The dehydration and recovery of wasted TFP solution using the pervaporation process

Transcription

1 Sustain. Environ. Res., 23(5, ( The dehydration and recovery of wasted solution using the pervaporation process Teng-Chien Chen, 1,2 Tai-Hsiang Chen, 1,2 Jen-Yi Lyu 1 and Yao-Hui Huang 1,2, * 1 Department of Chemical Engineering National Cheng Kung University Tainan 70101, Taiwan 2 Sustainable Environment Research Center National Cheng Kung University Tainan 70101, Taiwan Key Words: Pervaporation, tetrafloropropanol, PVA/PAN composite membrane ABSTRACT Commercial polyvinylalcohol/polyacrylonitrile hybrid membranes crosslinked separately by B1, B2, B3, and S1 were tested for their abilities to recover tetrafloropropanol ( by pervaporation (PV. The structure and of the membranes were also determined by scanning electron microscope. A preliminary PV experiment was conducted at 60 C with the water content in the feed solution fixed at 5 wt%. Both the separation factor and pervaporation separation index (PSI were highest with the S1 membrane. Analytical results reveal that the separator factor is approximately kg m -2 h -1, total flux kg m -2 h -1, and the PSI value kg m -2 h -1 in the temperature range of C and feed concentration of range of wt%. The separation factor increases and total flux decreases as the water concentration decreases and operational temperature decreases. INTRODUCTION 1 In the Compact Disc-Recordable and Digital Versatile Disc Recordable manufacturing processes, residual 2,2,3,3-tetrafluoro-1-propanol ( content typically exists in the wastewater. The highly fluorinated alkyl chain of is bio-accumulative and adversely affects the environment [1]. Many different wastewater treatment strategies for degrading TPE exist, including submerged membrane bioreactor [2], bio organic activated carbon [3], and the electro-fenton process [4]. However, biological process may not be successful since molecules are not de-fluorinated by either aerobic or anaerobic systems [5,6]. Also other processes only transfer pollutants from one phase to another, rather than eliminate them from the environment, thereby causing secondary pollution. is a high-value-added product with a price of US$ 6500 t -1 free on board. An average sized wafer fabricating company produces over 100 t of waste annually (water is usually less than 15 wt%. From economic (i.e., expensive solvent and environmental perspectives, recovering and reusing are important issues; necessary purity, water removal (dehydration from waste solvents is required. However, and water can form an azeotropic mixture at 92.5 C at a /water composition of 72.5/27.5 (wt% [7]. Moreover, water and have close boiling points and very similar Antoine parameters [8]. Several methods, such as OMIT distillation [9], adsorption, and extraction, have been used to recycle organic wastewater. Nevertheless, organic solvents typically form an azeotrope with water. Separating an azeotrope using distillation, adsorption, and extraction requires high energy consumption. Membrane pervaporation (PV, a process based on the sorption-diffusion mechanism for the separation of liquid mixtures with azeotropes or close boiling points, is an efficient approach for dehydration [10-13]. The PV process generally uses an integrally skinned or composite asymmetric membrane with a selective skin layer that can break the vapor-liquid equilibrium of the feed phase [14]. Because only a portion of the feed is vaporized and *Corresponding author yhhuang@mail.ncku.edu.tw

2 326 Chen et al., Sustain. Environ. Res., 23(5, (2013 the remaining feed does not undergo phase change, the PV process is significantly more energy efficient than the conventional distillation process. Hence, PV is widely used to eliminate trace amounts of substances from liquid mixtures, such as removing water from organic solvent to produce high-purity solvent. PV is a membrane separation process for separating liquid mixtures with upstream of dense PV membranes in contact with feed liquids and downstream kept in a vacuumstate or applied with sweeping gas [15-17]. PV, which has garnered considerable attention as a result of its low energy consumption and simple operation, is widely applied to dehydrate organic solvents and separate organic components from organic/water and organic/organic mixtures [18]. Chang et al. summarized comparisons between distillation and membrane PV processes, and concluded that membrane PV processes have many advantages [19]. Table 1 summarizes this comparison. A significant number of investigations was devoted to the development of dense homogeneous polymeric membranes for alcohol dehydration by PV [20-25]. Young et al. employed polyaniline PV membranes doped with poly acrylic acid to separate water-ethanol mixtures [26]. Heisler et al. utilized a cellophane membrane for dehydration of ethanol solutions [27]. Schrodt et al. used a cellophane/polyvinyl alcohol (PVA membrane to separate various organic solutions [28]. The choice of a membrane is very important since PV efficiency depends markedly on the membrane. Formation of any liquid permeate film in pores inhibits the driving force. Polymer membranes can be selective according to solubility and the diffusion constant [29]. To enhance the stability and permeation properties of a PVA membrane, methods such as cross-linking [30-36], grafting [37,38], and heat treatment [39] have been used. In this study, recovery efficiency was determined for the best membranes of four PVA membranes using PV. The effects of two operational conditions (i.e., water concentration in the feed solution, the operation temperature on PV performance were determined. 