FI58727B - FOERFARANDE FOER KATALYTISK UTVINNING AV SVAVEL UR EN GASSTROEM - Google Patents

Description

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Patent · och r «f ietaretyralean 'ΑμΚμ uthgd och utl.tk> ift« n pubiicand 31.12.80 (32) (33) (31) hW * · **? front »—B« | ird priority 09. OU. 73

France-France (FR) 7312658 (71) Rh6ne-Progil, 25 »Quai Paul Doumer, 92U08 Courbevoie, France-France (FR) (72) Georges Dupuy, Fontenay-aux-Roses, Jean-Claude Daumas, Orsay, Max Michel This invention relates to a process for the catalytic recovery of sulfur from a gas stream containing hydrogen sulphide, sulfur dioxide. water vapor and carbon disulphide compounds, mainly carbon disulphides and / or carbonyl sulphides.

In the chemical industry, as is known, there are often complex gas mixtures containing sulfur compounds, such as gas mixtures from the purification of naturally occurring gaseous or liquid hydrocarbons, and by refining these gas mixtures it is possible to recover large amounts of sulfur; however, these long-established sulfur recovery methods need to be continuously improved so that the amount of sulfur compounds in purified gas mixtures ready for removal to the atmosphere is as low as possible as pollution standards have become increasingly stringent.

Most of the sulfur contained in the gas mixtures to be treated is usually in the form of hydrogen sulfide and the recovery of this sulfur is therefore usually based on the well-known Claus reaction, which can be carried out in both gaseous and liquid media; the reaction takes place between the sulfur dioxide normally formed in the oxidation of the appropriate fraction of hydrogen sulfide and the remainder of the hydrogen sulfide.

2,58727 This Claus reaction, which is an equilibrium reaction, is preferably carried out at the lowest possible temperature, which favors the production of sulfur, and this is indeed possible at ordinary temperatures, provided that suitable catalysts are used for the activation.

However, the presence of other gaseous sulfur compounds, such as sulfuric carbon and thioic acid, very sensitively alters the performance of gas purification processes based on the Claus reaction because the more efficient catalysts for the Claus reaction are not the same as those more efficient at the optimal temperatures of the reactions are not the same and because the mere presence of sulfur dioxide prevents the hydrolysis reaction of sulfur carbon compounds.

In order to achieve efficient purification, the industry has to treat waste gases containing different sulfur compounds in several successive catalytic layers, but it still has to be found that the gas leaving the last layer contains hydrogen sulphide and sulfur carbon compounds in excess of the permitted standards; this purification becomes more and more incomplete over time and is apparently dependent on the sulphation of the catalysts, which may be due to the presence of small amounts of oxygen in the gas to be treated and is progressive, but may also be due to accidental overflow of catalysts solstice.

There are many catalysts previously recommended for various reactions to sulfur gaseous compounds, and many of them are indeed suitable and give advantageous results as long as no attempt is made to obtain the highest possible yield from each installation and subject to a relatively short service life unless the catalysts are replaced; therefore, bauxite, activated carbon, time substrates, active aluminum, and catalysts consisting of sulfides, oxides, or other compounds of molybdenum, titanium, cobalt, iron, and uranium placed on various substrates have been recommended.

Of these catalysts, which are intended exclusively for the Claus reaction, active aluminum is mentioned as the most suitable, provided that the sulphation is as low as possible so as not to shorten the service life; nevertheless, as soon as the gases to be purified contain significant amounts of sulfur carbon compounds, the aforementioned disadvantages appear.

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It has now been found that the only catalysts that can be granted all these properties together, i.e. good yields both in the decomposition of sulfur carbon compounds and in the Claus reaction itself, are longer catalysts due to their mechanical strength and the fact that sulphation does not catalysts composed mainly of active aluminum and titanium compounds, provided that these ready-to-use catalysts have a sufficiently large specific surface area and that the proportions of active aluminum and titanium compounds are determined; the chemical nature of the titanium compounds present in these catalysts is difficult to determine precisely under the conditions of use, in practice it is therefore advantageous to calculate the proportions of these compounds to correspond to titanium oxide.

It should be noted that activated bauxites, previously considered to be useful as catalysts for these various reactions, as previously reported, often contain oxides that have as effective a catalytic effect as oxides of iron and titanium and have a suitable specific surface area; whereas, however, the concentration of active oxides in bauxites is variable and insufficient and, moreover, they contain equally varying proportions of other compounds which may be inactive or even harmful; from this it is therefore concluded that bauxites do not have all the properties that would achieve the efficient and constant sulfur-containing gas cleaning result that is required today.

In the process of this invention, the reactions are carried out in the presence of a catalyst containing mainly active alumina and titanium compounds, wherein the titanium compound is present in an amount of 1 to 60% by weight of titanium oxide having a specific surface area p of greater than 80 m / g and a reaction zone temperature such that the product gases at the end of the reaction have a temperature of 260 ~ 335 ° C.

