Equilibrium, Kinetics, and Thermodynamics of Soybean Oil

Article pubs.acs.org/IECR

Equilibrium, Kinetics, and Thermodynamics of Soybean Oil Deacidification Using a Strong Anion Exchange Resin Taiana M. Deboni, Eduardo A. C. Batista, and Antonio J. A. Meirelles* Department of Food Engineering, University of Campinas, 13083-862 Campinas, São Paulo Brazil S Supporting Information *

ABSTRACT: This study investigated the adsorption kinetics, isotherms, and thermodynamic parameters of the removal of free fatty acids from soybean oil using the strong anion exchange resin Amberlyst A26 OH. The presence and type of organic solvents used in the solution and in the resin, due to its pretreatment, affected the reduction of acidity and the adsorption rate as well as its catalytic activity. Adsorption of free fatty acids was further studied in two systems involving the resin drying step and the adsorbate dissolved in either vegetable oil alone or vegetable oil with hexane. The fitting of pseudo-first-order and pseudosecond-order models showed high coefficients of determination. Langmuir, Freundlich, and Temkin isotherms could describe the equilibrium data. The adsorption in this study is a spontaneous and endothermic process. The reported results highlight that Amberlyst A26 OH has good adsorption capacity for the free fatty acids contained in vegetable oils.

1. INTRODUCTION Crude vegetable oils contain undesirable compounds that influence their stability and application, requiring purification steps.1 Among these undesirable compounds are free fatty acids (FFAs), which are more susceptible to oxidation and may affect product quality.2 A high FFA content is also harmful to biodiesel production with homogeneous basic catalysts. In this case, FFAs react with the catalyst to form soap; thus, the catalyst is consumed, and the process efficiency is reduced.3 In addition, the soap formed interferes with the phase separation of biodiesel and glycerin.4 The deacidification methods most commonly used in the vegetable oil industry are based on chemical and physical refining. However, alternative methods of deacidification have been investigated due to the disadvantages of the conventional methods employed at the industrial scale.2 Ion exchange resins have a high potential for application to various areas in aqueous5,6 and nonaqueous systems.7,8 These resins can also be used as an alternative method for removing FFAs from fatty systems. Cation exchange resins promote deacidification by catalyzing the esterification reaction between FFAs and an alcoholic solvent.9,10 In anion exchange resins, the removal of FFAs appears to occur by adsorption on the basic sites.11−14 An ion exchange equilibrium or a Lewis acid−base interaction have been proposed as reaction mechanisms, mainly depending on the functional group of the resin and on the system.11,13,14 The use of ion exchange resins containing basic sites for the deacidification of fatty systems has already been investigated in the literature and has recently attracted a great deal of attention.12−25 Amberlyst A26 OH resin is suitable for the adsorption of carboxylic acids for various purposes11,26−31 and for the removal of FFAs in fixed beds from different mixtures of vegetable oils with solvents19−22 and in batch containing only acidified oil as the liquid phase.23 However, in these studies with Amberlyst A26 OH resin, no equilibrium, kinetic, or thermodynamic data were reported on the removal of linoleic acid from soybean oil, an oil of great economic importance. © XXXX American Chemical Society

Moreover, no detailed investigation of the effect of organic solvents on the adsorption of FFAs from vegetable oils by ion exchange resins has been reported in the literature. Organic solvents may be present in the system to be deacidified either to improve the process or due to their use in resin pretreatment. The use of organic solvents together with lipid matter can decrease the viscosity of the medium and increase the diffusion within the polymer pores and therefore the accessibility to active sites. Lipophilic solvents are more suitable for solubilization.17 Furthermore, in the case of the extraction of vegetable oils with solvents, the miscella could be pumped to the deacidification step without previous removal of the solvent. In this context, there are solvents such as hexane, which is commonly used for oil leaching, and also alternative solvents, such as alcohols including ethanol and isopropanol, that have been well studied.32−36 Furthermore, organic solvents are often used in the pretreatment or regeneration of ion exchange resins, with or without drying, in processes involving nonaqueous systems and low-polarity compounds.7,8,11−13,15,29,30,37−39 Polar solvents, such as short-chain alcohols, are frequently used for displacing water. However, depending on the type of solvent used and the resin pretreatment, it is possible for other reactions to occur simultaneously with deacidification. Recently, the use of anion exchange resins as heterogeneous catalysts for transesterification in systems containing oil and alcoholic solvents has been extensively studied.40−42 Therefore, when alcoholic solvents are used, it is important to evaluate the behavior of FFA removal together with the formation of fatty acid alkyl esters. This work aimed to study the removal of FFAs, especially linoleic acid, from degummed soybean oil with Amberlyst A26 Received: July 20, 2015 Revised: October 15, 2015 Accepted: October 17, 2015

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DOI: 10.1021/acs.iecr.5b02653 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

chromatograph (HPLC, model LC-20AT, Shimadzu, Japan) equipped with a 100 Å Phenogel size exclusion column (300 mm × 7.8 mm ID, 5 μm; Phenomenex, USA) and a refractive index detector (model RID-10A, Shimadzu, Japan). The temperature of the column oven (CTO-10AS VP, Shimadzu, Japan) was 40 °C. The injection system was used with an autosampler (SIL-20A, Shimadzu, Japan) to inject 20 μL. Elution was carried out in isocratic mode using a mobile phase composed of a toluene solution with 0.25% acetic acid (v/v) at a flow rate of 1 mL/min.46,47 Compounds were identified by comparison with external standards and quantified by calibration curves with the reagent of the system and standards of fatty acid alkyl esters, ethyl linoleate and isopropyl oleate. Considering the relatively high molecular weight of linoleic acid, compared to water and organics solvents, and the possible decrease of the liquid solution mass caused by FFA adsorption, the experimental results are presented on a FFA-free basis. The initial liquid phase concentrations were recalculated considering the total volatiles carried by the resins into the cell. 2.2.1. Effect of Organic Solvents. The kinetics of acidity reduction and the formation of fatty acid alkyl esters were investigated for the five systems outlined in Table 1. The resin was conditioned with the solvent by passing 5 bed volumes of solvent at 2 bed volumes/h in a column packed with the resin.

OH resin. First, different systems were evaluated by varying the type and the presence of organic solvent in the solution as well as in the resin as a result of its pretreatment. The kinetics of acidity reduction and formation of fatty acid alkyl esters were investigated in these systems. Afterward, the resin pretreatment was specified to avoid the presence of excess alcohol, and the adsorption of FFAs was further investigated for systems containing only oil or oil and hexane. The kinetics and isotherms of adsorption were evaluated for different temperatures, and the corresponding thermodynamic parameters (Gibbs free energy, enthalpy, and entropy) were determined. The morphologies of the resin surface were evaluated by scanning electron microscopy. The results reported in this work allow a better understanding of the influence of organic solvents on the adsorption of fatty acids by strong anion exchange resins and offer quantitative data related to the kinetics, equilibrium, and thermodynamic parameters of this process.

