Recovery of Methacrylic Acid from the Aqueous Phase Using

Mar 7, 2016 - Recovery of Methacrylic Acid from the Aqueous Phase Using Trioctylmethylammonium Chloride (TOMAC) in Different Diluents. Akanksha Swarnk...
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Recovery of Methacrylic Acid from the Aqueous Phase Using Trioctylmethylammonium Chloride (TOMAC) in Different Diluents Akanksha Swarnkar,* Amit Keshav, and A. B. Soni Department of Chemical Engineering, National Institute of Technology, Raipur, (C.G) India ABSTRACT: Methacrylic acid and its derivatives are used in the manufacture of important industrial polymeric products. They have a variety of industrial applications including plastics, thickening agents, surfactants, and chelating agents, etc. In the present work, equilibrium extraction of methacrylic acid is carried out to recover it from aqueous solution. A quaternary ammonium salt, trioctylmethylammonium chloride (TOMAC), is used along with different diluents which belong to different categories. These include isoamyl alcohol, n-butyl acetate, methyl isobutyl ketone (MIBK), toluene, carbon tetrachloride, rice bran oil, and kerosene. Parameters such as distribution coefficients, extraction efficiency, loading ratio, stoichiometric loading ratios, and the equilibrium complexation constants are reported. In both physical and chemical extraction processes, MIBK, being proton−accepting, provides maximum extraction efficiency. The values of equilibrium complexation constant of the TOMAC−diluent systems studied decrease in the following order: rice bran oil > carbon tetrachloride > butyl acetate > toluene > kerosene > MIBK > isoamyl alcohol.

1. INTRODUCTION Reactive extraction is a solvent or liquid−liquid extraction system with a chemical reaction. An interfacial reaction takes place between the solute (to be extracted) and the extractant, and the physical process is the diffusion and solubilization of the system components. The process is named as complex extraction as well as dissociation extraction by some researchers. Reactive extraction finds a wide variety of applications, such as recovery of carboxylic acids from fermentation broth1 and industrial effluents,2 recovery of precious metals,3 biodiesel production,4,5 byproduct recovery,6 and effluent treatment,7,8 etc. Methacrylic acid, (MAA) or 2-methyl-2-propenoic acid), is a low molecular weight carboxylic acid that occurs naturally in small amounts in the oil of Roman chamomile. It is a colorless corrosive liquid (or crystals), with an acrid unpleasant odor. It is manufactured by hydrolysis of methacrylamide stream under pressure of up to 790 kPa (100 psig) at 100−150 °C. The reactor effluent is separated into two phases. The upper organic layer is distilled to provide high purity MAA. However, other methods are also being explored by many investigators because this method emits 5.5 kg CO2 per kg MAA produced and produces 1.5 tons of solid waste per ton of MAA.9 Pyo9 et al. synthesized MAA from an inexpensive industrial byproduct, 2-methyl-1,3-propanediol. All the reactions were performed in aqueous media, and each step provided high product yield. Endoh10 et al. invented a liquid−liquid extraction method for extracting MAA from its aqueous solution. They used an extractant solvent containing a mixture of t-butyl methacrylate and methyl methacrylate (MMA). MMA is in the range of 3−90% mass fraction of the extractant solvent. The method provides high extraction efficiency at low cost. Very recently, Rajagopalan11 et al. studied production of MAA via heterogeneous selective gas-phase oxidation of propene by CO2. They © 2016 American Chemical Society

