Extraction of acetic acid from aqueous solutions by emulsion type liquid membranes using Alamine 300 as a carrier

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1 Indian Journal of Chemical Technology Vol. 17, November 2010, pp Extraction of acetic acid from aqueous solutions by emulsion type liquid membranes using Alamine 300 as a carrier Aynur Manzak* & Melek Sonmezoglu Department of Chemistry, Faculty of Science, Sakarya University, Adapazari, Turkey * manzak@sakarya.edu.tr Received 4 March 2010; revised 25 August 2010 The extraction of acetic acid from aqueous solutions by an emulsion type liquid membrane process was investigated, using Alamine 300 as carrier, Span 80 as surfactant, and Na 2 CO 3 solution as stripping agent. A number of significant parameters viz. mixing speed, surfactant concentration, diluent type, concentration of the carrier Alamine 300, concentration of stripping agent, ph and concentration of feed solution were investigated. Acetic acid was successfully extracted and concentrated from aqueous solutions. Approximately 86% extraction of acetic acid was achieved within 10 min in a stirred vessel. Keywords: Acetic acid extraction, Alamine 300, Emulsion liquid membrane, Surfactant, Diluent Acetic acid is one of the simplest and most widely used carboxylic acids, and has many important chemical and industrial applications. Acetic acid is a valuable compound for agricultural application (preservative E280), and substrate for preparing natural and industrially uncontaminated products 1. Until recently, the acid waste containing acetic acid has been mostly subjected to neutralization without any proper treatment. However, the conventional neutralization treatment has problems of formation of precipitation in a large quantity, cost of alkali, and sludge disposal, which consequently cause an increase in the treatment cost 2. Recovery of carboxylic acids such as acetic acid is important in a number of industries. Removal of carboxylic acid from aqueous waste streams is also important in the petrochemical, chemical and pulp and paper industries 3. Classical methods for recovering low-volatility carboxylic acids involve formation of the insoluble calcium carboxylate salt 4. Many research groups are working in this field and some methods 5-10 have been proposed for the separation and recovery of acetic acid from different waste sources. Most of these processes are concerned with an aqueous solution that does not contain high concentration of inorganic acids. In the absence of any mature technology, a conventional physical separation method such as distillation is preferred by the industries; distillation is not economical because of the high energy cost involved in the vaporization process The extraction method has the potential to replace the existing distillation process used for acetic acid recovery. Solvent extraction processes have been proposed by several research groups to separate acetic acid from mixed acid waste 11. Acetic acid is generally recovered by a solvent extraction method 2. The recovery of acetic acid from waste streams is also possible by extractive distillation 10. Membrane separation processes have been used for many applications in the chemical industry, due to the compactness, simple and efficient operation and low energy consumption of membrane 12. Emulsion liquid membrane (ELM) is a highly sophisticated but an energy-saving separation technique. Some studies have been conducted to utilize liquid membrane technology for the removal of organic acids In this technology, solutes are not only removed but also concentrated. The external phase to be treated is contacted with an emulsion dispersed in globules. Each emulsion globule consists of droplets of an aqueous internal stripping phase, encapsulated in an organic membrane phase containing a surfactant. During this contact, solute transport occurs through the membrane phase into the internal stripping phase, where it is concentrated. Since extraction and stripping are done in a single step, ELM technology is preferred when treating effluents. The use of an emulsion liquid membrane in effluent treatment has received widespread attention, due to its ease of operation, lower power consumption and modular design. Odorous distillery effluent was treated for removal of acetic acid (solute) using ELM in a batch process 16. In the present investigation an

