Extraction of Picric Acid from Wastewater by a Secondary Amine

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Extraction of Picric Acid from Wastewater by a Secondary Amine (Amberlite LA2) in 1-Octanol: Equilibrium, Kinetics, Thermodynamics and Molecular Dynamic Simulation Hasan Uslu, Dipaloy Datta, and Hisham S Bamufleh Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b04750 • Publication Date (Web): 06 Mar 2016 Downloaded from http://pubs.acs.org on March 10, 2016

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Industrial & Engineering Chemistry Research

Extraction of Picric Acid from Wastewater by a Secondary Amine (Amberlite LA2) in Octan-1-ol: Equilibrium, Kinetics, Thermodynamics and Molecular Dynamic Simulation Hasan Uslua,c,*, Dipaloy Dattab, Hisham S. Bamuflehc a

Beykent University, Engineering and Architecture Faculty, Chemical Engineering Department, Ayazağa, Đstanbul, Turkey. *E-mail: [email protected]. b

Malaviya National Institute of Technology (MNIT), Department of Chemical Engineering, Jaipur, Rajasthan, India. c

Chemical and Materials Engineering Department, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia.

ABSTRACT The paper deals with the equilibrium and kinetic studies on the reactive extraction of picric acid (HPc: 0.021 - 0.061 kmol·m-3) using Amberlite LA2, a secondary amine (ALA2; 0.235 - 1.175 kmol·m-3) dissolved in an active diluent, octan-1-ol. Based upon the values of loading factor (Z < 0.5), the interaction between the molecules of HPc and ALA2 takes place by forming 1:1 solvates in the organic solvent phase, and confirmed from the FTIR analysis. The affect of temperature (298.2 K, 308.2 K and 318.2 K) on the performance of extraction is evaluated, and the thermodynamic parameters (entropy and enthalpy) are determined. The mass transfer coefficient (kL = 7.12×10-4 m·s-1) of picric acid in octan-1-ol is estimated experimentally to establish the kinetics of reaction. The Hatta number is found to be in the range of 0.009 to 0.011, suggesting a very slow extraction-reaction occurring in the bulk of the solvent phase. The reaction order is 1.2 w.r.t HPc, and 0.7 order w.r.t ALA2 with rate constants of forward and backward reactions as 18.3 × 10-6 (kmol·m-3)-0.9s-1 and 4.94 × 10-6 (kmol·m-3)-1.9s-1, respectively. Molecular dynamic behavior of HPc + ALA2 + octan-1-ol system in the organic solvent phase is predicted from the simulated results.

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Keywords: Picric acid; extraction; equilibrium; kinetics; thermodynamics; molecular modeling.

1. INTRODUCTION Processing industries produce substantial amounts of wastewater containing wide varieties of pollutants. Among these pollutants, the presence of phenols and/or nitrophenols1,2 in the wastewater streams causes tremendous environmental problems. The prime sources of phenols for the pollution of aquatic environment are wastewaters from different industries like paint, pesticide, coal conversion, polymeric resin, gasoline, rubber proofing, steel, petroleum and petrochemicals.3,4,5

Nitrophenol are essentially used in the production of the many valuable products such as pesticides, herbicides, explosives, dyes and plasticizers.1,2 Nitrophenols are resistant to biodegradation especially at high concentrations6 and are toxic chemicals that threaten the lives of the growing plants and microorganisms. They are also harmful to the humans and create polluting effects to the environment.1,2 As per the guidelines by US Environmental Protection Agency (EPA) and European Union (EU),the content of phenols in wastewater should not exceed 1 mg/L3, and 5 mg/L in Japan.7 Poly nitro-aromatic, 2,4,6-trinitrophenol or picric acid8 is one of the nitrophenols available in the industrial wastewater that should be minimized to decrease its harmful effects on the environment.1,2 Serine et al.9 studied the extraction of picric acid from aqueous chloride solutions into a solvent phase consisting of cyclohexane with trioctylphosphine oxide (TOPO) and trioctylamine (TOA). The association of acid molecule took place with one or two TOPO molecule, and with only one TOA molecule as confirmed from the data obtained from UV-visible spectrum of the organic phase. The spectrum of TOPO was largely depend on the free extractant content but in case of TOA spectrum did not show any dependency. Kusakabeet al.10 carried out extraction of phenol and nitrophenols into cyclohexane, and studied the association of these phenols with TOPO in the organic phase at 298 K. There was a linear relationship between logarithm of the partition coefficient of the phenols and logarithm of their association constants with TOPO. Extraction of picric acid from water or solutions containing (NH4)2SO4, Na2SO4, and NH4NO3 by 4-methyl-2-pentanone, 2-methylpropyl ethanoate, and diisopropyl ether was evaluated at 303.15 K and pH = 3.11 The extraction power of solvents was found to be 4-methyl-2-pentanone > 2-methylpropyl ethanoate > diisopropyl 2 ACS Paragon Plus Environment

