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Phase equilibria study of systems composed of refined babassu oil, lauric acid, ethanol, and water at 303.2 K
J. Chem. Thermodynamics 43 (2011) 1784–1790
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Phase equilibria study of systems composed of refined babassu oil, lauric acid, ethanol, and water at 303.2 K Érika C. D’Anton Reipert a, Christianne E.C. Rodrigues b,⇑, Antonio J.A. Meirelles a a b
EXTRAE, Department of Food Engineering (DEA-FEA), University of Campinas (UNICAMP), P.O. Box 6121, Zip Code 13083-862, Campinas, SP, Brazil LES, Department of Food Engineering (ZEA-FZEA), University of São Paulo (USP), P.O. Box 23, Zip Code 13635-900, Pirassununga, SP, Brazil
a r t i c l e
i n f o
Article history: Received 28 November 2010 Received in revised form 24 May 2011 Accepted 31 May 2011 Available online 24 June 2011 Keywords: Liquid–liquid extraction Liquid–liquid equilibrium Experimental data Deacidification Solvent extraction NRTL
a b s t r a c t Deacidification of vegetable oils can be performed using liquid–liquid extraction as an alternative method to the classical chemical and physical refining processes. This paper reports experimental data for systems containing refined babassu oil, lauric acid, ethanol, and water at 303.2 K with different water mass fractions in the alcoholic solvent (0, 0.0557, 0.1045, 0.2029, and 0.2972). The dilution of solvent with water reduced the distribution coefficient values, which indicates a reduction in the loss of neutral oil. The experimental data were used to adjust the NRTL equation parameters. The global deviation between the observed and the estimated compositions was 0.0085, indicating that the model can accurately predict the behavior of the compounds at different levels of solvent hydration. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Babassu (Orbignya ssp.) is a palm tree that grows up to 20 m tall and is native to the Amazon region in South America, especially Brazil and Colombia. The main product of the babassu palm is its fruit, small coconuts (drupes) that hang from its branches, with typically 15 to 25 coconuts per tree. Babassu oil is a clear, light yellow vegetable oil extracted from the seeds of the babassu palm. This oil contains a high level of short-chain saturated fatty acids, with lauric acid being the most abundant (40% to 55%, on a mass basis). This oil contains a higher concentration of unsaturated fatty acids (10% to 26%, on a mass basis) compared with coconut oil (6% to 12%, on a mass basis), an important textural agent in the food industry [1]. Vegetable oils are extracted from oilseeds, bran, nuts, or fruit pulps using mainly hexane petroleum fractions as a solvent [2,3]. Crude vegetable oils obtained from solid–liquid extraction operations contain variable amounts of non-glyceride impurities such as free fatty acids, phosphatides, and pigments that negatively affect the quality of the final product and should be removed. A variety of procedures including solvent stripping, degumming, bleaching, deacidification, and deodorization may be involved in the conversion of crude vegetable oils into edible products [4,5]. The deacidification step, where free fatty acids are ⇑ Corresponding author. Fax: +55 19 3565 4343. E-mail address: [email protected] (C.E.C. Rodrigues). 0021-9614/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2011.05.039
removed, is usually performed by chemical or physical refining. However, because of saponification and emulsification, chemical refining of oils containing high proportions of free fatty acids leads to large losses of neutral oil, resulting in a considerable amount of effluent [6]. Physical refining is also used to deacidify acidic oils, and it results in less neutral oil loss than in chemical processing, but it requires more energy. Additionally, in some cases, the refined oil experiences undesirable color changes and oxidation [7]. The liquid–liquid extraction technique has been considered as an alternative to the classical chemical and physical refining processes [6,8]. This alternative process is based on the different solubilities of free fatty acids and neutral triacylglycerols in an appropriate solvent [9] and can be performed at lower temperatures than traditional methods. Liquid–liquid extraction also prevents waste product formation and reduces the loss of both neutral oil and nutraceutical compounds [10–12]. Other reports on this extraction process have found a reduction in the free fatty acid content of vegetable oils [13,14]. The development of this approach for future commercial applications demands a systematic study of the phase equilibrium of fatty compounds and solvents [15,16]. Liquid–liquid equilibrium data for fatty systems containing several vegetable oils (canola, corn, palm, rice bran, macadamia nut, Brazil nut, cotton seed, grape seed, garlic, sesame seed, sunflower seed, and soybean oils) with short-chain alcohols as the solvent have been reported by our research group and other authors [10,11,15,17–26].
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Experimental data for the phase equilibrium of systems composed of vegetable oils + fatty acids + solvents are required to design equipment for industrial-scale liquid–liquid extraction of refined oils. Previous papers have reported phase equilibrium data for systems composed of vegetable oils and saturated or unsaturated free fatty acids such as palmitic, stearic, oleic, and linoleic acids at different temperatures [10,17,19,20,23]. The present work investigates the phase equilibrium of systems composed of refined babassu oil artificially acidified with lauric acid and ethanol with different water contents at 303.2 K. Correlations using the thermodynamic NRTL model are presented. In addition to obtaining the adjusted interaction parameters, which are used to design and to simulate liquid–liquid extractors, the present work also compares the partition coefficients of babassu oil and lauric acid with the available data for different vegetable oils and free fatty acids. 2. Experimental 2.1. Materials The solvents used in this work were absolute ethanol (Merck, Darmstadt, Germany, mass fraction purity higher than 0.995) and aqueous solvents with different water mass fractions (0.0557 ± 0.0005, 0.1045 ± 0.0006, 0.2029 ± 0.0005, and 0.2972 ± 0.0007) prepared by diluting absolute ethanol with deionized water (Millipore, Milli-Q, Bedford, MA, USA). To determine the fatty acid composition of the refined babassu oil (Oleama, Maranhão, Brazil), gas chromatography of fatty acid methyl esters (FAMEs) was performed according to the AOCS official method (1-62) [27]. Before the chromatographic analysis, the fatty samples were converted into FAMEs, according to the AOCS official method (2-66) [27]. A gas chromatograph with a flame ionization detector (HP, model 5890, Palo Alto, USA) was used according to the following experimental conditions: a fused silica column of cyanopropylsiloxane 0.25 lm, 60 m long, 0.32 mm i.d.; hydrogen as the carrier gas at a rate of 2.5 mL/min; an injection temperature of 548.2 K; a column temperature of (448.2 to 498.2) K varied at a rate of 1.3 K/min; and a detection temperature of 578.2 K. The FAMEs were compared with external standards purchased from Nu Check, Inc. (Elysian, USA). Lauric acid (CAS number 143-07-7) was used as received because of its high degree of mass fraction purity (>0.99, Sigma, Switzerland). 2.2. Experimental procedure The model fatty systems containing lauric acid and triacylglycerols were prepared by adding defined quantities of lauric acid to refined babassu oil according to the previously published methodology [10]. The model fatty systems were mixed with ethanolic solvents in a 1:1 oil:solvent mass ratio at (303.2 ± 0.1) K to determine the liquid–liquid equilibrium data used to adjust the NRTL parameters. The equilibrium data were determined using polypropylene centrifuge tubes (50 mL) (Corning, Inc., Lowell, MA, USA). The components were weighed on an analytical balance (Adam, model AAA 250L, Milton Keynes, UK) with a readability and an accuracy of 0.0001 g. The tubes were vigorously stirred for at least 15 min at room temperature (approximately 298 K), centrifuged for 10 min at 5000g and (303.2 ± 1.5) K (Jouan Centrifuge, model BR4i, equipped with a temperature controller, Saint-Herblain, France), and allowed to rest for at least 16 h in a thermostatic bath at (303.2 ± 0.1) K (Cole Parmer, model 12101-05, 0.1 K accuracy,
