DE2417092C3 - Process for the catalytic cleaning of hydrogen sulphide and possibly CO2 and ammonia containing exhaust gases - 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.

It is known that in the chemical industry, gas mixtures laden with sulfur compounds are often more complex Composition, for example in the purification of natural gaseous or liquid Hydrocarbons from which considerable amounts of sulfur can be recovered by cleaning exhaust gases be able. The processes for recovering the sulfur have generally been known for a long time; she however, they must be constantly refined and improved to keep pace with the ever more stringent requirements Requirements and regulations regarding air pollution have the lowest possible residual content To achieve sulfur compounds in the exhaust gases.

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 and in the case of SO2, which is generally through 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 severely impaired in practice by the presence of other gaseous sulfur compounds such as carbon disulfide or carbon oxysulphide, because the most effective catalysts for the Claus reaction are by no means most effective in the decomposition of the carbon compounds of sulfur, which is probably caused by Hydrolysis takes place, affect: the optimal temperatures for the different reactions are not the same and the presence of SO ₂ prevents the hydrolysis of the carbon compounds of the sulfur. As a result, the technical exhaust gases treated in several successive catalytic stages often contain more hydrogen sulphide and carbon compounds of sulfur than the usual standards allow.

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 arrived.

A great many catalysts have been recommended to achieve these various reactions of the gaseous sulfur compounds. Many of them are suitable and give satisfactory results unless the maximum power of a given one is used

Plant is sought and so lanjje relatively short periods of use without topping up with new catalysts are accepted. The recommended substances include those in Chemie-Ing.- Techn., 39th year, 1967, issue 9 / 10.5. 515-520, for the

Claus reaction described activated bauxites and clays or alumina gels as well as activated carbon, alkaline carriers and the catalysts consisting of sulfides, oxides or different compounds of molybdenum, titanium, cobalt, iron and / or uranium on various carriers .

The activated bauxites, of which it has long been known that they can be used as catalysts for the Claus reaction and the decomposition of the sulfur- carbon compounds , often contain oxides with catalytic activity, such as oxides of iron and titanium, and also have a specific surface area that may be suitable. However, the content of active oxides in the bauxites varies and is insufficient; in addition , they contain, in varying amounts, other compounds which are either inactive or even harmful to the reactions under consideration. Therefore Bauxite does not have all the properties of such an extensive and consistent emission control, as currently required.

Activated clay is best suited for the Claus reaction alone , provided that the sulfation is suppressed as much as possible so as not to impair the useful life.

However, once the exhaust gases that are to be cleaned. Containing carbon compounds of sulfur in a significant amount, the above-mentioned disadvantages occur.

It has now been shown that only catalysts made from

Where active alumina and titanium compounds exist, a combination of properties can be imparted on the basis of which both the decomposition of the carbon compounds of sulfur and the actual Claus reaction can be achieved with good yield.

hs Compared to the known catalysts , the new catalysts are characterized by their longer service life, which is due to their mechanical strength and, surprisingly, by the fact that

that the sulfalaiion does not impair its activity, The condition is that the ready-to-use catalysts have a sufficiently large specific surface and that the proportions of active alumina and titanium compound are defined. The chemical The nature of the titanium compounds contained in these catalysts 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 CO ₂ and H ₂ S and in the hydrogen sulfide combustion in the third contact furnace of a multi-stage Claus plant is. As the following comparative tests show, the bauxite 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 carrier made of activated alumina with the desired specific surface area with titanium salt solutions and subsequent thermal decomposition of the titanium salt to form the oxide; the concentration of the solution is chosen so that the desired amount of titanium is obtained in the finished catalyst. The easiest solutions to use for this purpose contain the chlorides, oxychlorides or sulphates of titanium. However , other titanium compounds can also be used, for example various organic salts such as titanium oxalate.

Another suitable method consists in mixing mixtures of aluminum oxides or hydroxides, for example activated alumina, with titanium compounds which are used in the form of gels, sols or solutions. The hydroxides or other compounds of aluminum and titanium can also be precipitated together or co-gels of hydroxides or compounds can be produced starting from brines and the mixtures can then be deformed.

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 according to the invention can be used in a fixed bed, in a fluidized bed, as a fluidized bed or in a fly ash system, depending on the dimensions of the catalyst grain.