2. MATERIALS AND METHODS 2.1. Materials. Degummed soybean oil was supplied by Cargill Agrı ́cola S/A (Brazil). In industrial practice, soybean oil is degummed and subsequently deacidified by caustic refining; therefore, use of the degummed oil allows investigation of an alternative deacidification process in conditions more similar to those observed in large-scale operations. Commercial linoleic acid (Sigma-Aldrich, USA) was added to the oil to adjust the acidity of the solution for the experiments with a higher initial content of FFAs (4%). Hexane with purity ≥96% and isopropanol of analytical grade were purchased from Merck (Germany). Toluene (99.9% purity) was obtained from Sigma-Aldrich (USA), and acetic acid (99.8% purity) was obtained from Merck (Germany). The solvents used in the resin pretreatment and chemical analyses were obtained from Synth (Brazil) and were of analytical grade. The strong anion exchange resin Amberlyst A26 OH is a trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow and was obtained from Coremal (Brazil). The resin characteristics are specified in Table S1 (see the Supporting Information).43 The original resin moisture was determined to be 0.744 ± 0.002 (g/g) on a wet basis. 2.2. Experimental Procedure. The fatty acid composition of degummed soybean oil and commercial linoleic acid used in this work were analyzed by gas chromatography of fatty acid methyl esters according to the official AOCS method (Ce 1f96).44 The fatty acid compositions of degummed soybean oil are shown in Table S2 (see the Supporting Information), with linoleic acid as the major fatty acid. The fatty acid composition of commercial linoleic acid is shown in Table S3 (see the Supporting Information). The resin’s total volatile content (water + organic solvents) was measured by drying samples of approximately 3 g in a circulating air oven (model MA 035, Marconi, Brazil) at 110 °C until a constant weight was obtained. The water content in the resin was determined by Karl Fischer titration (model KF 701, Metrohm, Switzerland) connected to an oven (model Thermoprep KF 832, Metrohm, Switzerland). An automatic titrator (model 808 Titrando, Metrohm, Switzerland) was used to determine the FFA content using the official method 2.201 IUPAC.45 The average molar mass of commercial linoleic acid was used to express the acidity results. The contents of fatty acid alkyl esters and triacylglycerols (TAG) were evaluated using a high performance liquid

Table 1. Different Systems Tested in Terms of Resin Pretreatment and Solution Composition system

resin pretreatment

1 2 3

conditioned with ethanol in a fixed bed conditioned with ethanol in a fixed bed + drying conditioned with ethanol in a fixed bed + conditioned with hexane in a fixed bed conditioned with ethanol in a fixed bed + drying + soaking with hexane conditioned with isopropanol in a fixed bed

4 5

solution composition acidified oil acidified oil acidified oil + hexane acidified oil + hexane acidified oil + isopropanol

The resin was dried at 50 °C until a constant weight was obtained. However, not all of the resin’s total volatile content could be evaporated under these conditions, and a remaining total volatile content of 0.246 ± 0.002 g/g was determined. The residual water content of the resin was 0.156 ± 0.005 g/g. Thus, most of the remaining total volatile content corresponds to water, but a residual alcoholic content was still present. In systems with wet resin, the excess solvent was removed by filtration. The moisture contents of systems 1, 3, 4, and 5 were 0.810 ± 0.001, 0.742 ± 0.002, 0.537 ± 0.005, and 0.803 ± 0.003 g/g, respectively, on a wet basis. To obtain the data, the following variables were fixed: a dry resin loading (weight of dry resin/weight of solution) equal to 3%, an initial acidity of the solution equal to 4%, and a temperature of 50 °C. In systems with solvent in the miscella, the oil content in the solution was fixed at 50%. The experiments were performed in a hermetically sealed glass cell of 1 L surrounded by a jacket with water circulation from a thermostatic bath (model 12101-15, Cole Parmer, USA) to maintain the temperature. Agitation was performed at 700 rpm with a suspended magnetic stirrer (Trevisan Tec, Brazil) to avoid resin breakage. Solution aliquots were collected at predetermined times. FFA removal of the solution was determined with respect to the initial acidity of the solution. The ester yield was B


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solvent in the miscella and in the resin as a result of its pretreatment. First, the removal of FFA was evaluated as a function of contact time (Figure 1), maintaining the same mass ratio of acid to resin (dry basis) at 50 °C.

determined relative to the initial amount of neutral oil. The change in the TAG content was studied as a function of contact time for systems 2 and 4. 2.2.2. Kinetics, Equilibrium, and Thermodynamic Parameters. In addition to the experiments mentioned above, FFA adsorption kinetics were also evaluated for systems 2 and 4 at temperatures of 25 to 35 °C, following the same scheme and fixed variables indicated above. The FFA amount adsorbed at each time was determined through mass balance. The data were modeled with pseudo-first-order and pseudo-second-order kinetic equations and the Weber-Morris intraparticle diffusion model. The equilibrium data were obtained using hermetically sealed, jacketed glass cells of 50 mL. The system was agitated at 550 rpm with a suspended magnetic stirrer, and the temperature was maintained by coupling with a thermostatic bath (model 12101−15, Cole Parmer, USA). Isotherms were obtained at 25, 35, and 50 °C for both systems (with and without hexane). The dry resin loading (weight of dry resin/ weight of solution) was varied between 0.5 to 9%. The initial acidity of the solution was fixed at 4%, and, when present, the hexane content in the miscella was fixed at 50%. The system was left in contact until equilibrium, when the acidity of the solution remained constant. The amount of FFA adsorbed was determined through mass balance. Langmuir, Freundlich, and Temkin adsorption isotherms were fitted to the experimental data. Thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy were determined using data obtained for the adsorption isotherms at each temperature. Resin morphologies were observed on a scanning electron microscope (model Leo 440i, LEO Electron Microscopy/ Oxford, England). The samples had previously been vacuumdried and sputtered with gold particles. 2.2.3. Uncertainties of Variables. Determination of the total volatile content of the resin and the FFA concentration in the collected samples and the chromatographic analyses were performed at least in triplicate. The uncertainties of these measurements were evaluated on the basis of the obtained standard deviations. On the other hand, the uncertainties associated with the FFA removal, the yield of fatty esters, and the FFA amount in the resin phase were calculated by error propagation. In the equilibrium runs (isotherms), additional experiments were performed to check the uncertainties related to the resinphase concentration. For each isotherm, the experiment containing a dry resin loading of 5% was carried out in triplicate, and the corresponding standard deviations of the solid phase composition were calculated. These standard deviations generated coefficients of variation within a range of 0.6−2.6%. The coefficients of variation obtained by error propagation for the same experimental runs varied within a range of 0.3−1.9%, only slightly lower than those obtained by performing the whole experiments in triplicate. The coefficients of variation for the entire set of equilibrium experiments, estimated by error propagation, varied from 0.3 to 5.4%. This result confirms the good quality of the experimental data measured in the present work.

