RU2242280C1 - Sulfur dioxide-into-sulfur trioxide conversion catalyst - Google Patents

Abstract

FIELD: oxidation catalysts.

SUBSTANCE: invention provides SO₂ to SO₃ conversion catalyst containing vanadium, alkali metal (K, Na, Rb, Contains), and sulfur oxides as well as siliceous skeleton made from natural of synthetic silica and including pores with radii up to 65000

, percentage of pores with radii 1000-10000

constituting at least 5%, that with radii more than 10000

up to 35%, and that with radii less than 1000

at least 40%, including pores with radii less than 75

, whose percentage is at least 31%. Percentage of sulfuric acid-insoluble vanadium compounds (calculated on conversion to V₂O₅) in skeleton does not exceed 4.0%. preferably not more than 2.0%.

EFFECT: improved performance characteristics of catalyst by extending catalyst operation temperature range in low-temperature region, that is increased activity at catalysis temperature 380^оС and simultaneously increased activity within middle temperature range (420-485^оС).

2 cl, 2 tbl, 7 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 ₃ is exothermic, the catalyst within each separate layer in the reactor operates under varying temperatures, i.e. 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 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 380 ° 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 support of the finished catalyst, called the framework. Advantageously, the characteristics of the porous structure of the starting support used for synthesis are given, which may differ significantly from the support of the finished catalyst, i.e. frame.

, при этом доля пор с радиусами 1000-10000

составляет от 5 до 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, в том числе и при достаточно низких температурах (405°С).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 100,000

while the proportion of pores with radii of 1000-10000

makes up 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 ° 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 below 405 ° 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 (up to 380 ° C) while increasing activity in the average temperature range (420-485 ° C).

, при этом в каркасе доля пор с радиусами 1000-10000

составляет не менее 5%, доля пор с радиусами более 10000

составляет не более 35%, а содержание в каркасе нерастворимых в серной кислоте соединений ванадия (в пересчете на V₂O₅) составляет не более 4,0 мас.%. Доля пор с радиусами менее 1000

составляет не менее 40%, при этом доля пор с радиусом менее 75

составляет не менее 31%. Предпочтительно содержание в каркасе нерастворимых в серной кислоте соединений ванадия (в пересчете на V₂O₅) составляет не более 2,0 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, including pores with radii up to 65000

, while in the frame the proportion of pores with radii of 1000-10000

is at least 5%, the proportion of pores with radii of more than 10,000

is not more than 35%, and the content in the framework of vanadium compounds insoluble in sulfuric acid (in terms of V ₂ O ₅ ) is not more than 4.0 wt.%. The proportion of pores with radii less than 1000

is at least 40%, while the proportion of pores with a radius of less than 75

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 wt.%.

. Вероятно, это связано как с увеличением величины внутренней поверхности катализатора, так и со стабилизацией расплавленного состояния активного компонента наиболее тонкими порами каркаса, затрудняющими процесс кристаллизации в расплаве. С повышением количества пор с радиусом менее 75

и уменьшением содержания блокированного ванадия активность катализатора при низких температурах возрастает. При этом наличие в каркасе пор с радиусом менее 75

в количестве менее 31% обуславливает решение технической задачи даже при содержании в каркасе катализатора блокированного ванадия, равном предельному.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 framework of a sufficient pore volume with radii less than 1000E allows you to increase 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

. 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 thinnest frame pores, which impede the crystallization process in the melt. With increasing number of pores with a radius of less than 75

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

in an amount of less than 31% determines the solution of the technical problem even when the content of blocked vanadium in the catalyst frame is equal to the limit.

The achievement of the technical task regarding the prototype is considered to be an increase in relative activity: at 420 ° C - at least 115%, at 380 ° 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 wt.% (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 sufficiently studied (mechanical pinching is assumed during the formation of the framework at the calcination stage under the influence of a melt of active components), but the authors established a clear inverse relationship between the content of vanadium insoluble in acid in the framework and the activity of the catalyst. The proportion of “blocked” vanadium depends both on the properties of the support 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 insoluble in sulfuric acid in the framework to more than 4.0% (in terms of V ₂ O ₅ ), the catalytic activity decreases over the entire temperature range. The highest activity of the catalyst at 380 ° C is achieved when the content of vanadium compounds in the framework is not more than 2.0 wt.%.

The present invention specifies the optimal ratio of the pore content of various sizes and the maximum permissible 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 (up to 380 ° C) while increasing 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 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 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 ° C to constant weight. In the framework thus obtained, the porous structure and content of vanadium compounds insoluble in sulfuric acid were determined.

10% и объемной скорости 4000 час^-1 при температурах 380, 420, 485°С. Концентрацию SO₂ на входе в реактор и на выходе из реактора определяли методом Рейха (барботируя пробу газа через титрованный раствор I₂). Активность образцов выражали относительной величиной - по отношению к активности прототипа при соответствующих температурах.The activity of the catalyst samples under standard conditions was determined by the flow method in accordance with TU 2175-001-12294550-2001 at

10% and a space velocity of 4000 h ^-1 at temperatures of 380, 420, 485 ° 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 1a and 1b. The catalyst was prepared similarly to the prototype. The carrier — hydrocreme silica gel — was obtained 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 ratio of 1: 0.5. Hydro silica gel was filtered off, washed with water, and its specific surface area was determined by alkaline titration with NaOH (S $\genfrac{}{}{0ex}{}{\text{Na}}{\text{gel}}$ ) 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, wt.%: V ₂ O ₅ 9.0, K ₂ O 14.5, SO ₃ 24.3. 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 was analyzed for the calcined catalyst 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 1A and 1B differ in the dilution of water glass and the calcination temperature (see table 1).

Examples 2-7. The catalyst was prepared mainly according to the prototype, with the exception of a number of differences.

. При синтезе варьировали также рН синтеза пульпы катализатора и режим прокалки катализатора. Режим приготовления и характеристики полученных катализаторов приведены в таблицах 1 и 2.The catalyst was synthesized using hydrosilica gel obtained from water glass with a different degree of dilution with water and aged by heating by heating of different durations, as a result of which it had a different specific surface (S $\genfrac{}{}{0ex}{}{\text{Na}}{\text{gel}}$ ), and the sample of the obtained xerogel contained a different fraction of pores with radii <75

. During the synthesis, the pH of the catalyst pulp synthesis and the calcination mode of the catalyst were also varied. The preparation mode and characteristics of the obtained catalysts are shown in tables 1 and 2.

In Example 2, the catalyst was synthesized on a mixed carrier — crushed diatomite (-0.5 mm fraction) was added to the hydrosilica gel before introducing solutions of the active components 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 ° C is significantly higher than that for the prototype.

Claims (2)

1. The catalyst for the conversion of SO ₂ to SO ₃ containing oxides of vanadium, an 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

, while in the frame the proportion of pores with radii of 1000-10000

is at least 5%, the proportion of pores with radii of more than 10,000

is not more than 35%, and the content in the framework of vanadium insoluble sulfuric acid compounds (in terms of V ₂ O ₅ ) is not more than 4.0 wt.%, characterized in that in the framework the proportion of pores with radii of less than 1000

at least 40%, including the proportion of pores with radii less than 75

is at least 31%. 2. The catalyst according to claim 1, characterized in that preferably the content in the skeleton of vanadium compounds insoluble in sulfuric acid (in terms of V ₂ O ₅ ) is not more than 2.0 wt.%.