concluded that lattice oxygen from the polyoxometalates (POM) catalysts (Keggin type (POM) Ni3[PW12O40]2 and Ni3[PMo12O40]2) acted as oxidizing agent. Catalytic selective oxidation of iso-butane to MAA, on a different catalyst, (NH4)3HPMo11VO40 (APMV) supported on Cs3PMo12O40 (CPM), has been studied by Jing12 et al. They studied the thermal stability, structural, and textural properties of catalysts. Cavani13 et al. have done a wide extensive study of the main aspects of the reaction, which include reactivity of Keggin-type (POMs), the POM requirements, reduction level of the POM, and, the generation of the active sites in the reaction environment. They also prepared the ammonium salt of 12-molybdophosphoric acid (a heterogeneous catalyst) which operated with higher selectivity at isobutene-rich conditions. In their earlier work, they reported that the addition of iron to the same catalyst composition made the catalyst stable, increased the acidity (and also the activity) of the catalyst, and also prevented the structural decomposition of the catalyst.14,15 Polymers containing (MAA) are used in a number of applications including surface coatings, flocculants, ion exchangers, and soil improvers. Methyl methacrylate, used in the preparation of Plexiglas, is the most valuable MAA derivative. MAA is also used in the manufacture of carboxylated rubber, safety glass, adhesives; polymethacrylic acid salts serve as emulsifiers. Recently, Panic16 et al. synthesized biodegradable hydrogel composites based on MAA which had an adsorption capacity as high as 180 mg/g for MAA/30A hydrogel composite. It has outstanding applications in drug delivery systems. Received: July 6, 2015 Accepted: February 25, 2016 Published: March 7, 2016 1412

DOI: 10.1021/acs.jced.5b00553 J. Chem. Eng. Data 2016, 61, 1412−1420

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and butyric acids by A336 in kerosene and 2-octanol was studied by Yang27 et al. It was reported A336 is composed of an organic cation associated with a chloride ion and it can function as an anion-exchanger under both acidic and basic conditions, so that it can extract both dissociated and undissociated forms of the acid. Keshav28 et al. used A336 in 2-octanol to recover propionic acid from aqueous phase and correlated their findings with linear solvation energy relationship (LSER) modeling parameters. They also studied the kinetics of the process and established that the reaction was fast pseudo-first-order.

Residues from production and cleaning operations as well as waste material from spills, if containing MAA, cannot be treated biologically as the MAA is toxic to the bacteria in the system. Hence, there is a need to search for a suitable method to treat effluents before they are discharged into navigable waters, and the concentration of MAA should not exceed 1000 mg/L in the stream to be disposed. Also, the reason to search for the recovery of MAA from a dilute, aqueous stream is further strengthened as it can be produced via fermentation from a renewable sugar feedstock.17 In the present work, reactive extraction of MAA is studied. The extractant used is a quaternary ammonium salt, trioctylmethylammonium chloride (TOMAC) commercially known as Aliquat 336. It is used with seven single solvents belonging to different categories: an alcohol (isoamyl alcohol), an aromatic hydrocarbon (toluene), a strong polar diluent (MIBK), an ester (butyl acetate), a natural solvent (rice bran oil), an inert diluent (kerosene), and a nonpolar solvent (carbon tetrachloride). Aliquat 336 (A336) has been used successfully to extract different acids by several researchers. Wasewar18 et al. studied the physical and reactive extraction of itaconic acid using A336 in four different diluents. They showed that the values of partition coefficient and the distribution coefficient obtained were in the order, ethyl acetate > hexane > toluene > kerosene. The extraction of levulinic acid by A336 dissolved in five alcohols, five esters, and two ketones was investigated by Uslu19 et al. In their study, they obtained extraction efficiency as high as 72.1 when they used isoamyl alcohol as a diluent. They also reported Freundlich, Langmuir, and LSER model equations. Pursell20 et al. investigated for extraction of phenylalanine using A336. They modeled the extent of extraction at equilibrium using the equilibrium constants for the reactions present in the process and concluded that the extent of extraction and co-extraction is controlled by the thermodynamics of each extraction reaction and, the interaction between each of the reactions. The extraction studies of Kumar21 et al. to recover propionic acid from aqueous solution by using A336 in a mixture of inert diluent and an active diluent (modifier) revealed that the solubility of extracted species increases in the organic phase. They also predicted the number of A336 molecules in the acid-amine complex through mathematical modeling. Kyuchoukov22 et al. modified A336 by adding aqueous ammonium carbonate and used it to recover lactic acid from an aqueous solution. They concluded that the carbonate form of A336 is more efficient. In their further study,23 they investigated the mechanism of extraction of lactic acid with A336 dissolved in dodecane and decanol. They concluded that as the pH increases, the overall distribution coefficient increases or decreases at a low and high acid concentration. Keshav24 et al. carried out reactive extraction of acrylic acid using A336 as an extractant and oleyl alcohol as a diluent to study the effect of temperature in the range 305−333 K. They found that the equilibrium complexation constant increases with temperature up to 313 K. Wasewar25 et al. used A336 with two different diluents (MIBK and xylene) for the recovery of caproic acid in which they observed that A336 does not show synergistic effect in diluents. Keshav26 et al. carried out the physical and chemical extraction to recover propionic acid from aqueous solution using A336 in four different diluents, n-heptane, petroleum ether, 1-decanol, and 1-octanol. They showed that the former two diluents caused third phase formation. They also discussed the water co-extraction and back extraction methods. The effect of the aqueous pH on the extraction of lactic, acetic, propionic,