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ether. The presence of ammonium nitrate in the solution enhanced the extraction yield but the presence of sulfates showed irregular behavior, and limited the extraction process. Recovery of picric acid from aqueous solutions was studied at 298 K by trioctylamine dissolved in various diluents like isoamyl alcohol, octan-1-ol, and 1-decanol.12 Isoamyl alcohol with TOA showed highest extraction efficiency with a distribution coefficient of 19.33 (95.08 %). The author also proposed Linear solvation energy relationship (LSER) models to predict the distribution coefficient. The experimental study on the equilibrium and kinetics for the adsorption of picric acid on the calcined and uncalcined mesoporous silicate MCM-41 adsorbent were studied.13 MCM-41 showed highest adsorption capacity of picric acid in the pH range of 1.4 to 4. Equilibrium, kinetics, and thermodynamic adsorption studies of picric acid14 were performed by using a weakly basic adsorbent (Amberlite IRA-67) at three different temperatures (298 K, 308 K, and 318 K). Optimum amount of adsorbent (Amberlite IRA-67) was found to be 1 g. The Langmuir isotherm and the pseudo-second-order model best described the experimental data in equilibrium and kinetic study, respectively. Thermodynamic parameters like ∆Hads0 (= -21.204 kJ·mol-1), ∆Sads0 (= -200.043 J·mol−1·K−1), and ∆Gads0 were also estimated. The separation methods such as the advanced oxidation15,16, adsorption17 and biological treatment18-20 were tried for the treatment of wastewater to remove different harmful compounds. These technologies have drawbacks of high costs and the formation of other toxic side products2 and limitation for application in industrial scale.8 Recently, a three phase liquid extraction (TLPE) system, a new technique was developed for the extraction of multi-component mixtures using multiphase separation in one extraction stage. The process is advantageous as there exists differences in physicochemical properties of the three coexisted phases21. It is also efficient and easy to be operated in a continuous lyon industrial scale.21 In TLPE process an ionizable compound is extracted from the donor phase to the organic phase, and then back extracted to the acceptor phase.22 Liquid-liquid-micro-extraction was involved in the organic membrane phase.2223

Liquid membranes were employed for the extraction of phenol from wastewater24-27 by using

unsupported liquid membrane28-29, liquid membrane supported with a hollow fiber30 and hollow fiber membrane20. These separation techniques were applied for the treatment of wastewater containing o-nitrophenol31, p-nitrophenol32-35 and 2-4 nitrophenols36.



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In designing an extraction process, there is a need to gather information and data on the equilibrium and kinetics of extraction, and mass-transfer parameters for the acid-extractantsolvent system to be considered. Sufficient work on the equilibrium of several acid-amine systems is available in the literature, but the knowledge of interaction of picric acid with new extractant-solvent system is inadequate. Therefore, the objective of this work is to study the liquid-liquid extraction of picric acid from wastewater by a secondary amine, Amberlite LA2 in octan-1-ol as the acceptor phase. Equilibrium, kinetics, and thermodynamic data were generated experimentally, and analyzed in the present work to be used for scaling-up the extraction process in the industrial application.

2. EXPERIMENTAL 2.1. Materials Picric acid (2,4,6-trinitrophenol) (Sigma-Aldrich, purity > 99 % in mass), Amberlite LA-2 (Sigma-Aldrich, purity > 99 % in mass), octan-1-ol (Sigma-Aldrich, purity > 99 % in mass), and NaOH (Merck, purity > 99 % in mass) were used as supplied.

