WO2004000442A1

WO2004000442A1 - Method for elimination of sulphur from a charge comprising hydrogen sulphide, benzene toluene and/or xylenes

Info

Publication number: WO2004000442A1
Application number: PCT/FR2002/001858
Authority: WO
Inventors: Christophe Nedez; Jean-François Chapat; Jean-Louis Ray
Original assignee: Institut Francais Du Petrole
Priority date: 2002-06-03
Filing date: 2002-06-03
Publication date: 2003-12-31
Also published as: AU2002319348A1

Abstract

A method for elimination of sulphur from a charge comprising hydrogen sulphide, sulphur dioxide, carbonyl sulphide, and/or carbon disulphide and a minimum quantity of benzene, toluene, and/or xylenes within at least one reaction zone containing a catalyst with recovery of elemental sulphur and an outlet stream at least partly free of sulphur. Said method is characterised in the use of a catalyst containing a support with at least one compound selected from alumina, titanium oxide and zirconium, said support further comprising at least one doping element selected from the group of iron, cobalt, nickel, copper and vanadium. The above finds application in the Claus process.

Description

PRODUCT FOR REMOVING SULFUR FROM A FILLER CONTAINING HYDROGEN SULFIDE AND BENZENE, TOLUENE AND / OR XYLENES

The invention relates to a process for removing sulfur from a charge containing hydrogen sulphide and minimal traces of benzene, toluene and / or xylenes (BTX). It applies in particular to charges containing for example up to 50,000 ppm (volume) of BTX and preferably between 50 and 5000 ppm.

Natural gas, refinery gases, gases from coal processing, etc. may contain H ₂ S in varying amounts. For environmental and safety reasons, it is often necessary to transform H S into an inert and, moreover, recoverable compound, for example elemental sulfur.

A standard process used industrially is the Claus process. After separation by absorption carried out with amines, a heat treatment is carried out on the so-called acid gas obtained, in the presence of an additional air, at a temperature generally between 900 and 1300 ° C. Reaction (1) is carried out in such a way as to aim, at the end of this treatment, for a molar ratio of 2 between HS and SO ₂ .

H ₂ S + 3/2 O ₂ → H ₂ O + SO ₂ (1)

At the same time, approximately 70% of the sulfur compounds are transformed into elemental sulfur S _x . The presence in the gases to be treated of hydrocarbons and CO ₂ could generate the formation of by-products such as COS and CS ₂ .

During a second step, catalytic thereof, it will be a question of continuing the transformation into sulfur of all of the sulfur compounds present, according to the so-called Claus reaction (2) such as hydrolysis reactions (3) and (4), in reactors placed in cascade, generally 2 or 3.

2 H ₂ S + SO ₂ → 3 / x S _x . + 2 H ₂ O (2)

CS ₂ + 2 H ₂ O → CO ₂ + 2 H ₂ S (3)

COS + H ₂ O → CO ₂ + H ₂ S (4)

A lesser discharge of toxic effluents will thus be directly linked to the use of efficient catalyst (s) for converting H ₂ S, COS and CS ₂ .

The presence of hydrocarbons is sometimes encountered directly in Claus reactors. It can, for example, come from a partial diversion of acid gas towards the inlet, for example example of the first Claus (Ri) catalytic reactor, without therefore passing through the furnace: this scheme is commonly encountered to correctly carry out the treatment of acid gases poor in H ₂ S. The hydrocarbons then present in

result from a mixture but are in particular often found: benzene, toluene, xylenes (hence the acronym BTX).

Those skilled in the art are well aware of this situation and in particular of its harmful consequences on the performance and the lifetime of the Claus catalysts used. By way of illustration, in practical industrial cases, it has already been seen that this lifespan could then be divided by more than ten, compared with a comparable treatment to be carried out in the absence of BTX. The above-mentioned deactivation is caused by a parasitic reaction on the surface of the catalyst used, giving rise to the generation of what the skilled person calls "carsuls". Said carsuls often consist of aromatic and / or polyaromatic compounds containing one or more sulfur atoms.

