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A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid
G Model JIEC 4468 No. of Pages 6
Journal of Industrial and Engineering Chemistry xxx (2019) xxx–xxx
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A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid Khavar Adhami, Hamideh Asadollahzadeh* , Mahdieh Ghazizadeh Department of Chemistry, Kerman Branch, Islamic Azad University, Kerman, Iran
A R T I C L E I N F O
A B S T R A C T
Article history: Received 17 April 2018 Received in revised form 15 March 2019 Accepted 27 March 2019 Available online xxx
In this study simultaneous degumming and deacidification of edible oils were done by tetrabutylphosphonium phosphate IL. Under the optimized extraction conditions of soybean oil (3 mass% IL, 60 C and 20 min), canola oil (2 mass% IL, 60 C and 20 min) and sunflower oil (1.5 mass% IL, 50 C, 15 min), the content of free fatty acid (FFA) and phosphorus reached 0.18% and 3.5 mg/kg; 0.12% and 3.8 mg/kg; and 0.17% and 3.5 mg/kg, respectively. In this work, soap stock and water washing stage were eliminated and no waste water, which pollutes the environment, was produced. © 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Keywords: Deacidification Degumming Ionic liquid Free fatty acid Tetrabutylphosphonium phosphate
Introduction Vegetable oils play a major role in our diet as they are sources of energy, include essential fatty acids and contain some fat-soluble vitamins such as vitamin A. The commercial resources of vegetable oils are oilseeds and fruit pulp [1–3], but the crude oil that is extracted from oilseeds and fruit pulp has impurity such as free fatty acids (FFA), phospholipids (PLs) and etc [1–6]. So, crude oil should be refined to remove FFA and other impurities that affect flavor, odor and appearance [1–7]. Among these impurities FFA constitute the highest content and tend to be more vulnerable to oxidation compared to glycerol esters of the fatty acids. This oxidation contributes to oxidative rancidity in edible oils and fat– containing foods. Therefore, any escalation in the acidity of any oil should be absolutely avoided [2]. Conventional methods for FFA removal are chemical and physical deacidification. In the first method, deacidification is accomplished by the addition of an alkali to deacidifided oil, thereby precipitating the FFA as soap stock; this stock is then removed by mechanical separation from the neutral oil. The disadvantage of this process is excessive loss in neutral oil with high FFA content. In addition, it is notable to say that this soap stock compared to the oil is commercially of low value. Physical deacidification method, although suited to high
* Corresponding author. E-mail address: [email protected] (H. Asadollahzadeh).
FFA content oils, requires pretreatments that are performed under very harsh conditions such as high temperature and high vacuum. These conditions cause thermal polymerization and decomposition of high value oil constituents [1–7]. Some unconventional methods for this removal are miscella, solvent and membrane deacidification. But, in this method, the cost of the process is high and deacidification is incomplete and also unsuitable for practical application [2,8]. As described above, the main aim behind refining edible oils is deacidification, but the maximum level of FFA in neutralization stage should be 0.15–0.18% based on chemical deacidification [5,9]. Another major impurity of edible oils is PLs including hydratable and non–hydratable phosphatides [6,8] of which the non–hydratable type is soluble in the oily layer [10]. The PL content of an average quality of oil is reduced to a range between 1800 and 6000 mg/kg and the corresponding range of phosphorus content is 60–200 mg/kg [11]. Acid degumming treatment generally reduces phosphorus to a range between 25–35 mg/kg. Neutralization with NaOH following the acid treatment steadily reduces the phosphorus content to a range between 15–25 mg/kg. These treatments accompanied by either water wash or the utilization of silica will further reduce the phosphorus steadily to 5 mg/kg [6]. Membrane techniques, seemingly unconventional degumming methods, may use many modern technologies to separate PLs from vegetable oils [12,13]. But, the highest oil flux achieved was only 0.8 l/ (m2h) which is very low for industrial adoption [8,11].
https://doi.org/10.1016/j.jiec.2019.03.048 1226-086X/© 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048
G Model JIEC 4468 No. of Pages 6
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Recently, ionic liquids (ILs) have been increasingly utilized in liquid–liquid extractions of metal and organic compounds. They are now being considered for the selective extraction of target compounds at finite concentrations from chemical process systems [14,15]. These compounds have low melting points (<100), no volatility and low vapor pressure, and these features have made them green solvent [15–20]. Moreover, ILs that have larger polar differences with crude oil can be quickly separated from crude oil. There is no water in this process; therefore, the emulsification problem connected with the most used aqueous solution is likely to be overcome [14]. In recent time, ILs have been used for a number of applications in industry. Anderson et al. removed naphthenic acids from crude oil using amino acid ILs [21]. In line with the above, Manic et al. removed FFA from soybean oil using IL [7], and Calvano et al. extracted PLs from extra virgin essential olive oil and hazelnut oil using ILs [22]. ILs can also be successfully used in large-scale processes for successful application of centrifugal separators [15,23–27]. Considering the above and the fact that conventional methods are not without their drawbacks, particularly high excessive loss in neutral oil in the chemical refining, it seems ILs with the above mentioned properties and their successful application in separators are better alternatives for refining of edible oils. Accordingly, in the current study, the IL was used based on phosphonium cation in simultaneous deacidification and degumming of soybean, canola and sunflower oils. As we know, ILs are usually formed by combining a diverse range of cations containing nitrogen or phosphorous with anions such as amino acids, acids etc [15,28–33]. Junko et al. used phosphonium cations which form salts with good chemical [34] and thermal stability [35] and also have a lower toxicity [36] than ammonium salts. For this reason, phosphonium cation was selected in the current experiment. Also tetrabutylphosphonium hydroxide [TBP] [OH] is quite stable and the corresponding salts can be obtained easily by mixing it with acids [36]. As a result, we used [TBP] [OH]. Moreover, as neutralization method for synthesizing of ILs is free of contaminants [17], we synthesized the IL using this method. In addition, since phosphate head is a part of PLs, phosphate anion was used in the present research. Then [TBP] [OH] was mixed with phosphoric acid because phosphonium– based ILs are prepared by mixing anions with aqueous solution of [TBP] [OH] [37]. Materials and methods Instrumentation IR spectra (4000–400 cm–1) were recorded with diamond ATR probe, using Bruker FT–IR (Tensor) spectrophotometer. 1H NMR analysis was done using Bruker Spectrospin 300. GC–MS analysis was also done using an Agilent HP 7890A, GC system coupled with an Agilent 5975C VLMSD mass spectrometer from Agilent Technologies, Inc., (Santa Clara, USA). MSD was operated in an electron impact ionization mode at 70 EV. The CHN element analyzer (ECS 4010, Costech, Italy) and spectrophotometer (UV120-01, Shimadzu, Japan,) was also used. A Karl Fischer moisture titrator (MKV-710, Kem, Japan) was used to detect the water content of the IL.
