Process for the reactivation of spent alumina-supported hydrotreating catalysts

Abstract: A process for reactivating a spent alumina-supported hydrotreating catalyst which comprises: (a) stripping process oil from the spent catalyst; and (b) treating the spent alumina-supported catalyst in a solvent treating zone with a heated organic solvent selected from 2-pyrrolidone, quinoline, N-methyl-2-pyrrolidone, phenol, furfural and mixtures thereof.

Description: This invention relates to a process for reactivation of spent inactive alumina-supported catalysts from a catalytic hydrotreating process. More particularly, this invention relates to method in which spent catalyst withdrawn from a hydrotreating process, such as an H-Oil® hydrogenation process in which ebullated-bed reactors are employed, is first stripped of process oil by, for example, washing with a hydrocarbon solvent and the oil-free catalyst is then contacted with a heated organic solvent, such as N-methyl-2-pyrrolidone, to remove hydrocarbon deposits from the catalyst surfaces including the catalyst pores thereby providing a reactivated catalyst. In another aspect of this invention the reactivated catalyst is additionally regenerated by burnoff of the carbon and sulfur deposits under controlled conditions in the presence of an oxygen-containing gas or, if desired, the reactivated catalyst can be subjected to a rejuvenation step in which a part or substantially all of the metallic deposits are removed after which the rejuvenated catalyst can be regenerated by burnoff of the carbon and sulfur deposits. During catalytic reaction processes, as exemplified by hydrotreating processes employing ebullated-bed reactors, the catalysts employed gradually are deactivated by virtue of an accumulation of carbonaceous deposits on the catalyst particles, and by virtue of various metallic elements such as vanadium, nickel, etc. being deposited thereon. There is a need in the art for a practical method for conveniently reactivating spent hydrotreating catalyst withdrawn from a fluidized-bed catalytic reactor system, such as a processing system utilizing ebullated-bed or continuous stirred tank reactors in hydroprocessing high sulfur and metals-containing hydrocarbon feedstocks. The prior art has disclosed a number of methods of recovery of used contaminated catalyst. Of note are CA-1159402, US-A-3809644, 4621069, 4720473, 4454240, 4795726, 4325818, 4311583, 4057491 and GB-A-1526927. In particular, US Patent No. 4,325,818 discloses a dual solvent refining process for solvent refining petroleum based lubricating oil stocks with N-methyl-2-pyrrolidone as a selective solvent for aromatic oils where a highly paraffinic oil having a narrow boiling range approximating the boiling point of N-methyl-2-pyrrolidone is employed as a backwash solvent. US Patent No. 4,311,583 discloses a solvent refining process utilizing N-methyl-2-pyrrolidone as solvent in which primary extract is cooled to form a secondary raffinate and secondary extract and the secondary and primary raffinates are blended to produce an increased yield of product of desired quality. Guillen et al in a paper entitled "Study of the Effectiveness of 27 Organic Solvents in the Extraction of Coal Tar Pitches" (Energy and Fuels, 1991, Vol. 5, pp. 192-204) disclose a study of the extractive ability of organic solvents including 2-pyrrolidone, N-methyl-2-pyrrolidone, etc. on coal tar pitches. US-A-4164481 describes the regeneration of noble metal catalysts according to a process comprising the steps of washing the deactivated catalyst with a polar organic solvent; contacting the washed catalyst with a hot aqueous alkali metal hydroxide solution; contacting the catalyst with an oxygen-containing gas at moderately elevated temperatures; and washing the catalyst a final time with a polar organic solvent. This method of regenerating the catalyst is particularly useful to reactivate palladium on carbon catalysts deactivated in the reduction of nitrophenol compounds to aminophenols. It is an object of the present invention to provide a process for reactivating spent or inactive alumina-supported catalysts having carbonaceous and variable metals contaminant contents so that reactivated catalyst material having a relatively high activity is suitable for further use in a petroleum residua hydroconversion process such as H-Oil® hydrogenation process using ebullated-bed or continuous-stirred-tank reactors. Specifically, this invention relates to a process for reactivating spent alumina-supported hydrotreating catalyst which is particularly useful for reactivating spent hydrotreating alumina-supported catalyst withdrawn, for example, from an H-Oil® reactor. The process comprises (1) stripping process oil from the