Determination of the Solubility of Ammonium Dihydrogen Phosphate

Article pubs.acs.org/jced

Determination of the Solubility of Ammonium Dihydrogen Phosphate in Water−Ethanol System at Different Temperatures from 283.2 to 343.2 K Dejun Xu, Xing Xiong, Lin Yang, Zhiye Zhang, and Xinlong Wang* College of Chemical Engineering, Sichuan University, Chengdu 610065, China ABSTRACT: The solubility of ammonium dihydrogen phosphate (MAP) was measured at the temperature range from 283.2 to 343.2 K by using dynamic and static methods in water−ethanol system. The experiment results showed that the solubility of MAP increased with the increase of the investigated temperatures under the constant ethanol concentration and decreased with increasing concentration of ethanol with isothermal operations. The solubility of MAP in water−ethanol system was fitted by the modified Apelblat equation, the correlation coefficient square was greater than 0.990, and the average of the root-mean-square deviation was 4.346 × 10−4, which indicated that the experiment data was well in agreement with the calculation value.

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through the filtration. Then, the residue fluid is distillated and the overhead product (high concentration ethanol) and the bottom product (MAP solution) can be recycled. Generally, the solubility of MAP in water−ethanol system plays a crucial role in antisolvent crystallization process but the data are not systematically demonstrated in published literatures. Thus, it is necessary to determine the solubility of MAP in the water− ethanol system. In this paper, the solubility of MAP in the water−ethanol system is measured from (283.2 to 343.2 K), and the result is fitted with the modified Apelblat Equation.

INTRODUCTION Ammonium dihydrogen phosphate (MAP) is a very important product in the phosphate systems, and it is widely used in various industries, such as flame retardants,1 fertilizers,2 food, feed, and wastewater treatment.3 According to previous studies,4,5 crystallization process is of great importance to the products. The crystallization of MAP is a very important step in solution systems. Cooling and evaporation, which are usually considered in the crystallization process, lead to high energy consumption and production cost. The antisolvent crystallization6−10 is usually considered a potential way to save energy and improve the crystal quality, because the water activity is lowered and the solubility of the salt is decreased with a suitable antisolvent added to the mother liquor. Adding ethanol to MAP solution to precipitate MAP is a novel method to produce MAP, and it is of great potential to energy saving. In Figure 1, a new process based on antisolvent crystallization technology is proposed to produce MAP. As an antisolvent, ethanol is added to the crystallizer during antisolvent crystallization. An amount of ethanol lowers the solubility of MAP to produce MAP in the mixture system and the MAP and residual fluid are obtained

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EXPERIMENTAL SECTION

Materials. The chemical reagents used (listed in Table 1) in the present paper are as follows: ammonium dihydrogen phosphate (analytical grade, mass fraction ≥99.0%) and ethanol (analytical grade, mass fraction ≥99.7%), which bought from Table 1. Chemical Reagents Used in this Work chemical name ammonium dihydrogen phosphate ethanol

purification method

Tianjin Bodi Chemical Co., Ltd.

0.990

none

Chengdu Haixing Chemical Reagents Factory

0.997

none

source

Received: March 10, 2015 Accepted: November 24, 2015

Figure 1. Process schematic of producing MAP by using the water− ethanol solution. © XXXX American Chemical Society

initial mass fraction purity

A

DOI: 10.1021/acs.jced.5b00224 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 2. Comparison of the Solubility of MAP in Literature17,18 and Experiment in Water at Pressure of 0.1 MPa T/K

