Study Of Support Affection On Catalysts In HDS Of Middle Distillate Oil

Middle distillate oil is an important component for vehicle diesel oil. Along with the lowering quality of crude oil, nature of middle distillate oil gradually deteriorates. Hence, it is necessary to modify the middle distillate oil for production of clean diesel with low sulfur and nitrogen content. Hydrotreatment process is a critical technology in production of clean oil currently, in which preparation of efficient hydrotreating catalyst is the key to improve hydrotreating technology.In this paper, on the basis of characteristics of middle distillate oils in different types, a variety of efficient hydrotreating catalyst preparation technologies were developed. The modification method of traditional catalyst support, new functional materials including TiO2 and various carbon materials, as catalyst supports were investigated. According to the influence of interactions between carrier and active components on the properties of catalysts, preparation processes of the catalysts were optimized to improve the dispersion of Mo component on the supports and the utilization rate of active component atom. Results showed that HDS activity and selectivity of the supported hydrotreating catalysts had been improved compared to that of traditional catalysts.The content and distribution of sulfur and nitrogen containing compounds, along with aromatics of different middle distillate oils, which were produced from different crude oils, were analyzed thoroughly. Results showed that characteristics of various middle distillates were affected by the nature of the crude oils and their processing passways. Hence, it is necessary to design catalysts and technology selectively for hydrotreating of these middle distillate oils on the basis of their properties.The reaction activity of hydrotreating reaction for different straight-run gas oils on the traditional SiO2-Al2O3 (ASA) supported NiMo catalysts were investigated. Results showed that for deep hydrodesulfurization of straight-run gas oils with high-sulfur and aromatic content, one way is to adjust hydrogenation process, such as multi-stage hydrodesulfurization, which is helpful to reduce the inhibitory effects of H2S gas on the active site of catalyst. Then, the desulfurization rate of some inert sulfur compounds (e.g. 4,6-DMDBT and 4,6,X-TMDBT) will be increased. The other way is to optimize the acidity of catalyst support, which will help to increase the active component reactivity.In order to optimize the acidity of traditional catalyst supports, a series of supports, ASA, with different surface and structure properties were prepared through different procedures of adding aluminum source and different SiO2 contents. Results showed that the microstructure and surface nature of support ASA2 are favorable for the dispersion of active components mostly. The active phase of MoS2 in the catalyst in which ASA2 was used as support has higher slab stacking and density, and uniform size. The evaluation of hydrodesulfurization activity of NiMo/ASAs for straight-run gas oil showed that NiMo/ASA2 has higher HDS activity compared with commercial NiMo/LX6 catalyst.Analysis of surface nature and active phase existing form of Ni(Co)Mo/TiO2 catalyst showed that the weak interactions between active components and TiO2 support promote reduction and sulfuration of the Mo species on the surface. MoS2 as active phase showed a unique way of stacking and depositing. Compared to Ni(Co)Mo/ACZ catalyst, Ni(Co)Mo/TiO2 catalyst showed higher HDS activity for LCO without severe cracking of hydrocarbon molecules at the reaction temperature range of 340℃-360℃, which indicated that Ni(Co)Mo/TiO2 catalyst has advantages of larger surface area, better thermal stability, as well as higher HDS activity and selectivity.The support effect of various carbon materials with different characteristics on hydrotreating catalysts was also investigated. By changing of gaseous carbon precursors, catalysts , and synthetic conditions, carbon nanofibers (CNFs) with high graphitization degree but with different morphology, such as tubular, platelet,and herringbone, were synthesized to act as supports of hydrotreating catalysts. HDS activity of NiMo/CNFs catalyst was improved by calcination after impregnation of active components. Straight-run gas oil was used to evaluate the HDS performance of NiMo/CNFs. The results showed that oxidized herringbone CNF with higher surface area and oxygen content is beneficial for dispersion of active metal components, which makes them easily reduced and sulfurized. Hence, the catalyst has the highest HDS activity.Four Acetylene carbon blacks (AB) with different sizes of structure units and oxygen contents were used as carriers to prepare NiMo/ABs hydrotreating catalyst. Nano-dispersion technology was employed to enhance the dispersion of active components during the preparation process. HDS performances for SRGO and LCO on NiMo/ABs were evaluated. The results showed that NiMo catalyst supported on OSAB with higher surface area and oxygen content gave the highest HDS activity and best inhibition against H2S, aromatics, etc. compared to conventional NiMo/Al2O3 catalysts.A series of activated carbons (ACs) with high surface area and mechanical strength synthesized with different carbon precursors and activation conditions were used as hydrotreating catalyst supports. The influences of active metal impregnation order and loading amount on the HDS performance of CoMo/ACs catalyst were investigated by treating of LCO. Results indicated that CoMo/BAC catalyst has better HDS activity for LCO with high aromatic and sulfur content than commercial CM/LX6 catalyst. Sulfur content of the product is lower than 10 ppm, which implies that goal of ultra deep desulfurization is achieved.