2 442 INDIAN J. CHEM. TECHNOL., NOVEMBER 2010 attempt has been made to use the ELM for removal and concentration of acetic acid from its solutions. Experimental Procedure Materials The liquid membrane phase (organic phase) is composed of a surfactant (emulsion stabilizer), carrier and diluent. Reagent grade surfactant Span 80 (sorbitan monooleate) was purchased from Fluka and used as such. The mobile carrier Alamine 300 was obtained from Cognis Corp. Kerosene, Toluene, Escaid 100 and Escaid 200 are used as diluents. Kerosene is a complex mixture of aliphatic origin and also contains aromatics about 15% w/w. Preparation of ELM The emulsion liquid membrane (ELM) used in this work was a water-oil-water (W/O/W) type of emulsion, formed by mixing the aqueous phase with the organic phase. The liquid membrane phase (organic phase) is composed of a nonionic surfactant, a carrier and diluent. The external or feed phase is an acetic acid solution. The surfactant is commercially known as Span 80. The mobile carrier is Alamine 300 (trioctylamine). Kerosene, Toluene, Escaid 100, Escaid 200 are used as diluents. The internal phase (V S ) is a Na 2 CO 3 solution. The external or feed phase (V F ) is an acetic acid solution. The stripping solution (V S : 50 ml) was added dropwise to the membrane solution (V m : 50 ml), stirred at 2000 rpm for 30 min and passed through a burette in about 20 min. The appropriate liquid membrane emulsion (V E ) was added to a feed solution (V F : 250 ml) in a 600 ml beaker with a Teflon-coated four vertical baffle. The two-phase system was stirred by a variable speed mixer, equipped with a turbine-type Teflon impeller. Samples of 1 ml of the feed phase were taken periodically for analysis. Extraction rates were measured by analyzing the feed phase acetic acid concentrations. Analysis of acetic acid samples was performed by high performance liquid chromatography (HPLC). At the end of each run, the emulsion was recovered and subsequently broken into its constituent organic and aqueous phases using a high-voltage splitter with niobium electrodes. All the extraction experiments were carried out batchwise. Analysis Acetic acid concentration was determined by high performance liquid chromatography (HPLC) (Shim-adzu LC-20AD, Japan), equipped with an Hypersil C18 ODS column ( mm) and detected with UV detector (Shimadzu SPD-M20A) at 210 nm. All the aqueous solutions were prepared using deionized water. Results and Discussion Effect of mixing speed of feed solution Figure 1 shows extraction efficiency at mixing speeds of 250, 300 and 400 rpm (C/C o which expresses the extent of remaining acetic acid in the feed solution). It was observed that the transfer of acetic acid increased on increasing the mixing speed from 250 to 400 rpm. According to Hirato et al. 17 increasing the mixing speed, reduces the size of the emulsion globules dispersed in the external phase, leading to greater surface area for mass transfer, and results in increased extraction rate. However, at the same time, the higher mixing speed affects the stability of emulsion globules, which may lead to breakage. Therefore, the rate of extraction decreases in the long run, as shown with data at 400 rpm. Thus, a mixing speed of 300 rpm was found to be appropriate for conducting the experiments. Effect of diluent Organic diluent influences the performance of many liquid membrane systems. The role of the diluent is not only to improve the physical properties of the extraction system, but also to remove the interaction product. This needs be taken into account in the choice of diluent 18. In the present study diluents like toluene, kerosene, Escaid 100 and Escaid 200 were used. The results shown in Fig. 2 prove that toluene provided the better performance. Effect of surfactant concentration Surfactant concentration has an important bearing on the stability of the emulsion. Too little surfactant renders the membrane weak, while an excess of Fig. 1 The effect of mixing speed of feed solution [diluent: Toluene (91% w/w), extractant: Alamine 300 (5% w/w), surfactant: Span 80 (4% w/w), external phase concentration: (10% w/v), stripping phase: 50 ml (10% w/v) Na 2 CO 3, treatment ratio (V F /V E ) : 5/2, phase ratio (V S /V m ): 1/1, emulsion mixing speed: 2000 rpm]

3 MANZAK & SONMEZOGLU: EXTRACTION OF ACETIC ACID FROM AQUEOUS SOLUTIONS 443 surfactant concentration leads to larger diffusional resistance. Experiments were performed with surfactant concentrations ranging from 3 to 6%. The emulsion stability improved with increased surfactant concentration. Figure 3 shows that increasing the surfactant concentration from 3 to 6% increased the stability of the liquid membrane, leading to a decrease in the break-up rate; hence the degree of extraction of acetic acid was also increased. Effect of Alamine 300 concentration The effect of carrier concentration is shown in Fig. 4. The efficiency of tertiary amines in the recovery of various organic acids has been demonstrated in some previous studies The initial extraction rate of acetic acid is slightly higher for 3 and 5% (w/w) Alamine 300 than for 8%, as shown in Fig. 4. A very high content of extractant in the membrane does