The application of membranes has gained acceptance in the chemical and process industries for separation and purification for over three decades and is currently being practiced for natural gas processing, waste water treatment among others. A crack-free composite membrane was employed in this paper. Scanning electron microscopy (SEM) observation was carried out to characterize the membrane. The operational parameters such as feed flow rate, permeation pressure, permeation temperature, kinetic diameter and gas molecular characteristics are examined at 25C to 450C and 0.05 to 1.0 barg feed pressure. The performance of gas selectivity is also provided. Separation factor of 2.554 was obtained for H2/CO2 at 450C and 0.8 barg. Activation energies of 1.0 and 0.42 kJ/mol were also obtained for H2 and CO2/CO/H2 gas mixtures at 1.0 barg

Gobina, E.

Kajama, M.N.

Shehu, H.

English

Abstract:The application of membranes has gained acceptance in the chemical and process industries for separation and purification for over three decades and is currently being practiced for natural gas processing, waste water treatment among others. A crack-free composite membrane was employed in this paper. Scanning electron microscopy (SEM) observation was carried out to characterize the membrane. The operational parameters such as feed flow rate, permeation pressure, permeation temperature, kinetic diameter and gas molecular characteristics are examined at 25 0 C to 450 0 C and 0.05 to 1.0 barg feed pressure. The performance of gas selectivity is also provided. Separation factor of 2.554 was obtained for H2/CO2 at 450 0 C and 0.8 barg. Activation energies of 1.0 and 0.42 kJ/mol were also obtained for H2 and CO2/CO/H2 gas mixtures at 1.0 barg

