.3. Membrane process procedure The working pressure of 10 MPa was chosen based on the best pressure conditions under which to obtain patchouli essential oil by supercritical extraction.
2.3.2. Patchouli essential oil fractionation and retention tests The temperature and P of the retention tests were chosen based on the results obtained during the characterization of the membrane with pure CO2 in order to minimize deviations from the optimum extraction conditions and the need to recompress CO2 . The cell (6) was loaded with patchouli essential oil to give an initial feed concentration of 10% wt. in relation to the CO2 that occupied the two cells at 10 MPa and 32 ◦ C. This concentration was set within the concentrations used for studies on the performance of membranes in the separation of scCO2 and essential oils [18,30]. Initially, the membrane used in the retention tests was characterized with pure CO2 at a P value of 1 MPa. The backpressure regulator (8) and the valve V7 were then closed, and the cell (6) contained the oil was pressurized by opening valves V4 and V5 , maintaining valve V6 closed. Once the working pressure was established in the cell (6), valve V6 was opened, placing the solubilized CO2 with the essential oil in contact with the membrane in the cell (7) and applying a P of 1 MPa via the backpressure regulator (8). At this moment, the fractionation and retention tests began. The retentate flux was maintained constant via valve V8 and the micrometer valve (VM ) in such a way that the relation between the permeate and retentate flows was around 2:1, avoiding the formation of a preferential pathway for the retentate. The collection and the quantification of the permeate and the retentate extracts were carried out during the process through collection and weighing in Erlenmeyer flasks (10). The concentration of essential oil in the permeate and retentate streams were determined based on the mass of the essential oil collected and on the mass of CO2 during the sampling period, calculated from the mass flux. The retention factor (˛) was calculated as one minus the ratio of the permeate essential oil concentration to the feed stream essential oil concentration. The experiments were performed until the essential oil concentration reached zero. At this time the feed of pure CO2 was interrupted by closing valves V4 and V7 , and maintaining the permeate and retentate fluxes until the system reached atmospheric pressure, with the aim of slowly depressurizing the cell (7). After the experiment, the cells, and also the tubing and valves through which the essential oil passed, were washed with isopropanol and purged with air. 2.4. Analytical procedure
2.3.1. Characterization of the membranes with pure supercritical CO2 During the membrane characterization tests with pure CO2 , the membrane cell (7) was isolated by closing valves V5 and V6 . For the pressurization of the separation unit, valves V6 , V8 and the backpressure regulator (8) were closed, while valve V7 was opened slowly, to promote equal pressurization on the two sides of the membrane at the beginning of the experiments. After the working pressure was established, a transmembrane pressure difference (P) was applied to the membrane by the backpressure regulator (8) on the permeate side. The feed pressure was maintained constant and the P values applied were 0.5, 1.0, 1.5, 2.0 and 2.5 MPa, to guarantee that the CO2 was under pressure conditions above its critical point (7.38 MPa, 31.4 ◦ C) on both sides of the membrane. For each P value applied, the CO2 flux on the permeate side was measured until a stationary flux was reached. The experiments were carried out at different temperatures (32 and 40 ◦ C) for each same membrane sample and using different samples of the same membrane. These temperatures were selected in order to maintain the CO2 in a supercritical state without surpassing the maximum temperature for operation of the commercial membranes (45 ◦ C). The pressure on the permeate side was varied gradually up to 2.5 MPa,
The structure of the membranes was investigated using scanning electron microscopy (Model XL-30, Philips, Netherlands). A cross-section of each membrane was analyzed by fracturing the sample with liquid nitrogen and coating it with a thin-gold film. The composition of the essential oil and the fractions obtained by the fractionation through different membranes was determined by separation and identification of the components in parallel using GC/FID and GC/MS, on a Varian CP-3800 instrument equipped with two split/splitless injectors, two CP-Wax 52CB bonded fused silica polar columns (50 m × 0.25 mm internal diameter, 0.2 m film thickness), a Varian FID-detector and a Varian Saturn 2000 MS iontrap mass spectrometer. The injection temperature was 240 ◦ C with a split rate of 1:50 for FID and 1:200 for MS. The oven temperature was programmed as isothermal at 50 ◦ C for 5 min, then increased from 50 to 200 ◦ C at a rate of 2 ◦ C/min and finally held isothermal for 40 min. The FID detector was maintained at 250 ◦ C. The carrier gas was helium at a flow rate of 1 mL/min, and the sample volume injected was 0.01 l of a solution containing 10% (w/w) of essential oil in ethanol. Due to the lack of standards available, it was not possible to identify all of the components present in the patchouli oil. Thus, the identification of the essential oil components was based