Illinois, USA). This process resulted in two clear and transparent phases with a well-defined interface [10]. The free fatty acid (lauric acid) content was determined by titration (IUPAC official method 2201 [28]) using an automatic burette (Metrohm, model Dosimat 715, Herisan, Switzerland). The total solvent composition was determined by evaporation. Samples were evaporated in a vacuum oven (inner absolute pressure = 126 mmHg, Napco, model 5831, USA) at 313.2 K until a constant mass was achieved. The experimental temperatures and pressures were chosen to prevent the degradation/volatilization of the fatty compounds. The drying period required for complete solvent removal from the oil or alcoholic phases was determined by successive sample weighings every 60 min until a constant mass was achieved. The water content was determined according to the Karl Fischer titration following the AOCS method Ca 23-55 [27] using a KF Titrino (Metrohm, model 701, Herisan, Switzerland). The triacylglycerol content was determined by the difference. All measurements were performed in triplicates. The type A standard uncertainties [29] of the equilibrium data varied within the following ranges, in mass fractions: (0.0001 to 0.0031) for oil, (0.0001 to 0.0009) for lauric acid, (0.0003 to 0.0030) for ethanol, and (0.0001 to 0.0007) for water, where the low ends of the ranges were obtained from the lowest concentrations. To evaluate the reliability of the results, the procedure developed by Marcilla et al. [30] was employed. This procedure permits the calculation of the mass of each phase MOP and MAP based on the experimental values wOP and wAP by a least-squares fitting. i i The deviations d between the sum MOP + MAP and MOC, the mass of the initial mixture, can be calculated according to equation (1)
d ¼ 102 ðjðMOP þ M AP Þ M OC j=MOC Þ:
ð1Þ
The relative deviation di of the mass balance for each compound i was calculated according to equation (2) for each equilibrium experiment. AP AP OC OC OC OC di ¼ 102 ðjðM OP wOP i þ M wi Þ M wi j=M wi Þ:
ð2Þ
In this work, the values of the relative deviation d were always below 0.5%, which indicates the high precision and the repeatability of the equilibrium data [20,23]. 2.3. Modeling procedure The experimental data were used to adjust the NRTL binary interaction parameters. Traditionally, mole fractions have been used in this model, but mass fractions provide a more convenient composition basis because of the large difference in the molar masses of the components, including vegetable oils, ethanol and water. Recently, several authors have reported using this approach with the NRTL model [17–25,31]. Thus, on the basis of mass fractions, the NRTL model for multicomponent mixtures is expressed as:
0P 2 K sji Gji wj K X B j Mj w 4 ln ci ¼ @ PK G w þ ji j j
Mi
j¼1
Mj K X
Mj
! wj =Mj ;
0 PK skj Gkj wk 131, k¼1 wj Gji Mk C PK Gkj wk @sij PK Gkj wk A5A k¼1 M k
k¼1 M k
ð3Þ
j¼1
sij ¼ Aij =T ðsij – sji Þ;
ð4Þ
Gij ¼ expðaij sij Þ ðaij ¼ aji Þ;
ð5Þ
where cw represents the corresponding activity coefficient of i component i expressed as a mass fraction; M and w represent the
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TABLE 1 Fatty acid mole fractions x and mass fractions w of the refined babassu oil.
a b
Symbol
Fatty acid
Cx:ya
Mb/(g mol1)
x
w
Cp C L M P S O Li
Octanoic Decanoic Dodecanoic Tetradecanoic Hexadecanoic Octadecanoic cis-Octadec-9-enoic cis,cis-Octadeca-9,12-dienoic
C8:0 C10:0 C12:0 C14:0 C16:0 C18:0 C18:1 C18:2
144.22 172.27 200.32 228.38 256.43 284.49 282.47 280.45
0.0806 0.0646 0.4742 0.1547 0.0760 0.0281 0.1028 0.0190
0.0541 0.0517 0.4420 0.1644 0.0906 0.0372 0.1352 0.0248
In Cx:y. x = number of carbons and y = number of double bonds. M = molar mass.
average molar mass and the mass fraction of the pseudocomponents, respectively; sij, sji, Aij, and Aji represent the molecular energy interactions between the components i and j; aij represents the non-randomness parameter of the mixture; T represents the absolute temperature; and Gij is a Boltzmann-type expression for the local composition energy interactions between components i and j. Thus, in the present study, there are three dependent parameters for each pair of components. These parameters can be estimated on the basis of the experimental data following the procedure below [31]. The adjustments were performed assuming that the model system of (refined babassu oil + lauric acid + absolute ethanol) is pseudoternary and that the model system of (refined babassu oil + lauric acid + ethanol + water) is pseudoquaternary. For the parameter adjustment, babassu oil was assumed to be composed of a single triacylglycerol with an average molar mass equal to that of the oil. It was assumed that the different triacylglycerols present in babassu oil all behave in a similar manner in the liquid–liquid system that was analyzed. In this case, these components can be replaced with a single pseudo-compound with the corresponding average physical–chemical properties. This approach was evaluated by Lanza et al. [32], who proved its feasibility. Regarding the free fatty acids, a representative fatty acid with the molar mass of lauric acid was used. The interaction parameter estimation was based on the minimization of the objective function of the composition (equation (6)) according to the algorithm developed by Stragevitch and d’Avila [33] in the FORTRANÒ language
OFðwÞ ¼
D X N X K1 X m¼1 n¼1 i¼1
2 4
OP;calc wOP;exp i;n;m wi;n;m
rwOPi;n;m
!2 þ
AP;calc wAP;exp i;n;m wi;n;m
rwOPi;n;m
!2 3 5; ð6Þ
where D represents the total number of data groups, N represents the total number of tie lines in the data groups, and K represents the total number of components or pseudo-compounds in the data group m. The mass fraction is given by w, and the subscripts i, n, and m represent the component, the tie line, and the group number, respectively. The superscripts OP and AP stand for the oil and alcoholic phases, respectively. exp and calc refer to the experimental and the calculated compositions. rwOP and rwAP represent the standard i;n;m i;n;m deviations observed in the composition of the two liquid phases. The average deviations between the experimental and the calculated compositions in both phases were calculated according to equation (7)
vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi u 2 2 uPN PK OP;exp AP;exp OP;calc AP;calc u n¼1 i¼1 wi;n wi;n þ wi;n wi;n t : Dw ¼ 2NK ð7Þ
3. Results The fatty acid composition of the refined babassu oil is presented in table 1. The triacylglycerol composition of refined oil was estimated on the basis of the fatty acid composition of babassu oil following the procedure suggested by Antoniosi Filho et al. [34] (table 2). In table 2, the main triacylglycerol represents the component of highest concentration in the isomer set with x carbons and y double bonds. This result allows the calculation of the average molar mass for refined babassu oil, which was 689.31 g mol1. The molar mass of lauric acid was 200.32 g mol1. The residual acidity of refined oil was (0.0010 ± 0.0001), expressed as mass fraction of lauric acid. As previously mentioned, babassu oil was assumed to be a pseudo-compound with the average molar mass as indicated above. Experimental equilibrium data reported for similar systems [19,32] indicate that fatty compounds may selectively split between both the alcoholic and the oil phases. Nevertheless, the observed differences in the partitioning behavior were restricted to a
TABLE 2 Probable triacylglycerol mole fractions x and mass fractions w of the refined babassu oil. Group main a
28:0 30:0 32:0 34:0 36:0 38:0 40:0 42:0 44:0 46:0 36:1 38:1 40:1 42:1 44:1 46:1 48:1 50:1 38:2 40:2 42:2 44:2 46:2 48:2
Main TAGb
Mc/(g mol1)
x
w
CpCpL CpCL CpLL CpLM LLL LLM LLP LMP LMS LPS CpCO CpLO CLO LOL LOM LOP LOS MOS CpLLi CLLi LLLi LLiM LLiP LOO
526.85 554.90 582.96 611.01 639.06 667.12 695.17 723.23 751.28 779.33 637.05 665.10 693.16 721.17 749.22 777.28 805.37 833.33 663.09 691.09 719.19 747.25 775.26 803.36
0.0084 0.0148 0.0546 0.0688 0.1313 0.1111 0.0808 0.0492 0.0222 0.0090 0.0052 0.0400 0.0428 0.1275 0.0799 0.0494 0.0249 0.0072 0.0074 0.0079 0.0236 0.0155 0.0097 0.0088
0.0064 0.0119 0.0462 0.0610 0.1217 0.1075 0.0815 0.0516 0.0242 0.0101 0.0048 0.0386 0.0430 0.1335 0.0869 0.0558 0.0291 0.0087 0.0071 0.0079 0.0246 0.0168 0.0109 0.0102
a x:y, x = number of carbons (except carbons of glycerol) and y = number of double bonds. b Groups with a total triacylglycerol (TAG) composition lower than 0.005 mass fraction were ignored. c M = molar mass.