spent hydrotreating catalyst having carbonaceous and metallic deposits thereon by, for example, washing the catalyst with a hydrocarbon solvent thus rendering the catalyst particles free flowing and (2) treating the free-flowing catalyst with a heated organic solvent, such as N-methyl-2-pyrrolidone, and recovering the reactivated catalyst of relatively high activity suitable for returning to the hydrotreating reactor. Optionally, the reactivated catalyst fractions can be passed to a regeneration zone where the carbonaceous deposits are removed by carbon burnoff or the reactivated catalyst can be acid leached prior to regeneration to remove undesired metals. The process of this invention is useful for treating spent catalyst withdrawn from a wide range of hydrotreating reactors including hydrodesulfurization units. The catalyst reactivation process is particularly useful for treating spent catalyst withdrawn from, for example, an ebullated-bed single stage hydrodesulfurization unit or from any of the stages of a multiple stage hydrodesulfurization ebullated-bed unit where catalysts comprising an oxide of nickel or cobalt and an oxide of tungsten or molybdenum supported on a porous alumina support, for example, are employed. Although a wide variety of spent or used hydrotreating catalysts can be reactivated utilizing the process of this invention, it is especially useful for treating spent hydrotreating catalysts having a regular geometric shape formed by extrusion or pelletizing and preferably which have a generally cylindrical shape with a generally circular cross-section and having a cross-sectional diameter ranging from 0.7 to 1.6 mm (0.030 to 0.065 inches). Catalyst-type particles which can be reactivated by the process of this invention may comprise any of the conventional shaped alumina-supported or silica-supported catalysts which usually contain active metals such as cobalt, molybdenum, nickel, phosphorus, tungsten or titanium used in hydroconversion or hydrorefining of hydrocarbons and particularly with regard to hydrotreating or hydrodesulfurization of residuum feedstocks. The process is of particular use in the treatment of molybdenum containing catalysts, such as combinations of molybdenum and nickel or cobalt. The process of the invention will now be more fully described: (A) Removal of Process Oils to Form Free-Flowing Catalyst Particles In the reactivation process of this invention spent hydrodesulfurization catalyst which has been removed from an ebullated-bed reactor such as an H-Oil® reactor operating under hydrodesulfurization conditions is sent to a catalyst stripping unit for deoiling. In this unit the spent catalyst particles, for example, are washed batchwise or in a continuous manner with a hydrocarbon solvent liquid for the purpose of removing process oils. A variety of methods may be utilized in washing the used catalyst such as by (a) adding the used catalyst with mixing to a tank containing the solvent liquid, or (b) the spent catalyst can be introduced into a catalyst washing unit where solvent is circulated uniformly upwardly through a generally vertical column by means of a pump and a flow distributor. In both washing methods the hydrocarbon can be, for example, naphtha and/or toluene, and mixtures thereof. Heat is added to the hydrocarbon solvent to maintain the solvent temperature at 95°-150°C (200°-300°F) in both methods (a) and (b). After the spent catalyst particles have been washed, free-flowing catalyst particles are obtained by drying the particles at a low temperature (i.e. <120°C (250°F)) in air or in air diluted with an inert gas such as nitrogen or at even lower temperatures (ambient) under vacuum conditions. Alternatively, the catalyst can be deoiled by stripping at high temperature (i.e. >260°C (500°F)) in a flowing inert gas such as nitrogen until no additional process oil is removed. After deoiling, it may be desirable to submit the catalyst particles to a separation process to remove highly-contaminated, old, broken catalyst particles. To accomplish this, a density separation by liquid fluidization, such as that disclosed in Canadian Patent No. 1,159,402, or a more complicated process such as that outlined in U.S. Patent No. 4,720,473 may be utilized. (B) Treatment of Spent Free-Flowing Catalyst Particles with the Heated Organic Solvent The dry, deoiled, free-flowing catalyst particles are next sent to the organic solvent treatment unit in which the used catalyst particles are treated by washing with the heated organic solvent at a temperature of 95° to 260°C (200° to 500°F) for a period of 1 to 12 hours preferably 4 to 12 hours. It has been found that a surprising increase in the hydrodesulfurization activity of the alumina-supported catalyst results