NO158285B - CATALYST FOR GAS PHASE-OXIDATION OF SULFUR COMPOUNDS. - Google Patents

Description

The present invention relates to the field of catalysis, more particularly it relates to a catalyst for gas-phase oxidation of sulfur compounds.

Naturally activated bauxite containing 50 - 70% by weight

Al2O3, 8-20 wt% Fe2O3, 2-8 wt% SiO2, 0.5-5 wt% Ti02 is used as a catalyst for mercaptan oxidation with oxygen to disulfides (U.S. Patent No. 2558221, June 6, 1951 , class 260-608).

This catalyst does not ensure more than 50% transfer of mercaptan to disulfides and furthermore it can only be used at a low space velocity for the reagent raw material. Because of this, the catalyst cannot be recommended for the treatment of gases for the removal of mercaptans.

A catalyst is also known for mercaptan oxidation with oxygen-containing gas to disulfides, such as e.g. activated bauxite, activated carbon, nickel oxide, iron oxide and cobalt oxide (U.S. Patent No. 2589249, November 4, 1958, Class 250-608).

The transfer rate of mercaptans using the above-mentioned catalysts at a temperature of 170 - 270°C is not higher than 95% at a space velocity of the reaction mixture of ~ 25 h _ i. Insufficient transfer rate and low activity of the catalyst make it unsuitable for gas treatment.

A catalyst is also known, which is used for oxidizing mercaptan with oxygen-containing gas to disulfides at a temperature of 150 - 220°C, which e.g. copper and iron oxides supported on activated carbon or other supports.

(U.S. Patent No. 2979532, April 11, 1961, Class 260-608). This catalyst also has an activity that does not exceed 96%.

Some catalysts for hydrogen sulphide oxidation in gases are also known. E.g. activated carbon is used to oxidize hydrogen sulfide to elemental sulfur which is then recovered in a coal regeneration process (Journal of Catalysis, 35, no. 1 1974; Steijnt M., Mart P. "The Role of Sulfur Trapped in Micropores in Oxidation of Hydrogen Sulfide with Oxygen", pages 11-17). The reaction on the coal surface takes place at a temperature of 20 - 250°C. However, sulphur, which is formed at a temperature of up to 200°C, is deposited on the coal surface and thereby reduces the activity of the catalyst. At a temperature higher than 200°C, sulfur is oxidized to SC>2, which results in a loss of coal selectivity.

Zeolites can be used as catalysts for the oxidation of hydrogen sulphide (Transaction of Mendeleev Moscow Chemical Engineering Institute, N 56, 1967, pages 160-164: N.V. Kelt-sev, M.A. Adlivankina, N.S. Torocheshnikov, Ju.J. Shumja-tsky "Investigation of Incomplete Oxidation of Hydrogen Sulfide using Zeolites"). Zeolites have a high activity for oxidizing low concentrations of hydrogen sulphide, but the activity decreases with time. Moreover, high activity is achieved for zeolites at low space velocities up to 1000 hours ^ and at temperatures higher than 300°C.

Bauxite is known as a catalyst for the oxidation of hydrogen sulfide (U.S.: patent No. 3781445; Gasovaya Promy-schlennost N 8, 1966, pages 42-44; Ju.N. Brodsky, V.J. Gerus, S.M. Goland, Ja.J. Frenkel " The Production of Sulfur at Pokhvistnevskaya Gas Compressor Station"). However, the maximum transfer of hydrogen sulphide at the station does not exceed 93%. Furthermore, the bauxite easily loses its activity in the presence of water vapour. The use of bauxite as a catalyst for the oxidation of hydrogen sulphide is associated with the necessity of precise control of the ratio between oxygen and hydrogen sulphide because an increase in the ratio results in decreasing catalyst selectivity in the formation of SO 2 , and this decrease results in degradation of the activity due to the residual amount of unreacted hydrogen sulfide.

Activated alumina is used as a catalyst for the oxidation of hydrogen sulphide (Ingener-neftjanik N4, pages 36-38, 1973: "Modern Processes for Purification, Drying and Processing of Hydrocarbon Gases"; Chimia i Pererabotka Uglevo-dorodov N10, pages 54-60, 1978: P. Granshe "Progress in Claus Process Technology" Part II. "Improvement of Industrial Plants and Operation Methods"; Inzhener-Neftjanik No.2, pages 104-111, 1973: M. Pirson, "Progress in the Developement of Catalyst for Claus Process"). , However, the catalyst activity decreases due to sulfation reactions on the surface and the presence of water. The hydrogen sulphide conversion decreases 2 -

2.5 times when the water content is increased from 5 to 35%.

The use of iron oxide catalyst is also limited (USSR inventor's certificate no. 865777, class C 01 B 17/04, 1981). As in the case mentioned above, when using this catalyst it is impossible to achieve 100% selectivity and activity within the temperature range 200 - 300°C and space velocities of 3000 - 15000 hour<-1>.