M. N. Kajama

H. Shehu

E. Gobina

CiteSeerX

Purification of Gases Using Nanoporous Inorganic Membranes

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   AUTHOR(S):   TITLE:    YEAR:   Publisher citation:    OpenAIR citation:    Publisher copyright statement:      OpenAIR takedown statement:   This publication is made freely available under ________ open access.      This is the ______________________ version of an article originally published by ____________________________ in __________________________________________________________________________________________ (ISSN _________; eISSN __________). This publication is distributed under a CC ____________ license. ____________________________________________________ Section 6 of the “Repository policy for OpenAIR @ RGU” (available from http://www.rgu.ac.uk/staff-and-current-students/library/library-policies/repository-policies) provides guidance on the criteria under which RGU will consider withdrawing material from OpenAIR. If you believe that this item is subject to any of these criteria, or for any other reason should not be held on OpenAIR, then please contact openair-help@rgu.ac.uk with the details of the item and the nature of your complaint.                    International Journal of Scientific Engineering and Technology                                                               (ISSN : 2277-1581)                 Volume No.3 Issue No.9, pp : 1156-1159                                                                                                        1 Sep 2014 IJSET@2014 Page 1156  Purification of Gases Using Nanoporous Inorganic Membranes  M. N. Kajama, H. Shehu, & E. Gobina* Centre for Process Integration and Membrane Technology, (CPIMT), School of Engineering, The Robert Gordon University, Aberdeen, United Kingdom. Email: m.n.kajama@rgu.ac.uk, h.shehu@rgu.ac.uk, e.gobina@rgu.ac.uk*  Abstract :The application of membranes has gained acceptance in the chemical and process industries for separation and purification for over three decades and is currently being practiced for natural gas processing, waste water treatment among others. A crack-free composite membrane was employed in this paper. Scanning electron microscopy (SEM) observation was carried out to characterize the membrane. The operational parameters such as feed flow rate, permeation pressure, permeation temperature, kinetic diameter and gas molecular characteristics are examined at 25 0C to 450 0C and 0.05 to 1.0 barg feed pressure. The performance of gas selectivity is also provided. Separation factor of 2.554 was obtained for H2/CO2 at 450 0C and 0.8 barg. Activation energies of 1.0 and 0.42 kJ/mol were also obtained for H2 and CO2/CO/H2 gas mixtures at 1.0 barg.   Keywords: composite membranes, gas permeation, separation factor, activation energy. 1  Introduction Membranes for gas separation are basically barriers that are selective to specific components in a feed gas mixture and is driven by a pressure difference across the membrane and are widely used for purification in the industries. Membranes can be classified into inorganic and organic/inorganic (hybrid) systems. The organic ones are further divided into biological and polymeric constituents, while the inorganic membranes can be divided into metallic and ceramic (porous and non-porous) membranes [1]. The International Union of Pure and Applied Chemistry (IUPAC) classified porous membranes as; Micropores 0.5 - 2 nm, mesopores is 2 - 50 nm and macropores is > 50 nm [2, 3]. In all cases, some considerations on productivity and separation selectivity, mechanical integrity, and membrane’s durability at the operating conditions needs to be taken into account against cost issues [1], because the importance of each of these requirements differs with their applications. Infarct, permeability and selectivity are the main basic properties of a membrane. It can be elaborated that; the higher the permeability, the lower the membrane area is required. Also, the higher the selectivity, the more efficient the process, the lower the driving force required to attain a separation and therefore the lesser the operating cost of the separation system [1]. On one hand, the technical merits of inorganic membranes include chemical stability in wide pH, high thermal stability, long term durability as well as high structural integrity. Some of the demerits include the fact that they are expensive, and have low hydrothermal stability. On the   other hand, the technical merits of polymeric membranes include the fact that they are cheap. The demerits of polymers are that they are prone to denature and be contaminated, they are structurally weak, and they are not stable [1] which hinders the use of such membranes for gas separation at high temperature. It is for these reasons that inorganic material membrane is receiving an ever increasing attention [4]. Inorganic membranes are commonly made from metal oxide or sintered metal, palladium metal, zeolite among others [1].  Gas transport through inorganic membranes depends on pore size and pore size distribution, membrane materials as well as the interaction between the diffusing gases and the membrane [5]. The main transport mechanisms are viscous flow, Knudsen diffusion, surface diffusion, multi-layer diffusion, capillary condensation, molecular sieving and Solution-diffusion transport mechanism [6, 7, 8]. Numerous factors influencing gas permeation across inorganic membranes have been recognised in many literatures [1-8] which are however very heterogeneous in nature which pose challenges to researchers in order to arrive with research conclusion.  