Method for activating hydrotreating catalysts

Abstract

The present invention relates to the use, in a method for in-situ activation of at least one hydrotreating, in particular hydrocracking, catalyst, of at least one nitrogen compound having at least one of the following characteristics: a) a nitrogen content by weight in the range from 15 to 35 wt %, relative to the total weight of the nitrogen compound; b) a number of nitrogen atoms in the range from 2 to 20; c) a boiling point in the range from 140° C. to 300° C.; and d) said nitrogen compound being in liquid form at room temperature and atmospheric pressure. The present invention also relates to the method for in-situ activation of at least one hydrotreating catalyst comprising at least one step of sulphiding said hydrotreating catalyst in the presence of a sulphiding agent, and a step of passivation of said hydrotreating catalyst in the presence of said at least one nitrogen compound.

Claims

1. A method for in-situ activation of a hydrotreating catalyst by in situ loading, passivation and sulphiding of the hydrotreating catalyst, the method comprising: loading at least one hydrotreating catalyst in at least one hydrotreating reactor; passivating acid sites of the hydrotreating catalyst in the hydrotreating reactor by contacting the hydrotreating catalyst with an effective amount of at least one nitrogen compound at a temperature of 120° C. to 300° C., where the nitrogen compound is selected from the group consisting of N,N′-diethyl-1,3-propanediamine (DEAPA), tetramethyl-1,3-propanediamine (TMPDA), N-methyl-1,3-propanediamine, N,N′-dibutyl-1,3-propanediamine, N-(3-dimethylaminopropyl)propane-1,3-diamine (DMAPAPA), N-(3-aminopropyl)-1,3-propanediamine, N,N′-1,2-ethanediyl-bis-1,3-propanediamine, N-(aminopropyl)diethanolamine (APDEA), and mixtures thereof; and sulphiding the hydrotreating catalyst in the hydrotreating reactor by contacting the hydrotreating catalyst with an effective amount of a sulphiding agent to provide the in-situ activated hydrotreating catalyst.

2. The method of claim 1, wherein the nitrogen compound is selected from the group consisting of N,N′-diethyl-1,3-propanediamine (DEAPA), tetramethyl-1,3-propanediamine (TMPDA), and mixtures thereof.

3. The method of claim 1, wherein the nitrogen compound comprises N,N′-diethyl-1,3-propanediamine (DEAPA).

4. The method of claim 1, wherein the hydrotreating catalyst is a hydrocracking catalyst.

5. The method of claim 1, wherein the nitrogen compound is introduced into the hydrotreating reactor after the loading step and before the passivation step in a liquid phase or in a gas phase.

6. The method of claim 5, wherein the nitrogen compound is present in an amount ranging from 0.01 to 20 wt %, relative to the total weight of the hydrotreating catalyst.

7. The method of claim 1, wherein the sulphiding agent is selected from the group consisting of hydrogen sulphide, carbon disulphide, dimethyl disulphide (DMDS), dimethyl sulphide, mercaptans, thiophenes and derivatives, alkyl polysulphides, dialkyl polysulphides, and all sulphide compounds capable of sulphiding metal oxides of the hydrotreating catalyst.

8. The method of claim 1, wherein the sulphiding agent is introduced into the hydrotreating reactor in a liquid phase or in a gas phase after the loading step and before the sulphiding step.

9. The method of claim 1, wherein the nitrogen compound and the sulphiding agent are simultaneously introduced into the hydrotreating reactor in a liquid phase or in a gas phase after the loading step and before the passivation step and the sulphiding step.

10. The method of claim 1, wherein the nitrogen compound is introduced into the hydrotreating reactor in a liquid phase or in a gas phase after the loading step and before the passivation step and the sulphiding agent is introduced into the hydrotreating reactor in a liquid phase or in a gas phase after the loading step and before the sulphiding step.

11. The method of claim 5, wherein the nitrogen compound is introduced into the hydrotreating reactor in a liquid phase.

12. The method of claim 8, wherein the sulphiding agent is introduced into the hydrotreating reactor in a liquid phase.

13. The method of claim 10, wherein the nitrogen compound and the sulphiding agent are each introduced into the hydrotreating reactor in a liquid phase.

14. The method of claim 1, further comprising drying the hydrotreating catalyst directly after the loading step at a temperature between 120° C. and 200° C.

