DE4000609B4 - Catalyst for the oxidation of sulfur dioxide to sulfur trioxide - Google Patents

Abstract

catalysts for the Oxidation of sulfur dioxide to sulfur trioxide, consisting of a silica-containing support material and thereon, active substance containing vanadium and Alkali metal compounds, characterized in that the silicic acid-containing support material a pore volume fraction of 10 to 30% of pores with a pore diameter to 15 nm, a pore volume fraction of 25 to 60% of pores with a pore diameter of 15 to 200 nm and a pore volume fraction from 10 to 60% of pores having a pore diameter of> 200 nm.

Description

This The invention relates to a catalyst for the oxidation of sulfur dioxide to sulfur trioxide.

to sulfuric acid production on an industrial scale becomes sulfur dioxide in the presence of catalysts with oxygen or oxygen-containing gases oxidized to sulfur trioxide and this subsequently with water to sulfuric acid implemented. For the oxidation of sulfur dioxide, in particular vanadium oxide containing catalysts used. These catalysts exist generally on vehicles, especially amorphous silicic acids, applied vanadium pentoxide, wherein for activation alkali metal compounds be added.

For the preparation of such catalysts, numerous processes have already become known. According to the DE 1 086 218 A For example, a dissolved or suspended compound of the tetravalent or pentavalent vanadium is contacted with an aqueous silicate solution, and diatomaceous earth is incorporated into the precipitate containing a vanadium compound and silicic acid containing both potassium and sodium compounds. The product obtained is treated after drying with sulfuric acid and then calcined.

According to the DE 1 091 547 A starting from a freshly precipitated sodium and / or potassium ions containing silica gel and impregnated with this also freshly precipitated sodium and / or potassium ions containing vanadium pentoxide. After drying, the product is contacted with sulfuric acid and calcined before use.

Finally, it is also known (Chem. Ztr. Bl., 1963, p. 5761) to start in the production of sulfuric acid catalysts from a mixture of vanadium pentoxide and potassium bisulfate to heat this to 300 to 400 ° C, the pulverized mixture with Diatomaceous earth and little water to knead and calcine the dried paste at 400 to 800 ° C. Instead of potassium bisulfate, it is also possible to use K ₂ S ₂ O ₇ , K ₂ S ₂ O ₈ or K ₂ SO ₄ + H ₂ SO ₄ .

• a) Vanadiumpentoxid in solchen Mengen von wäßrigen Lösungen von Kaliumhydroxid löst, daß das Molverhältnis in der Lösung V₂O₅:K₂O von 0,2 bis 0,8 beträgt,
• b) die erhaltene Lösung mit Schwefelsäure auf einen pH-Wert < 4 ansäuert, und die erhaltene Suspension
• c) unmittelbar anschließend mit einem Träger auf Basis von Kieselsäure zu einer pastösen Masse verarbeitet, mit der Maßgabe, daß das Molverhältnis SiO₂:V₂O₅ von 13,0 bis 45,0 beträgt,
• d) die Masse verformt und trocknet und
• e) bei Temperaturen von 450 bis 650°C tempert.

In the DE 29 19 662 A1 Finally, a method for producing a sulfuric acid catalyst is described, which consists in that

• a) dissolves vanadium pentoxide in such amounts of aqueous solutions of potassium hydroxide that the molar ratio in the solution is V ₂ O ₅ : K ₂ O from 0.2 to 0.8,
• b) acidifying the solution obtained with sulfuric acid to a pH <4, and the resulting suspension
• c) immediately after being processed with a support based on silicic acid to give a pasty mass, with the proviso that the molar ratio of SiO ₂ : V ₂ O _{5 is} from 13.0 to 45.0,
• d) the mass deforms and dries and
• e) annealed at temperatures of 450 to 650 ° C.

