MXPA98005793A - Method to remove contaminants containing azufre, aromatic substances and hydrocarbons, from a - Google Patents

Abstract

The present invention relates to a method for removing contaminants containing sulfur in the form of mercaptans and H2S, from natural gas, which can also contain CO2 and higher aliphatic and aromatic hydrocarbons, and recover elemental sulfur, where in a first absorption step the sulfur-containing contaminants are from the gas, to form on the one hand a stream of purified gas and on the other hand a sour gas, such sour gas is fed to a second absorption step in which the sour gas is separated into a first gas stream enriched in H2S and with a reduced content of mercaptan, which is fed to a Claus plant, followed by a step of selective oxidation of H2S to elemental sulfur in the exit gas, and a second stream of enriched gas in mercaptans and with a reduced H2S content, such a second gas stream, if desired after the treatment, is subjected to a selective oxidation of the sulfur compounds re a sulfur element

Description

METHOD FOR REMOVING CONTAMINANTS THAT CONTAIN SULFUR, AROMATIC SUBSTANCES AND HYDROCARBONS, OF U? GAS Field of the Invention The present invention relates to a method for purifying a hydrocarbon gas, more particularly natural gas, which is contaminated with sulfur compounds in the form of H 2 S and mercaptans, as well as with C 0 2 - More particularly, the invention comprises a method to convert mercaptans to H2S, and remove CO2 and adsorbed hydrocarbons and aromatics, from gas containing H2S, to form elemental sulfur from H2S.

Background of the Invention In the purification of natural gas, the purification of refinery gases and the purification of the synthesis gas, sulfur-containing gases are released, in particular H2S, which should be removed to limit the emission to the atmosphere of S02, particularly which is formed during the combustion of such sulfur compounds. The degree to Ref.028004 that the sulfur compounds are going to be removed from, for example, natural gas, depends on the proposed use of the gas and the fixing of the quality requirements. When the gas must meet the so-called "specifications of pipelines or gas pipelines", the content of H2S must be reduced to a value below 5 mg / Nm3. The requirements with respect to the maximum content of the other sulfur components must also be set. From the prior art, a large number of methods are already known by which the amount of the sulfur compounds in a gas, such as natural gas, can be reduced. For the removal of sulfur-containing components from gases, the following process route is usually employed. In a first step the gas to be treated is purified, whereby the sulfur-containing components are removed from the gas, followed by a recovery of the sulfur from these sulfur-containing components, after which a purification step of the sulfur is followed. Sulfur from waste gas. In this step of sulfur purification, it is tried to recover the last percentages of sulfur before the residual gas is emitted by means of a chimney to the atmosphere.

In the purification step, processes are used in which frequently aqueous solvents (absorption agents) are used. These processes are divided into five main groups, ie chemical solvent processes, physical solvent processes, physical / chemical processes, redox processes, by which H2S is oxidized directly to sulfur in aqueous solution and finally a group of bed processes. fixed by which the H2S is absorbed or adsorbed chemically or physically or is catalytically oxidized to elemental sulfur. The first three groups mentioned are normally employed in the industry for the removal of large quantities of sulfur-containing components, most often present in large quantities of gas. The last two groups are limited with respect to the amount of sulfur that will be removed and the concentration of the sulfur-containing components. These processes are therefore less suitable for the removal of high sulfur concentrations in large industrial gases purification plants. The processes of chemical solvents include the so-called amine processes in which use is made of aqueous solutions of alkanolamines or potassium carbonate solutions.

