DE2417092B2 - METHOD FOR CATALYTIC CLEANING OF HYDROGEN SULFUR AND, IF ANY, EXHAUST GASES CONTAINING LOW CO 2 AND AMMONIA - Google Patents

Description

The invention relates to the method described in more detail in the preceding claim Purification of exhaust gases, the hydrogen and carbon compounds of sulfur in addition to where appropriate Contain CO2 and ammonia.

Known to fall in the chemical industry often with sulfur compounds laden gas mixtures of complex composition to, for example, in the purification of natural gas or liquid hydrocarbons, advertising from which substantial amounts of sulfur by the exhaust gas purifying recovered so the can. The processes for recovering the sulfur have generally been known for a long time; However, they have to be constantly refined and improved in order to achieve the lowest possible residual content of sulfur compounds in the exhaust gases in accordance with the ever more stringent requirements and regulations relating to air pollution.

Most of the sulfur in the exhaust gases is usually present as hydrogen sulfide and the Recovery of the sulfur is then generally based on the Claus reaction, which takes place in gaseous or Liquid medium can run off unü in the case of SO2, which is generally caused by oxidation of a corresponding proportion H2S is obtained, with the remaining H2S for Implementation is brought. The Claus reaction is an equilibrium reaction and should be as low as possible Temperatures drain to encourage the formation of sulfur; it can namely with ordinary or Room temperature can be reached if it is accelerated by appropriate catalysts.

The exhaust gas purification processes based on the Claus reaction are being carried out in practice by the presence of other gaseous sulfur compounds such as carbon disulfide or Carbon oxysulphide strongly impaired, because the most effective catalysts for the (\ s Claus reaction by no means most effective the decomposition of the carbon compounds of sulfur, which is probably due to it Hydrolysis occurs, affect: the optimal temperatures for the various reactions are not those same and the presence of SO2 prevents the hydrolysis of the carbon compounds of sulfur.

As a result, contain the technical treated in several successive catalytic stages Exhaust gases often contain more hydrogen sulfide and carbon compounds when they exit the last cleaning stage of sulfur than the usual norms.

Incidentally, this inadequate exhaust gas purification increases over time and is probably in the Connection with the sulfation of the catalytic converters due to traces of what is present in the exhaust gas Oxygen, which then progressively increases; the sulfation can also be attributed to the fact that Incompletely cooled catalytic converters accidentally come into contact with air while the plant is idle came.

A great many catalysts have been recommended to prevent these various reactions of the gaseous To achieve sulfur compounds. Many of them are suitable and provide satisfactory results, as long as the maximum output of a given system is not sought and for so long proportionally short periods of use can be accepted without the need to replenish the system with new catalysts. To the Recommended substances include those in Chemie-Ing. Techn., 39th year, 1967, Issue 9/10, pp. 515-520, for the Claus reaction described activated bauxites and clays or alumina gels and activated carbon alone, alkalinized carriers and those made of sulfides, oxides or various compounds of molybdenum, titanium, Cobalt, iron and / or uranium on various carriers.

The activated bauxites, which have long been known to be used as catalysts for the Claus reaction and the decomposition of the sulfur-carbon compounds can be used, often contain oxides with catalytic activity, such as oxides of iron and titanium and have also a specific surface area that may be suitable. However, the content of active oxides varies in the Bauxites and not enough; They also contain other compounds in varying amounts, which are either inactive or even detrimental to the reactions under consideration. Own bauxite therefore not all of the properties for extensive and consistent exhaust gas cleaning as they are at present is required.

For the Claus reaction alone, activated alumina is best, provided that the sulfation is se is pushed back as much as possible in order not to impair the service life or service life However, once the exhaust gases are cleaned, carbon compounds of sulfur become more noticeable Contain amount, the above-mentioned disadvantages occur.

It has now been shown that only catalysts which consist of active alumina and titanium compounds, one Combination of properties can be imparted on the basis of which with good yield both dk Decomposition of the carbon compounds of sulfur; as well as the actual Claus reaction is achieved Compared to the known catalysts, the new catalysts are characterized by their longer service life which is due to its mechanical strength and surprisingly because of it

' Λ

The condition that the sulfation does not impair their activity is that the catalysts are ready for use have a sufficiently large specific surface and that the proportions of active clay and titanium compound are defined. The chemical nature of those contained in these catalysts Titanium compounds can only be precisely specified with difficulty under the conditions of use; in the In practice, the proportion of titanium compound is traced back to titanium oxide.

The catalysts provided according to the invention must, in order to have all the necessary properties, have a specific surface area of at least 80 m ² / g and contain titanium compounds corresponding to 1 to 60% by weight of titanium oxide, based on the finished catalyst.

