Method for treatment of gas

Abstract

A method for treatment of a gas having 10 to 0.5% by volume of at least one of COS and CS.sub.2, and 30 ppm to 5% by volume of unsaturated hydrocarbons: a) hydrogenation of organic compounds unsaturated with respect to paraffins by contacting the gas with a hydrogenation catalyst in the presence of hydrogen at 100 to 400 C., to provide an effluent that is low in unsaturated hydrocarbon compounds, the hydrogenation catalyst having at least one metal that is palladium, platinum, nickel, or cobalt deposited on a porous substrate. b) catalytic hydrolysis-hydrogenation in the presence of water of COS and/or CS.sub.2 present in the effluent of a) to provide an H.sub.2S-rich effluent by bringing the effluent from a) into contact with a hydrolysis-hydrogenation catalyst.

Claims

1. A method of reducing sulfur in a gas, comprising treatment of a gas that comprises from 10 ppm by volume to 0.5% by volume of at least one of the compounds COS and CS.sub.2, and from 30 ppm by volume to 5% by volume of unsaturated hydrocarbon compounds: a) hydrogenation (1) of hydrocarbon compounds that are unsaturated with respect to paraffins by contacting said gas with a hydrogenation catalyst in the presence of hydrogen at a temperature of between 100 and 400 C., in such a way as to provide an effluent that is low in unsaturated hydrocarbon compounds, with the hydrogenation catalyst comprising at least one metal that is palladium, platinum, nickel, or cobalt deposited on a porous substrate, b) catalytic hydrolysis-hydrogenation (2) in the presence of water from COS and/or CS.sub.2 that is present in the effluent that is obtained from a) in such a way as to provide an H.sub.2S-rich effluent, by contacting the effluent obtained from a), with a hydrolysis-hydrogenation catalyst, and with the addition of hydrogen, the hydrolysis-hydrogenation catalyst comprising at least one metal of group VIII that is nickel or cobalt, at least one metal of group VIB that is molybdenum or tungsten, and a substrate that consists essentially of alumina and in which the metal content of group VIII, expressed in terms of oxide, is between 1% and 10% by weight in relation to the total catalyst weight, in which the metal content of group VIB, expressed in terms of oxide, is between 3% and 20% by weight in relation to the total catalyst weight and in which the (metal of group VIII)/(metal of group VIB) molar ratio is between 0.4 and 2 (mol/mol) whereby hydrolysishydrogenation of the effluent from a) occurs.

2. The method according to claim 1, in which the hydrogenation catalyst has a platinum content, expressed in terms of metal, of between 0.2% by weight and 4% by weight in relation to the catalyst weight.

3. The method according to claim 1, in which the hydrogenation catalyst has a palladium content, expressed in terms of metal, of between 0.05% by weight and 5% by weight in relation to the catalyst weight.

4. The method according to claim 1, in which the hydrogenation catalyst has a nickel content, expressed in terms of oxide, of between 0.5% by weight and 15% by weight in relation to the catalyst weight.

5. The method according to claim 1, in which the hydrogenation catalyst has a cobalt content, expressed in terms of oxide, of between 0.5% by weight and 15% by weight in relation to the catalyst weight.

6. The method according to claim 1, in which the hydrogenation catalyst further comprises molybdenum at a content that is expressed in terms of oxide of between 1% and 20% by weight in relation to the catalyst weight.

7. The method according to claim 1, in which the hydrolysis-hydrogenation catalyst has a content of metal of group VIII, expressed in terms of oxide, of between 1% and 8% by weight in relation to the total catalyst weight.

8. The method according to claim 1, in which the hydrolysis-hydrogenation catalyst has a content of metal of group VIB, expressed in terms of oxide, of between 5% and 18% by weight in relation to the total catalyst weight.

9. The method according to claim 1, in which the hydrolysis-hydrogenation catalyst comprises cobalt and molybdenum.

10. The method according to claim 1, in which a) and b) are carried out in the same reactor that comprises a hydrogenation catalyst bed (13) and a hydrolysis-hydrogenation catalyst bed (14), with the beds (13, 14) being arranged in relation to one another in the reactor in such a way that the gas that is to be treated encounters the hydrogenation catalyst bed (13) before the hydrolysis-hydrogenation catalyst bed (14).