1. Materials MATERIALS AND METHODS All reagents used in this work were analytical reagent grade and used without further purification. Methanol solutions were made obtained from Merck. The (2,2,3,3-, 97%, which was purchased from Alfa Aesar was the target compound. Four different PVA membranes, S1, B1, B2, and B3, were purchased from a commercial company. 2. Scanning Electron Microscopy (SEM The PVA layer thickness in the PVA/polyacrylonitrile (PAN hybrid membrane was determined using SEM (S4100; Hitachi, Japan. Fractured surfaces were sputter-coated with Platinum/Palladium prior to SEM measurements. 3. Pervaporation Figure 1 shows a schematic of the PV apparatus. The effective membrane area was 19.6 cm 2 and downstream pressure was Pa. The permeate was collected in a tube and cooled by liquid nitrogen. The concentrations of the feed and permeate solution were measured by a Karl Fischer moisture titrator and a gas chromatograph (14A; Shimadzu, respectively. To choose the best membrane for dehydration, the experiments were first conducted with the feed concentration in water controlled at wt% and operation temperature at C. The respective effects of temperature and feed concentration on dehydration performance were then investigated. To determine PV performance, flux (F, the separation factor (α, and PV separation index (PSI, as defined below, were obtained using the following equations. W F A t Y ( Y X ( X water water (1 (2 PSI = F t (α-1 (3 where W (kg is the total amount of permeate collected at experimental time Δt (h, A (m 2 is the effective membrane area, and X and Y are the weight fractions of the test alcohol in the feed and permeate, respectively. RESULTS AND DISCUSSION 1. Membrane Selection The α and PSI were the main parameters used to select the optimal membrane for organic solution dehydration. Figure 2a shows the performance of the four membranes for dehydration of, with the concentration in the feed solution set at wt% and operational temperature controlled at 70 C. The PSI of the S1 membrane was highest for dehydration. The recovery efficiency of the four membranes was also evaluated as.

3 Chen et al., Sustain. Environ. Res., 23(5, ( Table 1. The comparisons between distillation and membrane pervaporation Technology Distillation Membrane pervaporation Flexibility Low High; can take feed of different composition Process design Custom design Modular Plant operation One operator required No operator required Purity control Difficult Simple Electricity Lower 150% Higher Steam 280% Higher Lower Total utilities cost 90% Higher Lower Extractive solvent Cyclohexane None Replacement parts Almost none Membrane Operating cost Equivalent Equivalent Equipment cost Lower 30% Higher Pollutants Volatile organics Very low Kα radiation source. The angle of diffraction (2θ varied were at 0-65 to identify any changes in the crystal morphology and intermolecular distances between inter-segmental chains of the polymer. Kariduraganavar et al. identified the significant peak for pure PVA at 2θ = 20 by XRD analysis [34]. The peak of the S1 membrane is consistent with this result; thus, S1 is a PVA membrane (Fig. 4. Fig.1. The schematic pervaporation apparatus. Recovery (% (4 Total mass - Permerat mass 100% Total mass The S1 membrane had the best recovery performance because of its high α (Fig. 2b. Approximately wt% of high-concentration solution was recovered by the S1 membrane in 6 h. Accordingly, the S1 membrane was selected as the optimal membrane 2. Membrane Characteristics The SEM micrograph on the cross section of the four membranes (Fig. 3 shows that the optimal membrane contains three layers: a compact PVA layer, a porous PAN layer, and a fiber support layer. The compact PVA layer has a separating ability, the porous PAN layer makes the permeate diffuse rapidly through the membrane, and the fiber is a nonwoven fabric serving as the support. According to the micrograph (Fig. 3d, the S1 membrane is about μm thick. To identify the components of the S1 membrane and study the solid-state morphology of the membrane, X- ray diffraction (XRD was utilized. The X-rays at wavelengths of A. were generated by a Cu Fig. 2. (a The pervaporation separation index with various concentration in four different membranes (b The recovery efficiency with various concentration in four different membranes.