A catalyst containing 0.1% by weight of iron oxide and 9.9% by weight of titanium oxide has high activity and selectivity (USSR inventor's certificate No. 856974, class C 01 B 17/04, 1981). 99.5% conversion of hydrogen sulphide and 100% catalyst selectivity can only be achieved by the two-stage process at a relatively high temperature of 285 - 300°C and at a low space velocity of 3000 hour<-1>.

The purpose of the present invention is to provide such a catalyst for the oxidation of sulphides which has high stable activity, selectivity and mechanical strength.

This purpose was achieved by providing a catalyst containing iron oxide for the oxidation of sulphides, which according to the invention is characterized in that it also contains chromium, cobalt, nickel, manganese, copper, zinc and titanium oxide and has the composition, expressed by weight %:

The catalyst has a high activity and selectivity for oxidizing hydrogen sulphide and mercaptans. At a space velocity for the gas mixture of 6000 h^ and a concentration of hydrogen sulphide and oxygen in the gas mixture of 3 and 4.5% by volume respectively at 250°C, the conversion of hydrogen sulphide is 97.6% and the selectivity for the oxidation to sulfur is not less than 98%. This catalyst has a high activity and selectivity also for oxidizing mercaptans.

The presence of cobalt, nickel, manganese, copper, zinc and titanium oxide in the catalyst causes an increase in the catalyst's activity. An oxidation process for hydrogen sulfide using a catalyst consisting of 28 wt% Fe^O^, 17 wt% Cr„0-, 25 wt% ZnO gives 99.9% conversion of hydrogen sulfide

-1 o at a space velocity of 6000 hours and a temperature of 220 C, and the process selectivity is 98.5%. The catalytic converter also has

a high activity for mercaptan oxidation: At a space velocity of 2000 h^ and a temperature of 140°C, the conversion of mercaptan is 100% at a concentration in the gas of 1.5% by volume.

It is recommended for the oxidation of hydrogen sulphide and mercaptan

to use a catalyst of the following composition, expressed in weight-%: Fe20 , 20"30; Cr2°3' 25~50' Ti02' 10-25' Zn0' 20-25. The catalyst according to the invention has high activity both for hydrogen sulphide - and mercaptan oxidation, it is, however, most effective for the oxidation of hydrogen sulphide.

At a space velocity of 6000 hours and a hydrogen sulphide concentration of 3% by volume with oxygen in excess, the conversion of hydrogen sulphide is approx. 100% at practically 100% selectivity for the oxidation to sulphur.

Based on the foregoing, it follows that the catalyst ensures high values in the processes for oxidizing hydrogen sulphide and mercaptan at high space velocity and high concentrations of oxygen in the gas mixture.

One of the catalyst designs for hydrogen sulphide and mercaptan oxidation is a catalyst of the following composition, expressed in weight %: Fe2C>3, 25-40; Cr2°3' 40-50 with an addition of zinc oxide, 20-25. The catalyst has a high activity and selectivity for hydrogen sulphide oxidation at high space velocity of the gas mixture. At a space velocity of the gas mixture of 9000 hours and a temperature of 230°C at concentrations of hydrogen sulphide and oxygen in the starting gas mixture of 3 and 2.25% by volume, respectively, the conversion of hydrogen sulphide is 98.7% and the selectivity for oxidation to sulfur is not less than 99%. The catalyst has a high activity also for oxidizing mercaptans:

At a space velocity of 2000 hour"^, a temperature of 180°C

and a concentration of mercaptans in the outlet gas of

1.5% by volume in the presence of an excess of oxygen, the catalyst gives practically 100% conversion of mercaptan.

Another, better alternative for the catalyst is a catalyst containing, expressed in weight %: Fe 2 O 3 , 20-25; Cr 2 O 3 , 25-50; TiO2' 1°-15; ZnO, 20-25. The catalyst has a high activity for oxidizing both hydrogen sulphide and mercaptans.

At a space velocity of 6000 h^ and a temperature of 240°C with a content of hydrogen sulfide and oxygen in the starting gas mixture of 3 and 3% by volume respectively, the catalyst ensures 99.6% conversion of hydrogen sulfide with practically 100% selectivity for the oxidation to elemental sulphur. Oxidation of mercaptan in a large excess of oxygen at a mercaptan concentration in the starting gas mixture of 1.5% by volume using this catalyst gives practically 100% conversion at 200°C and a space velocity of 4000 t~<1> .