Figure 1. FFA removal as a function of time for different systems with a dry resin loading of 3% and an initial acidity of 4% at 50 °C. (▼) Resin conditioned with ethanol + oil, (■) resin conditioned with ethanol and drying + oil, (◆) resin conditioned with ethanol and hexane + miscella (oil + hexane), (●) resin conditioned with ethanol, drying and soaking with hexane + miscella (oil + hexane), and (▲) resin conditioned with isopropanol + miscella (oil + isopropanol).

For low-polarity systems, despite some controversy on the subject,16 it was reported that excess water initially present within the resin pores can cause problems, such as difficulties in adsorbate diffusion within the resin and undesired side reactions.48,49 Thus, polar solvents, such as short-chain alcohols, are frequently used in resin pretreatment to displace water. Furthermore, a nonuniform change in resin appearance was observed when resins were dried without previous washing with alcohol. Martinola and Meyer50 reported that this change can occur when drying the resin in its hydrated form depending on the characteristics of the resin. They also reported a collapse of the resin pore structure, a problem that can be avoided by washing the resin before drying with isopropanol or heptane. In the present work, the resin was initially washed with an alcoholic solvent to remove organic extractives and displace water. Acidity reduction occurred more rapidly in systems containing solvent in the medium and/or if the resin was wet. In systems where the solution contained only acidified oil, adsorption was studied using resin conditioning with ethanol with and without a drying step. When the resin was not subjected to drying, the adsorption reached equilibrium in approximately 5 h, whereas the removal of FFAs with drying occurred more gradually, stabilizing in only approximately 14 h. In systems with hexane in the miscella, the resin underwent a further washing step with hexane after washing with ethanol. Many studies reported in the literature used previous washing with alcoholic solvents when using less polar solvents.7,29,37−39 The other pretreatment used was washing with ethanol and drying, and thereafter, the resin can be soaked with hexane to increase its swelling. Without drying, the FFA removal was very rapid, reaching equilibrium slightly after 2 h. In the case of drying and subsequent soaking in hexane, removal started to

3. RESULTS 3.1. Effect of Organic Solvents. A kinetic study was performed with the different systems described in section 2.2.1 to evaluate the influence of the presence and type of organic C


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presence of certain acidity.55 Conversely, other authors have found increasing catalytic activity in the presence of FFAs.56 Thus, the formation of fatty acid alkyl esters was also evaluated in the systems studied in the present work. Figure 2

settle at approximately 5 h, with a small additional removal later. In the system with isopropanol in the miscella, the resin was used after washing with isopropanol, and the acidity reduction also stabilized at approximately 2 h. Thus, when the resin was wet and solvent was present in the solution, the adsorption was faster, attaining similar rates of adsorption even for different types of solvent in the miscella and in the resin pretreatment. These results agree with the findings of Eychenne and Mouloungui,17 who suggested that the use of solvents to dissolve the oil can decrease the viscosity of the medium and increase diffusion into the polymer. However, the longer time required to reach equilibrium in systems in which the resin was subjected to a drying step may be due to low resin swelling and difficult rehydration with nonpolar solvents. Pietrzyk51 reports that the ion exchange rate-process or the penetration of the solute into the resin may be decreased when the resin is not swollen or is only partially swollen. It was observed, in general, a greater removal of FFAs in systems without resin drying. This behavior may be associated with less resin swelling or a change in active sites upon drying. However, this behavior was not applicable to the system with isopropanol, suggesting that the type of organic solvent may also affect the reduction of acidity. Furthermore, systems containing hexane in the miscella generated lower FFA removal values compared to the corresponding systems without the addition of this solvent in the miscella. Although the presence of the solvent may increase the accessibility to active sites, and thus the process rate, the composition of the medium in which the adsorption occurs can change the ability to remove FFAs. This change may be occurring due to the differences in the adsorption associated with the medium’s influence on the dissociation of active sites and FFAs, or even due an additional adsorption by physical interaction. Moreover, the approximation of the solute to the adsorbent can be affected by differences in polarity of the solution in the liquid phase and within the resin’s porous structure, especially due to the amphiphilic character of FFAs. The nature of the solvent affects the solubility, dissociation, and solvation of the solute and the behavior of the ion exchanger.52 For species with amphiphilic character, a more polar environment inside the resin can be beneficial until a limit, at which the species is still soluble and has an affinity and preference for the medium that occurs within the resin.53 Dı ́az and Brito14 evaluated the acidity reduction in oils with oleic acid using Dowex Monosphere 550A with and without the addition of methanol in the solution. However, the pretreatment of the resin was not described, and the adsorption kinetics were not evaluated. The authors reported less reduction for the system with added alcohol in the solution, similar to that obtained in the present work when the solution was composed of isopropanol. Nevertheless, together with the acidity reduction, the formation of new compounds in the system must be investigated. In the presence of oil and alcoholic solvent, anion exchange resin acts as a catalyst for transesterification.41,42 However, short-chain alcohols are commonly used for resin pretreatment. In addition, their use as solvent for oil extraction from solid matrices is usually proposed in the literature.34−36 Shibasaki-kitakawa et al.54 reported that a resin’s catalytic activity could decrease due to occupation of the active sites by fatty acids, although catalysis occurs despite the

Figure 2. Yield of fatty acid alkyl esters relative to the initial neutral oil content as a function of time for the different systems with a dry resin loading of 3% and an initial acidity of 4% at 50 °C. (▼) Resin conditioned with ethanol + oil, (◆) resin conditioned with ethanol and hexane + miscella (oil + hexane), and (▲) resin conditioned with isopropanol + miscella (oil + isopropanol).

shows the yield of ethyl or isopropyl esters of fatty acids formed relative to the initial amount of neutral oil. The resin catalyzes the transesterification reaction together with removal of FFAs in the presence of alcohol. The formation of esters occurs immediately at the beginning of contact with the resin such that the acid adsorption and catalysis of the transesterification reaction occur simultaneously. Even when ethanol is only used in resin pretreatment and is not eliminated by resin drying, ester formation occurs. Note that further resin washing with hexane after ethanol washing did not completely remove the ethanol present inside the resin. In fact, this type of system generated the highest yield of esters (Figure 2). This may be due to the greater access to active sites provided by blends of hexane with oil compared to pure oil and also to a closer approximation between ethanol molecules and oil due to the use of a cosolvent. Ren et al.42 and Kim et al.57 obtained good performance using hexane as a cosolvent in transesterification by heterogeneous catalysis. Decreased ester formation was observed in the system with isopropanol. In fact, the type of alcohol may affect the transesterification reaction.58 Marchetti and Errazu56 studied biodiesel production with Dowex Monosphere 550A using acidic oils and obtained an increase in the production of ethyl esters with an increasing initial concentration of FFAs. Jamal et al.59 studied the methanolysis of soybean oil with and without oleic acid using Amberlyst A26 OH resin. The authors reported an increase in the reaction rate of methanol consumption in the presence of FFAs and justified this behavior based on the facilitation of TAG migration to the surface of the resin from the lowered surface hydrophilicity due to the adsorption of FFAs. Despite this, many authors agree that the removal of FFAs occurs because of adsorption on the resin’s basic sites rather than the esterification of FFAs, with the latter occurring only with acid D


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Industrial & Engineering Chemistry Research catalysts.12,14,59 In contrast to prior work with Amberlyst A26 OH, the present paper systematically investigated the removal behavior of FFAs together with the formation of alkyl esters. Acidity reduction in systems with catalytic behavior occurred in a satisfactory manner, reaching equilibrium more quickly. The medium composition affected the reduction of acidity as well as the formation of fatty acid alkyl esters. Thus, considering the FFA removal process as a prestep for biodiesel production, the presence of alcohol as a solvent improves process rates and simultaneously contributes to the formation of alkyl esters. Deboni et al.19 reported good efficiencies during the removing of FFAs from miscellas composed of soybean oil and isopropanol using Amberlyst A26 OH resin in a fixed bed. Cuevas et al.20 reported similar results for the deacidification of miscellas composed of palm oil and n-propanol using the same resin. Nevertheless, the formation of alkyl esters was not evaluated in these works. However, to use the deacidified oil for edible purposes, it is necessary to avoid the presence of alcoholic solvents in the solid and liquid phases or to include an additional step for removing the formed compounds. In systems for which the resin pretreatment included a drying step and the liquid phase was miscella oil + hexane or only oil, no ethyl ester formation was detectable by the analysis used. Despite the drying step, a residual alcoholic content was still present within the resin pores because the use of extreme temperatures during solvent evaporation was not recommended. For this reason, it is still important to check whether there is any alkyl ester formation. On the other hand, solvents such as hexane are more stable from a chemical point of view, not probably reacting under the resin’s catalytic action. Moreover, the deacidification of the miscella of oil and hexane with a sodium hydroxide solution is already used industrially.2 However, this solvent can be commercialized in various degrees of purity,32 and the presence of other chemical components should therefore be observed. Further investigation was conducted for both systems that included resin pretreatment by drying after ethanol washing. Figure 3 shows the TAG content of the liquid phase as a

function of contact time. This study was performed to verify the possible decrease in the TAG portion by hydrolysis. ShibasakiKitakawa et al.54 suggested that the drop in catalytic activity of the resin may be due to the direct reaction of hydroxyl ions with the oleic acid groups of triolein, diolein, and monoolein. Jamal et al.59 discussed the hydrolysis of TAG caused by water in the system. Nevertheless, the TAG content showed no decreasing trend under the conditions used in the present study. 3.2. Adsorption Kinetics. The FFA adsorption kinetics were studied for systems 2 and 4 at three temperatures (25, 35, and 50 °C), keeping the dry resin loading (3%) and the initial acidity of the solution (4%) fixed. The adsorption capacities of FFAs by Amberlyst A26 OH as a function of time are shown in Figures 4 and 5 for the two systems. The previously mentioned

Figure 3. Triacylglycerol content as a function of time for systems 2 and 4 with a dry resin loading of 3% and an initial acidity of 4% at 50 °C. (■) Resin conditioned with ethanol and drying + oil and (●) resin conditioned with ethanol, drying and soaking with hexane + miscella (oil + hexane).

Figure 5. Adsorption kinetics for the system with the resin conditioned with ethanol, drying and soaking with hexane + miscella (oil + hexane), with a dry resin loading of 3% and an initial acidity of 4% at different temperatures: (■) 25 °C, (●) 35 °C, and (▲) 50 °C. () Pseudo-first-order model. (----) Pseudo-second-order model.

Figure 4. Adsorption kinetics for the system with resin conditioned with ethanol and drying + oil, with a dry resin loading of 3% and an initial acidity of 4% at different temperatures: (■) 25 °C, (●) 35 °C, and (▲) 50 °C. () Pseudo-first-order model. (----) Pseudo-secondorder model.

E


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Table 2. Adsorption Kinetics Parameters: Resin Conditioned with Ethanol and Drying + Oil (System 2) and Resin Conditioned with Ethanol, Drying and Soaking with Hexane + Miscella (Oil + Hexane; System 4) system 2 qe,expa pseudo-first-orderb

pseudo-second-orderc

intraparticle diffusiond

qe k1 × 103 R2 qe k2 × 106 R2 kid1 C1 R2 kid2 C2 R2 kid3 C3 R2

system 4

25 °C

35 °C

50 °C

25 °C

35 °C

50 °C

763.74 ± 2.73 712.57 ± 10.42 3.07 ± 0.12 0.9933 918.10 ± 11.76 3.20 ± 0.15 0.9978 24.27 ± 0.81 −13.48 ± 15.32 0.9846 8.29 ± 0.65 424.90 ± 20.79 0.9821

825.94 ± 10.72 802.64 ± 16.60 3.58 ± 0.23 0.9863 991.20 ± 22.73 3.76 ± 0.34 0.9925 28.56 ± 0.31 −1.10 ± 4.27 0.9992 13.12 ± 1.85 385.00 ± 51.24 0.9617 4.39 ± 1.23 646.20 ± 42.20 0.9274

890.79 ± 8.40 888.67 ± 8.76 5.59 ± 0.22 0.9909 1039.97 ± 11.29 6.58 ± 0.35 0.9953 39.65 ± 1.26 8.24 ± 17.40 0.9920 14.28 ± 2.81 494.50 ± 67.06 0.9282 2.65 ± 2.24 804.70 ± 69.35 0.3073

744.20 ± 10.73 708.65 ± 9.91 11.31 ± 0.79 0.9768 780.48 ± 3.32 22.00 ± 0.61 0.9989 43.12 ± 2.87 29.18 ± 28.75 0.9825 11.45 ± 2.04 455.30 ± 37.02 0.9404 3.16 ± 0.86 634.50 ± 24.65 0.7300

793.00 ± 15.65 764.64 ± 6.08 16.26 ± 0.85 0.9874 819.31 ± 4.24 34.00 ± 1.52 0.9971 58.88 ± 3.99 15.81 ± 30.92 0.9909 13.74 ± 1.11 510.10 ± 16.64 0.9871 1.80 ± 0.54 726.80 ± 14.39 0.5609

