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Malic acid extraction from aqueous solution by using aqueous two-phase system method
Journal Pre-proof Malic acid extraction from aqueous solution by using aqueous two-phase system method
Hadiseh Masoumie, Hamid Ramezanipour Penchah, Hossein Ghanadzadeh Gilani, Tahereh Jangjooye Shaldehi PII:
S2211-7156(19)30009-8
DOI:
https://doi.org/10.1016/j.rechem.2019.100009
Reference:
RECHEM 100009
To appear in: Received date:
13 July 2019
Accepted date:
16 September 2019
Please cite this article as: H. Masoumie, H.R. Penchah, H.G. Gilani, et al., Malic acid extraction from aqueous solution by using aqueous two-phase system method, (2019), https://doi.org/10.1016/j.rechem.2019.100009
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Journal Pre-proof
Malic acid extraction from aqueous solution by using aqueous two-phase system method Hadiseh Masoumie, Hamid Ramezanipour Penchah, Hossein Ghanadzadeh Gilani*, Tahereh Jangjooye Shaldehi Department of Chemical Engineering, University of Guilan, 41335 Rasht, Iran
Abstract
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In this investigation malic acid extraction by aqueous two-phase system method (ATPS) was performed. ATPS are involved polymer (PEG 4000 and 8000) and various phosphate salts. Effect of PEG molecular weight, pH, temperature and concentration of salt were studied as independent parameters and the partition coefficient (D) and percentage of extraction(Y %) were considered as responses of the system. In order to the results, increasing all of the independent parameters cause to decrease the partition coefficient and percentage of extraction. As these parameters decrease, malic acid tends to move in the top phase (PEG-rich phase), and consequently separation will be occurred properly. In addition, vant hoff equation was applied for discussing temperature effect on malic acid extraction. The obtained results show that increasing of temperature cause to increasing in Gibbs free energy. The best operation condition for malic acid extraction was obtained 4000, 25% w/w, 293 K and 5 for PEG molecular weight, Salt concentration, Temperature and pH, respectively.
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1. Introduction
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Keywords: Malic acid, Phosphate salt, Aqueous two-phase system, Partition coefficient, Extraction efficiency
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Malic acid that is an organic compound with high molecular weight was isolated and purified from mature apple fruits[1]. Malic acid is generated by a fermentation process with a lot of bacteria [2]. It is recognized “building block” in yielding the biodegradable polymers[3, 4]. Basically, malic acid was elicited from eggshells, fruits and apple juice but the price of malic acid extraction was very expensive [4]. Malic acid industrial applications include in metal cleaning , textile, finishing, pharmaceuticals and agriculture[3, 4]. Malic acid reinforces AlPO4 for imbibing in agronomical land[5]. In industry, malic acid is commonly generated by hydrating at high value of pressure and temperature, which mixture of two different structure of malic acid are synthesized[3, 4]. In comparison with citric acid, malic acid is less generated in industry, it has various industrial performances in the polymer, foods and pharmacy as an acidulant among other uses[2, 6]. There are only a few reports mentioning malic acid purification by common separation methods.
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Corresponding author. Tel.:+981333333262; fax: +981333333262. E-mail address: [email protected] (H.Ghanadzadeh Gilani).
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Malmary et al. in 1993 studied on tartaric and malic acid resumption which are existing in effluents by triisooctylamine + 1-octanol and tributylphosphate + dodecane as solvent at 298 K[7]. Uslu et al. in 2009 studied on L-malic acid purification with using reactive extraction in five different esters and alcohols with and without TOMAC[2]. Dilly in 1965 studied on purification and properties of apple fruit malic enzyme[1]. Seo and Kin in 2016 studied on separation of cobalt by using malic acid in pieces of hard metal, in this research,98.2% Co was dissolved after 144 hours in 3 M malic acid solution with 2 vol% H2O2 during wet milling [8]. Gao et al. in 2012 studied on sorption properties of malic acid with applying ion-exchange chromatography method, the optimum adsorption of malic acid at 30˚C, was obtained 0.345 g/g [9]. Gok et al. in 2014 studied on equilibrium, kinetics and thermodynamic characteristics in malic acid purification on LDH as an adsorbent, removal of malic acid at 25˚C was 96.73%[10]. Yu et al. in 2018 studied on p-aminobenzoic acid sorption by hypercross-linked resin, the maximum absorption capacity was 240 mg/g at 30 ° C[11]. Eiteman and Gainer investigated on determining the separation coefficient of malic acid with using aqueous two phase systems, the optimum partition coefficient of malic acid at 25˚C for PEG8000/MgSO4 was observed 1[12].
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Aqueous two phase systems(ATPS) was first discovered by Beijerinck[13] containing of gelatin, agar and water (the top and bottom phase were opulent in gelatin and agar, respectively) that were combined at specified concentrations. Dobry and Boyer-Kawenoki[14], investigated on solubility of two different polymers in the water or organic solvent and also observed that phase division was rather usual. Craig and Craig [15] introduced the application of organic-aqueous two phase systems for protein separation applying countercurrent dispensation.
