| Summary: | 碩士 === 元智大學 === 化學工程與材料科學學系 === 103 === CO2 is the main global warming potential (GWP) greenhouse gas with 50~60%. Direct influence on environmental and green-house effects has been an important issue for environmental protection all over the world. The direct synthesis of dimethyl carbonate (DMC) from CH3OH and CO2 has attracted considerable attention. DMC has been used as a green chemical and an alternative to corrosive and toxic reagent. Therefore, the direct synthesis of DMC is an effective way to solve environmental pollution. Due to its high mixing octane number (105), excellent compatibility with hydrocarbonates and high amount of O2 in the molecule (3 times than methyl-tert-butyl ether) can reduce the emission of offgas after adding it to gasoline/petroleum. DMC becomes an important additive of gasoline/fuel oil due to its many advantages nowadays. The main objectives of this study were divided into three parts: (I) To choose/establish the synthesis methods/selectivity of catalysts; (II) To characterize the properties/fine structure of catalysts (XRD, FE-SEM, HR-TEM, FT-IR, TGA, XPS, ASAP, NH3-TPD, 31P NMR, and XANES/EXAFS); (III) To calculate the conversion efficiencies, reaction mechanisms, and economic estimation of CO2 conversion catalysts.
Experimentally, Cu-Ni/AC and V-Cu-Ni/AC catalysts; Ce0.1Ti0.9O2, H3PW12O40/Ce0.1Ti0.9O2, and H3PW12O40/ZrO2 catalysts were synthesized by hydrothermal and sol-gel method, respectively. Furthermore, V2O5 and WO3 were added for the efficiencies of DMC conversions, selectivities, yields, and production technologies from methanol and carbon dioxide. Correlations between catalyst structures and DMC production efficiencies were also invetigated via the characterization of catalysts in this study. Particle size of Cu-Ni/AC, V-Cu-Ni/AC, H3PW12O40/Ce0.1Ti0.9O2, Ce0.1Ti0.9O2, and H3PW12O40/ZrO2 catalysts were 10~50 nm that were oberserved by FE-SEM micrographs. The particle sizes and aggregation effect increased and appeared after adding V2O5 and WO3. TGA curves showed one-step weight loss of Cu-Ni/AC and V-Cu-Ni/AC at 330 ~ 425oC, which is assigned to the decomposition of nitrate groups. BET surface area of synthesized catalysts decreased due to the addition of V2O5 and WO3. The differences of nitrogen adsorption-desorption isotherms between as-synthesized catalysts showed that the Cu-Ni/AC, V-Cu-Ni/AC, Ce0.1Ti0.9O2 or H3PW12O40/Ce0.1Ti0.9O2 are Type IV and H3PW12O40/ZrO2 was classified to Type V (mesoporous) adsorption isotherms.
Adsorption peaks of P-O (909 cm-1) and P-OH (923 cm-1) on the FT-IR spectra of Cu-Ni/AC, V-Cu-Ni/AC, H3PW12O40/Ce0.1Ti0.9O2, Ce0.1Ti0.9O2, and H3PW12O40/ZrO2 catalysts attributed to the addition of V2O5 and WO3. NH3-TPD profiles of Cu-Ni/AC, V-Cu-Ni/AC, H3PW12O40/Ce0.1Ti0.9O2, Ce0.1Ti0.9O2, and H3PW12O40/ZrO2 catalysts found that desorption temperatures (200 ~ 500oC) were classified to the mild-strong acid site (Acidity: Cu-Ni/AC> V-Cu-Ni/AC; H3PW12O40/ZrO2 > H3PW12O40/Ce0.1Ti0.9O2> Ce0.1Ti0.9O2). It can be seen that the conversion of CO2 into valuable chemicals and also reduce the greenhouse effect CO2 emission significantly with highly potential for industrial applications in the near future.
The methanol input rate (0.05 mL/min, high purity= 99.99%), pressure (50 bar), and GHSV (3,010 h-1) were fixed during the catalytic reactions. Various CO2/N2 ratios (1/4, 1/7, and 1/9) and temperatures (110, 170, 220oC) were adopted for DMC production. The optimized operation condition of V-Cu-Ni/AC was CO2/N2 = 1/7 and T/P = 170oC/50 bar. At this condition the methanol conversion, DMC selectivity, and yield were 8.14, 93.24, and 7.59%, respectively.
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