825.27 ± 12.15 822.30 ± 4.50 18.14 ± 0.60 0.9965 880.90 ± 9.43 36.00 ± 3.15 0.9923 70.17 ± 0.99 1.50 ± 6.28 0.9998 17.80 ± 3.46 528.80 ± 46.37 0.9299 1.58 ± 0.08 786.50 ± 2.03 0.9861

qe,exp (mg acid/g dry resin) and uncertainties evaluated by error propagation. bqe (mg acid/g dry resin) and k1 (min−1). cqe (mg acid/g dry resin) and k2 (g dry resin/mg acid·min). dqe = kidt0.5 + Ci, where Ci (mg acid/g dry resin) is the intercept related to the boundary layer thickness and kid (mg acid/g dry resin·min0.5); when Ci = 0, this equation reduces to eq 3. a

behavior obtained at 50 °C was extended to the other temperatures studied. The curves obtained for the system with hexane showed that the amount of solute adsorbed at the beginning increased rapidly with time, with only a small additional adsorption toward the end of the process. For the system without the addition of solvent, a more gradual increase in adsorption over time was observed. Three models were used to describe the adsorption kinetics: pseudo-first-order and pseudo-second-order rate equations and the Weber-Morris intraparticle diffusion model. The expression of Lagergren’s first-order rate equation is given in eq 1.60,61 To distinguish kinetic equations based on the adsorption capacity of solids rather than the concentration of the solution, Lagergren’s first-order rate equation has been called a pseudo-first-order model.61−63

qt = qe(1 − e−k1t )

t.64 The plot goes through the origin if intraparticle diffusion is the only rate-limiting step.65 qt = k idt 0.5

where kid is the intraparticle diffusion rate constant. The fits of the pseudo-first-order and pseudo-second-order models are shown in Figures 4 and 5. The kinetic parameters determined are shown in Table 2. High coefficients of determination were obtained for both models. In general, the pseudo-second-order model resulted in slightly larger coefficients of determination. However, the amounts of solute in the solid phase at equilibrium (qe) were closer to the experimental values for the pseudo-first-order equation. The experimental qe values were obtained independently by measuring the adsorption isotherms. Other studies involving FFA adsorption on anion exchange resins also found a good fit for these models. Jamal and Boulanger12 evaluated the adsorption of oleic acid from soybean oil in mixed-bed resins. In this study, high correlation coefficients were found for three kinetic models (pseudo-firstorder, pseudo-second-order and modified second-order) in the adsorption with Amberlite MB-150 resin. For the Dowex Monosphere MR-450 UPW resin, a better fit was obtained using the pseudo-first-order model, a result that was also confirmed in a later work by Jamal et al.25 for the most favorable conditions studied. Ilgen23 used the pseudo-first-order and pseudo-second-order kinetic models to describe the adsorption kinetics of oleic acid from sunflower oil on Amberlyst A26 OH resin and reported a better fit for the pseudo-second-order model. Maddikeri et al.13 reported a good fit of the pseudo-first-order model to the experimental data of the adsorption of stearic and oleic acids from sunflower oil on Indion 860 resin. Du et al.18 studied the adsorption of FFAs from adlay seed miscella with LSD-263 resin and reported higher regression coefficients of the pseudo-second-order equation model. The parameters for both models indicate an increasing trend of the amount of adsorbed solute at equilibrium and of the rate

(1)

where qt and qe are the amounts of solute in the solid phase (mg acid/g dry resin) at time t (min) and at equilibrium, respectively, and k1 is the rate constant of the first-order adsorption (min−1). Equation 2 expresses the equation of the pseudo-secondorder rate model.61 qt =

qe 2k 2t 1 + qek 2t

(3)

(2)

where qt and qe are the amounts of solute in the solid phase (mg acid/g dry resin) at time t (min) and at equilibrium, respectively, and k2 is the constant (g dry resin/mg acid·min). In the same way, the denomination of this model as a pseudosecond-order equation is used to distinguish equations based on the solution concentration from those based on the adsorption capacity of solids.61−63 The intraparticle diffusion model refers to the theory proposed by Weber and Morris, where the solute uptake varies almost proportionally with t0.5 rather than with the contact time F


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Industrial & Engineering Chemistry Research constant with increasing temperature. Malamis and Katsou66 described how the kinetics and equilibrium of adsorption can be affected by the temperature increase due to the increase in kinetic energy, which facilitates access to active sites, increases the surface activity of the adsorbent and decreases the mass transfer resistance. Jamal et al.25 also observed a positive impact of temperature on the rate constants of the model with best fit for FFA adsorption using Dowex monosphere MR-450 UPW mixed-bed resin. The same behavior was observed by Du et al.18 in the adsorption of FFAs onto LSD-263 resin. Although the resin pretreatment differs slightly for the two systems, the same experimental conditions were used in both cases to compare the models’ parameters. The system with the addition of hexane presented rate constants higher than those of the system without solvent, confirming the characteristic behavior observed at different temperatures for each system. The pseudo-first and pseudo-second-order equations are classified as adsorption reaction models deduced from chemical reaction kinetics and are based on the whole process of adsorption without considering the sequence of steps involved in the adsorption diffusion models.65 In this work, one diffusion model was also studied. The fit of the intraparticle diffusion model is shown in Figure 6. The plots are not linear over the

results suggest that intraparticle diffusion was not the sole ratecontrolling step even though it was involved in the adsorption process.65 3.3. Adsorption Isotherms. Adsorption isotherms for both systems at the three temperatures studied (25, 35, and 50 °C) are shown in Figures 7 and 8. For the construction of each adsorption isotherm, the dry resin loading (weight of dry resin/ weight of solution) was varied between 0.5 to 9%.

Figure 7. Adsorption isotherms for the system with resin conditioned with ethanol and drying + oil, with an initial acidity of 4% at different temperatures: (■) 25 °C, (●) 35 °C, and (▲) 50 °C. () Langmuir, (---) Temkin, and (−·−) Freundlich.

