Phenol Removal Process Development from Synthetic Wastewater

Article pubs.acs.org/IECR

Phenol Removal Process Development from Synthetic Wastewater Solutions Using a Polymer Inclusion Membrane Irma Pérez-Silva, Carlos A. Galán-Vidal, Maria Teresa Ramírez-Silva,† José A. Rodríguez, Giaan Arturo Á lvarez-Romero, and Maria Elena Páez-Hernández* Universidad Autónoma del Estado de Hidalgo, Á rea Académica de Química, Laboratorio 2, Carr. Pachuca-Tulancingo Km. 4.5, C.P. 42184, Mineral de la Reforma, Hidalgo, México ABSTRACT: This paper presents the results concerning the first use of a polymer inclusion membrane (PIM) for the removal and transport of phenol from an aqueous solution and polluted water. The PIM contains Cyanex 923 as the carrier, cellulose triacetate (CTA) as the base polymer, and o-nitrophenyl pentyl ether (ONPPE) as a plasticizer. The effects of variables on the transport percentage of phenol have been studied. These variables include the concentration of the carrier and the plasticizer in the membrane, pH of the aqueous phase, and the concentration of NaOH in the stripping phase. This study shows that PIM composition has a great influence in phenol recovery, while the pH of the feed phase is a determining factor for the transport of phenol. In optimal conditions (PIM: 1 cm3 ONPPE/g CTA, 0.5 M of Cyanex 923; feed phase: pH 2; stripping phase: NaOH 0.25 M), it is possible to transport 85% of phenol present in both the water lab feed phase and polluted water. Chemical oxygen demand (COD) shows that only 4.3% of organic compounds other than phenol are transported to the stripping phase, which indicates that the process is highly discriminative for phenol, even in extremely contaminated water.

1. INTRODUCTION

triacetate (CTA) or poly(vinyl chloride) (PVC) to form a thin, flexible, stable film. PIMs have been successfully applied to the extraction of metal ions6−16 while a limited number of applications involving the extraction and separation of organic compounds have been reported in the literature.17−20 This work synthesizes a novel class of PIM with CTA as support and Cyanex 923 as the carrier with ONPPE plasticizer to demonstrate the vast potential of applications of PIM technology. Many factors that influence the flux transport of Ph, such as the concentration of the carrier and plasticizer in the membrane, pH of the aqueous phase, and concentration of NaOH in the stripping phase, among others, are discussed.

Due to its toxicity, the extensive use of phenol (Ph) in different industrial processes has resulted in major environmental problems. Therefore, this compound has been labeled by the U.S. Environmental Protection Agency (EPA) as one of the Priority Pollutants, and a Lifetime Health Advisory Level of 2 mg/L in water has been established by the EPA.1 The Mexican Government has established a maximum phenol level of 0.001 mg L−1 in drinking water.2 Therefore, removal of phenols from phenolic effluents is an important environmental concern and can also achieve the additional objective of obtaining valuable phenolic compounds. This has influenced the evaluation of different techniques for the treatment of Ph.3 Membrane technology, which promises interesting alternatives to the conventional methods for phenol removal and recovery, has received significant attention. Membrane technology is favorable due to its selectivity, flexibility, and enrichment properties associated with traditional separation techniques, like solvent extraction, but without using large amounts of volatile, toxic, and flammable solvents, while also effectively reducing costs. Writers have previously reported the use of different liquid membranes for the elimination of Ph. However, despite the potential advantages offered by these membranes, their operability is limited due to poor stability resulting from the formation of emulsions that can cause the loss of the extractant.4 As an alternative, a new type of membrane system called polymer inclusion membranes (PIM) has been developed.5 This system has attracted considerable attention for its use as a solid phase absorbent with a selectivity given by the extractant agent. PIMs are formed by casting a solution containing a carrier, a plasticizer, and a base polymer such as cellulose © 2013 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Reagents. Organic reagents, dichloromethane, acetone, tetrahydrofuran (THF), cellulose triacetate (CTA), cellulose acetate (CA), poly(vinyl chloride) (PVC), o-nitrophenyl pentyl ether (ONPPE), 2-nitrophenyl octyl ether (ONPOE), and phenol (Ph) were purchased from Fluka (Buchs, Switzerland). The carrier trialkyl-phosphine oxides (Cyanex 923) were kindly supplied by Cytec Industries Inc. (Hermosillo, Mexico), and used as received. Other reagents were purchased from Aldrich (ACS grade) (St. Louis, MO, USA). Aqueous solutions were prepared by dissolving the respective analytical grade reagent in deionized water with a resistivity no less than 18.2 MΩ cm obtained with a Milli-Q Plus system (Millipore, Bedford, MA, USA) Received: Revised: Accepted: Published: 4919

