Solvent Polarity Effect when Amberlite-LA2 Is Used in the Extraction of

Article pubs.acs.org/jced

Solvent Polarity Effect when Amberlite-LA2 Is Used in the Extraction of Picric Acid Hasan Uslu,*,†,§ Dipaloy Datta,‡ and Hisham S. Bamufleh§ Iṡ tanbul Esenyurt University, Engineering and Architecture Faculty, Industrial Engineering Department, Esenyurt, Iṡ tanbul, 34510, Turkey ‡ Malaviya National Institute of Technology (MNIT), Department of Chemical Engineering, Jaipur, Rajasthan 302017, India § Chemical and Materials Engineering Department, Faculty of Engineering, King Abdulaziz University, Jeddah, 23218, Saudi Arabia †

ABSTRACT: The separation and recovery of picric acid (0.061 mol·kg−1) from its aqueous solution was studied at a fixed temperature of 298 K. The extraction experiments were performed by using a secondary amine, Amberlite-LA2 (ALA2), dissolved in five different solvents such as dichloromethane (DCM), dodecanol, toluene, benzene, and dodecane. Physical extraction data were also produced by pure solvent alone. The experimental data obtained from the batch studies were analyzed by calculating the distribution coefficient (KD), extraction efficiency (%E), and loading factor (Z). The highest synergistic effect was achieved with DCM in ALA2 at a concentration of 0.588 mol·kg−1 as 83.61%. The equilibrium constants for the complex formation between acid and amine (1:1 and 2:1) were calculated for all the solvents applying the mass action law.

1. INTRODUCTION Wastewater is continuously produced from many chemical and petrochemical plants through the production of pharmaceuticals, agricultural chemicals, dyes,1,2 herbicides, fungicides, insecticides, explosives, precursors of dyes and plasticizers, etc.3 2,4,6-Trinitrophenol (picric acid) is one of the nitro aromatic compounds found in wastewater, and this chemical is responsible for causing headache, nausea, dizziness, difficulty in swallowing, diarrhea, vomiting, shock, convulsions, or even death. It can affect the central nervous system, liver, and kidneys.4−7 The Environmental Protection Agency (EPA) and European Union (EU) have restricted the maximum concentration of total phenol allowed in the drinking water to be 10 ng·mL−1.8 Nitro phenols removal was studied by many researchers using different techniques. Among the investigated technologies, advanced oxidation,9,10 adsorption,11 and biological treatment12−14 were some of them. Extraction using liquid membrane was also used to remove nitrophenols from the wastewater.15−18 In this technique, two types of liquid membranes, unsupported liquid membrane19,20 and supported liquid membrane with hollow fiber,21 were used to remove different types of nitrophenols.22−27 The advantage of this process over other processes is its lower cost, no production of other toxic materials, and the flexibility of continuous operation on the industrial scale28 Not enough information is available in the literature for the extraction of picric acid from wastewater. Amberlite LA2, a secondary amine with high molecular weight can be used in the removal of acids from aqueous solution by forming waterinsoluble amine salts.29 The equilibrium study of the extraction © 2017 American Chemical Society

of picric acid from wastewater using Amberlite LA2 in different solvents was conducted and investigated in this work.

2. MATERIALS AND METHODS 2.1. Materials. All the reagents were used as supplied. Picric acid and solvents with purity greater than 98% in mass were procured from Sigma-Aldrich. Amberlite LA-2, (Sigma-Aldrich, purity >99%), an anion exchange extractant, is a yellow liquid with a density of 830 kg·m−3. Table 1 shows the chemicals’ information. 2.2. Methods. An aqueous solution of picric acid at a concentration of 0.061 mol·kg−1 was prepared. Different concentrations of organic phase containing ALA2 ranging from 0.353 to 1.763 mol·kg−1 were prepared using five solvents. This concentration range was chosen on the basis of the preliminary experiments performed and to achieve the best extraction efficiency. The same amount of organic and aqueous phase (20 mL each) was taken in a 100 mL Erlenmeyer flask, and this was placed in a temperature controlled shaker at 298 K for 2 h at 50 rpm. These experimental conditions were determined from preliminary tests. After the equilibrium, the flask was kept for 2 h at the specified temperature so to have a clear separation of the phases. The aqueous phase containing picric acid after separation was analyzed by base titration (0.01 N NaOH), using phenolphthalein as indicator. Picric acid concentration after the extraction in the organic phase was Received: November 20, 2016 Accepted: February 14, 2017 Published: February 21, 2017 1125