The separation of gas mixtures is now a significant component in industries such as natural gas processing plant [9], pharmaceuticals, food, waste water treatment and biochemistry among others [10]. Membrane technology has gained acceptance for gas separation and recovery. This includes carbon dioxide separation from fuel gas [11], hydrogen separation/recovery for fuel cell application [12], hydrogen sulphide separation from natural gas [13] and recovery of helium and methane from bio-gas [9]. The inorganic ceramic membranes are environmentally benign, cost-effective and energy efficient. Research is necessary to enhance more robust membrane materials that are capable of upholding their properties for long under demanding conditions. These membranes are in the form of a tubular or flat sheet [14].  In this paper, a crack-free composite membrane was employed in order to examine its operational parameters such as permeation pressure, permeation temperature, kinetic diameter and gas molecular characteristics at 25 0C to 450 0C and 0.05 to 1.0 bar feed pressure. The performance of gas selectivity is provided in the results. 2  Experimental 2.1 Membrane preparation and characterization                   International Journal of Scientific Engineering and Technology                                                               (ISSN : 2277-1581)                 Volume No.3 Issue No.9, pp : 1156-1159                                                                                                        1 Sep 2014 IJSET@2014 Page 1157  Porous alumina support of tubular configuration supplied by Ceramiques Techniques et Industrielles (CTI SA) France, consisted of (77% alumina + 23% TiO2) and an average pore diameter of 15 nm was employed for this experiment. The alumina support consisted of 7 and 10 mm internal and outer diameter respectively. It possesses a permeable length of 348 mm and 45% porosity (Fig. 1). A pressure 0.05 to 1.0 barg and temperatures of 25 0C (298 K) to 450 0C (723 K) were applied.    Figure 1: Porous tubular alumina support. The surface and cross-sectional morphologies of the support were analysed by scanning electron microscopy (SEM) (Zeiss EVO LS10) shown in Fig. 2. The gas species used consisted of single gases (CH4, CO2, H2, He, N2, Ar) and ternary gas mixture (CO2/CO/H2) (10/30/60) (BOC UK) with 99.999 (% v/v) purity.   Figure 2: SEM images of the support surface and cross-section. Gas species permeation was measured using the permeation test apparatus (Fig. 3) with the retentate valve fully opened. The tubular stainless steel membrane reactor is enclosed with a heating tape jacket, and the permeate flow tube was connected to the flowmeter to metre the gas flow rate. Gas permeance was obtained using equation (1) [13].                 (1) Where Q is the Permeance (mol m-2 s-1 Pa-1), q is the molar flow (mol/sec), A is the membrane area (m2), and ∆P is the pressure difference (Pa) across the membrane.  Gas selectivity was also considered in this experiment. Therefore, the membrane select a particular gas and reject others to pass through. The selectivity of the membrane was also obtained using equation (2) [13].  Sij = Qi/Qj                (2) Where Sij is the selectivity of i to j, Qi is the permeance of i (mol m-2 s-1 Pa-1), Qj is the permeance of j (mol m-2 s-1 Pa-1). TM5TM3TM1TM2TM4Valve 1Valve 2Valve 4Valve 3Pressure Gauge 3Pressure Gauge 4Digital Gas Flow MeterStainless Steel Membrane ReactorMembraneFeedRetentateExitPermeate to the Flow meter TM = ThermocoupleMain FeedPressure Gauge 1Pressure Gauge 2CO2/CO/H2H2CH4Figure 3: Schematic Diagram for the permeation Test. 3  Results and discussion 3.1 Effect of permeation pressure Figs. 4 and 5 shows the effect of feed pressure on the permeation rate of helium, carbon dioxide, hydrogen, methane and ternary mixture of CO2/CO/H2. At relatively low pressure, permeation is normally restricted to Knudsen diffusion mechanism [9]. However, as the pressure increased substantially, permeation of gases exceed Knudsen diffusion boundary and moved to viscous diffusion mechanism. Basically, permeation can be increased with proper material selection as stated under section 1 (introduction).                      International Journal of Scientific Engineering and Technology                                                               (ISSN : 2277-1581)                 Volume No.3 Issue No.9, pp : 1156-1159                                                                                                        1 Sep 2014 IJSET@2014 Page 1158   Figure 4: Helium permeate flux against feed pressure at 25 0C.  Figure 5: Gas flow rates against feed pressure at 450 0C. Based on the order of the kinetic diameter of the gases starting from the largest is Ar > N2 > CO2 > He (3.70 > 3.64 > 3.3 > 2.60) [9]. It can be seen in Fig. 6 that nitrogen having a kinetic diameter of (3.64 Å) is permeating at a rate that is higher than carbon dioxide with lower kinetic diameter. It can be seen from Fig. 6 that the membrane did not exhibit molecular sieving flow mechanism.  Figure 6: Permeance against gas kinetic diameter at 25 0C.   3.2 Effects of activation energy on ceramic supports. The permeation activation energy can be defined as shown in the following equation [7];                                            (3) Where Ea is the apparent activation energy (kJ/mol) which is composed of the required energy for diffusion in pores and heat of adsorption, R is the gas constant (8.314 J.K-1.mol-1) and T is the permeation temperature (K). Fig. 7 depicts the relationship between permeance and reciprocal temperature at 1.0 barg. The result reveals that both single and mixture gases with hydrogen decreased with permeation temperature. From Fig. 7, the activation value for hydrogen and CO2/CO/H2 mixture were calculated to be 1.0 and 0.42 kJ/mol, which almost corroborates with the literature [15] for permeation through silica-gamma alumina membrane.  