A METHOD OF PRESULFIDING A HYDROTREATING CATALYST

Abstract: An improved method of presulfiding a hydro­ treating catalyst which minimizes sulfur stripping upon start-up of a hydrotreating reactor utilizing such a catalyst. The method comprises the steps of contacting a hydrotreating 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 melt­ ing point of sulfur. Preferably, the sulfur-catalyst mixture is first mixed with a high boiling oil or a hydrocarbon solvent to form a prewet mixture prior to heating at a temperature above the melting point of sulfur.

Description: This invention relates to a method of presulfiding a supported metal oxide catalyst for use in hydrotreating hydrocarbon feed stocks and, a hydrotreating process utilizing a presulfided metal oxide catalyst. A hydrotreating catalyst may be defined as any catalyst composition which may be employed to catalyze the hydrogenation of hydrocarbon feedstocks. 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 this definition include cobalt-molybdenum, nickel-tungsten, and nickel-molybdenum. 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 catalyst have suffered from excessive stripping of sulphur upon start-up of a hydrotreating reactor. As a result of sulphur stripping, an increase in the product weight percent of sulphur is observed along with a decrease in catalyst activity. The use of high boiling oils and hydrocarbon solvents to aid the incorporation of sulphur into a catalyst is not believed to have been previously taught by prior presulfiding methods. Hereforth, a high boiling oil is defined as an oil whose initial boiling point is greater than 204°C (400°F). Hydrotreating catalyst are typically presulfided by incorporation sulphur compounds into the porous catalyst prior to hydrotreating 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 sulphur. Hydrogen is then used as a reducing agent to convert the elemental sulphur to H₂S in situ. Problems arise, however, upon start-up of a reactor due to excessive sulphur stripping. U.S. Patent No. 4,089.930 to Kittrell et al discloses the pretreatment of a catalyst with elemental sulphur in the presence of hydrogen. It is an object of the present invention to presulfide a hydrotreating catalyst in a manner which minimizes sulphur stripping upon start-up of a hydrotreating 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 sulphur required for activation. It is yet a further object of the present invention to prepare a safe, stable, presulfided hydrotreating catalyst. It is yet a furhter object of the present invention to provide a technique for activating a presulfided hydrotreating catalyst in-situ. The present invention relates to an improved method of presulfiding a hydrotreating catalyst which minimizes sulphur stripping upon start-up of a hydrotreating reactor and improves catalyst activity. The catalyst is preferably presulfided by one of two methods. The first method comprises the steps of (a) contacting the supported metal oxide catalyst with powdered elemental sulphur, to form a mixture, at a temperature below the melting point of sulphur, (b) contacting the resultant mixture with a high boiling oil or a hydrocarbon solvent in a hydrogen-free environment, and, preferably, (c) heating said mixture to a temperature above the melting point of sulphur The second method comprises the steps of (a) preparing a mixture of elemental sulphur and a high boiling oil or hydrocarbon solvent at a temperature below the melting point of sulphur, (b) contacting the supported metal oxide catalyst with the mixture to form a resultant catalyst mixture, and, preferably, (c) heating the resultant catalyst mixture to a temperature above the melting point of sulphur. Alternatively, the catalyst is mixed with elemental sulphur at a temperature below the melting point of sulphur and then heated, in the absence of oil and hydrocarbon solvents to a temperature above the melting point of sulphur but below temperatures where activity loss is observed. Thus, in accordance with the present invention there is provided a method of presulfiding a hydrotreating catalyst, the various aspects of which are defined in independent claims 1, 2, 11 and 14. Preferred embodiments of this aspect of the invention are set out in sub-claims 3-10, 12, 13, 15-19 and 21. In a second aspect, the present invention relates to a mixture as defined in claim 20. DESCRIPTION OF THE PREFERRED EMBODIMENTS Several techniques may be employed to contact sulphur with catalyst particles. The use of solid sulphur eliminates many hazards such as flammability and toxicity, which are encountered when using H₂S, liquid sulfide, polysulfides and/or mercaptans. Powdered sulphur may be physically mixed with the catalyst particles prior to loading the catalyst particles in a reactor. The elemental sulphur and the catalyst particles may be mixed together at a temperature below the melting point of sulphur, preferably in the range of from 82°C (180°F) to 99°C (210°F). In this temperature range, the elemental sulphur sublimes and is incorporated into the pores of the catalyst particles where, upon cooling, it condenses. The sulphur-catalyst mixture is then heated to a temperature above the melting point of sulphur preferably in the range of from 121°C (250°F) to 199°C (390°F). In the presence of hydrogen, activation of the catalyst takes place. That is, the metal oxides react with substantially all of the sulphur