The object of the present invention relates to at least one catalyst, in particular for treating gases containing H ₂ S and in the application of this catalyst or of an optimized combination of catalysts making it possible to resist very effectively an accelerated aging caused by the presence of hydrocarbons such as BTX. The overall performance of the sulfur recovery process will then be improved compared to that known hitherto.

More specifically, the invention relates to a process for removing at least part of the sulfur from a feed containing hydrogen sulfide, sulfur dioxide, carbon oxysulfide and / or carbon sulfide and a quantity minimal benzene, toluene and / or xylenes in at least one reaction zone containing a catalyst, and elemental sulfur and an effluent are recovered at least partially freed from sulfur, the process being characterized in that the catalyst used is at least one catalyst containing a support comprising at least one compound chosen from the group formed by alumina, titanium oxide and zirconia, the support comprising, in addition at least one doping element chosen from the group formed by iron , cobalt, nickel, copper and vanadium.

The formulations claimed in this particular application correspond to an alumina, titanium oxide or zirconia support modified by one or more doping elements. Doping will be provided by at least one element included in the following list: Fe, Co, Ni, Cu, V. The total mass content of doping element (s) will be included between 0.1 and 60%, preferably between 0.5 and 40%, still preferably between 0.5 and 20%, or even still between 1 and 10% relative to the total catalyst. Iron is the preferred doping element of the invention. The support could also consist of a combination of alumina, titanium oxide and / or zirconia.

According to a particular embodiment of the invention, the doping element may be accompanied by one or more co-dopants. The co-dopant will be an alkali metal, an alkaline earth metal or a rare earth, or a combination of several of these constituents. In this particular case of the invention, the total mass content of co-dopants will be included between 0.5 and 40%, advantageously between 1 and 30, and preferably between 1 and 15% relative to the total catalyst. The most commonly used co-dopant may be calcium, in the sulfate form.

The rare earth is chosen from the group formed by lanthanum, cerium, praseodymium, neodymium, prometheum, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, ryttrium and lutetium. Preferably, lanthanum and cerium can be used.

The catalyst may be in any known form: powder, ball, extruded, monolith, crushed for example. Two preferred forms of the invention are the extruded, whether cylindrical or multi-lobed, and the ball.

In the case of shaping by kneading followed by extrusion, the cross section of the extruded will advantageously be between 0.5 and 8 mm, preferably included between 0.8 and 5 mm.

As regards alumina, the alumina powder used as raw material for preparing the composition according to the invention can be obtained by conventional methods such as the precipitation or gel method, and the method by rapid dehydration of a alumina hydrate such as hydrargillite.

In the case of the use of alumina beads, they can come from a form by coagulation in drops of an aqueous suspension or dispersion of alumina or a solution of a basic salt aluminum in the form of an emulsion consisting of an organic phase, an aqueous phase and a surfactant or an emulsifier.

The alumina in balls can also be obtained by agglomeration of an alumina powder by rotating technology such as, for example, a rotating bezel or a rotating drum.

It will then be possible to obtain balls of controlled porous dimensions and distributions, the whole being generally generated during the agglomeration step.

The alumina extrudates can be obtained by kneading and then extrusion of an alumina-based material, said material possibly being obtained from the rapid dehydration of hydrargillite and / or the precipitation of one or more alumina gels. The alumina can also be put in the form of pellets.

Following its shaping, the alumina can be subjected to various operations in order to improve its mechanical properties, such as ripening by maintaining in an atmosphere at a controlled humidity level followed by calcination then, optionally, d 'Impregnation of the alumina with a solution of one or more mineral and / or organic acids, and hydrothermal treatment in a confined atmosphere. In general, after the treatments undergone, the alumina is dried and calcined.

In the case of shaping by kneading followed by extrusion, the cross section of the extruded will advantageously be between 0.5 and 5 mm, preferably included between 0.7 and 3 mm. In the case of obtaining beads, the diameter of the beads will generally be between 0.8 and 15 mm, advantageously between 1 and 8 mm, and preferably included between 2 and 7 mm.