"In the processes of physical solvents, different chemical substances are used, for example, polyethylene glycol (DMPEG) known under the name of Selexol, N-Methyl-pyrrolidone (NMP), known under the name of Purisol, or methanol, known under the name of Rectisol In the group of physical / chemical processes, the Sulfinol process is well known.In this process, a mixture of an alkanolamine with sulfolane is used dissolved in a small amount of water. In the three methods mentioned above, an absorbent device and a regenerator are used. In the absorbent device, the components containing the sulfur are chemically or physically bound to the solvent. By reducing the pressure and / or increasing the temperature in the regenerator, the sulfur-containing components are desorbed from the solvent, after which the solvent can be reused. A detailed description of this method is you will find in R. N. Medox "Gas and Liquid S eetening" Campbell Petroleum Series (1977). In this method, in addition to the sulfur-containing components, C02 is also partially or completely removed, depending on the solvent chosen. 25 The sulfur compounds removed together with the C02 are directed from the regenerator to a sulfur recovery plant to recover sulfur from H2S and other sulfur compounds. A process frequently used to recover sulfur from the sulfur compounds thus obtained, in particular H2S, is the Claus process. This process is described in detail in H. G. Paskall, "Capability of the modified Claus process", Western Research Development, Calgary, Alberta, Canada, 1979. 'The Claus process consists of a thermal step typically followed by 2 or 3 reactor steps. In the thermal passage one third of the H2S is burned to SO2 according to the reaction H S + 1. 5 02 ~ > S02 + H20 15 after this the remainder, that is, the 2/3 parts of the H2S react with the S02 formed, according to the Claus reaction, to form sulfur and water. 2 H2S + S02 - > 3 S + 2 H20.