incorporated into the catalyst pores, thus producing H₂S and metal sulfides. Mixing times for the powdered elemental sulphur and the catalyst can be minimized by heating the mixture at higher temperatures, within specified limitations, due to the increased vapour pressure of the sulphur. Preferably the amount of sulphur employed is 2 to 15% by weight of the catalyst charged. Most preferably, the amount of sulphur employed is about 6% to 8% by weight of the catalyst charged. Mixing times of the powdered sulphur and the catalyst particles are also minimized due to the reduced quantity of sulphur. While the use of greater amounts of sulphur does result in more sulphur being incorporated into the pores of the catalyst, the amount of sulphur stripping during reactor start-up is much greater than that of a 6 to 8% charge. When 6 to 8% sulphur by weight is employed, a minimum stripping effect is observed upon reactor start-up. 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 sulphur and sequentially or simultaneously contacting the sulphur-catalyst mixture with a high boiling oil or hydrocarbon solvent and heating to a temperature above the melting point of sulphur. Hereforth, this step will be referred to as prewetting. Subsequent activity tests on catalyst produced using such a technique have shown excellent results. Various high boiling oils and hydrocarbon solvents may be used as prewetting agents according to the claimed' invention. Good results have been achieved when using oils with boiling ranges from approximately 371°C . (700°F) to 538°C (1000°F). In particular, vacuum gas oils with low sulphur contents have been shown to be successful. If the prewetting step is independent of mixing the powdered sulphur 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 sulphur, then an oil or solvent. The catalyst particles are contacted with the powdered elemental sulphur at a temperature below the melting point of sulphur and preferably in the range of from 82°C (180°F) to 99°C (210°F). The catalyst and the sulphur are then mixed for a sufficient amount of time to allow incorporation of the sulphur into the catalyst pores. A catalyst-sulphur mixture is thus produced. To this mixture a high boiling oil or hydrocarbon solvent is added thus producing a prewet mixture. The prewet mixture is preferably further heated to a temperature above the melting point of sulphur. Most preferably, to a temperature in the range of 121°C (250°F) to 232°C (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 sulphur and the high boiling oil or hydrocarbon solvent simultaneously. According to this method, a mixture of elemental sulphur and a high boiling oil or hydrocarbon solvent is first produced. A ratio of approximately 4:1 oil to sulphur by weight is preferred. The mixture is then heated to approximately 38°C (100°F) to promote homogenous mixing of the components. Toluene or other light weight hydrocarbon solvents may be added to decrease the viscosity of the mixture. 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°C (250°F) to 232°C (450°F) under a nitrogen atmosphere or other inert atmosphere. Results of activity tests have shown that mixing the sulphur-catalyst particles with a high boiling oil or hydrocarbon solvent in an inert environment and heating to a temperature above the melting point of sulphur most significantly minimizes sulphur stripping upon reactor start-up. The elemental sulphur by itself was found to indeed presulfide the catalyst metals with only oil and hydrogen present and no other form of sulphur required. Alternatively, the catalyst may be activated with hydrogen at a later step, independent of mixing with a prewetting fluid. A versatile hydrotreating 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 may be presulfided according to the claimed invention. The processes of the present invention are further applicable to the sulfiding of spent catalysts which have been oxy-regenerated. After a conventional oxy-regeneration process, an oxy-regenerated catalyst may be presulfided as would fresh catalyst in the manner set forth above and specifically in a manner set forth by way of the following examples. EXAMPLES The following examples further illustrate the practice and advantages of specific embodiments of the claimed invention. These examples are illustrative only; in no event are they to be considered as limiting the scope of the claimed invention. Example 1 - Standard Method A sample of a nickel-molybdenum catalyst was dried at 371°C (700°F) for one hour and then cooled to ambient under vacuum. The sample was then placed in,a flask and enough elemental sulphur was added to produce a sulphur level of 6%. The flask was then sealed and placed in a 111°C (231°F) oven for one hour. During this time period, the flask was rotated continually to provide uniform distribution of sulphur. The final sulphur level was 6% sulphur. Example IIA: Standard Method and Simultaneous Prewet A sample of a nickel-molybdenum catalyst was dried at 371°C (700°F) for one hour and then cooled to ambient under vacuum. Into a beaker the following were added: 1.) 60.89 grams of a Vacuum Gas Oil Feedstock; 2.) 