2. THEORY Reactive extraction of carboxylic acids from aqueous phase using a quaternary amine such as A336 is a well-established technology. It is generally accepted that it involves transfer of the acid in its nondissociated form from the aqueous phase to the organic phase. At pH below the pKa, the acid exists in undissociated form. The extraction process is analyzed by means of the extraction efficiency and distribution coefficient. The experimentally accessible distribution coefficient, KD, is calculated using eq 1, [HA]org

KD =

[HA]aq

(1)

where [HA]org is the total concentration of methacrylic acid in organic phase and [HA]aq is the total acid concentration (dissociated and undissociated) in the aqueous phase at equilibrium. The extraction efficiency is defined as the ratio of acid concentration in the extracted phase to the initial acid concentration in aqueous solution by assuming no change in volume at equilibrium as given by eq 2, E% =

[HA]org × 100 [HA]org + [HA]aq

(2)

The extent to which the organic phase (extractant and diluents) may be loaded with acid is expressed by the loading ratio, Zt (ratio of total acid concentration in the organic phase to the total extractant concentration) as given by eq 3, Zt =

[HA]org [A336]o;org

(3)

where [A336]o;org is the initial concentration of A336 in the organic phase. The value of Zt depends on the extractability of the acid (strength of the acid base interaction) and its aqueous concentration. The stoichiometry of the overall extraction equilibrium depends on the loading ratio in the organic phase. If, however, the extraction by the pure diluent is significant (physical extraction experiments were carried out in separate batches), then it also has to be considered for better prediction of loading.29 The stoichiometric loading factor, Zs is the ratio of the overall complexed acid to organic phase. Zs includes a correction term for the amount of acid extracted by the diluent in the organic phase, Zs =

diluent [HA]org − ν[HA]org

[A336]o;org

(4)

where ν and designate the volume fraction of diluent in the solvent mixture and amount of acid extracted by the pure diluent alone. Assuming that the organic phase is not highly [HA]diluent org

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Table 1. Physical Equilibrium Results for the Diluent−MAA System diluent MIBK

n-butyl acetate

toluene

carbon tetrachloride

rice bran oil

kerosene

isoamyl alcohol

initial acid concn mol·kg−1

D

avg D

E

avg E

0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6

4.42 5.67 7.00 6.06 7.90 8.23 4.56 5.67 5.67 4.28 7.89 2.54 2.15 0.67 1.29 1.61 1.81 2.87 1.19 0.67 1.16 1.45 1.62 1.95 0.94 1.03 1.86 2.16 2.48 1.79 1.72 1.89 1.80 1.83 1.84 1.35 3.47 3.06 4.25 4.16 3.80 3.70

6.54

81.54 85.00 87.50 85.83 88.75 89.17 82.00 85.00 85.00 81.07 88.75 71.76 68.21 40.00 56.25 61.67 64.38 74.17 54.44 40.00 53.75 59.17 61.88 66.10 48.44 50.78 65.00 68.33 71.25 64.10 63.19 65.38 64.23 64.61 64.81 57.41 77.61 75.37 80.97 80.60 79.17 78.72

86.29

concentrated (later confirmed, as the value of Zs obtained is less than 0.5 in majority of the cases), formation of the 1:1 acidamine complex can be precisely assumed and the following equation holds, Zs = KE[HA]aq 1 − Zs

