RU2445162C2 - Catalyst (versions) and method of recovering sulfur dioxide from sulfur-containing gases (versions) - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to catalysts for recovery of sulfur dioxide from sulfur-containing gases. Proposed catalyst comprises active components based on ion and manganese compounds. Note here that said active compounds represent iron-manganese nodules and features the following composition in terms of oxides, in wt %: Fe₂O₃ - 20.0-35.0; MnO₂ - 20.0-35.0; SiO₂ - 17.0-25.0; Al₂O₃ - 5.0-10.0; Na₂O - 2.0-5.0; K₂O - 1.5-5.0; MgO - 1.5-3.0; CaO - 1.5-3.0; P₂O₅ - 3.0-10.0. Proposed catalyst comprises active components based on ion and manganese compounds. Note here that said active compounds represent iron-manganese nodules, while binder represents aluminium hydroxide or natural clays and features the following composition in terms of oxides, in wt %: Fe₂O₃ - 14.0-30.0; MnO₂ -14.0-30.0; SiO₂ - 12.0-22.0; Al₂O₃ - 20.0-40.0; Na₂O - 1.5-4.0; K₂O - 1.0-4.0; MgO - 1.0-2.5; CaO - 1.0-2.5; P₂O₅ - 2.0-8.5.

EFFECT: high catalytic activity at moderate temperatures.

12 cl, 2 tbl, 8 ex

Description

The invention relates to catalysts for the recovery of sulfur dioxide from sulfur-containing gases of industrial gas emissions to elemental sulfur. Sulfur-containing gases generated by non-ferrous metallurgy, petrochemical industry and energy enterprises pose a serious environmental problem.

For the processing of industrial gas emissions containing sulfur dioxide, various catalytic treatment technologies are proposed, however, developments that allow not only solving environmental problems, but additionally obtain useful marketable products, such as elemental sulfur, are of commercial interest.

The proposed catalyst is designed for the recovery of sulfur dioxide by synthesis gas or methane, the use of which on an industrial scale is promising and cost-effective. When developing such catalysts, which should be highly active and have a long service life, the possibility of side reactions, for example, should also be considered.

as well as the reverse Klaus reaction:

.

.

As the closest analogue of the claimed adopted catalyst for the recovery of sulfur dioxide in elemental sulfur, comprising active components based on oxides of Fe, Ni and Co with oxides of Mo, Mn or Cr in an amount of 0-80 wt.% And a carrier selected from the group including alumina, silica or molecular sieves (Application WO 94/19102, 09/01/1994). The catalyst is prepared by impregnation with nitrate solutions of the corresponding salts, followed by calcination at 600-1000 ° C, which leads to stabilization of the active component in crystal structures such as spinel or perovskite. The catalyst provides a reduction reaction of SO ₂ with synthesis gas high SO ₂ conversion (> 90%) and sulfur yield (> 90%) at high space velocities of 5,000-10,000 hr ^-1, temperature 440-480 ° C and a ratio of (H ₂ + CO) / SO ₂ = 2; in the reduction reaction of SO _{2 by} methane, the sulfur yield is about 90% at space velocities of 3750-5000 h ^-1 , 770-780 ° C and the ratio of CH ₄ / SC ₂ = 0.5. The achieved catalytic performance is ensured during cyclic operation when the by-products of H ₂ S and COS are introduced back into the reaction medium.

The disadvantages of the known catalyst include its high cost, due to the need to prepare highly concentrated and multicomponent systems from expensive reagents, as well as the difficulty of stabilizing the active component in the crystalline structure of perovskite, and the formation of side compounds such as aluminates or silicates during the interaction of the individual elements that make up perovskite, with carrier. In addition, a method of preparing a catalyst with a high content of the active component from nitric acid precursors with their subsequent thermal decomposition is accompanied by the release of a large amount of nitrogen oxides. Therefore, to solve the environmental problem, additional measures are needed to utilize gas emissions.

The invention solves the problem of creating a cheap, durable and highly active catalyst with high strength.

The problem is solved through the use of cheap natural raw materials - ferromanganese nodules (LMFs), containing a mixture of highly dispersed oxides or phosphates of iron, manganese, alkaline and alkaline-earth elements, as well as silicon oxide SiO ₂ , aluminum oxide Al ₂ O ₃ as active components. The catalyst, in which the active components are in a finely dispersed x-ray amorphous state, provides a large number of active surface centers necessary for the adsorption of reagents. This quality of the catalyst contributes to the efficient conduct of the reaction with high degrees of conversion of the reactants.