The invention is explained in more detail in the following examples on the basis of results which were obtained with catalysts used in a fixed bed, which consisted of alumina and titanium in different proportions and had been obtained in different ways. The comparative example relates to a catalyst of low mechanical strength without alumina, which consists exclusively of titanium oxide with the desired specific surface area, in order to clearly show the particular activity of titanium in converting 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 the exhaust gases were treated with the various catalysts in a small reactor with a diameter of 60 mm. The composition of the exhaust gases was:

35

4 °

45

(10 H ₂ S
CS ₂
SO ₂
H, O

6 mol%

1 mol%

4 mol%

28 mol%

61 mol%

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 ρ CS ₂ for carbon disulfide.

Comparative example

A titanium sol was produced in the usual way by heating an aqueous suspension containing 400 g / l TiO ₂ as titanium hydroxide, obtained by precipitation with ammonia from the sulfuric acid solution, to 80 ^° C. with subsequent 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 drops gelled, and spheres with a diameter of 2 to 5 mm were obtained in the lower part of the column, which were then dried in air at a temperature of 180.degree. 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.

Table 1 below shows the various Results summarized. In addition to the degree of conversion and the degree of hydrolysis, it is stated also the compressive strength grain per grain R in kg, determined before using the various catalysts.

Table 1

Balls AI2O3

New

sulfated
T1O2 balls

New

sulfated

15 15

3 3

100 98 100
90

100
100

100
100

100
100

100 100

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 Compressive strength (grain per grain) of the titanium oxide balls however, it is not sufficient to be able to use them on an industrial scale.

example 1

This example shows the results obtained with catalysts with different titanium oxide content; The catalysts were prepared by impregnating spheres of active alumina with a specific surface area of 300 m ² / g and a diameter of 2 to 4 mm with solutions of titanium chloride in such a way that the desired amounts of oxide after drying and firing at 500 ° 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 ⁰ C. The following table 2 summarizes the results that were determined for the degree of conversion SO2 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.

TiO:
'5% by weight ni -' / g

Spc /.
surface

kg

u SO: 5s

ο CS: 5s

5
10

220
200

14th
13th

100 100

75 85

Table 2

Wt%

Spec.
surface

mVg

kg

5s

ρ CS2 5s

8s

0 3 250 1 250 table

15th
14th

91 95

35 £ 0

80 95, n The results show the importance of the presence of titanium, which already in a proportion of 1%, calculated as TiO _2, causes the decomposition of the greater part of the carbon disulfide present. The different ca-

₂ <catalysts had good pressure resistance due to the use of alumina balls as a carrier material.

Example 2

This example concerns catalysts that run through

Agglomerating alumina powder with a titanium hydroxide gel; the titanium hydroxide gel was a suspension of hydrolyzed titanyl sulfate containing about 7 wt .-% sulfate ions based on TiO _2. This titanium hydroxide gel was dried and

3, finely ground and contained 79% by weight of TiO ₂ ; it was

"intimately mixed with powdery active clay,

Grain size <20μΐη, due to partial dewatering

obtained from hydrargillite in a hot gas stream

had been. The two powders were in one

Quantity ratio corresponding to 10%, 20%, 40% and 60% TiO ₂ in the finished catalyst mixed with one another, the mixture was moistened and agglomerated in the rotary granulator to form balls with a diameter of 2 to 5 mm. These balls were 24 h at a

4S temperature of about 100 ⁰ C and then ripened for 2 h fired at 450 ° C in order to activate the alumina. These catalysts were then sulfated as indicated in the comparative example.

The results are summarized in Table 3 below.

Sulphated catalysts

specific surface

m ² / g

kg

ρ CS2 at
3s 5s

310 ⁰ C 335 ° C

8s
335 ° C

ρ SO2 at Is 2s

26O ⁰ C 290 ° C

10% T1O2 + clay
20% T1O2 + clay
40% T1O2 + clay
60% T1O2 + clay

190 195 195 190 15

12th

20th
30th

45
65

45
57
87
95

98
100
100

"66

65

72 82 86

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 can be obtained, a little more titanium oxide must be used. to be very good Get results. However, this manufacturing method has the advantage that that in Example 1 described! impregnation process using titanium chloride is avoided, in which the somewhat difficult handling of this connection has a somewhat disadvantageous effect.

\ T0 £

24 177) 92

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 with one another in such amounts that the finished catalysts contained 10, 20, 30, 40 and 60% by weight of TiO ₂ . The catalysts were sulfated as already described and then tested for their effectiveness. The results are summarized in Table 4 below.

