Process for removing sulfur compounds from a gas with hydrogenation and direct oxidation steps

Abstract

A process for removing sulfur from a gas containing sulfur compounds as H2S, SO2, COS, CS2 . . . , in a quantity of up to 15% wt; particularly gases emanating from the Claus process: A first hydrogenation of the sulfur compounds into H2S, the hydrogenation gas being used to regenerate a deactivated bed of oxidation catalyst, both being carried out at 200-500 C. After sulfur removal, the resulting gas undergoes a second hydrogenation step and then a direct oxidation step, said step being operated under the dew point of sulfur to trap the formed sulfur in the catalyst. In the further cycle, the gas streams are switched so as to regenerate the catalyst in run which is deactivated.

Claims

1. A process for removal of sulfur compounds contained in a gas to be processed containing up to 15% volume of sulfur compounds expressed as H.sub.2S, said process comprising: 1) first hydrogenating of said sulfur compounds into H.sub.2S, in the presence of hydrogen over an hydrogenation catalyst, the gas entering at a temperature of 200-320 C., 2) directly oxidating of H.sub.2S into elemental sulfur in the presence of oxygen over a bed of direct oxidation catalyst, at a controlled temperature below sulfur dew point, depositing elemental sulfur in the catalyst bed and obtaining a purified gas, 3) regenerating of deactivated direct oxidation catalyst, regeneration being carried out in-situ by passage of a hot gas at a temperature above the sulfur dew point, then cooling gas obtained, condensing and separating of elemental sulfur, obtaining an elemental sulfur depleted gas and a regenerated catalyst, wherein regeneration is carried out by the passage of the hot gas issued from the first hydrogenation step, elemental sulfur depleted gas undergoes a second hydrogenation in the presence of hydrogen over an hydrogenation catalyst, the gas entering at a temperature of 122 to 320 C., and direct oxidation of the obtained gas.

2. The process according to claim 1 wherein the oxidation catalyst bed comprises an internal cooling for controlling the temperature.

3. The process according to claim 1 wherein the hydrogenation operates without cooling.

4. The process according to claim 1 carried out in: at least two separated direct oxidation zones in parallel, one (or several) being under reaction in a present cycle while deactivated catalyst is regenerated, said catalyst being issued from the zone previously under reaction in a previous cycle, the process operating as following successively: a) the feed (gas to be treated containing sulfur compounds+H.sub.2) undergoes a first hydrogenation of sulfur compounds into H.sub.2S, in the presence of hydrogen over an hydrogenation catalyst, the gas entering at a temperature of 200-320 C., b) regeneration of the direct oxidation catalyst deactivated in the previous cycle, said regeneration being carried out in-situ by the passage of the hot gas issued from the first hydrogenation, at a temperature above the sulfur dew point to desorb the sulfur, then cooling the obtained gas, condensation and separation of elemental sulfur, obtaining an elemental sulfur depleted gas and a regenerated catalyst, c) a second hydrogenation of elemental sulfur depleted gas in the presence of hydrogen over hydrogenation catalyst, the gas entering at a temperature of 122 to 320 C., d) direct oxidation of H.sub.2S formed in the first and second hydrogenations into elemental sulfur in the presence of oxygen over a bed of direct oxidation catalyst, at a controlled temperature below the sulfur dew point, depositing elemental sulfur in the catalyst bed and obtaining a purified gas.

5. The process according to claim 1, carried out in at least 2 identical reactors operating in downflow, said reactors effecting a process comprising: at the top of each reactor, a first zone of at least one catalytic bed of an hydrogenation catalyst, receiving a gas containing hydrogen, followed by a second zone of a direct oxidation catalyst comprising an internal cooling, and between the first zone and the direct oxidation zone, and before entering in the direct oxidation zone, an injection of an oxygen-containing gas, said injection being activated only during the oxidation reaction, the first reactor receiving the gas to be treated is at a temperature of 200-500 C. (called hot mode), the first hydrogenation takes place in the first zone and the regeneration takes place in the second zone, the gas withdrawn from the second zone of the first reactor entering in the first zone of the second reactor is at a temperature of 122 to 320 C. and the second hydrogenation takes place, the gas from the first zone of the second reactor, optionally cooled, flows in the second zone of the second reactor where the temperature is maintained at a temperature below the sulfur dew point (called cold mode), and a purified gas exits, prior to the deactivation of the oxidation catalyst of the second reactor, the gas steams are switched such that the second reactor becomes the first reactor operating in hot mode, and the first reactor becomes the second reactor operating in cold mode.