5.12

1.73

1.34

1.73

1.73

3.74

82.26

60.77

55.88

62.65

63.27

78.74

from Himedia and it had 90% purity, MAA was procured from Himedia having 99% purity, toluene was obtained from Loba Chemie (99.5% purity), butyl acetate and MIBK were obtained from Merck with 98% and 99% purity, carbon tetrachloride was 98% pure as obtained from Loba Chemie, isoamyl alcohol with 99% purity was obtained from Molychem, and sodium hydroxide with 97% purity was obtained from Merck. Rice bran oil and kerosene were purchased from local suppliers. All the chemicals were used without further treatment. MAA is dissolved in distilled water to prepare the aqueous solutions with initial concentration of acid in the range of 0.05−0.6 mol·kg−1. The pKa of the MAA is 4.65,30 and the aqueous solutions are of relatively small concentration; it can be precisely assumed that only undissociated acid exists. The organic solutions were prepared by dissolving A336 in respective diluents, and the concentration of A336 was kept as 0.22, 0.44, and 0.66 mol·kg−1 (or 10, 20, and 30% by volume).

(5)

where KE is the extraction equilibrium complexation constant. A higher KE value for a particular diluent suggests that it can extract MAA better than the other diluents along with A336. Also, KE can be related to the operating temperature to predict enthalpy and entropy of the reaction.24

3. MATERIALS AND METHODS A336 is a mixture of C8 and C10 chains with C8 predominating. It is a clear reddish brown liquid with the molecular mass of 0.404 kg/mol and density 0.88 kg/dm3. A336 was obtained 1414

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Figure 1. Physical extraction of methacrylic acid by individual diluents. Figure 4. Variation of stoichiometric loading factor with initial Aliquat 336 concentration (initial aqueous phase MAA concentration =0.1 mol·kg−1).

A higher concentration of A336 was not used as its high viscosity (1450 cP, at 303 K) may pose difficulty in handling or may cause a third phase (i.e., second organic phase) at equilibrium which is difficult to analyze. Further, decreasing the surface tension of the organic mixture helps in faster phase separation thereafter. Equal volumes of the aqueous and organic solution (2 × 10−5 m3 of each phase) were equilibrated in a temperature controlled water bath shaker (REMI Equipment Private Limited, India) for 4 h, which was found to be sufficient in preliminary works. The shaking speed was maintained at 120 strokes per minute, and the temperature was maintained at 303 (±1) K. After attaining equilibrium, both phases were allowed to settle for 2 h at the same temperature to reach full phase separation. Then, the aqueous phase was analyzed to determine the concentration of acid by titration using freshly prepared NaOH solution and phenolphthalein as an indicator. Some experiments were repeated to ensure the consistency in the results (of titration) and the variation was found within ±2%. The uncertainty is evaluated to be 2.9 × 10−4 by using the following relation,

Figure 2. Variation of distribution coefficient with initial Aliquat 336 concentration (initial aqueous phase MAA concentration = 0.2 mol·kg−1).

⎡ 1 u([HA]aq ) = ⎢ ⎢⎣ n(n − 1)

n

∑ ([HA]aq,k k=1

⎤0.5

2⎥

− [HA]aq )

⎥⎦ (6)

where [HA]aq is the mean value of n independent observations obtained under the same conditions of measurement. After phase separation, the change in volume of both the phases was negligible. Oxalic acid (Qualigens Fine Chemicals, 99.5% purity) was used for the standardization of NaOH. The acid concentration in the organic phase was calculated by material balance.

4. RESULTS AND DISCUSSION 4.1. Physical Extraction Using Various Diluents. The physical extraction of MAA using individual diluents, isoamyl alcohol, n-butyl acetate (BA), methyl isobutyl ketone (MIBK), toluene, carbon tetrachloride, rice bran oil (RBO), and kerosene was studied, and the results are tabulated (Table 1). The distribution ratio of acid referred to the pure diluent (D defined as the ratio of acid concentration in organic phase to that in aqueous phase at equilibrium, when only diluent is

Figure 3. Variation of distribution coefficient with initial Aliquat 336 concentration (initial aqueous phase MAA concentration = 0.2 mol·kg−1). 1415

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Table 2. Liquid−Liquid Equilibrium Results for the Aliquat 336−Diluent-MAA System concn of amine mol·kg−1 0.219

0.437

0.656

0.219

0.437

0.656

0.219

0.437

0.656

0.219

initial acid concn mol·kg−1 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2