11. The method according to claim 1, in which a) and b) are implemented with catalysts of identical formulation, a substrate that consists essentially of alumina, at least one metal of group VIII that is nickel or cobalt, and at least one metal of group VIB that is molybdenum or tungsten.

12. The method according to claim 1, in which a) is carried out at a pressure of between 0.1 and 5 MPa and a VVH of between 1,000 and 4,000 h.sup.1.

13. The method according to claim 1, in which b) is carried out at a pressure of between 0.1 and 5 MPa and a VVH of between 1,000 and 4,000 h.sup.1.

14. The method according to claim 1, comprising c) treating H.sub.2S-rich effluent obtained from b) in a unit trapping H.sub.2S or converting H.sub.2S into elementary sulfur.

15. The method according to claim 1, in which a liquid/gas separation of the gas that is to be treated is carried out before carrying out hydrogenation a).

16. The method according to claim 1, in which the gas that is to be treated is obtained from units for gasification of carbon or petcoke or biomass or calcination furnaces of units manufacturing carbon black.

17. The method according to claim 1, in which the hydrolysis-hydrogenation catalyst has a content of metal of group VIII, expressed in terms of oxide, of between 3% and 7% by weight in relation to the total catalyst weight.

18. The method according to claim 1, in which the hydrolysis-hydrogenation catalyst has a content of metal of group VIB, expressed in terms of oxide, of between 6% and 15% by weight in relation to the total catalyst weight.

19. The method according to claim 1, wherein the hydrolysis-hydrogenation catalyst substrate consists essentially of gamma alumina.

20. The method according to claim 1, wherein effluent from b) has a content of CS.sub.2 and COS of 0.008% or less by volume.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) These aspects as well as other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, with reference being made to the figures, in which:

(2) FIG. 1 shows a first embodiment of the method according to the invention.

(3) FIG. 2 shows a second embodiment of the method according to the invention.

(4) FIG. 3 shows a third embodiment of the method according to the invention.

(5) The figures are not drawn to scale. Generally, similar elements are denoted by identical references in the figures.

(6) With reference to FIG. 1, the method uses a first reactor 1 in which a catalyst for hydrogenation of unsaturated compounds is present, preferably a catalyst for selective hydrogenation. Any hydrogenation catalyst described above can be used in this embodiment.

(7) As shown in FIG. 1, the gaseous feedstock that is to be treated is introduced into the reactor 1 via the line 3 while an additional quantity of hydrogen, in addition to the hydrogen initially present in the gas that is to be treated, can optionally be provided in the reactor 1 using the line 4.

(8) The total quantity of hydrogen present in the gas to be treated and optionally added is such that the molar ratio between the hydrogen and the unsaturated hydrocarbon compounds to be hydrogenated is greater than the stoichiometry and preferably between 1.1 and 3,000 mol per mol, and preferably between 300 and 2,000 mol per mol.

(9) The hydrogenation step is conducted generally at a pressure of between 0.1 and 5 MPa, preferably between 0.5 and 3 MPa, at a temperature of between 100 and 400 C., preferably between 150 C. and 250 C., and a volume of catalyst in relation to the quantity of gas that is to be treated with 1 m.sup.3 of catalyst per 1,000 to 4,000 Nm.sup.3/h of gas that is to be treated, or a VVH of between 1,000 and 4,000 h.sup.1.

(10) With reference to FIG. 1, the effluent that is obtained from the hydrogenation reactor is then sent into the hydrolysis-hydrogenation reactor 2, via the line 5, in which is carried out the conversion of the sulfide compounds COS and CS.sub.2 into H.sub.2S on a specific catalyst in the presence of water and hydrogen.

(11) If the content of water or hydrogen of the feedstock is not sufficient, water or additional hydrogen can be introduced via the line 6 so as to carry out the hydrolysis-hydrogenation with excess water in relation to the hydrolyzable molecules (COS, CS.sub.2, HCN).

