FR2538716A1 - Process for catalytic desulphurisation of a sour gas containing H2S and optionally a total quantity of not more than 3 % by volume of CS2 and/or COS - Google Patents

Abstract

Process for catalytic desulphurisation of a sour gas as described in the main patent, with at least two catalytic oxidation zones in series, containing a catalyst based on TiO2 and on an alkaline-earth sulphate, and then a complementary purification stage on alumina. At least the final eighth, advantageously half, and preferably all of the catalyst present in the final oxidation zone consists of a catalyst made up of a support based on alumina on which at least one compound of Fe, Co, Ni, Cu and Zn is deposited, the said support having a specific surface of between 30 and 300 m<2>/g, while the said catalyst includes a total content of Fe, Co, Ni, Cu and Zn metal ranging from 0.5 to 10 % by weight of the calcined catalyst. This embodiment prevents the possibility of oxygen coming into contact with the alumina catalyst in the complementary purification stage.

Description

The present invention relates to an improvement to the process for the catalytic desulfurization of an acid gas containing H2 S and optionally an overall amount of at most 3% by volume of CS2 and / or COS, with recovery of these sulfur compounds under the form of sulfur.

Various industrial operations give rise to acid gases containing H25 in a concentration of at most 15 g by volume. The H2S content of these gases is too low to be able to be treated in conventional sulfur units, which include as a first step a combustion of the gas. acid gas in a burner. In fact, this combustion is technically feasible only with acid gases with a higher H2S- content. 15% by volume
To recover in the form of sulfur the H2S contained in acid gases containing less than 15 R of H2S by volume, it has been proposed to subject them to a catalytic oxidation in the presence of oxygen or air by making use of catalysts. varied
In French patent application N081 23611 of December 17, 1981, a process was proposed for the catalytic desulfurization of an acid gas containing H # 2S, and possibly an overall amount of at most 3% by volume of
CS2 and / or COS, with recovery of these sulfur compounds in the form of sulfur and optionally SO2, of the type in which said acid gas is brought into contact with a controlled quantity of a gas containing free oxygen, of prefer-
Pence in the form of a mixture, with a catalyst based on titanium oxide, at temperatures between 100aC and 6000C, and which is characterized in that the catalyst, in addition to titanium oxide, also comprises a sulfate of an alkaline earth metal selected from the group formed by calcium, strontium, barium, and magnesium
Among the catalysts comprising titanium oxide and a sulfate of an alkaline earth metal as mentioned above which can be used in the process mentioned above, reference is made to a catalyst comprising titanium oxide and calcium sulfate, such a catalyst exhibiting exceptional mechanical strength.

The catalysts comprising titanium oxide and an alkaline earth metal sulfate defined above may still contain up to 30% by weight of a constituent chosen from silica, alumina, clays, silicates, titanium sulfate, ceramic fibers.

In the aforementioned catalysts, whether they are formed essentially of titanium oxide and a sulphate of an alkaline earth metal or also contain an additional constituent of the type mentioned above, the proportion by weight of titanium oxide, based on the total weight of the calcined catalyst and expressed as TiO2, is advantageously between about #O% and about 99%, and is preferably between 80% and 99%, while the proportion by weight of alkaline metal sulphate earthy, also relative to the total weight of the calcined catalyst, is advantageously between about 40% and about 1 ~ and is preferably between 20 and 1%.

These catalysts can be prepared by any suitable process making it possible to obtain either a product in which the compounds titanium oxide, alkaline earth metal sulphate, and optional additional constituent are intimately mixed, or a product formed from titanium oxide and of the optional additional constituent impregnated with the alkaline earth metal sulphate.

The preparation of the catalyst can be carried out, for example, as described in the aforementioned patent application.

The catalysts based on titanium oxide and sulphate of an alkaline earth metal defined above have specific surfaces, measured by the nitrogen absorption method known as the BET method, of between 5 and 300 m2 / g. and preferably between 10 and 240 m2 / gt and total pore volumes, determined by the mercury penetration method, between 0.05 and 0.6 cm3 / g and preferably between 0.1 and 0.4 cm3 / g, Their resistance to attrition is less than 2%.

The resistance to attrition represents the quantity of dust, expressed in grams, produced by 100 grams of granules of the catalyst placed on a n 24 sieve of 20 cm in diameter of the AFNOR X 11-501 series and vibrated for 10 minutes at l using a vibrator from the brand FENWICK REX.

