Measurement and Correlation for the Solid Solubility of Antioxidants of

Dec 4, 2015 - Department of Chemical and Materials Engineering and Master Program of Nanomaterials, Chinese Culture University, Taipei, 111,. Taiwan...
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Measurement and Correlation for the Solid Solubility of Antioxidants of EDTA Disodium Salt Dihydrate, EDTA Calcium Disodium Salt Hydrate, and L‑Cysteine Hydrochloride in Supercritical Carbon Dioxide Tzu-Chi Wang* and Yueh-Ta Wu Department of Chemical and Materials Engineering and Master Program of Nanomaterials, Chinese Culture University, Taipei, 111, Taiwan ABSTRACT: This research focuses on measuring the solubility of three antioxidantsethylenediaminetetraacetic acid disodium salt hydrate, ethylenediaminetetraacetic acid calcium disodium salt hydrate, and L-cysteine hydrochloridein supercritical carbon dioxide. Using a semiflow apparatus, the experiment takes data at 308.15, 313.15, and 318.15 K with pressure ranging from 10 to 22 MPa (for ethylenediaminetetraacetic acid disodium salt dihydrate) or from 12 to 24 MPa (for ethylenediaminetetraacetic acid calcium disodium salt hydrate and L-cysteine hydrochloride). Two semiempirical equationsone proposed by Chrastil, the other Mendez-Santiago and Tejaare applied to find the correlated relationship of the experimental data. With the choice of fitted parameters, the correlation derived from the two equations are satisfactory: the average absolute relative deviation is under 5.1%.

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temperature.6 Wang et al. have their focus on antioxidants (D-isoascorbic acid, calcium L-ascorbate dehydrate, sodium L-ascorbate and sodium erythorbate monohydrate), collecting the solubility of these antioxidants in various pressures and temperatures.7,8 However, owing to the immense possibility of different combinations of chemical compounds, both experimental data for specialty chemicals and generalized correlation models are in great need. EDTA disodium salt dihydrate (IUPAC name, disodium 2-[2-[bis(carboxymethyl)amino]ethyl-(2-oxido-2oxoethyl)amino]acetate dihydrate, CAS No. 6381-92-6), EDTA calcium disodium salt hydrate (IUPAC name, calcium disodium 2-[2-[bis(2-oxido-2-oxoethyl)amino]ethyl-(2-oxido2-oxoethyl)amino]acetate hydrate, CAS No. 304695-78-1), and L-cysteine hydrochloride (IUPAC name, (2R)-2-amino-3sulfanylpropanoic acid hydrochloride, CAS No. 52-89-1) are, in addition to nutrient supplements, important antioxidants in preserving various kinds of food like meat, soups, and cakes. As a result, the solid solubility of them in supercritical CO2 has a variety of usage in the field for powder processing, crystallization, chemical reaction, separation, and extraction of food manufacturing and testing. To help researchers and engineers alike, this study centers on deriving essential solid solubility data, which are correlated with the use of either the semiempirical equation by Chrastil9 or the one by Mendez-Santiago and Teja,5 in diverse

INTRODUCTION Recent years have seen supercritical fluids (SCF) become intriguing materials to academic study as well as industrial applications. In synthetic and analytical chemistry, supercritical fluidsthe highly compressed gases characterized by properties of both gases and liquids, among them carbon dioxide, ethane, and xenonoffer a great range of exciting chemical possibilities to spark off reactions that are difficult or even impossible to be activated in ordinary solvents. The supercritical fluid, an essential part of green technology, is widely utilized in various fields, including reaction, particle formation, extraction, and material processing.1,2 When it comes to industrial processes that incorporate the use of supercritical fluids, the comprehensiveness and accuracy of their physical properties, such as diffusion coefficient or solubility, are essential for effective design and operation. With advantages both in its mild temperature ranges and in its environmental friendliness, supercritical carbon dioxide is an ideal solvent for the extraction process, which explains why several authors3−5 have studied the solubility of various solids in supercritical CO2. This study centers on measuring the solubility data in supercritical carbon dioxide of antioxidantsincluding ethylenediaminetetraacetic acid (EDTA) disodium salt dihydrate, EDTA calcium disodium salt hydrate, and L-cysteine hydrochloride. Cortest et al. have centered on a number of antioxidantsα-tocopherol succinate acid, ascorbic acid, butyl hydroxyl anisole, ascorbyl palmitate, gallic acid, dodecyl gallate, and propyl gallate, to name a fewand measure their solubilities in supercritical CO2 under conditions of various pressure and © 2015 American Chemical Society

Received: July 13, 2015 Accepted: November 24, 2015 Published: December 4, 2015 342