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However, Per-Aka Albertsson in 1955 discovered that poly ethylene glycol (PEG)/potassium phosphate/water and PEG/dextran/water formed two-phase systems[16]. The polymer-polymer and polymer-salt are commonly applied for refinement and separation of biomolecules with using ATPSs[17]. Generally, until now, the type of ATPS is mainly polymer-polymer, polymersalt and salt–salt combinations in an aqueous solution[17]. Albertsson has expanded a vast category of these systems and their ingredients[18].Having significant information about the mechanisms of solute distribution in ATPS is essential for purification and bioanalytical uses [19]. Thus, studying the effect of diverse parameters such as pH , salt concentration, salt type and etc., dispensation of yield and pollutants are very important [19]. Different procedures have been progressed for increasing the purity of products and also reducing the operational cost of residual polymer in aqueous solution, including centrifugation[20], electrophoresis[21], and using solvents for precipitating[22], copolymers which are sensitive to pH [23, 24]and temperature-sensitive copolymer[20, 25, 26]. In comparison with other separation methods, ATPS has great potential for the efficient and lowcost separation. ATPS has number of important advantages, such as ease of scale-up, Surface stress is relatively low in the two-phase interface, selectivity of extraction, being economical and also continuous operations are the advantages of ATPS[27, 28]. ATPS is the best and effective procedures for purifying diverse particles [18, 27, 29, 30].
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Journal Pre-proof One of the main characteristics of ATPS which makes it different from organic solvent-water systems, is the number of components which are in equilibrium states. In organic solvent- water systems, one composition simply stands in equilibrium while in ATPS, whether two immiscible polymers or polymer/salt, various compositions are in equilibrium. The most substantial properties in organic solvent-water systems is the linear correlation between the distribution coefficients logarithms of samples in various organic solvent-water systems [31]. In this research, extraction of malic acid using ATPS was interested. In addition, effect of PEG molecular weight (MW), pH, temperature and also salt concentration were evaluated on the malic acid partition. 2. Experimental
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2.1 Materials
Table 1. Provenance and Purity of the Materials IUPAC name
malic acid
hydroxybutanedioic acid
di-potassium hydrogen phosphate di-ammonium hydrogen phosphate di-sodium hydrogen phosphate sodium hydroxide Polyethylene glycol phenolphthalein
Potassium hydrogen phosphate
water
C4H6O5
Mass fraction purity >0.99
K2HPO4
>0.99
acid-base titration Chromatography
(NH4)2HPO4
>0.99
Chromatography
Merck
Sodium hydrogen phosphate
Na2HPO4
>0.99
Chromatography
Merck
Sodium hydroxide
NaOH
>0.99
Chromatography
Merck
poly(ethylene oxide)
C2nH4n+2On+1
>0.99
Chromatography
Merck
bis(4-hydroxyphenyl)isobenzofuran1(3H)-33one water
C20H14O4
>0.99
Chromatography
Merck
H2O
deionized and redistilled
conductometry
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component
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PEG with molecular weight of 4000 and 8000 (g/mol), phosphate salt (K2HPO4, (NH4)2HPO4, NaH2PO4), NaOH and malic acid were purchased from Merck (Darmstad, Germany) with highest purity (purity>99%). In addition, at all steps of the experiment, deionized water was used.
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ammonium hydrogen phosphate
2.2 Methods 3
Chemical formula
Purity analysis method
source
Merck Merck
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Biphasic systems were prepared by a mixture of PEG 4000, PEG8000, and phosphate salt solution at required pH. The pH of the salt solution was adjusted by 0.1M sodium hydroxide and cacodilic acid as buffer. In this work, for each of the mentioned systems four samples including 25 %, 30%, 35% and 40 % (w/w) of phosphate salt, PEG4000 and PEG8000 with concentration of 30 %( w/w) were arranged. All components were added into a graduated 15 ml tube as stock solution at constant pH and temperature (298.15k), then 0.2g malic acid was added to the tube. The pH values of the solutions were measured precisely with a pH meter (JENWAY 3345). The resulted solution was mixed by rigorously vortexing the solution for 2 min. The tubes were placed at different temperature for 2 h; and then centrifuged at 2400 rpm for 10 min. Finally, two clear phases with a visible interface were obtained and the solution reaches equilibrium. The samples of the top and bottom phase were carefully withdrawn with care being taken to leave a layer of solution at least 0.2 cm thick above the interface (Figure 1). The concentration of malic acid in the phases was measured using titration method[32].
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Figure 1: Phase separation process and the formation of ATPS
3. Analytical method:
r
t
(1)
b
V V
t b
(2)
D V r 100 1 ( D V r )
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Y%
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C C
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D
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Empirical results have evaluated by the partition coefficient (D) and percentage of extraction (%Y), which is defined below:
(3)
Where Ct is the concentration of malic acid and Cb is the concentration of malic acid at the bottom phase. Vr is the ratio of top and bottom phase volume. According to the equation (3), D and Vr are two fundamental factors which identifies percentage of extraction. Ct and Cb are also calculated by the following relations:
Ct
N NaOH M V t 2 ' Vt
(4)
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Cb
N NaOH M V b 2 ' Vb
(5)
Where NNaOH and M denote the concentration of NaOH(0.05 mol/lit) and molecular weight of malic acid(g/mol). Vt indicate the volume of top phase and Vb is the volume of bottom phase. V't and V’b indicate the volume of sample which is taken from top and bottom solution in centrifuge tube (ml) for titration method. The subscripts t and b express the top and bottom, respectively. 4. Results & Discussions
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In order to study malic acid extraction by ATPS, effect of operation condition such as PEG molecular weight, Salt concentration, Temperature and pH must be determined.