December 14, 2012 March 5, 2013 March 12, 2013 March 12, 2013 dx.doi.org/10.1021/ie3034569 | Ind. Eng. Chem. Res. 2013, 52, 4919−4923

Industrial & Engineering Chemistry Research

Article

2.2. Membrane Preparation. PIMs were prepared according to the procedure reported by Sigiura.21 The amount of each constituent was a function of the series of experiments to be performed. Thus, for CTA membrane 10 cm3 of a polymer solution (1 w/V % of CTA in dichloromethane), ion carrier (0−0.65 M), and plasticizer (0−6.4 cm3 of plasticizer/g CTA) were placed into a Petri dish of 9.0 cm diameter. This solution was allowed to evaporate overnight at room temperature. The film was then carefully peeled out of the bottom of the Petri dish and stored in deionized water for 12 h.22 2.3. Phenol Analyses. The influence of the studied parameters on the transport of Ph was analyzed during a 7-h transport experiment on a two-compartment cell. Samples of 2 cm3 were manually extracted with a pipet from both half-cells each hour (seven samples in total), and the phenol quantification in the transport experiments was carried out using a UV/vis spectrophotometer Lambda 40 (Perkin-Elmer, Waltham, MA, USA) at 510 nm with the method described by Woolard.23 2.4. Transport Experiments. The cell used to carry out the phenol transport experiments through the PIM was made in the lab according to Palet et al.,24 and had two main compartments (each one with 200 cm3 capacity): one of them contained 25 ppm of phenol as the feed phase, and the other, the stripping phase, contained NaOH in different compositions (Figure 1). The orifice at the center of the cell

compartments; the start of the process was marked by simultaneously switching on both stirrers.

3. RESULTS AND DISCUSSION 3.1. Influence of Base Polymers for PIM Preparation. PVC, CA, and CTA are still the most widely used base polymers in PIMs since they provide a high mechanical strength to the membranes and are compatible with most carriers. However, only a few studies have recently focused on the effects of their properties on the performance of PIMs. In this study, the results (see Table 1) prove that membranes Table 1. Influence of the Base Polymers in Phenol Transporta base polymers

% phenoltransported

PVCb CAc CTA

7.50 (3.40) 49.53 (8.26) 68.23 (4.02)

Feed phase: phenol 25 mg L−1, pH 2. Stripping phase: NaOH 0.25 M. Membrane: 11.32 cm2 of surface area, Cyanex 923 0.5 M, 1 cm3 ONPOE/g base polymer. Values obtained after 7 h of experimentation. %RSD in parentheses. b15% of PVC in tetrahydrofurane. c8% of CA in acetone. a

based on PVC and CA do not show the best performance in the phenol transport. For PVC, its partially negatively charged chlorine atom repels the partially negatively charged phosphoryl oxygen atom in the extractant, causing a lesser quantity of immobilized Cyanex.25 In the case of CTA, it has the higher ionizable groups participating in dipole−dipole interactions allowing a better immobilization of the extractant.26 3.2. Influence of the Chemical Nature of Plasticizer. To select a suitable plasticizer for the PIM preparation, characteristics such as high molecular weight, low tendency for exudation from the polymeric matrix, low vapor pressure and high capacity to dissolve the analyte, and the additives present in the membrane should be considered.27 In this work two plasticizers with different chemical properties, ONPOE and ONPPE, have been evaluated for the development of a PIM useful for the transport of phenol. Table 2 summarizes the date collected when doing this variation. Table 2. Influence of the Type of Plasticizer on the Transport of Phenola plasticizer

% phenoltransported

ONPOE ONPPE

68.22 (4.02) 80.73 (8.22)

Figure 1. Representation of the cell used to carry out the phenol transport based on Palet et al.24 The PIM is placed in the window between the feed and stripping aqueous compartments.

a

(with an area of 11.32 cm2) allowed communication between the compartments and served to place the PIM. Stirring devices with flat Teflon impellers were fitted to both cell compartments containing the aforementioned phases and connected to individual electric motors with variable speed controllers and tachometer readout. This setup was supported by a stable power supply (Cole-Palmer, Vernon Hills, IL, USA). All transport experiments were carried out in duplicate keeping the aforementioned cell at room temperature. The feed solution and the stripping phase were put into their respective

Even though o-nitrophenyl octyl ether (ONPOE) has been the most common plasticizer used for cellulose triacetate membranes, a higher transport was registered with o-nitrophenyl pentyl ether (ONPPE). This is due to the fact that this plasticizer prefers neutral molecules and phenol is in its protonated form and uncharged at pH 2, which is favorable for this interaction.