not result in a benefit, due to the respective increase in viscosity, which leads to larger globules 22. The increasing concentration of extractant also promotes permeation swelling, which dilutes the aqueous receiving phase and reduces the efficiency of the ELM process. Effect of feed solution ph The ph strongly affects the ionization of carboxylic acids. Acetic acid is a weak acid (HA) that partially ionizes in aqueous solutions. The concentrations of dissociated and undissociated acids (HA) are affected by the hydrogen ion (H + ) concentration or ph. At extremely low ph values, the acid is mainly in undissociated form. Most aliphatic amines extract undissociated acids from the aqueous phase by forming an acid-base complex. The effect of hydrogen ion concentration was examined by varying the initial ph of the external phase between 1 and 4, as shown in Fig. 5. The acetic acid solution had a ph of 1.8. The extraction rate and ultimate yield of acetic acid decreased with increasing ph. As the ph Fig. 2 The effect of diluent on the extraction of acetic acid [diluent: (91% w/w), extractant: Alamine 300 (5% w/w), surfactant: Span 80 (4% w/w), feed solution concentration: (10% w/v), stripping phase: 50 ml (10% w/v) Na 2 CO 3, ph of feed solution: 1.8, treatment ratio (V F /V E ): 5/2, phase ratio (V S /V m ): 1/1, emulsion mixing speed: 2000 rpm] Fig. 4 The effect of extractant on the extraction of acetic acid [diluent: Toluene (88-93% w/w), extractant: Alamine 300 (3 8% w/w), surfactant: Span 80 (4% w/w), feed solution concentration: (10% w/v), stripping phase: 50 ml (10% w/v) Na 2 CO 3, ph of feed solution: 1.8, treatment ratio (V F /V E ): 5/2, phase ratio (V S /V m ): 1/1, emulsion mixing speed: 2000 rpm] Fig. 3 The effect of surfactant on the extraction of acetic acid [diluent: Toluene (89-92% w/w), extractant: Alamine 300 (5% w/w), surfactant: Span 80 (3-6% w/w), feed solution concentration: (10% w/v), stripping phase: 50 ml (10% w/v) Na 2 CO 3, ph of feed solution: 1.8, treatment ratio (V F /V E ) : 5/2, phase ratio (V S /V m ): 1/1, emulsion mixing speed: 2000 rpm] Fig. 5 The effect of feed phase ph on the extraction of acetic acid [diluent: Toluene (91% w/w), extractant: Alamine 300 (5% w/w), surfactant: Span 80 (4% w/w), feed solution concentration: (10% w/v), stripping phase: 50 ml (10% w/v) Na 2 CO 3, ph of feed solution: 1-4, treatment ratio (V F /V E ) : 5/2, phase ratio (V S /V m ): 1/1, emulsion mixing speed: 2000 rpm]

4 444 INDIAN J. CHEM. TECHNOL., NOVEMBER 2010 increased, the resulting decrease in the external phase hydrogen ion concentration reduces the extent to which the amine can couple with the acetic acid, and thus the rate of extraction decreases. The data for a ph level of 1 show that further decrease in ph results in reduced extraction efficiency 23. This process is further accelerated by the stripping action of Na 2 CO 3. Effect of stripping solution concentration Strip phase concentration was varied from 5 to 20%, as shown in Fig. 6. The difference in hydrogen ion chemical potentials between the two aqueous phases is the main driving force in the emulsion liquid membrane process. It can be noted from Fig. 6 that, when Na 2 CO 3 concentration is increased from 5 to 10%, extraction efficiency increases, but decreases when Na 2 CO 3 concentration is further increased from 10 to 20%. At 20% Na 2 CO 3 concentration, the emulsion swells up, and the extraction efficiency of acetic acid is decreased. Fig. 6 The effect of stripping phase concentration on the extraction of acetic acid [diluent: Toluene (91% w/w), extractant: Alamine 300 (5% w/w), surfactant: Span 80 (4% w/w), feed solution concentration: (10% w/v), stripping phase: 50 ml (5-20% w/v) Na 2 CO 3, ph of feed solution: 1.8, treatment ratio (V F /V E ): 5/2, phase ratio (V S /V m ): 1/1, emulsion mixing speed: 2000 rpm] Effect of feed concentration The acetic acid concentration in the feed or external phase was varied from 2 to 10%. The rate of acetic acid extraction increased as the feed concentration decreased, as shown in Fig. 7. Extraction mechanism The transport mechanism of acetic acid in ELM can be explained via the following steps, as shown in Fig. 8. (i) The acetic acid dissociates into H + and acetate ions as shown in Eq. (1). HA H + + A -... (1) Fig. 7 The effect of feed phase concentration on the extraction of acetic acid [diluent: Toluene (91% w/w), extractant: Alamine 300 (5% w/w), surfactant: Span 80 (4% w/w), feed solution concentration: (2,10% w/v), stripping phase: 50 ml (10% w/v) Na 2 CO 3, ph of feed solution: 1.8, treatment ratio (V F /V E ): 5/2, phase ratio (V S /V m ): 1/1, emulsion mixing speed: 2000 rpm] Fig. 8 Schematic mechanism of acetic acid extraction and stripping by tertiary amine (Alamine 300) and sodium carbonate 15.

