The removal of acid gases from crude natural gas by using novel supported liquid membranes

The removal of acid gases from crude natural gas by using novel supported liquid membranes

Desalination 200 (2006) 21–22 The removal of acid gases from crude natural gas by using novel supported liquid membranes Sang-Hak Lee, Beom-Sik Kim, ...

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Desalination 200 (2006) 21–22

The removal of acid gases from crude natural gas by using novel supported liquid membranes Sang-Hak Lee, Beom-Sik Kim, Eun-Woo Lee, You-In Park, Jung-Min Lee Chemical Process and Engineering Center, Korea Research Institute of Chemical Technology, P.O. Box 107, Yusong, Daejeon 305-606, Korea email: [email protected] Received 17 October 2005; accepted 1 March 2006

Abstract In this study, the novel supported liquid membranes were prepared by incorporating room-temperature ionic liquids into poly(vinylidene fluoride)(PVDF) matrix via phase separation technique. The new technique which enables to prepare the novel supported liquid membranes consisted mainly of two processes; the low temperature phase separation and the high temperature quenching process. The membranes had excellent stability under sever operating conditions. Also the permeation behaviors of acid gases (H2S, CO2) and CH4 through the membranes were investigated for verifying usefulness of the membranes to remove acid gases from crude natural gas. The novel supported liquid membranes exhibited very high H2S, CO2 permeability coefficients and H2S/CH4, CO2/ CH4 selectivities, respectively.

1. Introduction The objective of this study was to determine the potential usefulness of novel supported liquid membranes which were prepared via phase separation process between room-temperature ionic liquids and PVDF matrix to remove acid gases such as H2S and CO2 from crude natural gas. The supported liquid membranes which have been called the early stage facilitated transport membrane have some fatal disadvantages. First of all, *Corresponding author.

they degrade easily and have too large membrane thickness [1]. Those main disadvantagesinfluence the flux and selectivity of the membranes in a negative way. Therefore, to utilize the supported liquid membranes at large scale industry, there are urgent needs to achieve stabilizing technique and decrease the thickness of the membranes. In this study, the new concept of supported liquid membrane was developed, in which the nano-size liquid domains were dispersed uniformly in the solid polymer matrix by using phase separation technique to stabilize the supported liquid

Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.desal.2006.03.227

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membrane. Ionic liquids were chosen as the liquid phase in the supported liquid membrane. They are low melting point salts that are usually used as a reaction solvent for catalysis. Some of those exiting materials have an excellent affinity toward acid gases such as H2S and CO2. Also we tried to fabricate composite membrane to coat a thin supported liquid membrane film on the surface of a porous membrane. In order to verify the potential application and stability of novel membranes in upgrading process of crude natural gas, the permeations of H2S, CO2, CH4 pure and mixture gases through the membranes were carried out at various operating conditions by new type of permeation apparatus that can measure gas permeation transients. From the permeation transient measured, the permeability, diffusion and solubility coefficients of the respective gases were evaluated [2,3]. 2. Result and discussion The novel supported liquid membrane can be prepared through two specific processes. In the first step, we named this process as a low temperature phase separation step; the solvent was gradually evaporated under controlled condition to induce thermodynamically unstable state of the casting film. As a result, the ionic liquid domains were formed within the casting film and were getting bigger with decreasing solvent concentration in the casting film. The second step conducted at high temperature to quench the phase separation progress at appropriate domain size. Hence the domain size can be controlled through determining the phase separation conditions in terms of the rate and time of solvent evaporation, temperature and quenching condition. Fig. 1 shows a SEM photograph of the surface of a novel supported liquid membrane. We considered that the nano-size ionic liquid domains dispersed uniformly in PVDF phase but that was not clear. And then we are analyzing detail and precise morphology of the

Fig. 1. SEM photographs of the surface of the novel supported liquid membrane.

membranes using other analytical instruments such as TEM. The permeability coefficients of H2S and CO2 through the membrane were very high compared to that of CH4 which is one of the essential elements of natural gas. Hence the membranes exhibited very high H2S/CH4 and CO2/CH4 selectivities, ranging from 200 to 600 and from 50 to 100 depending on volume fraction of ionic liquid in the membranes, respectively. From the permeation results, the novel supported liquid membrane can be expected to be an attractive alternative to conventional process in the upgrading of crude natural gas. References [1]

[2]

[3]

A. Figoli, W.F.C. Sager and M.H.V. Mulder, Micro-encapsulated liquid membranes with facilitated transport properties: a new perspective in the preparation of oxygen-enriched air, J. Membr. Sci., 181 (2001) 97–110. C.K. Yeom, B.S. Kim and J.M. Lee, Precise on-line measurements of permeation transients through dense polymeric membranes using a new permeation apparatus, J. Membr. Sci., 161 (1999) 55–66. C.K. Yeom, S.H. Lee and J.M. Lee, Study of transport of pure and mixed CO2/N2 gases through polymeric membranes, J. Appl. Polym. Sci., 78 (2000) 179–189.