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Table 1 Pure CO2 flux (kg h−1 m−2 ) and standard deviation according to the P applied. P (MPa)
0.5 1.0 1.5 2.0 2.5
NF-90
NF
BW-30
Average flux
Standard deviation
Average flux
Standard deviation
Average flux
Standard deviation
43.17 104.23 177.15 247.33 318.99
2.07 2.02 8.34 20.94 40.27
55.53 132.46 239.18 351.17 499.44
4.97 20.23 28.29 12.73 23.79
36.94 73.76 108.62 152.15 205.51
0.75 3.32 1.42 5.35 7.67
on comparison of mass spectra obtained in the gas chromatography with the mass spectra available in the NIST 98 mass spectral library and in the literature [20] and the composition was expressed in percentage values calculated directly from the peak areas of the GC spectra. The alteration in the extract color was evaluated through the analysis of 1% wt. solutions of the extract in ethanol using a Shimadzu UV/VIS spectrophotometer (Model UV-1650PC) between the wavelengths of 190 and 1100 nm. 3. Results and discussion 3.1. Characterization of the membranes with pure supercritical CO2 On analyzing Fig. 2, which shows the pure CO2 flux through the NF-90 membrane as a function of the temperature and the P, it can be verified that during the decompression no hysteresis was observed, indicating the good reversibility of the NF-90 membrane after the compacting. The experiments carried with the other commercial membranes, NF and BW-30, also indicated the non-occurrence of hysteresis during the decompression. In Fig. 2 it can also be evidenced that the temperature has no influence in the permeate flux of CO2 for the NF-90 membrane. This analysis was conducted using different samples of the same membrane for each evaluated temperature. Fig. 3 shows the variation in the flux as a function of P and temperature using the same membrane sample for both temperatures. On analyzing Fig. 3, it can be observed that for all commercial membranes, the temperature, at the values studied (32 and 40 ◦ C), did not affect the flux of pure CO2 . Moreover, on comparing the pure CO2 flux as a function P, it can be noted that, for all membranes, as the P increases the difference between the fluxes also increases, due to the difference in the permeance of the membranes. Thus,
Fig. 2. Dependence of pure CO2 flux on the P applied for the NF-90 membrane during the compression and decompression, at different temperatures.
Table 2 Average permeance of pure CO2 and coefficients of linear regression (R2 ) for each membrane.
Permeance (kg h−1 m−2 MPa−1 ) R2
NF-90
NF
BW-30
138.95 0.999
198.73 0.997
83.11 0.996
since the temperature, at the values studied, did not affect the permeate flux, the subsequent experiments were performed at 32 ◦ C, this being the best temperature for patchouli oil extraction [31]. The reproducibility and the permeability of each membrane were evaluated using the values calculated for the average pure CO2 flux and the standard deviation as a function of P based on the results obtained in the experiments carried out to evaluate the influence of temperature. The average flux and the standard deviations are shown in Table 1. It can be observed in Table 1 that the greatest variability was obtained with the NF membrane, followed by the NF-90 membrane, where the standard deviation increases as the P applied increases. These data were used to construct a graph of the flux of pure CO2 as a function of P (Fig. 4). Fig. 4 indicates a linear variation in the CO2 permeate mass flux with the P applied. This behavior was observed for all membranes except the NF membrane, where a non linearity was observed, probably due to the variation in the results as a consequence of the low reproducibility of this membrane, as well as the discrepancy in the value of the flux obtained at 2.5 MPa, attributable to the low mechanical resistance at this P value. Thus, the membrane permeance was calculated from the slope of lines in Fig. 4, neglecting the value obtained for the flux at 2.5 MPa in the case of the NF membrane. Table 2 shows the values for average permeance of the membranes in terms of pure CO2 .