Zinc oxide—reagent grade, Potassium hydroxide (KOH) pellets— reagent grade, Sulfuric acid (H2SO4)—concentrated, sp gr 1.84, Sodium molybdate—reagent grade, Hydrazine sulfate—reagent grade and Potassium dihydrogen phosphate—reagent grade, were provided by Merck Company. Crude soybean, canola and sunflower oils were obtained from Golnaz vegetable oil Company. The samples were delivered to the company’s laboratory and stored at a dry and cool place far from sunlight. Before use, the samples were shaken well. Synthesis of the ionic liquid Tetrabutylphosphonium phosphate ionic liquid [TBP] PO4 Fig. 1 was prepared according to the previously reported methods [38]. Briefly, the IL was prepared by mixing equimolar amounts of an aqueous solution of the phosphoric acid and tetrabutylphosphonium hydroxide. After the reaction was done, the solution was placed on a rotary evaporator at 80 C under magnetic stirrer set at 300 rpm to remove the water, and final traces of water were removed by heating (50–60 C) under vacuum (0.1 Pa) for 3 days. To ensure the purity of the ionic liquid, it was dissolved in acetonitrile and treated with activated charcoal for at least 24 h, and finally acetonitrile was evaporated in vacuum. The water content of the IL was checked by Karl Fischer moisture titrator. The structure and purity of the IL was checked by 1H NMR, FT–IR and CHN element analyzer. The molecular mass of it was confirmed by GC–MS spectra. Analysis of FFA and phosphorous The FFA were analyzed according to the AOCS Official Method Ca 5a–40 [39]. The phosphorous content of the samples was measured by the standard molybdenum blue method, the AOCS Method Ca 12–55, and the PL equivalent was calculated by multiplying the phosphorous content by a factor of 31 in soybean oil [40]. In the present study, all the tests were done at least three times. Procedure of simultaneous degumming and deacidification of edible oils by using the ionic liquid Liquid–liquid extractions were performed according to the following procedure. The simultaneous degumming and deacidification of the oils was performed by contacting 50 g of soybean, canola or sunflower crude oils with a known amount of the IL in a glass vessel; then the mixture was heated at 70 C in a paraffin bath for 15 min under magnetic stirrer set at 300 rpm. The solution was then subjected to centrifugation at 4000 rpm for 15 min to separate the IL phase from the oil phase. Then, the oil phase was treated (to remove traces of the IL) with 10 mL of hot distilled water for 10 min under magnetic stirrer set at 300 rpm, and subsequently centrifuged. After separating the phases of water and oil, the oil phase was dried over Na2SO4 and analyzed for FFA content and phosphorous. After analysis of FFA and phosphorus, the efficiency of the extraction was investigated. The optimization was also
Reagents and materials Sodium hydroxide solution (accurately standardized), Phenolphthalein indicator, Phosphoric acid 85% and Ethyl alcohol 95% were purchased from Merck Company. Tetrabutylphosphonium hydroxide [TBP] [OH] (40% by mass aqueous solution) was purchased from Sigma Aldrich. Hydrochloric acid (HCl)—concentrated, sp gr 1.19,
Fig. 1. Formula of the tetrabutylphosphonium phosphate IL ([TBP] PO4).
Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048
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carried out in varying extraction times (2, 5, 10, 15, 20 and 30 min), extraction temperatures (15, 27, 37, 50, 60, 70 and 80 C), and mass % of the ILs (0.5, 1, 1.5, 2 and 3). Each extraction was done at least three times. Comparison of loss of oil in this study with that in the chemical refining method Since it does not matter which oil (soybean, sunflower, and canola) should be used for investigation of loss of oil, soybean oil (Table 1) was chosen as an example. First, simultaneous degumming and deacidification was done in optimum conditions (3 mass % IL, 60 C and 20 min) using the IL as mentioned above (2.5). The solution was then subjected to centrifugation at 4000 rpm for 15 min to separate the IL phase from the oil phase. Then, the precipitates were measured based on ml per gram of oil at ambient temperature, according to international standard ISO 15301:2001 method. The precipitates are loss of oil and upper layer was measured as neutral oil. Second, degumming and deacidification were done using the chemical refining method in optimum conditions (0.1% H3PO4, 1.16% of 16 Be0 lye and 0.1% excess lye, 85– 95 C) by H3PO4 and NaOH, respectively [5]. The solution was then subjected to centrifugation at 4000 rpm for 15 min to separate soap phase from oil phase. Then, the precipitates (bottom layer) and upper layer were measured as loss of oil and neutral oil respectively. Finally, the results were compared. Recycling of the ionic liquid After the first extraction, the bottom layer (mixture of the IL, FFA and PLs) was dissolved in distilled water, boiled and was then allowed to be separated into two phases. The upper layer included FFA and PLs, and the bottom layer was the solution of the IL in water. After separating the latter, the water was removed on a rotary evaporator at 80 C and dried in vacuum. The structure of the IL was checked by 1H NMR and FT–IR. The recycled IL was used for simultaneous degumming and deacidification as described in section 2.5 under optimum conditions of each the oils. Results and discussions Synthesis of the ionic liquid The 1H of the [TBP] PO4 IL was recorded in DMSO, and 1H NMR spectrum showed four distinct peaks at 0.926–0.950 (t, J = 7.5 Hz, 3H, CH3), 1. 247–1.367 (m, 2H, CH2), 1.562–1.717 (m, 2H, CH2), and 3.152–3.205 (t, J = 8.4 Hz, 2H, CH2) ppm Fig. 2. In addition, to confirm the purity of this synthesized IL, 1H NMR spectrum was run in D2O–CDCl3 and no more signals for H3PO4 were observed between 9–14 ppm indicating the formation of the [TBP] PO4 IL. The FT–IR spectrum of the IL was observed at 1146 cm–1 for stretching frequency of ‘P = O’ and at 1683 cm–1 for that of ‘P–C’. The resauls of CHN analysis were as follow: Anal. Calc. for C48H108O4P4: C, 66.02; H, 12.47; Found C, 66.04; H, 12.51% and the molecular mass of this IL was 873.5 g based on
