SU762964A1 - Method of preparing pelletized catalyst for oxidizing carbon oxide to carbon dioxide - Google Patents

Description

The invention relates to the production of catalysts for the oxidation of CO and CO _g and can be used in ferrous metallurgy, petrochemical, oil refining and other industries where CO contains waste gas for the purification of exhaust gases of internal combustion engines.

Highly active catalysts are widely known, containing as active support active alumina (-A 1 ^ 0-) and as an active component oxides of Co, Ml, Cu, Н),

Re obtained by impregnating the prepared granules of the carrier with solutions of the salts of these metals, followed by heat treatment ’. [one] .

This method of preparation of the catalyst consists of several stages. First, an impregnating solution is prepared, dissolving in succession copper nitrates (at the rate of 8–20 wt.% CuO), cobalt (1–5 wt.% Co ^ C ^) manganese (0.5–3 wt.%) In water heated to 65 ° C. % Mn0 _g ) and nickel (15 weight.% N10). Then to the resulting solution is added

ammonium nitrate and nitric acid, and after adding an aqueous solution of ammonia, the temperature of the suspension is raised to 75-80 ° C to dissolve 5 the resulting precipitate. In the resulting impregnating solution pour granules of aluminum oxide (with a specific surface of 200-400 m ^g / g with a particle size of 3.2 mm and incubate them for 1 h at 75-80 ° C. Then the solution with the catalyst is cooled to 25 ° C, the solution is drained, and the obtained Granules are dried for 16 'hours at 220-230 ° C and further impregnated with the "5" merged solution and heat treated in a stream of hydrogen at 400-450 ° C.

However, this method of catalyst preparation is characterized by 20 stages and the complexity of the technology. One of the significant drawbacks of this method is the complexity of the preparation of the impregnating solution, as well as the use of two-fold impregnation with a solution of the active compounds with thermal activation after each impregnation stage.

There is also known a method for producing catalysts by the method of extrusion molding 30 pasta, prepared ob762964

treatment of the composition based on Semite acid (nitric, hydrochloric) and an aqueous solution of nitrate or ammonium chloride. The obtained granules are dried at 50-70 ° C and calcined at 800-900 ° C,

‘Then impregnated with a solution containing 0.5-3 g-atoms of chromium per 1 l, dried and activated at 750-850 ^ 0

 [2].

However, this method of obtaining

'characterized by low productivity, nostno and frequency of the process. Granules have low mechanical strength and cannot be used in intensive reactors, for example, with a moving or suspended layer; talazatora. B. The well-known method of obtaining the use of two high-temperature heat treatment, which significantly complicates the process.

The closest way According to the technical essence and the achieved effect is a method of manufacturing

 granulated catalyst'For the oxidation of carbon monoxide to carbon dioxide, which includes the mixing of the hydrated oxygen compound aluminii with the compounds of active components, ammonia hydrocarbon formation of the resulting mass and heat treatment of spherical granules [3].

By this method, it is possible to obtain spherical catalyst granules. To do this, a dilute solution of aluminum oxychloride in a mixture with insoluble hydroxides of the active components is introduced dropwise into a neutralization column filled with liquid in the upper part of hydrogen and in the lower part with a 12% solution of ammonia. In a hydrocarbon liquid, wa'ins mass take the form of a sphere, and in

'?' the solution of ammonia Verdeu !, as a result of the reaction of the oxychloride with ammonia and the formation of aluminum hydroxide. After leaving the column, the beads go to heat treatment. 10-14 h, and calcination 20600 ° C for 6 h) can be obtained from the granule active А 1 ^ 0 ^ with different porosity.

In a known method of obtaining in

 'as the original' substance is used diluted (30-100 g A1 ^ 0. / l) solution of the basic aluminum salt. When calcining pellets derived from

'low concentrations of trirated chloride salts, a large amount of water vapor and harmful impurities is recognized - "" hydrogen chloride. Thus, from the calculation of molding 1 kg of mass of oxychloride with a concentration of 50 g AC 0 ^ in 1 l, more than 930 g of H ^ 0 and 18 g of NCE are released.

The removal of a large amount of gaseous products leads to significant shrinkage of the granules.

we beat spherical granules reduced by 105-130 times. The latter leads to the formation of a fine-porous catalyst structure with a predominant pore radius

5 10-25 A (bulk density 1.1-1.2 g / cm ⁵ ). Upon contact with a drip liquid, due to large internal stresses, such granules are destroyed even without mechanical impact. By (0 this is the catalyst prepared by a known method, almost impossible to use in the processing of industrial waste gases containing a high concentration of water vapor

. (up to 50-60 g / m ³ ).

Using the method of obtaining

⁴ ё'rayuyrbvayny catalysts, described in the Prototype, for the preparation of · Oxidation catalysts! CO gave the highest "mechanical".

20 strength of both crushing and abrasion (determined in the airlift) of catalyst granules containing an increased amount of active oxides (over 6 wt.%); So, if

25 content of active ingredients up to 2-4 wt.% The calcined spherical granules have satisfactory mechanical crushing strength

. (180-245 kg / cm ^) and abrasion 90-95%,

30 then at 9-10 wt.% Of active oxides crushing strength and abrasion sharply reduced to 21-34 kg / cm *

- 'and 13-18% respectively .. Attempting to increase the content of oxides in the granule

□ with up to 6–8 wt.% Impregnation with the solution led to the complete destruction of the pellet. talizatora. - The disadvantages of this method include the contamination of the finished product (catalyst) with chlor40 ions in an amount of up to 7-8 wt.%, Remaining in the samples even after heating to 550-800 ° C. . .

