WO2006033589A1

WO2006033589A1 - Catalyst for converting so2 into so3

Info

Publication number: WO2006033589A1
Application number: PCT/RU2004/000353
Authority: WO
Inventors: Lubov Nikolaevna Manaeva; Veniamin Iosifovich Malkiman
Original assignee: Lubov Nikolaevna Manaeva; Veniamin Iosifovich Malkiman
Priority date: 2004-09-10
Filing date: 2004-09-10
Publication date: 2006-03-30

Abstract

The invention relates to producing vanadium catalysts for converting SO2 into SO3. The inventive catalyst for converting SO2 into SO3 comprises vanadium, alkali metal (K, Na, Rb, Cs) and sulfur oxides and a siliceous base which is made of a natural and/or synthetic silicon and whose pore radii are equal to or less than 6500 Å, wherein the part of pores whose radius ranges from 1000 to 10000 Å is equal to or greater than 5 %, the part of pores whose radius is greater than 10000 Å is equal to or less than 35 %, the part of pores whose radius is less than 1000 Å is equal to or greater than 40 %, the part of pores whose radius is less than 75 Å is equal to or greater than 31 %, the content of sulphuric acid-insoluble vanadium compounds is equal to or less than 4 mass %, preferably less than 2 % (in terms of V2O5). Said invention improves the performance characteristics of the catalyst by extending the temperature operating range thereof in a low-temperature range, i.e. increasing the activity thereof at a catalysis temperature of 380 °C and simultaneously increasing the activity in the range of medium temperatures ranging from 420 to 485 °C.

Description

SO ₂ CONVERSION CATALYST

The invention relates to the production of vanadium catalysts for the conversion of SO ₂ to SO ₃ . The catalysts for this process usually contain the active component - oxides of vanadium, alkali metals, sulfur, distributed on the surface of the siliceous support, and have a certain porous structure, which is the most important property of the catalyst that determines its operational characteristics.

Known technical solutions for the creation of catalysts that are highly active in narrow ranges of the operating temperature range obtained by using carriers with narrow pore ranges that are optimal for each particular temperature range [DE Patent N ° 1235274].

However, the known solution has significant drawbacks. Since the oxidation process of SO ₂ is exothermic, the catalyst within each separate layer in the reactor operates at varying temperatures, i.e., it requires the use of a set of catalysts with different pore ranges. In real conditions, due to the impossibility of accurately calculating temperature fields by height and volume of a layer, even a set of catalysts with given narrow pore ranges cannot work effectively.

It is more rational to prepare a supported catalyst with a wide range of pores of various sizes with a certain ratio of them that works effectively in wider temperature ranges. A known catalyst [Patent DE JY ° 4000609, 1991], the carrier of which has pores with diameters from several angstroms to more than 200 nm. The proportion of pores with a diameter of up to 15 nm is 10-30%, s with a diameter of 15-100 nm - 25-60%, with a diameter of more than 200 nm -10-60%. The known catalyst is obtained by impregnation of a preformed and calcined support with a given porosity. A disadvantage of the known catalyst is low activity at a temperature of 380 ⁰ C.

It should be noted that only in very few sources, the choice of an effective catalyst is based on the porous structure of the carrier of the finished catalyst, called the framework. The characteristics of the porous structure of the starting support used for synthesis are predominantly given, which may differ significantly from the support of the finished catalyst, i.e. frame.

The prototype of the proposed catalyst is a catalyst for the conversion of SO ₂ to SO ₃ containing oxides of vanadium, alkali metal (K, Na, Rb, Cs), sulfur, on a siliceous carrier [RF Patent N ° 2162367, 2000]. A commercial catalyst carrier or framework contains pores with radii from 100 to ΙOOOOOA, while the proportion of pores with radii of 1000 - ΙOOOOA is from 5 to 70%. In this case, the catalyst frame is formed from natural or synthetic silica, or a combination thereof. Under the catalyst framework, the authors understood the real structure of the carrier, which went through all stages of the preparation of the catalyst (including molding and calcining), i.e. the finished catalyst after removal of acid-soluble active components from it by extraction with sulfuric acid. The known catalyst has high activity in a wide temperature range, including at sufficiently low temperatures (405 ⁰ C).

This is achieved due to the appropriate chemical composition, the presence of pores with a wide range of radii and a rational ratio of pores of various sizes in the structure of the frame.