14.10 grams of Elemental Sulphur. The mixture was heated to 39°C (102°F) and mixed. The mixture was removed from the heat and 15.51 grams of toluene were added and mixed. To a preweighed catalyst sample (159.6 grams), 72.02 grams of the above mixture were added. The container was then sealed and mixed by shaking. The container was reopened and placed under vacuum for 16 hours to gently remove the majority of the toluene. The final sulphur level was 4.5% sulphur. Example IIB - Standard Method and Sequential Prewet A sample of a nickel-molybdenum catalyst was dried at 371°C (700°F) for one hour and then cooled to ambient under vacuum. The sample was then placed in a flask and enough elemental sulphur was added to produce a sulphur level of 6.6%. The flask was then sealed and placed in a 111°C (231°F) oven for one hour. During this time period, the flask was rotated continually to provide uniform distribution of sulphur. Into a better the following were added: 1) 35.01 grams of a vacuum gas oil feedstock; 2) 8.92 grams of toluene The contents of the mixture were then mixed. To a preweighed sample of the above sulphur impregnated catalyst (42.72 grams), 15.28 grams of the prepared oil-toluene mixture were added. The container was then sealed and mixed by shaking. The container was reopened and placed under vacuum for 16 hours to gently remove the majority of the toluene. The final sulphur level was 5.5% sulphur. Example III - Standard Method, Simultaneous Prewet and Heat The catalyst prepared in Example IIA was heat treated at 200°C (392°F) for one hour under a nitrogen blanket. The sample was also cooled under a nitrogen blanket. The final sulphur level was 4.9%. It is expected that the Standard Method, Sequential Prewet and Heat would produce comparable results. Activity tests were conducted on catalysts prepared according to Examples I-III. Oxide catalyst which were not presulfided were also tested as controls for each start-up procedure. Three start-up procedures were used in testing the activity of each presulfided catalyst. Fast Oil Start-Up Catalyst Charge: 48cc + diluent Reactor Pressure: 48bar (700 psig) H₂ Flow Rate: 12 l/h at 1.01 bar and 15.6°C (1000 SCF/Bb1) Liquid Feed: Diesel Fuel Sulphur = 0.17 wt. % Specific Gravity = 0.872 g/cm³ at 16°C (31.1° API) LHSV = 1.5 hr⁻¹ (approx. 63 gms/hr.) The hydrogen feed rate and reactor pressure are established at ambient temperature. The liquid feed is introduced and the reactor temperature is increased to 121°C (250°F) during the first hour on stream. The reactor temperature is then increased at a rate of about 25°C (45°F)/hour to 343°C (650°F). The reactor is then allowed to cool to 246°C (475°F) during the next two hours. Once the reactor is at 246°C (475°F), the diesel is discontinued and the standard 1.8 wt.% sulphur gas oil feedstock is started. Standard run conditions, heating rate, etc. followed. The standard gas oil feedstock consists of 2/3 vacuum gas oil and 1/3 light cycle oil. The specific gravity is 0.924 g/cm³ at 16°C (API gravity is 21.6°), the weight percent sulphur is 1.8% and the Total Nitrogen content is 880 ppm. Standard run conditions are: Reactor Temperature: 329°C (625°F) Reactor Pressure: 48bar (700 psig) LHSV: 1.5 hr⁻¹ H₂ Flow Rate: 12 l/h at 1.01 bar and 15.6°C (1000 SCR/Bb1) Slow Oil Start-Up Catalyst Charge: 48cc + diluent Reactor Pressure: 48bar (700 psig) H₂ Flow Rate: 12 l/h at 1.01 bar and 15.6°C (1000 SCF/Bb1) Liqiud Feed: 62 gms./hr of Diesel Oil LHSV = 1.5 hr⁻¹ (approx. 62 gms/hr.) The reactor pressure, hydrogen flow rate and liquid feed rate are established at ambient temperature. The reactor temperature was increased at a rate of 13°C (24°F)/hour to 343°C (650°F). When the reactor temperature reached 343°C (650°F), the heat was cut off and the temperature was reduced to 246°C (475°F). Immediately following the cut off of heat, the diesel oil was drained from the feed tank and the standard 1.8 wt.% sulphur feedstock was charged. Standard run conditions, heating rate, etc. followed. Hydrogen Start-Up (Feed in at 288°C (550°F) Catalyst Charge: 48cc + diluent Reactor Pressure: 48bar (700 psig) H₂ Flow Rate: 12.5 l/h at 1.01 bar and 15.6°C (0.467 SCFH) Liquid Feed: 0.0 gms/hr. The reactor was heated at a rate of 28°C (50°F)/hr until a temperature of 329°C (625°F) was reached. During this heat up period, liquid feed was introduced when the reactor temperature reached 288°C (550°F) at a feed rate of 65 gms/hr. In certain start-up situations, the standard method presulfided catalysts have difficulties. With the slow diesel start-up, excessive sulphur is displaced from the catalyst resulting in less activity. With the hydrogen to 288°C (550°F) start-up, the standard method presulfided catalysts yield poor results because of the exposure to hydrogen at high temperature without a hydrocarbon present. The modified procedures of the simultaneous and sequential prewet methods with and without heat overcome these difficulties by producing a catalyst that can tolerate a wide range of conceivable start-up procedures. The results presented below are for the three different types of start-up procedures. The test results verify that the use of vacuum gas oil and heat most greatly reduce the weight percent of sulphur in the product. The present invention has been described in some detail, including alternative embodiments thereof. It will be appreciated, however, that those skilled in the art, upon consideration of the present disclosure, may make modifications and improvements on this invention and still be within the scope and spirit of this invention as set forth in the following claims. In particular the amount of sulphur employed may be between 4.5% and 8% of the catalyst.