The catalysts used in the process of the invention can be prepared in various ways; in a well-known method, for example, active aluminum substrates having a desired specific surface area are impregnated with solutions of metal compounds which are easily converted to the corresponding oxides by thermal decomposition; the concentration of the solutions is chosen so as to obtain the desired amount of catalytic substances in the finished catalyst; more convenient solutions for adding titanium are titanium chlorides, oxychlorides or sulphates; other compounds may be used, such as, for example, various organic salts such as oxalates; the addition of other metals, if their presence is required, can easily take place, for example by the addition of nitrates.

In other suitable methods, alumina or hydroxide mixtures are agglomerated, for example, oxides or hydroxides of active aluminum and oxides, hydroxides or other compounds of various metals, and at least some of these various metal compounds may be in the form of a gel, sol or solution; it is also possible to co-precipitate various hydroxides or other compounds or to form gels of hydroxides or other compounds starting from the sols, as well as to add sols which introduce certain metals into the compounds of other metals.

The preparation of these catalysts is terminated in the usual way by drying and activation, and finally the sulfur is fixed more or less solidly; the nature of the incorporation of this element is not yet well known.

In the process according to the invention, the catalysts can be used as a solid or mobile substrate, as a liquid or as a floating air, always applying particle sizes as appropriate.

To illustrate the present invention, various examples of the results obtained using a solid support in which the catalysts are formed of aluminum and titanium in different proportions and prepared in different ways are given below; the first of these examples is a catalyst which is not very strong and does not contain aluminum, so that it is not within the scope of this patent, the catalyst being composed exclusively of titanium oxide having the desired specific surface; in this way it is desired to demonstrate the specific conversion efficiency of titanium with respect to sulfur carbon compounds; other examples can be used to set ranges for the most important parameters. In all these examples, the gases are treated with different catalysts in a small reactor with a diameter of 60 mm. The analytical composition of these gases is as follows: H2S 6% CS2 1% SO2 4% H2O 28% N2 61% 5 58727

Kontuktiaj at vaxh you algae and can be up to 8 sheets. and the exhaust gas temperatures range from 260 to 335 ° 0.

The gases leaving the reactor are analyzed chromomatromatically to determine the value of the conversion of sulfur dioxide p in relation to the thermodynamic catch as well as the value of the bydro-lysis of r k ihiii p p CS2 ·

Example 1

A titanium sol is prepared in a classical manner by heating to about 80 ° C, then adjusting the pH to about 1.1 with hydrochloric acid in an aqueous suspension of 400 g of TiO 2 per liter of titanium hydroxide obtained by treating a solution of its sulfur compound with ammonia; the particles of this sol are about 100,000 in diameter.

This sol is poured dropwise into glass columns at the top, with an oil mixed with chlorine and fluorine-containing hydrocarbons at the top and a mixture of 1/1 concentrated aqueous ammonia and saturated aqueous ammonium carbonate at the bottom; the temperature in the column is maintained at 25 ° C; in this way gel droplets are obtained and spheres with a diameter of 2 to 5 mm are obtained from the bottom of the column, which are then air-dried at 180 ° C. Spheres thus obtained, having a specific surface area:. is 220 m2 / g divided into two parts; the first is used as such and the second is artificially sulphated by heating at ^ 50 ° C for H hours in a gas mixture containing 70% air and 30% SC> 2. Both of these parts are used in the treatment of the gas mixture, the composition of which was stated above. In addition, for comparison, the gases are treated in an identical manner with active aluminum spheres having the same dimension and the same specific surface area, both in the freshly finished state and sulphated; the latter state is obtained by the same method used for titanium oxide spheres.

The following Table I summarizes the different results obtained and, in addition, the values of the breaking strength R in kg of granule per granule before the use of different catalysts.

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TABLE I

P Contact time Contact time Contact time

Catalysts T „, ono τ„ ^ r-o .. t, co torit irp- Temperature 320 Temperature 335 Temperature 335 S pS02 pCS2 PS02 PCS2 PS02 pCS2 A120, -spheres in the finished state 15 90 45 94.5 78 97 98

Sulphated 15 83 15 91 35 97 80

TiO2 spheres in the freshly finished state 3 100 100 100 100 100 100

Sulfated 3 98 90 100 100 100 100 These results show that titanium oxide is definitely superior to aluminum in terms of the conversion efficiency of both SO 2 and CS 2, and especially after sulfation; however, the tensile strength of titanium oxide spheres is not sufficient for industrial use.

Example 2 This example relates to the results obtained using catalysts with different titanium oxide contents obtained by impregnating active aluminum spheres with a specific surface area of 300 m / g and diameters of 2-4 mm with titanium chloride solutions so as to obtain the desired oxide concentrations after drying. and after firing at 500 ° C for 4 hours. Prior to use, these catalysts are sulfated as described in the previous example. All experiments were performed at 335 ° C. The following table summarizes the measured values of PSO2 at a contact time of 5 sec and likewise the values of pCS2 at a contact time of 5 and 8 sec, as well as the values of the specific surfaces of the catalysts and their breaking strength.