In the EP 0 129 903 A2 describes a process for the preparation of a catalyst which, in addition to a high catalytic activity, simultaneously has a high mechanical strength and a good high-temperature service life. This is achieved by using vanadium pentoxide solutions containing a dissolved alkali metal silicate and / or silica sol, bringing these solutions to pH <2 and processing the acidified solution with a solid silica-based carrier into a wet-crumb mass, deforming it and then calcined.

All described methods are intended to serve one at both high as well as to produce highly active catalyst at low temperatures, being the activity primarily by the composition of the active component whose Quantity and porosity of the finished. Depend on contact.

The Oxidation of sulfur dioxide to sulfur trioxide is used in plants carried out, consisting of several catalyst zones, the so-called contact hordes exist at different temperatures between about 380 up to 450 ° C be operated, leaving the one horde leaving by the exothermic Reaction heated Gases before entering the next Horde to be cooled to the working temperature of this horde.

In the DD 92 905 A Catalysts taking account of this fact are described with a selective porosity related to a specific working temperature range. Here is the Kataly depending on the working temperature range, a defined pore volume ratio of the pores greater / smaller than 100 nm and having a maximum of specific surface in a certain pore radius range. Thus, the low-temperature catalyst with a working temperature range <400 ° C such a pore volume ratio> 1.5 and a maximum of specific surface pore radii range between 7.5 and 50 nm, the medium-temperature catalyst with a working temperature range of 400 to 480 ° C such a pore volume ratio> 3 , 5 and a maximum of specific surface area in the pore radius range of 50 to 200 nm and the high-temperature catalyst having a working temperature range> 480 ° C a pore volume ratio> 10 and a maximum of specific surface in the pore radius range between 200 nm and 1000 nm. This means that one must use in the context of a plant for the oxidation of SO ₂ to SO ₃ different, adapted to the respective operating temperature of the contact Horde catalysts.

Out DE 12 35 274 A It is known to adapt catalysts with their porosities to the respective working temperature, since the catalytic activity at different temperatures depends on the pore size.

So far No catalysts have yet become known that over the Whole temperature range of a sulfuric acid contact a possible even high activity with good aging resistance and mechanical stability exhibit.

Of the The present invention was therefore based on the object, a catalyst for the Oxidation of sulfur dioxide to sulfur trioxide consisting of a silica containing carrier material and active substance applied thereto, containing vanadium and To provide alkali metal compounds, the disadvantages of does not have known catalysts and in particular via a wide temperature range has a high activity.

It it was found that these Problem solved that can be silica containing carrier material a pore volume fraction of 10 to 30% of pores with a pore diameter to 15 nm, a pore volume fraction of 25 to 60% of pores with a pore diameter of 15 to 200 nm and a pore volume fraction from 10 to 60% of pores having a pore diameter of> 200 nm.

In contrast to the previously known impregnation catalysts for the oxidation of SO ₂ to SO ₃ , silicas having different pore diameter ranges are used in the catalyst according to the invention. It is surprising that contrary to the assumption that due to the inevitably only small proportion of each pore diameter range, based on the total pore diameter range of the catalyst, which provides optimum results for a certain temperature range, in a catalyst according to the invention over the entire temperature range of the conversion not only does not deteriorate sales will even be increased for each temperature range.

The carriers according to the invention advantageously have a total pore volume of 0.8 to 1.0 cm ³ / g.

to Preparation of the catalyst support one proceeds in such a way that one of silicas starting with the corresponding pore diameter ranges. Sun sets for example, for the pore volume fraction goes back to pore diameters of up to 15 nm, Silica gels, in the form of hydrogels or xerogels and / or you go of sodium or potassium silicates obtained by acid addition, e.g. Sulfuric acid, lets it gel. For pore diameter from 50 to 200 nm, one uses precipitated silicas, while for silicas with Pore diameters> 200 Diatomaceous earth is used. The silica components are with such Amount of liquid, e.g. Water and / or sulfuric acid up to a loss of ignition the mass of 65% mixes to form a deformable mass, which then e.g. compressed into tablets or extruded into strands becomes. The shaped bodies thus obtained will be afterwards dried and calcined at a temperature which determines the pore diameter distribution not changed. For this reason, the temperature should not exceed 650 ° C, usually calcination at temperatures of 450 to 650 ° C.

