EP1361923A1

EP1361923A1 - Method for sulphurizing hydrotreating catalysts

Info

Publication number: EP1361923A1
Application number: EP02706852A
Authority: EP
Inventors: Claude Brun; Georges Fremy
Original assignee: Atofina SA
Current assignee: Arkema France SA
Priority date: 2001-02-22
Filing date: 2002-02-13
Publication date: 2003-11-19
Also published as: FR2820991A1; WO2002066161A1; AR032838A1; FR2820991B1; US20040112795A1; JP2004528962A; KR20030080228A; CA2438536A1

Abstract

The invention concerns a method for sulphurizing catalysts for hydrotreating of hydrocarbon feedstocks. The invention is characterised in that it consists in sulphurizing the catalyst in two steps: the first step consisting in sulphurization with tertiary mercaptan in the absence of hydrogen, and the second step, carried out consecutively in the same reactor, consisting sulphurization with another sulphurizing agent in the presence of hydrogen. The catalysts thus sulphurized prove to be more active than those sulphurized by only the second step.

Description

Sulphurization process for hydrotreatment catalysts.

The present invention relates to the field of hydrotreating hydrocarbon feedstocks and more particularly relates to a process for the sulfurization of catalysts used for this purpose.

The hydrotreatment catalysts of hydrocarbon feedstocks, concerned by the present invention, are used under suitable conditions for converting, in the presence of hydrogen, the organosulfur compounds into hydrogen sulfide, an operation which is called hydrodesulfurization (HDS), and for converting the organo-nitrogen compounds in ammonia in a process called hydro-denitrogenation (HDN).

These catalysts are generally based on metals of groups VI B and VIII of the periodic table of elements, such as molybdenum, tungsten, nickel and cobalt. The most common hydrotreatment catalysts are formulated from cobalt-molybdenum (Co-Mo), nickel-molybdenum (Ni-Mo) and nickel-tungsten (Ni-W) systems, deposited on porous mineral supports such as aluminas, silicas, silica-aluminas. These industrially produced catalysts at very large tonnages are supplied to the user in their oxide forms (for example, the cobalt oxide-molybdenum oxide on alumina catalysts symbolized by the abbreviation: Co-Mo / alumina).

However, these catalysts are only active in hydrotreatment operations in the form of metal sulfides. This is why, before being used, they must be sulfurized.

Regarding the activation of hydrotreatment catalysts, the sulfurization of these catalysts is an important step to obtain the maximum performance in HDS and HDN. As the authors of Hydrotreating Catalysts indicate (Catalysis, vol. 11, 1996, p. 25, edited by JR Anderson and M. Boudart), practical experience has shown that the sulfurization procedure can have a significant influence on catalyst activity and stability, and a lot of effort has gone into improving sulfurization procedures

The most direct method of sulfurizing a catalyst is to treat it with hydrogen sulfide mixed with hydrogen. However, this method, which has been the subject of several patents (US 3 016 347, US 3 140 994, GB 1 309 457, US 3 732 155, US 4 098 682, US 4 132 632, US 4 172 027, US 4 176 087, US 4 334 982, FR 2 476 118) has major drawbacks (acute toxicity, availability of H ₂ S) which does not allow its implementation on all industrial sites. Industrial catalyst sulfurization procedures are generally carried out under hydrogen pressure with liquid feedstocks already containing sulfur compounds as sulfurizing agents. The method mainly used in the past by refiners consisted of sulfurizing the catalysts with sulfur-containing petroleum feedstocks, but this technique had significant drawbacks because of the difficulty of transforming the sulfur-containing compounds into hydrogen-sulfur. To avoid reduction of the catalysts by hydrogen, the sulfurizations, started at low temperature, had to be carried out slowly to obtain complete sulfurization of the catalysts at high temperature. Sulfur additives have been proposed to improve the sulfurization of the catalysts. The method consists in incorporating a sulfur compound (spiking agent) into a filler such as a naphtha or into a particular cut such as a VGO (vacuum gas oil) or an LGO (light gas oil). US Patent 3,140,994 was the first to claim the use of compounds, liquid at room temperature, of different natures: carbon sulfide, thiophene, mercaptans, dialkyldisulfides, diaryldisulfides. Organic sulfides, in particular dimethyl sulfide, have also been the subject of claims. Dimethyldisulphide (DMDS) has been more particularly recommended for the sulphurization of catalysts and an effective method of sulphurization with dimethyldisulphide is described in patent EP 64429. H. Hallie (Oil and Gas Journal, Dec. 20, 1982, pp 69 - 74) gave an update on these hydrogen sulphidation procedures which are carried out directly in hydrotreatment reactors. These different techniques of sulfurization of catalysts, called "in-situ", have been compared and work has shown that sulfurization with a liquid charge added with a sulfurizing agent (spiked feedstock) having the property of decomposing at low temperature is the best sulfurization technique. The technique without additional sulfurizing agent (nonspiked feedstock) gives a less active sulfurized catalyst. The sulfurizing agent which it is preferred to add to the filler is dimethyldisulphide.