15. The method of claim 12, wherein the sulphiding agent is introduced into the hydrotreating reactor at a temperature ranging from 120° C. to 350° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) According to a first aspect, the present invention relates to the use, in a method for in-situ activation of at least one hydrotreating, in particular hydrocracking, catalyst, of at least one nitrogen compound having at least one, preferably at least two, more preferably at least three, even more preferably at least four of the characteristics as defined above.

(2) By using a nitrogen compound according to the invention it is possible to obtain at least one, and advantageously several, of the following advantages: the hydrotreating, in particular hydrocracking, activity of the hydrotreating, in particular hydrocracking, catalyst is inhibited throughout the operation of sulphiding of the latter; the hydrotreating, in particular hydrocracking, activity of the catalyst during the hydrotreating, in particular hydrocracking, operation is not diminished due to the action of the nitrogen compound of the invention during the operation of sulphiding of the catalyst; the use of a nitrogen compound according to the invention is facilitated: compared to the known nitrogen compounds generating less ammonia, the nitrogen compounds of the invention do not require heavy equipment for injection; the risks of exposure of the operator handling the nitrogen compound of the invention are reduced, relative to the known solutions such as those that employ aniline; advantageously, the nitrogen compound according to the invention is not CMR (carcinogenic, mutagenic, reprotoxic) according to the European CLP regulations.

(3) As stated above, the nitrogen compound of the invention has at least one, preferably at least two, more preferably at least three, even more preferably at least four of the characteristics a), b), c), d) defined above. All combinations are conceivable, for example: ab, abc, ac, acd, ad, abd, bc, bcd, cd, bd, and abcd.

(4) According to one embodiment, furthermore the nitrogen compound according to the invention has a molecular weight in the range from 80 g.Math.mol.sup.−1 to 300 g.Math.mol.sup.−1, preferably in the range from 100 g.Math.mol.sup.−1 to 250 g.Math.mol.sup.−1, even more preferably in the range from 100 g.Math.mol.sup.−1 to 200 g.Math.mol.sup.−1, advantageously in the range from 120 g.Math.mol.sup.−1 to 150 g.Math.mol.sup.−1; designated as characteristic e) hereinafter.

(5) According to this embodiment, the nitrogen compound has, besides characteristic e), at least one, preferably at least two, more preferably at least three, even more preferably at least four of the characteristics a), b), c), d) defined above. All combinations are conceivable, for example: ae, abe, abce, ace, acde, ade, abde, be, bce, ade, bcde, cde, de, and abcde.

(6) Advantageously, the nitrogen compounds according to the invention are selected from the nitrogen compounds comprising 2 to 20 nitrogen atoms; notably, the polyamines; the AAAs; and mixtures thereof. For example, the diamines, the triamines, and others. Preferably, the nitrogen compounds according to the invention do not comprise the compounds derived from urea as well as the nitrated, nitrous or nitroso compounds.

(7) According to another preferred embodiment, the nitrogen compounds of the invention do not contain a functional group containing an oxygen atom, such as the hydroxyl, carboxyl, carbonyl or alkoxy group.

(8) According to one embodiment, the nitrogen compound of the invention does not comprise an aromatic or cyclic group; designated as characteristic f) hereinafter.

(9) According to this embodiment, the nitrogen compound has, besides characteristic f), at least one, preferably at least two, preferably at least three, preferably at least four, more preferably at least five of the characteristics a), b), c), d), e) defined above. All combinations are conceivable, for example: af, abf, abcf, abcdf, acf, acdf, acdef, adf, adef, aef, abef, abdef, acef, abef, bf, bcf, bcdf, bcdef, bdf, bdef, bef, bcef, cf, cdf, cdef, cdf, df, def, and abcdef.

(10) According to a preferred embodiment, characteristic b) is particularly preferred. Thus, in a preferred embodiment, said at least one nitrogen compound has imperatively characteristic b), i.e. said at least one nitrogen compound has a number of nitrogen atoms in the range from 2 to 20, preferably in the range from 2 to 15, more preferably in the range from 2 to 10, even more preferably in the range from 2 to 5, per molecule, advantageously two nitrogen atoms per molecule.

(11) According to a preferred embodiment, said at least one nitrogen compound has characteristic b) and at least one, preferably at least two, more preferably at least three, characteristics a), c), d) defined above, as well as optionally in addition characteristic e) and/or characteristic f).