Figure 6. Intraparticle diffusion plots for adsorption in the system with the resin conditioned with ethanol and drying + oil (filled markers) and with the resin conditioned with ethanol, drying and soaking with hexane + miscella (oil + hexane) (open markers). The dry resin loading was 3% with an initial acidity of 4% at different temperatures: (■ or □) 25 °C, (● or ○) 35 °C, and (▲ or Δ) 50 °C.

entire time range, indicating that more than one step takes place. This behavior has been observed by many authors, reporting that the existence of intersecting lines depends on the mechanism. The first portion is attributed to the boundary layer diffusion of solute molecules or to the diffusion of adsorbate through the solution around the external adsorbent surface. The second part represents the gradual adsorption stage in which the rate-limiting step is intraparticle diffusion. The third portion is related to the final equilibrium stage where the intraparticle diffusion slows down due to the extremely low adsorbate concentration in the solution.67−69 As observed in Figure 6, the first step was especially faster in the system with hexane. Table 2 shows the corresponding model parameters. In the present study, no line passes through the origin. In this way, the

Figure 8. Adsorption isotherms for the system with resin conditioned with ethanol, drying and soaking with hexane + miscella (oil + hexane), with an initial acidity of 4% at different temperatures: (■) 25 °C, (●) 35 °C, and (▲) 50 °C. () Langmuir, (---) Temkin, and (−·−) Freundlich.

As expected, the reduction in acidity was greater when the resin loading was increased. In fact, in experiments with higher resin loading, an acidity reduction of approximately 90% was observed in relation to the initial acidity (4%). Dı ́az and Brito14 studied the FFA adsorption on Dowex Monosphere 550A and reported the importance of the amount of resin in achieving the required final acidity. G


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Industrial & Engineering Chemistry Research Table 3. Adsorption Isotherms Parameters: Resin Conditioned with Ethanol and Drying + Oil (System 2) and Resin Conditioned with Ethanol, Drying and Soaking with Hexane + Miscella (Oil + Hexane; System 4) system 2 Langmuira

Freundlichb

Temkinc

qm b R2 kf n R2 BT AT R2

system 4

25 °C

35 °C

50 °C

25 °C

35 °C

50 °C

1473.99 ± 78.94 0.071 ± 0.009 0.9803 202.40 ± 17.77 2.11 ± 0.13 0.9812 337.44 ± 18.78 0.64 ± 0.09 0.9788

1515.30 ± 68.09 0.078 ± 0.009 0.9837 243.09 ± 24.08 2.30 ± 0.17 0.9743 349.19 ± 20.47 0.69 ± 0.10 0.9798

1522.19 ± 42.86 0.102 ± 0.008 0.9914 282.67 ± 18.37 2.40 ± 0.12 0.9854 342.76 ± 12.06 0.95 ± 0.09 0.9914

1404.92 ± 24.44 0.057 ± 0.002 0.9691 130.67 ± 17.44 1.76 ± 0.13 0.9701 398.30 ± 12.39 0.33 ± 0.02 0.9933

1415.27 ± 20.76 0.069 ± 0.002 0.9781 171.98 ± 20.60 1.97 ± 0.15 0.9694 370.42 ± 16.15 0.45 ± 0.04 0.9869

1422.28 ± 62.40 0.102 ± 0.013 0.9786 262.74 ± 15.46 2.40 ± 0.11 0.9889 317.53 ± 14.35 0.96 ± 0.12 0.9859

qm (mg acid/g dry resin) and b (mg acid/g non-acid components)−1. bkf ((mg acid/g dry resin)·(g non-acid components/mg acid)1/n). cBT (mg acid/g dry resin) and AT (mg acid/g non-acid components)−1. a

demonstrated good adsorption capacity in the systems studied in this work. The Freundlich isotherm is shown in eq 5.70 This model assumes a heterogeneous surface energy, where molecules first occupy the stronger binding sites and the binding strength decreases with the increasing degree of site occupation.72

Temperature also affects the behavior of isotherms, showing a trend of increased adsorption capacity. The resin adsorption capacity was slightly higher in the system without hexane. As previously mentioned, the composition of the medium in which the adsorption occurs can change the removal of FFAs. The results obtained for FFA adsorption were correlated using well-known models as the Langmuir, Freundlich and Temkin isotherms to quantify and compare the performance of adsorption in different conditions and systems. The Langmuir isotherm is shown in eq 4.70 This model assumes a homogeneous structure of the adsorbent, where all sites are identical and equivalent in energy and adsorption occurs in a monolayer. Furthermore, an adsorption limit given by (qm) is considered, and there is no interaction between the adsorbed molecules in adjacent sites.71

qe =

qe = k f Ce1/ n

where qe (mg acid/g dry resin) is the amount of solute in the solid phase, Ce (mg acid/g non-acid components) is the amount of solute in the liquid phase, kf ((mg acid/g dry resin)· (g non-acid components/mg acid)1/n) is the isotherm constant related to the adsorption capacity and 1/n measures the adsorption intensity or surface heterogeneity. The model fitting is also shown in Figures 7 and 8, and the parameters are given in Table 3. The values of kf also showed an increasing trend with temperature. The values of n were greater than 1, indicating conditions favorable to adsorption.73 The Temkin isotherm model (eq 6) takes into the account adsorbent−adsorbate interactions and considers that the heat of adsorption of all molecules in the layer will decrease linearly with coverage resulting from adsorbent−adsorbate interactions.6,72

qmbCe 1 + bCe

(5)

(4)

where qe (mg acid/g dry resin) is the amount of solute in the solid phase, Ce (mg acid/g non-acid components) is the amount of the solute in the liquid phase, and qm (mg acid/g dry resin) and b (mg acid/g non-acid components)−1 are Langmuir constants related to the adsorption capacity and rate of adsorption, respectively. The obtained curves are also shown in Figures 7 and 8, and the parameters are given in Table 3. There is a trend of increasing b and qm with temperature in both systems, indicating the positive effect of temperature on adsorption. The adsorption capacity of the resin can be converted into a wet basis, as is usually reported in the literature, taking into account the original resin moisture content.11 In this case, qm values found for the two systems ranged from 359.84 to 389.88 mg/g (wet basis). Other studies that investigated FFA adsorption on Amberlyst A26 OH resin determined values between 476.19 to 500 mg/g for the adsorption of oleic acid from sunflower oil,23 342 mg/g for the adsorption of oleic acid11 and 296 mg/g for the adsorption of linoleic acid27 from solutions of ethanol + water. Jamal and Boulanger12 obtained values of 270 and 260 mg/g for Amberlite MB-150 and Dowex monosphere MR-450 UPW resins, respectively, for the adsorption of oleic acid from soybean oil. The variations in values might be associated with the medium composition and commercial fatty acid composition. Furthermore, an increase in the adsorption capacity may be due to additional physical interactions. Nevertheless, the Amberlyst A26 OH resin

qe = BT =

RT ln(A TCe) bT RT bT

(6)