2.2. Equilibrium Three initial concentrations of picric acid were prepared by using distilled water (0.021, 0.041, and 0.061 kmol·m-3). 0.061 kmol·m-3 concentration is the highest solubility of acid in water. For the organic phase, five different initial concentrations of Amberlite-LA2 were considered (0.235, 0.470, 0.705, 0.940, and 1.175 kmol·m-3). Octan-1-ol was selected as a diluent for making the organic phase. The amine concentration have been found by preliminary tests. These concentrations used to give the highest extraction efficiencies. Equal volumes (20 mL) of the organic and aqueous phase were mixed in an Erlenmeyer flask by shaking for 2 h at 50 rpm and at constant temperature in a temperature controlled shaker. After equilibrium, the phases were left for 2 h to have a clear separation of phases. After phase separation, the acid concentration in the aqueous phase was found by base titration (0.01 N NaOH) and using phenolphthalein as indicator. The organic phase concentration of picric acid after extraction was calculated by a mass balance. Equilibrium experiments and chemical analysis were done in duplicate, and the average values were used for the calculations of extraction parameters. Equilibrium experiments


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were done at three different equilibrium temperatures (293.2 K, 303.2 K, and 313.2 K) to determine the thermodynamic parameters of reaction extraction. 2.3. Kinetics Kinetic studies were performed in a custom-made glass stirred cell (inside diameter = 0.036 m, height = 0.113 m) as shown in Figure 1. Two impellers, made up of stainless steel were placed at the center of both the phases. The cell was provided with water circulation to keep the temperature constant. 50 mL of each of organic and aqueous phase was taken in the stirred cell to achieve experimental data on kinetics. At first, the aqueous phase was poured into the cell, and then the organic phase was poured slowly into the agitated cell without disturbing the interface. The stirring speed was selected as 20 rpm, 40 rpm, 60 rpm and 80 rpm so that the interface should not get disturbed, and to maintain the interfacial area almost equal to the geometric area of the cell. Samples were collected from the bottom side of the cell at 20 min interval of time until equilibrium is reached. Aqueous and organic phase acid concentrations were determined as mentioned in the equilibrium studies. Kinetic experiments and chemical analysis were performed in duplicate, and the average measurements were used for the calculation of kinetic parameters.

Agitator Sealing Water In

36

Stirrers Interface 113

Sample Port Water Out Figure 1. A line diagram of the stirred cell used in the present study (all dimensions are in millimeters). 5 ACS Paragon Plus Environment


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3. RESULTS AND DISCUSSION 3.1. Equilibrium The extraction of picric acid (HPc) by using a secondary amine (Amberlite LA2: ALA2) dissolved in an active polar solvent (octan-1-ol) at equilibrium can be described by the theory of Mass Action Law.37 The undissociated part of the acid molecule interacts with the amine molecule and forms acid-amine complex. At the aqueous-organic interface, the following reaction occurs. mHPc org + Torg ↔ (HPc org ) m (Torg )

Equilibrium constant , K E =

(1)

[( HPc org ) m (Torg )]

(2)

[ HPc org ] m [Torg ]

The experimentally calculated distribution coefficient [a ratio between total number of acid molecules in the organic phase (Corg) and aqueous phase (Caq) at equilibrium] is given by eq 3.

C org

KD =

(3)

C aq

Now, a model based on the loading ratio [Z], a ratio between acid concentration in the organic phase at equilibrium and the initial extractant concentration ( [Torg ]in ) in the organic phase] for formation of various types of complexes (1:1, 2:1 etc.) between acid and extractant can also be described (eq 4). The plots of the loading ratio against the acid and amine concentrations may be used to determine the stoichiometry, and the types of complexes formed in the organic solvent phase.

Z=

C org

(4)

[Torg ]in


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It is found that when the organic solvent phase is not highly concentrated with acid, and at low loading ratios (Z < 0.5), 1:1 acid-extractant complexes are formed. A plot of Z/(1-Z) versus [HPc] shows a straight line trend which passes through origin and the slope determines the complexation constant (K11), eq 5.