283.2

293.2

303.2

313.2

323.2

333.2

experimental mole fraction literature mole fraction17,18

0.0425 0.0411

0.0528 0.0533

0.0644 0.0663

0.0808 0.0806

0.0937 0.0976

0.1130 0.1153

Tianjin Bodi Chemical Co., Ltd. and Chengdu Haixing Chemical Reagents Factory, respectively. The water used in this work was deionized water. Apparatus and Procedure. The solubility of MAP in the water−ethanol system was measured by a dynamic method11,12 (mass fraction of ethanol was from 10.00 to 50.00%) and a static equilibrium method13 (mass fraction of ethanol was from 60.00 to 90.00%). Both methods were described in the literature.11−13 In this work, the experimental device for the determination of solubility was the same as the description in the literature.14 It consisted of a thermostatic bath, a jacketed glass bottle, a mercury thermometer, and a magnetic stirrer. The temperature of solution in the jacketed glass bottle was controlled by the smart thermostatic bath and measured by a mercury thermometer with a precision of 0.1 K. The magnetic stirrer was used to provide vigorous agitation to obtain homogeneous mixing and reach the equilibrium as early as possible. The solubilities of MAP were measured as follows. Because the solubility of MAP changes greatly with temperature at a low concentration of ethanol in ethanol−water mixtures, the solubility of MAP can be determined by using a dynamic method11,12 in the preliminary experiments. The ethanol−water solution, which was known by the mass and composition, was added to the jacketed glass bottle, and the system temperature was controlled by the smart thermostatic bath. A known weight of MAP was put into the solution, and then a small amount of weighed MAP was added again if the added MAP was dissolved. When the last addition of MAP was not dissolved or was not completely dissolved in the solvent, the solid liquid phase equilibria was established. The total addition of MAP before the last addition was the solubility of MAP in the known conditions. All of the additions were weighed by an analytical balance with an uncertainty of 0.0001 g. In the follow-up experiment process, the solubility of MAP was measured by static equilibrium method13 because the solubility of MAP was almost unchanged with temperature at high concentration of ethanol. The mixture was continuously stirred for 3.5 h and held still for 1.0 h to allow the insolubility to settle down; then about 25 g supernatant of the mixture was transferred to a beaker (250 mL). The content of MAP was determined by the gravimetric analysis of quimoline phosphomolybdate.15 This method is described in more detail as follows. Ten milliliters of dilute nitric acid (1 + 1) was added into the beaker, and diluted to about 100 mL with deionized water. The above solution was heated until boiling and then quimoline phosphomolybdate reagent was added to the solution with gentle swirling. At the same time, a yellow precipitate was generated. The beaker was covered with a watch bath glass and the solution was cooled to about room temperature and then was filtered, cleaned, dried, and so forth. The precipitate on the sand core crucible was dried for 45 min at 180 °C. The crucible containing the precipitate was cooled in a desiccator for 30 min and then weighed to the nearest 0.0001g. The solubility of MAP with static equilibrium method, S, expressed in weight percentage is given as

S=

m2 × 0.05199 × 100, wt% m1 − m2 × 0.05199

where m1 and m2 are the weight of the sample solution and the yellow precipitate, respectively, and 0.05199 is the coefficient of the mole mass of quimoline phosphomolybdate conversion to the weight of MAP. All of the measured experiments were repeated three times in this work, and the experimental solubility value was the average of these three experiments. The results was also expressed in mole fraction of solubility, and the total average relative uncertainly was estimated of 0.1 based on scatter of the experimental data. Verification of Procedure. In this experiment, the solubility of MAP was determined in water first. Compared to the literature data16−18 and the experimental data, which is listed in Table 2 and Figure 2, it can be clearly seen that the

Figure 2. Comparison of the solubility of MAP in literature and experiment in water.

consistency of the data was excellent, and the solubility of the relative deviation was less than 2%. Therefore, it was regarded as a reliable method of measuring the solubility data of MAP from 283.2 to 343.2 K. Xu et al.8 have inspected the morphology and structure of MAP in the water−ethanol system and have corroborated that the morphologies of MAP crystal was changed by the interaction between the hydrogen bonds of MAP crystal and the ethanol molecules. Figure 3 presents the XRD pattern of the crystal. Compared with the powder diffraction file of standard MAP, the pattern showed that the undissolved sample was MAP. Therefore, it was found that the morphologies of MAP was changed by the addition of ethanol.

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RESULTS AND DISCUSSION The solubility of MAP was measured in the water−ethanol system with ethanol concentrations from 10.00 to 90.00 wt % at 283.2−343.2 K. The results are shown in Table 3 and as dots in Figure 4. It can be observed that the solubility of MAP B



Article

Figure 3. XRD pattern of MAP.

maintained a close association with the concentration of ethanol and the temperature. The solubility of MAP was reduced by increasing the concentration of the antisolvent ethanol, which binds the free water. It can be clearly seen that the antisolvent ethanol in the solvent has greater influence on

Figure 4. Three-dimensional diagram of solubility of MAP in the water−ethanol system.

Table 3. Experiment Mole Fraction Solubility of MAP in Water−Ethanol System at the Pressure of 0.1 MPaa solvent pure water

mass fraction of ethanol = 10.00%




a

T/K

x·103

100(x − xcal)/x

solvent

T/K

x·103

100(x − xcal)/x

283.2 293.2 303.2 313.2 323.2 333.2 343.2 283.2 293.2 303.2 313.2 323.2 333.2 343.2 283.2 293.2 303.2 313.2 323.2 333.2 343.2 283.2 293.2 303.2 313.2 323.2 333.2 343.2 283.2 293.2 303.2 313.2 323.2 333.2 343.2

42.53 52.84 64.43 80.81 93.79 113.07 134.35 21.23 30.8 40.49 54.04 69.16 89.49 114.29 10.72 16.33 23.82 32.68 44.27 61.62 82.88 5.58 9.50 13.66 18.81 26.36 38.31 57.34 2.57 4.77 7.37 10.35 14.68 21.29 34.04

−2.81 −0.85 −0.38 3.25 −0.37 0.13 −0.44 −6.40 1.42 0.35 1.80 0.01 0.20 −0.09 −11.29 −2.15 2.49 1.48 −0.33 1.01 −0.58 −3.48 9.35 6.67 0.53 −3.38 −2.82 1.43 −5.35 10.99 10.86 3.04 −3.15 −6.00 2.24