DOI: 10.1021/acs.jced.5b00589 J. Chem. Eng. Data 2016, 61, 342−347

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Table 1. Physical Properties of Carbon Dioxide, EDTA Disodium Salt Dihydrate, EDTA Calcium Disodium Salt Hydrate, and L-Cysteine Hydrochloride

Article

EXPERIMENTAL SECTION

Materials. In this study, the researcher takes great caution in the preparation of compounds to prevent the experimental results from being spoiled by impure chemicals. With a minimum mass fraction purity of 99.5%, carbon dioxide is procured from Chiau-Chung Gas Co. (Taiwan). EDTA disodium salt dihydrate (C10H14N2Na2O8·2H2O), EDTA calcium cisodium hydrate (C10H12CaN2Na2O8·H2O), and L-cysteine hydrochloride(C3H7NO2S·HCl) are purchased from Sigma-Aldrich Co. The chemical structures, molecular weights, and mass fraction purity of carbon dioxide, EDTA disodium salt dihydrate, EDTA calcium cisodium hydrate, and L-cysteine hydrochloride are shown in Table 1. All the chemicals are applied as received with no further purification. Apparatus and Analysis. The installation of experimental apparatus is performed no less scrupulously than the preparation of chemicals. A semiflow type apparatus, of which the configuration is shown in Figure 1, is constructed to measure the solid solubility in supercritical CO2. There are three stages of the whole operation procedure: the feeding, the equilibrium, and the analysis. For a start, CO2 in a supercritical condition is injected into the apparatus in a measured manner for the later dissolution of the solid, which reaches equilibrium at the second stage. Lastly, the registered results are examined to find the models’ coefficients. At the first stage, the liquefied pure CO2, initially being cooled to the temperature of 275.15 K with a cooler (2), is compressed to several distinct pressures by an HPLC pump (3) (Thermo Separation Product) controlled by a back pressure regulator. The compressed CO2 is subsequently fed into a preheating coil (5) soaked in a water bath (6) for the purpose of keeping its temperature steady. The supercritical CO2 later flows through the pre-equilibrium cell (7) and the equilibrium cell (8). Each cell has a volume of 75 cm3, and 5 g of drug sample in it, with the sample mixed with

situations. Although many numerical models have been proposed,10 the Mendez-Santiago and Teja model and Christal model are widely used in the literature. Fewer parameters, easy applicability, and a reasonable range of error (within experiment’s range of error) are their advantages over other models. The researcher of this study set up a similar semiflow apparatus to measure the solid solubility of EDTA disodium salt dihydrate, EDTA calcium disodium salt hydrate, and L-cysteine hydrochloride in supercritical CO2 at different temperatures, 308.15, 313.15, and 318.15 K, over the pressure ranging from 10 to 22 MPa (for EDTA disodium salt dihydrate) or from 12 to 24 MPa (for EDTA calcium disodium salt hydrate and L-cysteine hydrochloride).

Figure 1. Schematic diagram of the experimental apparatus. 343

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Table 2. Solubility of EDTA Disodium Salt Dihydrate, EDTA Calcium Disodium Salt Hydrate, and L-Cysteine Hydrochloride in Supercritical Carbon Dioxidea solute EDTA disodium salt dihydrate

T (K) 308.15

313.15

318.15

EDTA calcium disodium salt hydrate

308.15

313.15

P (MPa) 10 12 14 16 18 20 22 10 12 14 16 18 20 22 10 12 14 16 18 20 22 12 14 16 18 20 22 24 12 14 16 18

solubility y (mole fraction) 1.99 2.59 3.05 3.40 3.58 3.69 3.80 1.51 2.42 3.19 3.66 4.01 4.32 4.63 1.12 2.31 3.36 4.02 4.45 4.90 5.17 5.90 6.46 7.42 8.64 9.09 1.01 1.11 5.57 6.61 8.10 9.20

× × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × ×

solute

10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−7 10−7 10−7 10−7 10−7 10−6 10−6 10−7 10−7 10−7 10−7

T (K)

318.15

L-cysteine

hydrochloride

308.15

313.15

318.15

P (MPa) 20 22 24 12 14 16 18 20 22 24 12 14 16 18 20 22 24 12 14 16 18 20 22 24 12 14 16 18 20 22 24

solubility y (mole fraction) 9.83 1.08 1.20 4.81 6.74 8.35 9.66 1.16 1.24 1.29 7.59 1.05 1.41 1.73 1.95 2.27 2.62 1.14 1.58 2.12 2.68 3.12 3.56 4.02 1.06 2.00 2.90 3.68 4.54 5.21 5.61