(7)

where R is the ideal gas constant (8.314 J/mol·K), T is the temperature in Kelvin, AT (mg acid/g non-acid components)−1 is the equilibrium binding constant corresponding to the maximum binding energy, and BT (mg acid/g dry resin) is associated with the heat of adsorption. Figures 7 and 8 also show this model’s fitting, and the parameters are given in Table 3. All models could describe the experimental data with similar R2 values (Table 3). Jamal and Boulanger12 also obtained good correlation using Freundlich and Langmuir isotherms to describe the adsorption of oleic acid from soybean oil with Amberlite MB-150 and Dowex Monosphere MR-450 UPW resins at 50 °C. Du et al.18 reported a better fit for the Freundlich isotherm in the adsorption of FFAs from adlay seed miscella with LSD-263 resin. Maddikeri et al.13 evaluated the Freundlich model for the adsorption isotherms of oleic and H


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Table 4. Thermodynamic Parameters of Adsorption: Resin Conditioned with Ethanol and Drying + Oil (System 2) and Resin Conditioned with Ethanol, Drying and Soaking with Hexane + Miscella (Oil + Hexane; System 4)a T

a

system 2

(°C)

K0

ΔG0ads

25 35 50

148.00 179.18 252.92

−12.39 −13.29 −14.87

system 4

ΔH0ads

ΔS0ads

17.32 ± 1.26

0.100 ± 0.004

K0

ΔG0ads

ΔH0ads

ΔS0ads

71.20 102.87 239.56

−10.57 −11.87 −14.72

39.43 ± 5.24

0.17 ± 0.02

ΔG0ads (kJ/mol); ΔH0ads (kJ/mol); ΔS0ads (kJ/mol·K).

stearic acids from sunflower oil on ion exchange resins at 20, 30, and 40 °C and obtained correlation coefficients in the range of 0.93−1.00. The adsorption of fatty acids from solutions of ethanol + water on Amberlyst A26 OH was investigated in the works of Cren and Meirelles11 for oleic acid and Cren et al.27 for linoleic acid. The authors reported that the Langmuir isotherm more appropriately described the equilibrium data. Ilgen23 considered that the Freundlich and Langmuir models appropriately described the adsorption of oleic acid from sunflower oil on Amberlyst A26 OH, with higher values of regression coefficients for the Freundlich model. 3.4. Estimation of Adsorption Thermodynamic Parameters. Thermodynamic parameters, such as the standard Gibbs free energy (ΔG0ads), the standard enthalpy (ΔH0ads), and the standard entropy (ΔS0ads), indicate whether the adsorption process is spontaneous and also assess the effect of temperature on adsorption, aiding the selection of the optimal process conditions.74 The thermodynamic parameters were calculated from the variation of the thermodynamic equilibrium constant K0 with the change in temperature. The value of K0 was determined as outlined in an earlier study of Khan and Singh.75 K 0 = lim

qe → 0

Figure 9. Plot for the determination of the thermodynamic parameters of the systems: (■) resin conditioned with ethanol and drying + oil and (●) resin conditioned with ethanol, drying and soaking with hexane + miscella (oil + hexane).

qe Ce

(8)

The positive values of ΔH0ads and ΔS0ads indicate that the adsorption is entropy-driven rather than energy-driven. This gain in entropy can result from the release of counterions or other components originally present on the surface of the adsorbent.82,83 These results are in agreement with those obtained by Jamal et al.,25 who reported that the adsorption of oleic acid from soybean oil onto Dowex monosphere MR-450 UPW is a spontaneous and endothermic process, with a positive entropy change from 25 to 50 °C. Du et al.18 also observed a similar behavior for FFA adsorption on LSD-263 resin. Maddikeri et al.13 reported negative values for the Gibbs energy change related to the adsorption of stearic and oleic acids from sunflower oil onto Indion 860 resin. However, they found that the adsorption process was exothermic, a different behavior that may be related to the type of adsorbent and the corresponding interactions between FFAs and the resin’s active sites. In fact, Indion 860 resin is a weak anion exchange adsorbent. 3.5. Resin Morphology. Figure 10a,b shows the SEM images of the surfaces of resin conditioned with ethanol + drying with or without soaking in hexane, respectively. Figure 10c also shows the resin after deacidification in system 2, washed with hexane to remove excess oil. The resins have a spherical structure with a smooth surface, which is similar in both pretreatments. After the process, a slight modification of the surface was observed, showing mild abrasions. A larger resin particle size was also observed, which may be due to the adsorption of FFA molecules.

The standard Gibbs free energy (ΔG0ads) was calculated by eqs 9 and 10.13,74,76 The standard enthalpy (ΔH0ads) and the standard entropy (ΔS0ads) were calculated by the slope and intercept, respectively, of the Van’t Hoff equation, which relates ln(K0) with 1/T (eq 10). 0 ΔGads = −RT ln K 0

ln(K 0) = −

0 0 0 ΔGads ΔSads ΔHads = − RT R RT

(9)

(10)

where R (8.314 J/mol·K) is the universal gas constant and T (K) is temperature. The thermodynamic parameters obtained are shown in Table 4. The value of the Gibbs free energy was negative for all temperatures in both systems, indicating that FFA adsorption on Amberlyst A26 OH resin, with and without addition of hexane, is feasible and spontaneous.77,78 There was an increase in the absolute value of the Gibbs free energy with the temperature increase, indicating a more energetically favorable adsorption.79 Figure 9 shows the graph of ln (K0) versus 1/T. The positive value of ΔH0ads for the two systems indicates that the process is endothermic.78,80 This confirms that the increased temperature favors adsorption. Positive values of ΔS0ads were also observed for both systems, indicating increased randomness in the solid− liquid interface as a result of energy redistribution between the adsorbate and adsorbent.81 I


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Figure 10. Scanning electron micrographs of the surfaces of Amberlyst A26 OH: (a) resin conditioned with ethanol and drying, magnification of 50, 200, and 10000 times; (b) resin conditioned with ethanol, drying and soaking with hexane, magnification of 50, 200, and 10000 times; and (c) resin after deacidification in system 2 (dry resin loading of 3%, initial acidity of 4%, 50 °C), magnification of 50, 200, and 10000 times.