A catalyst is proposed (the first option) for the reduction of sulfur dioxide from sulfur-containing gases to elemental sulfur, including active components based on compounds of iron and manganese, it contains ferromanganese nodules as active components and has the following composition in terms of oxides, wt.%: Fe ₂ O ₃ 20.0-35.0; MnO ₂ 20.0-35.0; SiO ₂ 17.0-25.0; Al ₂ O ₃ 5.0-10.0; Na ₂ O 2.0-5.0; K ₂ O 1.5-5.0; MgO 1.5-3.0; CaO 1.5-3.0; P ₂ O ₅ 3.0-10.0.

The catalyst may further comprise iron and manganese sulfides. A catalyst is proposed (the second option) for the reduction of sulfur dioxide from sulfur-containing gases to elemental sulfur, including active components based on iron and manganese compounds and a binder, it contains ferromanganese nodules as active components, aluminum hydroxide or natural clays as a binder, and has the following composition in terms of oxides, wt.%: Fe ₂ O ₃ 14,0-30,0; MnO ₂ 14.0-30.0; SiO ₂ 12.0-22.0; Al ₂ O ₃ 20.0-40.0; Na ₂ O 1.5-4.0; K ₂ O 1.0-4.0; MgO 1.0-2.5; CaO 1.0-2.5; P ₂ O ₅ 2.0-8.5.

The catalyst may also optionally contain iron and manganese sulfides.

The content of the binder - aluminum hydroxide in the calcined catalyst is 15-30 wt.% In terms of aluminum oxide Al ₂ O ₃ , natural clays in the calcined catalyst is 15-30 wt.% In terms of calcined clay.

As natural clays, Ca-montmorillonite, Na-montmorillonite, kaolin, quarry clay are used.

The catalyst containing the binder is in the form of cylinders with a diameter of 3.0-5.0 mm, a length of 5.0-7.0 mm; rings with an external diameter of 4.5-7.5 mm, an inner hole diameter of 1.5-3 mm, a length of 4.0-7.5 mm or honeycomb blocks with square, or triangular, or round channels, an external diameter of 9, 5-20 mm, length 18-25 mm.

The introduction of binders for the preparation of granular or block catalysts can significantly increase the mechanical strength of products without reducing the catalytic characteristics of ferromanganese nodules of LMFs.

The use of a catalyst in the form of blocks of a honeycomb structure can significantly reduce the hydraulic resistance in the catalyst layer and intensify the processes of heat and mass transfer.

To illustrate the claimed invention provide examples of its implementation.

Wet ferromanganese nodules in the form of pellets with a moisture content of 43-50 wt.% Are used as the basis for the preparation of catalysts. Pellets are dried in air to a total moisture content of 17-18% and ground to a powder with a particle size of less than 100 microns.

The chemical composition of the catalysts is studied by X-ray fluorescence spectroscopy on a VRA-30 analyzer with a Cr anode of an X-ray tube.

The phase composition of the samples is studied by x-ray phase analysis on a HZG-4 diffractometer with monochromatized Cu K _α radiation. The observed phases are identified in accordance with the data of the JCPDS X-ray card index.

The mechanical strength of the samples (cylinders, rings, blocks) is measured by crushing in static conditions on an MP-9C device with the application of force to the granule or end face. The value of the strength of the granules (P _i , kg / cm ² ) is calculated as the ratio of the breaking force to the cross-sectional area of the granules according to the formula:

,

,

where: N - indicator reading, division;

A - calibration factor (equal to 0.6025);

S is the cross-sectional area of the test granules, cm ² , calculated by the formula:

,1. When determining the strength of the generatrix

,

, где2. When determining the strength at the end

where

L is the length of the granule, cm;

D is the diameter of the granule, see

The dried LMC sample has the following chemical composition, in terms of oxides, wt.%:

Fe ₂ O ₃ - 25.7; MnO ₂ - 20.8; SiO ₂ - 19.1; Al ₂ O ₃ - 5.2; Na ₂ O - 2.2; K ₂ O - 1.4; MgO - 1.8; CaO - 2.4; P ₂ O ₅ - 3.4; the rest is H ₂ O.

