A method of presulfiding a hydrotreating hydrocracking or tail gas treating catalyst

Abstract: An improved method of presulfiding a hydrotreating or hydrocracking catalyst which minimizes sulfur stripping upon start-up of a hydrotreating or hydrocracking reactor utilizing such a catalyst. The method comprises the steps of contacting a hydrotreating or hydrocracking catalyst with elemental sulfur at a temperature below the melting point of sulfur, thereby forming a sulfur-catalyst mixture, and heating the sulfur-catalyst mixture to a temperature above the melting point of sulfur. Preferably, the sulfur-catalyst mixture is first mixed with at least one member selected from the group consisting of high boiling oils and hydrocarbon solvents to form a prewet mixture prior to heating at a temperature above the melting point of sulfur. Tail gas treating catalysts are also presulfided by these methods.

Description: This invention relates to a method of presulfiding a supported metal oxide catalyst for use in hydrotreating and/or hydrocracking hydrocarbon feed stocks, This invention further relates to a method of presulfiding a tail gas catalyst for use in treating effluent gas streams. A hydrotreating catalyst may be defined as any catalyst composition which may be employed to catalyze the hydrogenation of hydrocarbon feedstocks. A hydrocracking catalyst may be defined as any catalyst composition which may be employed to catalyze the addition of hydrogen to massive and complex petroleum derived molecules and the cracking of the molecules to attain smaller molecules. A tail gas catalyst may be defined as any catalyst which may be employed to catalyze the conversion of hazardous effluent gas streams to less harmful products. Such catalyst compositions are well known to those of ordinary skill in the art and several are commercially available. Metal oxide catalysts which come within these definitions include cobalt-molybdenum, nickel-tungsten, and nickel-molybdenum. Also, transition element catalysts may be employed for these purposes. Typical supports for hydrotreating metal oxide catalysts include alumina, silica and silica-alumina supports. In the past, ex-situ methods of presulfiding supported metal oxide catalysts have suffered from excessive stripping of sulfur upon start-up of a hydrotreating or hydrocracking reactor. As a result of sulfur stripping, an increase in the product weight percent of sulfur is observed along with a decrease in catalyst activity. The use of high boiling oils, hydrocarbon solvents and mixtures thereof to aid the incorporation of sulfur into a catalyst is not believed to have been previously taught by prior presulfiding methods. Herein, a high boiling oil is defined as an oil whose initial boiling point is greater than 200°C (400°F). Hydrotreating and hydrocracking catalysts are typically presulfided by incorporating sulfur compounds into the porous catalyst prior to hydrotreating or hydrocracking a hydrocarbon feedstock. For example, U.S. Patent No. 4,530,917 to Berrebi discloses a method of presulfiding a hydrotreating catalyst with organic polysulfides. U.S. Patent No. 4,177,136 to Herrington et al discloses a method of catalyst presulfiding wherein a catalyst is treated with elemental sulfur. Hydrogen is then used as a reducing agent to convert the elemental sulfur to H 2 S in situ. Problems arise, however, upon start-up of a reactor due to excessive sulfur stripping. U.S. Patent No. 4,089,930 to Kittrell et al discloses the pretreatment of a catalyst with elemental sulfur in the presence of hydrogen. EP-A-0359356 discloses a method of presulfiding a hydrotreating catalyst by contacting it with elemental sulfur at a temperature below the melting point of sulfur and then heath the resulting mixture to a temperature between the melting point of sulfur and 199°C. It is an object of the present invention to presulfide a hydrotreating, hydrocracking or tail gas treating catalyst in a manner which minimizes sulfur stripping upon start-up of a hydrotreating, hydrocracking or tail gas treating reactor. It is yet a further object of the present invention to activate spent catalyst in such a manner as to minimize the amount of sulfur required for activation. It is yet a further object of the present invention to prepare a safe, stable, presulfided hydrotreating, hydrocracking or tail gas treating catalyst. The present invention relates to an improved method of presulfiding a hydrotreating, hydrocracking or tail gas treating catalyst which minimizes sulfur stripping upon start-up of a hydrotreating, hydrocracking or tail gas treating reactor and improves catalyst activity. The catalyst is preferably presulfided by one of two methods. Thus, in accordance with the present invention there is provided a method of presulfiding a hydrotreating, hydrocracking or tail gas treating metal oxide catalyst, comprising: (a) contacting a hydrotreating, hydrocracking or tail gas treating metal oxide catalyst with powdered elemental sulfur heated at a temperature below the melting point of sulfur, said powdered elemental sulfur optionally being suspended in at least one liquid high boiling oil or hydrocarbon solvent, in a manner and for a time period long enough such that said elemental sulfur is substantially incorporated into the pores of said catalyst to form a mixture; (b) when the powdered elemental sulfur is not in the form of a suspension, it is contacted with the catalyst in such a way that the sulfur sublimes to be substantially incorporated into the pores of said catalyst to form said mixture, and the mixture is thereafter either: (i) heated in the presence of