One of the most important advantages of the catalyst according to the invention is its high activity and selectivity at high space velocities up to 5000 t _ i and in excess of oxygen. The catalyst has high stability when oxidizing hydrogen sulphide and mercaptans. When examining the catalyst's activity in the hydrogen sulphide oxidation process in the presence of hydrocarbons from natural gas at a space velocity of 6000 t -1, hydrogen sulphide and oxygen concentrations of 3 and 2.25 volume-% respectively at 240°C, the conversion of hydrogen sulphide, after a period of 100 hours, 98.5% and the selectivity was 98.9%. The catalyst activity in the mercaptan oxidation process remained high for a period of 1000 hours at a concentration of this in the gas of 1.5% by volume in an excess of oxygen at a space velocity of 2000 t<-1> and a temperature of 200°C ; the conversion of mercaptans was practically 100%. It should be noted that the catalyst in the aforementioned processes does not show a tendency to deactivation.

One of the important advantages of the catalyst is its high activity in the presence of water vapor, hydrogen chloride, carbon dioxide, methanol and saturated hydrocarbons containing 1 - 3 and 6 carbon atoms. The content of these components in the gas mixture does not affect the activity of the catalyst and the selective conversion to elemental sulfur without the formation of by-products, e.g. sulfur-containing anhydrides.

The desired effect is not achieved if the amount of the catalyst components is not changed. A reduction of the iron oxide content in the catalyst to less than 20% by weight results in a reduction of the catalyst activity, and an increase in the iron oxide content to more than 75% by weight results in a deterioration of the selectivity. Reducing the chromium oxide content to less than 25% by weight does not ensure any additional effect and an increase in the content of this component to more than 80% by weight degrades the catalyst activity.

A reduction of the metal oxide additives in the catalyst to less than 1.5% by weight is not fortunate because the properties of the catalyst thereby deteriorate, and an increase in the content of the additives to more than 25% by weight results in degradation of the catalyst selectivity in the case of cobalt, nickel-

and copper oxides; in the breakdown of the catalyst activity in the case of manganese and zinc oxides, and in reduced lifetime of the catalyst in the case of titanium oxide content.

An important advantage of the catalyst according to the invention is

that it is produced from cheap and easily available raw materials using simple technology. Water-soluble salts of iron, chromium, titanium and zinc are used to produce the catalyst. Prescribed amounts of the aforementioned salts are dissolved in distilled water.

The solutions are prepared in separate vessels. The corresponding hydroxides are then completely precipitated from the salt solutions using a 3N aqueous solution. The solution's pH value is used to determine the degree of precipitation. The resulting precipitates are placed in a vessel and stirred thoroughly, then the precipitate is washed with distilled water until obtaining

-2

negative reaction for chlorine ions or SO^ . The washed precipitate is filtered, formed and dried in air at room temperature and then calcined at 450 - 500°C for 4 hours.

The final catalyst has a cylindrical shape with a grain diameter of 3-5 mm and a height of 8-12 mm. The specific surface area of the catalyst is 35-45 m 2 /g. The catalyst has high strength: Mechanical abrasion resistance (residue) determined in a jet-type air mill is 85 - 90%. The catalyst is thermally stable at temperatures up to 950°C.

As can be seen from the description, the method for producing the catalyst is simple and does not require special equipment or expensive, and difficult to access, reagents.

In order to provide a better understanding of the present invention, the following specific examples illustrate the preparation and composition of the catalyst.

Example 1

Dissolve 15 g of iron sulphate in 550 ml of distilled water in a vessel and 10 g of chromium sulphate in 360 ml of distilled water in another vessel. A 6% solution of ammonia is then added to the solutions with continuous stirring until the precipitation of iron and chromium hydroxides is complete. The resulting suspensions are placed in a vessel, stirred thoroughly and allowed to settle for 12 hours; then the precipitate is washed with distilled water until a negative reaction for SO^ ions is obtained, filtered, shaped, dried for 1.5 hours at a temperature of 120°C and calcined for 5 hours at 450°C. The resulting catalyst has the following composition, expressed as wt%: Fe 2 O 2 , 60; Cr^O^, 40.

Example 2

The catalyst is prepared as described in example 1, using 7.5 g of Fe2(SO4)3; 12 g Cr2(S04>3; 4 g ZnS04.

The resulting catalyst has the composition, expressed in wt%: Fe 2 O 3 , 30 ; Cr2°3' 50; Zn0' 20•

Example 3

The catalyst is prepared as described in example 1, using 15 g of Fe2(SO4)3; 6.25 g of Cr2(SC>4)3; 3 g of CuSO 4 .

The resulting catalyst has the composition, expressed as wt%: Fe 2 O 3 , 60; Cr2C>3, 25; CuO, 15.

Example 4

The catalyst is prepared as described in example 1, using 15 g of Fe2(SO4)3; 9.6 g Cr2(SO4>3, 4.5 g Ti(SC>4)2. The resulting catalyst has the composition, expressed as wt%: Fe2O3, 54; Cr2O3, 33; TiO2' 13' as anatase modification .