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4.1 Effect of PEG molecular weight
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Partition coefficient (D) and percentage of extraction (Y %) of malic in PEG4000 and PEG8000 are shown in Figure 2 and 3. According to these figures, the PEG4000 is over the PEG8000 and lower PEG MW resulted in higher partition coefficient. Table 2 shows that the value of D and Y% in PEG4000 is greater than PEG8000. It was proved that at low molecular weight (4000 g/mol), hydrophobicity is decreased[33]. Other result relates to equilibrium volume, actually with increasing molecular weight of PEG, equilibrium volume of malic acid in PEG-rich phase decreased, consequently, the value of D and Y% decreased[34].
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Journal Pre-proof 0.8 K2HPO4 PEG4000 K2HPO4 PEG8000 (NH4)2HPO4 PEG4000 (NH4)2HPO4 PEG8000
0.6 0.5 0.4 0.3 0.2
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Partition coefficient of malic acid
0.7
0.1
0.2
0.25
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0 0.3
0.35
0.4
0.45
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Salt concentration
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Figure 2: Comparison the partition coefficient of salt in existence of PEG 4000 & 8000 g / mol at 293K.
K2HPO4 - PEG4000
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60 50
K2HPO4 - PEG8000 (NH4)2HPO4 PEG4000 (NH4)2HPO4 PEG8000
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Extraction efficiency of malic acid (%)
70
40 30 20 10 0
0.2
0.25
0.3
0.35
0.4
0.45
Salt concentration Figure 3: Comparison the percentage of extraction of salt in existence of PEG 4000 & 8000 g / mol at 293K.
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Journal Pre-proof 4.2 Effect of salt concentration
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Effect of concentration of K2HPO4, (NH4)2HPO4 and NaH2PO4 on partition coefficient and percentage of extraction at T=293K and PEG4000 are presented in Figure 4 and 5. According to these figures, the partition of the malic acid strongly depended on the concentration of salt concentration. At high salt concentration, malic acid partitioned to the bottom part quite strongly. At the intermediate concentrations of phosphate salt, malic acid partitioned more evenly between the phases but still favored the bottom phase. Besides, at the constant salt concentration, NaH2PO4, (NH4)2HPO4 and K2HPO4 have high partition coefficient and percentage of extraction, respectively. In the other hand, at low concentration of phosphate salt, malic acid moves preferentially to the top. This could be due to hydrophobic interactions with the PEG or saltingout[18]. Increasing salt concentration can partially reduce the free volume in the salt phase and cause the acid to shift to the polymer phase, but at high salt concentrations, salting-out leads to precipitation of malic acid at the interface[35]. Consequently, the partition coefficient is decreased.
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0.7 0.6
0.4
(NH4)2HPO4 NaH2PO4
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0.3 0.2 0.1 0
K2HPO4
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0.5
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Partition coefficient of malic acid
0.8
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0.2
0.25
0.3
0.35
0.4
0.45
Salt concentration
Figure 4: Effect of salt concentration on partition coefficient of malic acid at T=293K.
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Extraction efficiency (%)
60
(NH4)2HPO4
50
NaH2PO4
40 30 20
0 0.2
0.25
0.3
0.35
0.4
0.45
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Salt concentration
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Figure 5: Effect of salt concentration on extraction efficiency of malic acid at T=293K.
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4.3 Effect of temperature
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Temperature effect of malic acid extraction was investigated at 298,303,308 and 313 K in various systems consisting of dipotassium hydrogen phosphate, diammonium hydrogen phosphate and sodium hydrogen phosphate with PEG4000 and PEG8000.Then, thermodynamics of separation was studied by determining the parameters of the equation(6). ΔH, ΔS and ΔG were calculated by Eq. (6) and (7). According to Figure 6 and 7, when the logarithm of “D” is plotted in versus 1/T, Slope denotes enthalpy and intercept expresses entropy. Value of ΔH, ΔS and ΔG were classified in Table 1. According to the table, as temperature increases, ΔG tends to higher values and it was resulted that the process didn´t move to spontaneous state and finally separation process would be difficult. In addition, table2 shows also that, as temperature increases, partition coefficient and percentage of extraction decreases.