6. The process according to claim 5 wherein a volume is designed between the first and second zone of each reactor, said volume being used to cool down the gas emanating from the hydrogenation zone prior contact with the direct oxidation catalyst.

7. The process according to claim 1 wherein the hydrogenation catalyst comprises a GVIII and a GVIB element deposited on alumina.

8. The process according to claim 1, wherein the direct oxidation catalyst is a catalyst comprising titanium oxide, a catalyst comprising Fe, CoMo or NiMo supported on titanium oxide, a catalyst comprising copper supported on titanium oxide or alumina, or a catalyst comprising an oxysulfide of a transition metal that is Fe, Cu, Ni, Cr, Mo or W, supported on silicium carbide.

9. The process according to claim 1, wherein the first hydrogenation operates in the presence of an excess of hydrogen of 1 to 5% vol. regarding to the total stoichiometric quantities of components to be hydrogenated, and the direct oxidation operates in the presence of an excess of oxygen of 0.1 to 4% vol. regarding to the stoichiometric quantity of components to be oxidized.

10. The process according to claim 1, wherein hydrogen is produced on-site by a reducing gas generator fed with natural gas and air in sub-stoichiometric quantity.

11. The process according to claim 1, wherein the direct oxidation in (2) is conducted at 20-180 C., and the regeneration in (3) is conducted at 200-500 C.

12. The process according to claim 2, wherein the oxidation catalyst bed comprises an internal heat exchanger as thermoplates heat exchanger embedded in the catalytic bed.

13. The process according to claim 4, wherein regeneration in (b) is conducted at 200-500 C., cooling is conducted at 122-170 C., and oxidation in (d) is conducted at 20-180 C.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The figures illustrate the invention:

(2) FIG. 1 represents the invention with 4 reactors (one for each catalyst).

(3) FIG. 2 represents the preferred embodiment with 2 identical reactors.

(4) We will not reproduce all the conditions directed to each step as previously described, obviously they apply to the schemes of the figures.

(5) FIG. 1:

(6) The feed (line 1) to the first reactor (I) comprises the gas to be treated, as tail gas from Claus unit, and H2.

(7) In FIG. 1, H2 (line 2) coming from the utilities on the site or a H2 producing unit (reforming for example) is admixed with the gas to be treated (line3).

(8) In FIG. 2, it will be seen that H2 is produced on-site by a reducing gas generator which will be described in FIG. 2, but it can be used for the embodiment of FIG. 1.

(9) The feed enters at the top of the first reactor at a temperature preferably of 200-320 C. If necessary, it has been heated.

(10) The first reactor (I) and the third reactor (III) contain at least one catalytic bed (4) of hydrogenation catalyst. It is a fixed bed of solid catalyst. The nature, quantity/volume of catalyst in each bed could be different. In FIG. 1, this catalytic bed does not include any cooling means. In reactors (I) and (III), respectively first and second hydrogenation step of sulfur species into H2S occur exothermally.

(11) The second reactor (II) and the fourth reactor (IV) contain a catalytic bed (11) of a direct oxidation catalyst. It is a fixed bed of solid catalyst. Embedded in the catalyst is an internal heat exchanger (12) preferably made of thermoplates, in which a coolant can circulate (inlet line 13 and outlet line 14). In reactors (II) and (IV), respectively regeneration step and direct oxidation step are carried out. In both reactors an oxygen-containing gas can be injected; injection is activated for the oxidation reaction but deactivated for regeneration.

(12) The hot gaseous effluent withdrawn (line 5) at the top of the first reactor (I), which is the gas issued from the first hydrogenation step, is then sent (line 6) to the second reactor (II). It is at a temperature above the sulfur dew point. Reactor (I) operates in hot mode.

(13) In the second reactor (II) regeneration of the clogged oxidation catalytic bed occurs. The second reactor operates with coolant temperature adjusted to higher temperature and in the absence of oxygen injection (line 25 deactivated) in order to regenerate the oxidative catalyst bed. Reactor (II) operates in hot mode. Solid and/or liquid sulfur (accumulated from a previous cycle for which the catalyst of the reactor (II) worked in the oxidation reaction of H2S at sub dew point temperature) is delivered from catalyst and/or vaporized. The regeneration step of the catalyst (11) can lead to SO2 emanation.

(14) The gas (line 7) issued from reactor (II) is enriched in sulfur and is cooled (cooler 8) at a temperature below sulfur dew point, in order for vaporized sulfur to be condensed (condenser 9) and liquid sulfur is separated (line 10) from the gas to be treated.