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narrow range of compositions, and the pseudo component approach is approximately valid. Tables 3 and 4 present the overall experimental composition and the phase compositions in the alcoholic and the oil phases, respectively, for the pseudoternary (absolute ethanol as solvent) and pseudoquaternary (aqueous ethanol as solvent) model systems at (303.2 ± 0.1) K. All compositions are expressed as mass fractions. Figures 1 and 2 show the experimental data and the calculated tie lines for the systems composed of (refined babassu oil + lauric acid + ethanol) with (0.1045 ± 0.0006) water mass fraction and (babassu oil + lauric acid + ethanol) with (0.2972 ± 0.0007) water mass fraction, respectively, both at (303.2 ± 0.1) K. The equilibrium diagram is plotted in rectangular coordinates. To represent the pseudoquaternary system in rectangular coordinates, ethanol + water were assumed to be a mixed solvent. In these figures, the mass fraction composition of the vegetable oil can be obtained by the difference.
It is observed that the addition of water to the solvent expanded the phase splitting region, which allowed the refining of highly acidic oils by solvent extraction. Furthermore, it can be seen that the addition of water to the solvent minimized the loss of neutral oil to the alcoholic phase and the loss of solvent to the oil phase (see the baseline in figures 1 and 2) because the water decreased the mutual solubility between the oil and the solvent. On the other hand, it is observed that the addition of water reduced the capacity of the solvent to extract the free fatty acids. These findings are better observed in figure 3, which presents the distribution of lauric acid and refined babassu oil in the oily and the alcoholic phases. It can be observed that solvents with water mass fractions up to 0.10 demonstrated similar capacities to extract the free fatty acids. In fact, the capacity of the solvent to extract lauric acid was reduced only when water was present in high quantities (above 0.1045 in mass fraction). However, the loss of neutral oil was
TABLE 3 Liquid–liquid equilibrium data for the system {refined babassu oil (1) + lauric acid (2) + ethanol (3)}, at (303.2 ± 0.1) K. OCa
a b c
OPb
APc
w1
w2
w3
w1
w2
w3
w1
w2
w3
0.5000 0.4944 0.4895 0.4875 0.4845
0.0000 0.0055 0.0105 0.0125 0.0154
0.5000 0.5001 0.5000 0.5000 0.5001
0.6760 0.6600 0.5955 0.5864 0.5490
0.0000 0.0048 0.0100 0.0114 0.0146
0.3240 0.3352 0.3945 0.4022 0.4364
0.2787 0.2841 0.3459 0.3599 0.3890
0.0000 0.0060 0.0115 0.0133 0.0162
0.7213 0.7099 0.6426 0.6268 0.5948
OC = overall composition. OP = oil phase. AP = alcoholic phase.
TABLE 4 Liquid–liquid equilibrium data for the system {refined babassu oil (1) + lauric acid (2) + ethanol (3) + water (4)}, at (303.2 ± 0.1) K. w4Sa
a b c d
OCb
OPc
APd
w1
w2
w3
w4
w1
w2
w3
w4
w1
w2
w3
w4
0.0557
0.5000 0.4946 0.4893 0.4795 0.4595 0.4394 0.4189
0.0000 0.0055 0.0107 0.0205 0.0405 0.0605 0.0804
0.4721 0.4721 0.4721 0.4721 0.4721 0.4722 0.4728
0.0279 0.0278 0.0279 0.0279 0.0279 0.0279 0.0279
0.8930 0.8839 0.8656 0.8593 0.8030 0.7649 0.7087
0.0000 0.0027 0.0089 0.0176 0.0357 0.0542 0.0691
0.0994 0.1064 0.1199 0.1176 0.1537 0.1692 0.2098
0.0076 0.0070 0.0056 0.0055 0.0076 0.0117 0.0124
0.0468 0.0520 0.0468 0.0558 0.0764 0.0924 0.0901
0.0000 0.0068 0.0126 0.0255 0.0492 0.0727 0.0913
0.8855 0.8648 0.8843 0.8555 0.8141 0.7847 0.7711
0.0677 0.0764 0.0563 0.0632 0.0603 0.0502 0.0475
0.1045
0.5000 0.4890 0.4795 0.4695 0.4396 0.4096 0.3796
0.0000 0.0105 0.0205 0.0305 0.0605 0.0904 0.1204
0.4477 0.4482 0.4477 0.4477 0.4477 0.4478 0.4477
0.0523 0.0523 0.0523 0.0523 0.0522 0.0522 0.0523
0.9300 0.9138 0.8940 0.8870 0.8343 0.7832 0.7191
0.0000 0.0087 0.0190 0.0271 0.0552 0.0830 0.1129
0.0621 0.0743 0.0778 0.0836 0.0998 0.1194 0.1501
0.0079 0.0032 0.0092 0.0023 0.0107 0.0144 0.0179
0.0173 0.0201 0.0211 0.0260 0.0387 0.0541 0.0762
0.0000 0.0105 0.0233 0.0330 0.0665 0.0993 0.1327
0.9067 0.8799 0.8326 0.8524 0.7822 0.7460 0.6901
0.0760 0.0895 0.1230 0.0886 0.1126 0.1006 0.1010
0.2029
0.4999 0.4945 0.4898 0.4695 0.4392 0.3994 0.3501
0.0000 0.0055 0.0105 0.0305 0.0603 0.1003 0.1500
0.3986 0.3986 0.3983 0.3985 0.3988 0.3988 0.3985
0.1015 0.1014 0.1014 0.1015 0.1017 0.1015 0.1014
0.9425 0.9399 0.9251 0.9013 0.8423 0.7848 0.6887
0.0000 0.0058 0.0110 0.0323 0.0646 0.1063 0.1559
0.0496 0.0467 0.0560 0.0543 0.0817 0.0922 0.1330
0.0079 0.0076 0.0079 0.0121 0.0114 0.0167 0.0224
0.0048 0.0046 0.0045 0.0089 0.0104 0.0290 0.0328
0.0000 0.0050 0.0095 0.0277 0.0554 0.0939 0.1441
0.7949 0.7755 0.7838 0.7602 0.7220 0.6887 0.6390
0.2003 0.2149 0.2022 0.2032 0.2122 0.1884 0.1841
0.2972
0.5001 0.4945 0.4695 0.4393 0.3970 0.3498
0.0000 0.0055 0.0305 0.0604 0.0997 0.1502
0.3513 0.3514 0.3514 0.3516 0.3537 0.3514
0.1486 0.1486 0.1486 0.1487 0.1496 0.1486
0.9562 0.9457 0.8975 0.8401 0.7628 0.6683
0.0000 0.0073 0.0411 0.0818 0.1346 0.1949
0.0390 0.0411 0.0538 0.0676 0.0878 0.1172
0.0048 0.0059 0.0076 0.0105 0.0148 0.0196
0.0014 0.0002 0.0011 0.0006 0.0010 0.0065
0.0000 0.0033 0.0187 0.0376 0.0662 0.1047
0.7029 0.6942 0.6970 0.6796 0.6500 0.6087
0.2957 0.3023 0.2832 0.2822 0.2828 0.2801
w4S = water mass fraction in the solvent. OC = overall composition. OP = oil phase. AP = alcoholic phase.
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a
pair ija
Ai /K
Aji/K
aij
12 13 14 23 24 34
7015.20 258.51 892.15 520.06 193.82 398.57
361.42 1244.50 3316.60 7117.00 3100.7 516.45
0.30 0.47 0.20 0.22 0.35 0.47
Refined babassu oil (1), lauric acid (2), ethanol (3), and water (4).
TABLE 6 Mean deviations in phase compositions.
FIGURE 1. System of (refined babassu oil (1) + lauric acid (2) + aqueous solvent) [ethanol (3) + water (4), where w4S = 0.1045], at (303.2 ± 0.1) K. j, Experimental and - - -, NRTL model.
a
w4Sa
Dw
0.00 0.0557 0.1045 0.2029 0.2972 Global deviation of the correlation
0.0084 0.0078 0.0085 0.0076 0.0083 0.0085
w4S = water mass fraction in the solvent.
highly suppressed by the addition of water to the solvent, which is desirable for this system (observe the high mutual solubility between the oil and the absolute ethanol in table 3). The ability of the NRTL model to satisfactorily describe the distributions of the fatty compounds between the liquid phases can also be observed in figure 3. Table 5 presents the NRTL model adjusted parameters. The deviations between the experimental and the calculated compositions in both phases were estimated according to equation (7) and are shown in table 6. Figures 4 and 5 show the partition coefficient of refined babassu oil (kOil) and lauric acid (kFFA), respectively, as a function of the acidity level in the oil phase (wOP FFA ). The distribution coefficient was calculated according to equation (8) FIGURE 2. System of (refined babassu oil (1) + lauric acid (2) + aqueous solvent) [ethanol (3) + water (4), where w4S = 0.2972], at (303.2 ± 0.1) K. j, Experimental and - - -, NRTL model.