According to x-ray phase analysis, the dried LMC is characterized by a highly dispersed x-ray amorphous phase and the α-SiO ₂ phase. The mechanical crushing strength of the pellets ZhMK is 6 kg / cm ² .

As an alumina binder, an aqueous suspension of aluminum hydroxide of boehmite or pseudoboehmite modification with a content of 15-30 wt.% Of the solid phase in terms of Al ₂ O _{3 is used} . Aluminum hydroxide is pre-peptized with mineral or organic acids, such as nitric, hydrochloric, sulfuric, phosphoric, acetic or oxalic acid. The molar ratio [H ⁺ ] / Al ₂ O ₃ is 0.05-0.065.

As binders based on natural clays, aqueous suspensions of materials, such as Ca-montmorillonite, Na-montmorillonite, kaolin, quarry clay, with a solids content of 15-30 wt.% In terms of calcined clay, are used.

Test conditions

The conditions for the reaction of the reduction of sulfur dioxide by synthesis gas.

The composition of the synthesis gas is CO / H ₂ = 1 / 1-1 / 3. The reaction is carried out in a flow-type quartz reactor, at the outlet of which there is a sulfur capacitor and fine filters. The reaction is carried out in a temperature range of 200-600 ° C with a ratio of synthesis gas / SO ₂ = 1.8-2.25 / 1 and a space velocity of 500-5000 h ^-1 .

Reaction conditions for the reduction of sulfur dioxide with methane.

The reaction is carried out in a flow-type quartz reactor, at the outlet of which there is a sulfur capacitor and fine filters. The reaction is carried out in the temperature range of 600-900 ° C with a ratio of SO ₂ / methane = 1.8-2.25 / 1 and a space velocity of 400-1800 h ^-1 .

For experiments using a catalyst fraction of 0.5-1.0 mm Block type catalysts are tested in the form of a block with a diameter of 10 mm and a length of 20 mm. A portion of the catalyst with a volume of 1 cm ³ or the block is placed in a quartz reactor with an internal diameter of 13 mm The reaction mixture containing SO ₂ and a reducing agent is fed to the reactor inlet. The necessary initial concentrations of the reactants, the flow rate, and the necessary SO ₂ / reductant ratio at the reactor room temperature are established.

The concentration of gaseous reactants and reaction products is monitored by measuring the concentration of substances using a gas chromatograph. After setting the necessary initial concentrations of the reactants and the flow rate, the temperature of the reactor is increased to the initial one and the composition of the gas mixture after the reactor is analyzed until stationary concentrations of the reaction products are established. Then the temperature is raised to the final one in increments of 100 ° C. The composition of the reaction products is analyzed at each temperature of the reactor until stationary concentrations are established.

Based on the experimentally obtained values of the concentrations of the reactants and reaction products, the degree of conversion of SO ₂ and a reducing agent, as well as the yields of elemental sulfur and by-products (H ₂ S, COS) are calculated.

The test results of the catalysts in the reaction of sulfur dioxide synthesis gas synthesis are shown in table 1.

The test results of the catalysts in the reaction of reduction of sulfur dioxide with methane are shown in table 2.

Example 1 (prototype).

The catalyst is prepared by impregnating the γ-Al ₂ O ₃ support with a solution of a mixture of nitric acid salts of Fe, Co, Ni, Mo, Cr and Mn taken in the required quantities to obtain a composition of 30% Fe ₄ CoNiMoCr ₂ Mn ₂ O ₁₈ / γ-Al ₂ O ₃ . The impregnated carrier is dried at 100-150 ° C and calcined at a temperature in the range of 600-1000 ° C.

The catalyst is tested in the reactions of: 1) reduction of sulfur dioxide by synthesis gas under the conditions: ratio (H ₂ + CO) / SO ₂ = 2, ratio H ₂ / CO = 0.75, volumetric feed rate of the gas mixture 10000 h ^-1 , temperature 420 ° C; 2) reduction of sulfur dioxide with methane (natural gas) under the conditions: SO ₂ / CH ₄ ratio = 2, the volumetric feed rate of the gas mixture is 5000 h ^-1 , and the temperature is 770 ° C. If the selected test conditions, the catalyst provides a reduction reaction of the SO ₂ conversion of synthesis gas SO ₂ of 94% and sulfur 93% yield in the reduction reaction of SO ₂ sulfur methane yield is 91%.