(12) Any hydrolysis-hydrogenation catalyst described above can be used in this embodiment.

(13) The reactions employed during this step can be represented by the following reactions:
COS+H.sub.2O.fwdarw.CO.sub.2+H.sub.2S
CS.sub.2+2H.sub.2O.fwdarw.2H.sub.2S+CO.sub.2
COS+4H.sub.2.fwdarw.CH.sub.4+H.sub.2O+H.sub.2S
CS.sub.2+2H.sub.2.fwdarw.CH.sub.4+2H.sub.2S

(14) The hydrolysis-hydrogenation step is typically carried out at a pressure of between 0.1 and 5 MPa, preferably between 0.5 and 3 MPa, at a temperature of between 100 and 400 C., preferably between 150 C. and 250 C., and a volume of catalyst in relation to the quantity of gas that is to be treated of 1 m.sup.3 of catalyst for 1,000 to 4,000 Nm.sup.3/h of gas that is to be treated, or a VVH of between 1,000 and 4,000 h.sup.1.

(15) The procedure is performed in the presence of excess water in relation to the hydrolysis-hydrogenable molecules. Preferably, the procedure is performed with a water/hydrolyzable product molar ratio of between 5 and 1,000 mol per mol, and in a more preferred manner of between 10 and 500 mol per mol.

(16) The gaseous effluent that is treated in the hydrolysis-hydrogenation reactor 2 is then extracted and routed via the line 7 to a heat exchanger 8, for example a cooling tower, in such a way as to cool the treated gas. The treated and cooled gas is transferred via the line 9 into a liquid/gas separator 10. The liquid water for condensation is recovered at the bottom of the separator 10, while the gas that is low in H.sub.2O and that contains H.sub.2S is broughtthanks to the line 11to a treatment unit 12 that can be, for example, an H.sub.2S trapping unit or an H.sub.2S conversion unit, which carries out, for example, the oxidation of H.sub.2S to form elementary sulfur:
2H.sub.2S+SO.sub.2.fwdarw.3S+2H.sub.2O

(17) According to the invention, the two hydrogenation and hydrolysis-hydrogenation reactions of the feedstock that is to be treated can be carried out in the same reactor comprising a first hydrogenation catalyst bed and a second hydrolysis-hydrogenation catalyst bed, with the beds being arranged in relation to one another in the reactor in such a way that the gaseous feedstock that is to be treated encounters the hydrogenation catalyst bed before the hydrolysis-hydrogenation catalyst bed, as shown in FIG. 2.

(18) With reference to FIG. 2, the second embodiment employs a single reactor 1 in which the hydrogenation and hydrolysis-hydrogenation catalytic reactions are carried out. For this purpose, the reactor comprises two catalyst beds 13 and 14 respectively for hydrogenation and hydrolysis-hydrogenation. These two beds can be separated from one another by an inner space or in contrast can be consecutive without any intermediate space. The catalyst beds 13 and 14 are arranged in the reactor 1 in such a way that the feedstock that is to be treated first encounters the hydrogenation catalytic bed 13 and then the hydrolysis-hydrogenation catalytic bed.

(19) So as to carry out the hydrogenation of the gaseous feedstock that is introduced via the line 3, an additional supply of hydrogen can optionally be carried out by means of the line 4 that is located upstream from the catalyst bed 13. When this is necessary, an inner space separates the catalytic beds 13 and 14 so as to position in this space an injection point of an addition of water that is necessary to the hydrolysis-hydrogenation reaction via the line 6.

(20) The operating conditions that are used for the two catalytic reactions and described with reference to FIG. 1 can be applied in this second embodiment. Any hydrogenation catalyst or hydrolysis-hydrogenation catalyst described above can also be used in this embodiment.

(21) In a particular embodiment, for steps a) and b), the method according to the invention uses catalysts that have identical formulations that are arranged in two different reactors (according to FIG. 1) or in one and the same reactor (according to FIG. 2).