Fig. 3. Flux of pure CO2 as a function of P and temperature for the same membrane sample (NF-90, NF and BW-30).
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Table 3 CO2 density for different pressure and temperature conditions employed (feed pressure: 10 MPa). Temperature (◦ C)
P (MPa)
CO2 density on the feed side (g/mL)
CO2 density on the permeate side (g/mL)
Density difference (g/mL)
32
0.5 1.0 1.5 2.0 2.5
0.750 0.750 0.750 0.750 0.750
0.735 0.717 0.692 0.652 0.377
0.015 0.033 0.058 0.098 0.373
40
0.5 1.0 1.5 2.0 2.5
0.628 0.628 0.628 0.628 0.628
0.578 0.484 0.357 0.278 0.231
0.050 0.144 0.271 0.350 0.397
Fig. 4. Dependence of pure CO2 flux on P applied for the membranes NF-90, NF and BW-30.
From Table 2 it can be noted that the permeance of the membranes in terms of pure CO2 follows the order: BW-30 < NF-90 < NF. Finally, comparing the linear regression coefficients, it can be concluded that the results obtained show an excellent fit, confirming the linear dependence of the permeate flux in relation to P.
3.1.1. Mass transfer mechanisms of the commercial membranes In order to determine the behavior of the pure CO2 permeation through the membrane a graph similar to that in Fig. 4 was constructed for each membrane. The graph was obtained using data on the stationary fluxes, the difference between the CO2 density on the feed side and that on the permeate side for each temperature and the P value applied in the experiments (Table 3). Fig. 5 shows the dependence of the CO2 permeate flux on the difference in the density of the solvent on the two sides of the NF-90 membrane. No relation between the CO2 permeate flux and the density gradient was found, since the behavior of the density gradient changed according to the temperature employed, and the flux was practically constant for the same P. This fact, allied to the linear relation between the flux and the P value and the insensitivity of the flux to the temperatures tested, indicates a predominantly convective behavior during the CO2 permeation through the NF-90 membrane [32], since the P is the driving force for the flux. The same behavior was observed for all of the commercial membranes tested, and indicated that the supercritical CO2 is able to plasticize the membranes. The swelling of the polymer chains facilitates the transport of the solvent, and this may explain the insensitivity of the CO2 flux to the temperature and, consequently, to the CO2 viscosity variations.
Fig. 5. Dependence of pure CO2 flux on the difference between densities on the feed and permeate sides for the NF-90 membrane at the two temperatures tested. Feed pressure: 10 MPa.
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NF-90
NF
BW-30
RI
0.8472
0.9068
0.9509
Fig. 7. Retention index for patchouli essential oil during the separation process with NF-90, NF and BW-30 membranes.
Fig. 6. Average permeate and retentate fluxes during the fractionation of patchouli essential oil through membranes (a) NF-90, (b) NF and (c) BW-30. Conditions: 10 MPa, 32 ◦ C, P = 1.0 MPa and C0 = 10% wt.
