CN1072605C - Method and catalyst for catalytically oxidising a low concentration of H2S in a gas to give sulphur - Google Patents

Abstract

The present invention relates to a method for oxidizing H2S in a technical gas into sulfur and causing the sulfur to mutually contact at least one type of metal, particularly to a transition metal compound or an oxidation catalyst composed of corresponding elemental metal and a silicon carbide carrier at a determined temperature according to the implementation scheme, wherein the temperature can be above or below the dew-point of the generated sulfur. The method is suitable for removing H2S in various gases, and particularly recovering H2S in the form of sulfur.

Description

Method for catalytic oxidation of low-concentration hydrogen sulfide in gas to sulfur

The present invention relates to a process for the direct oxidation of low concentrations of hydrogen sulphide in a gas to sulphur by a catalytic procedure. Also relates to a catalyst for use in the process.

For recovering low-concentration H in gas from various sources₂S, i.e. a concentration of less than 20 (V)%, in particular between 0.001 and 20%, more in particular between 0.001 and 10% (V)%, can be determined according to the reaction scheme

And utilizing includes converting H₂A process for the direct catalytic oxidation of S to sulfur.

In such processes, the H-containing material being treated₂Mixing S gas with appropriate amount of free oxygen-containing gas (such as oxygen, air or oxygen-enriched air), and mixing H₂S is oxidized to sulfur. The contact temperature is about above the dew point temperature for sulfur formation (where oxidation occurs in the vapor phase) or below the dew point temperature for sulfur formation (where the sulfur deposits on the catalyst and requires purging with a non-oxidizing gas at a temperature between 200 ℃ and 500 ℃ over a time interval to regenerate the sulfur-laden catalyst).

Especially above the dew point of sulfur₂Oxidation of S to sulphur, i.e. at ｃA temperature above about 180 ℃ with ｃA catalyst consisting of titanium oxide (EP-A-0078690), with ｃA catalyst consisting of titanium oxide containing alkaline earth metal sulphates (WO-A-8302068), with ｃA catalyst consisting of titanium oxide containing nickel oxide and optionally aluminｃA (EP-A-0140045), with ｃA compound of an oxide of the titanium oxide, zirconium oxide or silicｃA type with one or more elements selected from the group consisting of the transition metals Fe, Cu, Zn, Cd, Cr, Mo, W, Co, Ni and preferably FeThe catalyst may be contacted with A catalyst consisting of one or more noble metal compounds selected from the group consisting of Pd, Pt, Ir and Rh, preferably Pd (FR-A-2511663), or with A thermally stable aluminA in combination with one or more compounds of the above-mentioned transition metals, preferably Fe, and also in combination with one or more noble metal compounds selected from the group consisting of Pd, Pt, Ir and Rh (FR-A-2540092).

H is reacted at a temperature at which the sulphur formed is deposited on the catalyst₂The oxidation of S to sulphur can be carried out in contact with A catalyst consisting, for example, of one or more salts, oxides or sulphides of transition metals chosen from Fe, Cu, Cr, Mo, W, V, Co, Ni, Ag and Mn, combined with A support of the activated aluminA, bauxite, silicA/aluminA or zeolite type (FR-A-2277877). This H, which is accompanied by the deposition of sulfur on the catalyst₂The oxidation reaction of S can also be carried out by contact with a catalyst consisting of a catalytic phase of oxides, salts or sulfides of metals V, Mo, W, Ni and Co with an activated carbon support (french patent application No.9302996,1993, 3, 16).

Catalysts such as the above-mentioned ones consist of a catalyst phase based on at least one transition metal oxide salt or sulfide, which is used in combination with a support consisting of at least one material selected from the group consisting of alumina, titania, zirconia, silica, zeolites, silica/alumina mixtures, silica/titania mixtures and activated carbon, which is used for the hydrogenation of H₂The catalytic oxidation of S to sulfur still presents certain disadvantages under conditions of extended service life. In particular, catalysts in which the support is based on alumina can change with an increase in the sulfiding time. With regard to the catalyst in which the carrier is composed of activated carbon, care must be taken not to burn the carrier. Furthermore, for these different catalysts, the catalytic phase of the impregnated support tends to migrate into the support lattice, making it difficult or even impossible to recover the catalyst phase from the spent catalyst. Finally, the catalysts have poor thermal conductivity, which makes it impossible to effectively control the catalyst bed temperature by heat exchange with a coolant.

It has been found that the above-mentioned use for the hydrogenation of H can be overcome by making the catalyst support from silicon carbide₂The catalyst for the oxidation of S to sulfur has the disadvantage of obtaining a process for maintaining a high selectivity for sulfur for a long period of time.

Silicon carbide supports differ from alumina supports in that no sulfidation reaction occurs and from activated carbon in that they are non-combustible. Furthermore, one has not observed the completion of the migration of the catalytic phase into the crystal lattice of the silicon carbide support, so that the metal recovered from the catalytic phase after deactivation of the catalyst is possible, which is particularly important in the case of catalytic phases containing harmful substances such as nickel compounds. Finally, the silicon carbide support has good thermal conductivity, especially for catalysts used to cool the catalyst bed, which enables a flatter temperature front to form within the catalyst bed and thus exhibits better selectivity for sulfur.