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the result of GC MS spectra. Also the water content of the IL was less than 1 wt%. Optimization of the extraction conditions Effect of the IL content To investigate the effect of the IL content, different amounts (mass %(of the IL were considered and were contacted with crude oil at 70 C for 15 min. The results of FFA and phosphorus are shown in Fig. 3. As shown, the optimum amounts of the IL were 1.5 mass% and 3 mass% for sunflower and soybean oils, respectively and also 2 mass% for canola oil. For soybean oil, these amounts decreased FFA and phosphorus to 0.18 and 3.5, respectively. And for sunflower oil, FFA and phosphorus reached 0.17 and 3.5, respectively, and also for canola oil, they reached 0.12 and 3.8, respectively. All the reached amounts in this respect in the present study were desirable as the maximum levels of FFA and phosphorus are respectively 0.15– 0.17.6% and 5 mg/kg in deacidification and degumming stage of oil refining [5,9]. Also the efficiency of this IL in removal of FFA and PLs is suitable and is shown in Table 1. The mechanism for the extraction of FFA by the IL [21] is illustrated in the equation below: [cation+1]3 [PO4]3– + 3 RCO2H $ [cation] 3 [O2C–R] 3 [H3PO4]. This equation shows the protonation of phosphate anion and ion exchange forming the carboxylate salt. Also the mechanism for the extraction of PLs by IL is based on interaction between phosphonium cation and phosphate group in PL molecules. In this study in order to know whether the amount of phosphorus is caused by PLs or is caused by the IL, we added a known amount of the IL to refined soybean oil and extraction was done under optimum conditions. After washing the oil phase with distilled water, the amount of phosphorus was measured in refined soybean oil. The amount of phosphorus measured was the same as the amount of phosphorus before the extraction. In conclusion, the IL has no effect on the amount of phosphorus and the amount of phosphorus measured is caused by PLs. In the present study it was found that deacidification and degumming happened simultaneously. Degumming can be explained based on the rule that like dissolves like so the IL solved PLs as both contained phosphate groups. It is stated that the non-hydratable types of PL are soluble in the oily layer [10]; however, in the current research, they were solved in the IL. Moreover, problems such as emulsification and reduction in the efficiency of bleaching earth are associated with high amounts of PLs [6,8], but in the present study we had a reduction in the amounts of PLs reaching even below the maximum level, 5 mg/kg, which can overcome these problems. Consequently, degumming and deacidification can be simultaneously done in one stage, removing one step of oils refining, and eliminating degumming equipment such as several mixers, reservoirs, dosing pump etc. It should be noted that the aforementioned degumming process is in fact the stage after providing lecithin from crude oils and PLs are the remaining part of the initial amount of PLs. Also, in our study, as FFA is extracted by the IL and separated in the recycling stage of it, there will be no soap stock and
Table 1 %FFA and Phosphorous removal using [TBP] PO4 IL at optimum conditions (Soybean oil: 3 mass% IL, 60 C and 20 min, Sunflower oil: 1.5 mass% IL, 50 C, 15 min and Canola oil: 2 mass% IL, 60 C and 20 min). Sample
Soybean oil Sunflower oil Canola oil
FFA (%)
Phosphorous (mg/kg)
Efficiency (%)
Before extraction with IL
After extraction with IL
Before extraction with IL
After extraction with IL
FFA
Phosphorous
0.93 0.04 0.52 0.02 0.78 0.02
0.18 0.02 0.17 0.02 0.12 0.03
105.7 2.1 51.4 1.2 199.5 1.86
3.5 0.8 3.8 0.5 3.5 0.4
80.6 67.3 84.6
96.7 92.6 98
Values are means SD, n 3.
Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048
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Fig. 2. 1H NMR spectra of the fresh [TBP] PO4 IL: (300 MHz, DMSO), 0.901–0.950 (t, J = 7.5 Hz, 3H, CH3), 1. 247–1.367 (m, 2H, CH2), 1.562–1.717 (m, 2H, CH2), and 3.152–3.205 (t, J = 8.4 Hz, 2H, CH2) ppm.
Fig. 3. Variations of FFA and phosphorus of soybean, sunflower and canola oils with mass% of the [TBP] PO4 IL. Conditions of extraction: temperature, 70 C and time, 15 min.
consequently no need for any sulfuric acid for its treatment, so no environmental pollution will be caused. But, in the chemical refining method of neutralization, soap stock is produced. In order to use soap stock, sulfuric acid is added and the mixture turns into fatty acid. So, in this stage, acidic waste water is produced and in order to neutralize it an alkaline is needed, resulting in environmental pollution [5]. Effect of temperature To investigate the optimum temperature, the optimum amount of the IL was treated at different temperatures at a constant time of extraction (15 min). The results of FFA are shown in Fig. 4. According to the present study’s results, the optimum temperature was 50 C for sunflower and 60 C for soybean and canola oils. The current experiments also showed that the amount of phosphors at the temperature of 15 C reached the desirable level, and further increasing of the temperature had no effect on its reduction. In chemical refining deacidification, the temperature of reaction is 85–95 C which increases the cost of energy. Also, high temperature damages oils [5], but in the current work, the temperature was 50–60 C that was less than the chemical refining method. This
Fig. 4. Variations of FFA of soybean, sunflower and canola oils with temperature by using [TBP] PO4 IL. Conditions of extraction: (Soybean oil: 3 mass% IL, Sunflower oil: 1.5 mass% IL, Canola oil: 2 mass% IL and 15 min extraction time for each).
Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048
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Fig. 5. Variations of FFA and phosphorus of soybean, sunflower and canola oils with extraction time by using [TBP] PO4 IL. Conditions of extraction: (Soybean oil: 3 mass% IL, 60 C, Sunflower oil: 1.5 mass% IL, 50 C and Canola oil: 2 mass% IL, 60 C).
reduction in temperature can result in saving of energy and avoiding damage to oils. Effect of extraction time To investigate the time of extraction, the optimum amounts of the IL at the optimum temperature were contacted with each other at the range of 2–30 min. According to the present research’s results, the optimum time of extraction was 15 min for sunflower and 20 min for soybean and canola oils. The results of FFA and phosphorus are shown in Fig.5. Comparison of loss of oil and neutral oil in this study with that in the chemical refining method After degumming and deacidification were done with two methods (the IL method and chemical refining method), the amounts of loss of oil and neutral oil were measured and the precipitates were 1.8 0.3 ml/45 g and neutral oils were 48.2 0.4 ml/45 g in the current method and 3 0.2 ml/45 g,
47 0.3 ml/45 g respectively in the chemical refining method, because in our study the IL extracts FFA and PLs. Also, as there is no water in this procedure, there would be no emulsion. But in the chemical refining, the presence of water and alkaline causes emulsification. It is noticeable that the 45 g of soybean oil has about 50 mL of volume in ambient temperature [5]. Degumming and deacidification of edible oils using the recycled IL The feasibility of the IL recycling can also be a critical subject for a power saving system. Accordingly, in the present research, the recycling of the IL and its reuse for subsequent FFA and PLs extraction were studied. According to the results of 1H NMR, the 1 H of the recycled [TBP] PO4 IL was recorded in DMSO. 1H NMR spectrum showed four distinct peaks at 0.910–0.959 (t, J = 7.5 Hz, 3H, CH3), 1.253–1.373 (m, 2H, CH2), 1.510–1.571 (m, 2H, CH2), and 3.154–3.209 (t, J = 8.4 Hz, 2H, CH2) ppm Fig. 6. The IR spectrum of the recycled IL was observed at 1110 cm–1for stretching frequency of ‘P = O’ and at 1683 cm–1 for that of ‘P–C’.
Fig. 6. 1H NMR spectra of the recycled [TBP] PO4 IL: (300 MHz, DMSO), 0.910–0.959 (t, J = 7.5 Hz, 3H, CH3), 1.253–1.373 (m, 2H, CH2), 1.510–1.571 (m, 2H, CH2), and 3.154–3.209 (t, J = 8.4 Hz, 2H, CH2) ppm.
Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048
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Table 2 %FFA and Phosphorous removal using recycled [TBP] PO4 IL at optimum conditions (Soybean oil: 3 mass% IL, 60 C and 20 min, Sunflower oil: 1.5 mass% IL, 50 C, 15 min and Canola oil: 2 mass% IL, 60 C and 20 min). Sample
Soybean oil Sunflower oil Canola oil
FFA (%)
Phosphorous (mg/kg)
Efficiency (%)
Before extraction with R-ILa
After extraction with R-IL
Before extraction with R-IL
After extraction with R-IL
FFA
Phosphorous
0.93 0.04 0.52 0.02 0.78 0.02
0.23 0.02 0.21 0.04 0.2 0.04
105.7 2.1 51.4 1.2 199.5 1.86
3.3 1.1 3.3 0.8 3.6 0.9
75.3 60 74.4
96.9 93.6 98.2
Values are means SD, n 3. a Recycled IL.
The results in Table 2 showed that the IL was stable even after treatment with oils at the extracting conditions. It was observed that this recycled IL displayed good reusability, especially for phosphorus. Conclusion Our experimental results showed the successful use of tetrabutylphosphonium IL [TBP] PO4 in deacidification and degumming of crude soybean, canola and sunflower oils. This IL can be used as a substitute for sodium hydroxide used in the chemical refining method. And it is notable to say that these two processes were simultaneously done. Consequently, based on the simultaneous deacidification and degumming, the latter can be eliminated in oil refining process (in the chemical refining, degumming is done before adding caustic soda solution) which results in eliminating the degumming equipment such as mixers, reservoirs, dosing pump etc. Moreover, deacidification and degumming by this IL can have several advantages over the chemical refining. First, it can decrease the loss of neutral oil in neutralization stage; second, it can eliminate soap stock and water washing stage in neutralization of oils. The latter can remove waste water consisting of soap and trace edible oils from neutralization stage which will be a great advantage to the environment since at present lime and aluminum sulfate are used for waste water treatment. Through the elimination of lime waste, environmental pollution would be avoided. It is clear that all the above are congruent with the use of a green and recyclable solvent. In addition, with respect to the extraction temperature reached in the current study, deacidification and degumming did not damage the oils whereas, in the chemical refining method, the temperature of 85–95 C is required which may damage oils and can also increase energy consumption. So, it is concluded that all these can contribute to having a greener environment. Acknowledgment The authors are grateful to Islamic Azad University, Kerman Branch, for financial assistance of this work. Also, the authors are grateful to the Board of Directors of Golnaz Vegetable Oil Company for their full support of the research.