Resistance to attrition is expressed in tO
The acid gas which is treated by the process of the aforementioned patent application, that is to say the gas containing H2S and optionally an overall concentration of at most 3% by volume of CS2 and / or COS, can have an H2S concentration varying within wide limits, The method is advantageously applied to the treatment of an acid gas containing H2 S in a concentration at most equal to 15% by volume and optionally an overall quantity of CS2 and / or
COS of at most 3%, and preferably at most 1%, by volume, said acid gas very particularly containing 0.01 to 12% by volume of H2S and optionally an overall amount of CS2 and / or COS of not more than 1% by volume,
The acid gas to be treated can have various origins. In particular, such an acid gas can be a natural gas, a gas obtained from the gasification of coal or heavy oils, or even a gas obtained by hydrogenation of sulfur compounds. a sulfur plant effluent.

The gas containing free oxygen used for the oxidation of H2S, and the transformation of compounds
CS2 and COS, acid gas is generally air, although it is possible to use pure oxygen, oxygen-enriched air, or even mixtures, in various proportions, of oxygen and an inert gas other than nitrogen.

The acid gas and the gas containing free oxygen can be brought separately into contact with the catalyst.
However, in order to obtain a very homogeneous gaseous reaction medium, it is preferable to firstly mix said acid gas with the gas containing free oxygen and to bring the mixture thus produced into contact with the catalytic converter.

As indicated above, the catalytic desulfurization can be carried out at temperatures between 1000C and 6000C, said temperatures preferably being between 1800C and 500C.

A particular embodiment of the process of the aforementioned patent application which applies to the desulphurization of an acid gas having a potential H2S content greater than approximately 5% by volume, consists in passing said acid gas in a plurality of
catalytic zones - in series comprising a catalytic zone
initial tick and final catalytic zone separated
optionally by one or more catalytic zones
intermediate, each of said catalytic zones renffl
closing a catalyst comprising titanium oxide and
sulphate of an alkaline earth metal of the defined type
previously, - also to be injected into each of said catalyzed areas
ticks, preferably mixed with the sour gas, a
quantity of the gas containing free oxygen such as
the proportion of oxygen entering each zone
initial and intermediate catalytic converter represents 0.7 to
1.2 times, and preferably 6.8 to approximately 1 time, that which
is theoretically necessary to transform into sulfur a
amount of potential H2S representing 3 to. 5th in volume
acid gas, - to adjust the temperatures of the gases entering each
catalytic zones at values ranging from 1800C to
3500C, and preferably from 200 to 250 C, - has maintained in each zone a gas contact time
reactions and catalyst between 1 and 6 seconds, - treating the gaseous effluent from each catalytic zone
initial and intermediates to separate by condensation
the sulfur it contains and to direct said effluent deba
collected sulfur towards the inlet of the next catalytic zone, - to adjust the molar ratio O2 :: H2S potential at the inlet
of the final catalytic zone to obtain an effluent
containing HZS and SO2 in an H2S: SO2 molar ratio
equal to approximately 2: 1 the number of catalytic zones inter-
medials being such as at the entrance to the catalytic zone
final acid gas contains at most 5% by volume of H2S
potential, then
- subjecting the gaseous effluent from the final catalytic zone,
after separation of the sulfur it contains, to a process
regenerative purification using the reaction of
formation of sulfur between H2S and SO2 on contact with a
classic CLAUS catalyst based on alumina, at temperate
erasures between 80 C and 160 C, said catalyst,
when loaded with sulfur, being regenerated by sweeping
using a free oxygen-free gas at a temperature
between 200 and 400 C.

By potential H2S content; means the sum of the free H2S content and the theoretically available HALOS content from the CS 2- and COS compounds that may be present
The realization of such an embodiment is delicate, because, due to the high sensitivity to oxygen of the C # US catalyst based on alumina used in the complementary purification process, it is necessary to avoid the presence of oxygen, even in small quantity, in the gaseous effluent from the final catalytic zone, which lion brings into contact with the Ct # US catalyst, to prevent any deactivation of this catalyst, which would result in a significant decrease in the effectiveness of additional purification.

The present invention proposes an improvement to the aforementioned embodiment, which easily prevents possible inflows of oxygen in contact with the CLAUS catalyst used in the regenerative purification process and which, therefore, facilitates the implementation of this embodiment. Implementation.

