Preparation, Characterization, and CO2 Conversion Efficiencies of Ni-Ga and Cu-based Catalysts for Methanol and Dimethyl Ether Formations

• Main Authors: Chao-Lung Chiang, 江昭龍
• Other Authors: Kuen-Song Lin
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/mstzzr

博士 === 元智大學 === 化學工程與材料科學學系 === 106 === In this study, catalytic nickel-gallium (Ni5Ga3) and Cu-based catalysts (CuO-ZnO-Al2O3, CZA) have been prepared with co-precipitation methods. Supported nickel-gallium and Cu-based catalysts have also been obtained by ultrasonic-stirring with supports including silica gel (SiO2), protonated Y-type zeolite (HYZ) and protonated Beta-type zeolite (HBZ) in a slurry form. Crystal structures and morphologies of catalysts have been investigated and observed by X-ray diffraction (XRD) and field-emission scanning electronic microscopy (FE-SEM), confirming that nickel-gallium and Cu-based catalysts were Ni5Ga3 and CuO-ZnO-Al2O3 structure. FE-SEM microphotos have shown that supports could maintain the particle size being uniform in the durations of MeOH and DME formations. X-ray photon spectroscopy (XPS) spectra indicated that the effective component in Ni-Ga and Cu-based catalysts were respectively gallium and copper species. Oxidation state and bond distances of metal and its neighbour atoms were analyzed by X-ray absorption near-edge structure (XANES)/Extended X-ray absorption fine structure (EXAFS). It displayed that the oxidation states of gallium were Ga(0) and Ga(III) before and after MeOH formation, but nickel remained Ni(0). For Cu-based catalyst, the oxidation states of copper and zinc were Cu(II) and Zn(II), respectively. The inverse relationship of bond distances of metal (Ni5Ga3: Ni and Ga; CZA: Cu and Zn) and its neighbour atoms during the reaction were exhibited in EXAFS excluding Ni5Ga3/SiO2, CZA/HYZ, and CZA/HBZ. It demonstrated that structure, morphology, chemical composition, and fine structure of catalyst could be remained during MeOH/DME formation by dispersing nickel-gallium and Cu-based catalysts onto supports. In addition, the produced species sorts and their concentrations have been respectively analyzed using a dual fixed-bed catalyst-filled column reactor with an online FTIR (Fourier transformed infrared spectrum) and GC (gas chromatograph) spectra at the terminal to obtain the conversion of feedstock and the selectivity/yield of products. Online FTIR and GC spectra show that catalytic performances of catalysts at a constant pressure and variable temperatures (P=50 bar, T=150, 250, and 350 oC) of Ni-Ga and Cu-based catalysts have been enhanced after nickel-gallium and Cu-based catalyst dispersed onto supports. The highest MeOH yield could reach to 62.1 (150 oC), 84.7 (250 oC), and 82.5% (350 oC) by using Ni5Ga3/SiO2. The highest DME yield of CZA was 60.2%; it could be raised to 71.5% (CZA/HYZ) by loading onto HYZ, but lowered to 31.8% by supporting onto HBZ (CZA/HBZ). Rate equilibrium constants of MeOH formation were 0.150 (150oC), 0.473 (250 oC), and 0.477 h-1 (350 oC) that were much higher than theoretical values of 4.67×10-4 (150 oC), 2.22×10-5 (250 oC), and 2.47×10-6 (350 oC) h-1 by using Ni5Ga3 catalyst. Activation energies of MeOH formation using Ni5Ga3 and Ni5Ga3/SiO2 were 3.21 and 2.72 kJ/mol, respectively. In terms of DME formation, the highest rate equilibrium constant using CZA was 1.65×103 L/mol-h. It could be raised to 2.26×103 L/mol-h L/mol-h after supporting onto HYZ (CZA/HYZ), but lowered to 0.70×103 L/mol-h using CZA/HBZ. Activation energies of DME formation using CZA, CZA/HBZ, and CZA/HYZ were respectively 2.04, 2.26, and 1.16 kJ/mol. In addition, Gibbs energies of MeOH formation were 6.67 (150 oC), 3.26 (250 oC), and 3.83 (350 oC) kJ/mol that were much lower than theoretical values including 26.97 (150 oC), 46.59 (250 oC), and 66.87 (350oC) kJ/mol. The Gibbs energies of DME formation by using CZA, CZA/HBZ, and CZA/HYZ were respectively -40.07, -40.00, and -40.67 kJ/mol that were much lower than theoretical values of -12.64, -9.96, and -7.28 kJ/mol. Eventually, the cost assessment for a 10-TPD (ton per day) off-gas utility process of a petrochemical refinery plant showed that the daily income was USD$ 5,002,359/d with 3.49 years of payback.