H 1 S ln(D) R T R
(6)
G H T .S
(7)
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-3.1
K2HPO4 (NH4)2HPO4
-2.6
y = 5808.8x - 21.224
NaH2PO4
y = 6120.5x - 21.952
-1.6 -1.1
y = 7145.3x - 24.466
0.0032
0.00325
0.0033
0.00335
0.0034
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1/T
(K-1)
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-0.1 0.00315
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-0.6
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Figure 6: ln(D) respect to 1/T in 30%w/w phosphate salt in presence of PEG4000
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-2.8
-2.4
NaH2PO4
y = 5495.2x - 20.388
(NH4)2HPO4 K2HPO4
y = 3219.9x - 11.987
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-2.2
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-2.6
ln (D)
ln(D)
-2.1
-2
-1.8 -1.6
y = 2160.6x - 9.0056
-1.4 -1.2 -1 0.00315
0.0032
0.00325
0.0033
0.00335
0.0034
1/T (K-1) Figure 7: ln(D) respect to 1/T in 30%w/w phosphate salt in presence of PEG800
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Table 1: Thermodynamic parameters for extraction of malic acid
T ΔS (KJ/mol.K)
∆𝑺° (KJ/mol)
𝜟𝑯° (KJ/mol)
ATPSs
1.568 2.448 3.328 4.208
-52.448 -53.328 -54.208 -55.088
-0.177
-50.88
1.084 2.099 3.114 4.129 3.86 4.735 5.61 6.485
-60.494 -61.509 -62.524 -63.539 -52.15 -53.025 -53.9 -54.775
-0.203
-59.41
-0.175
-48.29
(NH4)2HPO4 30% + PEG 30% 4000 NaH2PO4 30% + PEG 30% 4000 K2HPO4 30% + PEG 30% 4000
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ΔG (KJ/mol)
Temperature(K)
D
Y(%)
0.3
16
T=303
0.24
15
T=313
0.2
11
T=293
0.4
30
T=303
0.27
25
T=313 T=293
0.24
14
0.7
65
T=303
0.5
40
T=313
0.45
30
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Salt type
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different temperatures (T=293K, T=303K, T=313K)
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Table 2: Comparison the partition coefficient (D) and extraction efficiency(Y %) for malic acid with PEG4000 at
T=293
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K2HPO4
(NH4)2HPO4
NaH2PO4
T=293
4.4 Effect of pH pH test was conducted at T=293K in the range of 5-8. Actually, cacodylic acid was used as buffer for adjusting aqueous media in pH=5. In addition, sodium hydroxide was added for creating pH=6-8. 11
Journal Pre-proof Consequently, amount of malic acid was determined with titration method. pH effect on malic acid
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extraction are shown in figure 11 and 12.According to these figures, as pH decreased, the partition coefficient increased due to the interaction between malic acid and PEG became stronger and malic acid prefer the top phase. Consequently, the volume of top and bottom is reduced and increased, respectively, so that the residual volume decreases, which reduces the partition coefficient and percentage of extraction. Furthermore, PEG4000 has the higher value than PEG8000 for all salt and also in the whole range of pH. In Figure 8 and 9, NaH2PO4 with PEG4000 has the appropriate results among the rest, as pH increases from 5 to 8, the value of D & %Y decreases from (D=0.85 & Y= 80%) to (D=0.5 & D=50%).
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0.9
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0.8
K2HPO4 - PEG8000 (NH4)2HPO4- PEG4000
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(NH4)2HPO4 - PEG8000
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0.6
NaH2PO4 - PEG8000 K2HPO4 - PEG4000
0.5
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0.4
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0.3 0.2
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Partition coefficient of malic acid(%)
0.7
NaH2PO4 - PEG4000
0.1 0 4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
pH
Figure 8: Effect of pH on malic acid partition coefficient in 30%w/w phosphate salt/PEG4000 and PEG8000
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90
NaH2PO4 - PEG4000 NaH2PO4 - PEG8000
80
K2HPO4 - PEG4000 K2HPO4 - PEG8000 (NH4)2HPO4 - PEG4000 (NH4)2HPO4 - PEG8000
60
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50
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40 30
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Extraction efficiency of malic acid
70
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20 10
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7
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pH
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5. Conclusion
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Figure 9: Effect of pH on extraction efficiency (%) in 30%w/w phosphate salt/PEG4000
In this study, malic acid extraction was accomplished in ATPS and process parameters such as PEG MW, salt concentration, temperature and pH have been studied in PEG/phosphate systems. The values of D and Y for malic acid depend on the PEG MW. The lower the MW, the higher D achieved. Fig 5 to 9 show that the curve for PEG4000 is above the PEG8000 in all concentrations of salt. It was noted that the length of carbon chains were extended and hydrophobicity of polymer was increased, so that particles moved to salt rich phase. Ultimately, partition coefficient and percentage of extraction were decreased. Concentration of salt had the important effect on the partition coefficient and extraction efficiency. Fig 11 and 12 which relates to the effect of salt concentration on partition coefficient and extraction efficiency for NaH2PO4 at T=293K, showed that the lowest salt concentration (25%w/w) caused to phase volume ratio was decreased, so that the separation parameters were increased. Partition of malic acid was extremely affected by temperature. The results showed that the lowest temperature led to the highest D. Consequently, T=293K was the optimal choice. The pH had drastic influence on the partition of the malic acid. It is observed that pH=5 was an appropriate surrounding for PEG/phosphate system. 13
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6. Acknowledge This work was supported by a grant from the National Science Foundation. Financial assistance from the Guilan University is also acknowledged, as well as technical assistance from Dr. H. Ghanad zadeh in the whole parts of this project.