when the deoiled, used catalyst is treated with heated organic solvents in accordance with the process of this invention. The amount of the organic solvent employed in the washing operation can be varied over a wide range depending on the particular solvent employed, the temperature at which the operation is carried out, etc. The process is advantageously conducted with agitation at or near the boiling point of the organic solvent. Generally, the amount of solvent utilized will vary from about 20 to about 80 kg or more per kg of used catalyst being treated. Any of a variety of methods can be used in conducting the organic solvent treatment stop. For example, a cyclic washing treatment can be employed in which in each cycle the deoiled used catalyst can be treated with about 5 to about 20 kg or more of solvent per kg of used catalyst being treated for about 0.5 to about 3 hours. Usually in the cyclic treatment method about 3 to 8 cycles or more are carried out. The treating or washing step can be conducted utilizing a continuously operated, counter-current washing unit. In such a method utilizing a closed, insulated, tubular extraction unit into one end of which is introduced the deoiled catalyst which is caused to move toward the forward end (i.e., the catalyst discharge end) of the unit by means of a rotating, screw-type, close-fitting, open-bladed scraper mechanism. Hot solvent heated to the desired temperature is introduced into the forward end of the unit and passes and washes the oncoming deoiled catalyst which is discharged from the unit forward end while the organic solvent containing the hydrocarbon material removed from the catalyst is discharged through a suitably screened exit line near the location at which the used catalyst is introduced into the unit. The hydrocarbon contaminated organic solvent stream is sent to a recovery unit from which clean solvent is recovered using distillation or separation methods well known in the art after which the hydrocarbon material removed from the catalyst is sent as a portion of the feed to a hydrogen generation unit or to a coking unit for light hydrocarbon production. Another useful method for treating the deoiled catalyst with the heated organic solvent is set out in U.S. Patent No. 4,454,240 in Col. 3, lines 1-20. In this method the used, deoiled catalyst is introduced as a batch into a catalyst washing unit which is supplied with the organic solvent which is circulated upward through a generally vertical column by means of a pump and flow distributor. Heat is added to the organic solvent as needed to maintain the organic solvent at or near its boiling point. Preferably, the pressure used is atmospheric. The solvent liquid containing the oily carbonaceous material which overflows from the top of the washing unit is sent to a recovery unit where the organic solvent is recovered for recycling back to the washing unit, while the oily, carbonaceous waste is sent as a portion of the feed to a hydrogen generation unit or to a coking unit for light hydrocarbon production. Organic solvents useful in the process of this invention include, for example, 2-pyrrolidone, quinoline, N-methyl-2-pyrrolidone, phenol, furfural and mixtures thereof. N-methyl-2-pyrrolidone is preferred. (C) Catalyst Regeneration Optionally, the catalyst fraction recovered from the solvent treating zone is passed to regeneration zone for removal of remaining carbonaceous deposits. The regeneration zone may be a conventional regenerator in which a gas containing 1 - 6 V % oxygen (e.g., air diluted with an inert gas such as nitrogen), or air, is supplied to the regenerator under combustion conditions to oxidize the remaining carbonaceous deposits to carbon dioxide which is withdrawn from the regenerator. Suitable oxidation temperatures range from 370°-480°C (700° - 900°F). The reactivated catalyst fraction recovered from the regeneration zone may, if desired, be passed to a separate density grading zone. This step may be desirable since some catalyst particles are more contaminated with nickel and vanadium than other particles. A number of processes suitable for density grading of used or spent catalyst particles have been described in the art. For example, density grading of spent or used catalyst particles using an upward flow of gas such as air through an inclined vibrating surface to produce a light catalyst fraction which contains little or no heavy metal contamination is described in U.S. Patent No. 4,720,473. Canadian Patent No. 1,159,402 sets out a process for the recovery of lightly contaminated used or spent catalyst particles according to particle density differences by using a fluidization method in which a catalyst bed of used catalyst is fluidized by flowing a light