The subject of the invention is therefore the use of a catalytic route for the presence of H at low concentrations in gases₂SProcess for the direct oxidation to sulfur, wherein said hydrogen contains₂S gas and free oxygen-containing gas with O₂∶H₂S is in a molar ratio of 0.05 to 10 with respect to the amount of H₂S is selectively oxidized to sulphur, comprising a catalytically active phase for combination with a support, said active phase comprising at least one metal present in the metallic and/or elementary state, characterized in that the support consists of silicon carbide.

In particular, the active phase used in combination with the silicon carbide support in order to form the oxidation catalyst of the invention is advantageously constituted by at least one transition metal chosen from nickel, cobalt, iron, copper, silver, manganese, molybdenum, chromium, titanium, tungsten and vanadium, present in the oxide, sulfide or salt form and/or in the elemental state. The active phase, expressed as metal weight, represents in most cases from 0.1 to 20% by weight, more particularly from 0.2 to 15% by weight, and especially from 0.2 to 7% by weight, of the oxidation catalyst. The silicon carbide support advantageously constitutes from 40 to 99.9% by weight, more particularly from 50 to 99.8% by weight, of the oxidation catalyst.

For oxidizing H2SThe specific surface area of the sulphur-converting catalyst may vary widely depending on the conditions of application of the oxidation process. The specific surface determined by means of the BET nitrogen absorption method at aliquid nitrogen temperature (NF Standard XII to 621) is advantageously from 2 to 600m²A/g, more particularly from 10 to 300m²/g。

The Claus catalyst of the invention can be prepared by means of various known processes for incorporating one or more metal compounds into the dispersed solid constituting the catalyst support. Specifically, this operation may be performed in the following manner: the impregnation of the silicon carbide support in the form of powder, flakes, granules, extrudates or other agglomerates with the aid of a solution or sol of the desired metal compound in a solvent such as water is followed by drying of the impregnated support and calcination of the dried product at 250-500 ℃ and, as the case may be, in an inert atmosphere. The calcined catalyst may be subjected to a reduction treatment in hydrogen, for example at 200-500 c, in order to convert the metal of the metal compound present in the active phase into the elemental state. It is also conceivable to prepare the catalyst by inserting catalytically active metal atoms of a kind similar to that described above into the silicon carbide lattice.

The silicon carbide used for the support constituting the Claus catalyst of the invention may consist of any of the known silicon carbides, provided that it exhibits the desired specific surface characteristics, that is to say a specific surface determined according to the BET nitrogen adsorption-adsorption method, of, for example, from 2 to 600m²A/g, more particularly from 10 to 300m²/g。

In particular, the silicon carbide may be obtained by means of any of the techniques described in EP-A-0313480 (corresponding to US-A-4914070), EP-A-0440569, EP-A-0511919, EP-A-0543751 and EP-A-0543752.

For removing H from the gas to be treated₂The free oxygen-containing gas in which S is oxidized to sulfur is generally emptyGas, although pure oxygen, oxygen-enriched air or mixtures of oxygen and inert gases other than nitrogen in various proportions may also be employed.

Free oxygen-containing gas and H-containing gas to be treated₂The gases of S may be contacted with the oxidation catalyst, respectively. But to obtain a very homogeneous gas on contact with the catalystThe reaction mixture, preferably first containing H₂S is mixed with a free oxygen-containing gas, and the resulting mixture is brought into contact with an oxidation catalyst.

As mentioned above, the free oxygen-containing gas is used in an amount to provide an O in the reaction mixture of from 0.05 to 10, more particularly from 0.1 to 7, especially from 0.2 to 4₂∶H₂S molar ratio, contacting it with an oxidation catalyst to convert H₂S is oxidized to sulfur.

The contact time of the gaseous reaction mixture with the oxidation catalyst is from 0.5 to 20 seconds, preferably from 1 to 12 seconds, under standard temperature and standard pressure conditions.

The desulfurization process of the present invention can be used above H₂The dew point of the sulfur formed during the S oxidation reaction, which is then present in vapor form in the reaction mixture contacting the catalyst and collected at the outlet of the catalytic oxidation zone. The desulfurization process of the present invention can also be carried out at less than H₂S and SO₂At a temperature at which the dew point of the sulphur formed during the reaction, which is subsequently deposited on the catalyst, the gaseous effluent collected at the outlet of the catalytic reaction zone is substantially free of sulphur. The operating temperature of the process according to the invention is advantageously from 30 to 1000 ℃. To carry out the process above the dew point of the sulfur formed, 180-. To utilize the process at temperatures below the dew point of the sulfur formed, 30-180 deg.C, more specifically 80-160 deg.C, is selected, including a sulfur solidification zone near 120 deg.C.

Before carrying out the oxidation reaction step, the oxidation catalyst of the invention, in particular an oxidation catalyst in which the active phase comprises nickel, can be subjected to an activation treatment by contacting it with a slight excess, for example up to 300 mol%, of elemental sulphur relative to the stoichiometric excess corresponding to the maximum sulfidation of the active phase metal of the catalyst, in an inert atmosphere such as helium or argon at 250-400 ℃ for a sufficient period, most commonly 1-4 hours, to obtain the maximum sulfidation of the active phase metal of the catalyst.

The catalyst of the invention, in particular the nickel catalyst, initially activated as described above can be prepared byOxidation of H by oxygen in a gas containing free oxygen₂Starting from the initial time of S to H₂The conversion rate of S into sulfur reaches 100%.

The catalysts of the invention, very particularly the nickel catalysts, may also be identical to the above-mentioned simple substancesAn initial activation process of the sulfur activation process, wherein the catalyst is mixed with a catalyst containing H₂S and an inert gas, at a temperature of 250 ℃ and 400 ℃ for a time sufficient to maximize sulfidation of the catalyst active phase metal, usually 1-15 hours, and which may contain, in particular, 0.2-30% by volume and more of H₂And S. In particular, for the initial activation process of an oxidation catalyst, containing H₂The gas mixture of S may contain the gas to be treated, in which case the latter is other than H₂And no component other than S capable of reacting with the catalyst activity at the activation temperature.

Low concentration of H treated according to the method of the invention₂S gas can come from various routes, such as H in particular₂Natural gas with a low S content or gas derived from the gasification of coal or heavy oil, even gas obtained by hydrogenation of residual gas, e.g. sulphur-containing compounds (e.g. SO) from desulphurisation plants₂Thiol, COS or CS₂) Which can be converted into H by the action of hydrogen or water vapour₂S, or treating with H₂S and SO₂(H₂S∶SO₂In a molar ratio of more than 2: 1) of the gaseous effluent (to the gaseous effluent in H)₂S and SO₂Claus catalyst contact which promotes the reaction of sulphur formation) and the gas obtained contains only H₂S as a sulfur compound, containing no or little SO₂) The resulting gas. The process of the invention is applicable to H-containing₂A treatment process of a gas having an S concentration in the range of 0.001 to 25%, more specifically 0.01 to 20% (by volume). The gas to be treated may also contain organic sulfur compounds such as mercaptans, COS or CS in a total concentration of up to about 1% by volume₂. The method of the invention can be used to treat H-containing materials with a concentration of more than 25% by volume₂S gas; in this case, however, it is preferred to employ a conventional sulfur production process comprising a thermal reaction step。

H-containing compounds oxidized by contact with catalysts containing silicon carbide carriers₂The S gas may be free or substantially free of water or, conversely, contain more or less large amounts of water. Thus, H-containing materials having a water content of from 0 to about 50% by volume can be treated in accordance with the invention₂And (4) S gas. Advantageously, when containing H₂S gas undergoes an oxidation reaction at a temperature below the dew point of the sulfur produced by the oxidation, more particularly below the melting point of sulfur, by contact with a catalyst according to the invention comprising a silicon carbide support, very particularly a nickel catalyst₂The presence of 10-50% by volume, in particular 15-30% by volume, of water in the gas to be treated of S makes it possible to significantly prolong the time over which the catalyst maintains its optimum efficiency.

When the method of the invention is used at 180-₂This is particularly true when the S content is not greater than about 5% by volume, or in a plurality of oxidation zones containing oxidation catalysts in series, when H is present in the gas to be treated₂This is especially true at S contents greater than about 5% by volume, the single oxidationThe or each oxidation zone is operated within the above temperature ranges. Each oxidation zone is operated at a temperature range corresponding to substantially optimal sulfur selectivity for the catalyst.

At the outlet of each of the multiple oxidation zones or a single oxidation zone in series, the gaseous effluent is rich in sulfur vapour, and any subsequent removal of H₂Prior to S treatment, the collected gas effluent is passed to a desulfurization zone wherein a greater portion of the sulfur is removed by condensation. When passing through a reactor containing H₂When S gas is treated by passing the gas through a plurality of oxidation zones in series containing an oxidation catalyst support/silicon carbide support, H in only a portion of the gas to be treated in each zone₂S is oxidized to sulfur by injecting into the relevant zone an appropriate amount of a gas containing free oxygen for carrying out the oxidation to sulfur, preferably in admixture with said gas fed into the zone. H in each zone undergoing oxidation to sulfur₂Amount of SRepresenting H in the gas to be treated₂A fraction of the total quantity S, advantageously between 2 and 5% by volume of the gas to be treated, the number of catalytic oxidation zones being chosen so that the gas to be treated which reaches said final catalytic zone contains not more than 5% by volume of H₂S。

If necessary, the gaseous effluent collected at the outlet of the last catalytic reaction zone of a single catalytic reaction zone or of several catalytic reaction zones employed in series is subjected to an additional purification treatment after separation of the sulphur possibly contained therein, at a use temperature higher than the dew point of the sulphur formed in the reaction gas, said treatment depending on the nature of the gaseous sulphur compounds remaining in the effluent.

The process of the invention, carried out at a temperature above the dew point at which sulphur is formed, comprises, in particular, the H of the process for removing sulphur compounds from residual gases described in the references FRA2589141 and FRA2589082₂S oxidation step or H in acid gas treatment process described in reference FRA2589140₂And (3) oxidizing S. H may also be stoichiometrically Claus used in the process described by FRA2511663 or FRA2540092₂S to sulfur, at an elevated temperature, i.e., 200-₂In the presence of a catalyst of S₂The gas with an S content of less than 25% by volume is contacted with a controlled amount of a gas containing free oxygen to form H₂S∶SO₂H in a molar ratio substantially equal to 2: 1₂S、SO₂And a proportion of sulfur, which, after cooling and optionally separating the sulfur therefrom, is brought into contact with a Claus catalyst, either in a single catalytic converter or in a plurality, for example 2 or 3, catalytic converters in series, so as toform new sulfur.

When the inventive scheme is used below H₂S the dew point of the sulphur formed during the oxidation reaction, i.e. between 30 and 180 deg.C, more particularly between 80 and 160 deg.C, of which H₂The S content in this embodiment is generally not more than 5% by volume, in particular not more than 2% by volumeProduct) of the gas to be desulfurized is contacted with an oxidation catalyst having a silicon carbide support to produce sulfur deposited on the catalyst.

If H is present in the gas to be desulphurised in contact with the oxidation catalyst₂The S concentration and/or the temperature lead to the temperature of the reaction mixture at the end of the reaction due to the reaction Beyond the temperature limit so that the reaction no longer has the desired selectivity, the thermal energy released by the reaction can be removed by cooling the catalyst in any known manner. Cooling can be effected, for example, by means of a cooling fluid which is circulated through the catalyst for indirect heat exchange with the catalyst. It is likewise possible to operate by placing the catalyst in a tubular reactor consisting of tubes arranged in a shell, in which case, for example, the catalyst may be present in the tubes and there is a circulation of cold fluid between the tubes on the shell side. It is likewise possible to carry out the catalytic reaction in a reactor with multistage catalysts, the reaction mixture between adjacent catalyst stages not being cooled by indirect heat exchange by means of a cold fluid, the heat exchange taking place either inside or outside the catalytic reactor.

If the gas to be desulphurized is other than sulfur compound H₂If a large amount of water, for example, more than 10% by volume, is contained in addition to S, it is preferable that the temperature be lower than the dew point of sulfur formed during oxidation as H₂S is oxidized to the temperature of sulfur so that the temperature is above the water dew point present in the gas to be desulfurized.

At a temperature H below the dew point of the sulphur formed₂During the oxidation of S to elemental sulphur, the oxidation catalyst is gradually saturated with elemental sulphur. The catalyst saturated with elemental sulphur is periodically regenerated by purging with a non-oxidising gas, the regeneration being carried out at a temperature between 200 ℃ and 500 ℃, preferably between 230 ℃ and 450 ℃ to vaporise the elemental sulphur remaining on the catalyst, and the regenerated catalyst is cooled to a temperature below the dew point of the sulphur formed and reused for the oxidation reaction, this cooling being carried out with a gas at a suitable temperature below 180 ℃.

The purge gas used to regenerate the elemental sulfur saturated oxidation catalyst may be methane, nitrogen, CO₂Or a mixture of these gases, or a part of the gas stream resulting from the oxidation step or a part of the gas to be treated. The purge gas used for the regeneration may optionally contain a proportion of gaseous reducing compounds, such as H₂、CO、H₂S, at least in the final stage of regeneration, i.e. after the majority of the elemental sulphur deposited on the oxidation catalyst has been vaporised.

The catalytic oxidation reaction of the invention can be carried out at a temperature below the dew point of the sulphur formed in a single catalytic oxidation zone containing an oxidation catalyst with a SiC support, with alternating oxidation stages and regeneration/cooling stages, when the gas to be treated contains small amounts of H₂Regeneration of the S and subsequent catalyst is not very frequent. The catalytic oxidation of the present invention ispreferablyThe operation of a plurality of catalytic oxidation zones containing an oxidation catalyst with a SiC carrier is carried out so that at least one zone can operate in a regeneration/cooling phase while the other zones operate in a catalytic oxidation phase, and one or more zones can also operate in a catalytic oxidation reaction phase. At least one zone operates in a regeneration phase and at least one zone operates in a cooling phase.

The gas used for regenerating the oxidation catalyst is preferably circulated in a closed loop from the heating zone, successively through the catalytic zone to be regenerated and the cooling zone where most of the sulphur contained in the gas is separated by condensation, and back to the heating zone. Naturally, the regeneration gas can also be operated in an open circuit.

The gas used to cool the regenerated oxidation catalyst and the gas used to regenerate the sulfur-carrying catalyst are of the same type. The gas may optionally contain oxygen in a proportion less than or equal to that used in the catalytic oxidation stage. The circuits for regeneration gas and cooling gas may be independent of each other. However, according to a particular embodiment of the invention, the regeneration gas circuit defined above may also comprise a branch connected to the outlet of its cooling zone, bypassing its heating zone, connected to the inlet of the regeneration zone, which makes it possible to short-circuit said heating zone and to use the regeneration gas as cooling gas.

The process of the invention provides for the removal of H at a temperature below the dew point of the sulfur formed during oxidation₂S oxygenEmbodiments for the conversion to sulfur may advantageously form catalytic oxidation H₂S, said step is carried out in FRA2277877₂The S gas desulfurization process is carried out after a Claus reaction step carried outat 180 ℃ or below.

The following examples illustrate the invention without, however, limiting it in any way.

Example 1

A catalyst consisting of a silicon carbide support impregnated with an iron compound and a chromium compound and containing 3.2% iron and 0.35% chromium, expressed as metal weight relative to the weight of the catalyst, at a temperature above the dew point of the sulphur formed, to a content of 1% by volume of H is used₂S、5％H₂O and 94% CO₂Is processed.

The catalyst was prepared as follows. Firstly, the catalyst obtained is impregnated with a solution of an iron compound and a chromium compound in such concentrations that the desired amounts of iron and chromium are present in the catalyst, the catalyst having a drawdown diameter of 0.8 to 1mm and a BET specific surface area of 78m²Per g of SiC particles. The impregnated product obtained was dried at ambient temperature for 40 hours, subsequently dried at 120 ℃ for 50 hours and calcined at 500 ℃ for 20 hours to obtain a catalyst.

As mentioned above, the catalyst obtained contained 3.2% by weight of iron and 0.35% by weight of chromium and had a BET specific surface area of 77m²/g。

Containing H₂S gas in the amount of 1.1m²The catalyst is treated in a solid bed catalytic reactor equipped on the one hand with a conduit for conveying the gas to be treated and on the other hand with a gas discharge pipe constituting the outlet of the reactor. The gas supply line is provided with a tap for injecting air as the free oxygen-containing gas and is also provided with an indirect heat exchanger operating as a heater, which is arranged between the tap for injecting air and the reactor inlet. The gas outlet pipe is equipped with a sulphur condenser cooled by the circulation of the stream. The gas passes from the reactor inlet through the catalyst bed to the reactor outlet.

Gas to be treated, passing through a gas delivery line at 1000Nm²The flow rate/h was introduced at 40 ℃ and received via a tap.The flow rate of addition was 29Nm²The injection temperature/h is room temperature air. By passing through a heater to remove O therefrom₂∶H₂The mixture of gas to be treated and air with a molar ratio of S of 0.6 was warmed to 180 ℃ and subsequently injected into the reactor at this temperature. The contact time of the mixture with the catalyst in the reactor was 4 seconds. The gaseous effluent leaving the reactor through the vent pipe no longer contains free oxygen or H₂S at a temperature of 240 ℃. The effluent is cooled in a condenser to about 130 ℃ to separate the sulfur contained therein.

H₂The S conversion was complete and the sulfur selectivity was 92%.

Example 2

For H therein as the only sulfur compound₂The residual gas effluent containing 0.8% by volume of S is treated by feeding it with 70% by volume of H₂The acid gas of S is obtained by hydrogenation/hydrolysis of the treated residual gas of a Claus sulphur plant.

Below that caused by oxidation of H₂S the dew point of sulfur obtained by using a silicon carbide impregnated with a nickel compound and containing 4% by weight of nickel, the BET specific surface area of which is 220m²The catalyst per gram treats the gaseous effluent.

The catalyst was prepared by impregnating microporous SiC particles with the appropriate amount of nickel acetate in aqueous solution, followed by drying the impregnated product at 100 ℃ and finally calcining the dried product at 300 ℃ for 3 hours. The SiC particles had an average particle diameter of 1mm and a BET specific surface area of 240m²/g。

The operation was carried out in an apparatus consisting of 2 catalytic oxidation reactors arranged in parallel, the inlet and outlet of each reactor being separated by a fixed bed of the above-mentioned catalyst. Said reactor being arranged to operate alternately in the reaction phase by switching of the clocked valves, i.e. it has an inlet connected to the gas supply line, in which an indirect heat exchanger is installed, downstream of which a tap for injecting air is connected, and an outlet connected to the gas discharge line; or else the other reactors operating in the regeneration/cooling phase, i.e. arranged in a regeneration/cooling circuit equipped with means for ensuring the circulation of the purge gas, starting from the heater, through the oxidation reactor up to the sulphur cooler and back to the heater, and through the regeneration reactor for the second time with a circulation of the same composition cold gas as regeneration gas.

The gas effluent to be treated flows through a gas transfer line at a flow rate of 940kmol/h and is raised to 90 ℃ in a heat exchanger arranged on this line, whereupon 44kmol/h of ambient air is added via a tap. The mixture obtained enters the reactor in the oxidation step at a temperature substantially equal to 90 ℃. The contact time of the gas mixture entering the reactor in the oxidation reaction step with the catalyst layer in the reactor was 10 seconds. H of the reactor in the oxidation reaction step₂The conversion of S is equal to 100%. At the reactor outlet, the temperature of the gas stream withdrawn was about 140 ℃ and contained 160vpm SO₂The gas is sent to an incinerator before being discharged into the atmosphere.

A purge gas comprising nitrogen and having a flow rate of 10000Nm at a temperature of 250-350 ℃ is injected into the reactor operated in the regeneration/cooling step to regenerate the sulfur-rich oxidation catalyst³The/h is injected into the reactor. At the completion of the catalyst regeneration step, the purge gas temperature is reduced to about 125 deg.C and purging with cooled purge gas is continued until the regenerated catalyst bed substantially reaches that temperature. When regeneration is carried out with nitrogen, all the sulfur deposited on the catalyst is recovered.

The oxidation reactors were operated alternately in the reaction step for 30 hours; the operation was carried out for 30 hours in the regeneration/cooling step, with cooling being carried out for 10 hours.

When the process according to the invention is carried out for treating residual gases from sulfur plants, the gases are hydrogenated before being treated according to the invention, the overall sulfur yield being 99.9% over a period of months.

Example 3

For lean H₂The acid gas of S is treated, the gas containing 95.5 vol.% CO₂4% by volume of H₂O and 0.5% by volume of H₂S。

The treatment temperature is lower than that of the acid gas H by oxidation₂S dew point of sulfur generated, operating similarly to the examples2 in a device used with SiC, 4% by weight of nickel and a BET specific surface area of 210m²Per g of catalyst. The catalyst was prepared as in example 2 and, after calcination, was reduced in a hydrogen stream at 400 ℃ for 10 hours.

Lean acid gas to be treated is 2241Nm at about 30 DEG C³The flow rate was increased to 80 ℃ via a gas feed line in a heat exchanger arranged on the line, and 89.6Nm at 80 ℃ was subsequently added via a tap³H ambient air. The mixture obtained enters the reactor in the oxidation step at a temperature substantially equal to 80 ℃. Reaction of the gas mixture entering the reactor in the oxidation reaction stepThe contact time of the catalyst layer in the reactor was 10 seconds. H of the reactor in the oxidation reaction step₂The conversion of S is equal to 100%. At the reactor outlet, the temperature of the gas stream withdrawn was about 105 ℃ and contained less than 100vpm SO₂The gas is sent to an incinerator before being discharged into the atmosphere.

In the regeneration/cooling phase, a purge gas consisting of nitrogen is injected with the aim of regenerating the sulfur-rich oxidation catalyst and subsequently cooling the regenerated catalyst, the operation being carried out as described in example 2. When the regeneration is carried out under nitrogen, all the sulfur deposited on the catalyst is regenerated.

The oxidation reactors were operated alternately in the reaction step for 30 hours; the operation was carried out for 30 hours in the regeneration/cooling step, with cooling being carried out for 10 hours.

Example 4

The treatment contained 20% H by volume₂S、8％H₂O and 72% CO₂With a catalytic oxidation step carried out in Claus stoichiometry at a temperature above the dew point of the sulphur formed and a Claus reaction step carried out below this dew point.

The operation is carried out in an apparatus comprising: -a solid bed oxidation reactor containing the oxidation catalyst of the invention, provided with a transfer line for the mixture of acid gas and air and a discharge line for the oxidation effluent; gas/gas indirect heat exchangers, one of the heat exchange circuits of which is connected in series with a duct for the mixture of acid gas and air, the other heat exchange circuitof which is connected in series with a duct for the mixture of acid gas and airThe line is connected in series with the discharge line of the oxidation effluent; a first fixed-bed catalytic converter containing a Claus catalyst in the form of extrudates with a diameter of 3mm, the catalyst consisting of a catalyst containing 10% by weight of CaSO₄With the inlet thereof connected to an oxidation effluent discharge line via suitable heat exchange tubing of a heat exchanger; a catalytic conversion group comprising 2 second catalytic converters and one sulfur condenser cooled by steam, wherein on the one hand each of said second converters contains a Claus catalyst consisting of spherical activated alumina with a diameter of 4-6mm, and on the other hand the arrangement of the second converters and the sulfur condenser results in the outlet of the first converter being able to be alternately opened or closed with the inlet of one of the second converters and in the latter being connected in series by the sulfur condenser; a catalytic burner, the inlet of which is connected to the outlet of the catalytic conversion group and the outlet of which is connected to a chimney leading to the atmosphere, the burner using a catalyst consisting of silica impregnated with palladium oxide by means of iron sulphate.

The oxidation catalyst used in the oxidation stage carried out in Claus stoichiometry consists of a SiC support impregnated with an iron compound and containing 4.6% by weight of iron relative to the total weight of the catalyst.

The catalyst is prepared as described below, with a particle size of 0.8 to 1mm and a BET specific surface area of 78m²The SiC particles are first treated with FeSO in a concentration which provides the desired amount of iron for the resulting catalyst₄And (4) dipping in an aqueous solution. The impregnated product obtained was dried and calcined as described in example 1.

As mentioned above, the catalyst obtained contained 4.6% by weight of Fe and had a BET specific surface area of 76m²/g。

The flow rate of the sour gas is 1000Nm³H (standard conditions), to which 285.6Nm had been added³Air, the resulting gas mixture was preheated to 200 ℃ by passing it into a heat exchanger and subsequently injected into the oxidation reactor. The contact time between the gas mixture and the oxidation catalyst was 2 seconds (standard conditions) and the temperature in the catalyst bed rose to 800 ℃.

The oxidation reactor effluent contains a molar ratio of H₂S∶SO₂H of 2: 1₂S and SO₂And 6vpm free oxygen and corresponding to H₂S produces a certain amount of sulfur steam with a sulfur conversion of 59%.

The effluent is cooled in a heat exchanger to 150 ℃ to condense the sulfur therein and to utilize a portion of the heat therein to preheat the mixture of sour gas and air. The cooled effluent is then heated to 250 ℃ and sent to a first Claus catalytic converter. The contact time of the titania-based catalyst with the gaseous effluent in the converter was about 3 seconds, and the catalyst bed temperature was 300 ℃.

