RU2244590C1 - So2-into-so3 conversion catalyst - Google Patents

Abstract

FIELD: oxidation catalysts.

SUBSTANCE: SO₂-into-SO₃ conversion catalyst contains following active components: vanadium oxide, alkali metal (K, Na, Rb, Contains) oxides, sulfur oxides, and silica framework formed from natural and/or synthetic silica and having pores with radii up to 65000

, among which fraction of pores with radii larger 10000

does not exceed 50%, while content of sulfuric acid-insoluble vanadium compounds (on conversion to V₂O₅) does not exceed 4.0% by weight. Fraction of pores with radii 1000-10000

does not exceed 35% and that less than 75

at most 9%.

EFFECT: improved performance characteristics of catalyst operated in reactor zones at medium and maximum temperature due to under conditions activity at 420-530^оС.

3 cl, 1 tbl, 8 ex

Description

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 carrier, 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 by using carriers with narrow pore ranges that are optimal for each particular temperature range [Patent DE No. 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 under varying temperatures, i.e. requires the use of a large set of catalysts with different pore ranges. In real conditions, due to the impossibility of accurately calculating temperature fields by the height and volume of the layers, 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 No. 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%, 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 more than 450 ° C.

It should be noted that only in very few sources, the choice of an effective catalyst is carried out according to the porous structure of the initial carrier of the finished catalyst. The characteristics of the porous structure of the support used for synthesis are predominantly given, which may substantially differ in structure from the support of the finished catalyst, i.e. frame.

, при этом доля пор с радиусами 1000-10000 Е составляет 5-70%. При этом каркас катализатора формируется из природного или синтетического кремнезема или их комбинации. Под каркасом катализатора авторы понимали реальную структуру носителя, прошедшего все стадии получения катализатора (включая формование и прокалку) - т.е. готового катализатора после удаления с него кислоторастворимых активных компонентов путем экстрагирования серной кислотой. Известный катализатор обладает высокой активностью в широком диапазоне температур от 405 до 485°С. Это достигается за счет целесообразного химического состава, наличия пор с широким диапазоном радиусов и рационального соотношения пор различных размеров в структуре каркаса.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 No. 2162367, 2000]. A commercial catalyst carrier or framework contains pores with radii from 100 to 10,000

while the proportion of pores with radii of 1000-10000 E is 5-70%. 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 from 405 to 485 ° 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 object is not high enough activity at temperatures equal to and above 485 ° C.

The technical task of the invention is to improve the operational characteristics of the catalyst operating in the zones of the reactor at medium and maximum temperatures, by increasing activity at temperatures of 420-530 ° C.

, при этом доля пор с радиусами более 10000

не превышает 50%, доля пор с радиусами 1000-10000

составляет не менее 35%, доля пор с радиусами менее 1000

составляет не более 60%, в том числе доля пор с радиусами менее 75

составляет не более 9%, а содержание нерастворимых в серной кислоте соединений ванадия не превышает (в пересчете на V₂О₅) 4,0% (мас.). Предпочтительно доля пор с радиусами менее 1000

составляет не более 40%, а доля пор с радиусами 1000-10000

составляет не менее 50%. Предпочтительное содержание в каркасе нерастворимых в серной кислоте соединений ванадия (в пересчете на V₂O₅) не превышает 1,5% (мас.).The technical problem is solved in that the catalyst for the conversion of SO ₂ to SO ₃ contains active components - oxides of vanadium, alkali metal (K, Na, Rb, Cs), sulfur and a siliceous frame formed from natural and / or synthetic silica and including pores with a radius up to 65000

while the proportion of pores with radii of more than 10,000

does not exceed 50%, the proportion of pores with radii of 1000-10000

is not less than 35%, the proportion of pores with radii less than 1000

is not more than 60%, including the proportion of pores with radii less than 75

is not more than 9%, and the content of vanadium compounds insoluble in sulfuric acid does not exceed (in terms of V ₂ O ₅ ) 4.0% (wt.). Preferably the proportion of pores with radii less than 1000

is not more than 40%, and the proportion of pores with radii of 1000-10000

is at least 50%. The preferred content in the framework of insoluble sulfuric acid compounds of vanadium (in terms of V ₂ O ₅ ) does not exceed 1.5% (wt.).

The achievement of the technical problem is observed only for the aforementioned porous structure of the catalyst frame while limiting the content of vanadium compounds insoluble in sulfuric acid to 4.0% by weight in the frame.

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

With an increase in the carcass content of vanadium compounds insoluble in sulfuric acid to more than 4.0% (based on V ₂ O ₅ ), the catalytic activity also decreases over the entire temperature range.

It is known that the reaction of the conversion of SO ₂ to SO ₃ occurs in the melt of the active component distributed on the pore surface of the catalyst frame. At elevated catalysis temperatures, when the reaction rates are high, relatively large pores of the catalyst are used, formed by the pores of the frame with radii of more than 1000 E. In the proposed solution to increase the activity of the catalyst at 420-530 ° C, the pore volume of the frame with radii of 1000- 10000 E, due to the limitation of the volume of thinner pores with radii less than 1000 E, which are necessary at lower catalysis temperatures (less than 420 ° C).

наиболее эффективно в этом случае, если это уменьшение происходит за счет наиболее тонких пор этого диапазона, а именно пор с радиусами менее 75

.The experiment found that a decrease in the pore volume of the frame with radii less than 1000

most effective in this case, if this decrease occurs due to the thinnest pores of this range, namely, pores with radii less than 75

.

