Advances in Environmental Biology

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1 AENSI Journals Advances in Environmental Biology ISSN EISSN Journal home page: Investigation of Optimum Drying Conditions for Pure PES Membranes for Gas Separation Marjan Farnam, Hilmi Mukhtar, Azmi Shariff 1 Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia A R T I C L E I N F O Article history: Received 28 November 2015 Accepted 22 December 2015 Available online 31 December 2015 Keywords: Polymeric membranes - polyethersulfone - gas separation A B S T R A C T Polymeric membranes have been extensively applied in membranes gas separation industry. In this research, polyethersulfone (PES) was used as the polymeric matrix to prepare polymeric membranes and its optimum drying conditions were discussed. Different drying conditions were investigated to obtain the least residue solvent and to achieve a dense membrane structure. However only at 150 C for 1 hour, a homogenous dense structure was achieved. TGA results approved a very low remaining solvent percentage in the membranes and also FESEM images depicted that a dense membrane structure has been accomplished under this drying condition AENSI Publisher All rights reserved. To Cite This Article: Marjan Farnam, Hilmi Mukhtar, Azmi Shariff, Investigation of Optimum Drying Conditions for Pure PES Membranes for Gas Separation. Adv. Environ. Biol., 9(27), , 2015 INTRODUCTION Membranes have been the best choice for gas separation purposes over the last two decades [1]. Gas separation using membrane technology owns enormous economical merits over other conventional separation approaches. Carbon dioxide (CO 2 ) removal by membrane is a drastically fast growing area because of its various advantages in comparison with other separation methods such as low capital investment, light weight, low space requirement and high process flexibility. The membrane gas separation process has developed remarkably and currently can be mentioned as a vying industrial gas separation plan [2, 3]. The most common types of membranes tested for this purpose are polymeric membranes and inorganic membranes [4-6]. These membranes play effective role in gas separation, especially for carbon dioxide removal. However, inorganic membranes suffer from augmented cost, handling problems, and difficult processing and polymeric membranes have limitations like chemical degradation and thermal instability; but thanks to its economical advantages, polymeric membranes have highly extended for a diversity of industrial functions including gas separation. In fact, the major CO 2 separation approach in the market is currently occupied by polymeric membranes by virtue of their approximately low production cost, good processing ability as well as reproducibility and good mechanical strength [7, 8]. There is a variety of polymers used for gas separation membranes. The high performance engineering thermoplastic Polyethersulfone (PES) was chosen as the main polymer in this study thanks to its number of favorable properties including thermal stability. The repeating unit in the structure of PES possesses a certain degree of rigidity such that it has a glass transition temperature of 225 C [9] and is thus a glassy polymer. Such different properties have made PES a distinguished membrane material for numerous utilizations [10]. There are two categories of polymeric membranes: porous and nonporous [11]. Nonporous membranes are dense membranes that was produced in this current research study. In membrane preparation, in order to have a better gas separation performance, dense membranes are targeted to be obtained; therefore, a good and suitable drying condition which leads to a better and more uniform solvent evaporation and the lowest residue solvent amount in the membranes, is needed to be applied on the membranes after casting so dense membranes can be obtained. In fact, an appropriate and optimum drying condition will lead to the lowest residue solvent in the membrane and will also provide a dense structure in the membrane which is our objective. An extensive literature review has demonstrated that the investigation on optimum drying conditions for PES membranes has not been done yet specifically. We need to test different methods to achieve a dense Corresponding Author: Marjan Farnam, Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia. Mobile number: ; farnam.mm@gmail.com