3.2. Retention of patchouli essential oil by membrane separation The experiments on the fractionation and retention of patchouli oil were carried at 10 MPa, 32 ◦ C and with a P value of 1.0 MPa, since these were the best conditions identified during the membrane characterization. This P value was selected on the basis that on analyzing Fig. 4 it was observed that the difference between the fluxes of the membranes at this P was greater than that at a
P value of 0.5 MPa, which allows a better analysis of the distinct behavior of each membrane. Furthermore, at this low P value the need for recompression will be lower. Fig. 6 shows the permeate and retentate fluxes during the separation process using the NF-90, NF and BW-30 membranes. On analyzing the average flux of pure CO2 and the permeate flux during the separation process with the membranes, a lower flux is observed with the presence of the oil, particularly in the first 120 min, becoming closer to the flux of pure CO2 as the concentration of essential oil was reduced. Such a reduction in permeate mass flux in the presence of the essential oil may occur due the phenomenon of polarization at higher concentrations (reversible) or to the phenomenon of fouling (irreversible). In all the membranes the same behavior was observed, and the reduction in permeability in these experiments is attributable to polarization at higher concentrations, since this behavior was reversed with a reduction in the concentration of essential oil in the feed stream. However, using the BW-30 membrane (Fig. 6c) a lower reduction in the flux in the presence of the oil was observed (29.82%) when compared to the NF-90 (Fig. 6a) and NF (Fig. 6b) membranes, (33.78% and 41.67%, respectively). In relation to the retention index, it can be seen in Table 4 that the only retention index of the patchouli essential oil below 0.90 was obtained using the NF-90 membrane, making its application in the oil retention process unviable. This result has also been reported by Sarmento [27] who analyzed the commercial membranes NF-90, NF and BW-30 in the retention process of polyphenols from cocoa extract. On analyzing Fig. 7, a low retention index can be observed using the NF-90 membrane since the oil retention was significant only after the first 30 min. This behavior indicates that the oil retention occurred not only due to the characteristics of the membrane, but probably due to the effect of polarization at higher concentrations, where, due to the increase in the concentration of the solute retained at the surface of the membrane, an increase in the resistance to mass transfer occurred, leading to a reduction in the permeate flux and an increase in the retention index. However, using the NF membrane it was possible to achieve a good retention
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Table 5 Compositions of patchouli essential oil, permeate and retentate extracts obtained during the fractionation with the NF-90 membrane. Compounds identified
Peak area of the components (%) Oil
Permeate a
-Patchoulene ␣-Guaiene -Caryophyllene ␣-Patchoulene Seychellene ␥-Patchoulene ␣-Bulnesene Patchoulol
2.016 15.176 3.632 5.211 9.071 1.071 14.188 28.321
P1
– – – – – – – –
Retentate a
P2
– – – – – – – –
a
P3
– – – – – – – –
P4
a
2.794 18.446 4.549 6.003 10.681 1.228 14.675 23.619
– – – – – – – –
R1
R2
R3
R4
2.238 17.107 4.196 5.317 9.389 1.091 14.854 25.202
2.498 18.388 4.453 5.758 10.179 1.183 15.403 22.637
1.999 15.102 3.585 5.332 9.239 1.095 14.521 29.052
R2
R3
R4
2.447 18.428 4.481 5.465 9.735 1.116 15.067 21.627
2.400 18.163 4.333 5.570 9.853 1.137 15.358 22.995
2.022 15.381 3.601 5.375 9.320 1.104 14.690 28.394
R2
R3
R4
2.420 18.029 4.434 5.461 9.700 1.115 15.061 23.238
2.162 16.457 3.862 5.423 9.490 1.109 14.945 26.040
1.896 14.560 3.387 5.325 9.211 1.097 14.526 31.489
P1 and R1 → 0–30 min; P2 and R2 → 30–60 min; P3 and R3 → 60–90 min; P4 and R4 → 90–300 min. a Not possible to analyze chromatographically due to the low quantity of sample collected. Table 6 Compositions of patchouli essential oil, permeate and retentate extracts obtained during the fractionation with the NF membrane. Compounds identified
Peak area of the components (%) Oil
Permeate a
-Patchoulene ␣-Guaiene -Caryophyllene ␣-Patchoulene Seychellene ␥-Patchoulene ␣-Bulnesene Patchoulol
2.016 15.176 3.632 5.211 9.071 1.071 14.188 28.321
P1
– – – – – – – –
Retentate a
P2
– – – – – – – –
a
P3
– – – – – – – –
P4
a
2.380 16.868 4.028 5.672 9.969 1.165 14.449 25.063
– – – – – – – –
R1
P1 and R1 → 0–30 min; P2 and R2 → 30–60 min; P3 and R3 → 60–90 min; P4 and R4 → 90–300 min. a Not possible to analyze chromatographically due to the low quantity of sample collected. Table 7 Compositions of patchouli essential oil, permeate and retentate extracts obtained during the fractionation with the BW-30 membrane. Compounds identified
Peak area of the components (%) Oil
Permeate a
-Patchoulene ␣-Guaiene -Caryophyllene ␣-Patchoulene Seychellene ␥-Patchoulene ␣-Bulnesene Patchoulol
2.016 15.176 3.632 5.211 9.071 1.071 14.188 28.321
P1
– – – – – – – –
Retentate a
P2
– – – – – – – –
a
P3
– – – – – – – –
P4
a
2.809 18.083 4.375 6.318 11.214 1.323 13.937 22.037
– – – – – – – –
R1
P1 and R1 → 0–30 min; P2 and R2 → 30–60 min; P3 and R3 → 60–90 min; P4 and R4 → 90–300 min. a Not possible to analyze chromatographically due to the low quantity of sample collected.