The carrier thus prepared is then loaded in the usual way with the catalytically active substances by impregnation. For this purpose, for example, dissolves a soluble in alkali Vadadiumverbindung, eg ammonium polyvanadate in dilute potassium hydroxide solution (eg 40 to 50 wt .-% KOH) and then oxalic acid. Sulfuric acid is added to this solution to adjust the pH of the solution below 2. The solution may contain the components within the following ranges: 12 to 45 wt% K ₂ O, 6.5 to 31 wt%, 21 to 65% by weight of SO ₄ and 9 to 31% by weight of oxalic acid. By immersing the carrier in this solution, the carrier is loaded with the catalytically active substances. It should be ensured that after drying, the degree of filling of the pores with active mass is 40 to 60%.

• 1. sehr gute mechanische Eigenschaften, wie Härte und Abrieb sowohl im Originalzustand als auch im gealterten Zustand, was damit zu erklären ist, daß dem Katalysator ein in sich stabiler Trägerformkörper zugrundeliegt, der selbst nur in einem sehr geringen Maße altert gegenüber sogenannten Vollkatalysatoren, bei denen die Festigkeit zu einem großen Teil durch die Bindekraft der Aktivkomponenten erreicht wird, die jedoch selbst in einem stärkeren Maße altern,
• 2. sehr hohe Aktivitäten gegenüber handelsüblichen sog. hochaktiven Katalysatoren, was damit zu erklären ist, daß sowohl ein Anteil sehr enger Poren kleiner 15 nm mit einer großen spezifischen Oberfläche vorhan den ist, der dafür verantwortlich ist, daß bei sehr tiefen Temperaturen um 380°C hohe SO₂-Umsätze möglich sind als auch ein Anteil Poren zwischen 15 und 200 nm, der dafür verantwortlich ist, daß bei Temperaturen um 400°C hohe SO₂-Umsätze möglich sind als auch ein Anteil Poren zwischen 200 und 5000 nm, der dafür verantwortlich ist, daß auch bei Temperaturen oberhalb 420°C noch hohe SO₂-Umsätze möglich sind; darüber hinaus gewährleisten die jeweils größeren Poren, daß die kleineren Poren überhaupt zugänglich sind und damit ausgenutzt werden können,
• 3. sehr niedrige Druckverluste, da wegen der guten Verformbarkeit des Trägermaterials sehr günstige Formöperabmessungen erhalten werden können,
• 4. mögliche Kosteneinsparung in der Anwendung, da wegen der hohen Aktivitäten bei niedrigeren Temperaturen gearbeitet werden kann,
• 5. geringere SO₂-Emissionen, weil durch die hohen Tieftemperaturaktivitäten höhere Endumsätze möglich werden.

The catalyst according to the invention has the following advantages:

• 1. very good mechanical properties, such as hardness and abrasion both in the original state and in the aged state, which can be explained by the fact that the catalyst is based on a stable carrier molding in itself, which itself ages only very slightly compared to so-called full catalysts at which strength is achieved to a large extent by the binding power of the active components, but which themselves age to a greater extent,
• 2. very high activity compared to commercial so-called. Highly active catalysts, which is explained by the fact that both a proportion of very narrow pores less than 15 nm with a large specific surface IN ANY is the, which is responsible for ensuring that at very low temperatures around 380 ° C high SO ₂ sales are possible as well as a proportion of pores between 15 and 200 nm, which is responsible for the fact that at temperatures around 400 ° C high SO ₂ sales are possible as well as a proportion of pores between 200 and 5000 nm, the is responsible for the fact that even at temperatures above 420 ° C even high SO ₂ sales are possible; In addition, the larger pores each ensure that the smaller pores are accessible at all and thus can be exploited,
• 3. very low pressure losses, since due to the good deformability of the carrier material very favorable Formöperabmessungen can be obtained
• 4. possible cost savings in the application, because of the high activities at lower temperatures can be worked,
• 5. lower SO ₂ emissions, because the high low temperature activities enable higher end turnovers.