KD

avg KD

A336 + MIBK 6.50 7.25 5.67 7.89 7.00 7.42 9.00 7.86 9.02 7.00 9.00 9.91 10.43 9.90 8.75 10.78 9.00 10.43 10.48 12.54 13.47 A336 + n-Butyl Acetate 5.25 6.04 5.67 7.00 7.00 7.42 3.90 6.14 5.95 3.00 6.27 7.57 8.41 4.31 7.33 7.85 7.00 9.00 9.00 9.67 5.07 A336 + Toluene 3.17 4.46 4.71 3.71 5.00 5.40 4.78 3.76 5.70 3.44 7.00 6.50 7.42 6.06 4.56 7.03 7.00 7.89 7.57 7.89 7.57 A336 + CCl4 3.39 3.41 3.00 4.00 1416

E (%)

avg E

Zt

Zs

86.67 85.00 88.75 87.50 88.12 90.00 88.72 87.50 90.00 90.83 91.25 90.82 89.74 90.00 91.25 91.29 92.61 93.09

87.88

0.198 0.389 0.811 1.200 1.611 2.469 0.101 0.200 0.411 0.623 0.834 1.246 0.069 0.137 0.278 0.417 0.565 0.851

0.030 0.039 0.091 0.141 0.151 0.267 0.027 0.045 0.091 0.152 0.185 0.267 0.025 0.046 0.091 0.143 0.186 0.281

84.00 85.00 87.50 87.50 88.12 79.61 86.00 75.00 86.25 88.33 89.38 81.18 88.00 87.50 90.00 90.00 90.62 83.53

85.79

0.192 0.389 0.800 1.200 1.611 2.047 0.086 0.171 0.394 0.606 0.817 1.044 0.067 0.133 0.274 0.411 0.552 0.716

0.169 0.350 0.699 0.699 1.461 1.661 0.075 0.155 0.311 0.311 0.650 0.738 0.023 0.043 0.093 0.230 0.174 0.285

76.00 82.50 78.75 83.33 84.38 82.69 79.00 77.50 87.50 86.67 88.12 85.83 82.00 87.50 88.75 87.88 88.75 88.33

81.69

0.173 0.377 0.720 1.143 1.543 2.268 0.090 0.177 0.400 0.594 0.806 1.177 0.062 0.133 0.270 0.401 0.541 0.808

0.033 0.212 0.257 0.381 0.483 0.437 0.028 0.104 0.194 0.256 0.335 0.363 0.026 0.091 0.150 0.204 0.266 0.333

77.22 75.00 80.00

78.45

0.177 0.343 0.731

0.023 0.178 0.290

90.02

91.51

85.64

88.75

84.10

87.20

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Table 2. continued concn of amine mol·kg−1

0.437

0.656

0.219

0.437

0.656

0.219

0.437

0.656

0.219

initial acid concn mol·kg−1 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6

KD

avg KD

A336 + CCl4 3.80 3.21 3.08 5.59 5.97 5.67 6.27 6.06 5.67 6.59 6.90 7.87 7.00 7.89 9.15 8.41 7.85 A336 + Rice Bran Oil 4.64 5.51 6.11 6.76 5.74 4.89 4.94 5.58 7.30 7.53 7.53 8.85 8.48 5.79 6.90 10.15 13.22 8.48 13.22 12.13 6.92 A336 + Kerosene 2.70 3.96 5.19 6.22 2.42 3.03 4.20 3.53 5.98 6.22 6.88 6.22 5.93 7.12 5.79 7.16 7.15 7.67 7.12 7.25 7.96 A336 + Isoamyl Alcohol 2.72 3.02 2.72 3.47 2.72 3.50 2.98 1417

E (%) 79.17 76.25 83.06 84.81 85.00 86.25 85.83 85.00 86.82 87.34 87.50 88.75 90.15 89.38 88.70

avg E

85.66

88.64

82.28 85.94 87.11 85.16 83.00 83.17 81.25 83.60 84.76 85.94 86.52 86.33 87.34 92.97 89.45 92.19 92.38 87.38

77.15

73.00 83.85 86.15 70.77 75.19 80.77 77.91 86.15 87.31 86.15 85.58 87.69 85.28 87.73 88.46 87.69 87.88 88.85

68.48

73.13 73.13 77.61 73.13 77.78 74.85

74.94

84.73

90.29

85.13

87.65

Zt

Zs

1.086 1.394 2.279 0.097 0.194 0.394 0.589 0.777 1.211 0.067 0.133 0.270 0.412 0.545 0.769