index for the patchouli oil (0.9068), the retention giving significant results from the first 30 min onwards, with a slight drop occurring only at the end of the separation process. This drop in the retention index was accompanied by a sharp increase in the quantity of oil permeated at the end of the process, which may be due to affinity between the polymer of the membrane and the compounds of the oil, promoting diffusion of the oil through the membrane during the fractionation process. Using the BW-30 membrane the best oil retention index (RI) was achieved (0.9509), again with significant retention being observed from the first 30 min onwards and a slight drop at the end of the separation process. However, this reduction in the retention index at the end of separation process was lower for the BW-30 membrane (9.0%) when compared with the NF membrane (12%). In relation to selectivity, on comparing the concentrations of the compounds in Tables 5–7, it can be verified that no membrane
had the capacity to totally separate compounds from the oil. However, using the NF and BW-30 membranes, which showed greater retention indexes, an increase in the concentration of patchoulol present in the retentate stream was verified over time. This may have occurred due to the kinetics of the separation process, since patchoulol is a polar compound, as well as the lack of affinity with the solvent meaning that a longer time is required for the compound to be solubilized and carried by the CO2 . Donelian [31] also observed, during the extraction of patchouli oil with scCO2 , that patchoulol was extracted in greater quantity at the end of the process. However, due to the higher retention index, the use of the BW-30 membrane promoted an increase of approximately 11% in the concentration of patchoulol present in the retentate R4 (obtained between 90 and 300 min) in relation to the concentration in the essential oil.
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Fig. 8. Photographs of the surface of the NF-90 membrane: (a) new sample; (b) sample after characterization with pure CO2 ; and (c) sample after the separation process with patchouli essential oil.
Fig. 9. Photographs of the surface of the nf membrane: (a) new sample; (b) sample after characterization with pure CO2 ; and (c) sample after the separation process with patchouli essential oil.
Fig. 10. Photographs of the surface of the BW-30 membrane: (a) new sample; (b) sample after characterization with pure CO2 ; and (c) sample after the separation process with patchouli essential oil.
Fig. 11. Photograph of cross section of each membrane.
3.3. Morphologic and structural analysis of the membranes Fig. 8 shows the photographs of the surface of the NF-90 membrane before and after the characterization with pure CO2 and retention tests.
In photographs (b) and (c), from Fig. 8, deformations can be observed on the surface of the membrane, caused by the perforated metal used to support the membrane during the separation process. Despite these deformations, the support did not damage the structure of the NF-90 membrane. Also, in the case of the new sample (a)
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Fig. 12. CO2 flux before and after the presence of the patchouli essential oil for each membrane evaluated.