Example 5

The catalyst is prepared as described in example 1, using 10 g <Fe>2(SO4)3; 12.5 g of Cr(SO 4 ) 3 ; 2.1 g of MnSO 4 . The resulting catalyst has the composition, expressed as % by weight: Fe2°3' 40'" Cr2°3' 50; Mn0' 10"

Example 6

The catalyst is prepared as described in example 1, using 12.5 g of Fe2<SO4)3; 12.6 Cr 2 (SO 4 ) 3 ; 1.2 g of CoSO 4 . The resulting catalyst has the composition, expressed as % by weight: Fe 2 O 3 > 50; Cr2°3' 45 > Co°' 5-

Example 7

The catalyst is prepared as described in example 1, using 11.7 g of Fe2(SO4)3; 12.8 g Cr2(S04>3; 4 g NiS04. The resulting catalyst has the composition, expressed as % by weight: Fe2°3' 40Cr2°3' 43' Ni0' 1 7 '

The catalyst, according to examples 1 - 7, was investigated in mercaptan oxidation processes. The operating conditions and results are shown in table 1. As can be seen from the table, the catalyst according to the present invention is characterized by high selectivity (higher than 98%) and a high degree of mercaptan conversion (97 - 99.9%) which is far superior to the previously known catalysts used for mercaptan oxidation.

Example 8

To prepare the catalyst, dissolve in separate vessels: 25.5 g of iron chloride in 943 ml of distilled water, 26.3 g of chromium chloride in 1000 ml of water, 17.8 g of titanium chloride in 940 ml of water,

12.5 g of zinc chloride in 916 ml of water. A 3N aqueous solution of ammonia is added to the resulting solutions with continuous stirring until the corresponding hydroxides are completely precipitated. The pH value of the solution is used to determine the degree of precipitation. The resulting hydroxide precipitates are added to a vessel and stirred thoroughly and the precipitate is washed with distilled water until a negative reaction to chlorine ions is obtained. Then the precipitate is filtered, shaped, dried

in air at room temperature and calcined at a temperature of 500°C for 4 hours. The resulting catalyst has the composition, expressed as % by weight: 25 Fe 2 O 3 , 25 Cr 2 O 3 , 25 TiO 2 , 25 ZnO.

Example 9

To prepare the catalyst, dissolve 35 g of iron chloride in 1128 ml of distilled water, 21 g of chromium chloride in 788 ml of water,

21.5 g of titanium chloride in 1133 ml of water, 10 g of zinc chloride in 734 ml of water. The catalyst is then prepared according to the method described in example 8. The resulting catalyst has the composition, expressed in weight %: Fe 2 O 3 , 3 0; Cr 2 O 3 , 25; TiO2, 25; ZnO, 20.

Example 10

To prepare the catalyst, dissolve 20.3 g of iron chloride in 750 ml of distilled water, 52.6 g of chromium chloride in 19 75 ml of water,

7.1 g titanium chloride in 3 75 ml water, 10 g zinc chloride in 735 ml water. Next, the catalyst is prepared according to the method described in example 8. The resulting catalyst has the composition, expressed as % by weight: Fe2°3' 20; Cr2°3' 50' TiO2, 10; ZnO, 20.

The catalyst samples obtained include grains of cylindrical shape with a diameter of 3 - 5 mm and a height of 8 - 12 mm. The specific surface area of the catalyst is 35 -

45 m2/g. The mechanical abrasion resistance (residue) is

85 - 90%. The catalyst is thermally stable at temperatures up to 950°C.

The results from investigations of the obtained catalyst samples in the hydrogen sulphide oxidation process under different conditions are reproduced in table 2.

As can be seen from the table, the obtained catalysts show high activity (the H2S conversion is not lower than 98.5%)

and the selectivity for hydrogen sulfide oxidation to elemental sulfur is not lower than 98.8% at high speeds up to 15,000 t~^ and excess oxygen in the gas mixture.

The catalyst according to the invention can be used in the gas and petroleum refining industry for the removal of hydrogen sulphide and mercaptans from gases, as well as residual gases from Claus processes and regeneration gases which are obtained in the step for adsorptive purification of natural gas in the production of ammonia.

Claims (2)

1. Catalyst containing iron oxide for gas-phase oxidation of sulfur compounds, characterized in that it also contains chromium, cobalt, nickel, manganese, copper, zinc and titanium oxide and has the composition, expressed by weight %: Iron oxide, Fe203 , 20-60; Chromium oxide, Cr203, 25-50; Cobalt, nickel, manganese, copper, zinc, titanium oxide, 1.5-25. 2. Catalyst according to claim 1, characterized in that it contains iron, chromium, titanium and zinc oxide and has the following composition, expressed as % by weight: Iron oxide, 25-30; Chromium oxide, 2 5-50; Titanium oxide, 10-30; Zinc oxide, 20-25.