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Journal of Industrial and Engineering Chemistry xxx (2019) xxx–xxx
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A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid Khavar Adhami, Hamideh Asadollahzadeh* , Mahdieh Ghazizadeh Department of Chemistry, Kerman Branch, Islamic Azad University, Kerman, Iran
A R T I C L E I N F O
A B S T R A C T
Article history: Received 17 April 2018 Received in revised form 15 March 2019 Accepted 27 March 2019 Available online xxx
In this study simultaneous degumming and deacidification of edible oils were done by tetrabutylphosphonium phosphate IL. Under the optimized extraction conditions of soybean oil (3 mass% IL, 60 C and 20 min), canola oil (2 mass% IL, 60 C and 20 min) and sunflower oil (1.5 mass% IL, 50 C, 15 min), the content of free fatty acid (FFA) and phosphorus reached 0.18% and 3.5 mg/kg; 0.12% and 3.8 mg/kg; and 0.17% and 3.5 mg/kg, respectively. In this work, soap stock and water washing stage were eliminated and no waste water, which pollutes the environment, was produced. © 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Keywords: Deacidification Degumming Ionic liquid Free fatty acid Tetrabutylphosphonium phosphate
Introduction Vegetable oils play a major role in our diet as they are sources of energy, include essential fatty acids and contain some fat-soluble vitamins such as vitamin A. The commercial resources of vegetable oils are oilseeds and fruit pulp [1–3], but the crude oil that is extracted from oilseeds and fruit pulp has impurity such as free fatty acids (FFA), phospholipids (PLs) and etc [1–6]. So, crude oil should be refined to remove FFA and other impurities that affect flavor, odor and appearance [1–7]. Among these impurities FFA constitute the highest content and tend to be more vulnerable to oxidation compared to glycerol esters of the fatty acids. This oxidation contributes to oxidative rancidity in edible oils and fat– containing foods. Therefore, any escalation in the acidity of any oil should be absolutely avoided [2]. Conventional methods for FFA removal are chemical and physical deacidification. In the first method, deacidification is accomplished by the addition of an alkali to deacidifided oil, thereby precipitating the FFA as soap stock; this stock is then removed by mechanical separation from the neutral oil. The disadvantage of this process is excessive loss in neutral oil with high FFA content. In addition, it is notable to say that this soap stock compared to the oil is commercially of low value. Physical deacidification method, although suited to high
* Corresponding author. E-mail address: [email protected] (H. Asadollahzadeh).
FFA content oils, requires pretreatments that are performed under very harsh conditions such as high temperature and high vacuum. These conditions cause thermal polymerization and decomposition of high value oil constituents [1–7]. Some unconventional methods for this removal are miscella, solvent and membrane deacidification. But, in this method, the cost of the process is high and deacidification is incomplete and also unsuitable for practical application [2,8]. As described above, the main aim behind refining edible oils is deacidification, but the maximum level of FFA in neutralization stage should be 0.15–0.18% based on chemical deacidification [5,9]. Another major impurity of edible oils is PLs including hydratable and non–hydratable phosphatides [6,8] of which the non–hydratable type is soluble in the oily layer [10]. The PL content of an average quality of oil is reduced to a range between 1800 and 6000 mg/kg and the corresponding range of phosphorus content is 60–200 mg/kg [11]. Acid degumming treatment generally reduces phosphorus to a range between 25–35 mg/kg. Neutralization with NaOH following the acid treatment steadily reduces the phosphorus content to a range between 15–25 mg/kg. These treatments accompanied by either water wash or the utilization of silica will further reduce the phosphorus steadily to 5 mg/kg [6]. Membrane techniques, seemingly unconventional degumming methods, may use many modern technologies to separate PLs from vegetable oils [12,13]. But, the highest oil flux achieved was only 0.8 l/ (m2h) which is very low for industrial adoption [8,11].
https://doi.org/10.1016/j.jiec.2019.03.048 1226-086X/© 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048
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Recently, ionic liquids (ILs) have been increasingly utilized in liquid–liquid extractions of metal and organic compounds. They are now being considered for the selective extraction of target compounds at finite concentrations from chemical process systems [14,15]. These compounds have low melting points (<100), no volatility and low vapor pressure, and these features have made them green solvent [15–20]. Moreover, ILs that have larger polar differences with crude oil can be quickly separated from crude oil. There is no water in this process; therefore, the emulsification problem connected with the most used aqueous solution is likely to be overcome [14]. In recent time, ILs have been used for a number of applications in industry. Anderson et al. removed naphthenic acids from crude oil using amino acid ILs [21]. In line with the above, Manic et al. removed FFA from soybean oil using IL [7], and Calvano et al. extracted PLs from extra virgin essential olive oil and hazelnut oil using ILs [22]. ILs can also be successfully used in large-scale processes for successful application of centrifugal separators [15,23–27]. Considering the above and the fact that conventional methods are not without their drawbacks, particularly high excessive loss in neutral oil in the chemical refining, it seems ILs with the above mentioned properties and their successful application in separators are better alternatives for refining of edible oils. Accordingly, in the current study, the IL was used based on phosphonium cation in simultaneous deacidification and degumming of soybean, canola and sunflower oils. As we know, ILs are usually formed by combining a diverse range of cations containing nitrogen or phosphorous with anions such as amino acids, acids etc [15,28–33]. Junko et al. used phosphonium cations which form salts with good chemical [34] and thermal stability [35] and also have a lower toxicity [36] than ammonium salts. For this reason, phosphonium cation was selected in the current experiment. Also tetrabutylphosphonium hydroxide [TBP] [OH] is quite stable and the corresponding salts can be obtained easily by mixing it with acids [36]. As a result, we used [TBP] [OH]. Moreover, as neutralization method for synthesizing of ILs is free of contaminants [17], we synthesized the IL using this method. In addition, since phosphate head is a part of PLs, phosphate anion was used in the present research. Then [TBP] [OH] was mixed with phosphoric acid because phosphonium– based ILs are prepared by mixing anions with aqueous solution of [TBP] [OH] [37]. Materials and methods Instrumentation IR spectra (4000–400 cm–1) were recorded with diamond ATR probe, using Bruker FT–IR (Tensor) spectrophotometer. 1H NMR analysis was done using Bruker Spectrospin 300. GC–MS analysis was also done using an Agilent HP 7890A, GC system coupled with an Agilent 5975C VLMSD mass spectrometer from Agilent Technologies, Inc., (Santa Clara, USA). MSD was operated in an electron impact ionization mode at 70 EV. The CHN element analyzer (ECS 4010, Costech, Italy) and spectrophotometer (UV120-01, Shimadzu, Japan,) was also used. A Karl Fischer moisture titrator (MKV-710, Kem, Japan) was used to detect the water content of the IL.