hydrogen to an activation temperature in the range of 121-343°C (250-650°F) for a time period long enough for substantially all of the sulfur incorporated into the catalyst pores to react to produce metal sulfides and hydrogen sulfides and to achieve a final sulfur level sufficient to sulfide active and promoter metals in said catalyst, or (ii) mixed with a prewetting agent comprising at least one liquid hydrocarbon solvent or high boiling oil, thereby producing a prewet mixture, for a time period long enough such that thereafter in the presence of hydrogen and at an activation temperature in the range of 121-343°C (250-650°F) substantially all of the sulfur incorporated into the catalyst pores is reacted to produce metal sulfides and hydrogen sulfides and achieve a final sulfur level sufficient to sulfide active and promoter metals in said catalyst; and (c) when the powdered elemental sulfur is in the form of a suspension, said manner and time period are such that thereafter in the presence of hydrogen and at an activation temperature in the range of 121-343°C (250-650°F) substantially all of the sulfur incorporated into the catalyst pores is reacted to produce metal sulfides and hydrogen sulfides and achieve a final sulfur level sufficient to sulfide active and promoter metals in said catalyst; characterised in that the amount of sulphur contacted with the catalyst is in the range of 1½% by weight of the total catalyst less than or greater than a stoichiometric amount, said stoichiometric amount being based upon the metal content of the catalyst. Preferred embodiments and features of the invention are set out in sub-claims 2-13. Several techniques may be employed to contact sulfur with catalyst particles. The use of solid sulfur eliminates many hazards such as flammability and toxicity, which are encountered when using H 2 S, liquid sulfides, polysulfides and/or mercaptans. Powdered sulfur may be physically mixed with the catalyst particles prior to loading the catalyst particles in a reactor. The elemental sulfur and the catalyst particles may be physically mixed together at a temperature below the melting point of sulfur, preferably in the range of from 82-99°C (180°F to 210°F). In this temperature range, the elemental sulfur sublimes and is incorporated into the pores of the catalyst particles where, upon cooling, it condenses. By using the sublimed form of sulfur a uniform coating on the surfaces of the catalyst pores is achieved. The instant invention provides a presulfided catalyst having a higher efficiency of hydrodesulfurization than catalysts presulfided with molten sulfur. Incorporation deep into the catalyst pores is also more easily achieved with sublimed sulfur than with molten sulfur. The sulfur-catalyst mixture is then heated to a temperature above the melting point of sulfur preferably in the range of from 121-199°C (250°F to 390°F). In the presence of hydrogen, activation of the catalyst takes place. That is, the metal oxides react with substantially all of the sulfur incorporated into the catalyst pores, thus producing H 2 S and metal sulfides. Mixing times for the powdered elemental sulfur and the catalyst can be minimized by heating the mixture at higher temperatures, within specified limitations, due to the increased vapor pressure of the sulfur. Typically, the amount of sulfur employed is stoichiometric relative to the catalytic metals content of the catalyst charged. Mixing times of the powdered sulfur and the catalyst particles may be minimized due to the reduced stoichiometric amount of sulfur. While the use of greater amounts of sulfur does result in more sulfur being incorporated into the pores of the catalyst, the amount of sulfur stripping during reactor start-up is much greater than that of a stoichiometric charge depending on the composition of the catalyst. Amounts slightly less than stoichiometric also provide significant advantages over nonpresulfided catalysts. Also, when a stoichiometric amount of sulfur is employed, a minimum stripping effect is observed upon reactor start-up. Stoichiometric amounts of sulfur used for the presulfiding are calculated based on the metal content of the catalyst used. For example, a catalyst containing cobalt would require 8 molecules of sulfur to react with 9 molecules of cobalt to form a preferred cobalt sulfide of the formula Co 9 S 8 . By multiplying the molecular weight of cobalt by 9 and dividing into 8 times the molecular weight of sulfur, a ratio of 0.48 is calculated which, when multiplied by the weight percentage of cobalt in the catalyst, provides the optimum weight % of sulfur necessary to react with the available cobalt. Likewise, the amount of sulfur required to convert molybdenum in a catalyst to MoS 2 is calculated by multiplying the weight % of molybdenum by 0.67. For the conversion of nickel to Ni 3 S 2 , the weight % of nickel is multiplied by 0.36. For the conversion of tungsten to WS 2 , the weight percentage of tungsten is multiplied by 0.35. For a catalyst containing 2.4% Co and 9.8% Mo the stoichiometric amount of sulfur required is calculated as: 2.4% x 0.48 + 9.8% x 0.67 = 7.7% or 7.7kg of sulfur per 100kg of catalyst (7.7 lbs. of sulfur per 100 lbs. of catalyst). In another example, a catalyst containing 3.0% Ni and 13.0% Mo would require a stoichiometric amount of sulfur calculated as: 3.0% x 0.36 + 13.0% x 0.67 = 9.8% or 9.8kg of sulfur per 100kg of catalyst (9.8 lbs. of sulfur per 100 lbs. of catalyst). Target sulfur loading ranges are calculated as being from 1.5% higher than stoichiometric to 1.5% below stoichiometric, said percentage being based on the total weight of the