According to the invention, at least the last eighth, advantageously half and preferably all, of the catalyst used in the final catalytic oxidation zone is constituted by a catalyst formed from a support containing a major proportion by weight of alumina. on which is deposited at least one compound of a metal chosen from Fe, Co, Ni, Cu and Zn, said support having a specific area of between 30 and 300 m2 / g # while said catalyst with an alumina-based support contains a quantity of metal compound corresponding to an overall metal content ranging from 0.5 to 10 g by weight of the catalyst calcines the optional additional part of catalyst in the final catalytic zone being constituted by the catalyst based on titanium oxide and alkaline earth metal sulfate.

As indicated above, the catalyst forms an alumina-based support on which is deposited at least one compound of a metal chosen from Pep Co, Ni, Cu and Zn comprises a support containing a major proportion by weight of alumina, that is to say more than 50% by weight of alumina. Preferably said support consists essentially of alumina.

The specific area of the alumina-based support of the aforementioned catalyst, which is between 30 and 300 m 2 / g, is preferably between 50 and 120 m / g.

Psnni compounds of metals Fe, Co, Ni, Cu and
Zn capable of being deposited on the alumina support, it is possible to choose salts of inorganic acids of said metals such as chlorides, sulphates, nitrates or else salts of organic acids or even oxides or hydroxides of these metals. Most particularly suitable are iron compounds and more especially iron sulphate.

The amount of the metal compound (s) deposited on the alumina-based support, which can vary as indicated above, is preferably chosen to correspond to an overall content of metal Fe, Co, Ni, Cu and Zn ranging from 2 to 6th by weight of the calcined catalyst.

The above alumina-based supported catalyst can be obtained, for example, by impregnating the alumina-based support with one or more compounds of the metals.
Fe, Co, Ni, Cu and Zn, then drying of the impregnated support, and calcination of the dried product at a temperature in particular between 3500C and 500 C. The combination of the compound (s) of the metals mentioned above with the support can also be carried out. by coprecipitation techniques or else by mixing the constituents of the catalyst in the form of oxides.

The invention is illustrated by the following example given without limitation.

EXAMPLE
The catalytic desulfurization of an acid gas having the following composition by volume was carried out
H2S ........ 9%
HO ...... 7%
CO2 .... 84%
The operation was carried out in an installation comprising three catalytic oxidation reactors arranged in series, namely an initial reactor, an intermediate reactor, and a final reactor, said series of reactors being followed by an additional purification system comprising two catalytic converters mounted. in parallel
The catalytic reactors were similar to that used in Example 1 of the French patent application cited above and therefore each had an inlet and an outlet separated by a catalytic bed, a gas supply duct connected to L ' reactor inlet.

said pipe being provided with a nozzle for the injection of the gas containing free oxygen and with a heater located between this nozzle and the inlet of the reactor, and a gas discharge pipe extending the outlet of the reactor and on which was mounted a vapor-cooled sulfur condenser. The outlet for the gases from the sulfur condenser associated with each of the initial and intermediate catalytic rectifiers was connected to the gas supply pipe fitted to the next catalytic reactor in the series, upstream of the connection provided on the pipe concerned. 3 and intermediate each contained 1.1 m of the catalyst consisting of titanium oxide and e SQ, used in Example 1 of said patent application while the final catalytic reactor 3 contained 1.1 m of a catalyst consisting of balls, 4 to 6 mm in diameter, of an alumina having a specific area equal to 100 m2 / g impregnated with iron sulphate and having an iron content equal to 4% by weight
Each of the two catalytic converters of the complementary purification system contained a catalytic bed consisting of 2.5 m of beads, 4 to 6 mm in diameter, of an alumina with a specific area equal to 100 m and had an inlet and an outlet for the gas being treated and on the other hand, an inlet and an outlet for a regeneration gas, the inlets of the converter being separated from the corresponding outlets by the catalytic bed.