The disadvantage of this facility is not high enough activity at temperatures below 405 ⁰ C.

The technical task is to improve the operational characteristics of the catalyst by expanding the temperature range of its operation in the low temperature region to 38O ⁰ C while increasing activity in the average temperature range 420-485 ⁰ C.

The technical problem is solved in that the catalyst for the conversion of SO ₂ to SO3 contains active components - oxides of vanadium, an alkali metal (K, Na, Rb, Cs), sulfur and a siliceous framework formed from natural and / or synthetic silica, including pores with radii up to 65,000 A, while in the framework the proportion of pores with radii of 1000–10,000 A is at least 5%, the proportion of pores with radii greater than ΙOOOOA is not more than 35%, and the content of vanadium compounds insoluble in sulfuric acid in the framework (in terms of V ₂ Os ) is not more than 4.0% (May). The proportion of pores with radii less than 1000A is at least 40%, while the proportion of pores with a radius of less than 75 A is at least 31%. Preferably, the content of vanadium compounds insoluble in sulfuric acid in the framework (in terms of V ₂ O ₅ ) is not more than 2.0% (May).

It is known that the process of catalytic oxidation of SO ₂ in SO ₃ proceeds in the molten state of the active components. It is assumed that the lower limit of the operating range is limited by the crystallization temperature of the active components. The experiments established that the content in the skeleton of a sufficient pore volume with radii less than 10 ° C allows an increase in activity at a temperature of 380 ^° C. An even greater effect is observed with an increase in the content of pore volume with radii less than 75 A. This is probably due to both an increase in the value of the inner surface of the catalyst and stabilization of the molten state of the active component by the finest frame frames that impede the process of crystallization in the melt. With an increase in the number of pores with a radius of less than 75 A and a decrease in the content of blocked vanadium, the activity of the catalyst at low temperatures increases. Moreover, the presence in the framework of pores with a radius of less than 75 A in an amount of at least 31% determines the solution of the technical problem even when the content of blocked vanadium in the catalyst framework is equal to the limit.

The achievement of the technical task regarding the prototype is considered to be an increase in relative activity at 42O ⁰ C - at least 115%, at 380 ⁰ C - at least 140%.

If the above optimal ratio of the proportion of pores in the specified intervals is violated, the catalytic activity decreases over the entire temperature range.

The achievement of the technical problem is observed only when the content in the framework of vanadium compounds insoluble in sulfuric acid is limited to 4.0% (May.) (In terms of V ₂ O ₅ ).

Previously, the authors found that the catalyst frame after washing off the active components with sulfuric acid can retain (“block”) a different amount of vanadium compounds. The mechanism of this phenomenon has not been studied enough (mechanical jamming is assumed during the formation of the carcass at the calcination stage under the influence of a melt of active components), but the authors have established a clear inverse relationship between the content of vanadium insoluble in acid and the activity of the catalyst in the carcass. The proportion of “blocked” vanadium depends both on the properties of the carrier used and on the mode of catalyst synthesis, however, it was previously unclear what maximum vanadium content is allowed in a blocked form.

With an increase in the content of vanadium compounds in the framework, soluble in sulfuric acid to more than 4.0% (in terms of V ₂ O ₅ ) decreases catalytic activity in the entire temperature range. The highest catalyst activity at 38O ⁰ C is achieved when the content of vanadium compounds in the framework is not more than 2.0% (May).

The present invention specifies the optimal ratio of the pore content of various sizes and the maximum allowable content of vanadium compounds insoluble in sulfuric acid in the catalyst frame, which creates an unexpected effect - the expansion of the temperature range of the catalyst in the low temperature region at 380 ° C while simultaneously increasing the activity in the average temperature range - 420-485 ° C.

The catalyst preparation process is described in the examples.

The method of washing the catalyst from the active components and obtain the framework was as follows.

A sample of the calcined catalyst was crushed, the fraction (-3 + 2) mm was separated, poured with a 5% sulfuric acid solution at a ratio of T: W - 1: 20. After exposure for 24 hours, the solution was decanted (drained) and the operation was repeated two more times with sulfuric acid and then twice with water. Next, the solid residue was dried at 150 ⁰ C to constant weight. In the framework thus obtained, the porous structure and content of vanadium compounds insoluble in sulfuric acid were determined.