(12) Examples of nitrogen compounds that may be used in the present invention are: N,N′-diethyl-1,3-propanediamine (DEAPA) (T.sub.m=−50° C.), tetramethyl-1,3-propanediamine (TMPDA) (T.sub.m=−82° C.), N-methyl-1,3-propanediamine (T.sub.m=−72° C.), N,N′-dibutyl-1,3-propanediamine (T.sub.m=−50° C.), N-(3-dimethylaminopropyl)propane-1,3-diamine (DMAPAPA) (T.sub.m=−60° C.), N-(3-aminopropyl)-1,3-propanediamine (T.sub.m=−16° C.), N,N′-1,2-ethanediyl-bis-1,3-propanediamine (T.sub.m=−1.5° C.), N-(aminopropyl)diethanolamine (APDEA) (T.sub.m=−20° C.), and mixtures thereof.

(13) Preferably, the nitrogen compounds are the alkylamines selected from N,N′-diethyl-1,3-propanediamine (DEAPA), tetramethyl-1,3-propanediamine (TMPDA), N-methyl-1,3-propanediamine, N,N′-dibutyl-1,3-propanediamine, N-(3-dimethylaminopropyl)propane-1,3-diamine (DMAPAPA), N-(3-aminopropyl)-1,3-propanediamine, N,N′-1,2-ethanediyl-bis-1,3-propanediamine, and mixtures thereof.

(14) More preferably, the nitrogen compounds are selected from N,N′-diethyl-1,3-propanediamine (DEAPA) and tetramethyl-1,3-propanediamine (TMPDA), and the mixture of DEAPA and TMPDA.

(15) According to one embodiment, a mixture of at least two nitrogen compounds is used. In the mixture of two nitrogen compounds, the nitrogen content by weight in the mixture is equivalent to the content of a single nitrogen compound as defined above. In other words, this content is from 15 to 35 wt %, preferably from 20 to 35%, more preferably from 20 to 30%, and more advantageously from 20 to 25% relative to the total weight of the mixture of nitrogen compounds.

(16) More precisely, the following equations can be used for determining the relative amounts of nitrogen compounds to be used so that the nitrogen content by weight of the mixture complies with the invention. For a mixture of two nitrogen compounds A.sub.1 and A.sub.2, their relative amounts Q.sub.A1 and Q.sub.A2 are expressed as follows:

(17) $Q_{A1}=\frac{\left(\%N_{A1+A2}-\%N_{A2}\right)}{\left(\%N_{A1}-\%N_{A2}\right)}\times 100\mathrm{and}{Q}_{A2}=100-Q_{A1}$

(18) In these equations: A.sub.1 and A.sub.2 represent two nitrogen compounds, which may be identical or different; Q.sub.A1 represents the amount of the nitrogen compound A.sub.1, expressed in wt % relative to the total weight of the mixture of the nitrogen compounds; Q.sub.A2 represents the amount of the nitrogen compound A.sub.2, expressed by weight relative to the total weight of the mixture of the nitrogen compounds; % N.sub.A1 represents the nitrogen content by weight in the nitrogen compound A.sub.1, expressed in wt % relative to the weight of the nitrogen compound A.sub.1; % N.sub.A2 represents the nitrogen content by weight in the nitrogen compound A.sub.2, expressed in wt % relative to the weight of the nitrogen compound A.sub.2; and % N.sub.A1+A2 represents the nitrogen content by weight of the mixture of the two nitrogen compounds A.sub.1 and A.sub.2 according to the invention, expressed in wt % relative to the weight of the mixture.

(19) For example, if the nitrogen content by weight in the nitrogen compound A.sub.1 is % N.sub.A1=15%, that in the nitrogen compound A.sub.2 is % N.sub.A2=30% and if, according to the present invention, the target nitrogen content by weight for the mixture of A.sub.1+A.sub.2 is % N.sub.A1+A2=20%, then the relative amount of the nitrogen compound A.sub.1 to be used in the mixture is equal to Q.sub.A1=66.67 wt % relative to the total weight of the mixture of the nitrogen compounds and the relative amount of the nitrogen compound A.sub.2 to be used in the mixture is Q.sub.A2=33.33 wt % relative to the total weight of the mixture of the nitrogen compounds.

(20) When the mixture comprises at least three, at least four, at least five or more than five nitrogen compounds according to the invention, equations similar to the above may be established in order to determine the relative amounts of the nitrogen compounds to be used so that the nitrogen content by weight of the mixture complies with the invention.

(21) As stated above, the present invention finally relates to a method for in-situ activation of at least one hydrotreating, in particular hydrocracking, catalyst.

(22) Advantageously, said method for in-situ activation of at least one hydrotreating, in particular hydrocracking, catalyst consists of: 1) a step of sulphiding said hydrotreating, in particular hydrocracking, catalyst, in the presence of a sulphiding agent; and 2) a step of passivation of said hydrotreating catalyst, in particular of said hydrocracking catalyst, in the presence of at least one nitrogen compound as defined above.