The inlets for the gas in treatment provided on the converters were connected, through valves, to a pipe for supplying the gas in treatment, which was connected to the outlet of the sulfur condenser associated with the final catalytic reactor and constituted the pipe d. 'inlet of the additional purification system while the outlets for the gases in treatment provided on said converters were connected, through valves, to an evacuation duct of the ~ gases in treatment constituting the outlet duct of the epu system - additional ration The outlets for the regeneration gas provided on the converters were connected, through valves, to the inlet of a regeneration gas circuit comprising, in series on the circuit from said outlets, a sulfur condenser steam-cooled, a blower and a heater, the output of the heater being connected, through valves, to the inlets for regeneration gas provided on the converters. The valves mounted at the inlets and outlets of the converters were opened and closed cyclically so as to have one of the converters crossed by the gas from the sulfur condenser associated with the catalytic reactor while the other converter was crossed by the hot regeneration gas arriving from the heater and circulating to the sulfur condenser of the regeneration circuit.

The catalytic desulfurization of the acid gas defined at the start of the present example was carried out as indicated below.
The acid gas, introduced through the gas supply pipe of the initial catalytic reactor with a flow rate of 1000 Ns3 / h and a temperature of 40 ° C., received, by the tapping of said pipe, an addition of air injected at room temperature with a flow rate of 75 Nm3 / h. This quantity of air corresponds to the theoretical quantity necessary to oxidize into sulfur a quantity of H2S of the sour gas equal to 3 t by volume The mixture of acid gas and air, in which the molar ratio 02: H2S was equal at 0.17, was brought to a temperature of 200 ° C. by passing through the heater associated with the initial catalytic reactor and then injected into said reactor at this temperature. The contact time of said mixture with the catalyst contained in the initial catalytic reactor was equal to 4 seconds, which corresponds to a VVH of 900 h "l. The gaseous effluent leaving the initial catalytic reactor through the discharge pipe of said reactor no longer contained free oxygen and had a temperature of 333 C. This effluent was cooled to 1750C in the condenser associated with the initial catalytic reactor to separate the sulfur it contained. The gases leaving said condenser, which had a temperature of 1750C and an H2S content equal to 5.6% by volume, were added 75 Nm3 / h of air added, at room temperature, by the connection provided on the gas supply pipe of the intermediate catalytic reactor. 'air also corresponds to the theoretical quantity necessary to oxidize into sulfur a quantity of H2S corresponding to 3% by volume of the gas. The gas mixture obtained, in which the molar ratio 02: H2S was equal to 0.27, et ant heated to 200 ° C., by passing through the heater associated with the intermediate catalytic reactor, before being injected, # at this temperature, into said intermediate reactor. The contact time of this mixture with the catalyst present in the intermediate catalytic reactor was also 4 seconds (VVH equal to 900 h-1). The gaseous effluent leaving the intermediate catalytic reactor via the gas discharge line of said reactor no longer contained free oxygen and had a temperature equal to 3350C and an H2S content of 2.40% by volume.

This effluent was cooled to 175 ° C. in the condenser associated with the intermediate catalytic reactor so as to separate the sulfur it contains. The gases issuing from said condenser were added, by tapping the gas supply pipe of the final catalytic reactor, with a quantity of air added at ambient temperature and such that the molar ratio O 2: HZS in the gas mixture as well. achieved eAt a value equal to 0.5. This gas mixture was brought to a temperature of 2000C, by passing through the heater associated with the final catalytic reactor, then injected, at this temperature, into said reactor. The contact time of said gas mixture with the alumina-based catalyst contained in the final catalytic reactor was equal to 4 seconds (#TVH equal to 900 h-1).

The gaseous effluent from the final catalytic reactor no longer contained free oxygen and had a temperature of 3000C. This effluent was cooled to 135 ° C. in the condenser associated with the final catalytic reactor in order to separate the sulfur which it contained.

The gaseous effluent from said condenser, which bulges H2S and SO2 as the only sulfur compounds in molar proportions of approximately 2: 1 (0.77% H2S and 0.38% SO2 by volume), was injected at a temperature of 135 ° C. in that of the two converters of the complementary purification system, which worked in the purification phase, the other being in the regeneration phase. The contact time of this gaseous effluent with the alumina contained in the converter in the purification phase was equal to 8 seconds (V # 7H equal to 400 hl) and during this contact the H2S reacted with the 502 to form sulfur settling on the alumina. During this time, the converter in the regeneration phase was swept with nitrogen, leaving the heater of the regeneration gas circuit with a temperature of 3000 ° C., in order to remove the sulfur deposited on the catalyst and thus regenerate it, and the current d. nitrogen charged with sulfur vapor leaving said converter was cooled to 175 C, by passing through the sulfur condenser of the regeneration circuit, to condense the sulfur, while the stream of nitrogen cleared of the sulfur was recycled by the blower, through the heater to bring the temperature of said current to 3000C, to the input of the converter in the regeneration phase.