2 327 Marjan Farnam et al, 2015 membrane structure, one of the parts of the methodology is to check the drying conditions of the membranes in order to get the least residue solvent as well as a dense structure. Thus, in this research, a variety of drying conditions has been studied and finally the best method to dry PES membranes to get dense membranes after casting has been identified. Experimental: 2.1. Materials: In this study, PES (ULTRASON E 6020P) having an average molecular weight of 50,000 g/mol, was purchased from BASFs Germany; Dimethylformamide (DMF) is used as the solvent to dissolve PES because of its close solubility parameter with PES Synthesis of membranes: PES flakes were dried in the oven for 24hr at 100 C to remove the moisture. The membrane casting solutions were developed by mixing the weighed PES and DMF. Firstly, 50% of the whole PES amount that was calculated based on the solvent amount, was added to the solvent gradually to let the polymer disperse very homogenously in the solvent, the mixture was stirred gently until it formed a clear solution. Then, another half of weighed PES was gradually added into the solution and the mixing was continued overnight to assure that a homogenous mixture is gained. After that, the mixture was ultrasonicated for 30 min at a frequency of 100Hz to get a better homogenous solution. Then, the solution was cast on a glass plate by adjusting the knife gap at 180 micron. After casting, the membrane was dried according to the condition tabulated in table 1 and then after drying, it was peeled off from the glass plate itself and were kept in desiccators to be used for characterization. Table 1 shows the different drying methods for pure PES membranes. Table1: Different drying conditions for PES membranes Sample Number Drying Condition After Casting Drying Temp. Drying Time ( C) (hr) S1 Room (27) 24 S S S S S S S S Characterization of membranes: Physical characterization of the membranes prepared in this study was done by following standard instruments and procedure. The morphological analysis was carried out using a Variable Pressure Field Emission Scanning Electron Microscope (VPFESEM, Zeiss Supra55 VP). For this analysis, the samples were first immersed in liquid nitrogen to harden them before they were fractured to run the test. The thermal stability of the developed membranes was analyzed by thermogravimetric analysis (Perkin Elmer Simultaneous Analyzer STA 6000). Approximately 5 mg sample was placed in the sample holder and heated up to 800 C at a rate of 10 C/min. RESULTS AND DISCUSSION 3.1. Thermal analysis of membranes: The thermogravimetric (TGA) study was carried out to measure the weight loss of membranes across temperature range of 50 C to 800 C and to find out which drying conditions are going to be efficient for the membranes to have the least residue solvent. First of all, the drying temperature was fixed at 100 C while the drying time was changed at 1, 2 and 3 hours as shown in Fig. 1. For pure PES membrane, the weight loss launched at about 500 C demonstrating the approximate decomposition temperature of PES membranes. Boiling point of DMF is around 155 C. So, as it can be observed in Fig. 1, the residue solvent in pure PES having dried under room temperature was more than the sample dried in the oven at 100 C. Also, when the drying time increased, the residue solvent decreased which is a good sign; but still even after 3 hours drying at 100 C, there was around 8% residue solvent in the membrane which was not desirable for membrane [11-13].

3 328 Marjan Farnam et al, 2015 Fig. 1: TGA Comparison in different drying times To reduce the residue solvent more, this time, the drying temperature was altered from 110 C to 140 C in Fig. 2 in constant drying time (1hr) in which the more the temperature increased, the more the residue solvent in the membrane decreased but even at 140 C, the residue solvent was more than 8% which is not desirable because the solvent molecules will not allow the gas molecules to pass through the membrane freely and the gas permeability will decrease which is not favorable; therefore, the drying temperature was increased to 150 C to be compared with other drying temperatures at a fixed drying time (1hr) as it is shown in Fig. 3. As we can see in Fig. 3, in comparison with other temperatures, the best drying temperature was at 150 C for 1hr in which the residue solvent was around 2-3% weight percentage. Fig. 2: TGA Comparison in different drying temperatures

4 329 Marjan Farnam et al, 2015 Fig. 3: TGA Analysis for pure PES membranes in Different Drying Temperatures 3.2. Morphological analysis of membranes: The cross sectional and surface FESEM micrographs of pure PES dried in room temperature (S1) and pure PES dried at the best drying condition (S9) are shown in Fig. 4 and 5 respectively. In FESEM images in Fig. 4, it has been observed that pure PES membrane dried at room temperature showed a complete porous structure. Therefore, due to this porous structure that was achieved in room temperature, the need to change the drying conditions to a better one, which is oven drying, will arise. This structure might be due to the uneven evaporation of the solvent in membrane under the room temperature. (a) (b) Fig. 4: FESEM (a) cross-sectional and (b) surface images for pure PES dried at room temperature By changing the drying conditions, considering the TGA results, the pure PES membrane dried at 150 C for 1hr, showed the least residue solvent and also its cross sectional and surface FESEM images (Fig. 5) revealed that this membrane (S9) owns a very even and good dense structure which is the desirable kind of membrane for separation purposes as was mentioned before.