catalyst. Thus, for the catalyst containing 2.4% Co and 9.8% Mo, stoichiometric sulfur is 7.7% and the target range is from 6.2% to 9.2%. On regenerated catalysts, the level of sulfur on the catalyst prior to presulfiding needs to be measured and subtracted from the desired final sulfur level to determine the target level and target range. In this way, residual sulfur remaining after regeneration is not included as "presulfiding" sulfur. A significant aspect of the present invention is that improved results are obtained when catalyst presulfiding is accomplished by mixing the catalyst particles with powdered elemental sulfur and sequentially or simultaneously contacting the sulfur-catalyst mixture with at least one member selected from the group consisting of high boiling oils and hydrocarbon solvents and heating to a temperature above the melting point of sulfur. Herein, this step will be referred to as prewetting. Subsequent activity tests on catalysts produced using such a technique have shown excellent results. Various high boiling oils, hydrocarbon solvents and mixtures may be used as prewetting agents according to the claimed invention. Good results have been achieved when using oils with boiling ranges from approximately 370°C (700°F) to 540°C (1000° F). In particular, vacuum gas oils with low sulfur contents have been shown to be successful. If the prewetting step is independent of mixing the powdered sulfur with the catalyst, it may be performed in-situ or off-site of the reactor. If prewetted in-situ, the feedstock used in the reactor can be used as the prewetting oil, minimizing costs for the refinery. According to one embodiment of the present invention, catalyst particles are sequentially contacted with first, elemental sulfur, and then with at least one member selected from the group consisting of high boiling oils and hydrocarbon solvents. The catalyst particles are contacted with the powdered elemental sulfur at a temperature below the melting point of sulfur and preferably in the range of from 82-99°C (180°F to 210°F). The catalyst and the sulfur are then mixed for a sufficient amount of time to allow incorporation of the sulfur into the catalyst pores. A catalyst-sulfur mixture is thus produced. To this mixture is added a prewetting agent comprising at least one member selected from the group consisting of high boiling oils and hydrocarbon solvents thus producing a prewet mixture. The prewet mixture is preferably further heated to a temperature above the melting point of sulfur. Most preferably it is heated to a temperature in the range of 121-232°C (250°F to 450°F). The presulfided prewet catalyst so prepared may be conveniently activated by heating in the presence of hydrogen. In another embodiment according to the present invention, the catalyst particles are contacted with both the powdered elemental sulfur and a prewetting agent comprising at least one member selected from the group consisting of high boiling oils and hydrocarbon solvents simultaneously. According to this method, a mixture of elemental sulfur and a prewetting agent is first produced. A ratio of approximately 4:1 prewetting agent to sulfur by weight is preferred. This ratio provides sufficient sulfur to fully sulfide the catalyst with a minimum of liquid carrier which keeps weight and thus shipping costs to a minimum. The mixture is then heated to approximately 38°C (100°F) to promote homogenous mixing of the components. Toluene, other light weight hydrocarbon solvents and paraffins may be added to decrease the viscosity of the mixture which facilitates the incorporation of sulfur in the catalyst. Light weight paraffins are preferred and are hereby defined as those paraffins having 16 or less carbon atoms. Also, increased heat will achieve the same effect. The mixture is then added to a preweighed catalyst sample and mixed. In a preferred embodiment, catalyst particles prewet by the simultaneous method described above are further heat treated at a temperature in the range of from 121-232°C (250°F to 450°F) under a nitrogen atmosphere or other inert atmosphere. Results of activity tests have shown that mixing the sulfur-catalyst particles with a high boiling oil, hydrocarbon solvent or mixture as described above in an inert environment and heating to a temperature above the melting point of sulfur most significantly minimizes sulfur stripping upon reactor start-up. The elemental sulfur by itself was found to indeed presulfide the catalyst metals with only oil and hydrogen present and no other form of sulfur required. Alternatively, the catalyst may be activated with hydrogen at a later step, independent of mixing with a prewetting fluid. A versatile hydrotreating or hydrocracking catalyst which shows good activity under various reactor conditions is a nickel-molybdenum catalyst. Cobalt-molybdenum and nickel-tungsten catalysts are also preferred although many other metal oxide catalysts and transition element catalysts may be presulfided according to the claimed invention. These include catalysts comprising at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W Rh, Pd, Pt, Ag, Au, Cd, Sn, Sb, Bi and Te. The processes of the present invention are further applicable to the sulfiding of spent catalysts which have been regenerated. After a conventional regeneration process, a regenerated catalyst may be presulfided as would fresh catalyst in the manner set forth above. The invention can be carried out using the process steps described in Examples I-III of EP-A-0359 356, but with the relative amounts of catalyst and sulphur used being selected in accordance with the foregoing instructions.