H-containing from the first Claus converter₂S、SO₂The reaction mixture with sulfur steam was passed through a "regeneration" stage converter of a catalytic conversion train to purge the sulfur-rich catalyst in this converter, the purging being carried out at about 300 c and a gas/catalyst contact time of about 6 seconds. The sulfur-rich gas from the reformer is regenerated and passed through a steam-cooled sulfur condenser, where the gas is cooled to about 1500 ℃ and the sulfur is removed by condensation. The obtained product containing H₂S and SO₂The cooling gas withvery little sulphur vapour is fed to the catalytic converter of the Claus reaction stage of the catalytic conversion group operating at 150 ℃ and the gas/catalyst contact time is about 6 seconds, in order to pass H₂S and SO₂The reaction between them forms sulphur, which is deposited on the catalyst.

The residual gases coming from the converter in the Claus reaction stage are sent to a catalytic incineration step, which generates a flue gas containing a very low concentration of SO as the only sulphur compound₂And is discharged into the atmosphere through a chimney.

The residual gas from the catalytic conversion group contained only 800vpm of total sulfur, i.e., H₂S、SO₂Sulfur vapour and/or blister sulfur, indicating H₂The overall yield of S to sulfur was 99.6%.

After 800 hours of operation under the above conditions, the effluent of the reactor, which is catalytically oxidized with Claus stoichiometry, contains H₂S∶SO₂H with a molar ratio of 2.02₂S and SO₂Corresponding to the numberIn H₂Sulfur vapour, H, with an S conversion of 56%₂The total yield of S to sulfur was 99.4％。

Example 5

A catalyst consisting of a silicon carbide support impregnated with an iron compound and a chromium compound and containing 3.2% iron and 0.35% chromium, expressed as metal weight relative to the weight of the catalyst, at a temperature above the dew point of the sulphur formed, to a content of 1% by volume of H is used₂S、5％H₂O and 94% CO₂The catalyst is activated by direct sulfidation.

The catalyst was prepared as follows. Firstly, the catalyst is impregnated by a solution of iron compound and chromium compound with the concentration of the iron compound and chromium compound which can lead the obtained catalyst to have the required quantity of iron and chromium, the grain diameter is 0.8-1mm, and the BET specific surface is 78m²Per g of SiC particles. The impregnated product obtained was dried at ambient temperature for 40 hours, subsequently dried at 120 ℃ for 50 hours and calcined at 500 ℃ for 20 hours. Then diluted to 1% by volume with H in a stream of nitrogen₂S or together with the catalyst, in an amount of 6.2% by weight of the catalyst, of solid sulfur, and the calcined product obtained containing elemental iron and chromium supported on SiC in the form of oxides. The treatment is carried out at 300 ℃ for 2 hours in order to bring the metallic iron and chromium into the sulphide form constituting the active phase of the catalyst.

The resulting sulfur-containing catalyst contained 3.2% by weight of iron and 0.35% by weight of chromium as described above and had a BET specific surface area of 76m²/g。

Treatment of H-containing catalyst with Sulfur-containing catalyst as described in example 1₂And (4) S gas.

From the beginning of the treatment containing H₂H of S gas meter₂The S conversion rate reaches 100 percent, and the vulcanization selectivity is 93 percent.

Example 6

For lean H₂The acid gas of S is treated, the gas containing 95.5 vol.% CO₂4% by volume of H₂O and 0.5% by volume of H₂S。

The treatment temperature is 100 ℃ lower than that of H in acid gas by oxidation₂The dew point of the sulfur formed by S was determined in an apparatus similar to that used in example 2, using a reactor containing SiC, 4% by weight of nickel and having a BET specific surface area of 210m²Per g of catalyst. Thecatalyst was prepared as in example 2 and, after calcination, was reduced in a hydrogen stream at 400 ℃ for 10 hours.

Lean acid gas to be treated at 2241Nm³Flowing through the gas transfer line at a flow rate of about 30 ℃ and being heated to 80 ℃ in a heat exchanger provided on the conduit and subsequently connected via a tap to 89.6Nm³H air and 1000Nm³H inert gas with 55% by volume of water vapor and heating to 100 ℃. The amount of water vapour in the final mixture was about 20% by volume. Obtained byThe mixture of (a) was passed into an oxidation stage reactor at a temperature of 86 ℃. The gas mixture entering the oxidation reaction stage was in contact with the catalyst layer in the reactor for a period of 10 seconds. Oxidation stage reactor H₂The conversion of S was 100%. At the reactor outlet, the discharge was about 110 ℃ with less than 100vpmSO₂Before being discharged into the atmosphere, is fed into an incinerator.

A purge gas consisting of nitrogen is injected into the reactor operating in the regeneration/cooling stage for the purpose of regenerating the sulfur-rich oxidation catalyst and subsequently cooling the regenerated catalyst. The procedure is as in example 2. Regeneration was carried out in nitrogen and the total amount of sulfur deposited on the catalyst was recovered.

The above-mentioned amounts, more generally from 10 to 15% by volume, in particular from 15 to 30% by volume, of steam present in the reaction mixture make it possible to substantially prolong the time over which the catalyst maintains its optimum desulfurization activity. The water vapor acts as a dispersant for the sulfur deposited on the catalyst, thereby protecting the access of the reactants to the active sites of the catalyst.