The activity of the catalyst samples under standard conditions was determined by the flow method in accordance with TU 2175-001-12294550-2001 "Vanadium catalysts of the CBC type for the production of sulfuric acid" at C _S o2 - 10% and a space velocity of 4000 hours ^"1 at temperatures 380, 420, 485 ⁰ C. The concentration of SO ₂ at the inlet to the reactor and at the outlet of the reactor was determined by the Reich method (bubbling a gas sample through a titrated solution of I ₂ ). b

Noah - in relation to the activity of the prototype at appropriate temperatures.

The characteristics of the porous structure were analyzed by mercury porosimetry and adsorption methods.

Example JVa Ia and 16. The catalyst was prepared similarly to the prototype. The carrier, hydrosilicon gel, was prepared by precipitation from liquid sodium glass with sulfuric acid at a pulp pH of 5.8–7.5. Before precipitation, the liquid glass was diluted with water in a predetermined ratio. _{Hydro silica gel was} filtered off, washed with water, and its specific surface area was determined by alkaline titration with NaOH (S ^Na _gel ). A sample of the washed hydrosilicon gel was dried and the porous structure was determined from the obtained dry xerogel sample.

To prepare the catalyst, solutions of the active components — sulfuric acid and potassium vanadate — were added to hydrosilicon gel based on the content in the finished catalyst in% (May): V ₂ O ₅ -9.0, K ₂ O - 14.5, SO ₃ -24.3, SiO ₂ — residue. After stirring for 2 hours, the resulting pulp was evaporated, the powder was dried to a moisture content of 38% and extruded. The granules were dried and calcined, and the catalytic activity of the calcined catalyst was analyzed at temperatures of 380, 420, and 485 ° C. A sample of the calcined catalyst was washed from the active components according to the above procedure, the resulting framework was analyzed for the porous structure and content of vanadium. Examples Ia and 16 are distinguished by dilution of water glass and calcination temperature (see table 1).

Examples N ° 2-8. The catalyst was prepared mainly according to the prototype, with the exception of a number of differences.

For the synthesis of the catalyst used hydrosilicon gel obtained from water glass with varying degrees of dilution with water and passed aging by heating of different durations, as a result of which it had a different specific surface (S ^a _gel ) _> and the xerogel sample contained a different fraction of pores with radii <75 A. During the synthesis, the pH of the synthesis of catalyst pulp and the mode of catalyst calcination were also varied. The preparation mode and characteristics of the obtained catalysts are shown in tables 1, 2.

In Example 2, the catalyst was synthesized on a mixed support — before the introduction of solutions of the active components, crushed diatomite (-0.5 mm fraction) was added to the hydrosilica gel at a mass ratio of synthetic silica (SiO ₂ ) and diatomite (D) equal to (0.8: 0.2 ) (based on dry).

The table shows that the activity of the catalyst with the stated characteristics at a temperature of 380 ⁰ C is significantly higher than that for the prototype.

Table 1

The mode of preparation of samples obtained in accordance with examples

w n

Oh with

H

The mass ratio in the composition of the carrier of synthetic silica (SiO ₂ ) and diatomite (D) (calculated on dry.). Hydro silica gel prototype was not subjected to aging

table 2

Characterization of samples obtained in accordance with examples

About VO

The activity of the prototype of example 16 is taken as 100%.

Claims

CLAIM

1. The catalyst for the conversion of SO ₂ to SO ₃ containing oxides of vanadium, an alkali metal (K ₅ Na, Rb, Cs), sulfur and a siliceous framework formed from natural and / or synthetic silica and comprising pores with radii up to 65,000 A, while in the framework the proportion of pores with radii of 1000-10,000 A is at least 5%, the proportion of pores with radii of more than 10,000 A is not more than 35%, and the content of vanadium compounds insoluble in sulfuric acid in the framework (in terms of V ₂ O ₅ ) is not more than 4.0% (May), characterized in that in the framework the proportion of pores with radii less than 1000 A is n e less than 40%, while the proportion of pores with radii less than 75 A is at least 31%.

2. The catalyst according to claim 1, characterized in that preferably the content in the framework of vanadium compounds insoluble in sulfuric acid (in terms of V ₂ O ₅ ) is not more than 2.0% (mass.)