× × × × × × × × × × × × × × × × × × × × × × × × × × × × × × ×

10−7 10−6 10−6 10−7 10−7 10−7 10−7 10−6 10−6 10−6 10−7 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6 10−6

a Standard uncertainties u are u(T) = 0.1 K, u(P) = 0.1 MPa, the combined expanded uncertainty Uc is Uc(y) = 1.294 × 10−7 (0.95 level of confidence) for EDTA disodium salt dihydrate, Uc(y) = 4.472 × 10−8 (0.95 level of confidence) for EDTA calcium disodium salt hydrate, and Uc(y) = 1.157 × 10−7 for L-cysteine hydrochloride (0.95 level of confidence).

concentration. To ensure the instrument’s exactitude, the UV− VIS detector is calibrated with solutions of specific concentrations. The sharp absorption peaks of EDTA disodium salt dihydrate, EDTA calcium cisodium hydrate, and L-cysteine hydrochloride are studied in the UV−VIS detector at the band of 192.5, 198.1, and 203.0 nm, respectively. Repeatability about the measurement is confirmed in each round of the experiment. For every specific condition of pressure and temperature, the relevant data are recorded at least three times. With the measurement of thermal decomposition, it is found that the solid residue of EDTA disodium salt dihydrate and EDTA calcium disodium hydrate after the experiment still hold the original hydrate. Through the measurement of the pH value of the water solution, L-cysteine hydrochloride is verified to keep its original hydrogenchloride. Finally, it must be noted that the experimental results are all attested as data collected at the equilibrium: measurements are made at different effluent CO2 flow rates between 67 mL·min−1 and 83 mL·min−1 at atmospheric conditions, although the flow rate does not have anything to do with the solid solubility measurement. Modeling. In this research, the author uses two semiempirical equations to find the correlation of the solid solubility in

glass beads. For fear that any physical entrainment would spoil the experiment results, filter or glass wool is used at the ends of the cell to make it entrainment free. The temperature is taken by a calibrated thermocouple (9) with a resolution of 0.1 K; the pressure is determined with a Druck pressure transducer (10) (PTX 1400) with a resolution of 0.1 MPa. When released from the equilibrium cell, supercritical CO2 is expanded through a needle valve, and its pressure decreases to atmospheric pressure in the condition that the needle valve is enveloped with heating tapes (11) to keep the temperature constant, at 333.15 K, preventing EDTA disodium salt dihydrate, EDTA calcium cisodium hydrate, and L-cysteine hydrochloride from freezing and blocking the pipeline. At this stage, the solid part is divided from the gas and dissolved into the pure water flask (12). For the residual solute in the line to be retrieved, water solvent is applied and later purged by air in the sampling line to remove it. To guarantee the reliability of the experimental results, the solvability data are taken with great care. A wet test meter (15) (Ritter TG05) is responsible for the measurement of the total volume of CO2 flow; for the water solution in the flask, the UV−vis (Cary 50 spectrophotometer) detector takes its 344

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Figure 2. Solubility for EDTA disodium salt dihydrate (2) in supercritical carbon dioxide (1) . (▲, 308.15 K; ●, 313.15 K; ⧫, 318.15 K; ---, MST model; , Chrastil model).

Figure 4. Solubility for L-cysteine hdrochloride (4) in supercritical carbon dioxide (1) . (▲, 308.15 K; ●, 313.15 K; ⧫, 318.15 K; ---, MST model; , Chrastil model).

Table 3. Correlated Results of Solid Solubility Data in Supercritical Carbon Dioxide model

parameters

CO2 + EDTA disodium salt dihydrate Chrastil k = 4.17906, a = −4527.01, b = 4.78470 Mendenz-Santiago and A = −9183.98, B = 105678, Teja C = 13.4919 CO2 + EDTA calcium disodium salt hydrate Chrastil k = 5.02621, a = −4247.56, b = 2.65277 Mendenz-Santiago and A = −9512.90, B = 131222, Teja C = 11.5749 CO2 + L-cysteine hydrochloride Chrastil k = 7.92765, a = −12543.1, b = 29.8311 Mendenz-Santiago and A = −18787.7, B = 182682, Teja C = 39.1470

100 Obj = n

Figure 3. Solubility for EDTA calcium disodium salt hydrate (3) in supercritical carbon dioxide (1) . (▲, 308.15 K; ●, 313.15 K; ⧫, 318.15 K; ---, MST model; , Chrastil model).