TABLE II

Catalysts by weight- Catalyst- Fraction per cent property of titanium octers pSO2 pCS2 bond calculated from the surface of the mine substrate m2 / g kg 5s 5s 8s 0 '250 15 91 35 80 1 250 14 95 60 95 5 220 14 100 75 100 10 200 13 100 85 100 7 58727 It is clear from these examples how advantageous the presence of titanium is, since the amount of 1? Calculated as oxide ensures that most of the carbon disulphide decomposes; the durability of these different catalysts is sufficient and is due to the use of aluminum spheres as a substrate.

Example 3 This example relates to catalysts obtained by agglomeration of aluminum powder and titanium hydroxide gel, a suspension of hydrolysed titanyl sulphate containing approximately 7% by weight of SO 2 anions relative to Science. This titanium hydroxide gel, which has been dried and ground and contains 79% by weight of ΤΐO 2 and active aluminum, which is in the form of a powder and has a grain size of less than 20 μm and is obtained by partial dewatering of hydrargillite in a hot gas stream, is mixed in such a proportion that finished catalysts contain 10, 20, 40 and 60 weight- $ From the road. The mixture is moistened and agglomerated in a rotary granulator into spheres with a diameter of 2 to 5 mm. These spheres are allowed to cure for 24 hours at about 100 ° C and then fired for 2 hours at 450 ° C to activate. These catalysts are sulfated according to the method reported in the previous examples.

Table 3 shows the results obtained.

TABLE III

Sulfated Characteristic Fraction p CS2 p SO2 catalyst surface strength 3 sec 5 sec 8 sec χ sec 2 sec 5 sec

m2 / g kg 310 ° C 335 ° C 335 ° C 260 ° C 290 ° C 335 ° C

10! TiO2 + 190 15 20 45 97 35 65 100 aluminum 20% TiO2 + aluminum 195 12 30 57 98 45 72 100 40% TiO2 + aluminum 195 11 45 87 100 65 82 100 60% TiO2 + aluminum 190 9 65 95 100 66 86 100 This table shows the benefit of using titanium-containing catalysts compared to the results obtained with aluminum alone; it also shows that in this type of catalyst, obtained by agglomeration of a mixture of oxides, it is necessary to use more titanium oxide in order to obtain correct 8 58727 good results; however, this method of preparation has the advantage that it is possible to avoid using the impregnation method of Example 2 with titanium chloride, which is sometimes cumbersome because this product is difficult to handle.

Example 4 This example relates to agglomerated catalysts in the form of spheres with a diameter of 2 to 5 mm obtained from aluminum and titanium hydroxide sol identical to those used in the previous example, taken in a weight ratio to give TiO 2 contents of 10, 20, 30, 10 and 60% in finished catalysts. Sulfated catalysts are tested as described above; the results are summarized in Table 4 below.

TABLE IV

Sulfate- Characteristic- Fraction- p CS ~ p SCU

dut catapult cheese 3 sec 5 sec 8 sec 1 sec 2 sec 5 sec

lysators mp / g kg 320 ° C 335 ° C 335 ° C 260 ° C 280 ° C 335 ° C

10% T1O2 + aluminum 200 14 25 54 96 40 70 100 20% TiO2 + aluminum 195 12 35 65 98 49 76 100 30% TiOp + aluminum 194 12 45 85 100 58 8l 100 40% TiOp + aluminum 198 10 50 94 100 69 86 100 60% TiOp + aluminum 191 8 70 96 100 65 90 100 The results obtained here are very close to those obtained in Example 3.

Example 5 The purpose of this example is to demonstrate the significance of the specific surface area of the catalysts in the results obtained.

The catalysts tested have all been obtained by the impregnation process shown in Example 2, when they already contain 5% by weight of TiO2. These impregnated spheres of active aluminum have different specific surfaces, so that the finished catalysts also have different specific surfaces. These catalysts are tested in the sulfated state with a contact time of 5 sec p to determine SO 2, and 5 and 8 sec p to determine CS 2.

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The results obtained are stored in the following Table 5. TABLE V

The specific surface area of the catalysts p SO2 p CS2 m2 / g 5 sec 5 sec 8 sec 30 40 41 70 80 70 62 90 150 95 73 98 200 100 75 100 250 100 85 100 This table shows the inevitability of a sufficiently large specific surface area so that 80 m / g is the limit below which catches have fallen too much.

The above examples do not limit the invention to the treatment of gases having the above-mentioned composition, which has been used only because the main object of the invention is to decompose both sulfur-containing air hydrogen sulfide and sulfur carbon compounds at the same time; it is self-evident that the catalysts according to the invention can be used for the treatment of gas mixtures which are much more abundant in sulfur compounds and which may additionally contain, for example, carbon dioxide and ammonia which do not take part in the reaction.