Organic polysulfides have also been claimed as sulfurizing agents for the sulfurization of catalysts. US Pat. No. 4,725,569 describes a method of using organic polysulphides of the RS _X R 'type (R and R' which may be identical or different, with x equal to or greater than 3) which consists in impregnating the catalyst at room temperature with a solution containing the polysulfide, then removing the inert solvent, and finally carrying out the sulfurization under hydrogen of the catalyst loaded in the hydrotreatment reactor. In patent EP 298 111, the polysulphide of RS _X R 'type, diluted in a liquid feed, is injected during the sulphurization of the catalyst in the presence of hydrogen. Functionalized mercaptans, such as mercaptocarboxylic acids or esters, dithiols, aminomercaptans, hydroxymercaptans, as well as thiocarboxylic acids or esters, are claimed in patent EP 289211 for the sulfurization of catalysts. More recently, new techniques for sulfurizing catalysts have been developed, comprising two stages. In a first step, called "ex-situ", the catalyst is preactivated in the absence of hydrogen outside the refinery after having been impregnated with a sulfurizing agent. The complete sulfurization of the catalyst is carried out in the hydrotreatment reactor in the presence of hydrogen. The "ex-situ" presulphurization exempts the refiner from injecting a sulphurizing agent during the sulphurization of the catalyst under hydrogen. The "ex-situ" techniques currently developed use organic polysulphides or sulfur as sulfur products.

An industrial technique of presulfurization of catalysts in "ex-situ", based on the use of organic polysulfides of the RS _X R 'type (R and R' can be identical or different and x> 3), was the subject of Patent EP 130,850. This process consists in impregnating the catalyst in oxide form with a solution of organic polysulphides, such as tertiononylpolysulphides (TPS 37 or TNPS marketed by ATOFINA), in a white spirit type hydrocarbon. This preliminary stage of incorporation into the catalyst of a sulfur compound of a particular nature is completed by a heat treatment of the catalyst in the absence of hydrogen at temperatures not exceeding 150 ° C. This operation has the effect of eliminating the organic solvent and ensuring the fixing of the sulfur to the catalyst via the organic polysulphides. At this stage of presulphurization, the catalyst is stable in air and can be handled without special precautions. It is supplied in this state to the user who, after loading into the hydrotreatment reactor, can complete the sulfurization of the catalyst under hydrogen for the total transformation of metals into metal sulfides.

Other polysulphide organic compounds, of different structures, have also been claimed for the presulphurization of the catalysts "in situ". The products recommended in patents FR 2 627 104 and EP 329 499 have the general formula: R '- (S _y -RS _x -RS _y ) -R' and are obtained from olefins and sulfur chloride by a series of successive steps which involve a reaction with an organic monohalide followed by a reaction with an alkaline polysulfide. In patent EP 338 897, the products claimed are synthesized from olefins and sulfur chloride with a complementary reaction with an alkaline mercaptide or an alkaline polysulfide mercaptate.