DOI: 10.1021/acs.jced.6b00970 J. Chem. Eng. Data 2017, 62, 1125−1129

Journal of Chemical & Engineering Data

Article

Table 1. Chemicals Used in the Present Studya

a

compound

IUPAC name

source

CAS No

assay

picric acid Amberlite LA-2 dichloromethane dodecanol toluene benzene dodecane

2,4,6-trinitrophenol N-lauryltrialkyl-methyl amine dichloromethane dodecan-1-ol metil benzen benzene dodecane

Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich

88-89-1 11128-96-4 75-09-2 112-53-8 108-88-3 71-43-2 112-40-3

98% 99% 99.8% 99% 99.8% 99.9% 99%

The reported purities were stated by the suppliers, and the samples were not further purified.

obtained as 5.1 at highest ALA2 concentration (1.763 mol· kg−1) with DCM. 3.3. Mass Action Law Modeling and Reaction Stoichiometry. The extraction path of picric acid with an amine extractant (Amberlite LA2) dissolved in an organic solvent at equilibrium could be explained by the mass action law. An equilibrium reaction between one acid molecule (PAH represents the undissociated part of the acid molecule in the aqueous phase), and n molecules of extractant forming 1:n complexes in the organic phase30,31 could be written as

calculated by a mass balance. Equilibrium experiments and chemical analyses were done in duplicate, and the average values were used for the calculation. In maximum circumstances, the deviation in analyzing the concentration in each experiment did not exceed beyond ±3%.

3. RESULTS AND DISCUSSION 3.1. Physical Extraction. The solubility of picric acid in pure solvent alone is considerably insignificant with a maximum value of the distribution coefficient about 0.151 for DCM, 0.089 for dodecanol, 0.034 for toluene, 0.034 for benzene, and 0.017 for dodecane as given in Table 2. These solvents (usual)

KE

PAH + nS ̅ ↔ (S)n (PAH)

where n is the solvation number of extractant. As the acid− ALA2 complex is formed, it is quickly extracted into the organic phase, and the equilibrium constant of a complex formation may be written by using the law of mass action.

Table 2. Physical Equilibrium Data of Picric Acid in Five Different Solvents at a Temperature of T = 298.5 K and P = 101.3 kPaa maq solvent

(mol·kg )

m̅ org (mol·kg‑1)

DCM dodecanol toluene benzene dodecane

0.053 0.056 0.059 0.059 0.060

0.008 0.005 0.002 0.002 0.001

‑1

KD

E

(−)

(%)

0.151 0.089 0.034 0.034 0.017

13.11 8.20 3.28 3.28 1.64

(1)

KE =

[(PAH)·(S)n ] [PAH]·[S]̅ n

(2)

The distribution coefficient for the extraction reaction as shown in eq 1 may be expressed as KD =

a

maq is the molality of the picric acid in the aqueous phase, m̅ org is the molality of the picric acid in the organic phase, KD is the distribution coefficient, E is the extraction efficiency, Z is the loading factor. Standard uncertainties u are u(maq) = 0.001 mol·kg−1, u(m̅ org) = 0.001 mol·kg−1, u(T) = 0.1 K, u(P) = 0.5 kPa.