Zinc oxide—reagent grade, Potassium hydroxide (KOH) pellets— reagent grade, Sulfuric acid (H2SO4)—concentrated, sp gr 1.84, Sodium molybdate—reagent grade, Hydrazine sulfate—reagent grade and Potassium dihydrogen phosphate—reagent grade, were provided by Merck Company. Crude soybean, canola and sunflower oils were obtained from Golnaz vegetable oil Company. The samples were delivered to the company’s laboratory and stored at a dry and cool place far from sunlight. Before use, the samples were shaken well. Synthesis of the ionic liquid Tetrabutylphosphonium phosphate ionic liquid [TBP] PO4 Fig. 1 was prepared according to the previously reported methods [38]. Briefly, the IL was prepared by mixing equimolar amounts of an aqueous solution of the phosphoric acid and tetrabutylphosphonium hydroxide. After the reaction was done, the solution was placed on a rotary evaporator at 80 C under magnetic stirrer set at 300 rpm to remove the water, and final traces of water were removed by heating (50–60 C) under vacuum (0.1 Pa) for 3 days. To ensure the purity of the ionic liquid, it was dissolved in acetonitrile and treated with activated charcoal for at least 24 h, and finally acetonitrile was evaporated in vacuum. The water content of the IL was checked by Karl Fischer moisture titrator. The structure and purity of the IL was checked by 1H NMR, FT–IR and CHN element analyzer. The molecular mass of it was confirmed by GC–MS spectra. Analysis of FFA and phosphorous The FFA were analyzed according to the AOCS Official Method Ca 5a–40 [39]. The phosphorous content of the samples was measured by the standard molybdenum blue method, the AOCS Method Ca 12–55, and the PL equivalent was calculated by multiplying the phosphorous content by a factor of 31 in soybean oil [40]. In the present study, all the tests were done at least three times. Procedure of simultaneous degumming and deacidification of edible oils by using the ionic liquid Liquid–liquid extractions were performed according to the following procedure. The simultaneous degumming and deacidification of the oils was performed by contacting 50 g of soybean, canola or sunflower crude oils with a known amount of the IL in a glass vessel; then the mixture was heated at 70 C in a paraffin bath for 15 min under magnetic stirrer set at 300 rpm. The solution was then subjected to centrifugation at 4000 rpm for 15 min to separate the IL phase from the oil phase. Then, the oil phase was treated (to remove traces of the IL) with 10 mL of hot distilled water for 10 min under magnetic stirrer set at 300 rpm, and subsequently centrifuged. After separating the phases of water and oil, the oil phase was dried over Na2SO4 and analyzed for FFA content and phosphorous. After analysis of FFA and phosphorus, the efficiency of the extraction was investigated. The optimization was also
Reagents and materials Sodium hydroxide solution (accurately standardized), Phenolphthalein indicator, Phosphoric acid 85% and Ethyl alcohol 95% were purchased from Merck Company. Tetrabutylphosphonium hydroxide [TBP] [OH] (40% by mass aqueous solution) was purchased from Sigma Aldrich. Hydrochloric acid (HCl)—concentrated, sp gr 1.19,
Fig. 1. Formula of the tetrabutylphosphonium phosphate IL ([TBP] PO4).
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carried out in varying extraction times (2, 5, 10, 15, 20 and 30 min), extraction temperatures (15, 27, 37, 50, 60, 70 and 80 C), and mass % of the ILs (0.5, 1, 1.5, 2 and 3). Each extraction was done at least three times. Comparison of loss of oil in this study with that in the chemical refining method Since it does not matter which oil (soybean, sunflower, and canola) should be used for investigation of loss of oil, soybean oil (Table 1) was chosen as an example. First, simultaneous degumming and deacidification was done in optimum conditions (3 mass % IL, 60 C and 20 min) using the IL as mentioned above (2.5). The solution was then subjected to centrifugation at 4000 rpm for 15 min to separate the IL phase from the oil phase. Then, the precipitates were measured based on ml per gram of oil at ambient temperature, according to international standard ISO 15301:2001 method. The precipitates are loss of oil and upper layer was measured as neutral oil. Second, degumming and deacidification were done using the chemical refining method in optimum conditions (0.1% H3PO4, 1.16% of 16 Be0 lye and 0.1% excess lye, 85– 95 C) by H3PO4 and NaOH, respectively [5]. The solution was then subjected to centrifugation at 4000 rpm for 15 min to separate soap phase from oil phase. Then, the precipitates (bottom layer) and upper layer were measured as loss of oil and neutral oil respectively. Finally, the results were compared. Recycling of the ionic liquid After the first extraction, the bottom layer (mixture of the IL, FFA and PLs) was dissolved in distilled water, boiled and was then allowed to be separated into two phases. The upper layer included FFA and PLs, and the bottom layer was the solution of the IL in water. After separating the latter, the water was removed on a rotary evaporator at 80 C and dried in vacuum. The structure of the IL was checked by 1H NMR and FT–IR. The recycled IL was used for simultaneous degumming and deacidification as described in section 2.5 under optimum conditions of each the oils. Results and discussions Synthesis of the ionic liquid The 1H of the [TBP] PO4 IL was recorded in DMSO, and 1H NMR spectrum showed four distinct peaks at 0.926–0.950 (t, J = 7.5 Hz, 3H, CH3), 1. 247–1.367 (m, 2H, CH2), 1.562–1.717 (m, 2H, CH2), and 3.152–3.205 (t, J = 8.4 Hz, 2H, CH2) ppm Fig. 2. In addition, to confirm the purity of this synthesized IL, 1H NMR spectrum was run in D2O–CDCl3 and no more signals for H3PO4 were observed between 9–14 ppm indicating the formation of the [TBP] PO4 IL. The FT–IR spectrum of the IL was observed at 1146 cm–1 for stretching frequency of ‘P = O’ and at 1683 cm–1 for that of ‘P–C’. The resauls of CHN analysis were as follow: Anal. Calc. for C48H108O4P4: C, 66.02; H, 12.47; Found C, 66.04; H, 12.51% and the molecular mass of this IL was 873.5 g based on
3
the result of GC MS spectra. Also the water content of the IL was less than 1 wt%. Optimization of the extraction conditions Effect of the IL content To investigate the effect of the IL content, different amounts (mass %(of the IL were considered and were contacted with crude oil at 70 C for 15 min. The results of FFA and phosphorus are shown in Fig. 3. As shown, the optimum amounts of the IL were 1.5 mass% and 3 mass% for sunflower and soybean oils, respectively and also 2 mass% for canola oil. For soybean oil, these amounts decreased FFA and phosphorus to 0.18 and 3.5, respectively. And for sunflower oil, FFA and phosphorus reached 0.17 and 3.5, respectively, and also for canola oil, they reached 0.12 and 3.8, respectively. All the reached amounts in this respect in the present study were desirable as the maximum levels of FFA and phosphorus are respectively 0.15– 0.17.6% and 5 mg/kg in deacidification and degumming stage of oil refining [5,9]. Also the efficiency of this IL in removal of FFA and PLs is suitable and is shown in Table 1. The mechanism for the extraction of FFA by the IL [21] is illustrated in the equation below: [cation+1]3 [PO4]3– + 3 RCO2H $ [cation] 3 [O2C–R] 3 [H3PO4]. This equation shows the protonation of phosphate anion and ion exchange forming the carboxylate salt. Also the mechanism for the extraction of PLs by IL is based on interaction between phosphonium cation and phosphate group in PL molecules. In this study in order to know whether the amount of phosphorus is caused by PLs or is caused by the IL, we added a known amount of the IL to refined soybean oil and extraction was done under optimum conditions. After washing the oil phase with distilled water, the amount of phosphorus was measured in refined soybean oil. The amount of phosphorus measured was the same as the amount of phosphorus before the extraction. In conclusion, the IL has no effect on the amount of phosphorus and the amount of phosphorus measured is caused by PLs. In the present study it was found that deacidification and degumming happened simultaneously. Degumming can be explained based on the rule that like dissolves like so the IL solved PLs as both contained phosphate groups. It is stated that the non-hydratable types of PL are soluble in the oily layer [10]; however, in the current research, they were solved in the IL. Moreover, problems such as emulsification and reduction in the efficiency of bleaching earth are associated with high amounts of PLs [6,8], but in the present study we had a reduction in the amounts of PLs reaching even below the maximum level, 5 mg/kg, which can overcome these problems. Consequently, degumming and deacidification can be simultaneously done in one stage, removing one step of oils refining, and eliminating degumming equipment such as several mixers, reservoirs, dosing pump etc. It should be noted that the aforementioned degumming process is in fact the stage after providing lecithin from crude oils and PLs are the remaining part of the initial amount of PLs. Also, in our study, as FFA is extracted by the IL and separated in the recycling stage of it, there will be no soap stock and
Table 1 %FFA and Phosphorous removal using [TBP] PO4 IL at optimum conditions (Soybean oil: 3 mass% IL, 60 C and 20 min, Sunflower oil: 1.5 mass% IL, 50 C, 15 min and Canola oil: 2 mass% IL, 60 C and 20 min). Sample
Soybean oil Sunflower oil Canola oil
FFA (%)
Phosphorous (mg/kg)
Efficiency (%)
Before extraction with IL
After extraction with IL
Before extraction with IL
After extraction with IL
FFA
Phosphorous
0.93 0.04 0.52 0.02 0.78 0.02
0.18 0.02 0.17 0.02 0.12 0.03
105.7 2.1 51.4 1.2 199.5 1.86
3.5 0.8 3.8 0.5 3.5 0.4
80.6 67.3 84.6
96.7 92.6 98
Values are means SD, n 3.
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Fig. 2. 1H NMR spectra of the fresh [TBP] PO4 IL: (300 MHz, DMSO), 0.901–0.950 (t, J = 7.5 Hz, 3H, CH3), 1. 247–1.367 (m, 2H, CH2), 1.562–1.717 (m, 2H, CH2), and 3.152–3.205 (t, J = 8.4 Hz, 2H, CH2) ppm.
Fig. 3. Variations of FFA and phosphorus of soybean, sunflower and canola oils with mass% of the [TBP] PO4 IL. Conditions of extraction: temperature, 70 C and time, 15 min.
consequently no need for any sulfuric acid for its treatment, so no environmental pollution will be caused. But, in the chemical refining method of neutralization, soap stock is produced. In order to use soap stock, sulfuric acid is added and the mixture turns into fatty acid. So, in this stage, acidic waste water is produced and in order to neutralize it an alkaline is needed, resulting in environmental pollution [5]. Effect of temperature To investigate the optimum temperature, the optimum amount of the IL was treated at different temperatures at a constant time of extraction (15 min). The results of FFA are shown in Fig. 4. According to the present study’s results, the optimum temperature was 50 C for sunflower and 60 C for soybean and canola oils. The current experiments also showed that the amount of phosphors at the temperature of 15 C reached the desirable level, and further increasing of the temperature had no effect on its reduction. In chemical refining deacidification, the temperature of reaction is 85–95 C which increases the cost of energy. Also, high temperature damages oils [5], but in the current work, the temperature was 50–60 C that was less than the chemical refining method. This
Fig. 4. Variations of FFA of soybean, sunflower and canola oils with temperature by using [TBP] PO4 IL. Conditions of extraction: (Soybean oil: 3 mass% IL, Sunflower oil: 1.5 mass% IL, Canola oil: 2 mass% IL and 15 min extraction time for each).
Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048
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Fig. 5. Variations of FFA and phosphorus of soybean, sunflower and canola oils with extraction time by using [TBP] PO4 IL. Conditions of extraction: (Soybean oil: 3 mass% IL, 60 C, Sunflower oil: 1.5 mass% IL, 50 C and Canola oil: 2 mass% IL, 60 C).
reduction in temperature can result in saving of energy and avoiding damage to oils. Effect of extraction time To investigate the time of extraction, the optimum amounts of the IL at the optimum temperature were contacted with each other at the range of 2–30 min. According to the present research’s results, the optimum time of extraction was 15 min for sunflower and 20 min for soybean and canola oils. The results of FFA and phosphorus are shown in Fig.5. Comparison of loss of oil and neutral oil in this study with that in the chemical refining method After degumming and deacidification were done with two methods (the IL method and chemical refining method), the amounts of loss of oil and neutral oil were measured and the precipitates were 1.8 0.3 ml/45 g and neutral oils were 48.2 0.4 ml/45 g in the current method and 3 0.2 ml/45 g,
47 0.3 ml/45 g respectively in the chemical refining method, because in our study the IL extracts FFA and PLs. Also, as there is no water in this procedure, there would be no emulsion. But in the chemical refining, the presence of water and alkaline causes emulsification. It is noticeable that the 45 g of soybean oil has about 50 mL of volume in ambient temperature [5]. Degumming and deacidification of edible oils using the recycled IL The feasibility of the IL recycling can also be a critical subject for a power saving system. Accordingly, in the present research, the recycling of the IL and its reuse for subsequent FFA and PLs extraction were studied. According to the results of 1H NMR, the 1 H of the recycled [TBP] PO4 IL was recorded in DMSO. 1H NMR spectrum showed four distinct peaks at 0.910–0.959 (t, J = 7.5 Hz, 3H, CH3), 1.253–1.373 (m, 2H, CH2), 1.510–1.571 (m, 2H, CH2), and 3.154–3.209 (t, J = 8.4 Hz, 2H, CH2) ppm Fig. 6. The IR spectrum of the recycled IL was observed at 1110 cm–1for stretching frequency of ‘P = O’ and at 1683 cm–1 for that of ‘P–C’.
Fig. 6. 1H NMR spectra of the recycled [TBP] PO4 IL: (300 MHz, DMSO), 0.910–0.959 (t, J = 7.5 Hz, 3H, CH3), 1.253–1.373 (m, 2H, CH2), 1.510–1.571 (m, 2H, CH2), and 3.154–3.209 (t, J = 8.4 Hz, 2H, CH2) ppm.
Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048
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Table 2 %FFA and Phosphorous removal using recycled [TBP] PO4 IL at optimum conditions (Soybean oil: 3 mass% IL, 60 C and 20 min, Sunflower oil: 1.5 mass% IL, 50 C, 15 min and Canola oil: 2 mass% IL, 60 C and 20 min). Sample
Soybean oil Sunflower oil Canola oil
FFA (%)
Phosphorous (mg/kg)
Efficiency (%)
Before extraction with R-ILa
After extraction with R-IL
Before extraction with R-IL
After extraction with R-IL
FFA
Phosphorous
0.93 0.04 0.52 0.02 0.78 0.02
0.23 0.02 0.21 0.04 0.2 0.04
105.7 2.1 51.4 1.2 199.5 1.86
3.3 1.1 3.3 0.8 3.6 0.9
75.3 60 74.4
96.9 93.6 98.2
Values are means SD, n 3. a Recycled IL.
The results in Table 2 showed that the IL was stable even after treatment with oils at the extracting conditions. It was observed that this recycled IL displayed good reusability, especially for phosphorus. Conclusion Our experimental results showed the successful use of tetrabutylphosphonium IL [TBP] PO4 in deacidification and degumming of crude soybean, canola and sunflower oils. This IL can be used as a substitute for sodium hydroxide used in the chemical refining method. And it is notable to say that these two processes were simultaneously done. Consequently, based on the simultaneous deacidification and degumming, the latter can be eliminated in oil refining process (in the chemical refining, degumming is done before adding caustic soda solution) which results in eliminating the degumming equipment such as mixers, reservoirs, dosing pump etc. Moreover, deacidification and degumming by this IL can have several advantages over the chemical refining. First, it can decrease the loss of neutral oil in neutralization stage; second, it can eliminate soap stock and water washing stage in neutralization of oils. The latter can remove waste water consisting of soap and trace edible oils from neutralization stage which will be a great advantage to the environment since at present lime and aluminum sulfate are used for waste water treatment. Through the elimination of lime waste, environmental pollution would be avoided. It is clear that all the above are congruent with the use of a green and recyclable solvent. In addition, with respect to the extraction temperature reached in the current study, deacidification and degumming did not damage the oils whereas, in the chemical refining method, the temperature of 85–95 C is required which may damage oils and can also increase energy consumption. So, it is concluded that all these can contribute to having a greener environment. Acknowledgment The authors are grateful to Islamic Azad University, Kerman Branch, for financial assistance of this work. Also, the authors are grateful to the Board of Directors of Golnaz Vegetable Oil Company for their full support of the research.
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Please cite this article in press as: K. Adhami, et al., A novel process for simultaneous degumming and deacidification of Soybean, Canola and Sunflower oils by tetrabutylphosphonium phosphate ionic liquid, J. Ind. Eng. Chem. (2019), https://doi.org/10.1016/j.jiec.2019.03.048