The efficiency of the Claus process depends on several factors. For example, the balance of the Claus reaction moves in the direction of the H2S with a growing water content in the gas. The efficiency of the sulfur recovery plant can be increased by the use of a sulfur recovery plant for the exhaust gases; the known processes are the SUPERCLAUSR process and the SCOT process. In the SUPERCLAUSR process, a catalyst is used as discloses in European patent applications Nos. 242,920 and 409,353, as well as in international patent application WO-A 95,07856, wherein this catalyst is employed in a third or fourth stage of the reactor as described inter alia in "Hydrocarbon Processing". "April 1989, pp. 40-42. Using this method, the last H2S residues present in the process gas stream are selectively oxidized to the elemental sulfur according to the reaction H2S + 0.5 02 - - > S + H20. In this way the efficiency of the sulfur recovery unit can easily be raised to 99.5%. The gas feed to the Claus plant can sometimes contain large amounts of C02, for example up to 98.5%, which has a highly adverse effect on the temperature of the flame in the thermal passage. A large amount of C02 can cause instability of the flame and also the efficiency in the thermal passage will be reduced, so that the total efficiency of the Claus plant will decrease. Also, the gas may contain large amounts of hydrocarbons. When the gas it contains sulfur is processed in a petroleum refinery gas, the hydrocarbon content will generally be lower, mostly < 2% in volume. In the purification of natural gas where physical or physical / chemical processes are used, such as The result of the absorption of larger quantities of hydrocarbons and aromatic substances, respectively, can be completed with the gas which is passed to the sulfur recovery plant (Claus gas). In the thermal stage of a Claus plant these hydrocarbons are burned completely because the reaction rate of the hydrocarbons with oxygen is higher than the reaction rate of H2S and oxygen. When large amounts of C02 are present, the temperature of the flame will consequently be more , and consequently also the rate of reaction of the components during combustion. As a result, soot formation may occur in the flame of the thermal stage burner. The formation of soot causes problems of plugging in the catalytic reactors of a Claus plant, in particular the first reactor. Also, the relationship between the requirement of oxygen for the conversion of H2S to sulfur and the requirement of oxygen for the combustion of hydrocarbons and aromatic substances can take values such that the Claus process can no longer be controlled properly. These problems are already known in the industry. What's more, in addition to the H2S and the large amounts of C02 mentioned above, Often, mercaptans are also present in the gas. In the industry, chemical processes are used in which these mercaptans are not removed from the gas to be purified, for example natural gas, so that no further cleaning is necessary with a fixed bed process. Frequently molecular sieves are used for the removal of these mercaptans. However, when such a fixed bed is saturated with the mercaptans, the molecular sieves should be For regeneration purposes, purified natural gas is often used for this purpose. This regeneration gas must then be purified in turn. In the regeneration of molecular sieves, mercaptans are released for the most part at the beginning of regeneration. As well There are processes in which the mercaptans of a subsequent purification stage are returned to the Claus plant. These raercaptans then give a maximum load in the thermal stage of the Claus plant so that air control is seriously altered. Such a process route is described in Oil and Gas Journal 57, 19 August 5, 1991, pp. 57 - 59. In addition, this leads to the loss of natural gas, which can easily extend up to about 10%. There is a well-known method for ^ processing of gases containing sulfur, Which contain carbonyl sulphide and / or other organic components such as mercaptans and / or dialkyl disulfides. This method is described in British Patent No. 1563251 and in British Patent No. 1470950. It is an object of the present invention to provide a method for the removal of »Contaminants containing sulfur in the form of mercaptans and H2S of the hydrocarbon gas, which may also contain C02 and aliphatic hydrocarbons and Higher aromatics, and the recovery of elemental sulfur, in such a method the disadvantages described above do not occur. More particularly, it is an object of the invention to provide a method by which the exhaust gases do not contain or only contain very few harmful substances, so that these gases can be discharged into the atmosphere without any objection. It is also an object of the invention to provide a method by which sulfur-containing contaminants are recovered to a high degree as elemental sulfur, for example up to an amount of more of 90%, more particularly, more than 95%. Surprisingly, it has been found that with the method according to the invention, large gas streams can be purified in a very efficient manner, although at the same time they can be satisfied more stringent requirements with respect to the emission of harmful substances and the recovery efficiency of sulfur. The present invention provides a simple method for purifying hydrocarbon gas contaminated with the recovery of sulfur, according to which in a first step of absorption the sulfur-containing contaminants are removed from the gas, to form on the one hand a stream of purified gas and on the other hand a sour gas, such gas sour fed to a second absorption step in which the sour gas is separated in a first stream of gas enriched in H2S and reduced in mercaptans, which is fed to a Claus plant, followed by a step of selective oxidation of H2S to elemental sulfur in the gas , and a second gas stream reduced in H2S and enriched in mercaptans, such a second gas stream, if additional further treatment is desired, is subjected to a selective oxidation of the sulfur compounds to elemental sulfur. According to a preferred embodiment of the In the invention, the first step of absorption is carried out using a chemical, physical or chemical / physical absorption agent which removes all the contaminants from the natural gas. Preferably, this is an absorption agent which is based on sulfolane, in combination with a secondary and / or tertiary amine. As already indicated, such systems are already known and are used on a large scale to purify natural gas, especially when natural gas is liquefied after purification. Absorption, as it is Conventionally, it is based on a system by means of which the contaminants are absorbed into the solvent in a first column, after which, when the solvent is loaded with the contaminants, this solvent is regenerated in a second column, by example by means of heating and / or by means of pressure reduction. The temperature at which the absorption is carried out depends to a high degree of the solvent and the pressure used. At the common pressures for natural gas from 2 to 100 bar, the absorption temperature is generally 15 to 50 ° C, although outside these intervals good results can also be obtained. The natural gas is preferably purified to meet the specifications of the pipeline or gas pipeline, which means that in general no more than 10, more particularly not more than 5 ppm 5 of the H2S may be present. According to the method of the invention, in a second absorption stage the sour gas is separated first into two other gases, that is to say a gas rich in H2S and # a gas rich in C02, which in addition to C02 contains hydrocarbons, aromatic substances and mercaptans not absorbed. With this method the concentration of H2S can be increased 2 to 6 times. This second absorption preferably occurs using a solvent based on a secondary amine or Tertiary, more particularly with an aqueous solution of methyldiethanolamine, optionally in combination with an activator for the same, or with a hindered tertiary amine. Such processes are already known and described in the literature (MDEA process, UCARSOL, FLEXSORB-SE, and similar). The way to operate such processes is comparable to the first stage of absorption. The degree of enrichment is preferably at least 2 to 6 times or greater, which depends partially on the initial concentration of the H2S. The degree of The enrichment can be fixed by means of an appropriate choice of the construction of the absorber. Üfr \ 1 The first gas stream rich in H2S can be processed very well in the Claus plant, although the absence of a large part of the CO2, hydrocarbons and aromatic substances does not cause any production additional gas in the plant during combustion. As a consequence, the Claus plant can be made with a much smaller design, although the sulfur recovery efficiencies are much higher. Such a Claus plant is already known and the manner in which it is operated in terms of temperature, pressure and the like is described in detail in the publications cited in the introduction. The exit gas from the Claus plant, which still contains residual sulfur compounds, is fed, if desired after further hydrogenation, to an outlet gas processing apparatus where elemental sulfur is formed through the selective oxidation of the sulfur compounds, which is separated into a plant suitable for this purpose, for example as described in European Patent Application No. 655,414. After separation of the sulfur, the remaining gas can be burned in a subsequent burner. He The heat released can be usefully employed for the generation of steam. vt Selective oxidation is preferably carried out in the presence of a catalyst which selectively converts the sulfur compounds to the elemental sulfur, for example the catalysts described in the European and international patent applications mentioned previously. These publications, whose content is incorporated here for reference, also indicate the most appropriate process conditions, such 'like the temperature and the pressure. In general, without However, the pressure is not critical and the temperatures may be between the dew point of the sulfur and about 300 ° C, more particularly less than 250 ° C. The second gas stream rich in C02 with the The hydrocarbons, the aromatic substances and the mercaptans present are mixed with the exit gas from the Claus sulfur recovery plant and passed to the outlet gas recovery plant based on the selective oxidation of the compounds of sulfur to elemental sulfur. The outlet gas recovery plant in this case is preferably the SUPERCLAUS reactor stage, whereby the mercaptans are oxidized to the elemental sulfur with the oxygen present. Alternatively, the gas rich in C02 also can be treated separately in a SUPERCLAUS reactor stage. When the mercaptan content of the gas is high, it may be required to cool the SUPERCLAUS reactor to prevent the possibility that the run of the temperature is too high, as a result of which the selectivity decreases and too large an amount is formed. S02. According to another embodiment of the method according to the invention, the gas rich in C02, the second gas stream, coming from the enrichment unit, is passed with the hydrogen over a hydrogenation reactor containing a metal catalyst of the group 6 and / or group 8, sulfurized, supported on a carrier. As a carrier, the alumina is preferably used with this class of catalysts, since this material, in addition to the desired thermal stability, also makes possible a good dispersion of the active component. As the catalytically active material, a combination of cobalt and molybdenum is preferably used. For hydrogenation, the gas stream must be heated from the absorption / desorption temperature of about 40 ° C to the temperature of 200 to 300 ° C required for hydrogenation. This heating preferably occurs indirectly and not with a burner placed or adapted in the gas stream, as is conventional. In fact, the disadvantage of direct heating is that the direct heating in this case causes a substantial formation of soot, which can lead to fouling and clogging in the hydrogenation and in the subsequent selective oxidation. In the hydrogenation step the mercaptans in the gas are converted to H2S with the help of the hydrogen supplied. The C02-rich gas from the hydrogenation step, containing C02, H2S, hydrocarbons and aromatics, is mixed with the exit gas from the Claus plant and then passed to the sulfur recovery unit of the exit gas, preferably one stage of the SUPERCLAUS reactor. The hydrogenation reactor gas can also be treated in a separate SUPERCLAUS reactor. It may be necessary to cool the SUPERCLAUS reactor to prevent the catalyst temperature from rising too high. As indicated, the gas coming from the selective oxidation is finally burned, whereby the organic contaminants are converted to water and C02. The invention will now be analyzed with reference to the drawing, Figure 1 showing in the form of a block diagram the variant with a step of additional hydrogenation of the second gas stream with a low H2S content. Figure 2 shows the variant without hydrogenation.