The development of an "ex-situ" presulfurization technique for catalysts using sulfur suspended in an oil (US 4,943,547) has posed such problems of industrial application that it was necessary to develop a new sulfur sulfurization process which consists in bringing the catalyst into contact with sulfur and an olefin of high boiling point. The catalyst thus impregnated is then heat treated at a temperature above 150 ° C., then the sulfurization of the catalyst is completed under hydrogen at temperatures above 200 ° C.

Very recently, in patent FR 2 758 478, it was indicated that the joint use of a tertiary mercaptan and another sulphurizing agent, such as dimethyldisulphide for example, makes it possible to obtain hydrotreatment catalysts more active in hydrodesulfurization of hydrocarbon feedstocks than sulfurized catalysts in the absence of tertiary mercaptan. According to this patent, the tertiary mercaptan can be incorporated during an "in situ" sulfurization under a stream of hydrogen, before or during the introduction of the sulfurization agents usually used. For those skilled in the art, an "in situ" sulfurization of the catalyst is always carried out under a stream of hydrogen. In this type of operation, the catalyst is introduced into the hydrotreatment reactor in oxide form and is sulfurized in the presence of the sulfurizing agent under a stream of hydrogen as opposed to "ex situ" presulphurization where the catalyst is presulphurized in outside the hydrotreatment reactor.

The present invention now relates to a particular mode of implementation "in situ" of this tertiary mercaptan. It has indeed been found, surprisingly, that the prior "in situ" introduction of the tertiary mercaptan in the absence of hydrogen, followed by the subsequent introduction into the same reactor of the other sulfurizing agent ( for example, dimethyldisulfide) in the presence of hydrogen this time, also made it possible to obtain significantly more active catalysts than those sulfide with dimethyldisulfide alone.

The subject of the invention is therefore a process for the in situ sulfurization of a metal hydrotreatment catalyst comprising a step of treating the catalyst with a tertiary mercaptan in the absence of hydrogen, followed in the same reactor by a step of treatment with another sulfurizing agent in the presence of hydrogen. The tertiary mercaptans relating to the present invention are the same as those mentioned in patent FR 2 758 478 and correspond to the general formula:

in which the symbols R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ , identical or different, each represent a hydrogen atom or an alkyl radical, linear or branched, aryl, alkylaryl or aralkyl, these radicals being able to contain one or more heteroatoms such as oxygen and / or sulfur.

The preferred tertiary mercaptans of the invention are those which contain from 4 to 16 carbon atoms. Such mercaptans are manufactured industrially from hydrogen sulphide and olefins by catalytic processes such as those described in particular in US patents 4,102,931, EP 101,356 and EP 329,521. Tertiobutylmercaptan (TBM) is thus manufactured at from isobutene, tertiononylmercaptan (TNM) from tripropylene and tertiododecylmercaptan (TDM) from tetrapropylene or triisobutylene. CT is the most particularly preferred tertiary mercaptan. The first step of the process according to the invention (in situ treatment of the catalyst with a tertiary mercaptan in the absence of hydrogen) essentially consists in incorporating the tertiary mercaptan in the pores of the catalyst and in subjecting the catalyst thus impregnated to thermal activation. under an atmosphere of an inert gas (for example, nitrogen or methane). For the impregnation of the catalyst, it is possible to use pure tertiary mercaptan, but it is advantageous to use it in the form of a solution in an organic solvent (preferably an alkane or a desulfurized gas oil) the concentration in tertiary mercaptan of this solution which can vary within wide limits depending on the nature of the tertiary mercaptan, its sulfur content and the pore volume of the catalyst to be sulfurized. The in situ impregnation of the catalyst with tertiary mercaptan in the absence of hydrogen can be done according to 2 methods:

The first method, when the pore volume is saturated, consists in passing a volume of solution comprising the tertiary mercaptan and the organic solvent described above in the desired proportions over the catalyst. The volume of this solution corresponds to the total pore volume of the mass of catalyst. This volume is then slightly increased to take account of the inert wetting volume (SiC - Carborundum) which is placed before the catalyst. The second method, by recirculation, consists in circulating in a loop a volume of solution comprising the tertiary mercaptan and the organic solvent in the desired proportions on the catalyst. This volume of solution is greater than the total pore volume of the mass of catalyst. Analysis over time shows that the recycled solution depletes tertiary mercaptan and that it is retained by the catalyst.