(22) In a similar way to the embodiment of FIG. 1, the gaseous effluentafter the hydrolysis-hydrogenation catalytic stepis evacuated from the reactor 1 and sent via the line 5 into a heat exchanger 8, and then into a separator tank 10 via the line 9. Condensation water is extracted from the separator tank 10 at the bottom, and a gas charged with H.sub.2S that is transferred to a unit for trapping or for conversion of H.sub.2S 12 is extracted from the tank separator 10 at the top.

(23) The third embodiment of the method according to the invention is shown in FIG. 3 and essentially differs from the embodiments of FIGS. 1 and 2 in that it comprises a preliminary step for gas/liquid separation carried out on the gas that is to be treated. It is actually advantageous essentially to remove excess water and/or optionally liquid organic compounds that may or may not be dissolved in the gaseous phase so as to reduce the volume of feedstock that is to be treated, while preserving excess water to carry out the hydrolysis-hydrogenation reaction.

(24) In this case, as shown in FIG. 3, the gas that is to be treated that is generally hot is sent to a heat exchanger 21 via the line 20 where it is cooled, and then sent via the line 22 to a separator tank 23. In the tank 23, two phases, namely a gas phase at the top and a liquid phase at the bottom that contains the water of the feedstock, are separated. The gas that is separated from this liquid and optionally a portion of the dissolved water that is obtained from the separator tank 23 is sent via the pipe 25 into a compressor 26 to be compressed there.

(25) The compressed gas optionally undergoes, as shown in FIG. 3, a step of heating through the optional heat exchanger 28, which, when it is present, is fed by a hot fluid. This hot fluid ispreferably and according to the example of FIG. 3the hot gaseous effluent that is obtained from the reaction zone 32 for hydrogenation and hydrolysis-hydrogenation. The previously-heated compressed gas can optionally be brought to the operational temperature by means of an optional heating unit 30, for example an exchanger, before being introduced into the reaction zone 32 where the hydrogenation and hydrolysis-hydrogenation reactions are carried out according to the method of the invention. The hot effluent that is obtained from the reaction zone 32 is evacuated via the line 33 and is introduced into the heat exchanger 28 to reheat the gas that is to be treated. After having been cooled with contact of the gas that is to be treated, the treated gas that is rich in H.sub.2S can optionally be sent via the line 34 into a second optional condenser 35, for example a cooling tower, and/or optionally into a heat exchanger 36 that is also optional. This cooling makes it possible to regulate the temperature of the flow to a temperature that is compatible with possible treatments downstream. Thus, the cooled flow can then be treated in particular in a unit (not shown) for trapping H.sub.2S or for conversion of H.sub.2S into elementary sulfur.

EXAMPLES

(26) The examples presented below have been obtained from a gaseous feedstock A that corresponds to an effluent that is obtained from a unit for production of carbon black and comprises sulfur-containing and nitrogen-containing compounds (COS, CS.sub.2, and HCN), and acetylene.

(27) TABLE-US-00001 TABLE 1 Composition of the Feedstock A Composition of the Feedstock A Content (% by Volume) CS.sub.2 0.08 HCN 0.05 COS 0.013 SO.sub.2 0.007 H.sub.2S 0.15 CH.sub.4 0.3 C.sub.2H.sub.2 0.3 CO 8 H.sub.2 9 CO.sub.2 2 H.sub.2O 45 O.sub.2 0.1 N.sub.2 35

(28) The gaseous feedstock that is to be treated therefore contains a non-negligible quantity of acetylene at a level of 0.3% by volume.

Example 1 (for Comparison)

(29) The feedstock A that is described in Table 1 is first sent into a first reactor according to step a) of the invention. The hydrogenation catalyst that is used during step a) consists of 0.28% by weight of Pd on a substrate that consists of agglomerated gamma-alumina in the form of balls with a 1.7 mm diameter. Step a) is implemented under the following operating conditions: Temperature ( C.): 220 Pressure (MPa): 0.2 VVH (h.sup.1): 3,200 Content of H.sub.2 in the feedstock: 9% by volume; additional hydrogen therefore is not added.