Figure 7: Relationship between Permeance and Reciprocal Temperature at 1.0 barg. Fig. 8 shows the influence of permeation temperature on hydrogen selectivity (H2/CO2, H2/N2, H2/CH4 and H2/Ar) at feed pressure 0.8 barg. From the graph, a highest separation factor of 2.554 was obtained from H2/CO2 at 450 0C which implies that more hydrogen is recovered from CO2 than for H2/N2, H2/CH4 and H2/Ar.      Figure 8: Hydrogen separation factor as a function of temperature across porous alumina support at feed pressure 0.8 barg.                   International Journal of Scientific Engineering and Technology                                                               (ISSN : 2277-1581)                 Volume No.3 Issue No.9, pp : 1156-1159                                                                                                        1 Sep 2014 IJSET@2014 Page 1159  4 Conclusions Membrane technology for gas separation and purification particularly in remote locations such as offshore gas treatment is receiving substantial attention due to their uniqueness e.g. light weight. Membrane also possesses limited parts which make its processes less risky in operation. In this paper, Nanoporous tubular alumina membrane was used to examine the operational parameters such as feed flow rate, permeation pressure, permeation temperature and kinetic diameter at 25 0C to 450 0C and 0.05 to 1.0 barg feed pressure. Scanning electron microscopy (SEM) observation was carried out to examine the membrane performance and was found to be defect free. Hydrogen flow rate of 3.852 l/min was obtained at 450 0C and 1.0 barg. Also, separation factor of 2.554 was obtained for H2/CO2 at 450 0C and 0.8 barg. These membranes can be used preferably at higher temperature for separating hydrogen from other hydrocarbons.    Acknowledgement The authors gratefully acknowledge Petroleum Technology Development Fund (PTDF) Nigeria for funding this research, and School of Pharmacy & Life Sciences RGU Aberdeen for the SEM results. References i.  Lu, G.Q., Diniz da Costa, J.C., Duke, M., Giessler, S., Socolow, R., Williams, R.H., & Kreutz, T. Inorganic membranes for hydrogen production and purification: A critical review and perspective. Journal of Colloid and Interface Science, 314, pp. 589-603, 2007. ii.  Zhang, L., Park, I., Shqau, K., Winston Ho, W.S., & Verweij, H. Supported inorganic membranes. Promises & Challenges, 61, pp. 61-71, 2009. iii.  Ahmad, A.L., & Mustafa, N.N.N. Sol-gel synthesized of nanocomposite palladium-alumina ceramic membrane for H2 permeability: preparation and characterisation. International Journal of Hydrogen Energy, 32, pp. 2010-2021, 2007.   iv. Adom, P.K., Bekoe, W., Amuakwa-Mensah, F., Mensah, J.T., & Botchway, E. Carbon dioxide emissions, economic growth, industrial structure, and technical efficiency: Empirical evidence from Ghana, Senegal, and Morocco on the causal dynamics. Energy, 47, pp. 314-325, 2012. v.  Lee, H-J., Suda, H., & Haraya, K. Gas permeation properties in a composite mesoporous alumina ceramic membrane. Korean J. Chem. Eng. 22, pp. 721-728, 2005. vi.  Scholes, C.A., Kentish, S.E., & Stevens, G.W. Carbon dioxide separation through polymeric membrane systems for flue gas applications. Recent Patents on Chemical Engineering, 1, pp. 52-66, 2008. vii.  Kim, Y., Kusakabe, K., Morooka, S., & Yang, S. Preparation of microporous silica membranes for gas separation. Korean Journal of Chemical Engineering, 18, pp. 106-112, 2001. viii.  Ohwoka, A., Ogbuke, I., & Gobina, E. Performance of pure and mixed gas transport in reconfigured hybrid inorganic membranes part 2. Membrane Technology, pp. 7-9, 2012. ix.  Othman, M. R., Mukhtar, H., & Ahmad, A. L. Gas permeation characteristics across nano-Porous inorganic membranes. IIUM Engineering Journal, 5, pp. 17-33, 2004. x.  Jin, Z., Yiqun, F., & Nanping, X. Preparation and characterization of alumina membranes on capillary supports: Effects of film-coating on crack-free membrane preparation. Chinese Journal of Chemical Engineering, 18, pp. 377-383, 2010. xi.  Luebke, D. R., Pennline, H. W., and Myers, C. R. Surface selective membranes for carbon dioxide separation. Conference: 22nd Annual International Pittsburgh Coal Conference, Pittsburgh, PA, Sept. 12-15, 2005. xii.  Shah, S.H., Uemura, Y., Yusup, S., Kusakabe, K. High temperature separation of hydrogen from mixture of gases by using microporous silica membranes. Journal of Materials Science and Engineering, B1, pp. 90-96, 2011. xiii.  Kajama, M. N., Nwogu, N. C., and Gobina E. Gas Permeation Study Using Porous Ceramic Membranes. Energy and Environment Research journal, 4(3), pp. 43-49, 2014. xiv.  Budd, P. M., and McKeown, N. B. Highly permeable polymers for gas separation membranes. Polymer chemistry, 1, 63-68, 2010. xv. Yildirim, Y., and Hughes, R. An experimental study of CO2 separation using a silica based composite membrane, Trans IChemE., part B Vol. 81, pp. 257-261, 2003.        

Purification of gases using nanoporous inorganic membranes.

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Purification of gases using nanoporous inorganic membranes.

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