FIGURE 3. Distribution diagram at (303.2 ± 0.1) K for systems of (babassu oil (1) + lauric acid (2) + aqueous solvent) [ethanol (3) + water (4)]: h, w4S = 0; j, w4S = 0.0557; N, w4S = 0.1045; r, w4S = 0.2029; d, w4S = 0.2972; and - - -, NRTL model.
OP ki ¼ wAP i =wi ;
ð8Þ
where ki represents the distribution coefficient of the fatty compound i, the oil or the free fatty acid; w represents the mass fraction; and the superscripts OP and AP stand for the oil and the alcoholic phases, respectively. Figures 4 and 5 also present distribution coefficient data related to other fatty systems, including cotton seed oil and linoleic acid at 298.2 K [20], rice bran oil and oleic acid at 298.2 K [10], soybean oil and linoleic acid at 323.2 K [23], as well as palm oil and palmitic acid at 318.2 K [19]. In figure 4, it is observed that the higher free fatty acid contents in the system resulted in a higher oil partition coefficient regardless of the oil type, which can be attributed to an increase in the mutual solubility of the oil and the solvent. However, the loss of neutral oil in the alcoholic phase was drastically suppressed by water in the solvent. On the basis of figure 4, one can estimate the influence of the carbon chain length of the triacylglycerol molecules on the solubility of the fatty system. The solubility of babassu oil in the alcoholic solvent was higher compared with that of cotton seed and rice bran oils, and such an effect cannot be explained by temperature alone (see figure 4a to c). Note that the systems composed of soybean oil and palm oil (d and e) were obtained at 323.2 K and 318.2 K, respectively, and that they exhibited lower solubilities than babassu oil.
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FIGURE 4. Distribution coefficients of oils: h, w4S = 0; j, w4S = 0.05; N, w4S = 0.10; r, w4S = 0.20; d, and w4S = 0.30. (a) Babassu, at 303.2 K (this work); (b) cotton seed, at 298.2 K [20]; (c) rice bran, at 298.2 K [10]; (d) soybean, at 323.2 K [23]; and (e) palm, at 318.2 K [19].
FIGURE 5. Distribution coefficients of free fatty acids: h, w4S = 0; j, w4S = 0.05; N, w4S = 0.10; r, w4S = 0.20; and d, w4S = 0.30. (a) Lauric acid, at 303.2 K (this work); (b) linoleic acid, at 298.2 K [20]; (c) oleic acid, at 298.2 K [10]; (d) linoleic acid, at 323.2 K [23]; and (e) palmitic acid, at 318.2 K [19].
The partitioning of the free fatty acids as a function of the acidity level in the oil phase (wOP FFA ) can be observed in figure 5. Regarding the behavior of the free fatty acids, it is reasonable to state that lauric acid was more soluble than other free fatty acids. Again, such an effect is not explained solely by temperature (in figure 5, observe the similarity among the results related to other free fatty acids at different temperatures, from 298.2 K to 323.2 K, for each water level in the solvent) [10,19,20,23]. Previous reports have shown that the partitioning of the free fatty acids is not significantly affected by the temperature of the solution [24,35], indicating that the high solubility of lauric acid can be explained by the fewer number of carbon atoms in the carbon chain (C12:0) as compared with palmitic (C16:0), oleic (C18:1), and linoleic (C18:2) acids.
4. Conclusions In the presented paper, experimental equilibrium data for systems containing refined babassu oil were measured at (303.2 ± 0.1) K. The results presented in this article demonstrate that the distribution coefficient of lauric acid and the mutual solubility of oil and the solvent (ethanol and water) were affected by the water content of the solvent. It was also observed that the carbon chain length of the fatty molecules (triacylglycerols and free fatty acids) influenced the solubility of the fatty system, regardless of the temperature of the process. The distribution coefficients of the free fatty acids, assumed to be lauric acid, and refined oil are required to properly design liquid–liquid extractors for oil deacidification processes and to
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construct equipment for solvent recovery. The estimated parameters of the NRTL model can be used to model and to simulate LLE and recovery processes. Acknowledgments The authors thank FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo – 09/17855-3, 08/56258-8), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), FINEP (Financiadora de Estudos e Projetos) and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for the financial support. References [1] R. Ceriani, F.R. Paiva, C.B. Gonçalves, E.A.C. Batista, A.J.A. Meirelles, J. Chem. Eng. Data 53 (2008) 1846–1853. [2] T. Fornari, S. Bottini, E. Brignole, J. Am. Oil Chem. Soc. 71 (1994) 391–395. [3] C. González, J.M. Resa, A. Ruiz, J.I. Gutiérrez, J. Chem. Eng. Data 41 (1996) 796– 798. [4] Z. Leibovitz, C. Ruckenstein, J. Am. Oil Chem. Soc. 60 (1983) 347A–351A. [5] J. Cvengros, J. Am. Oil Chem. Soc. 72 (1995) 1193–1196. [6] D. Swern, in: K.F. Mattil, F.A. Norris, A.J. Stirton (Eds.), Bailey’s Industrial Oil and Fat Products, Wiley, New York, 1964. [7] R. Antoniassi, W. Esteves, A.J.A. Meirelles, J. Am. Oil Chem. Soc. 75 (1998) 1411–1415. [8] K.J. Shah, T.K. Venkatesan, J. Am. Oil Chem. Soc. 66 (1989) 783–787. [9] C. Thomopoulos, Rev. Fran. des. Corps Gras. 18 (1971) 143–150. [10] C.E.C. Rodrigues, R. Antoniassi, A.J.A. Meirelles, J. Chem. Eng. Data 48 (2003) 367–373. [11] C.E.C. Rodrigues, P.A. Pessôa Filho, A.J.A. Meirelles, Fluid Phase Equilib. 216 (2004) 271–283. [12] C.E.C. Rodrigues, M.M. Onoyama, A.J.A. Meirelles, J. Food Eng. 73 (2006) 370– 378. [13] A.C. Bhattacharyya, S. Majumdar, D.K. Bhattacharyya, Oléagineaux 42 (1987) 431–433.
[14] V. Kale, S.P.R. Katikaneni, M. Cheryan, J. Am. Oil Chem. Soc. 76 (1999) 723–727. [15] M. Mohsen-Nia, A. Khodayari, J. Chem. Thermodyn. 40 (2008) 1325–1329. [16] A. Apelblat, T. Zaharoskin, J. Wisniak, E. Korngold, J. Am. Oil Chem. Soc. 73 (1996) 239–244. [17] E. Batista, S. Monnerat, K. Kato, L. Stragevitch, A.J.A. Meirelles, J. Chem. Eng. Data 44 (1999) 1360–1364. [18] C.B. Gonçalves, E. Batista, A.J.A. Meirelles, J. Chem. Eng. Data 47 (2002) 416– 420. [19] C.B. Gonçalves, A.J.A. Meirelles, Fluid Phase Equilib. 221 (2004) 139–150. [20] C.E.C. Rodrigues, E.C.D. Reipert, A.F. Souza, P.A. Pessôa Filho, A.J.A. Meirelles, Fluid Phase Equilib. 238 (2005) 193–203. [21] C.E.C. Rodrigues, F.A. Silva, A. Marsaioli Jr., A.J.A. Meirelles, J. Chem. Eng. Data 50 (2005) 517–523. [22] C.E.C. Rodrigues, A. Filipini, A.J.A. Meirelles, J. Chem. Eng. Data 51 (2006) 15– 21. [23] C.E.C. Rodrigues, E.C.D. Peixoto, A.J.A. Meirelles, Fluid Phase Equilib. 261 (2007) 122–128. [24] M.S. Cuevas, C.E.C. Rodrigues, A.J.A. Meirelles, J. Food Eng. 95 (2009) 291–297. [25] C.E.C. Rodrigues, A.J.A. Meirelles, J. Chem. Eng. Data 53 (2008) 1698–1704. [26] G. Sanaiotti, J.S.R. Coimbra, J.C. Gomes, L.A. Minim, J. Chem. Eng. Data 53 (2008) 1492–1497. [27] AOCS, Official Methods and Recommended Practices of the American Oil Chemists’ Society, fifth ed., AOCS Press, Champaign, 1998. [28] C. Paquot (Ed.), IUPAC Standard Methods for the Analysis of Oils, Fats and Derivatives, sixth ed., part 1 (sections I and II), Pergamon Press, 1979. [29] B.N. Taylor, C.E. Kuyatt, Guidelines for the Evaluation and Expression of Uncertainty in NIST Measurement Results, NIST Technical Note 1297, 1994. [30] A. Marcilla, F. Ruiz, A.N. García, Fluid Phase Equilib. 112 (1995) 273–289. [31] C.A.S. Silva, G. Sanaiotti, M. Lanza, L.A. Follegatti-Romero, A.J.A. Meirelles, E.A.C. Batista, J. Chem. Eng. Data 55 (2010) 440–447. [32] M. Lanza, W. Borges Neto, E. Batista, R.J. Poppi, A.J.A. Meirelles, J. Chem. Eng. Data 53 (2008) 5–15. [33] L. Stragevitch, S.G. d’Avila, Braz. J. Chem. Eng. 14 (1997) 41–52. [34] N.R. Antoniosi Filho, O.L. Mendes, F.M. Lanças, Chromatographia 40 (1995) 557–562. [35] C. Chiyoda, E.C.D. Peixoto, A.J.A. Meirelles, C.E.C. Rodrigues, Fluid Phase Equilib. 299 (2010) 141–147.
JCT 10-406
Contents lists available at ScienceDirect
J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct
Phase equilibria study of systems composed of refined babassu oil, lauric acid, ethanol, and water at 303.2 K Érika C. D’Anton Reipert a, Christianne E.C. Rodrigues b,⇑, Antonio J.A. Meirelles a a b
EXTRAE, Department of Food Engineering (DEA-FEA), University of Campinas (UNICAMP), P.O. Box 6121, Zip Code 13083-862, Campinas, SP, Brazil LES, Department of Food Engineering (ZEA-FZEA), University of São Paulo (USP), P.O. Box 23, Zip Code 13635-900, Pirassununga, SP, Brazil
a r t i c l e
i n f o
Article history: Received 28 November 2010 Received in revised form 24 May 2011 Accepted 31 May 2011 Available online 24 June 2011 Keywords: Liquid–liquid extraction Liquid–liquid equilibrium Experimental data Deacidification Solvent extraction NRTL
a b s t r a c t Deacidification of vegetable oils can be performed using liquid–liquid extraction as an alternative method to the classical chemical and physical refining processes. This paper reports experimental data for systems containing refined babassu oil, lauric acid, ethanol, and water at 303.2 K with different water mass fractions in the alcoholic solvent (0, 0.0557, 0.1045, 0.2029, and 0.2972). The dilution of solvent with water reduced the distribution coefficient values, which indicates a reduction in the loss of neutral oil. The experimental data were used to adjust the NRTL equation parameters. The global deviation between the observed and the estimated compositions was 0.0085, indicating that the model can accurately predict the behavior of the compounds at different levels of solvent hydration. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Babassu (Orbignya ssp.) is a palm tree that grows up to 20 m tall and is native to the Amazon region in South America, especially Brazil and Colombia. The main product of the babassu palm is its fruit, small coconuts (drupes) that hang from its branches, with typically 15 to 25 coconuts per tree. Babassu oil is a clear, light yellow vegetable oil extracted from the seeds of the babassu palm. This oil contains a high level of short-chain saturated fatty acids, with lauric acid being the most abundant (40% to 55%, on a mass basis). This oil contains a higher concentration of unsaturated fatty acids (10% to 26%, on a mass basis) compared with coconut oil (6% to 12%, on a mass basis), an important textural agent in the food industry [1]. Vegetable oils are extracted from oilseeds, bran, nuts, or fruit pulps using mainly hexane petroleum fractions as a solvent [2,3]. Crude vegetable oils obtained from solid–liquid extraction operations contain variable amounts of non-glyceride impurities such as free fatty acids, phosphatides, and pigments that negatively affect the quality of the final product and should be removed. A variety of procedures including solvent stripping, degumming, bleaching, deacidification, and deodorization may be involved in the conversion of crude vegetable oils into edible products [4,5]. The deacidification step, where free fatty acids are ⇑ Corresponding author. Fax: +55 19 3565 4343. E-mail address: [email protected] (C.E.C. Rodrigues). 0021-9614/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2011.05.039
removed, is usually performed by chemical or physical refining. However, because of saponification and emulsification, chemical refining of oils containing high proportions of free fatty acids leads to large losses of neutral oil, resulting in a considerable amount of effluent [6]. Physical refining is also used to deacidify acidic oils, and it results in less neutral oil loss than in chemical processing, but it requires more energy. Additionally, in some cases, the refined oil experiences undesirable color changes and oxidation [7]. The liquid–liquid extraction technique has been considered as an alternative to the classical chemical and physical refining processes [6,8]. This alternative process is based on the different solubilities of free fatty acids and neutral triacylglycerols in an appropriate solvent [9] and can be performed at lower temperatures than traditional methods. Liquid–liquid extraction also prevents waste product formation and reduces the loss of both neutral oil and nutraceutical compounds [10–12]. Other reports on this extraction process have found a reduction in the free fatty acid content of vegetable oils [13,14]. The development of this approach for future commercial applications demands a systematic study of the phase equilibrium of fatty compounds and solvents [15,16]. Liquid–liquid equilibrium data for fatty systems containing several vegetable oils (canola, corn, palm, rice bran, macadamia nut, Brazil nut, cotton seed, grape seed, garlic, sesame seed, sunflower seed, and soybean oils) with short-chain alcohols as the solvent have been reported by our research group and other authors [10,11,15,17–26].
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Experimental data for the phase equilibrium of systems composed of vegetable oils + fatty acids + solvents are required to design equipment for industrial-scale liquid–liquid extraction of refined oils. Previous papers have reported phase equilibrium data for systems composed of vegetable oils and saturated or unsaturated free fatty acids such as palmitic, stearic, oleic, and linoleic acids at different temperatures [10,17,19,20,23]. The present work investigates the phase equilibrium of systems composed of refined babassu oil artificially acidified with lauric acid and ethanol with different water contents at 303.2 K. Correlations using the thermodynamic NRTL model are presented. In addition to obtaining the adjusted interaction parameters, which are used to design and to simulate liquid–liquid extractors, the present work also compares the partition coefficients of babassu oil and lauric acid with the available data for different vegetable oils and free fatty acids. 2. Experimental 2.1. Materials The solvents used in this work were absolute ethanol (Merck, Darmstadt, Germany, mass fraction purity higher than 0.995) and aqueous solvents with different water mass fractions (0.0557 ± 0.0005, 0.1045 ± 0.0006, 0.2029 ± 0.0005, and 0.2972 ± 0.0007) prepared by diluting absolute ethanol with deionized water (Millipore, Milli-Q, Bedford, MA, USA). To determine the fatty acid composition of the refined babassu oil (Oleama, Maranhão, Brazil), gas chromatography of fatty acid methyl esters (FAMEs) was performed according to the AOCS official method (1-62) [27]. Before the chromatographic analysis, the fatty samples were converted into FAMEs, according to the AOCS official method (2-66) [27]. A gas chromatograph with a flame ionization detector (HP, model 5890, Palo Alto, USA) was used according to the following experimental conditions: a fused silica column of cyanopropylsiloxane 0.25 lm, 60 m long, 0.32 mm i.d.; hydrogen as the carrier gas at a rate of 2.5 mL/min; an injection temperature of 548.2 K; a column temperature of (448.2 to 498.2) K varied at a rate of 1.3 K/min; and a detection temperature of 578.2 K. The FAMEs were compared with external standards purchased from Nu Check, Inc. (Elysian, USA). Lauric acid (CAS number 143-07-7) was used as received because of its high degree of mass fraction purity (>0.99, Sigma, Switzerland). 2.2. Experimental procedure The model fatty systems containing lauric acid and triacylglycerols were prepared by adding defined quantities of lauric acid to refined babassu oil according to the previously published methodology [10]. The model fatty systems were mixed with ethanolic solvents in a 1:1 oil:solvent mass ratio at (303.2 ± 0.1) K to determine the liquid–liquid equilibrium data used to adjust the NRTL parameters. The equilibrium data were determined using polypropylene centrifuge tubes (50 mL) (Corning, Inc., Lowell, MA, USA). The components were weighed on an analytical balance (Adam, model AAA 250L, Milton Keynes, UK) with a readability and an accuracy of 0.0001 g. The tubes were vigorously stirred for at least 15 min at room temperature (approximately 298 K), centrifuged for 10 min at 5000g and (303.2 ± 1.5) K (Jouan Centrifuge, model BR4i, equipped with a temperature controller, Saint-Herblain, France), and allowed to rest for at least 16 h in a thermostatic bath at (303.2 ± 0.1) K (Cole Parmer, model 12101-05, 0.1 K accuracy,
Illinois, USA). This process resulted in two clear and transparent phases with a well-defined interface [10]. The free fatty acid (lauric acid) content was determined by titration (IUPAC official method 2201 [28]) using an automatic burette (Metrohm, model Dosimat 715, Herisan, Switzerland). The total solvent composition was determined by evaporation. Samples were evaporated in a vacuum oven (inner absolute pressure = 126 mmHg, Napco, model 5831, USA) at 313.2 K until a constant mass was achieved. The experimental temperatures and pressures were chosen to prevent the degradation/volatilization of the fatty compounds. The drying period required for complete solvent removal from the oil or alcoholic phases was determined by successive sample weighings every 60 min until a constant mass was achieved. The water content was determined according to the Karl Fischer titration following the AOCS method Ca 23-55 [27] using a KF Titrino (Metrohm, model 701, Herisan, Switzerland). The triacylglycerol content was determined by the difference. All measurements were performed in triplicates. The type A standard uncertainties [29] of the equilibrium data varied within the following ranges, in mass fractions: (0.0001 to 0.0031) for oil, (0.0001 to 0.0009) for lauric acid, (0.0003 to 0.0030) for ethanol, and (0.0001 to 0.0007) for water, where the low ends of the ranges were obtained from the lowest concentrations. To evaluate the reliability of the results, the procedure developed by Marcilla et al. [30] was employed. This procedure permits the calculation of the mass of each phase MOP and MAP based on the experimental values wOP and wAP by a least-squares fitting. i i The deviations d between the sum MOP + MAP and MOC, the mass of the initial mixture, can be calculated according to equation (1)
d ¼ 102 ðjðMOP þ M AP Þ M OC j=MOC Þ:
ð1Þ
The relative deviation di of the mass balance for each compound i was calculated according to equation (2) for each equilibrium experiment. AP AP OC OC OC OC di ¼ 102 ðjðM OP wOP i þ M wi Þ M wi j=M wi Þ:
ð2Þ
In this work, the values of the relative deviation d were always below 0.5%, which indicates the high precision and the repeatability of the equilibrium data [20,23]. 2.3. Modeling procedure The experimental data were used to adjust the NRTL binary interaction parameters. Traditionally, mole fractions have been used in this model, but mass fractions provide a more convenient composition basis because of the large difference in the molar masses of the components, including vegetable oils, ethanol and water. Recently, several authors have reported using this approach with the NRTL model [17–25,31]. Thus, on the basis of mass fractions, the NRTL model for multicomponent mixtures is expressed as:
0P 2 K sji Gji wj K X B j Mj w 4 ln ci ¼ @ PK G w þ ji j j
Mi
j¼1
Mj K X
Mj
! wj =Mj ;
0 PK skj Gkj wk 131, k¼1 wj Gji Mk C PK Gkj wk @sij PK Gkj wk A5A k¼1 M k
k¼1 M k
ð3Þ
j¼1
sij ¼ Aij =T ðsij – sji Þ;
ð4Þ
Gij ¼ expðaij sij Þ ðaij ¼ aji Þ;
ð5Þ
where cw represents the corresponding activity coefficient of i component i expressed as a mass fraction; M and w represent the
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TABLE 1 Fatty acid mole fractions x and mass fractions w of the refined babassu oil.
a b
Symbol
Fatty acid
Cx:ya
Mb/(g mol1)
x
w
Cp C L M P S O Li
Octanoic Decanoic Dodecanoic Tetradecanoic Hexadecanoic Octadecanoic cis-Octadec-9-enoic cis,cis-Octadeca-9,12-dienoic
C8:0 C10:0 C12:0 C14:0 C16:0 C18:0 C18:1 C18:2
144.22 172.27 200.32 228.38 256.43 284.49 282.47 280.45
0.0806 0.0646 0.4742 0.1547 0.0760 0.0281 0.1028 0.0190
0.0541 0.0517 0.4420 0.1644 0.0906 0.0372 0.1352 0.0248
In Cx:y. x = number of carbons and y = number of double bonds. M = molar mass.
average molar mass and the mass fraction of the pseudocomponents, respectively; sij, sji, Aij, and Aji represent the molecular energy interactions between the components i and j; aij represents the non-randomness parameter of the mixture; T represents the absolute temperature; and Gij is a Boltzmann-type expression for the local composition energy interactions between components i and j. Thus, in the present study, there are three dependent parameters for each pair of components. These parameters can be estimated on the basis of the experimental data following the procedure below [31]. The adjustments were performed assuming that the model system of (refined babassu oil + lauric acid + absolute ethanol) is pseudoternary and that the model system of (refined babassu oil + lauric acid + ethanol + water) is pseudoquaternary. For the parameter adjustment, babassu oil was assumed to be composed of a single triacylglycerol with an average molar mass equal to that of the oil. It was assumed that the different triacylglycerols present in babassu oil all behave in a similar manner in the liquid–liquid system that was analyzed. In this case, these components can be replaced with a single pseudo-compound with the corresponding average physical–chemical properties. This approach was evaluated by Lanza et al. [32], who proved its feasibility. Regarding the free fatty acids, a representative fatty acid with the molar mass of lauric acid was used. The interaction parameter estimation was based on the minimization of the objective function of the composition (equation (6)) according to the algorithm developed by Stragevitch and d’Avila [33] in the FORTRANÒ language
OFðwÞ ¼
D X N X K1 X m¼1 n¼1 i¼1
2 4
OP;calc wOP;exp i;n;m wi;n;m
rwOPi;n;m
!2 þ
AP;calc wAP;exp i;n;m wi;n;m
rwOPi;n;m
!2 3 5; ð6Þ
where D represents the total number of data groups, N represents the total number of tie lines in the data groups, and K represents the total number of components or pseudo-compounds in the data group m. The mass fraction is given by w, and the subscripts i, n, and m represent the component, the tie line, and the group number, respectively. The superscripts OP and AP stand for the oil and alcoholic phases, respectively. exp and calc refer to the experimental and the calculated compositions. rwOP and rwAP represent the standard i;n;m i;n;m deviations observed in the composition of the two liquid phases. The average deviations between the experimental and the calculated compositions in both phases were calculated according to equation (7)
vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi u 2 2 uPN PK OP;exp AP;exp OP;calc AP;calc u n¼1 i¼1 wi;n wi;n þ wi;n wi;n t : Dw ¼ 2NK ð7Þ
3. Results The fatty acid composition of the refined babassu oil is presented in table 1. The triacylglycerol composition of refined oil was estimated on the basis of the fatty acid composition of babassu oil following the procedure suggested by Antoniosi Filho et al. [34] (table 2). In table 2, the main triacylglycerol represents the component of highest concentration in the isomer set with x carbons and y double bonds. This result allows the calculation of the average molar mass for refined babassu oil, which was 689.31 g mol1. The molar mass of lauric acid was 200.32 g mol1. The residual acidity of refined oil was (0.0010 ± 0.0001), expressed as mass fraction of lauric acid. As previously mentioned, babassu oil was assumed to be a pseudo-compound with the average molar mass as indicated above. Experimental equilibrium data reported for similar systems [19,32] indicate that fatty compounds may selectively split between both the alcoholic and the oil phases. Nevertheless, the observed differences in the partitioning behavior were restricted to a
TABLE 2 Probable triacylglycerol mole fractions x and mass fractions w of the refined babassu oil. Group main a
28:0 30:0 32:0 34:0 36:0 38:0 40:0 42:0 44:0 46:0 36:1 38:1 40:1 42:1 44:1 46:1 48:1 50:1 38:2 40:2 42:2 44:2 46:2 48:2
Main TAGb
Mc/(g mol1)
x
w
CpCpL CpCL CpLL CpLM LLL LLM LLP LMP LMS LPS CpCO CpLO CLO LOL LOM LOP LOS MOS CpLLi CLLi LLLi LLiM LLiP LOO
526.85 554.90 582.96 611.01 639.06 667.12 695.17 723.23 751.28 779.33 637.05 665.10 693.16 721.17 749.22 777.28 805.37 833.33 663.09 691.09 719.19 747.25 775.26 803.36
0.0084 0.0148 0.0546 0.0688 0.1313 0.1111 0.0808 0.0492 0.0222 0.0090 0.0052 0.0400 0.0428 0.1275 0.0799 0.0494 0.0249 0.0072 0.0074 0.0079 0.0236 0.0155 0.0097 0.0088
0.0064 0.0119 0.0462 0.0610 0.1217 0.1075 0.0815 0.0516 0.0242 0.0101 0.0048 0.0386 0.0430 0.1335 0.0869 0.0558 0.0291 0.0087 0.0071 0.0079 0.0246 0.0168 0.0109 0.0102
a x:y, x = number of carbons (except carbons of glycerol) and y = number of double bonds. b Groups with a total triacylglycerol (TAG) composition lower than 0.005 mass fraction were ignored. c M = molar mass.