Claims: 1. A method of presulfiding a hydrotreating catalyst comprising the steps of: (a) contacting said catalyst with powdered elemental sulphur at a temperature of at least 82°C but below the melting point of sulphur such that said elemental sulphur sublimes and is substantially incorporated in the pores of said catalyst, thereby forming a mixture, and (b) heating said mixture in the presence of hydrogen to a temperature above the melting point of sulphur and below 199°C (390°F). 2. A method of presulfiding a hydrotreating catalyst comprising the steps of: (a) contacting said catalyst with powdered elemental sulphur at a temperature below the melting point of sulphur such that said elemental sulphur sublimes and is substantially incorporated in the pores of said catalyst; (b) mixing said sulphur-incorporated catalyst with at least one member selected from the group consisting of hydrocarbon solvents and high boiling oils, thereby producing a prewet mixture. 3. The method of claim 2, wherein said method further comprises heating said prewet mixture to a temperature above the melting point of sulphur. 4. The method of claim 2, wherein said method further comprises heating the prewet mixture. 5. The method of claim 2, wherein said method further comprises contacting said catalyst with powdered elemental sulphur in the absence of oxygen. 6. The method of claim 5, wherein said method further comprises contacting said catalyst with said powdered elemental sulphur in the presence of an inert gas. 7. The method of claim 1 or 2, wherein said catalyst contains at least one element selected from the group consisting of Co, Mo, Ni and W. 8. The method of claim 1 or 2, wherein the amount of elemental sulphur mixed with said catalyst is from 2 to 15% the weight of said catalyst. 9. The method of claim 8, wherein said elemental sulphur is about 6%-8% the weight of said catalyst. 10. The method of claim 2, wherein said member is a hydrocarbon feedstock. 11. A method of presulfiding a hydrotreating catalyst comprising the steps of (a) preparing a presulfiding suspension containing particulate elemental sulphur by mixing together powdered elemental sulphur and one member from the group consisting of high boiling oils and hydrocarbon solvents, (b) heating said suspension to a temperature below the melting point of sulphur, and (c) contacting a hydrotreating catalyst with said suspension in a manner such that said elemental sulphur is substantially incorporated into the pores of said catalyst. 12. The method of claim 11, wherein said method further comprises heating said catalyst, after contacting with said mixture, to a temperature above the melting point of sulphur. 13. A presulfided hydrotreating catalyst produced by the process of claim 1, 2 or 11. 14. A method of hydrotreating a hydrocarbon feedstock comprising the steps of contacting the hydrocarbon feedstock with hydrogen and with a presulfided hydrotreating catalyst, wherein said catalyst is presulfided by the steps of: (a) contacting said catalyst with elemental sulphur at a temperature below the melting point of sulphur, (b) mixing said catalyst with one member selected from the group consisting of high boiling oils and hydrocarbon solvents, to form a prewet mixture, and (c) heating said prewet mixture at a temperature above the melting point of sulphur. 15. The method of claim 14, wherein said catalyst is contacted with elemental sulphur at a temperature of 82°-99°C (180° to 210°F). 16. The method of claim 14, wherein said prewet mixture is heated to a temperature in the range of 121°-232°C (250° to 450°F). 17. The method of claim 14, wherein said catalyst contains at least one element selected from the group consisting of Co, Mo, Ni and W. 18. A method as in claim 2, wherein said method further comprises the step of exposing said prewet mixture to hydrogen. 19. A method as in claim 11, wherein said method further comprises the step of exposing said catalyst contacted with said suspension to hydrogen. 20. A mixture comprising a metal oxide catalyst and a suspension, wherein said suspension comprises: an amount of elemental sulphur sufficient to sulfide active and promoter metals in said catalyst upon exposure to hydrogen; and an amount of a hydrocarbon solvent or high boiling oil which can be substantially incorporated into said catalyst. 21. A method as claimed in any of claims 1-10, wherein the catalyst is contacted with powdered elemental sulphur at a temperature below 99°C (210°F).

Inventors: ADAMS, CHARLES TERRELL, GASSER, NEAL G., SEAMANS, JAMES D, WELCH, JAMES G.
Applicants: CRI VENTURES, INC.
Application year: 1989
Main classification: B01J37
IPC codes: C10G45, B01J23, B01J37, B01J27