The thermal activation is carried out at a temperature which can range from 50 to 250 ° C., but is preferably between 100 and 175 ° C. For this operation, the pressure is not a critical parameter and can range from atmospheric pressure up to 35 bars.

The sulfur compounds to be used as sulfurizing agents in the second step of the process according to the invention can be of different types: feed to be desulphurized, carbon sulphide, light mercaptans (for example, ethyl mercaptan and n-butyl mercaptan), dimethyl sulphide, dimethyldisulphide ( DMDS), and optionally polysulfides such as ditertiononylpolysulfide or ditertiobutylpolysulfide; can also be used polysulfides obtained from sulfur and olefins. DMDS is the most particularly preferred sulfurizing agent.

This sulfurization agent is generally introduced in mixture with a diesel fuel, under a hydrogen pressure which can range from atmospheric pressure up to 200 bars, but is preferably between 10 and 50 bars, pressure range commonly used industrially. This second step of the process according to the invention (in situ treatment of the catalyst with the other sulfurizing agent in the presence of hydrogen) is carried out at a temperature which can range up to 350 ° C .; a higher temperature would reduce the sulfurization time, but would increase the risk of coking. It is advantageous to carry out this second stage in two stages:

- primary sulphurization carried out at a temperature between 150 and 250 ° C, preferably between 210 and 230 ° C so as to minimize the time necessary to obtain the breakthrough of H ₂ S in the outlet gases without risking premature reduction and then

- Secondary sulphurization carried out at a temperature between 250 and 350 ° C, preferably between 290 and 330 ° C, and of a duration sufficient to have a constant concentration of H ₂ S in the outlet gases.

The hydrogen coverage expressed by the ratio of the volume flow rate of hydrogen in normal liters to the volume flow rate of diesel fuel in liters can be between 50 and 500 Nl / I, preferably between 100 and 300 Nl / I.

The hourly space velocity (WH), defined as the ratio between the hourly volume flow of diesel fuel and the volume of catalyst, can range from 0.1 to 5 h ^"1 and is preferably between 1 and 3 h ^"1 , the interval commonly used industrially.

The total amount of sulfur supplied by the tertiary mercaptan and the other sulfurizing agent can range from 100 to 250% of the weight of sulfur stoichiometrically required for the total conversion of the oxides of the catalyst to sulphides. The proportion of tertiary mercaptan, used in the implementation of the process according to the invention, can represent from 1 to 100% of the weight of total sulfur necessary for the sulfurization of the catalyst. The sulfur provided by the tertiary mercaptan has a particularly sensitive effect from 10% by weight of the total sulfur necessary for the sulfurization of the catalyst.

The present invention will be better understood with the aid of the experimental part which follows by way of illustration. The purpose of Examples 1 and 2 presented is to show the gains in catalytic activity which can be obtained in a hydrotreatment test reaction, hydrodesulfurization (HDS) of thiophene, with an industrial catalyst Co-Mo / alumina which has been subjected to in-situ sulfurization under conventional sulfurization conditions (Example 1) and in-situ sulfurization under conditions specific to the present invention (Example 2). The purpose of Examples 3 and 4 is to illustrate the in-situ impregnation of the catalyst with tertiary mercaptan according to the recirculation method.