5 330 Marjan Farnam et al, 2015 (a) (b) Fig. 5: FESEM (a) cross-sectional and (b) surface images of pure PES membranes dried at 150 C for 1hr Conclusion: As it was discussed in this current research work, the drying conditions at room temperature for pure PES membranes were not resulting in a dense membrane structure so not only the residue solvent in the membrane was not less than 2-3% but also a porous structure was obtained which directed us to alter the drying conditions in order to accomplish the optimum drying method which was at 150 C for 1hr that gave us a homogenous dense structure as well which is favorable. ACKNOWLEDGMENT The authors sincerely thank Universiti Teknologi PETRONAS for giving financial support to conduct this research work. REFERENCES [1] Yeo, Z.Y., T.L. Chew, P.W. Zhu, A.R. Mohamed, S.P. Chai, Conventional Processes and Memrane Technology for Carbon Dioxide Removal from Natural Gas. Journal of Natural Gas Chemistry, 21: [2] Goh, P.S., A.F. Ismail, S.M. Sanip, B.C. Ng, M. Aziz, Recent Advances of Inorganic Fillers in Mixed Matrix Membrane for Gas Separation. Separation and Purification Techology, 81: [3] Budd, P.M., N.B. McKeown, Highly Permeable Polymers for Gas Separation Membranes. Polym. Chem, 1: [4] Aroon, M., A. Ismail, T. Matsuura, M. Montazer-Rahmati, Performance studies of mixed matrix membranes for gas separation: a review. Sep. Purif. Technol., 75: [5] Chung, T.-S., L.Y. Jiang, Y. Li, S. Kulprathipanja, Mixed matrix membranes (MMMs) comprising organic polymers with dispersed inorganic fillers for gas separation. Prog. Polym. Sci., 32: [6] Shen, J., J. Qiu, L. Wu, C. Gao, Facilitated transport of carbon dioxide through poly(2-n,n-dimethyl aminoethyl methacrylate-co-acrylic acid sodium) membrane. Sep. Purif. Technol., 51: [7] Zhang, Y., J. Sunarso, Sh. Liu, R. Wang, Current Status and Development of Membranes for CO 2 /CH 4 Separation. International Journal of Greenhouse Gas Control, 12: [8] Aroon, M.A., A.F. Ismail, T. Matsuura, M.M. Montazer-Rahmati, Performance Studies of Mixed Matrix Membranes for Gas Separation. Sep. Purif. Technol., 75: [9] Bakeri, Gh., A.F. Ismail, M. Rezaei DashtArzhandi, T. Matsuura, Porous PES and PEI hollow fiber membranes in a gas liquid contacting process A comparative study, J. Membr. Sci., 475: [10] Ahmed, I., A. Idris, A. Hussain, Z.A.M. Yusof, M. Saad Khan, Influence of Co-Solvent Concentration on the Properties of Dope Solution and Performance of Polyethersulfone Membranes, Chem. Eng. Technol., 36: [11] Hassani, F., M. Mousavi, N. Saghatoleslami, V. Ghaffarian, Polyethersulfone/Poly(D,L-lactide) Blend Membranes: Preparation, Characterization, and Performance, Chem. Eng. Technol., 37: [12] Dorosti, F., M.R. Omidkhah, M.Z. Pedram, F. Moghadam, Fabrication and Characterization of Polysulfone/Polyimide-Zeolite Mixed Matrix Membranes for Gas Separation. Chemical Engineering Journal, 171:

6 331 Marjan Farnam et al, 2015 [13] Shena, L., L. Li, J. Chen, H. Hong, H. Yu, Zh. Hou, H. Lina, X. Lu, Effects of molecular weight distribution (M d ) on the performances of the polyethersulfone (PES) ultrafiltration membranes, J. Membr. Sci., 490: