Steam Catalytic Reactions on Vacuum Residue for Producing Petroleum Fuels

Abstract

ABSTRACT Humans are facing the biggest energy challenges, transportation fuels especially. In this study, the effect factors of catalytic characters on the catalytic upgrading of petroleum residues in supercritical water, researched to produce more petroleum transportation fuels, were deeply investigated. In the first study, NiK/yCe x Zr 1-x O 2 -macroporous Al 2 O 3 catalysts (y = 0, 10, 20, and 30; x = 0.73-0.92) were synthesized by dispersing different amounts of Ce x Zr 1-x O 2 phase onto macroporous -Al 2 O 3 as supports, and then subsequently impregnating Ni and K into the supports, which possessed advantageous properties, such as a high surface area, ordered macropores and high oxygen storage capacity. Moreover, the introduction of Ni and K metals into these supports created more oxygen vacancies in them. We applied these catalysts to the cracking of vacuum residue with steam. It was found that the variation of the liquid yield with the amount of Ce x Zr 1-x O 2 phase showed a volcano pattern. The macropores in the supports played an important role in enhancing the diffusion of large molecules to the active sites, while the high oxygen storage capacity over the Ce x Zr 1-x O 2 phase improved the oxidative cracking rate, thereby increasing the lighter oil fraction from the vacuum residue. In the second study, a NiK/CeO 2 catalyst was employed to investigate the interaction between Ni metal and CeO 2 support and its effect on oxidative cracking of vacuum residue. In the reaction results, a large amount of light oils, including naphtha, diesel and VGO, was produced through oxidative cracking over CeO 2 , and the quality of the liquid products was significantly improved by hydrogenation. The interaction between Ni metal and CeO 2 support induced the formation of a Ce y Ni 1-y O 2- solid solution and increased the number of oxygen vacancies, thus enhancing the oxidative cracking of vacuum residue. Further, the addition of NiK into the supports provided Ni metallic sites

for hydrogenation, producing more liquid products with a high H/C ratio. As a result, NiK/CeO 2 catalyst showed a higher diesel yield (22.87%) than that without catalyst (9.14%). In the third study, NiK/ceria-zirconia (CZ) and NiK/ceria-zirconia-alumina (CZ-A) catalysts were investigated in order to further understand the roles of mixed-oxide supports in the steam catalytic cracking of vacuum residue (VR). Compared to thermal cracking, higher conversions and liquid yields were achieved over the catalysts. Steam decomposition occurring over the CZ and ZrO 2 phases provided an alternative hydrogen and oxygen sources for hydrogenation and oxidative cracking, respectively. The introduction of Ni into the CZ support induced the formation of Ce x (Zr-Ni) 1-x O 2-δ solid solution and the isolation of the ZrO 2 phase via a strong metal-support interaction, resulting in greater oxygen vacancy in the bulk structure. In contrast, the strong interaction of CZ and Ni phases with Al 2 O 3 induced higher dispersions of CZ and Ni phases in the NiK/CZ-A catalyst, which resulted in a greater density of oxygen vacancies on the surface and higher CeO 2 reducibility. As a result, the quality of the liquid products and naphtha yields were significantly improved by hydrogenation over the nickel metallic sites and oxidative cracking through the metal- support interaction. In the fourth study, steam oxidative cracking route of 1-methylnaphthalene were investigated through the combination of oxidation and hydrogenation over nickel- containing mixed oxide catalysts. Depending on the used supports, several types of active sites for oxidation, hydrogenation, and steam decomposition were generated by various metal–support and support–support interactions. The steam-reforming routes were dominant without nickel, resulting in high gas selectivity due to a full-cracking process. With nickel, steam oxidative cracking routes were strongly enhanced by a synergistic combination between hydrogenation occurring on the Ni metallic sites and oxidation over

mobile lattice oxygens in a Ce x Zr 1-x O 2 solid solution, resulting to the higher selectivity of liquid products than that of gas products. Among the prepared catalysts, an optimal interaction between Ni and Ceria-Zirconia-Alumina mixed oxide support caused not only an increase of oxygen vacancies in solid solutions, but also the formation of smaller Ni metallic nanoparticles, resulting in reinforcement of steam oxidative cracking of 1-methyl naphthalene. Finally, the hierarchically macro-mesoporous grainy aluminas containing the novel properties were prepared for being a support in xK/Ni-Al 2 O 3 catalyst which are applied to study 1-methyl naphthalene steam reforming. The impact of a hierarchically ordered macro- mesoporous structure on steam reforming of 1-methyl naphthalene at the low temperature (600 o C) was investigated over xK/Ni-MeAl (mesoporous alumina-supported nickel & potassium) and xK/Ni-MaAl (macro-mesoporous alumina-supported nickel & potassium) catalysts in a fixed-bed reactor system. The hierarchical ordered macro-mesoporous structure in Al 2 O 3 support played an important role in enhancing the reactant diffusion to the active sites promoted both the catalytic cracking and steam reforming, resulting in high gas yields and 1-methyl naphthalene conversion. The introduction of potassium on Ni- MeAl and Ni-MaAl supports created more nickel active sites enhancing significantly the steam reforming rate. In addition, using macro-mesoporous alumina as support also increased the nickel site dispersion, leading to enrichment of potassium location on alumina, which makes the catalytic deactivation being slow down.