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8. 9. 10. 11.
12. 13. 14. 15.
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Hadiseh Masoumie, Hamid Ramezanipour Penchah, Hossein Ghanadzadeh Gilani, Tahereh Jangjooye Shaldehi PII:
S2211-7156(19)30009-8
DOI:
https://doi.org/10.1016/j.rechem.2019.100009
Reference:
RECHEM 100009
To appear in: Received date:
13 July 2019
Accepted date:
16 September 2019
Please cite this article as: H. Masoumie, H.R. Penchah, H.G. Gilani, et al., Malic acid extraction from aqueous solution by using aqueous two-phase system method, (2019), https://doi.org/10.1016/j.rechem.2019.100009
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Malic acid extraction from aqueous solution by using aqueous two-phase system method Hadiseh Masoumie, Hamid Ramezanipour Penchah, Hossein Ghanadzadeh Gilani*, Tahereh Jangjooye Shaldehi Department of Chemical Engineering, University of Guilan, 41335 Rasht, Iran
Abstract
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In this investigation malic acid extraction by aqueous two-phase system method (ATPS) was performed. ATPS are involved polymer (PEG 4000 and 8000) and various phosphate salts. Effect of PEG molecular weight, pH, temperature and concentration of salt were studied as independent parameters and the partition coefficient (D) and percentage of extraction(Y %) were considered as responses of the system. In order to the results, increasing all of the independent parameters cause to decrease the partition coefficient and percentage of extraction. As these parameters decrease, malic acid tends to move in the top phase (PEG-rich phase), and consequently separation will be occurred properly. In addition, vant hoff equation was applied for discussing temperature effect on malic acid extraction. The obtained results show that increasing of temperature cause to increasing in Gibbs free energy. The best operation condition for malic acid extraction was obtained 4000, 25% w/w, 293 K and 5 for PEG molecular weight, Salt concentration, Temperature and pH, respectively.
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1. Introduction
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Keywords: Malic acid, Phosphate salt, Aqueous two-phase system, Partition coefficient, Extraction efficiency
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Malic acid that is an organic compound with high molecular weight was isolated and purified from mature apple fruits[1]. Malic acid is generated by a fermentation process with a lot of bacteria [2]. It is recognized “building block” in yielding the biodegradable polymers[3, 4]. Basically, malic acid was elicited from eggshells, fruits and apple juice but the price of malic acid extraction was very expensive [4]. Malic acid industrial applications include in metal cleaning , textile, finishing, pharmaceuticals and agriculture[3, 4]. Malic acid reinforces AlPO4 for imbibing in agronomical land[5]. In industry, malic acid is commonly generated by hydrating at high value of pressure and temperature, which mixture of two different structure of malic acid are synthesized[3, 4]. In comparison with citric acid, malic acid is less generated in industry, it has various industrial performances in the polymer, foods and pharmacy as an acidulant among other uses[2, 6]. There are only a few reports mentioning malic acid purification by common separation methods.
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Corresponding author. Tel.:+981333333262; fax: +981333333262. E-mail address: [email protected] (H.Ghanadzadeh Gilani).
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Malmary et al. in 1993 studied on tartaric and malic acid resumption which are existing in effluents by triisooctylamine + 1-octanol and tributylphosphate + dodecane as solvent at 298 K[7]. Uslu et al. in 2009 studied on L-malic acid purification with using reactive extraction in five different esters and alcohols with and without TOMAC[2]. Dilly in 1965 studied on purification and properties of apple fruit malic enzyme[1]. Seo and Kin in 2016 studied on separation of cobalt by using malic acid in pieces of hard metal, in this research,98.2% Co was dissolved after 144 hours in 3 M malic acid solution with 2 vol% H2O2 during wet milling [8]. Gao et al. in 2012 studied on sorption properties of malic acid with applying ion-exchange chromatography method, the optimum adsorption of malic acid at 30˚C, was obtained 0.345 g/g [9]. Gok et al. in 2014 studied on equilibrium, kinetics and thermodynamic characteristics in malic acid purification on LDH as an adsorbent, removal of malic acid at 25˚C was 96.73%[10]. Yu et al. in 2018 studied on p-aminobenzoic acid sorption by hypercross-linked resin, the maximum absorption capacity was 240 mg/g at 30 ° C[11]. Eiteman and Gainer investigated on determining the separation coefficient of malic acid with using aqueous two phase systems, the optimum partition coefficient of malic acid at 25˚C for PEG8000/MgSO4 was observed 1[12].
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Aqueous two phase systems(ATPS) was first discovered by Beijerinck[13] containing of gelatin, agar and water (the top and bottom phase were opulent in gelatin and agar, respectively) that were combined at specified concentrations. Dobry and Boyer-Kawenoki[14], investigated on solubility of two different polymers in the water or organic solvent and also observed that phase division was rather usual. Craig and Craig [15] introduced the application of organic-aqueous two phase systems for protein separation applying countercurrent dispensation.