Compared to activated bauxite with 2 to 3% TiO ₂ , the new catalysts are characterized by a superior effectiveness, which is _{particularly pronounced in the conversion of carbon disulfide into CO2 and H 2} S and in the hydrogen sulfide combustion in the third contact furnace of a multi-stage Claus plant . As the following comparative tests show, the bauxite in the carbon disulfide conversion achieves only about 20% of the effectiveness of the catalysts according to the invention with a contact time of 4 s and only about 50% of the effectiveness of the catalysts according to the invention with a contact time of 8 s. In the case of hydrogen sulfide combustion in the third contact furnace of the multi-stage Claus plant, the effectiveness of bauxite is initially 0% and after a contact time of 4 s only 10% of the effectiveness of the catalysts according to the invention.

The catalysts provided according to the invention are obtained in various ways, for example by impregnating the activated alumina carrier with the desired specific surface Titanium salt solutions and subsequent thermal decomposition of the titanium salt to form the oxide; the concentration the solution is chosen so that the desired amount of titanium is obtained in the finished catalyst. The on The simplest solutions to be used for this purpose contain the chlorides, oxychlorides or sulphates of titanium. It however, other titanium compounds can also be used, for example various organic ones Salts such as titanium oxalate

Another suitable method is that mixtures of aluminum oxides or hydroxides, for example activated alumina mixed with titanium compounds in the form of gels, sols or Solutions are applied. It can also use the hydroxides or other compounds of aluminum and titanium precipitated together or co-gels from hydroxides or compounds based on brines produced and the mixtures are then shaped.

In general, the catalysts are dried and activated at the end of the production process and their subsequent ones Use results in a more or less strong fixation of sulfur, whereby the exact The nature of the binding of this element has not yet been clarified.

The catalysts of the invention can be in a fixed bed, in a fluidized bed, as a fluidized bed or in the Airborne dust system can be applied, depending on the dimensions of the catalyst grain.

The invention is explained in more detail in the following examples using results obtained with im Fixed bed applied catalysts were obtained, which are made of alumina and titanium in different Ratios existed and had been obtained in various ways. The comparison example relates to a catalyst of low mechanical strength without alumina, which consists exclusively of Titanium oxide consists of the desired specific surface area in order to clearly show the special activity of titanium to show in the conversion of the carbon compounds of sulfur. With the help of the other examples the limits for the fluctuations of the main parameters can be determined. In all examples were the exhaust gases with the various catalysts in a small diameter reactor 60 mm treated. The composition of the exhaust gases was:

6 mol%

1 mol%

4 mol%

28 mol%

61 mol%

CS,
SO,
H ₂ O

N ₂

The contact times were up to 8 s and the temperatures at the exit from the reactor were 260 to 335 ^° C.

The gases emerging from the reactor were analyzed chromatographically in order to determine the degree of conversion ρ SO ₂ with reference to the thermodynamic yield and the degree of hydrolysis 0 CS ₂ for carbon sulfide.

Comparative example

There was a titanium oxide sol prepared in conventional manner by mixing an aqueous suspension containing 400 g / l TiO ₂ was heated as titanium hydroxide obtained by precipitation with ammonia of the sulfuric acid solution at 8O ⁰ C, followed by adjustment of the pH to about 1.1 with hydrochloric acid; the micelles of this sol were about 40 nm (400 Å) in diameter.

This sol was added dropwise to a glass column which was filled in the upper part with a mixture of petroleum and a chlorofluorocarbon and in the lower part with a 1: 1 mixture of a concentrated aqueous ammonia solution and a saturated aqueous ammonium carbonate solution. The temperature of the column was kept at 25 ° C. The droplets gelled, and was obtained in the lower part of the column balls with a diameter of 2 to 5 mm which were finally dried in air at a temperature of 180 ⁰ C. These spheres with a specific surface area of 220 m ² / g were divided into two equal parts. The first part was used as it was; the second part has been artificially 4stündiges sulfated by heating at 45O ⁰ C in a mixture of 70% air and 30% SO _2. For comparison, the exhaust gas cleaning was carried out in an identical manner with balls made of active alumina with the same dimensions and the same specific surface, which were also used fresh (new) and sulfated as above.

The various results are summarized in Table I below. Is specified

fts except for the degree of conversion and the degree of hydrolysis also the compressive strength grain per grain R in kg, determined before using the various catalysts.