it can be observed that the surface is not homogeneous, showing some scratches and marks, which explains the low reproducibility of the results. The photographs in Fig. 9 show that the surface profile of the NF membrane has the same characteristics as the NF-90 membrane. In Fig. 10 the photographs of the BW-30 membrane show that the surface of the new sample (a) was smoother and more homogeneous when compared to the surfaces of the NF-90 and NF membranes, which allows a higher reproducibility of results for this membrane. The photographs in Fig. 11 show the cross section of a new sample of each membrane and a thin layer of polyamide can be observed on the surface of the NF-90 membrane, responsible for the selectivity of the membrane, followed by a thicker layer which acts as a support, maintaining the structure of the membrane. For the NF membrane, the structure is the same as that of the NF90 membrane, but the thin layer on the surface, responsible for the selectivity, is comprised of the polymer polypiperazine amide instead of polyamide. Finally, for the BW-30 membrane the layer of polyamide on the surface is not as well defined as in the case of the nanofiltration membranes. However, the large apertures observed on the support facilitate the permeate flux, leading to less resistance. 3.4. Comparison between membranes The results presented in Table 4 and Fig. 12 show that although the permeate fluxes of the NF and BW-30 membranes in the presence of the oil were similar, the retention index obtained with the NF membrane was significantly lower when compared with the BW-30 membrane. Also, a lower reduction in the permeate flux of CO2 in the presence of the oil (29.82%) was obtained with the BW-30 membrane, maintaining a good permeate flux (53.03 kg h−1 m−2 ) and higher retention index (0.9509) in the separation process of the patchouli oil. Thus, the use of the BW-30 membrane promoted the best combination between retention index and permeate flux in the presence of the oil, allowing its use in the regeneration of CO2 with a minimal fall in pressure (1.0 MPa), aiming at the solvent recirculation in the supercritical extraction of patchouli essential oil. Another advantage of the separation process using membranes was a visible reduction in the greenish yellow color of the patchouli essential oil both in the permeate and retentate extracts for the
9
Fig. 13. Spectra for the solutions of 1.0% wt. of patchouli essential oil, permeate P4 , retentate R2 , retentate R3 and retentate R4 obtained using the BW-30 membrane. (For interpretation of the references to color in the text, the reader is referred to the web version of this article.)
process using the BW-30 membrane. In Fig. 13 the spectra for the patchouli essential oil, permeate and retentate extracts obtained using the BW-30 membrane are presented. In the oil spectrum the presence of peaks between the wavelengths of 400 and 500 nm was verified, which correspond to the blue region, and the wavelength of 675 nm (red region). However, between the wavelengths of 500 and 590 nm (green and yellow regions) the light absorption is almost zero and these bands are thus reflected leading to the greenish yellow color of the patchouli oil. On analyzing Fig. 13, it can be noted that the extracts are colorless since they do not show absorbance in the visible wavelength (above 400 nm). As the permeate and retentate showed the same change in the coloration, the dye was probably retained by the membrane. This color reduction was observed for all membranes, being the absorption of the dye by the amide group in the membranes the most likely explanation. This modification in the color of the oil is of great importance in the perfumery industry, since a yellow color can cause marks on clothes and hinder the development of perfumes with other colors.
4. Conclusions This study showed that besides promoting the retention of the patchouli essential oil (RI = 0.9509) with a good permeate flow, the use of the BW-30 membrane also allows the color of the oil to be retained, eliminating its greenish yellow coloration. In relation to the selective capacity, the use of the membranes did not promote the total separation of any component or the concentration of ␣bulnesene, and only in the process with the BW-30 membrane a significant increase in the patchoulol concentration occurred (11% in the retentate) in relation to the patchouli oil, mainly due to the process kinetics. Other aspects, such as an evaluation of the growing conditions of patchouli and the yield of essential oil should also be considered in future researches. Additionally, with the knowledge acquired from the process, as well as of the essential oil composition, it is possible to explore the development of specific membranes to enhance the separation process.
Acknowledgements The authors wish to thank CAPES (Brazil) and GRICES (Portugal) for their financial support to this study.
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Please cite this article in press as: A. Donelian, et al., Performance of reverse osmosis and nanofiltration membranes in the fractionation and retention of patchouli essential oil, J. Supercrit. Fluids (2015), http://dx.doi.org/10.1016/j.supflu.2015.07.026