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However, Per-Aka Albertsson in 1955 discovered that poly ethylene glycol (PEG)/potassium phosphate/water and PEG/dextran/water formed two-phase systems[16]. The polymer-polymer and polymer-salt are commonly applied for refinement and separation of biomolecules with using ATPSs[17]. Generally, until now, the type of ATPS is mainly polymer-polymer, polymersalt and salt–salt combinations in an aqueous solution[17]. Albertsson has expanded a vast category of these systems and their ingredients[18].Having significant information about the mechanisms of solute distribution in ATPS is essential for purification and bioanalytical uses [19]. Thus, studying the effect of diverse parameters such as pH , salt concentration, salt type and etc., dispensation of yield and pollutants are very important [19]. Different procedures have been progressed for increasing the purity of products and also reducing the operational cost of residual polymer in aqueous solution, including centrifugation[20], electrophoresis[21], and using solvents for precipitating[22], copolymers which are sensitive to pH [23, 24]and temperature-sensitive copolymer[20, 25, 26]. In comparison with other separation methods, ATPS has great potential for the efficient and lowcost separation. ATPS has number of important advantages, such as ease of scale-up, Surface stress is relatively low in the two-phase interface, selectivity of extraction, being economical and also continuous operations are the advantages of ATPS[27, 28]. ATPS is the best and effective procedures for purifying diverse particles [18, 27, 29, 30].
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Journal Pre-proof One of the main characteristics of ATPS which makes it different from organic solvent-water systems, is the number of components which are in equilibrium states. In organic solvent- water systems, one composition simply stands in equilibrium while in ATPS, whether two immiscible polymers or polymer/salt, various compositions are in equilibrium. The most substantial properties in organic solvent-water systems is the linear correlation between the distribution coefficients logarithms of samples in various organic solvent-water systems [31]. In this research, extraction of malic acid using ATPS was interested. In addition, effect of PEG molecular weight (MW), pH, temperature and also salt concentration were evaluated on the malic acid partition. 2. Experimental
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2.1 Materials
Table 1. Provenance and Purity of the Materials IUPAC name
malic acid
hydroxybutanedioic acid
di-potassium hydrogen phosphate di-ammonium hydrogen phosphate di-sodium hydrogen phosphate sodium hydroxide Polyethylene glycol phenolphthalein
Potassium hydrogen phosphate
water
C4H6O5
Mass fraction purity >0.99
K2HPO4
>0.99
acid-base titration Chromatography
(NH4)2HPO4
>0.99
Chromatography
Merck
Sodium hydrogen phosphate
Na2HPO4
>0.99
Chromatography
Merck
Sodium hydroxide
NaOH
>0.99
Chromatography
Merck
poly(ethylene oxide)
C2nH4n+2On+1
>0.99
Chromatography
Merck
bis(4-hydroxyphenyl)isobenzofuran1(3H)-33one water
C20H14O4
>0.99
Chromatography
Merck
H2O
deionized and redistilled
conductometry
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component
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PEG with molecular weight of 4000 and 8000 (g/mol), phosphate salt (K2HPO4, (NH4)2HPO4, NaH2PO4), NaOH and malic acid were purchased from Merck (Darmstad, Germany) with highest purity (purity>99%). In addition, at all steps of the experiment, deionized water was used.
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ammonium hydrogen phosphate
2.2 Methods 3
Chemical formula
Purity analysis method
source
Merck Merck
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Biphasic systems were prepared by a mixture of PEG 4000, PEG8000, and phosphate salt solution at required pH. The pH of the salt solution was adjusted by 0.1M sodium hydroxide and cacodilic acid as buffer. In this work, for each of the mentioned systems four samples including 25 %, 30%, 35% and 40 % (w/w) of phosphate salt, PEG4000 and PEG8000 with concentration of 30 %( w/w) were arranged. All components were added into a graduated 15 ml tube as stock solution at constant pH and temperature (298.15k), then 0.2g malic acid was added to the tube. The pH values of the solutions were measured precisely with a pH meter (JENWAY 3345). The resulted solution was mixed by rigorously vortexing the solution for 2 min. The tubes were placed at different temperature for 2 h; and then centrifuged at 2400 rpm for 10 min. Finally, two clear phases with a visible interface were obtained and the solution reaches equilibrium. The samples of the top and bottom phase were carefully withdrawn with care being taken to leave a layer of solution at least 0.2 cm thick above the interface (Figure 1). The concentration of malic acid in the phases was measured using titration method[32].
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Figure 1: Phase separation process and the formation of ATPS
3. Analytical method:
r
t
(1)
b
V V
t b
(2)
D V r 100 1 ( D V r )
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C C
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D
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Empirical results have evaluated by the partition coefficient (D) and percentage of extraction (%Y), which is defined below:
(3)
Where Ct is the concentration of malic acid and Cb is the concentration of malic acid at the bottom phase. Vr is the ratio of top and bottom phase volume. According to the equation (3), D and Vr are two fundamental factors which identifies percentage of extraction. Ct and Cb are also calculated by the following relations:
Ct
N NaOH M V t 2 ' Vt
(4)
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Cb
N NaOH M V b 2 ' Vb
(5)
Where NNaOH and M denote the concentration of NaOH(0.05 mol/lit) and molecular weight of malic acid(g/mol). Vt indicate the volume of top phase and Vb is the volume of bottom phase. V't and V’b indicate the volume of sample which is taken from top and bottom solution in centrifuge tube (ml) for titration method. The subscripts t and b express the top and bottom, respectively. 4. Results & Discussions
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In order to study malic acid extraction by ATPS, effect of operation condition such as PEG molecular weight, Salt concentration, Temperature and pH must be determined.