(15) The gas to be treated is sent (line 15) to the third reactor (III) after optional heating (heater 16). Hydrogen can be added (line 17) if necessary. Hydrogenation of potential sulfur species issued from regeneration step into H2S can occur exothermally. That means that if sulfur species are present, hydrogenation takes place, if absent, gas passes through the hydrogenation catalytic bed without hydrogenation reaction. The feed (gas+H2) of the third reactor is at a temperature of 122-320 C.

(16) The gas withdrawn (line 18) from the third reactor (III) is sent (line 19) to the fourth reactor (IV) where direct oxidation takes place, in the presence of an injection of an oxygen-containing gas (line 25 is activated) and with the coolant circulating in the internal heat exchanger (12) preferably made of thermoplates (inlet line 13 and outlet line 14 activated). Reactor (III) operates in cold mode.

(17) The purified gas is withdrawn (line 20), then flows through the valve 22 and exits by line 24.

(18) Prior to total deactivation of catalyst in the fourth reactor (IV), the bed is regenerated, by switching the inlet and outlet streams of the second reactor (II) and fourth reactor (IV) with valves (21) and (22), to proceed alternatively for each reactor to direct oxidize H2S together with sulfur accumulation, and then to regenerate the catalyst bed.

(19) After switching, feed (1) passes in reactor (I), then is sent to reactor (IV) via line (5), valve (21), line (19) where regeneration takes place. The gas is sent to condenser (9) for sulfur separation via line (20), valve (22), cooler (8). The sulfur depleted gas, after optional heating, passes in reactor (III) and is transferred by line (18), valve 21 and line (6) to reactor (II) where it undergoes the oxidation reaction. The purified gas is withdrawn (line 24) after flowing through line (7) and valve (22).

(20) FIG. 2:

(21) The first reactor (I) and the second reactor (II) are identical. Each reactor contains at its top (where the feed enters) a first zone where the hydrogenation catalyst bed (4) is. The first zone is followed by a second zone where the direct oxidation catalyst (11) is where an internal heat exchanger (12) is embedded, with its inlet (13) and outlet (14) of coolant. The first zone does not necessarily contain any means of cooling, while the second zone request an internal heat exchanger.

(22) Compared to FIG. 1, the first reactor of FIG. 2 includes the first and second reactors of FIG. 1 and the second reactor of FIG. 2 includes the third and fourth reactor of FIG. 1.

(23) The catalysts and conditions . . . are the same as recited above, however in this embodiment, the gas flows downwardly in both reactors.

(24) On this figure, H2 is produced on-site by a reducing gas generator here called RGG (30) in which a fuel as natural gas (line 31) with air (line 32) undergo combustion in sub-stoichiometric proportion by a burner (33), gases containing H2 and water are produced and mixed with the gas to be treated (line 34) in zone (35). If necessary, external H2 (line 36) can also be added to the stream to be treated. If necessary, the stream can be heated.

(25) The feed (line 1) is sent (line 6) to the first reactor (first and second zones) at a high temperature of 200-320 C. (hot mode). In reactor (I) the first hydrogenation step is carried out in the first zone and the hot gas passes directly in the second zone where regeneration of the deactivated oxidation catalyst occurs. There is no injection of oxygen (line 25 deactivated). Reactor (I) operates in hot mode. The resulting gas is withdrawn (line 7), cooled (cooler 8) below the sulfur dew point so that liquid sulfur obtained from regeneration of catalyst (11) of second zone of first reactor, is condensed (condenser 9) and separated (line 10).

(26) After optional heating (heater 16), and optional addition of hydrogen (line 17), the obtained gas (line 15) is sent (line 18) to the second reactor (II). Thereafter oxygen (line 25) is injected in between both zones of the second reactor and allows direct oxidation of H2S to occur in the second zone of the second reactor at sulfur sub dew point temperature. The second zone of reactor (II) operates in cold mode. The gas depleted in H2S is withdrawn (line 20).

(27) Before the oxidation catalyst of the second zone of the second reactor is deactivated, reactors are switched by means of valves (21) and (22) as previously explained.

(28) The invention presents the following advantages: consideration of stream containing over 5000 ppm (expressed as H2S) of sulfur compounds, and preferably up to 15% vol., water addition is avoided and the temperature in the process is maintained above the temperature of water condensation, in the H2S oxidation step, the temperature is maintained low, so that SO2 production is substantially reduced, the performance of the process is independent of the H2S/SO2 ratio, and more, it is independent of the source of the gas to be treated.

(29) Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

(30) The entire disclosures of all applications, patents and publications, cited herein and of corresponding application No. EP 15158886.0, filed Mar. 12, 2015 are incorporated by reference herein.

(31) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.