The deposition of doping or even co-doping elements may be carried out by any method known to those skilled in the art.

It may for example be produced by impregnating the support already prepared with the elements to be added or precursors of these elements (nitrates, sulfates, or carbonates for example), or by mixing the elements or precursors of these elements with the support during or downstream of the shaping of the latter. The deposition of doping or even co-doping elements in the support can also be carried out by co-precipitation.

In the case of a deposition by impregnation, this will be done in a known manner by bringing the support into contact with one or more solutions, one or more soils and / or one or more gels comprising at least one element in the form of oxide or salt or one of their precursors. The operation is generally carried out by soaking the support in a determined volume of solution of at least one precursor of at least one doping or even co-doping element. According to a preferred mode, the addition of the doping or even co-doping elements is carried out by deposition by dry impregnation. According to an alternative mode, it can be produced by excess impregnation, said excess solution then being removed by draining.

The compounds deposited on the support can be chosen from organic compounds, preferably oxalates and formates and / or inorganic. They are preferably chosen from inorganic compounds (sulfates, nitrates, chlorides and oxychlorares for example). The composition used in the process according to the invention is obtained by subjecting the support on which the above-mentioned compound is deposited to a drying and calcination operation. The support, after deposition, can be calcined at a temperature generally greater than 150 ° C., preferably between 250 and 800 ° C. Generally, the calcination temperature, after deposition on the support, does not exceed 1200 ° C.

According to a preferred embodiment of the invention, the catalyst obtained will have a specific surface greater than 10 m 9 / g, advantageously exceeding 30 m 9 / g, for example 50-400 m 9 / g.

The catalyst may completely fill one or more or only part of Claus reactors. In the latter case, it will be located at the top of the reactor, knowing that the supply of gas to be treated to a Claus reactor is traditionally done from top to bottom. More specifically, the reactor can comprise at least one bed containing said catalyst disposed upstream of another catalytic mass called A as a protective layer of said catalytic mass, the volume of the bed representing from 1 to 70% of the volume of the reactor. When the support used as catalytic mass will be titanium oxide, it may advantageously comprise at least one sulphate of an alkaline earth metal chosen from the group consisting of calcium, barium, strontium and magnesium. The preferred alkaline earth of the invention will then be calcium.

According to a variant, the reactor may comprise at least two catalyst beds, in series, of different composition and each of them occupying as protective layer of the mass A an equal or different volume of the reaction zone. According to one characteristic of the invention, the volume of catalyst will represent between 1 and 70% of all the volumes of the catalysts and catalytic mass A placed in the reactors, advantageously between 5 and 60%, and preferably between 10 and 50 %. The objective then will be to serve as a protective layer for the catalytic masses A placed downstream (TiO ₂ for example). It should be noted that the catalyst will also have a performance advantage in conducting reactions (2), (3) and (4) as a complementary advantage.

According to one mode of implementation, the reaction zone can comprise in series an alternation of a bed of catalyst and a bed of catalytic mass A.

According to another preferred embodiment, the reaction zone can comprise in series two reactors, each of them containing a catalyst bed followed by a catalytic mass A bed, a sulfur condensation zone possibly being interposed between the two reactors.

By condensing the sulfur and recovering it, sulfur vapors are avoided in the second reactor which would not fail to disturb the equilibrium of the Claus reaction.

The operating conditions of the process are generally as follows:

VVH (h ^"1 ) = 100 to 3000, preferably 500 to 1500

T ° = 200-380 ° C, preferably 250-300 ° C

P = 0.02 to 0.2 MPa in relative, preferably 0.05 to 0.1 MPa.

The invention is illustrated by the following examples:

EXAMPLES

CR-3S is the trade name for a Claus alumina marketed by Axens. It is in the form of balls with a diameter included between 3.15 and 6.3 mm.