Claims: A method of presulfiding a hydrotreating, hydrocracking or tail gas treating metal oxide catalyst, comprising: (a) contacting a hydrotreating, hydrocracking or tail gas treating metal oxide catalyst with powdered elemental sulfur heated at a temperature below the melting point of sulfur, said powdered elemental sulfur optionally being suspended in at least one liquid high boiling oil or hydrocarbon solvent, in a manner and for a time period long enough such that said elemental sulfur is substantially incorporated into the pores of said catalyst to form a mixture; (b) when the powdered elemental sulfur is not in the form of a suspension, it is contacted with the catalyst in such a way that the sulfur sublimes to be substantially incorporated into the pores of said catalyst to form said mixture, and the mixture is thereafter either: (i) heated in the presence of hydrogen to an activation temperature in the range of 121-343°C (250-650°F) for a time period long enough for substantially all of the sulfur incorporated into the catalyst pores to react to produce metal sulfides and hydrogen sulfides and to achieve a final sulfur level sufficient to sulfide active and promoter metals in said catalyst, or (ii) mixed with a prewetting agent comprising at least one liquid hydrocarbon solvent or high boiling oil, thereby producing a prewet mixture, for a time period long enough such that thereafter in the presence of hydrogen and at an activation temperature in the range of 121-343°C (250-650°F) substantially all of the sulfur incorporated into the catalyst pores is reacted to produce metal sulfides and hydrogen sulfides and achieve a final sulfur level sufficient to sulfide active and promoter metals in said catalyst; and (c) when the powdered elemental sulfur is in the form of a suspension, said manner and time period are such that thereafter in the presence of hydrogen and at an activation temperature in the range of 121-343°C (250-650°F) substantially all of the sulfur incorporated into the catalyst pores is reacted to produce metal sulfides and hydrogen sulfides and achieve a final sulfur level sufficient to sulfide active and promoter metals in said catalyst; characterised in that the amount of sulphur contacted with the catalyst is in the range of 1½% by weight of the total catalyst less than or greater than a stoichiometric amount, said stoichiometric amount being based upon the metal content of the catalyst. A method as claimed in claim 1, wherein the activation temperature specified in claim 1 part (b)(i), part (b)(ii) and/or part (c), is in the range of 121-232°C (250-450°F). A method as claimed in claim 1, wherein the activation temperature specified in claim 1 part (b)(i), part (b)(ii) and/or part (c), is in the range of 121-199°C (250-390°F). A method as claimed in any one of claims 1-3, wherein the elemental sulfur of step (a) is not suspended in a liquid. A method as claimed in claim 4, comprising step (b)(i). A method as claimed in claim 4, comprising step (b)(ii). A method as claimed in any one of claims 1-3, wherein the elemental sulfur of step (a) is in the form of said suspension. A method as claimed in any one of claims 1-3, wherein said method further comprises the step of exposing said prewet mixture or said suspension to hydrogen. A method as claimed in any one of claims 1-3, wherein the liquid prewetting agent or in said suspension comprises a paraffin and/or toluene. A method as claimed in claim 7, wherein said suspension is heated before being contacted with the catalyst. A method as claimed in claim 7, wherein said suspension is heated after being contacted with the catalyst. A method as claimed in any one of claims 1-3, wherein said catalyst comprises at least one member selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, Rh, Pd, Pt, Ag, Au, Cd, Sn, Sb, Bi and Te. A method as claimed in claim 1, wherein said metal oxide catalyst is a hydrocracking or tail gas treating catalyst.

Inventors: ADAMS CHARLES TERRELL, GASSER NEAL G, SEAMANS JAMES D, WELCH JAMES G, ADAMS, CHARLES TERRELL, GASSER, NEAL G., SEAMANS, JAMES D., WELCH, JAMES G.
Applicants: CRI VENTURES INC, CRI VENTURES, INC.
Application year: 1991
Main classification: B01J37
IPC codes: B01J23, C10L3, C10G47, B01J27, B01J37, C10G49, C10G45