4 328 Chen et al., Sustain. Environ. Res., 23(5, (2013 Fig. 3. The SEM photograph of cross-section of (a B1 (b B2 (c B3 and (d S1 membranes. component to be absorbed by the membrane [44]. Figures 5a and 5b show the effect of water concentration in the feed solution on F and α, respectively. A high feed water concentration means that PVA hydrophilic PVA layer swells (Fig. 5b [45]. In the dehydration PV system, total flux and the α were around 1.44 kg m -2 h -1 and 21, respectively, in the 75 wt% of concentration at 50 C. However, at 2 wt% of water concentration, α increased to 251, and total flux declined to 0.17 kg m -2 h -1. Thus, both water and permeate molecules require little diffusion resistance through the membrane; thus, total permeation flux increases and α decreases. When the water concentration decreases, swelling of the S1 membrane will decrease and the free volume between polymer molecules will reduce. In PV, the permeate molecule can diffuse through free volumes [46]. The large molecules diffuse minimally when free volumes become small. Since molecules are larger than water molecules, the size of the free volume affects more sensitively the diffusion of the. This result is consistent with that obtained by Kariduraganavar [34]. 4. Effect of Temperature on Membrane Sorption Fig. 4. The XRD analysis of four different membranes. The contact angle, an important parameter in surface science, is a common measure of the hydrophobicity of a solid surface. Meaningful contact angle measurements can be used when calculating solid surface tensions [40-43]. The contact angle for S1 was 40. As the contact angle for a hydrophilic membrane < 90 ; the S1 membrane should be a hydrophilic membrane. 3. Effect of Water Concentration in the Feed Solution According to the solution-diffusion model, the concentration of a component in a feed solution is one of the determinants, which include temperature, membrane type, and concentration, that affect the Feed temperature has a marked influence on the α (Fig. 5a. A high temperature loosens the membrane structure and enhances the permeation of both components because high temperature boosts the free volume produced by the random thermal motion of the polymer chain and improves the frequency of diffusion jumps of absorbed solvent molecules [47]. Figure 5b shows the effects of feed temperature on PV performance of a wt% aqueous solution through the S1 membrane. Analytical results show that the total permeation flux and permeation flux increase while the α decreases as the feed temperature increases. Generally, during PV operation, feed temperature affects both the permeate transport behavior and the membrane structure. The mass transfer coefficients of both water and increase as feed temperature increases. Moreover, the flexibility of polymer chains of the membrane increases as feed temperature increases, which increases the free volume, frequency, and amplitude of polymer chain motions [48]. This produce more free space for the permeate diffusing through the membrane. This analytical result is consistent with those obtained by others [32,49]. The recovery efficiency was high at around 99% at 60 C with a 6-h reaction time (Fig. 5c. 5. Activation Energy Since permeation flux depends on operation temperature, the Arrhenius Eq. 5 [50] is as follows:

5 Chen et al., Sustain. Environ. Res., 23(5, ( F t A exp( Ea RT Fig. 6. The relationship between separation factor and the Arrhenius equation. Table 2. The activation energy values are calculated from the permeation flux concentration in the feed (% water solution (kj mol -1 solution (kj mol -1 Water (kj mol CONCLUSIONS Fig. 5. (a The separation factor at various concentration of feed in the (b The total flux and the water flux at various temperatures and feed concentration in the, (c The recovery concentration at various temperatures. F t A exp( Ea RT (5 where Ea (kj mol -1 is the apparent activation energy of permeation; A (molm -2 s -1 the pre-exponential factor; R the gas constant (8.314 J mol -1 K -1 ; and T (K is the Kelvin temperature. Then Ea can be obtained from the relationship of ln F t versus 1000/RT (Fig. 6. The Ea values are calculated from permeation flux data (Table 2. Analytical results indicate that high activation energy is needed for to permeate through the S1 membrane because S1 has a preferential affinity to water and molecules are much larger than those of water. The S1 membrane was chosen because it had the highest separation efficiency. The effect of temperature and feed concentration on separation efficiency, including flux, the α, the PSI, and masstransfer coefficient were discussed using the S1 membrane. The α was approximately 4-369, total flux was about kg m -2 h -1, the PSI value was around kg m -2 h -1 in the temperature range of C and feed concentration of of wt%. As operating temperature increases, the α decreases, but the water and flux increase. The mass-transfer coefficient increases when temperature and water content increases. Analytical results indicate that PV is a high-performance technology for recycling. ACKNOWLEDGEMENT The authors thank the Ministry of Economic Affairs of Republic of China for financial support of this research under Contract No. 101-EC-17-A-10-S REFERENCES 1. Guruge, K.S., L.W.Y. Yeung, P. Li, S. Taniyasu, N. Yamashita and M. Nakamura, Fluorinated alkyl compounds including long chain carboxylic

6 330 Chen et al., Sustain. Environ. Res., 23(5, (2013 acids in wild bird livers from Japan. Chemosphere, 83(3, ( Guo, W., H.H. Ngo, Z. Wu, A.Y.J. Hu and A. Listowski, Application of bioflocculant and nonwoven supporting media for better biological nutrient removal and fouling control in a submerged MBR. Sustain. Environ. Res., 21(1, ( Soonglerdsongpha, S., I. Kasuga, F. Kurisu and H. Furumai, Comparison of assimilable organic carbon removal and bacterial community structures in biological activated carbon process for advanced drinking water treatment plants. Sustain. Environ. Res., 21(1, ( Anotai, J., S. Sairiam and M.C. Lu, Enhancing treatment efficiency of wastewater containing aniline by electro-fenton process. Sustain. Environ. Res., 21(3, ( Wang, N., B. Szostek, R.C. Buck, P.W. Folsom, L.M. Sulecki, V. Capka, W.R. Berti and J.T. Gannon, Fluorotelomer alcohol biodegradationdirect evidence that perfluorinated carbon chains breakdown. Environ. Sci. Technol., 39(19, ( Dinglasan, M.J.A., Y. Ye, E.A. Edwards and S.A. Mabury, Fluorotelomer alcohol biodegradation yields poly- and perfluorinated acids. Environ. Sci. Technol., 38(10, ( Fumihiko, Y. and K. Toshiyuki, Method for Recovering Fuoroalcohol, US Patent ( Rocheste, C. H. and J.R. Symonds, Thermodynamic studies of fluoroalcohols. Part 1. Vapor pressures and enthalpies of vaporization. J. Chem. Soc. Farad. T. 1, 69, ( Stepnowski, P., K.H. Blotevogel, P. Ganczarek, U. Fischer and