Table 1

Catalysts

R in
kg

s / 320 C

ρ SO2 ρ CS2

5s / 335 ° C

ρ SOs ρ CS2

8 s / 335 ° C

ρ SO ₂ ρ CS2

Balls AI2O3

New

sulfated
T1O2 balls

New

sulfated

This table clearly shows the superiority of titanium oxide over alumina in terms of activity both for the conversion of SO2 and for the hydrolysis of CS2, especially after sulphation. the However, compressive strength (grain per grain) of the titanium oxide spheres is not sufficient to achieve this on an industrial scale to be able to apply.

example 1

This example shows the results obtained with catalysts with different titanium oxide content; The catalysts were prepared by balls of active alumina having a specific surface area of 300 m ² / g and a diameter of 2 to 4 mm with solutions of titanium chloride was impregnated in such a way that the desired amounts of oxide after the drying and firing at 500 ⁰ C for 4 hours. These catalysts were sulfated before use, as described in the comparative example. All experiments were carried out at a temperature of 335 ° C. The following table 2 summarizes the results that were determined for the degree of conversion SOj with a contact time of 5 s and for the degree of hydrolysis CS2 with contact times of 5 and 8 s, as well as the values for the specific surface areas and the compressive strength of the catalysts used.

Table 2

• 5 90 45 94.5 78 97 98 15th 83 15th 91 35 100 80 3 100 100 100 100 100 100 3 98 90 100 100 100

TiO:

Wt%

Spo /.

Ohorri

m - '/ g

ο SOj

5s

CS:

5b

5 220 14th 100 75 100 10 200 13th 100 85 100

Wt%

Spec.
surface

kg

5s

5s

The results show the importance of the presence of titanium, which is already in a Quantity fraction of 1%, calculated as TiO2, the Causes decomposition of the greater part of the carbon disulfide present. The different ca-

The use of alumina balls as a carrier material made the catalysts have good pressure resistance.

Example 2

This example concerns catalysts that run through

Agglomerating clay powder with a titanium hydroxide gel; which was titanium hydroxide gel a suspension of hydrolyzed titanyl sulfate containing about 7 wt .-% sulfate ions based on T1O2. This titanium hydroxide gel was dried and

finely ground and contained 79% by weight T1O2; it was intimately mixed with powdery active clay. Grain size <20μηι, which had been obtained by partial dewatering of hydrargillite in a hot gas stream. The two powders were in a proportion corresponding to 10%. 20%, 40% and 60% T1O2 mixed together in the finished catalyst; the mixture was moistened and agglomerated in a rotary granulator to form balls with a diameter of 2 to 5 mm. These spheres were left to mature for 24 hours at a temperature of about 100 ^° C. and then fired for 2 hours at 450 ^° C. in order to activate the clay. These catalysts were then sulfated as indicated in the comparative example.

O 250 15th 91 35 80 the Results s2 at 5s are in of following 2s Tabel 1 250 14th 95 60 95 so summarized. 'C 335 "C ⁰ C 290 ° Table 3 45 65 Sulfated Catalysts Specific R. ρ Ci 57 ρ SC2 at 72 surface 3s 87 8s I s 82 5s mVg kg 310 ' 95 335 ° C 260 86 C 335 ° C 10% TiO2 + Clay 190 15th 20th 97 35 100 20% T1O2 + Clay 195 I? 30th 98 45 100 40% T1O2 + Clay 195 11th 45 100 65 100 60% T1O2 -f clay 190 9 65 100 66 100

The comparison shows the importance of catalysts containing titanium compared to Clay alone. The results also show that with this type of catalyst, by agglomeration of the mixture of oxides are obtained, a little more titanium oxide must be used in order to achieve very good Get results. However, this manufacturing method has the advantage that that in Example 1 Impregnation process described using titanium chloride is avoided, in which the somewhat difficult Handling this connection has a somewhat detrimental effect.

Example 3

This example relates to catalysts which agglomerate in the form of spheres with a diameter of 2 to 5 mm starting from an alumina as used in the previous example and from a titanium hydroxide sol; the two components

Table 4

were mixed together in such amounts that the finished catalysts 10, 20, 30.40 and 60 wt .-% TiO> contained. The catalysts were as before described sulfated and then tested for effectiveness. The results are in the Table 4 summarized below.

Sulfaticrtc catalysts

10% T1O2 + clay

20% TiO. ' + Clay

30% TiO: + alumina

40% TiO: + alumina

60% TiO: + alumina

The results are similar to dun results Example 2.

Example 4

This example shows the influence of the specific surface area of the catalysts on those obtained Results.

All the catalysts tested were produced according to the impregnation process described in Example 1, in such a way that the finished catalyst had 5% by weight of TiO? contained. The impregnated spheres of active alumina had different specific surface areas such that the finished catalysts also had different specific surface areas. These catalysts were tested for sulfated with a contact time of 5 s for the determination of the degree of conversion for SO2 and with a contact / cit of 5 s and of 8 s for the determination of the _{degree of hydrolysis for CS 2} , temperature 335 ° C.

The results are summarized in Table 5 below.