Feed phase: phenol 25 mg L−1, pH 2. Stripping phase: NaOH 0.25 M. Membrane: 11.32 cm2 of surface area, Cyanex 923 0.5 M, 1 cm3 plasticizer/g CTA. Values obtained after 7 h of experimentation. % RSD in parentheses.

4920

dx.doi.org/10.1021/ie3034569 | Ind. Eng. Chem. Res. 2013, 52, 4919−4923


Article

3.5. Influence of pH Solution. The dependence of the Ph extraction with pH solutions in the range of 2 to 11, imposed with NaOH and HCl in the feed phase was studied (Table 5).

3.3. Influence of Plasticizer Concentration. The plasticizer is an important component of the PIMs due to its influence on the mass transfer rates. To understand the effect of the plasticizer concentration on the Ph transport, different membranes were prepared keeping the carrier concentration constant, but varying the concentration of ONPPE added to the polymeric matrix just before the membrane was visibly deforming. Thus, membranes were considered successful when they looked homogeneous, transparent, flexible, and mechanically strong enough to withstand stress such as bending without tearing. The results of these experiments are presented in Table 3.

Table 5. Phenol Transport Percentages of the PIM Varying pH Value in Feed Phasea pH

Table 3. Phenol Transport Percentages at Different Concentrations of ONPPE in PIMa cm3ONPPE/gCTA 0.0 0.2 0.5 1.0 2.0 6.4

(4.55) (2.28) (6.37) (5.16) (2.56) (6.41)

The decrease of the extraction percentage noted at pH 11 can be explained by the presence of phenolate, the predominant specie at this pH which cannot be extracted with Cyanex 923. In contrast, the extraction favors a pH value of 2 because of the higher amount of polar specie present. 3.6. Effect of NaOH Concentration of Stripping Phase. According to the literature the stripping phase is considered one key factor for an effective transport; thus, different stripping solutions were evaluated in order to obtain the highest phenol re-extraction through a PIM prepared with a 0.5 M Cyanex 923 solutions. The composition of stripping phase was a sodium hydroxide solution in different concentrations. From results shown in Table 6, it becomes clear that re-

Feed phase: phenol 25 mg L−1, pH 2. Membrane: 11.32 cm2 of surface area, Cyanex 923 0.5 M. Stripping phase: NaOH 0.25 M. Values obtained after 7 h of experimentation. %RSD in parentheses.

From the experiments, it is possible to see that Ph transport increases when the value of 1 cm3 ONPPE/1g CTA of plasticizer is reached. Then, at higher plasticizer/CTA ratios, the transport decreases and the membranes become brittle. Nghiem5 reports that an excessive plasticizer concentration is problematic because it could migrate or exude to the membrane/aqueous interface and form a film on the membrane surface which would create an additional barrier to the transport of Ph across the membrane and at the same time decrease the mechanical strength. 3.4. Influence of Carrier Concentration. Cyanex 923 is widely used for the extraction of Ph from aqueous solutions.28−31 The effect of the quantity of the carrier fixed in the membrane was studied by preparing PIMs from several solutions at different Cyanex concentrations. Table 4 shows

Table 6. Effect of Variation of the Stripping Phase on the Phenol Transporta NaOH concentration (mol L‑1) in the stripping solution 0.05 0.10 0.25 0.50 1.00

% phenoltransported 84.26 83.35 85.56 76.03 79.57

(0.84) (4.83) (5.56) (7.01) (2.31)

a

Membrane: 11.32 cm2 of surface area, Cyanex 923 0.5 M, 1 cm3 ONPPE/g CTA. Feed phase: phenol 25 mg L−1, pH 2. Stripping phase: NaOH. Values obtained after 7 h of experimentation. %RSD in parentheses.

Table 4. Phenol Transport Percentages with a PIM with Different Concentrations of Carriera 0.00 0.05 0.10 0.50 0.65

(5.56) (1.51) (5.72) (2.59) (8.64) (5.37)

Membrane: 11.32 cm2 of surface area, Cyanex 923 0.5 M, 1 cm3 ONPPE/g CTA. Feed phase: phenol 25 mg L−1, pH variable. Stripping phase: NaOH 0.25 M. Values obtained after 7 h of experimentation. %RSD in parentheses.

a

carrier concentration (M)