Claims (23)

1. For introducing H in the gas at low concentration₂Process for the catalytic oxidation of S to sulfur, wherein said S contains H₂S gas and free oxygen-containing gas with O₂∶H₂S is in a molar ratio of 0.05 to 10 with respect to the amount of H₂S is selectively oxidized to sulfur, and the catalyst is combined with a carrier to form a catalytic active phase containing at least one oxide, sulfide salt and/or elementary substanceThe metal is characterized in that the carrier of the catalyst is a silicon carbide carrier, the metal of the active phase of the catalyst is selected from nickel, cobalt, iron, copper, silver, manganese, molybdenum, chromium, titanium, tungsten and vanadium, the active phase quantity expressed by the weight of the metal is 0.1-20 percent of the weight of the catalyst, and the silicon carbide carrier accounts for 40-99.9 percent of the weight of the catalyst.

2. A process according to claim 1, characterised in that the silicon carbide support constitutes from 50 to 99.8% by weight of the catalyst.

3. A process according to claim 1 or 2, characterized in that the amount of active phase in the catalyst, expressed as weight of metal, is from 0.2 to 15% by weight, based on the weight of the catalyst.

4. A process according to claim 1 or 2, characterized in that the amount of active phase in the catalyst, expressed as weight of metal, is from 0.2 to 7% by weight, based on the weight of the catalyst.

5. A process according to claim 1, characterized in that the specific surface area of the catalyst, measured by the BET nitrogen adsorption method, is from 2 to 600m²/g。

6. A process according to claim 1, characterized in that the gas containing free oxygen is such as to be able to make O₂∶H₂An amount of 0.1 to 7 in terms of S molar ratio is used.

7. A process according to claim 1, characterized in that the contact time of the gaseous reaction mixture with the oxidation catalyst under standard pressure and temperature conditions is between 0.5 and 20 seconds.

8. The process according to claim 1, characterized in that H is contacted with the catalyst₂The oxidation process of S is carried out at 30-1000 deg.C.

9. The process according to claim 8, characterized in that H is contacted with the catalyst₂The oxidation process of S is carried out at 180-1000 ℃.

10. The process according to claim 8, characterized in that H is contacted with the catalyst₂The oxidation of S is carried out below the dew point of the sulphur formed by this oxidation, which is between 30 and 180 ℃, and the sulphur formed is deposited on the catalyst.

11. A method according to claim 10, characterized in that the purging is performed periodically by purging with gasRegenerating the sulfur-rich oxidation catalyst at 200 ℃ and 500 ℃ to gasify the sulfur remaining on the catalyst, the regenerated catalyst being cooled to a temperature below the dew point of the sulfur to effect fresh H₂S oxidation reaction and cooling operation are carried out by gas at the temperature of less than 180 ℃.

12. A method according to claim 1, characterized in that H is present in the gas to be treated₂The S content is 0.001-25% by volume.

13. Process according to claim 1, characterized in that the oxidation catalyst comprising a silicon carbide support is activated before it is subjected to oxidation by contacting it with sulfur in an amount between the amount required for the maximum sulfidation of the active phase metal in the oxidation catalyst and an amount exceeding this maximum sulfidation by 300% by moles, the operation being carried out in an inert atmosphere at 250 ℃ and 400 ℃.

14. A process according to claim 1, characterized in that the oxidation catalyst comprising a silicon carbide support is passed over a catalyst comprising H before the oxidation is carried out₂The contact of S with the mixture of inert gases is activated and operated at 250-400 ℃ for 1-15 hours in order to produce maximum sulfidation of the metals of the active phase of the oxidation catalyst.

15. A process according to claim 1, characterized in that the oxidation reaction of hydrogen sulphide is carried out by reacting a hydrogen-containing stream containing H₂S in a carrier containing silicon carbideIs contacted with a controlled amount of a free oxygen containing gas in Claus stoichiometry in the presence of an oxidation catalyst at 200-1000 ℃ to obtain a catalyst containing H₂S∶SO₂H in a molar ratio of substantially 2: 1₂S and SO₂And a quantity of sulfur, and is further characterized in that said gaseous effluent, after cooling and optionally separating the sulfur contained therein, is contacted with a Claus catalyst so as to generate new sulfur.

16. A method according to claim 6, characterized in that the gas containing free oxygen is such as to enable O₂∶H₂The S is used in an amount within a molar ratio of 0.2 to 4.

17. A process according to claim 7, characterized in that the contact time of the gaseous reaction mixture with the oxidation catalyst under standard pressure and temperature conditions is between 1 and 12 seconds.

18. The process according to claim 9, characterized in that H is contacted with an oxidation catalyst₂The oxidation process of S is carried out at 200-900 ℃.

19. The method according to claim 10, characterized in that H is₂The oxidation process of S is carried out at 80-160 ℃.

20. A process according to claim 11, characterized in that the regeneration reaction is carried out at 230 to 450 ℃.

21. A method according to claim 12, characterized in that H is present in the gas to be treated₂The S concentration is 0.01-20% by volume.

22. A process according to claim 14, characterized in that the gas mixture used for activating the oxidation catalyst contains 0.2 to 30% by volume of H₂S。

23. A method according to claim 15Process, characterized by H carried out according to Claus stoichiometry₂The S oxidation reaction is carried out at 350-900 ℃.