As refineries are being forced to process crudes with larger amounts of sulfur and nitrogen, while at the same time environmental regulations are mandating lower levels of these heteroatoms in products, a need exists to synthesize catalysts that can do more efficient desulfurization and denitrogenation, particularly where existing units are limited in their pressure capability. In addition, more refractory feeds are desirable from a cost perspective. Since residual sulfur- and/or nitrogen-containing molecules can poison metal or acid sites on catalysts used downstream of the hydrotreating process (such as in hydrocrackers), improvements in the hydroprocessing feed pretreatment (e.g., to FCC and/or hydrocracking units) can have a large impact on how acid and/or metal catalysts operate. Alumina-supported Ni or Ni/Co-promoted molybdenum sulfides are the traditional catalysts used for hydrodenitrogenation (HDN) or hydrodesulfurization (HDS) at intermediate and relatively high pressures, and alumina-supported Co-promoted molybdenum sulfides are the traditional catalysts for HDS at relatively low pressures.
Hydroprocessing catalysts usually comprise one or more sulfided Group 6 metals with one or more Group 8 to 10 metals as promoters on a refractory support, such as alumina. Bulk, unsupported catalysts are also known. Hydroprocessing catalysts that are particularly suitable for hydrodesulfurization, as well as hydrodenitrogenation, generally comprise molybdenum or tungsten sulfide promoted with a metal such as cobalt, nickel, iron, or a combination thereof. These sulfided catalysts generally have a layered or platelet morphology.
The ability to modify the nanostructural morphology of hydroprocessing catalysts appears to provide a possible way to control their activity and selectivity. Thus one of the important thrusts in hydroprocessing catalyst research appears to be the realization that a key synthesis tool for modifying nanostructure involves the incorporation of carbon into the sulfide structure. For example, U.S. Pat. No. 4,528,089 teaches that the use of carbon-containing catalyst precursors gives more active catalysts than catalysts prepared from sulfide precursors without organic groups. Use of organic impregnation aids in preparing oxide catalyst precursors has also been studied for some time (Kotter, M.; Riekeft, L.; Weyland, F.; Studies in Surface Science and Catalysis (1983), 16 (Prep. Catal. 3), 521-30, and U.S. Pat. No. 3,975,302).
Improved modeling efforts have been underway worldwide to better understand the complex structure sensitivity of these metal sulfide catalysts. From a synthetic perspective, learning how to systematically control metal sulfide morphology remains a huge scientific and critically important technological challenge. For the layered structures of Group 6 (e.g., Mo and/or W) sulfides, this can involve considerations such as controlling lateral dimension, number of stacks in a crystallite, and properly siting the promoter atoms on the Group 6 sulfide stacks. A lower number of stacks, by itself, does generally indicate smaller sulfide crystallites, but it does not ensure higher catalyst activity nor that the promoter atoms (Co or Ni) are properly located on the sulfide stacks. It had been previously observed that substitution of a variety of inorganic components into a Group 6/Groups 8-10 (e.g., NiW, NiMoW, and/or NiW) oxide precursor did not significantly change the nanostructure of the resulting bulk sulfide catalysts. Although bulk NiMoW catalysts perform hydroprocessing reactions well at relatively high pressures, there is still an opportunity to develop improved catalysts.
In U.S. Pat. No. 7,591,942, it was demonstrated that sulfiding a bulk bimetallic Ni (or Co)/Mo (or W) phase containing a surfactant amine (located within the crystalline lattice of the oxide phase) with a backbone containing at least 10 carbon atoms gave a catalyst comprising stacked layers of MoS2 (or WS2) having a reduced number of stacks as compared to that obtained by sulfiding the carbon-free bulk oxide. A similar result was reported for bulk ternary Ni—Mo—W catalysts in U.S. Pat. No. 7,544,632. A lower number of stacks is important, since it may imply the presence of smaller crystals of Mo/W sulfides, which in turn can result in a larger surface area available for catalysis.
U.S. Published Patent Application No. 2007/0072765 discloses a method for preparing a catalyst composition, which method comprises: (a) impregnating an inorganic catalyst support with an aqueous solution containing (i) a salt of a Group VIII metal selected from Co and Ni, (ii) a salt of a Group VI metal selected from Mo and W, and (iii) an effective amount of an organic agent selected from amino alcohols and amino acids; (b) drying the impregnated catalyst support to remove substantially all water, thereby resulting in a metal-organic component on support catalyst precursor; (c) calcining the substantially dried catalyst precursor in the presence of an oxygen-containing atmosphere under conditions to oxidize at least 30%, but not all, of the organic agent and produce a partially oxidized catalyst precursor containing carbon; and (d) sulfiding the partially oxidized catalyst precursor in the presence of a sulfiding agent to produce a sulfided catalyst composition. Again the sulfide catalyst composition is found to have a lower number of stacks than equivalent compositions produced without organics present in the precursor.
Other publications include U.S. Pat. Nos. 6,989,348 and 6,280,610, European Patent Nos. 0601722, 1041133, and 0181035, and International Publication Nos. WO 96/41848, WO 95/31280, WO 00/41810, and WO 00/41811.
Although, reducing number of stacks can be important in increasing catalyst surface area, it is not, in itself, sufficient to maximize catalyst activity, since it does not necessarily ensure that the promoter atoms (e.g., Co, Ni) are properly located on the sulfide stacks.
Application Ser. No. 13/150,662, filed 1 Jun. 2011, to which reference is made for a description of the catalysts, their manufacture and use, discloses a class of catalysts having improved hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activity. These catalysts are made from a bulk mixed metal oxide catalyst precursor which, when sulfided, not only reduces the number of stacks of the sulfided product but also enhances the efficiency of the promoter metal, thereby resulting in a catalyst of improved hydroprocessing activity. These catalyst precursors and the catalysts made from them contain, in addition to the metal oxide component of Group 6 and Group 8 metals, an organic amide component formed in situ by the reaction of an amine with a carboxylic acid. The amine and the acid may be separately impregnated into the metal oxide component to form a catalyst precursor which can then be sulfided to form the active catalyst or, alternatively, the amine salt can be formed with the acid and then impregnated into the metal oxide component. Thermal treatment then follows to form the amide in situ and optionally to form additional unsaturation in the organic component.