Z = K11 [HPc] 1− Z

(5)

The equilibrium extraction with octan-1-ol (physical) and with Amberlite LA2 (ALA2) in octan1-ol (chemical) were performed for picric acid. In the physical extraction with pure octan-1-ol a distribution coefficient of 0.13 (%E = 11.45%) is achieved at 0.061 kmol·m-3 of picric acid aqueous solution. Very low distribution of acid in octan-1-ol necessitates the use of an extractant. Therefore, a secondary amine (ALA2: 0.235, 0.470, 0.705 and 1.175 kmol·m-3) was used with octan-1-ol (an active diluent) to carry out the chemical extraction equilibrium experiments at three different equilibrium temperatures (298.2 K, 308.2 K and 318.2 K). The equilibrium results are shown in supporting information in Table S1. The addition of ALA2 shows a considerable increase in the removal efficiency. Also, by increasing the amount of ALA2 from 0.235 to 1.175 kmol·m-3 in the organic solvent phase improves the uptake of picric acid, and facilitates easy transfer of acid molecules. It has been observed that there is a 5.71 to 70.51 fold increase in the values of KD at 0.061 kmol·m-3 of picric acid using ALA2 + octan-1-ol system than using octan1-ol alone.

The loading of acid (Z) in the organic phase is an important factor and their values can be used to determine the stoichiometry of the overall extraction process. The values of Z are plotted against equilibrium concentration of acid in the aqueous phase for different concentrations of ALA2 in octan-1-ol (0.235, 0.470, 0.705 and 1.175 kmol·m-3) in Figure 2. It was observed that Z (0.017 to 0.111) values followed an increasing trend with the equilibrium concentration of acid in the aqueous phase, and irrespective of the initial ALA2 concentration in the organic phase. These interpretation are consistent with the results reported by Kings and Kertes38, and also confirms the similar types of acid-amine complex formation at different concentrations of ALA2. The Fourier transform infrared was done using Nicolette FTIR to confirm the interaction between



ALA2 and HPc molecules. Figure 3 demonstrates the FTIR spectra of (a) ALA2 and (b) ALA2 + HPc. The broad and strong band at 3337 cm-1 is due to the overlapping of (-OH), aromatic (C-H), and NH2 stretching vibrations. Also, the peak at 1635 cm-1 was attributed to the stretching vibration of the amine group (N-H). After the extraction, the stretching vibration peaks at 3320 cm-1 and 1635 cm-1 were shifted to 3275 cm-1 and 1630 cm-1, respectively, and the NO2 group of picric acid appears at 1563 cm-1 as an asymmetric group, and at 1260 cm-1 as a symmetric group. The outcome of FTIR analysis pointed out that the extraction of HPc molecules by ALA2 molecules were done by the formation of H-bonds. In this study, the equilibrium constants (K11) were estimated by plotting Z/(1-Z) versus [HPc], and fitting it by a straight line for lower values of loading ratio. From the slope of this line, the complexation constant (K11) was determined and shown in Table 1. An average value of K11 [= 3.739 (kmol·m-3)-1] was considered at 298.2 K, and used to establish the intrinsic kinetics of reactive extraction.

0.10

0.08

0.06

Z

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0.04

0.02

0.00 0.00

0.01

0.02

0.03

0.04

-3

Caq, kmol m

Figure 2. Loading of Amberlite LA2 in octan-1-ol with picric acid at 298.2 K. Symbols: ○, 0.021 kmol·m-3; ∆, 0.041 kmol·m-3; □, 0.061 kmol·m-3


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112,8 110

105

(b) 100

(a) 95

90 1170

85 1037 1260

%T

80

75

1465

70 3275

65

1563

60

55

1635 3320

48,5 4000,0

3600

3200

2800

2400

2000

1800

1600

1400

1200

1000

800

-1

cm

Figure 3. FTIR Spectra of (a) ALA2, and (b) ALA2 + Picric Acid

Table 1. The estimated values of the equilibrium constants (K11) with R2 for the reactive extraction of picric acid (0.021 - 0.061 kmol·m-3) at three different temperatures

Temperature / K

298.2

308.2

318.2

Caq / kmol·m-3

K11 / (kmol·m-3)-1

R2 / (-)