(23) The contacting of the hydrotreating catalyst, in particular of the hydrocracking catalyst, with the nitrogen compound of the invention during said passivation step may be carried out by any method known by a person skilled in the art, in particular by liquid-phase or gas-phase injection of the nitrogen compound of the invention into the reactor comprising at least one hydrotreating catalyst, in particular at least one hydrocracking catalyst. If gas-phase injection is employed, the nitrogen compound is vaporized during injection or before injection. Preferably, liquid-phase injection is employed.

(24) Injection of the nitrogen compound of the invention may be carried out by any means known by a person skilled in the art such as a metering pump, an injection pump, or a feed pump.

(25) The passivation step is advantageously carried out at a temperature in the range from 120 to 350° C.

(26) The passivation step is advantageously carried out under a hydrogen atmosphere. The hydrogen pressure corresponds to the usual operating pressure of hydrotreating, in particular hydrocracking, reactors. It is preferably in the range from 1 bar to 200 bar (or from 1.Math.10.sup.5 Pa to 200.Math.10.sup.5 Pa), preferably from 15 bar to 100 bar (or from 15.Math.10.sup.5 Pa to 100.Math.10.sup.5 Pa).

(27) During the passivation step, the nitrogen compound is advantageously injected at a content in the range from 0.01 to 20 wt %, preferably from 0.01 to 10 wt %, more preferably from 0.01 to 5 wt % relative to the total weight of the hydrotreating, in particular hydrocracking, catalyst.

(28) During the passivation step, the content of the nitrogen compound is advantageously adjusted so that the ammonia content generated is from 0.01 to 40 wt %, preferably from 0.01 to 20 wt %, more preferably from 0.01 to 10 wt %, even more preferably from 0.01 to 5% relative to the total weight of the hydrotreating catalyst, in particular of the hydrocracking catalyst.

(29) The hydrotreating, in particular hydrocracking, catalyst employed in the present invention is preferably bifunctional, having an acid function and a hydrogenating function. This type of catalyst, known by a person skilled in the art, is generally in the form of a supported metal. The acid function is supplied by the support (for example alumina or amorphous and/or crystalline silico-aluminate) or by halogenated dopants, such as fluorine for example, and the hydrogenating function is supplied by metal oxides or metal sulphides, made operational by the sulphiding step.

(30) According to one embodiment, the supports are generally porous refractory oxides. The porous refractory oxides are preferably selected from zeolites, alumina, silica, zirconia, and the beryllium, chromium, titanium, magnesium and thorium oxides, as well as combinations thereof, such as silico-aluminates and silica-titanium oxide.

(31) The supports most used in the field of hydrotreating, in particular hydrocracking, are the crystalline silico-aluminates, called zeolites. The zeolites employed possess exchangeable cations, generally metal cations or hydronium ions, preferably hydronium ions.

(32) The zeolites are preferably selected from the natural zeolites, for example ferrierite, the artificial and synthetic zeolites such as, non-exhaustively, the zeolites ZSM, for example ZSM-22, ZSM-23, ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and their analogues, the zeolites SAPO, for example SAPO-11, SAPO-31; zeolites beta and zeolites Y.

(33) The porous refractory oxides may also optionally be combined with zeolites, for example the combinations of zeolites with a silica, a zirconia or an alumina.

(34) The hydrotreating, in particular hydrocracking, catalyst used in the invention preferably comprises transition metals selected from columns 5, 6, 8, 9 and 10 of the periodic table of the elements of the IUPAC.

(35) Preferably, the hydrotreating, in particular hydrocracking, catalyst comprises one or more transition metals selected from vanadium, niobium, tantalum, chromium, molybdenum, tungsten, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum and mixtures of two or more of them in all proportions.

(36) The preferred combinations of metals are: nickel-tungsten, cobalt-molybdenum, nickel-vanadium, nickel-molybdenum, molybdenum-tungsten and nickel-cobalt. In particular, the nickel/tungsten catalyst has excellent isomerization and dearomatization properties, while displaying the capacity for performing reactions of hydrodeoxygenation and other hydrotreating reactions, especially hydrocracking of organic raw materials, whether they are of fossil origin (hydrocarbons derived from petroleum) or of animal or vegetable origin.