Example 2

The binder-free catalyst is prepared from dried LMIC pellets, which are pre-fractionated to obtain granules with a size of 0.5-1.0 mm. The granular catalyst is calcined at 550 ° C. in air for 4 hours.

The calcined catalyst has the following composition in terms of oxides, wt.%:

Fe ₂ O ₃ - 31.2; MnO ₂ 25.7; SiO ₂ 23.4; Al ₂ O ₃ - 6.3; Na ₂ O - 2.7; K ₂ O - 1.7; MgO - 2.2; CaO - 2.9; P ₂ O ₅ - 3.9.

The phase composition is represented by phases of α-SiO ₂ , magnetite, and a phase whose main maxima appear at d / n = 3.247 and 3.194Ǻ.

The catalyst provides in the reduction reaction of SO _{2 with} synthesis gas at a temperature of 600 ° C, the conversion of SO ₂ at a level of 90%, the yield of sulfur at a level of 90%. The test results are shown in table 1.

Example 3

The binder-free catalyst is prepared from dried LMIC pellets, which are pre-fractionated to obtain granules with a size of 0.5-1.0 mm. The granular catalyst is calcined at 550 ° C. in air for 4 hours, then in an H ₂ S atmosphere at 400 ° C. for 2 hours.

The calcined catalyst has the following composition in terms of oxides, wt.%:

Fe ₂ O ₃ - 25.6; MnO ₂ - 21.1; SiO ₂ - 19.2; Al ₂ O ₃ - 5.2; Na ₂ O - 2.2; K ₂ O - 1.5; MgO - 1.8; CaO - 2.4; P ₂ O ₅ - 3.2; the rest is S.

According to x-ray phase analysis, the catalyst has the following phase composition: α-SiO ₂ , FeS ₂ , MnOS, MnS, phases whose maxima appear at d / n = 4.04, 3.247, 3.21 Ǻ.

The catalyst provides in the reduction reaction of SO _{2 with} synthesis gas at temperatures of 500-600 ° C, the conversion of SO ₂ at the level of 90%, the yield of sulfur at the level of 90%. The test results are shown in table 1.

Example 4

The catalyst is prepared by extrusion of the molding material. To obtain a molding material, the ZhMK powder is mixed with a binder in a Z-shaped mixer in the ratio of 75 wt.% ZhMK and 25 wt.% Binder in terms of anhydrous substance. As a binder, a 30% suspension of aluminum hydroxide peptized with nitric acid is used with a ratio of [H ⁺ ] / Al ₂ O ₃ = 0.05. The moisture content of the molding material is 45-50 wt.%. Cylinders are molded from the mass and calcined at 550 ° C in air for 4 hours.

The calcined catalyst has the following composition in terms of oxides, wt.%:

Fe ₂ O ₃ - 23.4; MnO ₂ - 19.3; SiO ₂ - 17.6; Al ₂ O ₃ - 29.7; Na ₂ O - 2.0; K ₂ O - 1.3; MgO - 1.6; CaO - 2.2; P ₂ O ₅ - 2.9.

According to x-ray phase analysis, the catalyst has the following phase composition: α-SiO ₂ , highly dispersed hematite Fe ₂ O ₃ and phases whose main maxima appear at d / n = 4.91, 3.86, 3.247, 3.19 Ǻ. The mechanical crushing strength (for cylinders) is: along the generatrix - 18 kg / cm ² , along the end - 40 kg / cm ² .

The catalyst provides in the reduction reaction of SO _{2 with} synthesis gas 100% SO ₂ conversion and 93% sulfur yield at a temperature of 600 ° C; in the reaction of reduction of SO _{2 with} methane, the conversion of SO _{2 is} 100% at temperatures of 700-900 ° C and the sulfur yield is 80% at a temperature of 700 ° C. The test results are shown in tables 1, 2.

Example 5

The catalyst is similar to example 4 and differs in that after calcination in air, the catalyst is calcined in an atmosphere of H ₂ S at 400 ° C for 2 hours. The calcined catalyst has the following composition in terms of oxides, wt.%:

Fe ₂ O ₃ - 19.5; MnO ₂ - 16.0; SiO ₂ - 14.5; Al ₂ O ₃ - 24.2; Na ₂ O - 1.6; K ₂ O - 1.1; MgO - 1.3; CaO - 1.8; P ₂ O ₅ - 2.3; the rest is S.