0.021

4.069 ± 0.346

0.979

0.041

3.871 ± 0.241

0.989

0.061

3.276 ± 0.284

0.978

0.021

3.383 ± 0.351

0.959

0.041

3.150 ± 0.200

0.984

0.061

2.676 ± 0.229

0.972

0.021

2.764 ± 0.238

0.971

0.041

2.472 ± 0.162

0.983

0.061

2.263 ± 0.164

0.980


650,0


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Effect of Temperature The effect of temperature (298.2 to 318.2 K) on the reactive extraction of picric acid using ALA2 dissolved in octan-1-ol was also studied. The distribution of acid into the organic solvent phase decreases sharply by increasing the temperature. This is because at higher temperature backextraction of the acid from the organic solvent phase to the fresh aqueous phase took place decreasing the extraction efficiency. The equilibrium (K11) constants at three different temperatures (298.2, 308.2, and 318.2 K) were estimated (Table1). Temperature affects different parameters of the reactive extraction system like pKa of acid, the acid-amine interaction, the solubility of the acid in both phases, the extractant basicity, and water co-extraction.39 With increase in temperature, the pKa values of organic acids decrease slightly leading to the dissociation of acid molecule in the aqueous phase, and lower recovery. Also, the solubility of carboxylic acids in water increases with temperature.40 The temperature also has effect on the acid-ALA2 complex formation. At a temperature of 298.2 K, higher values of K11 were obtained as compared to what were obtained at 318.2 K. Therefore, at higher temperatures the reactionextraction system becomes more unstable facilitating back-extraction increases.41 At the equilibrium, the randomness of the system decreases by the formation of acid-amine complex and decrease in the entropy. For constant enthalpy and constant entropy in the range of studied temperature, the equilibrium constant (K11) may be related to the temperature (T) by eq 6.42

ln K11 =

− ∆H ∆S + RT R

(6)

Plots of lnK11 vs 1/T are fitted linearly to determine the enthalpy (∆H) from the slope and the entropy (∆S) from the intercept (Table 2). Larger change in the values of ∆H and ∆S shows that the reaction is exothermic, and sensitive to the equilibrium. Also, the negative value of ∆H dictates that extraction accompanied with reaction has been favored at low temperature.


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Table 2. Values of entropy and enthalpy for the reactive extraction of picric acid using ALA2 dissolved in octan-1-ol

Caq / kmol·m-3

-∆H / kJ·mol-1

-∆S / J·mol-1·K-1

R2

0.021

15.24

39.40

0.998

0.041

17.67

47.93

0.996

0.061

14.60

39.13

0.999

3.2. Kinetics The mechanism of simultaneous extraction and chemical reaction in a stirred cell was proposed by Doraiswamy and Sharma.43 Based on the film and renewal theories, they established the fact that the specific extraction rate gets effected by the chemical reaction, and to identify these facts there is a need to study physico-chemical and hydrodynamic parameters of the system. According to their theory, they indentified four regimes in the reactive-separation system: (i) very slow, (ii) slow, (iii) fast and (iv) instantaneous (Table S2 in supporting information). Therefore, to identify the reaction regime, and to determine the intrinsic kinetics of the reactive extraction process, the effect of parameters like agitation speed (N), phase volume ratio (Vorg/Vaq), concentrations of picric acid and ALA2 on the specific extraction rate is to be studied and analyzed thoroughly.37

3.2.1. Determination of Mass-Transfer Coefficient (kL) in octan-1-ol Mass transfer coefficient has to be determined to find out the reaction regime in reactingextracting system. Therefore, its value is to be estimated with pure octan-1-ol. The molecules of picric acid show almost insufficient distribution coefficient in water/octan-1-ol system. Assuming, the diffusion film resistance in the aqueous phase is negligible, and considering only the existence of diffusion film resistance in the organic, an equation representing the masstransfer rate or molar flux can be written in form of eq 7.

Vorg dCorg A

dt

(

* = k L Corg − C org

)

(7)



* where, A is the interfacial area (m2), Vorg is the organic phase volume (m3) and Corg represents the

concentration of acid at the aqueous-organic interface.

By integrating eq 7, the acid concentration in the organic phase can be expressed in terms of time, obtained as in eq 8.

*  Corg  kL A  = ln * t C −C  V org  org  org

(8)

The mass-transfer coefficient of picric acid (kL) in octan-1-ol is determined by plotting the values *  Corg  -3  of ln *  C − C  against time (t) at a constant speed of stirrer (60 rpm), at 0.061 kmol·m of org   org

acid concentration, and equal volumes of phases (Vorg/Vaq = 1). This plot was fitted by a straight line as shown in Figure 4, and the value of kL is estimated to be 7.12 × 10-4 m·s-1 from the slope of the plot.

3.0 2

R = 0.962

2.5

-4

Slope = 7.12x10 2.0

1.5

*

ln[C org/(C org - Corg)]

1.0

*

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0.5

0.0 0

500

1000

1500

2000

2500

3000

t, sec *  Corg   versus time (t) to determine kL Figure 4. The plot of ln *  C − C org   org


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3.2.2. Reaction Kinetics Commonly, the simultaneous extraction and reaction between the solute (picric acid) and the solvent (ALA2 + octan-1-ol) molecules is a reversible process. Therefore, in determining the extraction kinetics, the application of the initial rate method (governed only by the forward reaction) could be a better option as the problem of reversibility can be avoided.44 Hence, initial specific rate, RHPc,0 (kmol·m-2·s-1) was calculated from the experimental data on kinetics, and using eq 9.

RHPc,0 =

Vorg  dCorg    A  dt  t =0

(9)

The kinetic equation and the Hatta number (Ha) is given by eqs10 and 11, respectively. * R HPc,0 = k [C org ]α [( Torg )in ] β

(10)

2 * α −1 k[Corg ] [(Torg ) in ]β DHPc Ha = α + 1 kL

(11)

where, α and β are the orders of the reaction with respect to picric acid and ALA2, respectively; k is the reaction rate constant; and DHPc is the diffusion coefficient of acid into diluent (m2·s-1).

The initial specific rate of reaction (RHPc,0) were calculated from the experimental values at different HPc and ALA2 concentrations, agitation speed, and phase-volume ratios. The effects of agitation speed (N), and phase-volume ratio (Vorg/Vaq) on RHPc,0 will confirm the regime of reaction.43

3.2.3. Effect of Agitation Speed (N) on RHPc,0 The diffusion or the chemical reaction taking place in the reacting system governs the extraction with chemical reaction in a stirred cell. Generally, in the diffusion controlled regime, an increase in the stirring speed will increase the extraction rate and reaches to a constant value but in the 13 ACS Paragon Plus Environment


reaction controlled regime, there is no effect of stirring speed on the extraction rate.44 In the latter case, the chemical reaction limits the overall rate of mass transfer and diffusion contributions are almost negligible or does not exist. The reason may be that the interfacial boundary layer becomes thinnest hence minimizing the individual film resistance to mass transfer. In the present study, the kinetic experiments were performed at four different stirring speed (20, 40, 60, and 80 rpm) using 0.061 kmol·m-3 of picric acid solution, and 1.175 kmol·m-3 of ALA2 in octan-1-ol at 1:1 Vorg/Vaq ratio and at 298.2 K. This study will confirm the hydrodynamic effect on the initial rate of extraction. The highest stirring speed was chosen to be 80 rpm. As it was found that beyond this speed the interfacial area between the aqueous and organic phase gets disturbed, and hence a constant area of mass transfer cannot be maintained. In this range of speed of agitation, the RHPc,0 was found to be almost constant (0.354 × 10-6 to 0.367 × 10-6 kmol·m-2·s-1) showing no affect on the initial specific rate of extraction. As per Table S2 and Figure 5, and from the effect of N, it may be said that the extraction-reaction will fall either in Regime1 (very slow) or 3 (slow).

0.5

0.4 2

RHPc, 0 x 10 , kmol/m s

0.3

6

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0.2

0.1 20

40

60

80

100

N, rpm

Figure 5. Effect of N on RHPc,0 for the reactive extraction of picric acid with Amberlite LA2 in octan-1-ol (T = 298.2 K, Vorg/Vaq = 1, CHPc,in = 0.061 kmol·m-3, [Torg]in = 1.175 kmol·m-3)

3.2.4. Effect of Phase Volume Ratio (Vorg/Vaq) on RHPc,0 14 ACS Paragon Plus Environment

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Further study on the kinetics was carried out at four volume-phase ratios (Vorg/Vaq = 0.5, 1, 1.5 and 2) using 0.061 kmol·m-3 of picric acid solution, and 1.175 kmol·m-3 of ALA2 in octan-1-ol at 40 rpm and at 298.2 K to make a conclusion between Regime 1 and 3. The initial specific extraction rate was calculated and plotted against Vorg/Vaqin Figure 6. This shows an increase in the values of RHPc,0 with Vorg/Vaq and confirming that the reaction between HPc and ALA2 takes place in the bulk of the organic phase. Therefore, based on the analysis done in previous two paragraphs, and the theory provided by Doraiswamy and Sharma, it may be concluded that the extraction-reaction of picric acid with ALA2 + octan-1-ol system falls in Regime 1 (extraction accompanied with a very slow chemical reaction).

0.6

0.5

2

RHC, 0 x 10 , kmol/m s

0.4

6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.3

0.2

0.1 0.5

1.0

1.5

2.0

Vorg/Vaq

Figure 6. Variation of RHPc,0 with Vorg/Vaq for the reactive extraction of picric acid with Amberlite LA2 in octan-1-ol (T = 298.2 K, N = 40 rpm, CHPc,in = 0.061 kmol·m-3, [Torg]in = 1.175 kmol·m-3)

3.2.5.Order of the Reaction (α, β) To determine the order of the reaction with respect to HPc (α), kinetic experiments were performed by changing initial acid concentration from 0.021 to 0.061 kmol·m-3 at 1.175 kmol·m3

of ALA2 + octan-1-ol, at 40 rpm, and 298.2 K. The experimental results were used to calculate

* RHPc,0 and plotted against Corg as shown in Figure S1. Calculated RHPc,0 showed a linear trend



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Page 16 of 26

with the equilibrium concentration of picric acid at 1.175 kmol·m-3 of ALA2 + octan-1-ol (constant concentration). The regression analysis gave a value of α equal to 1.2. Similarly, the order of reaction with respect to ALA2 (β) was found from the calculated values of RHPc,0 which were determined from the experimental values found by varying ALA2 concentration from 0.235 to 1.175 kmol·m-3 at 0.061 kmol·m-3 of acid concentration, at 60 rpm, and at 298.2 K (Figure S2). The value of β was estimated to be 0.7. The forward reaction rate constant [k = 18.3 × 10-6 (kmol·m-3)-0.9s-1] was obtained using Figure S3, and using the value of equilibrium constant, the backward rate constant of reaction [k-1 = 4.94 × 10-6 (kmol·m-3)-1.9s-1] was estimated at 298.2 K.

3.2.6. Criteria for the Reaction Regime For α = 1.2 and β = 0.7, the Hatta number (Ha) was calculated using the following expression, eq 12.

Ha =

* 0.91k[C org ]0.2 [Torg,in ]0.7 DHPc

(12)

kL

The value of DHPc was determined from the equation proposed by Reddy-Doraiswamy45 and Wilke-Chang46 as 9.027 × 10-6 m2·s-1 and 1.373 × 10-5 m2·s-1, respectively at 298.2 K. Average of these two values i.e. 1.138 × 10-5 m2·s-1 was used in the calculation of Hatta number. The values of Ha were found in the range of 0.009 to 0.011 at 298.2 K which also validates the Regime

1.

The

values

of

RHPc,0

were

predicted

by

the

kinetic

equation

(

* R HPc,0 = 18.3 × 10 -6 [C org ]−0.2 [( Torg )in ]0.7 ) and plotted against experimental values of RHPc,0 in

Figure 7. Therefore, these equilibrium, kinetic and thermodynamic data and findings on the extraction-reaction of picric acid with ALA2 + octan-1-ol system would be helpful in designing a continuous extraction process.


Page 17 of 26

-1

0.7

0.6

6

-2

RHPc,0 (pred) x 10 , kmol m s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.5

0.4

0.3

0.2

0.1 0.1

0.2

0.3

0.4

0.5 6

0.6 -2

0.7

-1

RHPc,0 (exp) x 10 , kmol m s

Figure 7. Comparison of predicted and experimental values of specific reaction rates, RHPc,0 (kmol·m-2·s-1)

3.2.7. Molecular Dynamic Simulation Molecular dynamics simulation consist in solving Newton's equations or other related to a collection of particles, thereby getting the speed and the position of each particle that makes up the system in every minute of the simulation. The potential for interaction between the particles that compose the system is calculated based on tabulated parameters for each one of them and then calculate the resulting force on each particle through the potential gradient. The quality in the prediction of physical properties are directly related to choice of interaction potential. In this work we use the type inter-atomic interaction potential CHARMM47: Vtot = ∑ k b ( r-r0 ) + ∑ k θ ( θ-θ 0 ) + 2

bonds

2

angles

∑

dihedrals

 R  R  + ∑ ε  minij  -  min ij   r   r  nonbonded   ij   ij   12

∑

Urey-Bradley

k u ( u-u 0 )

2

k λ 1+cos ( nλ-δ )  + 6

∑

k ψ ( ψ-ψ 0 ) + 2

improper

 qq + i j  εrij 


(13)