(30) The composition of the effluent that is obtained from step a) is analyzed, by gas phase chromatography, after 48 hours of operation. The composition of the effluent that is obtained from step a) is provided in Table 2.

(31) TABLE-US-00002 TABLE 2 Composition of the Effluent from the Hydrogenation Step Effluent Obtained from Step a) Content (% by Volume) CS.sub.2 0.07 HCN 0.005 COS 0.008 SO.sub.2 0.001 H.sub.2S 0.18 CH.sub.4 0.3 C.sub.2H.sub.2 <0.01 C.sub.2H.sub.6 0.3 CO 7.8 H.sub.2 9 CO.sub.2 2.1 H.sub.2O 45 O.sub.2 <0.001 N.sub.2 35

(32) The preliminary treatment of the gas from the feedstock by hydrogenation thus makes it possible to transform acetylene into ethane and consequently to bring the acetylene content to a value of less than 0.01% by volume.

(33) The effluent that is obtained from step a) is then directed treated in a second reactor (step b) of the invention). The catalyst that is used during step b) has the following composition (expressed relative to the total catalyst weight): 2.5% by weight of nickel oxide (NiO), 9.0% by weight of molybdenum trioxide (MoO.sub.3), and 88.5% by weight of titanium oxide.

(34) The operating conditions of this step b) are as follows: Temperature ( C.): 220 Pressure (MPa): 0.2 VVH (h.sup.1): 2,000

(35) The water content in the effluent is 45% by volume; additional water is therefore not added to carry out step b).

(36) The composition of the effluent that is obtained from step b) is analyzed by gas phase chromatography. The results are presented in Table 3.

(37) TABLE-US-00003 TABLE 3 Composition of the Effluent of the Hydrolysis-Hydrogenation Step Effluent Obtained from Step b) Content (% by Volume) CS.sub.2 0.01 HCN <0.001 COS 0.005 SO.sub.2 0.001 H.sub.2S 0.30 CH.sub.4 0.3 C.sub.2H.sub.2 <0.01 C.sub.2H.sub.6 0.3 CO 4.6 H.sub.2 12.2 CO.sub.2 5.3 H.sub.2O 42 O.sub.2 <0.001 N.sub.2 35

(38) The analyses indicate that the preliminary hydrogenation step for the purpose of saturating the unsaturated organic compounds makes it possible to preserve the catalytic performances of the catalyst, in particular the activity by hydrolysis-hydrogenation relative to carbon disulfides.

(39) A lowering of the CS.sub.2 content on the order of 87% is achieved.

Example 2 (According to the Invention)

(40) The same feedstock A whose composition was provided in Table 1 is treated in a hydrogenation step under the same conditions as Example 1.

(41) The effluent that is obtained from step a) after 48 hours of operation is then treated in a second reactor (step b) of the invention). The catalyst that is used during step b) consists of 3% by weight of cobalt oxide, 14% by weight of molybdenum oxide, with a gamma-alumina substrate. The hydrolysis-hydrogenation catalyst that is used therefore has a molar ratio (Co/Mo) that is equal to 0.4.

(42) Step b) is implemented under the following operating conditions: Temperature ( C.): 220 Pressure (MPa): 0.2 VVH (h1): 2,000

(43) The content of H.sub.2O in the effluent that is obtained from step a) (see Table 2) is 45% by volume; it is not necessary to add water to the effluent before treating it according to step b).

(44) The composition of the effluent that is obtained from step b) is provided in Table 4.

(45) TABLE-US-00004 TABLE 4 Composition of the Effluent from the Hydrolysis-Hydrogenation Step Effluent Obtained from Step b) Content (% by Volume) CS.sub.2 0.006 HCN <0.001 COS 0.005 SO.sub.2 <0.001 H.sub.2S 0.46 CH.sub.4 0.31 C.sub.2H.sub.2 <0.01 C.sub.2H.sub.6 0.30 CO 1.20 H.sub.2 15.7 CO.sub.2 9.0 H.sub.2O 38.0 O.sub.2 <0.001 N.sub.2 35.0

(46) It is observed that the hydrogenation step (step a)) carried out on the gas has a positive effect on the conversion yield, and the use of a hydrolysis-hydrogenation catalyst that meets the characteristics of the invention makes it possible to improve the conversion of CS.sub.2. Thus, a lowering of the CS.sub.2 content on the order of 92% is achieved.