According to x-ray phase analysis, the catalyst has the following phase composition: α-SiO ₂ , FeS ₂ , MnOS, MnS and phases whose maxima appear at d / n = 4.04, 3.247, 3.21 Ǻ.

The catalyst provides in the reduction reaction of SO _{2 with} synthesis gas 100% SO ₂ conversion at a temperature of 400-500 ° C and a sulfur yield of 95% at a temperature of 500 ° C; in the reaction of reduction of SO _{2 with} methane, the conversion of SO _{2 is} 98-100% at temperatures of 800-900 ° C and the yield of sulfur is 85% at a temperature of 800 ° C. The test results are shown in tables 1, 2.

Example 6

The catalyst is similar to example 4 and differs in that a 50% aqueous suspension of Ca-montmorillonite is used as a binder. Rings are formed from the mass and calcined at 550 ° C in air for 4 hours.

The calcined catalyst has the following composition in terms of oxides, wt.%:

Fe ₂ O ₃ - 23.8; MnO ₂ - 19.3; SiO ₂ - 33.6; Al ₂ O ₃ - 10.7; Na ₂ O - 2.1; K ₂ O - 1.3; MgO - 2.5; CaO - 3.8; P ₂ O ₅ - 2.9.

According to x-ray phase analysis, the catalyst has the following phase composition: α-SiO ₂ , highly dispersed hematite Fe ₂ O ₃ , Ca-montmorrilonite and phases, the main maxima of which appear at d / n = 4.91, 3.86, 3.247, 3.19 Ǻ. The mechanical crushing strength (for rings) is: along the generatrix - 30 kg / cm ² , along the end - 68 kg / cm ² .

The catalyst in the reduction reaction provides SO ₂ conversion of synthesis gas 100% SO ₂ and the sulfur yield of 92% at a temperature of 600 ° C. The test results are shown in table 1.

Example 7

The catalyst is similar to example 6, characterized in that after calcination in air, the catalyst is calcined in an atmosphere of H ₂ S at 400 ° C for 2 hours. The calcined catalyst has the following composition in terms of oxides, wt.%:

Fe ₂ O ₃ - 19.2; MnO ₂ - 15.8; SiO ₂ - 27.0; Al ₂ O ₃ - 8.5; Na ₂ O - 1.7; K ₂ O - 1.0; MgO - 2.0; CaO - 3.1; P ₂ O ₅ - 2.3; the rest is S.

According to x-ray phase analysis, the catalyst has the following phase composition: α-SiO ₂ , FeS ₂ , MnOS, MnS, phases whose maxima appear at d / n = 4.04, 3.247, 3.21 Ǻ.

The catalyst in the reduction reaction provides SO ₂ conversion of synthesis gas 100% SO ₂ and the sulfur yield of 90% at a temperature of 600 ° C; in the reaction of reduction of SO _{2 with} methane, the conversion of SO _{2 is} 100% at temperatures of 800-900 ° C and the sulfur yield is 94% at a temperature of 900 ° C. The test results are shown in tables 1, 2.

Example 8

The catalyst is similar to example 7 and is characterized in that honeycomb blocks with square channels, an external diameter of 10 mm, and a length of 20 mm are prepared from the molding mass. The blocks are calcined at 700 ° C in air for 4 hours, then in an H ₂ S atmosphere at 400 ° C for 2 hours.

The catalyst has an identical chemical and phase composition with the catalyst of example 6.

The mechanical crushing strength (for blocks) is: along the generatrix - 28 kg / cm ² , along the end - 60 kg / cm ² .

The catalyst provides 99% SO ₂ conversion in the SO ₂ synthesis gas reduction reaction and 91% sulfur yield at a temperature of 600 ° C. The test results are shown in table 1.

As studies have shown, the claimed catalyst provides high catalytic performance at moderate temperatures. In the reduction reaction of SO _{2 with} synthesis gas, a 100% level of SO ₂ conversion and a sulfur yield of 90-95% are achieved in the range of 400-500 ° C. In the reduction reaction of SO _{2 with} methane, a 100% level of SO ₂ conversion and a sulfur yield of 88% is achieved at 800 ° C. These figures are comparable with the level of the prototype at a relatively lower cost of the claimed catalyst.