n

∑ k=1

AARD (%) 3.24 5.10

2.43 3.54

3.33 4.13

|yjexp − yjcal | .k .k yjexp .k

(2)

where the subscript k denotes the kth experimental data point for solid solute j. Developed by Mendez-Santiago and Teja, the second semiempirical equation (the MST model) has three parameters:

supercritical CO2one propounded by Chrastil and one by Mendez-Santiago and Teja. The Chrastil model shows that there is a linear relationship between the density of pure CO2 (component 1) and the solubility of the solid, both in their logarithmic form: a ln yj = k ln ρ1 + +b (1) T where yj is the concentration of solute j in the supercritical fluid (kg/m3) and ρ1 is the density of the supercritical fluid (pure CO2) (kg/m3). Constants a and b and the association number k are empirical model parameters. The values of these parameters can be calculated by minimizing with regression the objective function:

T ln(yj P) = A + Bρ1 + CT

(3)

with the minimization of the objective function of eq 2, the parameters A, B, and C can be computed using a simple leastsquare analysis. The value of ρ1 in eq 1 and eq 3 is computed with the method 32 term modified Benedict−Webb−Rubin (MBWR-32) equation.11

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RESULTS AND DISCUSSION After close examination of the isothermal solid solubility data of the three antioxidants (EDTA disodium salt dihydrate, EDTA 345

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Table 2 lists the solid compounds’ mole fractions at the equilibrium state. It should be noted that the equilibrium solubility can be satisfactorily reproduced. Furthermore, the flow rate, ranging from 67 mL·min−1 and 83 mL·min−1, has no effect on the solubility for either solid compound. Statistically, standard deviations of the experimental data are sufficiently small (Table 2). The solid solubility measurement’s coefficient of variance, that is, the standard deviation divided by mean value, is below 5%, which indicates that the experiment can be performed repeatedly with high accuracy. The results are shown graphically in Figure 2, Figure 3, and Figure 4. To simplify, the subscripts 1, 2, 3, 4 are used in this article to represent carbon dioxide, EDTA disodium salt dihydrate, EDTA calcium cisodium hydrate, and L-cysteine hydrochloride, respectively. The effect of temperature on solid solubility can be derived from the crossover points in the relevant figures. The crossover pressures for EDTA disodium salt dihydrate, EDTA calcium cisodium hydrate, and L-cysteine hydrochloride are determined at 12, 14, and 12 MPa, respectively. Shown in Table 3 are the parameters of the two semiempirical equations and correlation results. The average absolute relative deviation (AARD) of the calculated solid solubility is under 5.1%, which suggests that the experimental results are satisfactorily accurate. Figure 2, Figure 3, and Figure 4 show the graphical results of correlation obtained from the two semiempirical equations. The literature reports that whether the experimental data are self-consistent can be analyzed by the MST model. Shown in Figure 5 is a typical example, in which the plot of Tln(yjP) − TC against the density of supercritical CO2 is almost a straight line, which amounts to an assurance that the parameters derived from the MST model are correct in this study.

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CONCLUSION New solid solubility data for three antioxidants of EDTA disodium salt dihydrate, EDTA calcium cisodium hydrate, and L-cysteine hydrochloride (at temperatures 308.15, 313.15, and 318.15K) in supercritical CO2 are put forward in this study with pressures ranging from 10 to 22 MPa or from 12 to 24 MPa. The range of solubility of these antioxidants is between 10−6 and 10−7. The crossover pressures for EDTA disodium salt dihydrate, EDTA calcium disodium hydrate, and L-cysteine hydrochloride are at 12, 14, and 12 MPa, respectively. With AARD in solid solubility under 5.1%, both the Chrastil and the MST semiempirical equations yield convincing correlation results for solid solubility. Considering the limited amounts of antioxidants added to foods as preservatives, the supercritical fluid technique is safe enough for those compounds.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +886-2-2861-4011. Notes

The authors declare no competing financial interest.

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Figure 5. Test of consistence for solubility data of EDTA disodium salt dihydrate (2), EDTA calcium disodium salt hydrate (3), and L-cysteine hydrochloride (4) using the Mendez-Santiago and Teja (MST) model. (▲, 308.15 K; ●, 313.15 K; ⧫, 318.15 K).

REFERENCES

(1) Teja, A. S.; Eckert, C. A. Commentary on supercritical fluids: research and application. Ind. Eng. Chem. Res. 2000, 39, 4442−4444. (2) Beckman, E. J. Supercritical and near-critical CO2 in green chemical synthesis and processing. J. Supercrit. Fluids 2004, 28, 121− 191. (3) Lucien, F. P.; Foster, N. R. Solubilities of solid mixtures in supercritical carbon dioxide: a review. J. Supercrit. Fluids 2000, 17, 111− 134.

calcium disodium hydrate, and L-cysteine hydrochloride) in supercritical CO2 at different pressures (ranging from 10 to 22 MPa or from 12 to 24 MPa), it is obvious that the solubility increases with the pressure along an isotherm; specifically, all antioxidants have a similar solubility range, from 10−7 to 10−6. 346

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