The catalytic mass A is prepared as follows:

To a suspension of titanium oxide obtained by hydrolysis and filtration in the conventional process of sulfuric attack of ilmenite, a suspension of lime is added in order to neutralize all the sulphates present. This done, the suspension is dried at 150 ° C for one hour. The powder is then kneaded in the presence of water and nitric acid. The dough generated is extradited through a die to obtain extradates having a cylindrical shape. After drying at 120 ° C and calcination at 450 ° C, the extrudates have a diameter of 3.5 mm, a specific surface of 116 m ² / g for a total pore volume of 36 ml / 100 g. The TiO _{2 content} is 88% for a CaSO ₄ content of 11%, the loss on ignition completing the balance at 100%. The catalytic mass will be called A. Its mass content of Ca (expressed as Ca) is 3%.

Catalyst B results from a dry impregnation of an aqueous acid solution of iron sulphate on A, followed by drying at 120 ° C. and calcination at 350 ° C. B then displays a mass rate of iron (expressed as Fe) of 2%. B therefore contains iron and calcium.

Catalyst C results from a dry impregnation of an aqueous acid solution of iron sulphate on CR-3S, followed by drying at 120 ° C and calcination at 350 ° C. C ^shows' then a mass content of iron (expressed as Fe) of 4%.

Catalyst D results from a dry impregnation of an aqueous solution of nickel nitrate on CR-3S, followed by drying at 120 ° C and calcination at 350 ° C. D then displays a mass rate of nickel (expressed as Ni) of 4%.

Catalyst E results from a dry impregnation of an aqueous solution of copper nitrate on CR-3S, followed by drying at 120 ° C and calcination at 350 ° C. E then displays a mass content of copper (expressed as Cu) of 6%.

B, C, D and E meet the requirements of the invention.

The catalysts or combinations of catalysts are tested, for 100 hours, under the conditions of the first Claus reactor (Ri), with a charge containing by volume: 4.9% H ₂ S,

3.1% SO ₂ , 0.83% COS, 0.59% CS ₂ , 21.6% CO ₂ , 2.3% CO, 1.3% H ₂ , 22.8% H ₂ O, 200 ppm

O ₂ , N ₂ (qs). Certain experiments are carried out as such, others in the permanent presence, in addition, of 2000 ppm volume of toluene. The space velocity VVH is, in all cases, 1300 h ^-1 , the pressure is close to atmospheric pressure, the temperature is maintained at 270 ° C. The crucial reaction, because the most difficult to carry out, is the hydrolysis reaction of CS ₂ (3) in reactor Ri: it will therefore serve us here as a reference reaction.

The results collected are summarized in Table I where the proportions are given.

(%) by volume of the reactor occupied by the various catalysts as a protective layer then the proportions by volume of the reactor occupied by the catalytic mass. In the absence of BTX, a reactor filled with 100% catalytic mass A will display the best performance, in sulfur recovery. On the other hand, under conditions of possible formation of carsuls (therefore here in the presence of toluene), A is the worst of the solutions tested, due to rapid deactivation. Conversely, the arrangements according to the invention (application of B, C, D and E as a protective layer of A) provide clearly superior results, where the protection of A by an alumina seems ineffective. Catalyst B ′ contains as support pure titanium oxide resulting from a hydrolysis of titanium alkoxide then from a kneading followed by an extrusion, drying at 120 ° C. and calcination at 450 ° C.

Table I.

Catalysts Toluene free toluene

1% 2000 ppm

100% A 82% 44%

20% CR-3S then 80% A 74%

40% B then 60% A 65%

100% to 20%

100% B 70%

30% C then 70% A 74% 70%

30% D then 70% A 64%

25% C then 75% A 69%

25% E then 75% A 74% 65%

40% B then 60% A 77% 72%

40% B 'then 60% A 67%

20% B then 10% E then 70% A 77% 71%

Other examples:

- Catalysts doped with cobalt or vanadium:

The preparation of catalyst D was resumed, but instead of introducing nickel nitrate, cobalt nitrate or vanadium nitrate was introduced to obtain respectively a catalyst doped with cobalt and a catalyst doped with vanadium. These two catalysts give substantially the same result as catalyst D doped with nickel, when used as a protective layer for the titanium catalytic mass A, this protective layer occupying 30% of the volume of the reactor.