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narrow range of compositions, and the pseudo component approach is approximately valid. Tables 3 and 4 present the overall experimental composition and the phase compositions in the alcoholic and the oil phases, respectively, for the pseudoternary (absolute ethanol as solvent) and pseudoquaternary (aqueous ethanol as solvent) model systems at (303.2 ± 0.1) K. All compositions are expressed as mass fractions. Figures 1 and 2 show the experimental data and the calculated tie lines for the systems composed of (refined babassu oil + lauric acid + ethanol) with (0.1045 ± 0.0006) water mass fraction and (babassu oil + lauric acid + ethanol) with (0.2972 ± 0.0007) water mass fraction, respectively, both at (303.2 ± 0.1) K. The equilibrium diagram is plotted in rectangular coordinates. To represent the pseudoquaternary system in rectangular coordinates, ethanol + water were assumed to be a mixed solvent. In these figures, the mass fraction composition of the vegetable oil can be obtained by the difference.
It is observed that the addition of water to the solvent expanded the phase splitting region, which allowed the refining of highly acidic oils by solvent extraction. Furthermore, it can be seen that the addition of water to the solvent minimized the loss of neutral oil to the alcoholic phase and the loss of solvent to the oil phase (see the baseline in figures 1 and 2) because the water decreased the mutual solubility between the oil and the solvent. On the other hand, it is observed that the addition of water reduced the capacity of the solvent to extract the free fatty acids. These findings are better observed in figure 3, which presents the distribution of lauric acid and refined babassu oil in the oily and the alcoholic phases. It can be observed that solvents with water mass fractions up to 0.10 demonstrated similar capacities to extract the free fatty acids. In fact, the capacity of the solvent to extract lauric acid was reduced only when water was present in high quantities (above 0.1045 in mass fraction). However, the loss of neutral oil was
TABLE 3 Liquid–liquid equilibrium data for the system {refined babassu oil (1) + lauric acid (2) + ethanol (3)}, at (303.2 ± 0.1) K. OCa
a b c
OPb
APc
w1
w2
w3
w1
w2
w3
w1
w2
w3
0.5000 0.4944 0.4895 0.4875 0.4845
0.0000 0.0055 0.0105 0.0125 0.0154
0.5000 0.5001 0.5000 0.5000 0.5001
0.6760 0.6600 0.5955 0.5864 0.5490
0.0000 0.0048 0.0100 0.0114 0.0146
0.3240 0.3352 0.3945 0.4022 0.4364
0.2787 0.2841 0.3459 0.3599 0.3890
0.0000 0.0060 0.0115 0.0133 0.0162
0.7213 0.7099 0.6426 0.6268 0.5948
OC = overall composition. OP = oil phase. AP = alcoholic phase.
TABLE 4 Liquid–liquid equilibrium data for the system {refined babassu oil (1) + lauric acid (2) + ethanol (3) + water (4)}, at (303.2 ± 0.1) K. w4Sa
a b c d
OCb
OPc
APd
w1
w2
w3
w4
w1
w2
w3
w4
w1
w2
w3
w4
0.0557
0.5000 0.4946 0.4893 0.4795 0.4595 0.4394 0.4189
0.0000 0.0055 0.0107 0.0205 0.0405 0.0605 0.0804
0.4721 0.4721 0.4721 0.4721 0.4721 0.4722 0.4728
0.0279 0.0278 0.0279 0.0279 0.0279 0.0279 0.0279
0.8930 0.8839 0.8656 0.8593 0.8030 0.7649 0.7087
0.0000 0.0027 0.0089 0.0176 0.0357 0.0542 0.0691
0.0994 0.1064 0.1199 0.1176 0.1537 0.1692 0.2098
0.0076 0.0070 0.0056 0.0055 0.0076 0.0117 0.0124
0.0468 0.0520 0.0468 0.0558 0.0764 0.0924 0.0901
0.0000 0.0068 0.0126 0.0255 0.0492 0.0727 0.0913
0.8855 0.8648 0.8843 0.8555 0.8141 0.7847 0.7711
0.0677 0.0764 0.0563 0.0632 0.0603 0.0502 0.0475
0.1045
0.5000 0.4890 0.4795 0.4695 0.4396 0.4096 0.3796
0.0000 0.0105 0.0205 0.0305 0.0605 0.0904 0.1204
0.4477 0.4482 0.4477 0.4477 0.4477 0.4478 0.4477
0.0523 0.0523 0.0523 0.0523 0.0522 0.0522 0.0523
0.9300 0.9138 0.8940 0.8870 0.8343 0.7832 0.7191
0.0000 0.0087 0.0190 0.0271 0.0552 0.0830 0.1129
0.0621 0.0743 0.0778 0.0836 0.0998 0.1194 0.1501
0.0079 0.0032 0.0092 0.0023 0.0107 0.0144 0.0179
0.0173 0.0201 0.0211 0.0260 0.0387 0.0541 0.0762
0.0000 0.0105 0.0233 0.0330 0.0665 0.0993 0.1327
0.9067 0.8799 0.8326 0.8524 0.7822 0.7460 0.6901
0.0760 0.0895 0.1230 0.0886 0.1126 0.1006 0.1010
0.2029
0.4999 0.4945 0.4898 0.4695 0.4392 0.3994 0.3501
0.0000 0.0055 0.0105 0.0305 0.0603 0.1003 0.1500
0.3986 0.3986 0.3983 0.3985 0.3988 0.3988 0.3985
0.1015 0.1014 0.1014 0.1015 0.1017 0.1015 0.1014
0.9425 0.9399 0.9251 0.9013 0.8423 0.7848 0.6887
0.0000 0.0058 0.0110 0.0323 0.0646 0.1063 0.1559
0.0496 0.0467 0.0560 0.0543 0.0817 0.0922 0.1330
0.0079 0.0076 0.0079 0.0121 0.0114 0.0167 0.0224
0.0048 0.0046 0.0045 0.0089 0.0104 0.0290 0.0328
0.0000 0.0050 0.0095 0.0277 0.0554 0.0939 0.1441
0.7949 0.7755 0.7838 0.7602 0.7220 0.6887 0.6390
0.2003 0.2149 0.2022 0.2032 0.2122 0.1884 0.1841
0.2972
0.5001 0.4945 0.4695 0.4393 0.3970 0.3498
0.0000 0.0055 0.0305 0.0604 0.0997 0.1502
0.3513 0.3514 0.3514 0.3516 0.3537 0.3514
0.1486 0.1486 0.1486 0.1487 0.1496 0.1486
0.9562 0.9457 0.8975 0.8401 0.7628 0.6683
0.0000 0.0073 0.0411 0.0818 0.1346 0.1949
0.0390 0.0411 0.0538 0.0676 0.0878 0.1172
0.0048 0.0059 0.0076 0.0105 0.0148 0.0196
0.0014 0.0002 0.0011 0.0006 0.0010 0.0065
0.0000 0.0033 0.0187 0.0376 0.0662 0.1047
0.7029 0.6942 0.6970 0.6796 0.6500 0.6087
0.2957 0.3023 0.2832 0.2822 0.2828 0.2801
w4S = water mass fraction in the solvent. OC = overall composition. OP = oil phase. AP = alcoholic phase.