B. Jastorff, Total recycling of chromatographic solvents-applied management of methanol and acetonitrile waste. Resour. Conserv. Recy., 35(3, ( Matsuura, T., Synthetic Membranes and Membrane Separation Processes. CRC Press, Boca Raton, FL ( Mulder, M., Basic Principles of Membrane Technology. Kluwer, Dordrecht ( Freeman, B.D. and I. Pinnau, Polymer Membranes for Gas and Vapor Separation: Chemistry and Materials Science. American Chemical Society, Washington, DC ( Ho, W.S.W. and K.K. Sirkar, Membrane Handbook. Van Nostrand Reinhold, New York ( Mulder, M.H.V., T. Franken and C.A. Smolders, Preferential sorption versus preferential permeability in pervaporation. J. Membr. Sci., 22(2-3, ( Shao, P. and R.Y.M. Huang, Polymeric membrane pervaporation. J. Membr. Sci., 287(2, ( Chapman, P.D., T. Oliveira, A.G. Livingston and K. Li, Membranes for the dehydration of solvents by pervaporation. J. Membr. Sci., 318(1-2, 5-37 ( Sae-Khow, O. and S. Mitra, Pervaporation in chemical analysis. J. Chromatogr. A, 1217(16, ( Khayet, M., C. Cojocaru and G. Zakrzewska- Trznadel, Studies on pervaporation separation of acetone, acetonitrile and ethanol from aqueous solutions. Sep. Purif. Technol., 63(2, ( Chang, J.I., C.H. Chen and G.S.Y. Liu, The experience of waste minimization at a nitrocellulose manufacturing plant. Resour. Conserv. Recy., 30(4, ( Yoshikawa, M., A. Higuchi, M. Ishikawa, M.D. Guiver and G.P. Robertson, Vapor permeation of aqueous 2-propanol solutions through gelatin/torlon poly(amide imide blended membranes. J. Membr. Sci., 243(1-2, ( Higuchi, A., M. Yoshikawa, M.D. Guiver and G.P. Robertson, Vapor permeation and pervaporation of aqueous 2-propanol solutions through the Torlono poly(amide imide membrane. Sep. Sci. Technol., 40(13, ( Qiao, X.Y. and T.S. Chung, Fundamental characteristics of sorption, swelling, and permeation of P84 co-polyimide membranes for pervaporation dehydration of alcohols. Ind. Eng. Chem. Res., 44(23, ( Qiao, X.Y., T.S. Chung and K.P. Pramoda, Fabrication and characterization of BTDA- TDI/MDI (P84 co-polyimide membranes for the pervaporation dehydration of isopropanol. J. Membr. Sci., 264(1-2, ( Jiang, L.Y., T.S. Chung and R. Rajagopalan, Matrimid /MgO mixed matrix membranes for pervaporation. AIChE J., 53(7, ( Veerapur, R.S., K.B. Gudasi and T.M. Aminabhavi, Pervaporation dehydration of isopropanol using blend membranes of chitosan and hydroxypropyl cellulose. J. Membr. Sci., 304(1-2, ( Lee, Y.M., S.Y. Nam and S.Y. Ha, Pervaporation of water/isopropanol mixtures through polyaniline membranes doped with poly(acrylic acid. J. Membr. Sci., 159(1-2, ( Heisler, E.G., A.S. Hunter, J. Siciliano and R.H. Treadway, Solute and temperature effects in the

7 Chen et al., Sustain. Environ. Res., 23(5, ( pervaporation of aqueous alcoholic solutions. Science, 124(3211, ( Rose, A., R.F. Sweeny and V.N. Schrodt, Continuous distillation calculations by relaxation method. Ind. Eng. Chem., 50(5, ( Atra, R., G. Vatai and E. Békássy-Molnár, Isopropanol dehydration by pervaporation. Chem. Eng. Process., 38(2, ( Yeom, C.K., S.H. Lee and J.M. Lee, Pervaporative permeations of homologous series of alcohol aqueous mixtures through a hydrophilic membrane. J. Appl. Polym. Sci., 79(4, ( Uragami, T., K. Okazaki, H. Matsugi and T. Miyata, Structure and permeation characteristics of an aqueous ethanol solution of organicinorganic hybrid membranes composed of poly(vinyl alcohol and tetraethoxysilane. Macromolecules, 