- Influence of the zirconia support in the catalyst:

Hydrated zirconium oxide is obtained by treatment with sodium hydroxide and then washing with nitric acid and with basic zirconium sulphate water, in the following proportions: 75% powder, 10% nitric acid and 15 % water. Said powder is then kneaded for one hour and then extruded. The extrudates are then dried at 120 ° C for 2 hours and then calcined at 450 ° C for two hours. The catalyst obtained has a diameter of 3.5 mm, for a specific surface of 91 m ² / g and a total pore volume of 34 ml / 100 g. An Fe / ZrO ₂ catalyst is prepared by dry impregnation of an aqueous acid solution of iron sulphate on the zirconia previously synthesized, followed by drying at 120 ° C and calcination at 350 ° C. The catalyst then displays a mass rate of iron (expressed as Fe) of 4%.

The sequence: 30% of the volume of the reactor containing 4% Fe / ZrO ₂ then 70% of the volume of reactor containing A will lead, under the experimental conditions presented, in the presence of 2000 ppm of toluene, to a conversion of 76% of CS ₂ , after 100 hours of reaction.

- Influence of zirconia as a catalytic mass:

Zirconia previously synthesized with or without calcium sulphate is placed as a catalytic mass in the Claus reactor according to the following sequence: 30% of the volume of the reactor containing the catalyst C (Al ₂ O ₃ - 4% Fe) then 70% the volume of the reactor containing the catalytic mass with zirconia, which leads to a conversion of 78% of CS in the presence of 2000 ppm of toluene, under the same experimental conditions as those of the previous examples.

Claims

1. Process for removing sulfur from a charge containing hydrogen sulfide, sulfur dioxide, carbon oxysulfide and / or carbon sulfide and a minimal amount of benzene, toluene and / or of xylenes in at least one reaction zone containing a catalyst, and elemental sulfur and an effluent at least partially freed of sulfur are recovered, the process being characterized in that at least one catalyst containing a support comprising at least one catalyst is used at least one compound chosen from the group formed by alumina, titanium oxide and zirconia, the support further comprising at least one doping element chosen from the group formed by iron, cobalt, nickel, copper and vanadium.

2. The method of claim 1, wherein the support further comprises at least one co-doping element selected from the group formed by an alkali metal, an alkaline earth metal and a rare earth.

3. Method according to one of claims 1 and 2, wherein the doping element of the support, alone or as a mixture, has a metal oxide content expressed in percent by mass of said metal of between 0.1 and 60% of the total catalyst mass.

4. Method according to one of claims 1 to 3, wherein the co-doping element, alone or in mixture has a mass content representing 0.5 to 40% of the mass of total catalyst.

5. Method according to one of claims 1 to 4, in which the operating conditions are as follows:

Temperature: 200 - 380 ° C, preferably 250 - 300 ° C

Pressure: 0.02 to 0.2 MPa in relative, preferably 0.05 to 0.1 MPa

VVH (h-l): 100 - 3000, preferably 500 to 1500

6. Method according to one of claims 1 to 5, wherein the reaction zone comprises at least one bed containing said catalyst disposed upstream of another catalytic mass as a protective layer of said catalytic mass, the volume of the bed representing from 1 to 70% of the volume of the reaction zone.

7. Method according to one of claims 1 to 6, wherein the reaction zone comprises at least two catalyst beds, in series, of different composition and each of them occupying an equal or different volume of the reaction zone.

8. Method according to one of claims 1 to 7 wherein the catalyst is in the form of powder, beads, extruded, monolith or crushed, preferably in the form of beads or extruded.

9. Method according to one of claims 6 to 8, wherein the catalytic mass is titanium oxide comprising a calcium salt of the reaction zone, the mass being arranged in the downstream part.

10. Method according to one of claims 6 to 8, wherein the reaction zone comprises in series an alternation of a catalyst bed and a bed of catalytic mass A.

11. Method according to one of claims 6 to 8, in which the reaction zone comprises in series two reactors, each of them containing a bed of catalyst followed by a bed of catalytic mass A, a sulfur condensation zone being possibly interposed between the two reactors.