(37) These metals are generally on a support as defined above. For the nickel/tungsten catalysts, the silico-aluminate and silica-titanium oxide supports are quite particularly suitable. These metals are in oxidized form on a support such as an alumina or an amorphous or crystalline silico-aluminate. Preferably, the metal oxides are on a zeolitic support.

(38) The catalysts are, as nonlimiting examples, Pt/SAPO-11/Al.sub.2O.sub.3, Pt/ZSM-22/Al.sub.2O.sub.3, Pt/ZSM-23/Al.sub.2O.sub.3, NiW/Al.sub.2O.sub.3, NiW/zeolite/Al.sub.2O.sub.3 and Pt/SAPO-11/SiO.sub.2. Preferably, the hydrotreating, in particular hydrocracking, catalyst is selected from NiW/Al.sub.2O.sub.3 and NiW/zeolite/Al.sub.2O.sub.3.

(39) It is particularly advisable to use, jointly or mixed, hydrotreating catalysts with hydrodeoxygenation catalysts, since they both require a sulphiding step. Thus, hydrodenitrogenation, hydrodesulfurization, dearomatization, hydroconversion, hydrogenation, hydroisomerization, hydrodeoxygenation, dearomatization and hydrocracking may take place simultaneously, sequentially or alternately.

(40) The method for in-situ activation of the hydrotreating, in particular hydrocracking, catalysts according to the invention comprises at least one sulphiding step, in which a sulphiding agent is introduced into the hydrotreating, in particular hydrocracking, reactor.

(41) Advantageously, the sulphiding agent is selected from hydrogen sulphide, carbon disulphide, dimethyl disulphide (DMDS), dimethyl sulphide, mercaptans, thiophenes and derivatives, alkyl polysulphides, dialkyl polysulphides and all sulphide compounds capable of sulphiding the metal oxides of the hydrotreating, in particular hydrocracking, catalysts. Preferably, the sulphiding agent is DMDS, notably marketed by the company ARKEMA, for example under the trade names DMDS Evolution® and DMDS Evolution® E2.

(42) The sulphiding step may be carried out either in the gas phase or in the liquid phase. Preferably, the sulphiding step is carried out in the liquid phase by contacting a liquid feed comprising a light cut such as kerosene or gas oil at temperatures between 120 and 350° C. at a hydrogen pressure in the range from 1 bar to 200 bar (or from 1.Math.10.sup.5 Pa to 200.Math.10.sup.5 Pa). Preferably, the hydrogen pressure is in the range from 15 bar to 100 bar (or from 15.Math.10.sup.5 Pa to 100.Math.10.sup.5 Pa).

(43) More particularly, during the method for in-situ activation of the hydrotreating catalysts, in particular hydrocracking catalysts according to the invention, after loading at least one hydrotreating, in particular hydrocracking, catalyst, in one or more hydrotreating, in particular hydrocracking, reactors, the liquid feed is then injected at temperatures preferably from 120° C. to 350° C. The liquid feed has a sulphide content preferably between 0.01 and 20 wt % and preferably from 0.01 to 5 wt % relative to the total weight of the feed.

(44) According to one embodiment, after loading the catalyst, and an optional step of drying between 120° C. and 200° C. with nitrogen or hydrogen to remove the water adsorbed during the loading operation, the pressure of the unit is brought to the pressure corresponding to the usual operating pressure of said unit, preferably between 1 bar and 200 bar (or between 1.Math.10.sup.5 Pa and 200.Math.10.sup.5 Pa), more preferably between 15 bar and 100 bar (or between 15.Math.10.sup.5 Pa and 100.Math.10.sup.5 Pa). The temperature of the catalytic reactors is then increased in successive stages from 200° C. to 350° C. for carrying out the reactions of sulphiding and of passivation of the hydrotreating, in particular hydrocracking, catalysts.

(45) In the course of the sulphiding step, the sulphiding agent is injected into the liquid feed or the hydrogen that is supplied to the hydrotreating, in particular hydrocracking, reactors, according to any means known by a person skilled in the art, such as a piston-type metering pump, a multi-stage positive-displacement pump, or any other pumping system providing control of the injection flow rate.

(46) According to a preferred embodiment, the sulphiding step and the passivation step are carried out simultaneously. In this embodiment, the sulphiding agent and the nitrogen compound are injected into the hydrotreating, in particular hydrocracking, reactor or reactors simultaneously. Mixtures comprising at least one sulphiding agent and at least one nitrogen compound as defined above are also included.

(47) According to another embodiment, the sulphiding step and the step of passivation of the acid sites of the catalysts are carried out intermittently, i.e. in the hydrotreating, in particular hydrocracking, reactor or reactors, the sulphiding agent is injected and then at least one nitrogen compound according to the invention, or vice versa, and this operation is repeated one or more times.

