Column Adsorption of the Mixed Organic-Solvent by Y Type Zeolite

Abstract

Fixed-bed adsorption experiments of laboratory-scale were carried out to remove organic solvent vapors by Y-type zeolite adsorbent. Some of binary adsorption equilibria of azeotropic mixture-HSZ systems showed one or two azeotropic points. Breakthrough curve could be simulated using the Stop & Go method for these systems. INTRODUCTION Discharge of organic substances into air has been strongly prohibited since some decades ago, to preserve comfortable natural environment. Though hydrocarbons, alcohols and chlorinated hydrocarbons had been used as the degreasing agent in industries, these solvents may also affect to our environment, and it is necessary to remove them from air as much as possible. This study was performed aiming at presenting useful data for the design of adsorption processes, especially the removal of the solvent vapors, as above, from air by adsorption. The solvents used were trichloroethylene (TCE), iso-propanol (IPA) and ethanol (EtOH). EXPERIMENTAL Adsorbent Y-type of high silica zeolite (HSZ) (from TOSOH Corp.,Ltd JAPAN.) were used. SiO2/Al2O3 ratio was 460. Experimental Procedure Solvents used were iso-propanol (IPA), trichloroethylene (TCE) and ethanol (EtOH). Adsorbents were packed in a glass column of 0.10m length and 0.0156m i.d. Experimental conditions were as follows: linear flow rate; 0.2 m/s, influent concentration; in the range of 0.004~0.2 mol/m3, and temperature; 298 K. (Figure 1) RESULT AND DISCUSSION Breakthrough Curves Figure 2 and Figure 3 show several types of breakthrough curves obtained for IPA-TCE -Y-type zeolite system. There, the range of the total concentration of IPA and TCE shows 2000~4000ppm and 5000~5500ppm, respectively. For this system, reversal of the order of break (turn over) occurred twice at concentrations of 0.25 and 0.75 mole fractions of IPA. When the mole fractions were 0.25 and 0.75, the mixture of two components a. Blower d. Flow control-valve b. Silica gel bed e. Thermometer c. Mass flow controller f, f'. Solvent vaporizer h. Constant temperature bath i. Sampler j. Gas chromatograph g. Glass column (adsorber) a d f i air b c h G.C. (FID) j g e f' k やはり天才 Figure 1. Schematic diagram of experimental apparatus for adsorption behaved as if it was a single component system as shown in Figure 2 (B) and (D). For other azeotropic mixture systems, the turnover occurred only once. The breakthrough curves for other systems always showed so-called constant pattern behaviour for the whole concentration range [1]. Figure 4 show several types of breakthrough curves obtained for EtOH-TCE -Y-type zeolite system. The range of the total concentration of EtOH and TCE shows 5500~6500ppm. For this system, reversal of the order of break (turn over) occurred once at concentrations of about 0.25 mole fractions of EtOH. When the mole fractions were 0.25 , the mixture of two components behaved as if it was a single component system as shown in Figure 5 (B). Adsorption Equilibria Binary adsorption equilibria for the system of IPA-TCE of several concentrations are shown in Figure 5 in form of X-Y diagram (X and Y are the mole fractions of feed concentration and the amount adsorbed at equilibrium, respectively). For this system, it is reported that the azeotropic point of vapor-liquid equilibrium is only one, but two azeotropic points were observed in the adsorption equilibrium. When the saturation vapor pressures of each component were almost the same, appearance of two azeotropic points were reported for vapor-liquid equilibrium. It is thought, therefore, that the phenomenon occurred in adsorption equilibrium for these systems can be ascribed to the fact that the saturation vapor pressure and the boiling points of each component were almost the same. The same thing can be said about the system of EtOH and TCE, which are shown in Figure 6. For example, in the case of Figure 5, (B) and (D), and in the case of Figure 6, (B) are azeotropic points. Figure 2. Several types of breakthrough curves observed for IPA-TCEsystem (2000~4000ppm) 0.00 0.25 0.50 0.75 1.00 mole fraction (C0-IPA/C0-total) 0 0.5 1 1.5 0 50 100 150 Tim e Elapsed [m in] C / C o [ ] 0 0.5 1 1.5 0 50 100 150 Tim e Elapsed [m in] C / C o [ ]