| Summary: | 碩士 === 國立高雄科技大學 === 化學工程與材料工程系 === 107 === Magnesium hydroxide (Mg(OH)2) one-dimensional (1D) nanotubes and nanorods solid adsorbent (M), was prepared by solvent method, and after calcination, magnesium oxide (MgO) was formed. Moreover, MgO is used as the adsorbent substrate (G), and further modify by aluminum and molten salt to enhance its adsorption ability of carbon dioxide (CO2). These samples are MgAl2O4¬ (GAl), which modified by aluminum salts; G-ms, which modified by molten salts; and GAl-ms, which is MgAl2O4 further modified by molten salts. These samples using magnesium oxide as a substrate were identified by X-ray diffractometer and still retain MgO crystal phase (JCPDS#45-0946). The cyclic CO2 adsorption test was measured by thermogravimetric analyzer in the interval of 25~350℃ under atmospheric pressure. The maximum adsorption capacity of CO2 is 3.48 wt% of M and 3.72 wt% of G-ms, respectively. From the trend of CO2 adsorption and desorption cycle diagram, the adsorption amount of G-ms gradually increases in 10 adsorption and desorption cycles, different from the gradual decline trend of other adsorbents.
The adsorption enthalpy (Qst) of the Mg(OH)2 was carried out at a temperature of 25℃, 35℃, and 45℃ under atmospheric pressure by volumetric adsorption analyzer. The Qst was negative throughout the whole process, indicating that this adsorption process was spontaneous. We could find the adsorption enthalpy changed from -137.85 kJ/mol to -93.36 kJ/mol. The characteristic of Qst changing with the amount of adsorption, which implied that the adsorption system is heterogeneous.
The CO2 adsorption mechanism of the adsorbent is to use the -OH group on the surface of the adsorbent to react with the CO2. The Qst of steady state is near -115 kJ/mol, and the -OH starts to chemically bonded with CO2. After that, the Qst value was increased to -91.92 kJ/mol, which proved that Mg(OH)2 not only has physical adsorption but also chemical adsorption behavior.
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