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Page 18 of 26

Where is the total energy of the system formed from contributions of bonds, angles, drihedraletc. The parameters of Lennar-Jones are obtained using classical blend rule. The conformational energy minimum was determined by ab initio calculations using package GAMESS.48 The molecular dynamics simulations were performed in the LAMMPS package49 with 200 acid molecules, 200 amine molecules and 200 octan-1-ol molecules in a cubic simulation box with periodic boundary conditions. The simulations were realized as using the statistical Isothermal– isobaric ensemble (NPT) using the barostato of Nosé-Hoover the 1 bar. The initial setup was randomly generated by the convergence criterion (to avoid overlap was set a distance > 2.0 A) the simulation box using a open source developed with object-oriented programming PLAYMOL package. The initial setup was relaxed by using statistical ensemble NVE, the longrange interactions out using computed sum pppm (particle-particle particle-mesh), 1 ns were used for the equilibration step and 5 ns to production stage. The thermodynamic properties of the system in question (total energy, temperature, pressure, kinetic energy, and potential) are saved for each 100 time step of integration and the atomic coordinates were saved every 1000 time step of the numerical integration. The simulations were conducted the 1 bar pressure and 293 K. Molecular dynamic simulation was applied by using 200 molecules of each component to determine behavior of complex in both interphase and organic phase. Figures 8 shows molecules and complexes in the organic phases.


Page 19 of 26

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Secondary amine

+

Picric acid

+

octan-1-ol

Figure 8. Simulation box for the mixture of (picric acid + secondary amine + octan-1-ol) in the organic phase after extraction.

Figure 9 shows intra-molecular interaction energy changes for the system of picric acid + secondary amine + octan-1-ol by model of molecular dynamics. In Figure 11 different interatomic energies interaction (Emol-molecular energy (bond + angle + dihedral + improper, Epairpair wise energy (Vander Waal + Coulombic pair wise energy+ Vander Waal energy long-range tail correction), Evdwl (Vander Waal pair wise energy) and Eecoul (Columbic pair wise energy) ) are shown for the system of secondary amine + picric acid + octan-1-ol over certain time step. 19 ACS Paragon Plus Environment


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Page 20 of 26

Over time, the total energies tend to increase suffering fluctuations and these results are related to the model set initially for the substances. Power fluctuations are associated with different levels of configuration that the mixture can take and also the possibility of different configuraciones regions. An important point to note with this plot is that all the energies decreased during the first 100 ps. The total initially declined and then stabilized for the rest of our simulation indicating that the relaxation was completed and State of equilibrium was reached. It is important to remember that van der Waals' interactions are forces that exist between dispersive regions. They are quite different from the forces that make up the molecule. In this study an alcohol and acid are made up of hydrogen and oxygen, which are bonded together by the sharing of electrons. These electrostatic forces that keep a molecule intact are existent in covalent and ionic bonding but they are not van der Waals' forces are forces Columbic pair wise energy.

Figure 9. Intra-molecular interaction energy changes (E) for the system of (picric acid + secondary amine + octan-1-ol)


Page 21 of 26

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4. CONCLUSIONS Equilibrium, kinetic and thermodynamic studies were performed for the reactive extraction of picric acid with Amberlite-LA2 + octan-1-ol in a stirred cell. From the equilibrium data and calculated values of loading ratio (Z < 0.5), the equilibrium constant of 1:1complex formation in the organic phase were determined at three different temperatures (298.2 K, 308.2 K and 318.2 K). The kinetic experiments were done to investigate the affect of agitation speed and volumephase ratio on the specific rate of extraction, and confirm the regime of extraction with reaction. It was observed that the specific rate of extraction remained almost constant with agitation speed but increases with increase in the volume-phase ratio. Based on the Hatta number, the criterion proposed by Doraiswamy and Sharma, the reaction regime was found to be very slow occurring at the bulk of the organic phase. This proposed extraction-reaction model could be successfully utilized for designing an extraction process to recover picric acid using Amberlite-LA2 in octan1-ol from wastewater streams. Molecular dynamic behavior was simulated for the system of HPc (picric acid) + ALA2 (secondary amine) + octan-1-ol in the organic phase. The complex formation of acid-amine was presented with good demonstration.

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Secondary amine

+

Picric acid

+

TOC Figure


octan-1-ol

Page 26 of 26

Extraction of Picric Acid from Wastewater by a Secondary Amine

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