35(24, ( Yu, J., C.H. Lee and W.H. Hong, Performances of crosslinked asymmetric poly(vinyl alcohol membranes for isopropanol dehydration by pervaporation. Chem. Eng. Process., 41(8, ( Sharma, A., S.P. Thampi, S.V. Suggala and P.K. Bhattacharya, Pervaporation from a dense membrane: Roles of permeant-membrane interactions, Kelvin effect, and membrane swelling. Langmuir, 20(11, ( Kariduraganavar, M.Y., S.S. Kulkarni and A.A. Kittur, Pervaporation separation of water-acetic acid mixtures through poly(vinyl alcohol- silicone based hybrid membranes. J. Membr. Sci., 246(1, ( Guan, H.M., T.S. Chung, Z. Huang, M.L. Chng and S. Kulprathipanja, Poly(vinyl alcohol multilayer mixed matrix membranes for the dehydration of ethanol-water mixture. J. Membr. Sci., 268(2, ( Chen, J., J.Q. Huang, J.D. Li, X. Zhan and C.X. Chen, Mass transport study of PVA membranes for the pervaporation separation of water/ethanol mixtures. Desalination, 256(1-3, ( Chiang, W.Y. and C.L. Chen, Separation of water-alcohol mixture by using polymer membranes - 6. Water-alcohol pervaporation through terpolymer of PVA grafted with hydrazine reacted SMA. Polymer, 39(11, ( Alghezawi, N., O. Şanlı, L. Aras and G. Asman, Separation of acetic acid-water mixtures through acrylonitrile grafted poly(vinyl alcohol membranes by pervaporation. Chem. Eng. Process., 44(1, ( Cai, B.X., L. Yu, H. Ye and C.J. Gao, Effect of separating layer in pervaporation composite membrane for MTBE/MeOH separation. J. Membr. Sci., 194(2, ( Zisman, W.A., Contact Angle, Wettability and Adhesion. Advances in Chemistry Series, Vol. 43. American Chemical Society, Washington, DC ( Li, D. and A.W. Neumann, Contact angles on hydrophobic solid surfaces and their interpretation. J. Colloid Interface Sci., 148(1, ( Li, D. and A.W. Neumann, Equation of State for Interfacial-Tensions of Solid-Liquid Systems. Adv. Colloid Interface Sci., 39, ( Kwok, D.Y. and A.W. Neumann, Contact angle measurement and contact angle interpretation. Adv. Colloid Interface Sci., 81(3, ( Wijmans, J.G. and R.W. Baker, The solutiondiffusion model: A review. J. Membr. Sci., 107(1-2, 1-21 ( Guo, W.F., T.S. Chung and T. Matsuuraa, Pervaporation study on the dehydration of aqueous butanol solutions: A comparison of flux vs. permeance, separation factor vs. selectivity. J. Membr. Sci., 245(1-2, ( Yeom, C.K. and K.H. Lee, Pervaporation separation of water-acetic acid mixtures through poly(vinyl alcohol membranes crosslinked with glutaraldehyde. J. Membr. Sci., 109(2, ( Hu, C.C., C.S. Chang, R.C. Ruaan and J.Y. Lai, Effect of free volume and sorption on membrane gas transport. J. Membr. Sci., 226(1-2, ( Tsai, H.A., Y.S. Ciou, C.C. Hu, K.R. Lee, D.G. Yu and J.Y. Lai, Heat-treatment effect on the morphology and pervaporation performances of asymmetric PAN hollow fiber membranes. J. Membr. Sci., 255(1-2, ( Lee, C.H. and W.H. Hong, Influence of different degrees of hydrolysis of poly(vinyl alcohol membrane on transport properties in pervaporation of IPA/water mixture. J. Membr. Sci., 135(2, ( Feng, X.S. and R.Y.M. Huang, Estimation of activation energy for permeation in pervaporation processes. J. Membr. Sci., 118(1, (1996. Discussions of this paper may appear in the discussion section of a future issue. All discussions should be submitted to the Editor-in-Chief within six months of publication. Manuscript Received: November 23, 2012 Revision Received: January 15, 2013 and Accepted: February 20, 2013