[(PAH)·(S)n ] [PAH] + [PA−]

(3)

−

where PA is the dissociated part of acid. The dissociation reaction of acid in the aqueous phase at equilibrium is shown as Ka

PAH ↔ H+ + PA−

(4)

The dissociation constant (Ka) of acid in water is given by eq 5.

will not able to achieve the standards of an ideal extractant and do not fulfill the requirement of a higher distribution of acid. Thus, to achieve a better recovery of acid in terms of a high distribution coefficient and high selectivity, an extractant will be needed that will contribute to the enhancement of extraction efficiency. The distribution of picric acid between the phases with all solvents used in this study was low. The pure DCM and dodecanol reached the highest extraction efficiency with the values of 13.11% and 8.20%, respectively. 3.2. Chemical Extraction. The results for chemical extraction were obtained using five different concentrations of the extractant, Amberlite-LA2 (ALA2:0.353 to 1.763 mol·kg−1) with initial picric acid concentration of 0.061 mol·kg−1. The results are reported in Table 3. The KD values obtained by using the organic phases including ALA2 extractant dissolved in five different solvents were found to be in the range of 0.089 to 0.794 with dodecane, 0.109 to 0.968 with benzene, 0.130 to 1.103 with toluene, 0.386 to 1.652 with dodecanol, and 0.564 to 5.100 with DCM. There was an increase in the trend of extraction efficiency with the addition of a greater amount of extractant in the organic phase, and the highest KD was

Ka =

[H+][PA−] [PAH]

(5) −

From eq 5, the concentration of the dissociated part ([PA ]) of acid may be written in terms of undissociated acid concentration ([PAH]), pKa, and pH of the aqueous solution as [PA−] = [PAH](1 + 10 pKa − pH)

(6)

Then, substituting the values of [(PAH)·(T)n ] and [PA−] from eq 2 and eq 6, respectively, in eq 3, eq 7 was obtained. KD =

KE • [S]̅ n (1 + 10 pH − pKa)

(7)

The remaining amine concentration which is unreacted with the acid molecule in the extract phase at equilibrium ([T̅ ]) is represented as [S]̅ = [S]̅ in − n[(PAH)(S)n ]

(8)

The value of [S̅] from eq 8 is placed in eq 7 resulting in eq 9. 1126



Article

Table 3. Equilibrium Data for the Reactive Extraction of Picric Acid with Amberlite-LA2 in Five Different Solvents at a Temperature of T = 298.5 K and Pressure P = 101.3 kPaa [S̅]in, ALA2 concentration

maq

E

Z

(mol·kg−1)

m̅ org (mol·kg−1)

KD

(mol·kg−1)

(−)

(%)

(−)

n

log KE

R2

SD

0.353 0.705 1.058 1.410 1.763

0.056 0.052 0.046 0.039 0.034

0.005 0.009 0.015 0.022 0.027

0.089 0.173 0.326 0.564 0.794

8.17 14.75 24.59 36.06 44.26

0.014 0.013 0.014 0.016 0.015

1.63

0.582

0.970

0.0919

0.353 0.705 1.058 1.410 1.763

0.055 0.05 0.044 0.038 0.031

0.006 0.011 0.017 0.023 0.03

0.109 0.22 0.386 0.605 0.968

9.83 18.03 27.85 37.69 49.19

0.017 0.016 0.016 0.016 0.017

1.61

0.678

0.968

0.0931

0.353 0.705 1.058 1.410 1.763

0.054 0.049 0.043 0.037 0.029

0.007 0.012 0.018 0.024 0.032

0.13 0.245 0.419 0.649 1.103

11.5 19.68 29.53 39.36 52.45

0.02 0.017 0.017 0.017 0.018

1.59

0.737

0.949

0.1176

0.353 0.705 1.058 1.410 1.763

0.044 0.036 0.031 0.027 0.023

0.017 0.025 0.03 0.034 0.038

0.386 0.694 0.968 1.259 1.652

27.85 40.97 49.19 55.73 62.29

0.048 0.035 0.028 0.024 0.022

1.22

1.175

0.991

0.0371

0.353 0.705 1.058 1.410 1.763

0.039 0.033 0.024 0.019 0.01

0.022 0.028 0.037 0.042 0.051

0.564 0.848 1.542 2.211 5.1

36.06 45.89 60.66 68.86 83.61

0.062 0.04 0.035 0.03 0.029

1.96

1.568

0.862

0.2501

solvent Dodecane

Benzene

Toluene

Dodecanol

DCM

a [S̅]inis the ALA2 initial molality in the organic phase, maq is the molality of the picric acid in the aqueous phase, m̅ org is the molality of the picric acid in the organic phase, KD is the distribution coefficient, E is the extraction efficiency, Z is the loading factor. Standard uncertainties u are u(maq) = 0.001 mol·kg−1, u(m̅ org) = 0.001 mol·kg−1, u([S̅]in) = 0.01 mol·kg−1, u(T)=0.1 K, u(P)=0.5 kPa

KD =

KE·([S]̅ in − n[(PAH)(S)n ])n (1 + 10 pH − pKa)

(9)

For the estimation of KE and n it may be assumed that the initial concentration of ALA2 is more compared to that of acid−extractant complex concentration in the organic phase (i.e., [S̅]in ≫ n[(PAH)(S)n]. With this simplification, eq 9 may be represented as KD =

KE·[S]̅ n (1 + 10 pH − pKa)

(10)

When the concentration of the solute is more in the aqueous phase, then this particular assumption is not valid as the concentration of acid−amine solvate in the organic phase will increase. Now eq 10 is linearized by taking the log on both sides to determine the equilibrium parameters, n and KE. log[KD(1 + 10 pH − pKa)] = log KE + n·log[S]̅ in

(11) Figure 1. Determination of KE and n using Amberlite LA2 dissolved in ■, dodecane; ○, benzene; ∗, toluene; ×, dodecanol, and +, DCM, for the picric acid reactive extraction. ---, linear fit lines.

The graphs between log[KD·(1 + 10pH−pKa)] and log[S̅]in were drawn, and best fitted to estimate the value of equilibrium constant (log KE) from the intercept, and n from the slope. Figure 1 shows the plot, and the results are presented in Table 2 for different solvents. The values of n were mostly obtained as 1127



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above 1 for all the solvents tested. The values of n show 1:1 and 2:1 order of stoichiometric reactions between acid and amine. The solvent’s strength of the complex solvation was observed in the following order with ALA2: DCM > dodecanol > toluene > benzene > dodecane. Among the tested diluents, DCM (chlorinated hydrocarbon) provided best solvating medium for the acid−ALA2 complex. An extremely low value of equilibrium constant was found with dodecane. The acid− amine solvates are stabilized by hydrogen bonding between the diluent and the complex. This is confirmed from the significant difference between the KE values of diluents used.

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CONCLUSION In the present study, Amberlite-LA2, an amine-based extractant, was tested in various solvents for the reactive extraction of picric acid from aqueous solutions. Using the equilibrium data, KD, Z, %E, and KE values were calculated. Physical extraction experiments showed that the KD of picric acid with solvents alone was very low. The addition of extractant resulted in a positive influence on the recovery. The enhancement increased with the increase in extractant concentration. The KD, E%, and KE values obtained were in the order of DCM > dodecanol > toluene > benzene > dodecane. The highest KD (5.1) was obtained with the DCM + Amberlite LA2 system. The n values prompted the formation of a 1:1 and 2:1 acid−extractant complex. The extraction system comprising 1.763 mol·kg−1 Amberlite LA2 + DCM is found to be the best among the solvents studied.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Hasan Uslu: 0000-0002-4985-7246 Dipaloy Datta: 0000-0002-2048-9064 Notes

The authors declare no competing financial interest.

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REFERENCES

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Solvent Polarity Effect when Amberlite-LA2 Is Used in the Extraction of

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