Reference EXAMPLE 1 (Sulfurization with dimethyldisulfide)

The catalyst used is a commercial hydrodesulfurization catalyst (KF756 from the company AKZO), consisting of cobalt and molybdenum oxides supported on alumina and having the following characteristics: - form: four-lobe

- diameter: 1, 3 mm

- density: 760 g / l

- pore volume: 0.6 ml / g

- stoichiometric sulfur to sulfurize 100 g of catalyst: 11 g

Sulphurization procedure at DMDS:

The operation was carried out in a reactor (internal volume: 120 ml) placed in an oven with three heating zones and provided at its outlet with a device making it possible to separate the liquid phase and the gas phase and to recycle them. A sampler is used to collect liquids in order to determine the total sulfur level present in the diesel fuel and then to carry out analyzes by gas chromatography. In the reactor, 30 g of catalyst (approximately 40 ml) were introduced between two layers of carborundum (SiC), an inert agent which promotes the wetting of the catalyst and which also serves as a thermal buffer. After drying under nitrogen at 150 ° C., the catalyst was wetted with a diesel fuel obtained from the atmospheric distillation of crude oil (Straight Run GasOil; hereinafter SRGO) and having the characteristics gathered in the following table:

Table 1

ASTM D86: Standard for petroleum fraction distillation

After putting the reactor under hydrogen pressure, the DMDS was injected so as to add 1.5% of sulfur to the SRGO. Sulphurization with DMDS was carried out under the following conditions: - Pressure H ₂ = 35 bars

- H ₂ / SRGO = 250 Nl / I

- Hourly volume speed WH = 2 hr ^"1

After primary sulfurization with a plateau at 220 ° C maintained until an H ₂ S breakthrough of at least 3000 ppmV was carried out, sulfurization was carried out at high temperature (320 ° C), temperature maintained as long as there is sulfur fixation.

The catalyst was then collected, washed and dried, then part of the catalyst was ground under argon to obtain particles of 0.2 to 0.5 mm which were mixed with SiC for the activity test. . Activity test (HDS of thiophene):

The hydrodesulfurization reaction of the thiophene was carried out at atmospheric pressure according to the following operating protocol: The temperature of the reactor is maintained at 400 ° C., while a mixture

H2S-H2 with an H2S content of 2% by volume and a gas flow rate set at 5.4 l / h is introduced into the reactor. Before mixing with IΗ2S, the hydrogen is sent to a saturator containing the liquid thiophene thermostatically controlled at a temperature such that the partial pressure of the thiophene in the gas entering the reactor is 60 torr (8 kPa).

These reaction conditions make it possible to measure low rates of transformation of the thiophene.

The gaseous effluents leaving the reactor are analyzed by chromatography to determine the unconverted thiophene and the C 4 hydrocarbons formed. The reaction is followed for 3 hours with periodic analyzes of the gaseous effluents.

Evaluation of the Activity of the Thiophene Catalyst in HDS The conversion rate of the thiophene is calculated from the chromatographic analyzes of the reaction effluents.

The evaluation of the activity of the catalyst for the hydrodesulfurization test reaction is determined by the rate of disappearance of the thiophene under these conditions.

For the Co-Mo / alumina catalyst KF 756, presulphurized according to the conditions described in this example 1 with dimethyldisulphide, in this reference test a transformation rate of thiophene (k _ref ) of 5.39 kg per hour is obtained and per liter of catalyst.

To facilitate the comparison of the results of catalytic activity of the various tests which have been carried out to demonstrate the gains in speed of conversion of thiophene obtained in the context of the present invention, this reference test has been assigned a relative activity expressed in RVA (Relative Volumic

Activity) of value equal to 100.

EXAMPLE 2 according to the invention

40 ml (30 g) of KF756 catalyst were introduced into the reactor, then impregnated with 21.7 g of a 15% by mass solution of tertiododecylmercaptan (TDM) in hexane at room temperature. The impregnated catalyst was then dried under nitrogen at a pressure of 7 bars and a temperature of 150 ° C. The dry catalyst was then subjected to a sulfurization with DMDS identical to that described in Example 1, then the activity of the catalyst thus sulfurized in HDS of thiophene was tested as in Example 1.