283.2 293.2 303.2 313.2 323.2 333.2 343.2 283.2 293.2 303.2 313.2 323.2 333.2 343.2 283.2 293.2 303.2 313.2 323.2 333.2 343.2 283.2 293.2 303.2 313.2 323.2 333.2 343.2 283.2 293.2 303.2 313.2 323.2 333.2 343.2

1.354 2.368 3.889 5.269 7.451 9.889 14.998 0.845 1.238 1.845 2.596 3.300 4.319 5.673 0.556 0.721 0.911 1.087 1.321 1.573 1.877 0.203 0.245 0.312 0.352 0.406 0.454 0.545 0.056 0.063 0.072 0.081 0.093 0.104 0.120

−21.04 −2.26 8.97 2.71 1.32 −5.71 1.74 −6.77 −4.59 1.82 4.56 −0.63 −1.17 0.34 −2.07 0.58 2.02 −0.61 −0.17 −0.59 0.33 −2.09 −2.09 4.62 0.72 −0.31 −3.35 1.59 −0.05 −1.41 1.12 −0.49 0.35 −1.17 0.50





Standard uncertainties u are u(T) = 0.1 K, ur(p) = 0.05, ur(x) = 0.1, ur(ethanol) = 0.0018 C



Article

antisolvent. The key solubility of MAP in the water−ethanol system has been determined by dynamic method and static method at 283.2−343.2 K. It increases with temperature under the constant ethanol concentration in the water−ethanol system. However, it decreases with the increasing concentration of ethanol under isothermal operations in water−ethanol system. The modified Apelblat equation was used to correlate the solubility of MAP in water−ethanol system, and the results showed that good agreement was obtained between the experimental and the calculated data.

the solubility of MAP than temperature. With increasing ethanol−water ratio, the solubility isotherms decline significantly, which shows that the influence of ethanol on the solubility of MAP was very obvious. Compared with the solubility of MAP in water, the solubility of MAP was decreased sharply first and then almost unchanged with the ethanol− water ratio increasing. This turning point of the ethanol−water ratio was increased with the increase of temperature. For example, the turning point of the ethanol−water ratio was about 30% (ethanol concentration) when the system temperature was 283.2 K, but the turning point was 60% when the system temperature was 343.2 K. At the same ethanol−water ratio, the solubility of MAP increased with the increase of temperature over the investigated temperature. Figure 4 and Table 3 also show that the solubility of MAP was very low when the ethanol concentration was relatively high. Therefore, the MAP can be separated by antisolvent crystallization using the ethanol as antisolvent. The solubility of MAP was fitted with the follow modified Apelblat equation19,20

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Corresponding Author

*E-mail: [email protected]. Tel./Fax: +86-28-85405235. Funding

Thank you very much from the Yunnan provincial Science and Technology Department (no. 2014IB004) of the financial support. Notes

The authors declare no competing financial interest.

A ln x = + B + C ln T T

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where x is the mole fraction solubility of MAP; T is the absolute temperature (K); and A, B, and C are the model parameters that are obtained through a nonlinear regression method. The

mass fraction of ethanol/%

A

B

C

R2

104 rmsd

0 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00

632.976 −276.174 1748.142 1334.162 316.037 722.506 −3283.869 −2143.188 −1680.728 1759.077

−49.961 −45.462 −99.447 −101.085 −86.457 −86.598 10.236 3.907 0.002 −70.190

7.899 7.553 15.735 16.156 14.068 13.750 −1.001 −0.675 −0.451 9.598

0.998 0.999 0.999 0.997 0.993 0.993 0.998 0.999 0.990 0.999

11.394 6.602 6.342 7.840 7.031 2.983 0.598 0.097 0.090 0.007

REFERENCES

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Table 4. Parameters of the Modified Apelblat Equation for the Solubility of MAP in the Water−Ethanol System

values of these parameters are given in Table 4. The root-meansquare deviation (rmsd) is calculated as follows ⎡1 rmsd = ⎢ ⎢⎣ N

AUTHOR INFORMATION

⎤1/2 cal 2 ⎥ ( x x ) − ∑ ⎥⎦ i=1 N

where N is the number of experiments points and x and xcal are the experimental and calculated data solubility of MAP, respectively. R2 is the square of correlation coefficient. It can be seen from Table 4 that all of the R2 were more than 0.990 and the largest of the rmsd was 1.139 × 10−3 and the smallest rmsd was 1.6 × 10−6 for the solubilities of MAP in water− ethanol solutions. These indicate that the solubility of MAP can be well described by the modified Apelblat equation in the water−ethanol system.

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CONCLUSIONS A new process based on antisolvent crystallization technology was proposed to produce MAP and ethanol was used as the D



Article

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Determination of the Solubility of Ammonium Dihydrogen Phosphate

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