Detailed description of the invention As indicated in Figure 1, the sour gas coming from the first absorption unit (not shown) in which the contaminated natural gas has been separated, on the one hand, into a gas stream with the desired specifications and, for the other part, in the sour gas, is passed through line 1 to an absorber of an absorption / regeneration plant 3. The non-absorbed components of the gas, consisting mainly of carbon dioxide, hydrocarbons (including aromatic substances) ), mercaptans and a low content of H2S, are directed by means of line 2 to the hydrogenation reactor 6. In line 2 the gas is brought to the desired hydrogenation temperature, under the addition of hydrogen and / or carbon monoxide, before being passed into the hydrogenation reactor 6. In the hydrogenation reactor 6, the mercaptans and the other organic sulfur components present in the gas are converted to the H2S. The gas from the hydrogenation reactor 6, after cooling, is passed through line 5 to step 11 of removal of sulfur from the outlet gas, from the Claus 8 plant, to convert the present H2S to the elemental sulfur. The H 2 S-rich gas mixture coming from the regeneration section of the absorption / regeneration plant 3 is supplied via line 7 to the Claus 8 plant, in which the largest part of the sulfur compounds is converted to elemental sulfur, which is discharged through line 9. To increase the efficiency of the plant Claus 8, the outlet gas is passed through line 10 to a step 11 of removal of the sulfur from the outlet gas. This sulfur removal step can be a known sulfur removal process, such as, for example, a dry bed oxidation step, a step of adsorption, or a liquid oxidation step. The air required for oxidation is supplied via line 12. The sulfur formed is discharged by means of line 13. The gas is then passed through the line 14 to the rear burner 15 before the gas is discharged through the chimney 16. As indicated in Figure 2, the sour gas, which comes from a first absorption unit (not shown) in which the gas natural polluted has been separated into, on the one hand, a gas stream with the desired specifications and, on the other hand, the sour gas, is passed through line 1 to an absorber of an absorption / regeneration plant 3. The gas mixture rich in H2S that comes from the regeneration section of the absorption / regeneration plant 3, it is supplied via line 4 to the Claus 5 plant, in which the largest part of the sulfur compounds is converted to sulfur elementary, which is downloaded through line 6. To increase the efficiency of the plant Claus 5, the exit gas is passed through line 7 to a step 8 of removal of sulfur from the outlet gas. Stage 8 of sulfur removal operates in accordance with the principle of dry-bed oxidation. The non-absorbed components of the gas coming from the absorption section of the absorption / regeneration plant, which consist mainly of carbon dioxide, hydrocarbons (including aromatic substances), mercaptans and a low H2S content, are directed by means of the line 2 to the oxidation reactor of the sulfur removal stage 8 of the exit gas. The air required for the oxidation of H2S and mercaptans is supplied via line 9. To limit the temperature rise in the oxidation reactor, the cooled process gas is recycled from line 12 to line 7 with the aid of a condenser 14. The sulfur formed is discharged by means of line 11. The gas is then passed through line 12 to back burner 16 before the gas is discharged by means of chimney 17. The invention is clarified in and by the following examples, which are not proposed as a limitation.

