Effects of Catalyst Properties on Hydrodesulfurization Activity for Sulfur Removal from Fluid Catalytic Cracking Decant Oils

Abstract

Removing sulfur from larger ring systems in fluid catalytic cracking decant oils used as needle coke feedstock is the most effective way of reducing the needle coke sulfur content. The large sulfur compounds found in decant oil are incorporated into coke in larger proportions than smaller sulfur compounds upon carbonization. The desirable outcome of decant oil hydrodesulfurization is, therefore, removing sulfur selectively from large polyaromatic ring systems with minimum hydrogen consumption. This study investigates the effects of catalyst properties on hydrodesulfurization activity to remove sulfur from decant oils. Two decant oils (DO-HS and DO-LS) representing a high (2.5 wt %) and low (0.9 wt %) sulfur content decant oil and their vacuum distillation fractions were hydrotreated in a fixed-bed flow reactor. Four catalysts (with varying average pore sizes, promoter atoms, and supports) were prepared with sequential incipient wetness impregnation to evaluate their activities for hydrodesulfurization and hydrogenation of decant oils. An increase in the average pore diameter from 7 to 14 nm for CoMo catalysts supported on Al2O3 proved capable of meeting the desired requirements for hydrodesulfurization of decant oil used in needle coke production. Of the four catalysts evaluated, CoMo supported on TiO2 outperformed the other three catalysts supported on Al2O3; however, focus was placed on the Al2O3-supported catalysts as a result of the superior mechanical integrity and proven longevity of Al2O3 in hydrodesulfurization reactors. It was shown by proton nuclear magnetic resonance that promoting Mo supported on Al2O3 with Ni instead of Co results in equivalent hydrogenation activity and decreased desulfurization. Upon carbonization of treated oils, the sulfur content of the resulting coke increased from the feed treated with a CoMo catalyst supported on Al2O3 with an average pore diameter of 7 nm, whereas coke produced from feeds treated over the CoMo catalyst supported on Al2O3 with an average pore diameter of 14 nm had a lower sulfur content compared to the feed. Therefore, with a proper catalyst design, sulfur in decant oil that tends to be retained in the coke can selectively be removed. Thus, hydrodesulfurization can favor the direct desulfurization route over the hydrogenation route by employing high reaction temperatures and modest hydrogen pressures.

Carbon Nanostructure Curvature Induced from the Rapid Release of Sulfur upon Laser Heating

“…As such, sulfur imparts a relatively unobservable impact on the nanostructure, but rather acts to cause micro-cracks upon rapid evolution in the form of H 2 S and CS 2 upon subsequent graphitization heat treatment. The micro-cracks result in an observed volume increase, and therefore, the process has been termed puffing [28][29][30]. Puffing has been evaluated on the micro-and macro-length scales.…”

“…The structural defects imparted on the carbon from oxygen removal set the stage for the trajectory of lamellae growth upon additional heat treatment, whereas in the case of sulfur, the lamellae are significantly annealed with trajectory set after heat treatment at 1000 • C. As such, sulfur imparts a relatively unobservable impact on the nanostructure, but rather, acts to cause micro-cracks upon release upon subsequent graphitization heat treatment, in the forms of H 2 S and CS 2 . The micro-cracks result in an observed volume increase, and therefore, the process has been termed puffing [28][29][30]. This is primarily a problem for the needle coke industry as needle coke is often used as the primary filler in the production of graphite electrodes and micro-cracks, acting to reduce the electrodes' desired properties [28][29][30].…”

“…The micro-cracks result in an observed volume increase, and therefore, the process has been termed puffing [28][29][30]. This is primarily a problem for the needle coke industry as needle coke is often used as the primary filler in the production of graphite electrodes and micro-cracks, acting to reduce the electrodes' desired properties [28][29][30]. The added thermal stability of sulfur in carbon versus oxygen is understood by the enthalpy of formation of the leaving species.…”

Ionothermal Synthesis of Metal Oxide-Based Nanocatalysts and Their Application towards the Oxidative Desulfurization of Dibenzothiophene

“…[4]. Typically, the sulfur contents in fuel is removed using the conventional hydrodesulfurization (HDS) technique, which efficiently removes various sulfur compounds including thiols, sulfides, and disulfides [5,6]. However, several aromatic sulfur compounds, like benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyl dibenzothiophene (4,6-DMDBT), which are usually present in large proportion in diesel are difficult to remove by HDS due to their steric hindrance [7,8].…”

Spinnable Mesophase Pitch Prepared via Co-carbonization of Fluid Catalytic Cracking Decant Oil and Synthetic Naphthalene Pitch

“…As a result, such mesophase pitches usually exhibit high softening point and low solubility. In order to avoid these problems, several additional steps such as hydrotreatment [7][8], extensive removal of volatile components [9][10] and extraction of non-fusible components [11][12] have been used to prepare high quality mesophase pitch. However, this inevitably decreases the yield and raises the process complexity and cost of the mesophase pitch.…”