Example 3 (for Comparison)

(47) The same gaseous feedstock A whose composition was provided in Table 1 is first sent into a first reactor for hydrogenation of the unsaturated compounds according to step a) of the invention, under the same conditions as those of Example 1.

(48) The effluent that is obtained from step a) is then directed toward a second reactor (step b) of the invention). The catalyst that is used during step b) consists of 0.65% by weight of cobalt oxide, 14% by weight of molybdenum oxide, with a gamma-alumina substrate. The hydrolysis-hydrogenation catalyst that is used therefore has a molar ratio (Co/Mo) that is equal to 0.09.

(49) Step b) is implemented under the following operating conditions: Temperature ( C.): 220 Pressure (MPa): 0.2 VVH (h.sup.1): 2,000

(50) The content of H.sub.2O in the effluent that is obtained from step a) (see Table 2) is 45% by volume; it is not necessary to add water in the effluent before treating it according to step b).

(51) The composition of the effluent that is obtained from step b) is provided in Table 5.

(52) TABLE-US-00005 TABLE 5 Composition of the Effluent from the Hydrolysis-Hydrogenation Step Effluent Obtained from Step b) Content (% by Volume) CS.sub.2 0.025 HCN 0.005 COS 0.009 SO.sub.2 0.020 H.sub.2S 0.46 CH.sub.4 0.35 C.sub.2H.sub.2 <0.01 C.sub.2H.sub.6 0.30 CO 3.10 H.sub.2 13.60 CO.sub.2 6.90 H.sub.2O 40.2 O.sub.2 <0.001 N.sub.2 35.0

(53) A lowering of the CS.sub.2 content, which is only on the order of 69%, is achieved.

Example 4 (According to the Invention)

(54) The same feedstock A whose composition was provided in Table 1 is first sent into a first reactor for hydrogenation of the unsaturated compounds according to step a) of the invention, under the same conditions as those of Example 1.

(55) The effluent that is obtained from step a) is then directed to a second reactor (step b) of the invention). The catalyst that is used during step b) consists of 3.9% by weight of nickel oxide, 28% by weight of tungsten oxide, with a gamma-alumina substrate. The hydrolysis-hydrogenation catalyst that is used therefore has a molar ratio (Ni/W) that is equal to 0.43.

(56) Step b) is implemented under the following operating conditions: Temperature ( C.): 220 Pressure (MPa): 0.2 VVH (h.sup.1): 2,000

(57) The content of H.sub.2O in the effluent that is obtained from step a) (see Table 2) is 45% by volume; it is not necessary to add water in the effluent before treating it according to step b).

(58) The composition of the effluent that is obtained from step b) is provided in Table 6.

(59) TABLE-US-00006 TABLE 6 Composition of the Effluent from the Hydrolysis-Hydrogenation Step Effluent Obtained from Step b) Content (% by Volume) CS.sub.2 0.008 HCN 0.004 COS 0.006 SO.sub.2 0.01 H.sub.2S 0.45 CH.sub.4 0.35 C.sub.2H.sub.2 <0.01 C.sub.2H.sub.6 0.30 CO 3.25 H.sub.2 13.60 CO.sub.2 6.80 H.sub.2O 40.2 O.sub.2 <0.001 N.sub.2 35.0

(60) A lowering of the CS.sub.2 content on the order of 90% is achieved.

Example 5 (According to the Invention)

(61) The feedstock A whose composition is provided in Table 1 is first sent into a first reactor for hydrogenation of unsaturated compounds according to step a) of the invention. Step a) is implemented under the operating conditions and with the catalyst of step a) of Example 1.