5 MANZAK & SONMEZOGLU: EXTRACTION OF ACETIC ACID FROM AQUEOUS SOLUTIONS 445 (ii) The tertiary amine reacts with the acetic acid to form amine salt at the interface between the external and membrane phases in the extraction step, as given in Eq. (2). H + (aq) + A - (aq) + R 3 N (org) R 3 N H + A - (org) (2) (iii) Transport of the amine salt followed by stripping at the interface between the membrane and internal phase, after the amine salt had diffused across the membrane, the complex reacts with the stripping solution (Na 2 CO 3 ) at the membranestripping phase interface, as indicated in Eq. (3). 2R 3 NH + A - (org) + 2Na + (aq) + CO 2-3(aq) (R 3 NH + ) 2 CO 2-3(org) + 2Na + (aq) + 2A - (aq) (3) (iv) Finally, the amine carbonate formed in the stripping reaction diffuses back to the external phase interface where it dissociates into carbon dioxide and water, and thus regenerates the free amine as given by Eq. (4). (R 3 NH + ) 2 CO 2-3(org) 2R 3 N (org) + CO 2 + H 2 O (4) Conclusions The proposed ELM can be successfully employed to achieve acetic acid extraction from aqueous solutions. The concentration of the carrier, Alamine 300, affects the extraction rate. The highest acetic acid extraction rate was obtained with 5% concentration of alamine 300. The optimum conditions obtained from the experimets were: membrane phase with surfactant Span 80 (4% w/w), the carrier alamine 300 (5% w/w), and the diluent toluene (91% w/w), Na 2 CO 3 concentration in the feed solution (10% w/v). The optimal feed phase ph was 1.8, and the mixing speed of feed solution was 300 rpm. The use of toluene as a diluent achieved 86% extraction of acetic acid. Acknowledgements The authors wish to express their sincere gratitude to the State Planning Organization of Turkey which supported this work, and Mehmet Yilmaz, coordinator of BAPK in Sakarya University. Special thanks to Assist. Prof. Osman Kola, Department of Food Engineering, Sakarya University, for analyzing HPLC data. References 1 Wodzki R & Nowaczyk J, Sep Purif Technol, 26 (2002) Shin C H, Kim J Y, Kim H S, Lee H S, Mohapatra D, Ahn J W, Ahn J G & Bae W, J Hazard Mater, 162(2-3) (2009) Husson S M & King C J, Ind Eng Chem Res, 37 (1998) Tung L A & King C J, Ind Eng Chem Res, 33 (1994) Koga K & Kishimoto R, U.S. Pat. 4,353,784 (1978). 6 Chand S, Deepak D & Jain S K, Res Ind, 39 (1994) Sano T, Eijiri S, Hasegawa M, Kawakami Y, Enomoto N, Tamai Y & Yanagishita H, Chem Lett, 2 (1995) Saha B, Chopade S P & Mahajani S M, Catal Today, 60 (2000) Singh A, Tiwari A, Mahajani S M & Gudi R D, Ind Eng Chem Res, 45 (2006) Demiral H & Yildirim M E, Water Sci Technol, 47 (2003) Shin C H, Kim J Y, Kim H S, Lee H S, Mohapatra D, Kim J Y, Ahn J W &. Ahn J G, KOCS Int Symp, South Korea, July, (2007) Hagg M B, J Sep Purif, 27(1) (1998) Thien M P & Hatton T A, Sep Sci Technol, 23 (1988) Brien D J O & Senske G E, Sep Sci Technol, 24 (1989) Manzak A & Tutkun O, Sep Sci Technol, 39 (2005) Kumaresan T, Meera K M, Begum S, Sıvashanmugam P, Anantharaman N & Sundaram S, Chem Eng J, 95 (2003) Hirato T, Kishigami I, Awakura Y & Majima H, Hydrometallurgy, 26 (1991) Kyuchoukov G, Labbaci A, Albert J & Molinier J, Ind Eng Chem Res, 45 (2006) Yabbanavar V M & Wang D I C, Ann N Y Acad Sci, (1987), 506, Wennersten R, J Chem Technol Biotechnol, 33B (1983) Chaudhury J B & Pyle D L, in Separation for biotechnology edited by D L Pyle (Elsevier, Amsterdam), 2 (1990) Teramoto M, Sakai T, Yanagawa K, Ohsuga M & Miyake Y, Sep Sci Technol, 18 (1983) Schöller C, Chaudhuri J B & Pyle D L, Biotechnol Bioeng, 42 (1993) 50.

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