hydrocarbon liquid upwardly through the bed thereby accomplishing substantial segregation of the catalyst particles into an upper less metal contaminated fraction and a lower more contaminated fraction followed by recovery of the upper fraction. (D) Acid Leaching of Catalyst Particles In a final optional step, the reactivated catalyst particles after being treated with the organic solvent and prior to regeneration are sent to a rejuvenation unit for the purpose of removing metallic deposits where the catalyst particles are preferably first washed with water to fill the catalyst pores. Next, the catalyst particles are passed to an acid treating column and a solution of 5 - 50 weight percent sulfuric acid and 0 - 10 weight percent ammonium ion is introduced into the lower section of the column which is made of corrosion resistant material. The acid solution is recovered from the top of the acid treating column and generally is recycled by means of a pump to the bottom of the column together with additional make-up acid as required. Usually the acid treatment is conducted at temperatures ranging from 15° - 120°C (60° - 250°F). In a final step after the acid treatment to remove metallic deposits has been carried out, the catalyst particles are passed to a washing unit where the acid-treatment particles are washed with water to remove the acid following which the recovered, washed catalyst particles are preferably dried in air or in air diluted with nitrogen at a temperature of 65° - 120°C (150° to 250°F). This process for removing metallic deposits from the catalyst particles is more completely described in US Patent No. 4,454,240. As previously pointed out, the alumina-based catalysts usually employed in ebullated-bed reactors operating under hydrodesulfurization conditions contain one or more metals with hydrogenating activity such as cobalt, molybdenum, nickel, phosphorus, tungsten and titanium and the reactivation process together with the regeneration and rejuvenation may result in removal of a part of the metals with hydrogenation activity from the catalysts. If needed, additional amounts of the required metals can be supplied to the reactivated catalyst particles by methods well known in the art, Solvent included in the hydrocarbon-contaminated solvent mixture recovered from the organic solvent treating unit may be separated using conventional means such as appropriate distillation procedures. The solvent recovered may then be recycled to the organic solvent treating unit and the recovered hydrocarbon mixture can be disposed of in a hydrogen generation unit utilized to produce hydrogen for use in a hydrotreating unit or in a coking unit utilized to produce light hydrocarbons. In another aspect, this invention relates to a hydrotreating process especially useful for producing low sulfur liquid products which comprises passing a metals contaminated hydrocarbon residuum feedstock having a metals content of from about 50 to about 500 wppm and a sulfur content of 2.0 to about 5 weight percent through multiple reaction zones in an upflow manner, with internal recycle of reactor liquid contents, under hydrogenation conditions of temperature and pressure in the presence of an alumina-supported catalyst containing one or more metals with hydrogenating activity such as cobalt, molybdenum, tungsten, phosphorus, nickel and vanadium which is ebullated in the liquid environment, adding fresh particulate high activity catalyst to the final reaction zone, withdrawing spent catalyst from the final reaction zone, reactivating the said spent catalyst by: a) stripping process oil from the spent catalyst, b) treating the spent alumina-supported catalyst at a temperature of 94°-260°C (200° to 500 F. for a period of about 1 to about 12 hours in a solvent treating zone with an organic solvent selected from 2-pyrrolidone, quinoline, N-methyl-2-pyrrolidone, phenol, furfural and mixtures thereof, and c) recovering a reactivated alumina-supported catalyst from the said solvent treating zone, backstaging the recovered reactivated alumina-supported catalyst to said preceding reaction zones in reverse flow relative to the residuum and introducing make-up hydrogen directly to the final reaction zone whereby the desulfurization rate is maintained at a maximum. In another embodiment this invention relates to a two-stage hydroconversion process for the production of low-sulfur, low boiling-range product streams, the unconverted residuum stream being blended to fuel oil, from a petroleum residuum (having e.g. a sulfur content of about 2 to about 5 weight percent and more than 50 wppm of metallic compounds)where the residuum is passed through each of two reaction zones in succession in the presence of hydrogen and under