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a
pair ija
Ai /K
Aji/K
aij
12 13 14 23 24 34
7015.20 258.51 892.15 520.06 193.82 398.57
361.42 1244.50 3316.60 7117.00 3100.7 516.45
0.30 0.47 0.20 0.22 0.35 0.47
Refined babassu oil (1), lauric acid (2), ethanol (3), and water (4).
TABLE 6 Mean deviations in phase compositions.
FIGURE 1. System of (refined babassu oil (1) + lauric acid (2) + aqueous solvent) [ethanol (3) + water (4), where w4S = 0.1045], at (303.2 ± 0.1) K. j, Experimental and - - -, NRTL model.
a
w4Sa
Dw
0.00 0.0557 0.1045 0.2029 0.2972 Global deviation of the correlation
0.0084 0.0078 0.0085 0.0076 0.0083 0.0085
w4S = water mass fraction in the solvent.
highly suppressed by the addition of water to the solvent, which is desirable for this system (observe the high mutual solubility between the oil and the absolute ethanol in table 3). The ability of the NRTL model to satisfactorily describe the distributions of the fatty compounds between the liquid phases can also be observed in figure 3. Table 5 presents the NRTL model adjusted parameters. The deviations between the experimental and the calculated compositions in both phases were estimated according to equation (7) and are shown in table 6. Figures 4 and 5 show the partition coefficient of refined babassu oil (kOil) and lauric acid (kFFA), respectively, as a function of the acidity level in the oil phase (wOP FFA ). The distribution coefficient was calculated according to equation (8) FIGURE 2. System of (refined babassu oil (1) + lauric acid (2) + aqueous solvent) [ethanol (3) + water (4), where w4S = 0.2972], at (303.2 ± 0.1) K. j, Experimental and - - -, NRTL model.
FIGURE 3. Distribution diagram at (303.2 ± 0.1) K for systems of (babassu oil (1) + lauric acid (2) + aqueous solvent) [ethanol (3) + water (4)]: h, w4S = 0; j, w4S = 0.0557; N, w4S = 0.1045; r, w4S = 0.2029; d, w4S = 0.2972; and - - -, NRTL model.
OP ki ¼ wAP i =wi ;
ð8Þ
where ki represents the distribution coefficient of the fatty compound i, the oil or the free fatty acid; w represents the mass fraction; and the superscripts OP and AP stand for the oil and the alcoholic phases, respectively. Figures 4 and 5 also present distribution coefficient data related to other fatty systems, including cotton seed oil and linoleic acid at 298.2 K [20], rice bran oil and oleic acid at 298.2 K [10], soybean oil and linoleic acid at 323.2 K [23], as well as palm oil and palmitic acid at 318.2 K [19]. In figure 4, it is observed that the higher free fatty acid contents in the system resulted in a higher oil partition coefficient regardless of the oil type, which can be attributed to an increase in the mutual solubility of the oil and the solvent. However, the loss of neutral oil in the alcoholic phase was drastically suppressed by water in the solvent. On the basis of figure 4, one can estimate the influence of the carbon chain length of the triacylglycerol molecules on the solubility of the fatty system. The solubility of babassu oil in the alcoholic solvent was higher compared with that of cotton seed and rice bran oils, and such an effect cannot be explained by temperature alone (see figure 4a to c). Note that the systems composed of soybean oil and palm oil (d and e) were obtained at 323.2 K and 318.2 K, respectively, and that they exhibited lower solubilities than babassu oil.
É.C. D’Anton Reipert et al. / J. Chem. Thermodynamics 43 (2011) 1784–1790
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FIGURE 4. Distribution coefficients of oils: h, w4S = 0; j, w4S = 0.05; N, w4S = 0.10; r, w4S = 0.20; d, and w4S = 0.30. (a) Babassu, at 303.2 K (this work); (b) cotton seed, at 298.2 K [20]; (c) rice bran, at 298.2 K [10]; (d) soybean, at 323.2 K [23]; and (e) palm, at 318.2 K [19].
FIGURE 5. Distribution coefficients of free fatty acids: h, w4S = 0; j, w4S = 0.05; N, w4S = 0.10; r, w4S = 0.20; and d, w4S = 0.30. (a) Lauric acid, at 303.2 K (this work); (b) linoleic acid, at 298.2 K [20]; (c) oleic acid, at 298.2 K [10]; (d) linoleic acid, at 323.2 K [23]; and (e) palmitic acid, at 318.2 K [19].
The partitioning of the free fatty acids as a function of the acidity level in the oil phase (wOP FFA ) can be observed in figure 5. Regarding the behavior of the free fatty acids, it is reasonable to state that lauric acid was more soluble than other free fatty acids. Again, such an effect is not explained solely by temperature (in figure 5, observe the similarity among the results related to other free fatty acids at different temperatures, from 298.2 K to 323.2 K, for each water level in the solvent) [10,19,20,23]. Previous reports have shown that the partitioning of the free fatty acids is not significantly affected by the temperature of the solution [24,35], indicating that the high solubility of lauric acid can be explained by the fewer number of carbon atoms in the carbon chain (C12:0) as compared with palmitic (C16:0), oleic (C18:1), and linoleic (C18:2) acids.
4. Conclusions In the presented paper, experimental equilibrium data for systems containing refined babassu oil were measured at (303.2 ± 0.1) K. The results presented in this article demonstrate that the distribution coefficient of lauric acid and the mutual solubility of oil and the solvent (ethanol and water) were affected by the water content of the solvent. It was also observed that the carbon chain length of the fatty molecules (triacylglycerols and free fatty acids) influenced the solubility of the fatty system, regardless of the temperature of the process. The distribution coefficients of the free fatty acids, assumed to be lauric acid, and refined oil are required to properly design liquid–liquid extractors for oil deacidification processes and to
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construct equipment for solvent recovery. The estimated parameters of the NRTL model can be used to model and to simulate LLE and recovery processes. Acknowledgments The authors thank FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo – 09/17855-3, 08/56258-8), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), FINEP (Financiadora de Estudos e Projetos) and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for the financial support. References [1] R. Ceriani, F.R. Paiva, C.B. Gonçalves, E.A.C. Batista, A.J.A. Meirelles, J. Chem. Eng. Data 53 (2008) 1846–1853. [2] T. Fornari, S. Bottini, E. Brignole, J. Am. Oil Chem. Soc. 71 (1994) 391–395. [3] C. González, J.M. Resa, A. Ruiz, J.I. Gutiérrez, J. Chem. Eng. Data 41 (1996) 796– 798. [4] Z. Leibovitz, C. Ruckenstein, J. Am. Oil Chem. Soc. 60 (1983) 347A–351A. [5] J. Cvengros, J. Am. Oil Chem. Soc. 72 (1995) 1193–1196. [6] D. Swern, in: K.F. Mattil, F.A. Norris, A.J. Stirton (Eds.), Bailey’s Industrial Oil and Fat Products, Wiley, New York, 1964. [7] R. Antoniassi, W. Esteves, A.J.A. Meirelles, J. Am. Oil Chem. Soc. 75 (1998) 1411–1415. [8] K.J. Shah, T.K. Venkatesan, J. Am. Oil Chem. Soc. 66 (1989) 783–787. [9] C. Thomopoulos, Rev. Fran. des. Corps Gras. 18 (1971) 143–150. [10] C.E.C. Rodrigues, R. Antoniassi, A.J.A. Meirelles, J. Chem. Eng. Data 48 (2003) 367–373. [11] C.E.C. Rodrigues, P.A. Pessôa Filho, A.J.A. Meirelles, Fluid Phase Equilib. 216 (2004) 271–283. [12] C.E.C. Rodrigues, M.M. Onoyama, A.J.A. Meirelles, J. Food Eng. 73 (2006) 370– 378. [13] A.C. Bhattacharyya, S. Majumdar, D.K. Bhattacharyya, Oléagineaux 42 (1987) 431–433.
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JCT 10-406