Measurement Method

1. Determination of activity

a. Determination of turnover

The conversion of SO ₂ to SO ₃ is determined by measuring the SO ₂ content in the input and output gas of a reactor. The SO ₂ contents are determined by titration with a chloramine solution. The measured values are the volumes of gas required for the decolorization of 10 ml of a 0.1N chloramine solution.

b. The calculation of Activity:

If one takes a commercial catalyst, as described in Example 3, as a standard and defines its SO ₂ sales at different temperatures each as 100% activity, then a catalyst to be measured, for example, 200% activity, if you reach the same Turnover at the same temperature as in the standard catalyst either doubling the amount of SO ₂ gas or can halve the amount of catalyst.

2. Determination of the cutting hardness

It is the force measured to cut through an extrusion with a 0.3 mm blade is required.

The Cutting edge is moved with a feed of 14 mm / minute. The power comes with a strain gauge detected.

It will be a total of 25 extrusions severed. From the determined forces, the mean value is formed.

3. Determination of the abrasion:

The sample is screened through a 2 mm sieve, 100 g of the unsorted sample are weighed into a 1 liter container; For this purpose, 30 g of porcelain balls (10 to 11 mm in diameter) are added. The container is sealed and agitated for 2 hours on a vibratory mill at 1400 rpm and an amplitude of 10 mm. Thereafter, the proportion is determined less than 2 mm. This value - based on the amount used - gives the abrasion.

4. Determination of abrasion after aging

Approximately 120 g of the catalyst are installed in a 250 ml reactor tube. The tube is heated in a Salzbadofen to about 700 ° C and with about 3 l / h of a gas composition 10 vol.% SO ₂ , 11 vol.% O ₂ and 79 vol.% N ₂ applied.

After that the abrasion of the entire sample is described as under 2) Function of the service life determined. Each sample is installed only once.

The Percentages given in the examples are, if not otherwise vermekt, weight percentages.

example 1

4.94 kg of a 15% silica hydrogel (pore diameter of about 1 to 15 nm) with 92 g of 48% sulfuric acid, 2.11 kg of a precipitated silica (pore diameter of 15 to 200 nm) (Sipernat 22 from Degussa), 1 , 95 kg of a soda waterglass with 27% SiO ₂ and 8% Na ₂ O, 400 g of a diatomaceous earth (pore diameter 200 to 2500 nm and a small proportion of 25 mm) and 510 g of a 10% sodium alginate solution thoroughly mixed and deformed into 10 × 5 mm hollow strands.

The Moldings are at 130 ° C dried and at 550 ° C calcined.

The support has a pore volume of 0.88 m ³ / g, which is distributed over the pore diameters as follows:
21% <15 nm
56% 15-200 nm
23%> 200 nm

The Calcined moldings are made with a solution that consists of 4.95 kg of a 46% potassium hydroxide solution, 1.38 kg of a 90% ammonium polyvanadate, 1.56 kg of crystalline oxalic acid and 7.67 kg of a 48% sulfuric acid was prepared soaked.