It is assumed that one of the purposes of these thinnest pores of the framework is to stabilize the active component in the molten state at temperatures less than 420 ° C, which is not relevant in this case. Previously, the authors found that the catalyst frame retains, “blocks” a different amount of vanadium compounds.

A decrease in the activity of the catalyst at 420 and 485 ° C was shown with an increase in the content of vanadium compounds insoluble in sulfuric acid in the framework.

The blocking mechanism is not well understood. It can be assumed that blocking removes vanadium compounds from the melt of active components, depleting the melt with catalytically active substances.

The present invention has proposed an optimal ratio of pores of various sizes in the framework and specified the maximum permissible content of blocked vanadium compounds, the combination of which gives an unexpected effect - the expansion of the effective range of the catalyst from 420 to 530 ° C.

The process of preparation of the catalysts is described in the examples.

The method of washing the catalyst from the active components and obtain the frame 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 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 ° 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 at C _SO2 - 10% and a space velocity of 4000 h ^-1 at temperatures of 420, 485, 530 ° 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 (sparging a gas sample through a titrated solution of I ₂ ). The activity of the samples was expressed by a relative value - 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 No. 1A and 1B. The catalyst was prepared basically similar to the prototype. The carrier — hydrosilica gel — was obtained from liquid sodium glass diluted with water by precipitation with sulfuric acid at pH ~ 6. Hydro silica gel was filtered and washed with water and its specific surface was determined by alkaline titration (S ^Na gel).

To obtain a catalyst, solutions of the active components — sulfuric acid and potassium vanadate — were added to hydrosilicon gel based on the preparation of the following catalyst composition,% (wt.): V ₂ O ₅ - 8.0%, K ₂ O -12.5%, SO ₃ - 15.9%, SiO ₂ - ost.%. The catalyst pulp was evaporated, the powder was extruded at a humidity of ~ 40%, the granules were dried and calcined. Examples 1A and 1B differ in the dilution of water glass and the temperature of calcination (see table.).

Examples No. 2-8. The catalyst was prepared in accordance with the prototype with the exception of the following differences.

Hydro silica gel was partially or completely replaced by diatomite based on the preparation of the specified mass ratio of synthetic silica and diatomite (in terms of dry weight) as a part of the carrier. The pH of the synthesis of catalyst pulp, the temperature and time of calcination of the catalyst were changed. The specific parameters for the preparation of the catalyst by examples and characteristics of the samples are shown in the table.

The calcined catalyst was analyzed for catalytic activity at temperatures of 420, 485 and 530 ° 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.

From the table it is seen that the activity of the catalyst with the characteristics specified in the claims is significantly higher than that of the prototype.

Table The mode of preparation and characterization of samples obtained in accordance with examples Example Sample Preparation Mode The frame of the calcined catalyst Calcined catalyst Liquid glass dilution S ^Na gel m ² / g catalyst synthesis pH The ratio (SiO ₂ : D) ^* Calcination The proportion of pores,% (vol.) The content of V ₂ O ₅ ,% (wt.) Relative activity,% Temperature ° C Time hour The radii of the pores, E 420 ° C 485 ° C 530 ° C <75 75-1000 1000-10000 > 10,000 1a (prototype) 1: 0.45 1050 1,0 1-0 550 2 0 62 twenty eighteen 4.3 94 96 96 1b (prototype) 1: 1.8 630 1,0 1-0 500 2 12 53 23 12 2,5 100 100 100 2 1: 2.5 575 2.1 0.7: 0.3 550 7 0 60 35 5 4.0 103 105 105 3 - // - - // - 1,0 0.4: 0.6 550 2 1 39 fifty 10 1,5 104 106 106 4 - // - - // - 1.9 0.3: 0.7 500 2 nine 21 52 eighteen 3.8 102 102 102 5 - // - - // - 1,0 0: 1 600 4 0 3 61 36 1,0 101 101 101 6 (for comparison) - // - - // - 2.0 0.6: 0.4 500 2 eleven 44 thirty fifteen 3.9 100 99 99 7 (for comparison) - // - - // - 2.2 0.8: 0.2 600 4 0 62 34 4 4.0 100 98 98 8 (for comparison) - // - - // - 2,3 0.9: 0.1 650 2 0 nine 81 10 4.2 95 97 97 * Mass ratio in the composition of the carrier of synthetic silica (SiO ₂ ) and diatomite (D) (calculated on dry.). ** The activity of the prototype according to example 1b is taken as 100%.

Claims (3)

1. The catalyst for the conversion of SO ₂ to SO ₃ containing active components - oxides of vanadium, alkali metal (K, Na, Rb, Cs), sulfur and a siliceous framework formed from natural and / or synthetic silica and including pores with radii up to 65,000 Å moreover, in the framework, the proportion of pores with radii of more than 10,000 Å does not exceed 50%, and the content of vanadium compounds insoluble in sulfuric acid (in terms of V ₂ O ₅ ) does not exceed 4.0 wt.%, characterized in that in the framework pores with radii of 1000-10000 Å is at least 35%; the proportion of pores with radii of less than 1000 Å is no more than e 60%, including the fraction of pores with radii less than 75 Å is not more than 9%. 2. The catalyst according to claim 1, characterized in that in the framework the proportion of pores with radii of less than 1000 Å is preferably not more than 40%, and the proportion of pores with radii of 1000-10000 Å is not less than 50%. 3. The catalyst according to claim 1, characterized in that the content in the skeleton of vanadium compounds insoluble in sulfuric acid (in terms of V ₂ O ₅ ) preferably does not exceed 1.5 wt.%.