Chihara, Kazuyuki

Omi, Naoki

Suzuki, Ryota

English

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 Diffusion of BTX in MSC5A in Supercritical CO2  Kazuyuki Chihara, Ryota Suzuki, Naoki Omi  Department of Industrial Chemistry, Meiji University 1-1-1 HIGASHI-MITA, TAMA-KU, KAWASAKI, 214-8571, JAPAN Tel & Fax: +81-44-934-7197, e-mail: chihara@isc.meiji.ac.jp  1.Introduction  Separation by adsorption in supercritical fluid might have some possibility. There, diffusion in micropore of adsorbent might be a controlling factor. In this study, chromatographic measurements were made for the adsorption of benzene, toluene and m-xylene on molecular sieving carbon (MSC) in supercritical fluid CO2. Supercritical chromatograph packed with MSC was used to detect pulse responses of organics. Adsorption equilibria and adsorption dynamics for organics were obtained by moment analysis of the response peaks. Dependences of apparent adsorption equilibrium constants, K*, and micropore diffusivity, D, on the amount adsorbed were examined.   2.Result and discussion Figure 1 shows adsorption isotherm of benzene at 313 K. According to Fig.1, the amount   adsorbed increased with increases of molarity of benzene, and reached to saturation. The amounts adsorbed became larger with decreases of column pressure. It was considered that the situation is competitive adsorption and amount adsorbed of benzene decreases as CO2 adsorption increase with increases of column pressure. Figure 2 shows dependency of adsorption equilibrium constants, K*, for benzene, toluene, and m-xylene on amount adsorbed of benzene at 20 MPa. This is reasonably decreasing. 0.00.10.20.30 20 40 60Concentration [mol/m3]Amount adsorbed [mol/kg] 15MPa20MPa25MPaadsorbate:benzenesolute:benzeneFigure 1. Adsorption isotherm : benzene at 313K Fig.3 shows dependency of micropore diffusivity, D/ā2exp(σ2), for benzene, toluene, and m-xylene on amount adsorbed of benzene at 20 MPa. The increase of D/ā2exp(σ2) for benzene could be reasonably explained by chemical potential driving force. However, as for dependency of D/ā2exp(σ2) of toluene and m-xylene on amount adsorbed of benzene, further discussion would be necessary.     The Open-Access Journal for the Basic Principles of Diffusion Theory, Experiment and Application© 2005, R. SuzukiDiffusion Fundamentals 3 (2005) 17.1 - 17.2 1 0.00010.0010.010.110 0.1 0.2 0.3Amount adsorbated of benzene [mol/kg]D/a2exp(σ2) [1/sec]0.00010.0010.010.110.0 0.1 0.2 0.3amount adsorbated of benzene [mol/kg]K* [m3/kg]benzenebenzenetoluenetolueneFigure 4 shows contribution of four mass transfer steps of benzene in pulse response (μ’2). The effect of micropore diffusion is dominant in all the conditions examined. 3.Conclusion Adsorption equilibrium and adsorption dynamics on MSC were evaluated for each organics in supercritical CO2 fluid mixed with adsorbate by chromatographic measurement. The dependencies of adsorption equilibrium constants, K*, and micropore diffusivity, D, of benzene, toluene and m-xylene, on molarity of benzene, toluene or m-xylene with each parameters of temperature or pressure were obtained, respectively. It was found that the values of K* and D for an organic substance depended on the amount adsorbed of other organics strongly.  References [1] Chihara, K., Kawazoe, K., Suzuki, M., AIChE J, 24, 237-246. (1978) [2] Chihara, K., Aoki, K., AIChE, Annual Meeting, (1993) [3] Chihara, K., Oomori, K., Kaneko, R., Takeuchi, Y., AIChE, Annual Meeting, (1995) Benzene0.11101001000100000 0.01 0.03 0.06adsorbate flow rate in thecarrier [ml/min]δi＋δa＋δf＋δd [sec]effect ofmicroporediffusioneffect ofmacroporediffusioneffect of fluid-to-particle masstransfereffect of axialdispersionTemperature:333 K Pressure:20 MPa Carrier:CO2 + Benzene Figure.4 Contribution of four mass transfer steps m-xylenetemperature:333Kpressure:20Mpam-xylenetemperature:333Kpressure:20MPaFigure 2.  Dependencies of K* on the amount adsorbed of benzene Figure 3. Dependencies of D/a2exp(σ2) onthe amount adsorbed of benzene Diffusion Fundamentals 3 (2005) 17.1 - 17.2 2

Diffusion of BTX in MSC5A in supercritical CO2

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Diffusion of BTX in MSC5A in supercritical CO2

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