0.386 0.376 0.571 0.065 0.121 0.198 0.278 0.325 0.452 0.037 0.091 0.156 0.223 0.281 0.368

0.188 0.393 0.797 1.168 1.518 2.119 0.093 0.191 0.387 0.589 0.791 1.184 0.064 0.138 0.273 0.418 0.563 0.848

0.088 0.184 0.262 0.324 0.345 0.649 0.053 0.109 0.166 0.241 0.297 0.433 0.041 0.088 0.134 0.203 0.259 0.361

0.167 0.383 0.788 0.970 1.375 2.215 0.083 0.171 0.362 0.554 0.746 1.108 0.058 0.117 0.252 0.387 0.521 0.777

0.037 0.114 0.259 0.173 0.308 0.798 0.031 0.077 0.164 0.236 0.308 0.573 0.031 0.064 0.132 0.194 0.259 0.445

0.167 0.334 0.710 1.003 1.422 1.965

0.008 0.024 0.043 0.008 0.119 0.105

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Table 2. continued concn of amine mol·kg−1 0.437

0.656

initial acid concn mol·kg−1 0.05 0.1 0.2 0.3 0.4 0.6 0.05 0.1 0.2 0.3 0.4 0.6

KD

avg KD

A336 + Isoamyl Alcohol 2.19 3.02 2.72 3.25 2.83 4.27 2.83 1.79 2.79 2.44 3.25 2.94 3.50 2.83

E (%)

avg E

Zt

Zs

68.66 73.13 76.49 73.88 81.04 73.88 64.18 70.89 76.49 74.63 77.78 73.88

74.54

0.078 0.167 0.350 0.510 0.741 0.970 0.062 0.133 0.270 0.401 0.541 0.808

0.008 0.029 0.054 0.064 0.162 0.143 0.008 0.027 0.060 0.083 0.136 0.164

73.61

efficiency only slightly in active diluents such as BA and MIBK (E% increases from 85 to 90%, in physical and chemical extraction, respectively). The extraction results for (10−30%) A336 in the respective diluents for the distribution of MAA between water and the organic phase are shown in Table 2. A significant increase in %E was observed in the case of toluene and CCl4, which when used alone could give only 40% extraction efficiency but when A336 was dissolved in them (individually), could provide %E = 87.5. In the extraction involving kerosene as diluent, % extraction increased by 72−74% in no A336 and with A336 in the respective diluent. Similarly, when rice bran oil was used as diluent, it provided %E as high as 91% with A336, which when used alone could give only extraction less than 30%. An increase in A336 concentration gives a two-fold increase in KD values even when used with “poor” diluents such as CCl4, kerosene, or RBO. The effect of increase in A336 concentration is more prominent when it is dissolved in RBO. At low initial acid concentration, its KD increases from 4.64 to 5.58, when A336 concentration increases from 10% to 20% in the organic phase. Also, further increment of A336 (up to 30%) caused KD to reach as high as 6.9. 4.2.2. Effect of Type of Diluents. MIBK and BA were found to provide high extractions; however, it has been reported that the use of these solvents increases the mutual solubility of MAA and water, consequently the overall process bears the drawback of migration of water and dissolution loss of solvent. Thus, though these diluents were very successful in providing high extraction when present alone, when present with A336, the presence of A336 could not enhance the extraction significantly. This occurs because A336 is insoluble in aqueous solutions, and it finds difficulty in associating with the hydrated molecule of the acid. Nonactive diluents, on the other hand, must be used with care, since with them, there is a problem of third phase formation. Kerosene and carbon tetrachloride are not recommended to be used as diluents as they formed a third phase, even at low initial acid concentrations in the aqueous phase. Also, RBO should be preferred over kerosene as it is nontoxic, and the toxic nature of kerosene may pollute the aquifers if the organic phase is disposed after extracting back the acid. However, toluene and RBO give “moderate” extraction efficiency when compared with the relatively high values given by MIBK and n-butyl acetate. 4.2.3. Equilibrium Complexation Constant. Figures 5 and 6 show the plot of Zs/(1 − Zs) versus [HA]aq for the extraction of MAA using A336 in various diluents. A straight line passing