The impregnated moldings are then dried at 200 ° C. The pore volumes of the carrier have a degree of filling of 51%. The finished catalyst has a content of V ₂ O ₅ of 7.3%, K ₂ O of 11.5 and Na ₂ O of 2.5%. cutting hardness 4.5 kg abrasion 1.5% Abrasion after aging 8.5% activity at 450 ° C: 100% at 430 ° C: 130% at 410 ° C: 180% at 390 ° C: 265%

Example 2

11.33 kg of a 15% Kieselsäsehydehydrol with pore diameters of about 1 to 15 nm with 310 g of 48% sulfuric acid, 3.58 kg of a precipitated silica with pore diameters of 15 to 200 nm (Sipernat 22 from Degussa), 4.71 kg of a soda waterglass with 27% SiO ₂ , 3.39 kg of a kieselguhr with pore diameters of 200 to 2500 nm and a small proportion of 25 nm and 510 g of a 10% sodium alginate solution mixed thoroughly and 10 × 5 mm hollow strands deformed.

The Moldings are at 130 ° C dried and at 550 ° C calcined.

The support has a pore volume of 0.95, which is distributed over the pore diameters as follows:
15% <15 nm
28% 15-200 nm
57%> 200 nm

The calcined moldings are filled with a solution that consists of 4.11 kg 46% potassium hydroxide solution, 1.38 kg of a 90% ammonium polyvanadate, 1.56 kg of crystalline oxalic acid and 6.29 kg of a 48% sulfuric acid was prepared soaked.

The impregnated moldings are then dried at 200 ° C. The pore volumes of the carrier have a degree of filling of 49%. The finished catalyst has a content of
7.6% V ₂ O ₅
10.1% K ₂ O
3.0% Na ₂ O cutting hardness 4.3 kg abrasion 1.9% Abrasion after aging 9.5% activity at 450 ° C: 100% at 430 ° C: 120% at 410 ° C: 245% at 390 ° C: 330%

In the figure is the pore volume distribution of the examples 1 and 2 produced carrier illustrates where the marked with the crosses measuring points the carrier according to example 1 and the points marked with the squares the carrier according to example 2 are assigned.

Example 3 (comparative example)

A commercially available unsupported catalyst was prepared by the following method:
A suspension is prepared from 6.03 kg 46% potassium hydroxide solution, 1.94 kg 90% ammonium polyvanadate, 25% sodium hydroxide solution and 9.73 kg of a 32% sulfuric acid. This is intensively mixed with a kieselguhr (pore volume about 2.0 cm ³ · g ^-1 ) and shaped into 10 × 5 mm hollow strands.

The moldings are dried at 130 ° C and calcined at 550 ° C. The catalyst has a pore volume of 0.45 cm ³ · g ^-1 .

Properties:

The pore diameter distribution shows a maximum at about 1000 nm. activity at 450 ° C: 100% at 430 ° C: 100% at 410 ° C: 100% at 390 ° C: 100%

The activities the example 1 and 2 produced catalysts show the superiority of the catalysts of the invention.

Claims (6)

Catalysts for the oxidation of sulfur dioxide to sulfur trioxide, consisting of a silica-containing carrier material and an active substance containing vanadium and alkali metal compounds, characterized in that the silica-containing carrier material has a pore volume fraction of 10 to 30% of pores having a pore diameter of up to 15 nm, a pore volume fraction of 25 to 60% of pores having a pore diameter of 15 to 200 nm and a pore volume fraction of 10 to 60% of pores having a pore diameter of> 200 nm. Catalyst according to claim 1, characterized in that the carrier material has a pore volume of 0.8 to 1.0 cm ³ / g. Catalyst according to Claims 1 to 2, characterized that this Pore volume of the carrier a degree of filling having active mass of 40 to 60%. Process for the preparation of the catalyst according to claims 1 to 3, characterized in that silicas with Pore diameters substantially a) <15 nm b) 15 to 200 nm c)> 200 nm with a such amount of a liquid mixed that one deformable mass arises, the. Mass deformed, the moldings dry and calcined and the calcined mass with catalytically active Substances soaks and subsequently dries. Method according to claim 4, characterized in that that he calcined at temperatures of 450 to 650 ° C. Process according to claims 4 and 5, characterized that he as a liquid Water and / or sulfuric acid used.