(48) According to one embodiment, after activation of the hydrotreating catalyst(s), the temperature is gradually increased in the hydrotreating reactor, to reach the usual operating temperature of the hydrotreating reactors, in so-called production mode, for example between 350° C. and 450° C. The compounds to be hydrotreated may be introduced into the hydrotreating reactor under hydrogen pressure for example in the range from 50 bar to 200 bar (or from 50.Math.10.sup.5 Pa to 200.Math.10.sup.5 Pa). The hydrogen present desorbs the ammonia from the hydrotreating catalyst, thus allowing the catalyst to regain all its hydrotreating activity for transforming the compounds derived from biomass. Advantageously, desorption is gradual, which makes it possible to control the exothermic nature of the hydrotreating reaction.

(49) According to one embodiment, after activation of the hydrocracking catalyst(s), the temperature is gradually increased in the hydrocracking reactor, to reach the usual operating temperature of the hydrocracking reactors, in so-called production mode, preferably between 350° C. and 450° C. The fractions with heavy hydrocarbon chains to be cracked are introduced into the hydrocracking reactor under hydrogen pressure in the range from 50 bar to 200 bar (or from 50.Math.10.sup.5 Pa to 200.Math.10.sup.5 Pa). The hydrogen present desorbs the ammonia from the hydrocracking catalyst, thus allowing the catalyst to regain all its hydrocracking activity for converting the heavy fraction. Advantageously, desorption is gradual, which makes it possible to control the exothermic nature of the hydrocracking reaction.

(50) The invention will be understood more clearly in the light of the non-limiting examples that follow, which are given for purely illustrative purposes and are not intended to limit the scope of the invention, defined by the attached claims.

EXAMPLE

(51) The objective of this test is to compare the decomposition of amines to ammonia, on hydrotreating catalysts. The comparison is carried out between the amines according to the invention, and the amines already described in the prior art and known in the market as tri-n-butylamine and aniline. The catalyst used for this test contains 17% by weight of molybdenum oxide and 3.5% by weight of nickel oxide supported on a y alumina. The DMDS (dimethyl disulphide) and DEAPA (diethylaminopropylamine) used in this test are supplied by the company ARKEMA. The conversion of the amines to ammonia is obtained at the outlet of the reactor containing this catalyst. The catalyst must be activated by a “sulphurization” treatment which converts the nickel and molybdenum metal oxides into corresponding metal sulphides. A solution of dimethyl disulphide diluted to 1.5% by weight in dodecane is used as follows: 4 ml of catalyst are placed in a catalytic reactor and dried at 150° C. for 1 hour under nitrogen (10 NL/h) at 0.5 MPa, then the nitrogen is replaced with 1 NL/h of hydrogen and the pressure in the reactor is brought to 6 MPa. 4 ml/h of DMDS-doped dodecane (1.5% by weight) are introduced into the entering stream of hydrogen and the temperature of the reactor is brought to 230° C. according to a temperature ramp of 25° C./h, and then stabilized at this temperature for 6 hours, said duration being sufficient to observe a concentration of hydrogen sulphide in the hydrogen at the reactor outlet of greater than 0.5 mol %. This hydrogen sulphide concentration was measured on-line by gas chromatography. The temperature of the reactor is then increased to 350° C. according to a ramp of 25° C./h and then kept at this temperature for at least 10 hours. The catalyst thus activated is then brought into contact with various solutions of amines diluted in dodecane. The ammonia concentration in the hydrogen at the outlet is measured using the same gas chromatography apparatus. The test conditions were the following: Flowrate of amine-doped dodecane (0.5% by weight of nitrogen): 4 ml/h Hydrogen pressure: 6 MPa Flowrate of hydrogen: 1 NL/h. The temperature of the catalytic reactor was adjusted to between 200 and 300° C. in successive steps so as to determine the temperature required for the formation of 50% of the expected ammonia corresponding to 50% conversion of the amine into ammonia. Depending on the amine used, the following temperature values were obtained: Aniline: 256° C. Tri-n-butylamine: 254° C. Diethylaminopropylamine: 245° C. These tests show the formation of ammonia at a lower temperature by virtue of the amines of the invention, compared with the amines used in the prior art. The amine corresponding to the criteria of the invention has a greater tendency to form ammonia on contact with a nickel-based and molybdenum-based catalyst, compared with the amines normally used in the prior art.