4. CONCLUSIONS The present study indicates that the type and presence of an organic solvent in the solution and in the resin pretreatment influence the rate and capacity of adsorption of FFAs from soybean oil. When an alcoholic solvent was present in the fatty solution or within the resin pores, there was formation of alkyl esters as well as simultaneous adsorption of FFAs. Thus, it is important to consider the environment in which the FFA removal by anion exchange occurs because it will affect not only the process performance but also the composition of the final product. In this way, when the process is used for edible purposes, the formation of components such as alkyl esters should be considered. Even when the resin is dried, alcoholic solvents can remain within the pores of the resin, and the catalytic activity should be checked. The adsorption of FFAs was further investigated in two systems after resin drying, using solutions composed only of oil or of an oil mixture with hexane. The adsorption kinetics, isotherms, and thermodynamic parameters were studied in both systems. The fitting of pseudo-first-order and pseudo-secondorder models showed high coefficients of determination, with an observed increase in the rate constant with increasing temperature. Although intraparticle diffusion was involved in

the adsorption process, it was not the sole rate-controlling step. The Langmuir, Freundlich, and Temkin isotherms described the equilibrium data for the adsorption of FFAs from soybean oil onto Amberlyst A26 OH with similar coefficients of determination. The system with hexane had a higher adsorption rate but an adsorption capacity that was somewhat lower than the system without solvent addition. The thermodynamic parameters for both systems revealed that the adsorption is a spontaneous, endothermic, and entropy-driven process. Adsorption in both systems presented favorable conditions, demonstrating that Amberlyst A26 OH has a good capacity for adsorbing FFAs.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.5b02653. Table S1 gives the properties of the strong anion exchange resin Amberlyst A26 OH, and Tables S2 and S3 show the fatty acid compositions of soybean oil and commercial linoleic acid, respectively (PDF) J


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(18) Du, S.-L.; Zhou, C.-S.; Yang, L.-Q. Deacidification of Adlay seed (Coix Lachryma-Jobi Var. Mayuen) miscella with anion-exchange resin. J. Food Process Eng. 2007, 30, 729. (19) Deboni, T. M.; Cuevas, M. S.; Mielke Neto, P.; Mota, R. V.; Damasceno, F. S.; da Silva, L. H. M.; Rodrigues, C. E. C.; Meirelles, A. J. A. Deacidification of Soybean Oil by Ion Exchange. Food Bioprocess Technol. 2013, 6, 3335. (20) Cuevas, M. S.; Deboni, T. M.; Mielke Neto, P.; Damasceno, F. S.; Mota, R. V.; da Silva, L. H. M.; Rodrigues, C. E. C.; Meirelles, A. J. A. Using a Strong Anion-Exchange Resin to Deacidify Red Palm Oil. J. Am. Oil Chem. Soc. 2013, 90, 1589. (21) Damasceno, F. S.; Mota, R. V.; Da Silva, L. H. M.; Meirelles, A. J. A. Oil deacidification of pequi (Caryocar sp.) by adsorption in ion exchange resin. Proceedings of the 16th World Congress of Food Science and Technology, Foz do Iguaçu, Brazil, Aug 05−09, 2012. (22) Mota, R. V.; Damasceno, F. S.; Da Silva, L. H. M.; Meirelles, A. J. A.; Rodrigues, A. M. C. Free fatty acids removal buriti (Mauritia f lexuosa L.) oil by adsorption in ion exchange resin. Proceedings of the 16th World Congress of Food Science and Technology, Foz do Iguaçu, Brazil, Aug 05−09, 2012. (23) Ilgen, O. Adsorption of oleic acid from sunflower oil on Amberlyst A26 (OH). Fuel Process. Technol. 2014, 118, 69. (24) Wu, W.-L.; Tan, Z.-Q.; Wu, G.-J.; Lu, Y.; Zhu, W.-L.; Bao, Y.-L.; Pan, L.-Y.; Yang, Y.-J.; Zheng, J.-X. Deacidification of crude low-calorie cocoa butter with liquid−liquid extraction and strong-base anion exchange resin. Sep. Purif. Technol. 2013, 102, 163. (25) Jamal, Y.; Luo, G.; Kuo, C. H.; Rabie, A.; Boulanger, B. O. Sorption kinetics, thermodynamics and regeneration for lipid feedstock deacidification using a mixed-bed ion-exchange resin. J. Food Process Eng. 2014, 37, 27. (26) Cren, E. C.; Cardozo Filho, L.; Silva, E. A.; Meirelles, A. J. A. Breakthrough curves for oleic acid removal from ethanolic solutions using a strong anion exchange resin. Sep. Purif. Technol. 2009, 69, 1. (27) Cren, E. C.; Morelli, A. C.; Sanches, T.; Rodrigues, C. E.; Meirelles, A. J. A. Adsorption isotherms for removal of linoleic acid from ethanolic solutions using the strong anion exchange resin Amberlyst A26 OH. J. Chem. Eng. Data 2010, 55, 2563. (28) Cren, E. C.; Meirelles, A. J. A. Oleic acid removal from ethanolic solutions by ion exchange. Chem. Eng. J. 2012, 184, 125. (29) Cooper, J. E. Oil recovery method employing acids extracted from crudes using an ion exchange process. U.S. Patent 4,037,656, July 26, 1977. (30) Needs, E. C.; Ford, G. D.; Owen, A. J.; Tuckley, B.; Anderson, M. A method for the quantitative determination of individual free fatty acids in milk by ion exchange resin adsorption and gas-liquid chromatography. J. Dairy Res. 1983, 50, 321. (31) Zalacain, I.; Zapelena, M. J.; De Peña, M. P.; Astiasarán, I.; Bello, J. Use of Lipase from Rhizomucor miehei in Dry Fermented Sausages Elaboration: Microbial, Chemical and Sensory Analysis. Meat Sci. 1997, 45, 99. (32) Sivaraos, K.; Ali, N.; Taufik, A.; Malingam, S. D.; Kassim, M. S.; Sulaiman, M. A. Heat Exchanger Analysis to Reduce Hexane Loss in Palm Kernel Oil Extraction Plant. Int. J. Mech. Mechatron. Eng., August, 2013, 13, p 29. (33) Cai, W.; Sun, Y.; Piao, X.; Li, J.; Zhu, S. Solvent Recovery from Soybean Oil/Hexane Miscella by PDMS Composite Membrane. Chin. J. Chem. Eng. 2011, 19, 575. (34) Johnson, L. A.; Lusas, E. W. Comparison of alternate solvents for oil extraction. J. Am. Oil Chem. Soc. 1983, 60, 181A. (35) Sawada, M. M.; Venâncio, L. L.; Toda, T. A.; Rodrigues, C. E. C. Effects of different alcoholic extraction conditions on soybean oil yield, fatty acid composition and protein solubility of defatted meal. Food Res. Int. 2014, 62, 662. (36) Seth, S.; Agrawal, Y. C.; Ghosh, P. K.; Jayas, D. S. Effect of moisture content on the quality of soybean oil and meal extracted by isopropyl alcohol and hexane. Food Bioprocess Technol. 2010, 3, 121. (37) Bills, D. D.; Khatri, L. L.; Day, E. A. Method for the determination of the free fatty acids of milk fat. J. Dairy Sci. 1963, 46, 1342.

AUTHOR INFORMATION

Corresponding Author

*Phone: + 55 19 35214037. Fax: + 55 19 35214027. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors wish to acknowledge CAPES for the scholarship, CNPq (483340/2012-0 + 406856/2013-3 + 305870/2014-9 + 309780/2014-4) for their financial support, and Cargill S/A for kindly supplying the samples of soybean oil.

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