hydrogenation/hydroconversion conditions of temperature and pressure, both of the said zones containing a particulate alumina-supported catalyst which is placed in ebullation in the liquid phase environment by the upflow of said residuum and hydrogen and the internal recycle of reactor liquid products, wherein (a) in the final reaction zone introducing a fresh, particulate, high activity alumina-supported hydrotreating catalyst containing one or more metals of hydrotreating activity such as cobalt, molybdenum, tungsten, phosphorus, nickel and vanadium, (b) withdrawing spent catalyst from the final reaction zone, said spent catalyst being partially deactivated by carbon and metals deposited thereon in the final reaction zone, (c) reactivating the spent catalyst by (A) stripping process oil from the spent catalyst, (B) treating the spent alumina-supported catalyst at a temperature of from 94°-260°C (200°-500°F) for about 1 to about 12 hours in a solvent treating zone with an organic solvent selected from the group consisting of 2-pyrrolidone, quinoline, N-methyl-2-pyrrolidone, phenol, furfural and mixtures thereof, (c) recovering a reactivated alumina-supported catalyst from the solvent treating zone, (d) passing the entire effluent from the first reaction zone to the second final reaction zone, (e) passing the reactivated catalyst from the final reaction zone to the first reaction zone, and (f) withdrawing from the final reaction zone a liquid hydrocarbon stream which can be fractionated to recover the unconverted residuum stream with a boiling range of greater than or equal to 540°C (1000°F) and a sulfur content of about 2 - 3 weight percent which is suitable for blending to a low sulfur fuel oil product. The invention will now be described with reference to the following Examples. EXAMPLES 1-4 In these examples samples of about 100 ml of used catalyst particles withdrawn from an ebullated-bed reactor processing residual crudes having a boiling point range such that at least 89 volume percent boils at temperatures greater than or equal to 540°C (1000°F) and sulfur content in excess of 2 weight percent operating under hydrodesulfurization conditions were placed as a fixed bed in the solvent treating unit and treated with the heated organic solvent. The catalyst treated in these examples was Criterion® HDS-1443B, a nickel-molybdenum catalyst, on an alumina support. Each used catalyst sample was, prior to being treated with the organic solvent, washed with toluene at a temperature of about 110°C (230°F), afterwards dried in air at a temperature of about 120°C (250°F) and the hydrodesulfurization activity of the deoiled catalyst was determined by the hydrodesulfurization micro-activity test (HDS-MAT test). In these examples the deoiled, used catalyst was charged to a three-neck flask equipped with a thermometer, a condenser, a nitrogen purge and a bottoms draw-off. N-methyl-2-pyrrolidone (i.e., MP) was introduced into the flask and the system was heated to the boiling point of the N-methyl-2-pyrrolidone (∼ 200°C). After two hours, the system was allowed to cool and the waste N-methyl-2-pyrrolidone, which was dark black on the first washing cycle, was drawn off. Fresh n-methyl-2-pyrrolidone was introduced and the washing cycle was repeated. After a number of cycles had been carried out, no additional hydrocarbon was dissolved from the catalyst and the N-methyl-2-pyrrolidone remained clear and colorless upon boiling for two hours. The MP washed samples were then dried in a vacuum at 200°C (400°F). With each washing cycle approximately 10 grams of MP was used and generally from 4 to 6 cycles for a total of 40 to 60 grams of MP per gram of spent catalyst were required to complete the washing process. Finally, the hydrodesulfurization activity of the MP treated catalyst was determined by the HDS-MAT test. The V/Mo atomic ratio of the deoiled catalysts, the hydrodesulfurization activity of the deoiled catalysts as well as the hydrodesulfurization activity of the MP washed catalysts (HDS-MAT tests) for Examples 1-4 were determined and these values are reported in Table I which follows: A catalyst ages on exposure to oil. The more oil the catalyst has been exposed to, the more aged is the catalyst. Catalyst age is expressed in barrels of oil per lb of catalyst, or cubic metres of oil per kg of catalyst. Analyses of Samples 1-4 with regard to H/C atomic ratio is set out in Table II which follows: EFFECT OF MP WASHING ON H/C ATOMIC RATIO Example Toluene Washed H/C Toluene and MP Washed H/C 1 0.89 0.48 2 0.96 0.66 3 1.22 0.71 4 1.02 0.58 The values shown in Table II for H/C atomic ratios indicate that the ratios are decreased by 30% to 46% of their initial values by the subsequent washing with hot N-methyl-2-pyrrolidone. The