The purified gaseous effluent, which left the reactor in the purification phase and was evacuated through the outlet pipe of the additional purification system, had a temperature equal to 1400C and no longer contained an overall content of H25 and 502 equal to 0.092 e in volume.

The overall conversion of H2S was 99%, this converted H2S being recovered entirely as sulfur.

Claims (6)

1- Catalytic desulfurization process of an acid gas containing H2S and possibly an aggregate amount at most 3% by volume of CS2 and / or COS, applied to treatment of an acid gas with a potential H2S content greater than about 5% by volume with recovery of sulfur compounds in the form of sulfur, said process being of the type in which - said acid gas is passed through a plurality of serial catalytic zones comprising a catalytic zone initial lytic and a separate final catalytic zone optionally by one or more catalytic zones intermediate, each of said catalytic zones initial and intermediates containing a catalyst comprising titanium oxide and the sulphate of a metal alkaline earth metal chosen from Ca, Sr, Ba and Mg, - is also injected into each of said cata zones lytic, preferably mixed with the acid gas, a quantity of gas containing free oxygen such as that the proportion of oxygen entering each of the zones initial and intermediate catalytic converter represents 0.7 to 1.2 times, and preferably 0.8 to I times approximately, that which is theoretically necessary to transform into sulfur a quantity of potential H2S representing from 3 to ' 5% by volume of the sour gas, - the temperatures of the gases entering each are adjusted catalytic zones at values ranging from 1800C to 3500C, and preferably from 200 to 2500C, - a contact time between reaction gases and catalyst between 1 and 6 seconds, - the gaseous effluent from each catalyzed zone is treated initial and intermediate tick to separate the sulfur that it contains by condensation and the said effluent free of sulfur to the entrance to the zone next catalytic, - we adjust the molar ratio O2: potential H2S at the inlet of the final catalytic zone to obtain an effluent containing H2S and SO2 in an H2S: SO2 molar ratio equal to approximately 2 :: 1, the number of catalytic zones intermediaries being such as at the entrance to the area final catalytic acid gas contains at most 5% in volume of potential H2S, then - the gaseous effluent from the catalytic zone is subjected final, after separation of the sulfur it contains, to a regenerative purification process using the sulfur formation reaction between H25 and 502 at contact with a classic CLAUS catalyst based on alumina, at temperatures between 800C and 1600C, said catalyst, when loaded with sulfur, being rege- born by flushing with an oxygen-free gas free at a temperature between 200 and 4000C, and characterized in that at least the last eighth of the catalyst used in the catalyzation zone final tick is constituted by a catalyst formed by a support containing a majority weight proportion of alumina on which is deposited at least one compound of a metal selected from Fe, Co, Ni, Cu and Zn, said support with a specific area between 30 and 300 m2 / g while said supported catalyst based on of alumina contains a quantity of metallic compound of Fe, -Co, Ni, Cu and Zn corresponding to a content overall metal ranging from 0.5 to 10% by weight of the cat calcined lyser, the possible complementary part of catalyst in the final catalytic zone being constituted killed by the catalyst based on titanium oxide and alkaline earth metal sulfate. Fe, Co, Ni, Cu and Zn. alumina on which is deposited at least one compound of final consists of the catalyst based on support of the catalyst contained in the catalytic oxidation zone that advantageously half, and preferably all, 2 A method according to claim 1 characterized in that 3- A method according to claim 1 or 2, characterized in that that the alumina-based support of the catalyst consists essentially alumina. 4- Method according to one of claims 1 to 3, charac terized in that the specific area of the base support of alumina is between 50 and 12G m2 / g. 5- Method according to one of claims 1 to 4, charac terized in that the metal compound deposited on the Alumina-based carrier consists of iron sulfate. 6- Method according to one of claims l a s, charac terized in that the amount of the Fe compound (s), Co, Ni, Cu and Zn deposited on the alumina-based support is chosen to correspond to an overall content of metal Fe, Co, Ni, Cu and Zn ranging from 2 to 6% by weight calcined catalyst.