used) is plotted against initial aqueous phase acid concentration in Figure 1. D was found to increase with an increase in acid concentration in all diluents except butyl acetate. Low D values have been found for kerosene, RBO, toluene, and CCl4. This occurs because these diluents do not contain any active groups that involve in interaction with the acid molecule. On the other hand, MIBK, BA, and isoamyl alcohol are good solvents providing very high extractions. MIBK when used alone provides 85% extraction (%E) because of the presence of an ion pair interaction group or H bonding ability. Similarly, BA, being a dipolar aprotic solvent, provides anion salvation by ion−dipole and ion−induced dipole forces; which further results in high D values. Overall, it can be seen that except for MIBK, BA, and isoamyl alcohol, all other diluents provide low D values at low acid concentration; that is, physical extraction is not successful in extracting the acid present in dilute concentrations. 4.2. Chemical Extraction Using A336. 4.2.1. Effect of A336 and Acid Concentration. A336 volume fraction was varied from 10 to 30 vol % in various diluents. It was found that KD increases with an increase in A336 concentration. Higher KD was obtained in MIBK, BA, and isoamyl alcohol, owing the contribution of both physical and chemical extraction in the KD obtained. Isoamyl alcohol, being active, polar, and protondonating, gives high distribution because of the formation of solvates through specific hydrogen bonding between the proton of the diluent and the acid-amine complex. The effects of A336 (in organic phase) on KD are shown through Figures 2 and 3. A very slight effect of the addition of A336 is observed in active diluents such as butyl acetate and MIBK. This was due to very high extraction ability of these diluents alone so the addition of a small volume fraction of A336 just compensates the corresponding decrease in volume percentage of these diluents. However, at higher A336 concentration (30%), a significant increase in KD was observed. For all acid concentrations, the overall loading ratio was found to decrease with an increase in A336 concentration. A 60 to 65% decrease in overall loading value was observed at both low and high concentrations of acid employed in the study. Higher loading was observed at low A336 concentration and higher acid concentrations. The stoichiometric loading ratio, Zs observes a similar trend of decrease in loading with an increase in A336 concentration (Figure 4). In all the cases, Zs were found to be less than 0.5 in low and high A336 concentrations and all acid concentrations chosen in the study. In comparison to physical extraction studied in various diluents, the addition of A336 to diluent increased its extraction 1418

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the systems was found in all cases (Zs < 0.5). The values of the equilibrium complexation constant obtained of the Aliquat 336−diluent systems followed the trend rice bran oil > carbon tetra chloride > butyl acetate > toluene > kerosene > MIBK > isoamyl alcohol.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.. + 919098529073. Notes

The authors declare no competing financial interest.

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REFERENCES

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Figure 5. Plot of Zs/(1 − Zs) versus [HA]aq for estimation of 1:1 MAA−amine equilibrium complexation constant in various diluents: (butyl acetate) y = 8.517x, R2 = 0.950; (isoamyl alcohol) y = 1.231x, R2 = 0.962; (MIBK) y = 4.645x, R2 = 0.954; (toluene) y = 7.516x, R2 = 0.969.

Figure 6. Plot of Zs/(1 − Zs) versus [HA]aq for estimation of 1:1 MAA−amine equilibrium complexation constant in various diluents: (carbon tetrachloride) y = 9.195x, R2 = 0.970; (rice bran oil) y = 9.216x, R2 = 0.956; (kerosene) y = 5.914x, R2 = 0.949.

through the origin was obtained and the slope of the straight line represents the equilibrium extraction constant, KE. Good R2 values (>0.95) were obtained in the case of all the diluents. The highest value of KE was obtained for A336 in RBO as 9.22, followed by 9.19 for carbon tetrachloride, 8.52 for butyl acetate, 7.52 for toluene, 5.91 in kerosene, 4.64 in MIBK, and the lowest, 1.23 in the case of isoamyl alcohol.

5. CONCLUSIONS Physical and reactive extractions of methacrylic acid using Aliquat 336 dissolved in seven individual diluents were performed, and it can be concluded that the largest distribution coefficients were obtained with MIBK. After physical extraction also, the degree of extraction of methacrylic acid in MIBK and butyl acetate were fairly good, lying between 85−90%. Kerosene and CCl4 when used as a diluent caused third phase formation in some cases. No overloading of amine in any of 1419

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