85.56 62.34 63.06 66.56 37.67 12.74

a

% phenoltransported 62.42 65.39 78.79 80.92 79.19 78.19

% phenoltransported

2 3 5 7 9 11

% phenoltransported 26.82 75.03 80.92 85.56 63.68

(8.87) (6.12) (5.16) (5.56) (1.50)

extraction process is not the determinant stage on the phenol transport at this concentration level, since there are not remarkable differences at various NaOH concentrations (Figure 2). 3.7. Studies with Synthetic Phenol Wastewater. The study of phenol transport through PIMs with a synthetic wastewater sample (phenol free) was conducted by doping polluted water from an industrial park of Hidalgo State (Mexico) with urea (0.5 mg L−1), KH2PO4 (0.3 mg L−1), formaldehyde (23 mg L−1), and phenol.32 As seen in Figure 3, it is remarkable that PIM works as in a single component solution. Moreover, an analysis of the chemical oxygen demand (COD) of the solutions before and after the transport process shows a change consistent with phenol carrying (Table 7). The COD found in the stripping phase at the end of the experiment using wastewater phenol doped (CODsww = 136.20,) is only

Feed phase: phenol 25 mg L−1, pH 2. Membrane: 11.32 cm2 of surface area, Cyanex 923 as carrier, 1 cm3 ONPPE/g CTA. Stripping phase: NaOH 0.25 M. Values obtained after 7 h of experimentation. % RSD in parentheses. a

that Ph concentration in the stripping phase increases with the increasing of Cyanex concentration and reaches a maximum when the membrane contains 0.5 M of the carrier. At a higher Cyanex concentration, the viscosity of the media makes the transport difficult, diminishing the amount of transported phenol. 4921



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4.3% of the initial COD attributable to organic matter other than phenol (625.98 mg O2 L−1). The above-mentioned showed the developed PIM as a highly discriminative device for Ph removal given that this compound does not exceed 18% of the total amount of organic compounds in the doped wastewater. To verify the behavior of the PIM system at higher phenol concentrations, an experiment was carried out by systematically adding Ph to the feed phase every 3 h. A total amount of 200 mg L−1 was added to the feed phase, and after 12 h of experimentation 64% of the Ph was transported at a rate of 11.9 mgPh h−1.

Figure 2. Mechanism scheme for the transport of phenol from acidic aqueous solution to hydroxide stripping aqueous solution. Cy = Cyanex 923.

4. CONCLUSIONS This is the first report concerning the use of a polymer inclusion membrane (PIM) for the removal and transport of phenol from an aqueous solution. According to these results, the developed PIM is an excellent option for the removal of phenol from water lab feed phase and polluted water, reaching up to 80% of the initial amount of this compound in a single stage process. Chemical oxygen demand (COD) shows that only 4.3% of organic compounds other than phenol are transported to the stripping phase making the developed PIM a very selective device for Ph removal.

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +52 (771) 717 20 00 ext. 2217. Fax: +52 (771) 717 20 00 ext. 6502. E-mail: [email protected]. Present Address

Universidad Autónoma Metropolitana-Iztapalapa, Á rea de ́ ́ Quimica Analitica, Laboratorio R-105, San Rafael Atlixco 186, Col. Vicentina, C.P. 09340, AP 55-534, D.F. México. †

Figure 3. Phenol recovery from synthetic wastewater and deionized water. Membrane: 11.32 cm2 of surface area, Cyanex 923 0.5 M, 2 cm3 ONPPE/gCTA. Stripping phase: NaOH 0.25 M. Feed phase (deionized water): phenol 50 mg L−1, pH 2. Feed phase (synthetic wastewater): wastewater, urea (0.5 mg L−1), KH2PO4 (0.3 mg L−1), formaldehyde (23 mg L−1), phenol 50 mg L−1.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS M.E.P.H. acknowledges CONACyT for the financial support for the project 2006-62581. I.P.S. is grateful for the postgraduate studies grant. M.E.P.H., C.A.G.V., G.A.A.R., J.A.R.A., and M.T.R.S. gratefully thank the SNI for the distinction of their membership.

Table 7. COD Values for Feed and Stripping Solutions during Phenol Transport Experimenta COD

initial

(mg O2 L‑1)

COD

final

■

(mg O2 L‑1)

system

feed phase

stripping phase

feed phase

stripping phase

deionized water synthetic wastewater

136.59 762.57

3.85 1.14

20.76 609.77

109.27 136.20

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Membrane: 11.32 cm2 of surface area, Cyanex 923 0.5 M, 2 cm3 ONPPE/gCTA. Stripping phase: NaOH 0.25 M. Feed phase (deionized water): phenol 50 mg L−1, pH 2. Feed phase (synthetic wastewater): wastewater, urea (0.5 mg L−1), KH2PO4 (0.3 mg L−1), formaldehyde (23 mg L−1), phenol 50 mg L−1. Values obtained after 7 h of experimentation.

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Phenol Removal Process Development from Synthetic Wastewater

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