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4.1 Effect of PEG molecular weight
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Partition coefficient (D) and percentage of extraction (Y %) of malic in PEG4000 and PEG8000 are shown in Figure 2 and 3. According to these figures, the PEG4000 is over the PEG8000 and lower PEG MW resulted in higher partition coefficient. Table 2 shows that the value of D and Y% in PEG4000 is greater than PEG8000. It was proved that at low molecular weight (4000 g/mol), hydrophobicity is decreased[33]. Other result relates to equilibrium volume, actually with increasing molecular weight of PEG, equilibrium volume of malic acid in PEG-rich phase decreased, consequently, the value of D and Y% decreased[34].
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Journal Pre-proof 0.8 K2HPO4 PEG4000 K2HPO4 PEG8000 (NH4)2HPO4 PEG4000 (NH4)2HPO4 PEG8000
0.6 0.5 0.4 0.3 0.2
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Partition coefficient of malic acid
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0.1
0.2
0.25
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0 0.3
0.35
0.4
0.45
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Salt concentration
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Figure 2: Comparison the partition coefficient of salt in existence of PEG 4000 & 8000 g / mol at 293K.
K2HPO4 - PEG4000
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60 50
K2HPO4 - PEG8000 (NH4)2HPO4 PEG4000 (NH4)2HPO4 PEG8000
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Extraction efficiency of malic acid (%)
70
40 30 20 10 0
0.2
0.25
0.3
0.35
0.4
0.45
Salt concentration Figure 3: Comparison the percentage of extraction of salt in existence of PEG 4000 & 8000 g / mol at 293K.
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Effect of concentration of K2HPO4, (NH4)2HPO4 and NaH2PO4 on partition coefficient and percentage of extraction at T=293K and PEG4000 are presented in Figure 4 and 5. According to these figures, the partition of the malic acid strongly depended on the concentration of salt concentration. At high salt concentration, malic acid partitioned to the bottom part quite strongly. At the intermediate concentrations of phosphate salt, malic acid partitioned more evenly between the phases but still favored the bottom phase. Besides, at the constant salt concentration, NaH2PO4, (NH4)2HPO4 and K2HPO4 have high partition coefficient and percentage of extraction, respectively. In the other hand, at low concentration of phosphate salt, malic acid moves preferentially to the top. This could be due to hydrophobic interactions with the PEG or saltingout[18]. Increasing salt concentration can partially reduce the free volume in the salt phase and cause the acid to shift to the polymer phase, but at high salt concentrations, salting-out leads to precipitation of malic acid at the interface[35]. Consequently, the partition coefficient is decreased.
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0.7 0.6
0.4
(NH4)2HPO4 NaH2PO4
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0.3 0.2 0.1 0
K2HPO4
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0.5
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Partition coefficient of malic acid
0.8
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0.2
0.25
0.3
0.35
0.4
0.45
Salt concentration
Figure 4: Effect of salt concentration on partition coefficient of malic acid at T=293K.
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Extraction efficiency (%)
60
(NH4)2HPO4
50
NaH2PO4
40 30 20
0 0.2
0.25
0.3
0.35
0.4
0.45
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Salt concentration
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Figure 5: Effect of salt concentration on extraction efficiency of malic acid at T=293K.
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4.3 Effect of temperature
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Temperature effect of malic acid extraction was investigated at 298,303,308 and 313 K in various systems consisting of dipotassium hydrogen phosphate, diammonium hydrogen phosphate and sodium hydrogen phosphate with PEG4000 and PEG8000.Then, thermodynamics of separation was studied by determining the parameters of the equation(6). ΔH, ΔS and ΔG were calculated by Eq. (6) and (7). According to Figure 6 and 7, when the logarithm of “D” is plotted in versus 1/T, Slope denotes enthalpy and intercept expresses entropy. Value of ΔH, ΔS and ΔG were classified in Table 1. According to the table, as temperature increases, ΔG tends to higher values and it was resulted that the process didn´t move to spontaneous state and finally separation process would be difficult. In addition, table2 shows also that, as temperature increases, partition coefficient and percentage of extraction decreases.