low H/C atomic ratios on each of the MP treated samples indicates that entrapped hydrocarbons were successfully being removed from the catalysts leaving only a graphitelike substance in the catalyst pores and some residual MP. In the HDS-MAT procedure a one-half gram of ground catalyst is presulfided with 10%H₂S/H₂ flowing at 50 ml/minute for one hour at 400°C. The catalyst is then exposed to a model feed and hydrogen for approximately four hours. Cuts are taken periodically and analyzed by gas chromatograph for the conversion of benzothiophene to ethylbenzene. The average hydrodesulfurization activity is reported as C 0.5 g. The HDS-MAT run conditions are as follows: Temperature 290°C (550°F) Pressure Atmospheric Chargestock 0.857 molar benzothiophene in ASTM reagent grade heptane (3.68 wt % S) Space Velocity 4 hr.⁻¹ Catalyst Charge 0.5 grams Hydrogen Flow 50 ml/min. of ultra-high purity H₂ The calculation is performed as follows:

Claims: A process for reactivating a spent alumina-supported hydrotreating catalyst which comprises: (a) stripping process oil from the spent catalyst; and (b) treating the spent alumina-supported catalyst in a solvent treating zone with an organic solvent selected from 2-pyrrolidone, quinoline, N-methyl-2-pyrrolidone, phenol, furfural and mixtures thereof, heated at a temperature of 95°-260°C. A process as claimed in Claim 1 wherein in step (a) the spent alumina-supported catalyst is stripped of process oil by washing with a hydrocarbon solvent selected from toluene and naphtha and mixtures thereof at a temperature of 95° to 150°C (200° to 300°F). A process as claimed in Claim 1 or Claim 2 wherein in step (b) the spent alumina-supported catalyst is treated with said heated organic solvent for a period of from 1 to 12 hours. A process as claimed in any one of Claims 1 to 3 wherein the said organic solvent is N-methyl-2-pyrrolidone. A process as claimed in any one of the preceding claims wherein the reactivated catalyst is regenerated by contacting the said reactivated catalyst with an oxygen-containing gas at a temperature of 370° to 480°C (700° to 900°F) A process as claimed in Claim 5 wherein prior to regeneration the said reactivated catalyst is treated at a temperature of from 15° to 120°C (60° to 250°F) with an aqueous solution consisting of sulfuric acid and an ammonium ion whereby the metal contaminants are converted to their respective sulfate compounds and the said metal contaminants removed from the catalyst and afterwards washing the treated catalyst to remove the aqueous solution. A hydrodesulfurization process which comprises passing a metals contaminated hydrocarbon residuum feedstock through multiple reaction zones in an upflow manner under hydrogenation conditions of temperature and pressure in the presence of an alumina-supported catalyst which is ebullated in the liquid environment, adding fresh particulate high activity catalyst to the final reaction zone, withdrawing spent catalyst from the final reaction zone, reactivating the said spent catalyst by a process as claimed in any one of Claims 1 to 6, and backstaging the recovered reactivated alumina-supported catalyst to said reaction zones in reverse flow relative to the residuum and introducing make-up hydrogen directly to the final reaction zone whereby the desulfurization rate is maintained at a maximum. A hydroconversion process for the production of low-boiling range, low-sulfur product streams from a petroleum residuum feedstock wherein the residuum is passed upwardly through each of two reaction zones in succession in the presence of hydrogen and under hydrogenation/hydroconversion conditions of temperature and pressure, both of the said zones containing a particulate alumina-supported catalyst which is placed in ebullation in the liquid phase environment by the upflow of said residuum and hydrogen and the internal recycle of reactor liquid products, which comprises: (a) introducing in the final reaction zone a fresh, particulate, high activity alumina-supported hydrotreating catalyst; (b) withdrawing spent catalyst from the final reaction zone; (c) reactivating the spent catalyst by a process as claimed in any one of Claims 1 to 6; (d) passing the entire effluent from the first reaction zone to the subsequent final reaction zone; (e) passing the reactivated catalyst from the final reaction zone to the first reaction zone; and (f) withdrawing from the final reaction zone a liquid hydrocarbon stream which can be fractionated to recover the unconverted residuum stream.

Inventors: SHERWOOD DAVID EDWARD JR, SHERWOOD, DAVID EDWARD JR.
Applicants: TEXACO DEVELOPMENT CORP, TEXACO DEVELOPMENT CORPORATION
Application year: 1992
Main classification: B01J38
IPC codes: B01J23, C10G45, C10G65, B01J38