FIELD OF THE INVENTION
This invention is directed to a high activity hydrotreating catalyst having low density and a method of preparing it. This invention is further concerned with processes employing this catalyst in the removal of sulfur, nitrogen, micro-carbon residue and organometallic contaminants from hydrocarbon feedstocks.
BACKGROUND OF THE INVENTION
Crude oil and heavier fractions and/or distillates derived from crude oils contain various contaminants, including sulfur, nitrogen, micro-carbon residue and organometallic compounds. Feedstocks have a wide range of contaminants level, depending on the origin of the crude oil, and the actual boiling range of the feedstock. These contaminants may poison catalysts used in the refining and upgrading of petroleum fractions, or be otherwise objectionable because combustion of fuels containing some of these contaminants releases noxious, corrosive and polluting byproduct gases. The removal of these contaminants is most commonly done by catalytic hydrotreating, where the contaminated feedstock is contacted with a supported catalyst in the presence of hydrogen, under a wide range of temperature, pressure and space velocity depending on the specifics of the refinery.
The profitability of a hydrotreating unit is highly dependent on the performance of the catalyst, mainly its activity and stability over time, and its cost. Refiners are facing increasingly stringent pressure to improve the profitability of their hydrotreating units, and have turned to catalyst suppliers to secure lower-cost and higher-performance hydrotreating catalysts. It has generally been very difficult to develop hydrotreating catalysts with improved performance at lower cost. Generally, better-performing catalysts tend to be more expensive, while lower-cost catalysts typically sacrifice some aspect of catalytic performance.
SUMMARY OF THE INVENTION
This invention is directed to the composition and preparation of a low density, high activity hydrotreating catalyst for deep removal of sulfur, nitrogen, micro-carbon residue and organometallic contaminants in petroleum feedstocks. High activity hydrotreating catalysts can operate effectively at high space velocities and relatively low temperatures. The invention is especially directed toward the preparation of a catalyst having excellent hydrotreating activity and stability for the deep removal of sulfur, nitrogen, micro-carbon residue and organometallic contaminants in feedstocks containing low to moderate levels of organometallic compounds. Alternately, the catalyst of this invention may be used in the back-end of hydrotreating units processing where heavier feedstocks containing larger levels of organometallic compounds would have been pre-hydrotreated in the front-end. Examples of feedstocks well suited for the present invention include total crude oil, atmospheric and vacuum residue, deasphalted oils, and atmospheric and vacuum gas oils.
The catalyst of the current invention provides overall better performance at a lower cost to the refiner. The catalyst cost savings are principally related to a lower catalyst density, which allows refiners to fill up reactor volume with a lower total weight of catalyst, therefore lowering the overall catalyst cost. The catalyst activity was optimized by the effective combination of pore structure and active metals, thereby resulting in a high activity, low density catalyst.
A preferred method of making the hydrotreating catalyst of this invention comprises: (a) mixing a refractory inorganic oxide carrier with at least one metal promoter from Group IVB; (b) adding an aqueous acidic solution comprising at least one component from Group VIII and at least one component from Group VIB and potentially additional acidic compounds; (c) shaping, drying and calcining the catalyst particles; and (d) post-impregnating the catalyst with additional hydrogenation components including at least one component from Group VIII metal and at least one component from Group VIB metal, drying and calcining and the use of the catalyst so prepared for deep removal of sulfur, nitrogen, micro-carbon residue and organometallic contaminants in hydrotreating service. This catalyst is most effective at the back end of hydrotreating units where exposure to organometallic contaminants is minimal, or in applications where feedstocks with lower concentration of organometallic contaminants are processed. The Group IVB metal promotes hydrodesulfurization.
DETAILED DESCRIPTION OF THE INVENTION
A method is described for making a catalyst wherein an aqueous acidic solution is made with at least one component from Group VIII and at least one component from Group VIB. The preferred Group VIII metal compounds used in this method include nickel and cobalt compounds. The preferred Group VIB metal compounds which may be used include molybdenum and tungsten. This aqueous acidic solution is added to a refractory inorganic oxide carrier. The carrier may have been previously mixed with at least one metal promoter from Group IVB. The Group IVB metal promoters which could be used in this method include titanium, zirconium and hafnium, with titanium compounds preferred. Alumina is the preferred inorganic oxide carrier used in the present invention, although alumina may be combined with other refractory support materials such as silica or magnesia. The mixture could be further treated by a suitable acid, including acetic acid, sulfuric acid, oxalic acid, hydrochloric acid, formic acid, nitric acid, phosphoric acid and citric acid. The catalyst particles are shaped, dried and calcined in air at temperatures from about 750° F. to 1500° F. for 30 to 180 minutes. The catalyst may be further impregnated using standard impregnating procedures with hydrogenation components from Group VIII and Group VIB. The broad ranges and preferred ranges of Group IVB metal promoter and Group VIII and Group VIB hydrogenation metal components are shown below:
| ||TABLE 1 |
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| || |
| ||Broad Range ||Preferred Range |
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| ||Group IVB Metal Promoter ||0.3-10% ||3-6% |
| ||Group VIB Metal Component || 5-25% ||10-20% |
| ||Group VIII Metal Component ||1-8% ||2-4% |
| || |
The catalyst of this invention has a pore volume falling within a range of 0.40-0.70 cc/g, a pore size distribution peak falling within a range of 50-110 angstroms, and less than 5% macropores, defined as pores larger than 1000 angstroms. The pore size distribution is relatively narrow with at least 40% of the pore volume contained in pores with diameters falling within 20 angstroms of the peak.
Preferably, the catalyst of this invention has a pore volume falling within a range of 0.450.55 cc/g, a pore size distribution peak falling within a range of 55-90 angstrom, and less than 3.5% macropores. The pore size distribution is relatively narrow with at least 45% of the pore volume contained in pores with diameters falling within 20 angstroms of the peak, on either side.
Pore volume as described here is the volume of a liquid which is adsorbed into the pore structure of the sample at saturation vapor pressure, assuming that the adsorbed liquid has the same density as the bulk density of the liquid. The liquid used for this analysis was liquid nitrogen. The procedure for measuring pore volumes by nitrogen physisorption is further laid out in D. H. Everett and F. S. Stone, Proceedings of the Tenth Symposium of the Colstom Research Society, Bristol, England: Academic Press, March 1958, pp. 109-110.
Feeds and Conditions
The catalyst of the present invention can be used for hydrotreating feedstocks, including crude oils, unprocessed and partially hydrodemetallized vacuum and atmospheric residua, deasphalted oils, and vacuum and atmospheric gas oils. The present invention is particularly well suited for deep removal of sulfur, nitrogen, micro-carbon residue, and organometallic compounds contained in these feedstocks.
These feedstocks can be passed over the catalyst of the present invention at a liquid hourly space velocity in a reactor of about 0.05 to about 5.0, preferably from about 0.1 to about 3.0, while maintaining the reaction zone at a temperature of from 500° F. to about 850° F., preferably from about 550° F. to about 800° F., while under a total pressure of about 450 to about 3500 pounds per square inch gauge, preferably from about 600 to about 2800 pounds per square inch gauge, and a hydrogen partial pressure of from about 350 to about 3200 pounds per square inch gauge, preferably from about 500 to about 2500 pounds per square inch gauge.