EXAMPLE 1 An amount of the sour gas of 15545 Nm3 / h that comes from the regenerator of a gas purification plant, has the following composition at 40 ° C and at a pressure of 1.70 absolute bar. 15 9.0 in vol H2S 0.01 in vol COS 0.22 in vol CH3SH 0.38 in vol C2H5SH 20 0.03 in vol C3H7SH 0.01 in vol C5H9SH 81.53 in vol co2 4.23 in vol H20 3.51 in vol Hydrocarbons (Cx a C? 7) 25 1.08 in vol Substances aromatics (Benzene, Toluene, Xylene)% This sour gas is brought into contact in an absorber of a gas purification plant with a methyldiethanolamine solution, whereby the H2S and a part of the CO2 were absorbed. The amount of the gas in the product (gas rich in C02) of the absorber was 13000 Nm3 / h with the following composition: - 10 88.47 * or in vol co2 500 ppm in vol. H2S 70 ppm in vol. COS 0.26 in vol. CH3SH 0.46 in vol. C2H5SH 15 0.04 in vol. C3H7SH 0.01% vol. C4H9SH 5.21 or in vol. H20 4.2 in vol. Hydrocarbons (Ci to C? 7) 1.29 or, in vol. Aromatic substances (Benzene, Toluene, Xylene) To this produced gas are supplied 2700 Nm3 / h of a reducing gas containing hydrogen and carbon monoxide and then heated to 205 ° C to hydrogenate All the mercaptans present to the H2S in the hydrogenation reactor which contained a sulfurized group 6 and / or group 8 metal catalyst, which is supported on an alumina carrier, in this case a Co-Mo catalyst. The temperature of the reactor gas was 232 ° C. The sour gas was then cooled to 226 ° C and supplied to the sulfur removal step of the exit gas from the sulfur recovery plant. The amount of gas coming from the reactor # hydrogenation was 15700 Nm3 / h and had the following composition: 0. 68 Q. "5 in vol H2S 60 ppm in volume COS 74.22 in volume C02 15 8.14 Q, O in volume H20 3.48 Q." 6 in vol. Hydrocarbons (Ci to C? 7) 1.07 Q. O in vol. Aromatic substances (Benzene, Toluene, Xylene) 0.86 in vol. H2 20 11.56 Q. O in vol. N2 After desorption in a regenerator, the gaseous mixture of H2S / C02, sour (gas rich in H2S), is passed to a sulfur recovery plant. This The mixture of H2S / C02 was 2690 Nm3 / h and had the following composition at 40 ° C and 1.7 bar absolute. 51 7% in vol. H2S 44. 0% in vol. C02 4. 3% in vol. H20 To the burner of the thermal stage of the sulfur recovery plant are supplied 2780 Nm3 / h of air, so that after the second stage of the Claus reactor, 1.14% by volume of H2S and 0.07% by volume of S02 were present in the process gas. The process gas was then fed to the sulfur removal step of the exit gas. 875 Nm3 / h of air are supplied to this gas. The inlet temperature of the selective oxidation reactor was 220 ° C and the outlet temperature was 267 ° C. The selective oxidation reactor is filled with a catalyst as described in the European patents 242,920 and 409,353 and in the international patent application WO-A 95/07856. The sulfur formed in the sulfur recovery plant is condensed after each stage and discharged. The inert exhaust gas is passed through a burner after the chimney. The amount of sulfur was 2068 kg / h. Total desulfurization efficiency based on the original sour gas, which contained 9.0% by volume of H2S, was 96.5%.