(62) The effluent that is obtained from step a) is then directed to a second reactor (step b) of the invention). The catalyst that is used during step b) consists of 2.5% by weight of nickel oxide, 9.0% by weight of molybdenum oxide, with a gamma-alumina substrate. The hydrolysis-hydrogenation catalyst that is used therefore has a molar ratio (Ni/Mo) equal to 0.53.

(63) Step b) is implemented under the following operating conditions: Temperature ( C.): 220 Pressure (MPa): 0.2 VVH (h.sup.1): 2,100

(64) The content of H.sub.2O in the effluent that is obtained from step a) (see Table 2) is 45% by volume; it is not necessary to add water to the effluent before treating it according to step b). The composition of the effluent that is obtained from step b) is provided in Table 7.

(65) TABLE-US-00007 TABLE 7 Composition of the Effluent from the Hydrolysis-Hydrogenation Step Effluent Obtained from Step b) Content (% by Volume) CS.sub.2 0.007 HCN <0.001 COS 0.007 SO.sub.2 <0.001 H.sub.2S 0.46 CH.sub.4 0.3 C.sub.2H.sub.2 <0.01 C.sub.2H.sub.6 0.3 CO 0.89 H.sub.2 15.3 CO.sub.2 8.6 H.sub.2O 36 O.sub.2 <0.001 N.sub.2 35

(66) A lowering of the CS.sub.2 content on the order of 91% is achieved.

Example 6 (for Comparison)

(67) The feedstock A whose composition is provided in Table 1 is first sent into a first reactor for hydrogenation of the unsaturated compounds according to step a) of the invention. Step a) is implemented under the operating conditions and with the catalyst of step a) of Example 1.

(68) The effluent that is obtained from step a) is then directed toward a second reactor according to step b) of the invention. The catalyst that is used during step b) consists of 17% by weight of cobalt oxide, 14% by weight of molybdenum oxide, with a gamma-alumina substrate. During the preparation of this catalyst, the total quantity of cobalt and molybdenum was impregnated in a single impregnation step on the substrate. The hydrolysis-hydrogenation catalyst that was used has a molar ratio (Co/Mo) that is equal to 2.3.

(69) Step b) is implemented under the following operating conditions: Temperature ( C.): 220 Pressure (MPa): 0.2 VVH (h.sup.1): 2,100

(70) The content of H.sub.2O in the effluent that is obtained from step a) (see Table 2) is 45% by volume; it is not necessary to add water in the effluent before treating it according to step b).

(71) The composition of the effluent that is obtained from step b) is provided in Table 8.

(72) TABLE-US-00008 TABLE 8 Composition of the Effluent from the Hydrolysis-Hydrogenation Step Effluent Obtained from Step b) Content (% by Volume) CS.sub.2 0.03 HCN 0.004 COS 0.010 SO.sub.2 0.01 H.sub.2S 0.46 CH.sub.4 0.3 C.sub.2H.sub.2 <0.01 C.sub.2H.sub.6 0.3 CO 0.89 H.sub.2 15.3 CO.sub.2 8.6 H.sub.2O 36 O.sub.2 <0.001 N.sub.2 35

(73) The results of Examples 2, 4, and 5 show that the catalysts according to the invention based on the formulation NiMo/Al.sub.2O.sub.3, NiW/Al.sub.2O.sub.3 or CoMo/Al.sub.2O.sub.3 with metal contents according to the invention and metal of group VIII/metal of group VIB molar ratios of between 0.2 and 4 mol/mol lead to effluents having CS.sub.2 and COS contents that are less than or equal to 0.008. Moreover, the use of the catalysts of comparison examples 3 and 6 lead to effluents having CS.sub.2 and COS contents respectively of 0.025 to 0.03 and 0.009 to 0.010.

(74) Furthermore, it is noted that the CS.sub.2 contents of the effluents obtained at the end of the treatment with the catalysts according to the invention are also smaller than in the case of Example 1 (for comparison) that uses an NiMo/TiO.sub.2 catalyst.