Sulphated catalysts Specific R. Q CS2 at 5s 8s ρ SO2 at 2s 5s surface 3s 335 ° C 335 ° C 1 s 280 ° C 335 ⁵ C m ³ / g kg 320 ° C 54 96 260 ° C 70 100 10% T1O2 + clay 200 14th 25th 65 98 40 76 100 20% TiCh + alumina 195 12th 35 85 100 49 81 100 30% T1O2 + clay 194 12th 45 94 100 58 86 100 40% T1O2 + clay 198 10 50 96 100 69 90 100 60% T1O2 + clay 191 8th 70 65

The results are similar to the results from 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 by the impregnation process described in Example 1, in such a way that the finished catalyst contained 5% by weight of TiO ₂ . The impregnated spheres of active clay had different specific surface areas, such that the finished catalysts also had different specific surface areas. These catalysts were tested for sulfation with a contact time of 5 s to determine the degree of conversion for SO _? and with a contact time of 5 s and 8 s when determining the _{degree of hydrolysis for CS 2} , temperature 335 ° C.

The results are summarized in Table 5 below.

Table 5

specific surface
m '/ g

l> SOj

5s

40

95 100 100

0 CSj 5s

8s

41 62 73 75 85

70

90

98

100

100 The composition of the activated bauxite corresponded to the “Porocel” catalysts (Chemie-Ing. Techn. 39 [1967], No. 9/10, page 520), ie it contained 2 to 3% TiO ₂ . The catalysts according to the invention contained 5 and 60% 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 catalysts were used in the form of 4 to 6 mm thick spheres and had been sulfated to 450 ^° _{C. by heating in SO 2 -containing air before use.} The exhaust gases from the contact furnace were analyzed by chromatography.

I. attempt
Claus reaction (alone)

Work was carried out under the conditions of the first contact furnace of a multi-stage Claus plant. The gas fed in 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 ° C.

results

This comparison clearly shows that there is a sufficient specific surface area must in order to achieve good results and that with values below 80 m »/ g the yields are too high sink.

Comparison vei-iuehe

It became the suitability of activated bauxite as a catalyst for the purification of industrial exhaust gases investigated after the Claus reaction and / or conversion (hydrolysis) of CSa and examined the effectiveness of catalysts produced according to the invention as well as of active clay alone.

catalyst

50% yield of S.

a contact SAcit

from

Is 2s 3s 4s

AhO3 active 55 79 80 81

AIjOs active + TiOj (5%) 58 80 80 81 Bauxite (2.8% TiOj) 35 55 63 6E

Second attempt Hydrolysis of CSj

It was as in the first experiment under d <conditions of the first contact furnace with the same El and outlet temperatures of the gas as there gcarbi tct. The injected gas contained 6% HjS, 1% CSj, 4 SOj and 28% HjOi the H produced during hydrolysis added to what was originally available (8% HjS in total).

70S 627/21

The following table only gives the results for the hydrolysis or conversion of CS? again.

catalyst

% Conversion CS:
after a contact time of
2s 4s 6s 8s

AI2O3 active + 60% TiO;
AI2O3 active + 5% T1O2
AI2O3 active
Bauxite (2.8% TiO?)

62 98 100 100

15 60 92 100

11 26 54 83

9 20 34 52

3. Attempt
Claus reaction (alone)

This experiment was carried out under the conditions of the third contact furnace of a Claus plant, inlet temperature 210 C, Ausintt temperature 225 ° C. The incoming gas contained 1% H ₂ S. 0.5% SO ₂ and 28% H ₂ O.

results

Catalyst% yield of S nacl

a contact time

from

Is 2s 3s 4s

Al: 03 active + 60% TiO:
ΑΙ2Ο3 active + 5% TiO:
AbOj active
bauxite

22 35 43 50

17 25 32 40

15 23 28 30

0 13 5

Conclusion

The test results clearly show:

1) that with the known bauxite catalysts of the Porocel type in all 3 experiments with Abstanc poorer results are achieved than with the TiO-containing catalyst according to the invention and

2) that active clay alone gives unsatisfactory results _{in the hydrolysis before CS 2 and}

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

Claims (1)

/ 59: 24 1,092 Claim: Process for the catalytic purification of hydrogen sulfide and possibly CO _{; |} 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 mVg, characterized in that exhaust gases which contain additional carbon compounds of sulfur are cleaned with a catalyst that corresponds to 1 up 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 joint precipitation of the hydroxides or other compounds of aluminum and titanium and subsequent shaping of the mixtures, drying and activation of the moldings has been produced.