EXAMPLE 2 An amount of the sour gas of 15545 Nm3 / h that comes from the regenerator of a gas purification plant, had the following composition at 40 ° C and a pressure of 1.70 absolute bars. 9. 0"or in vol. H S 0.01 in volume COS 0.22 in volume CH3SH 0.38" 5 in volume. C2H5SH 0.03 or in vol. C3H7SH 81.53% vol. C02 4.23 in vol. H20 3.51. or, * or in vol. Hydrocarbons (Ci a Ci) 1.08 or in vol. Aromatic substances (Benzene, Toluene, Xylene) This sour gas was contacted in an absorber of a gas purification plant with a methyldiethanolamine solution, whereby the H2S and a part of the C02 were absorbed. The amount of gas produced (gas rich in C02) from the absorber was 13000 Nm3 / h with the following composition: # 88.47% vol. C02 500 ppm in vol. H2S 70 ppm in vol. COS 0.26 o. in vol. CH3SH 0.46 in vol. C2H5SH 0.04% vol. C3H7SH 0.01% vol. C4H9SH 5.21% vol. H20 * s 4.2 in vol. Hydrocarbons (Ci to Ci7) 10 1.29 in vol. Aromatic substances (Benzene, Toluene, Xylene) The produced gas is then heated to 230 ° C and fed to the sulfur removal step of the outlet gas from the sulfur recovery plant. After desorption in a regenerator, the gas mixture of sour H2S / C02 (gas rich in H2S) is passed to a sulfur recovery plant. This mixture of H2S / C02 gas is quantified in 2690 Nm3 / h and had the following composition at 40 ° C and 1.7 absolute bars. 51. 7% in vol. H2S 44.0% vol, C02 4.3% vol, H20 25 • 2780 Nm3 / h of air are supplied to the burner of the thermal stage of the sulfur recovery plant, so that after the second stage of the Claus reactor, 1.14% by volume of H2S and 0.07% by volume of S02 were present in the process gas. The process gas was then fed to the sulfur removal step of the exit gas. To this gas and to the gas of the product supplied, 875 Nm3 / h of air are fed. The entry temperature of the selective oxidation reactor was 230 ° C and the outlet temperature was 290 ° C. To limit the temperature rise in the oxidation reactor to 60 ° C, 13000 Nm3 / h of the cooled gas after the reactor was recycled onto the reactor. The oxidation reactor The catalyst was filled with the catalyst as described in the European patents Nos. 242,920 and 409,353 and in the international patent application WO-A 95/07856. The sulfur formed in the sulfur recovery plant condensed after each stage and downloaded. The inert exhaust gas was passed to the chimney by means of a rear burner. The amount of sulfur was 2050 kg / h. The total desulfurization efficiency based on the original sour gas, which contained 9.0% by volume of H2S was 95.7%.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following fifteen twenty