Catalysts prepared using a montmorillonite-based binder provide a high level of purification at higher temperatures compared to catalysts containing an alumina binder. However, this disadvantage is compensated by the high mechanical strength of this type of catalyst, ensuring its high performance.

An important result of the invention is to obtain high catalytic performance in the reduction reaction of SO _{2 with} synthesis gas on a block type catalyst (Example 8). A SO ₂ conversion level above 90% is reached at a temperature of 500 ° C. The use of block catalysts, which are characterized by low hydraulic resistance, is promising for the process of cleaning large volumes of gas emissions at high linear gas flow rates.

Claims (12)

1. The catalyst for the recovery of sulfur dioxide from sulfur-containing gases to elemental sulfur, comprising active components based on iron and manganese compounds, characterized in that it contains ferromanganese nodules as active components and has the following composition in terms of oxides, wt.%: Fe ₂ O ₃ 20.0-35.0; MnO ₂ 20.0-35.0; SiO ₂ 17.0-25.0; Al ₂ O ₃ 5.0-10.0; Na ₂ O 2.0-5.0; K ₂ O 1.5-5.0; MgO 1.5-3.0; CaO 1.5-3.0; P ₂ O ₅ 3.0-10.0. 2. The catalyst according to claim 1, characterized in that it further comprises iron and manganese sulfides. 3. A catalyst for reducing sulfur dioxide from sulfur-containing gases to elemental sulfur, comprising active components based on iron and manganese compounds and a binder, characterized in that it contains ferromanganese nodules as active components, aluminum hydroxide or natural clays as a binder and has the following composition in terms of oxides, wt.%: Fe ₂ O ₃ 14,0-30,0; MnO ₂ 14.0-30.0; SiO ₂ 12.0-22.0; Al ₂ O ₃ 20.0-40.0; Na ₂ O 1.5-4.0; K ₂ O 1.0-4.0; MgO 1.0-2.5; CaO 1.0-2.5; P ₂ O ₅ 2.0-8.5. 4. The catalyst according to claim 3, characterized in that the content of the binder - aluminum hydroxide in the calcined catalyst is 15-30 wt.% In terms of aluminum oxide Al ₂ O ₃ . 5. The catalyst according to claim 3, characterized in that the content of the binder - natural clays in the calcined catalyst is 15-30 wt.% In terms of calcined clay. 6. The catalyst according to claim 3, characterized in that Ca-montmorillonite, Na-montmorillonite, kaolin, quarry clay are used as natural clays. 7. The catalyst according to claim 3, characterized in that it has the shape of cylinders with a diameter of 3.0-5.0 mm, a length of 5.0-7.0 mm; rings with an external diameter of 4.5-7.5 mm, a diameter of an internal hole of 1.5-3 mm, a length of 4.0-7.5 mm or honeycomb blocks with square or triangular or round channels, an external diameter of 9.5 -20 mm, length 18-25 mm. 8. The catalyst according to claim 3, characterized in that it further comprises iron and manganese sulfides. 9. A method of reducing sulfur dioxide from sulfur-containing gases to elemental sulfur by synthesis gas using a catalyst comprising active components based on iron and manganese compounds, characterized in that the catalyst used in accordance with any one of claims 1 to 2 or 3-8 is . 10. The method according to claim 9, characterized in that the method is carried out in a temperature range of 200-600 ° C, a volumetric flow rate of 500-5000 h ^-1 , the ratio of reducing agent / SO ₂ = 1.8-2.25 / 1, as a reducing agent use synthesis gas - H ₂ + CO in the range 1 / 1-1 / 3. 11. A method of reducing sulfur dioxide from sulfur-containing gases to elemental sulfur with methane using a catalyst comprising active components based on iron and manganese compounds, characterized in that the catalyst used is any one of claims 1 to 2 or 3 to 8. 12. The method according to claim 11, characterized in that the method is carried out in a temperature range of 600-900 ° C, a space velocity of 400-1800 h ^-1 , methane is used as a reducing agent, mainly in the form of natural gas, with a ratio of SO ₂ / methane in the range of 1.8-2.25 / 1.