Table 5

Specific R. / ι CS2 at 5s 8 s Q SO2 at 2s 5s surface 3s 335 "C 335 ° C 1 s 280 ⁰ C 335 ° C ni ² / g kg 320 C 54 96 260 ⁰ C 70 100 200 14th 25th 65 98 40 76 100 195 12th 35 85 100 49 81 100 194 12th 45 94 100 58 86 100 198 10 50 96 KH) 69 90 100 191 8th 70 65

Specific surface area ρ SO: ρ CS2

m ² / g 5 s 5 s

The composition of the activated bauxite corresponded to the "Porocel" catalysts (Chemie-Ing.-Techn. 39 [1967], issue 9/10, page 520), d. it contained 2 to}% T1O2. The catalysts of the invention

2 «, contained 5 and b0% TiO ₂ and were produced by impregnating active alumina with a titanium salt solution as in Example 1 (5%) or by mixing and agglomerating active alumina and titanium dioxide powder as in Example 2 (60%). All

τ, ο catalysts were used in the form of 4 to 6 mm thick spheres and had _{been sulfated before use by heating in SO 2} -containing air to 450 ° C. The exhaust gases from the contact furnace were analyzed by chromatography.

3 s

1st attempt
Claus Reaklion (alone)

Work was carried out under the conditions of the first contact furnace of a multi-stage Claus plant. The feed gas contained 8% H ₂ S, 4% SO ₂ and 28% H ₂ O (no COS and CS _2), inlet temperature 225 ° C, outlet temperature 335 ⁰ C.

45

Results

40 41 70 70 62 90 95 73 98 100 75 100 100 85 100

catalyst

_. "-Ji-Ljo- AhO3 active

This comparison clearly shows that a _{MiQi aktjv + TiQ2.5 %} .

Sufficient specific surface must be available 55 g _aux j _t ρ g _O / _o T ₁ Q ₂ ). to achieve good results and that with '

Values below 80m ² / g, the yields drop too much.

% Yield of S.

a period of rebirth

from

Is 2s 3s 4s

55 58 35

79 80 55

80 80 63

Comparative experiments

60

The suitability of activated bauxite as a catalyst for the purification of industrial exhaust gases after the Claus reaction and for the conversion (hydrolysis) of CS _{2 was} investigated and compared with the effectiveness of catalysts produced according to the invention and of active alumina alone.

Second attempt
Hydrolysis of CS ₂

The procedure was as in the first experiment under the conditions of the first contact furnace with the same inlet and outlet temperatures of the gas as there. The gas fed in contained 6% H ₂ S, 1% CS ₂ , 4% SO ₂ and 28% H ₂ O; _{the H 2} S formed during hydrolysis was added to the originally present (a total of 8% H ₂ S).

The following table only gives the brgebms .-> e for Jie hydrolysis or conversion of CSi again.

catalyst

^ü / o conversion CS? after a contact / cit of 2s 4s 6s 8s

AbOi active + 60% TiOz 62 98 H) O 100

AbOi active + 5% TiO ₂ 15 60 92 100

AbO ₁ active 11 26 54 83

Bauxite (2.8% T1O2) 9 20 34 52

3. Attempt
Claus reaction (alone)

In this experiment, a Claus plant was processed under the conditions of the conventional kneading furnace. Downstream temperature 210 "C Exit temperature 225" C The entering gas contained 1% HiS, 0.5% SO2 and 28% H ₂ O.

Results
catalyst

% Yield of S.

a contact time

from

1s 2s 3s 4s

active + 60% T1O2 22 35 43 50

AbOi active + 5% TiO ₂ 17 25 32 40

AbOi active 15 23 28 30

Bauxite 0 13 5 Conclusion

The test results clearly show:

1) that with the known bauxite catalysts of the Porocel type in all 3 experiments by far poorer results can be achieved than with the TiO2-containing catalysts according to the invention and

2) that active alumina alone gives unsatisfactory results in the hydrolysis of CS2 and

3) that even in the third contact furnace the effectiveness of the catalysts according to the invention of active clay and bauxite is superior.

Claims (1)

Claim: Process for the catalytic purification of hydrogen sulfide and optionally CO2 and ammonia containing exhaust gases after the Claus reaction in the presence of catalysts based on active alumina with a specific surface area of at least 80 m ² / g, characterized in that exhaust gases containing additional carbon compounds containing sulfur, cleans with a catalyst which consists of 1 to 60% by weight of titanium dioxide and by impregnating active alumina with titanium salt solutions and subsequent thermal decomposition of the titanium salts, or by agglomerating mixtures of aluminum oxide or hydroxide and titanium compounds, or by jointly filling in the hydroxides or other compounds of aluminum and titanium and then shaping the mixtures, drying and activating the moldings.