In this test, with the sulfurized catalyst according to the invention, a thiophene (k) transformation rate of 6.77 kg per hour and per liter of catalyst was obtained, ie an RVA, expressed by the relationship:

RVA = 100 xk / k _ref of 126.

Table 2: Results

A very significant gain in hydrodesulfurizing activity is therefore obtained when using the sulfurization procedure relating to the invention (example 2) compared to a conventional method of sulfurization (example 1).

EXAMPLE 3:

40 ml (30 g) of KF756 catalyst were introduced into the reactor and 138.6 g of a mixture consisting of 19.4 g of TDM and 119.2 g of desulfurized gas oil were introduced into the recycle loop in 30 minutes liquid.

At an initial temperature of 50 ° C, the solution is recirculated in an up-flow with respect to the catalytic bed with a flow rate of 80 cm ³ / h, under a nitrogen flow of 20 l / h at a pressure of 4 bars, and with a temperature rise of 50 ° C / h up to a plateau temperature of 150 ° C. After 8 hours of leveling at 150 ° C., ie 10 hours after the introduction of the solution, the analysis of the liquid recycle shows that 83%> of the TDM initially present reacted on the catalyst.

EXAMPLE 4 40 ml (30 g) of catalyst KF756 were introduced into the reactor and 138.6 g of a mixture consisting of 19.4 g of TDM and 11.8 g of desulfurized gas oil were introduced in 30 minutes into the liquid recycle loop.

At an initial temperature of 50 ° C, the solution is recirculated in up-flow relative to the catalytic bed with a flow rate of 80 cm3 / h, under a nitrogen flow of 20 l / h at a pressure of 4 bar, and with a temperature rise of 50 ° C / h up to a plateau temperature of 120 ° C. The 120 ° C level is maintained for 1.5 hours, then with a rise of 50 ° C / h, a second level of 135 ° C is reached which is maintained for 2 hours. We then reach the third level of 150 ° C with an increase of 50 ° C / h.

After 1 hour of leveling at 150 ° C., ie approximately 6 hours after the end of the introduction of the solution, the analysis of the liquid recycle shows that 92% of the TDM initially present reacted on the catalyst.

Claims

1. A method of in situ sulfurization of a metal hydrotreatment catalyst comprising a step of treating the catalyst with a tertiary mercaptan in the absence of hydrogen, followed in the same reactor by a step of treatment with another agent of sulfurization in the presence of hydrogen.

2. The method of claim 1 wherein the metal catalyst to be sulfurized is a mixture of cobalt and molybdenum oxides, a mixture of nickel and molybdenum oxides or a mixture of nickel and tungsten oxides or any other combination of these oxides, this mixture of oxides being supported by an alumina, a silica or a silica-alumina.

3. Method according to claim 1 or 2 wherein the tertiary mercaptan is tertiododecylmercaptan.

4. Method according to one of claims 1 to 3 wherein the other sulfiding agent is dimethyldisulfide.

5. Method according to one of claims 1 to 4 wherein the first step comprises impregnation of the catalyst with tertiary mercaptan, then thermal activation under an inert atmosphere.

6. The method of claim 5 wherein the thermal activation is carried out at a temperature between 100 and 175 ° C.

7. Method according to one of claims 1 to 6 wherein the second step is carried out in two stages, first at a temperature between 150 and 250 ° C until obtaining a breakthrough of H ₂ S in the outlet gases, then at a temperature between 250 and 350 ° C until a constant concentration of H ₂ S in the outlet gases is obtained. ^•

8. Method according to one of claims 1 to 7 wherein the total amount of sulfur provided by the tertiary mercaptan and the other sulfurizing agent ranges from 100 to 250% of the weight of sulfur stoichiometrically required for the total transformation into sulfides of catalyst oxides.

9. The method of claim 8 wherein the proportion of tertiary mercaptan corresponds to more than 10% by weight of the total sulfur necessary for the sulfurization of the catalyst.

10. Use of a metal catalyst, sulfurized by a process according to one of claims 1 to 9, for the hydrotreatment of hydrocarbon feedstocks.