Claims (14)

1. A method to remove sulfur-containing contaminants in the form of mercaptans and H2S from hydrocarbon gas, which can also contain C02 and higher aliphatic and aromatic hydrocarbons, and recover elemental sulfur, characterized in that in a first step of absorption the contaminants containing sulfur are removed from the gas, to form on the one hand a stream of purified gas and on the other hand a sour gas, such sour gas is fed to a second absorption step in which the sour gas is separated in a first stream of gas enriched in H2S and with a reduced amount of mercaptans, which is fed to a Claus plant, followed by a step of selective oxidation of H2S to elemental sulfur in the exit gas, and a second gas stream enriched in mercaptans and with a reduced amount of H2S, such a second gas stream, if desired after further treatment, is subjected to selective oxidation of the coasters. sulfur compounds to elemental sulfur.

2. A method according to claim 1, characterized in that the second gas stream is hydrogenated prior to selective oxidation.

3. A method according to claim 1 or 2, characterized in that the selective oxidation of the exit gas of the first gas stream and of the second gas stream takes place in the same reactor.

4. A method according to claim 1 or 2, characterized in that the selective oxidation of the exit gas of the first stream of 10 gas and the second gas stream occurs in two separate reactors.

5. A method according to claims 1-4, characterized in that the first absorption step 15 is carried out using a chemical, physical or chemical / physical absorption agent which removes substantially all the sulfur compounds and the CO 2 from the gas.

6. A method according to claim 5, characterized in that a sulfolane absorption agent is used in combination with a secondary or tertiary amine.

7. A method according to claims 1-6, characterized in that the second absorption step is carried out using an absorption agent based on a secondary and / or tertiary amine.

8. A method according to claims 1-7, characterized in that the first absorption step is carried out in such a way that the purified gas contains not more than 10, more particularly not more than 5 ppm of sulfur-containing contaminants.

9. A method according to claims 1-8, characterized in that the natural gas is used as the gas to be purified, which is optionally liquefied after purification.

10. A method according to claims 1-9, characterized in that the second absorption step is carried out in such a way that the content of H2S in the first gas stream is at least 2.5 times, more particularly at least 4 times. times higher than the H2S content in the sour gas.

11. A method according to claims 1-10, characterized in that the content of the mercaptans in the first gas stream is less than 1 ppm.

12. A method according to claims 2-11, characterized in that the hydrogenation occurs in the presence of a catalyst on a support, with a catalytically active component based on at least one metal of Group VIB and at least one metal of Group VIII of the System Periodic of the Elements, more particularly on a combination of cobalt and molybdenum.

13. A method according to claims 2-12, characterized in that the hydrogenation occurs in the presence of a quantity of water.

14. A method according to claims 2-13, characterized in that the second gas stream is indirectly heated prior to hydrogenation.