H 1 S ln(D) R T R
(6)
G H T .S
(7)
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-3.1
K2HPO4 (NH4)2HPO4
-2.6
y = 5808.8x - 21.224
NaH2PO4
y = 6120.5x - 21.952
-1.6 -1.1
y = 7145.3x - 24.466
0.0032
0.00325
0.0033
0.00335
0.0034
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1/T
(K-1)
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-0.1 0.00315
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Figure 6: ln(D) respect to 1/T in 30%w/w phosphate salt in presence of PEG4000
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-2.8
-2.4
NaH2PO4
y = 5495.2x - 20.388
(NH4)2HPO4 K2HPO4
y = 3219.9x - 11.987
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-2.2
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-2.6
ln (D)
ln(D)
-2.1
-2
-1.8 -1.6
y = 2160.6x - 9.0056
-1.4 -1.2 -1 0.00315
0.0032
0.00325
0.0033
0.00335
0.0034
1/T (K-1) Figure 7: ln(D) respect to 1/T in 30%w/w phosphate salt in presence of PEG800
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Table 1: Thermodynamic parameters for extraction of malic acid
T ΔS (KJ/mol.K)
∆𝑺° (KJ/mol)
𝜟𝑯° (KJ/mol)
ATPSs
1.568 2.448 3.328 4.208
-52.448 -53.328 -54.208 -55.088
-0.177
-50.88
1.084 2.099 3.114 4.129 3.86 4.735 5.61 6.485
-60.494 -61.509 -62.524 -63.539 -52.15 -53.025 -53.9 -54.775
-0.203
-59.41
-0.175
-48.29
(NH4)2HPO4 30% + PEG 30% 4000 NaH2PO4 30% + PEG 30% 4000 K2HPO4 30% + PEG 30% 4000
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ΔG (KJ/mol)
Temperature(K)
D
Y(%)
0.3
16
T=303
0.24
15
T=313
0.2
11
T=293
0.4
30
T=303
0.27
25
T=313 T=293
0.24
14
0.7
65
T=303
0.5
40
T=313
0.45
30
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Salt type
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different temperatures (T=293K, T=303K, T=313K)
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Table 2: Comparison the partition coefficient (D) and extraction efficiency(Y %) for malic acid with PEG4000 at
T=293
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K2HPO4
(NH4)2HPO4
NaH2PO4
T=293
4.4 Effect of pH pH test was conducted at T=293K in the range of 5-8. Actually, cacodylic acid was used as buffer for adjusting aqueous media in pH=5. In addition, sodium hydroxide was added for creating pH=6-8. 11
Journal Pre-proof Consequently, amount of malic acid was determined with titration method. pH effect on malic acid
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extraction are shown in figure 11 and 12.According to these figures, as pH decreased, the partition coefficient increased due to the interaction between malic acid and PEG became stronger and malic acid prefer the top phase. Consequently, the volume of top and bottom is reduced and increased, respectively, so that the residual volume decreases, which reduces the partition coefficient and percentage of extraction. Furthermore, PEG4000 has the higher value than PEG8000 for all salt and also in the whole range of pH. In Figure 8 and 9, NaH2PO4 with PEG4000 has the appropriate results among the rest, as pH increases from 5 to 8, the value of D & %Y decreases from (D=0.85 & Y= 80%) to (D=0.5 & D=50%).
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0.9
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0.8
K2HPO4 - PEG8000 (NH4)2HPO4- PEG4000
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(NH4)2HPO4 - PEG8000
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0.6
NaH2PO4 - PEG8000 K2HPO4 - PEG4000
0.5
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0.4
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0.3 0.2
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Partition coefficient of malic acid(%)
0.7
NaH2PO4 - PEG4000
0.1 0 4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
pH
Figure 8: Effect of pH on malic acid partition coefficient in 30%w/w phosphate salt/PEG4000 and PEG8000
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90
NaH2PO4 - PEG4000 NaH2PO4 - PEG8000
80
K2HPO4 - PEG4000 K2HPO4 - PEG8000 (NH4)2HPO4 - PEG4000 (NH4)2HPO4 - PEG8000
60
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40 30
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Extraction efficiency of malic acid
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pH
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5. Conclusion
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Figure 9: Effect of pH on extraction efficiency (%) in 30%w/w phosphate salt/PEG4000
In this study, malic acid extraction was accomplished in ATPS and process parameters such as PEG MW, salt concentration, temperature and pH have been studied in PEG/phosphate systems. The values of D and Y for malic acid depend on the PEG MW. The lower the MW, the higher D achieved. Fig 5 to 9 show that the curve for PEG4000 is above the PEG8000 in all concentrations of salt. It was noted that the length of carbon chains were extended and hydrophobicity of polymer was increased, so that particles moved to salt rich phase. Ultimately, partition coefficient and percentage of extraction were decreased. Concentration of salt had the important effect on the partition coefficient and extraction efficiency. Fig 11 and 12 which relates to the effect of salt concentration on partition coefficient and extraction efficiency for NaH2PO4 at T=293K, showed that the lowest salt concentration (25%w/w) caused to phase volume ratio was decreased, so that the separation parameters were increased. Partition of malic acid was extremely affected by temperature. The results showed that the lowest temperature led to the highest D. Consequently, T=293K was the optimal choice. The pH had drastic influence on the partition of the malic acid. It is observed that pH=5 was an appropriate surrounding for PEG/phosphate system. 13
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6. Acknowledge This work was supported by a grant from the National Science Foundation. Financial assistance from the Guilan University is also acknowledged, as well as technical assistance from Dr. H. Ghanad zadeh in the whole parts of this project.
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