The aim of the invention is to obtain a catalyst with increased mechanical strength and improved

Sanitary and hygienic conditions for its receipt.

To achieve this goal

50 proposed a method of manufacturing a granular catalyst for the oxidation of carbon monoxide to carbon dioxide by means of mixing the hydrated oxygen compound of aluminum, in which the pseudo-boehmite aluminum hydroxide gel is used.

structures with a humidity of 55-85 wt.% with compounds of active components, taken in the form of a suspension, consisting of formates, acetates, or oxal-.

60 tov of Mn, Co, No., Fe, Cu, or from their mixture, in the amount of 0.5-12 wt.% Or their mixtures I acid with the same anion with a concentration of 3-7 wt.%, Molding the resulting mass into hydrocarbon ammonia liquid with con762964

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concentration ^ 15-25 wt.% ₃ and heat treatment of spherical granules.

Distinctive features of this method are the use of aluminum hydroxide gel of pseudo-boehmite structure with a humidity of 55-85 wt.% As an aluminum compound, its treatment with a suspension consisting of formates or acetates or oxalates Mn, Co,, Cu, D or from their mixture in the amount of 0.5-12 wt.%, or their mixtures and acids with the same anion with a concentration of 3-7 wt.% and the formation of the mass is carried out in a hydrocarbon-ammonia liquid with a concentration of 15-25 wt.%.

This method of preparation of the catalyst in comparison with the existing has the following advantages:

- the elimination of the emission of harmful impurities upon receipt of the catalyst at the stage of calcination,

- increase the mechanical strength of spherical catalyst granules

with a high content of active oxides (crushing strength increased 10-15 times, abrasion 5-7 times).

The possibility of using pseudoboehmite for these purposes is due to the fact that in an acidic environment, as a result of interaction with H-ions, the oriented structure (needles, fibers) is destroyed. Pseudoboehmite and the formation of water-soluble salts. These effects result in a flowing liquid mass with a viscosity of 12-35 Pz, capable of hydrocarbon-ammonia molding.

A feature of the application of aluminum hydroxide in the form of crystallized precipitates of a pseudo-boehmite nature is also the fact that the active component of the substrate is located on the faces of hydroxide crystals, as a result of which a uniform degree of their coverage is ensured and a high catalytic activity of the catalyst is achieved. In the case of the use of basic aluminum salt as an initial substance, as is done according to the proto-type, the compound of active components is randomly distributed over the granule, as a result of which a certain proportion of them is isolated from the catalytic process.

One of the differences in the use of the aluminum hydroxide gel of a pseudo-Boehmite structure for the preparation of spherical catalyst granules is the possibility of obtaining from it highly concentrated forming masses containing 220–380 g A ^ O ^ / l.

The choice of the humidity range of the original aluminium hydroxide gel (5585 wt.%) Is due to the peculiarities of the hydrocarbon-ammonia process.

molding and properties obtained from it moldable masses. From the gel hydro- ^: aluminum oxide having a moisture content of less than 55 wt.%, A highly concentrated (more than 370–380 g A0 ₃ in 1 liter) is prepared, but the mass quickly enters: after 15–25 s after intensive mixing, the moisture content of the mass increases from 22 to 49 Pz ', the result of which practically stops the molding process. Low-concentrated (less than 210-220 g A ^ O ^ 1 l) masses with a viscosity of 5-8 Pz are prepared from aluminum hydroxide gel having a moisture content of more than 85 wt.%, Resulting in the formation of non-spherical granules (pellets, etc.) .

The use of acetoate, formate and oxalate of the metals of the active components, as well as acids with the same anions (formic, acetic, oxalic) allows you to completely eliminate the emission of harmful impurities from / 'the resulting catalyst during the heat treatment, as these salts and acids decompose to carbon dioxide and water.

The choice of the concentration range of the active components is determined, on the one hand (12 wt.%), By a rather high activity of the catalysts (97100% degree of CO conversion already at 200-240 ° C), and on the other hand (0.5 wt.%) The effectiveness of on changes in the parameters of the porous structure and an increase in catalytic activity in multicomponent catalysts.

When used as a ney? the concentration of ammonia solution with a concentration of less than 15 wt.% dramatically increases the time of complete neutralization of mold granules (more than 5 minutes), which with the continuous method of forming greatly complicates the process (for example, it is necessary to increase the height of the neutralizing column, etc.). Using ammonia solution with a concentration of more than 24 ^{Jan. 25} wt.% Is technologically and economically disadvantageous since as a result of evaporation of ammonia intonsivnogo need constant replenishment of the solution with ammonia gas. This concentration range of the ammonia solution (15-25 wt.%) Was also chosen because during neutralization for 3 min and when the concentration ΝΗ ₃ changes in a given range, the structural-strength properties of the finished product change significantly (see Table 1), which allows to obtain a wide range of granular catalysts, suitable for almost any catalytic process.

The essence of the proposed method of obtaining is as follows. In order to obtain a catalyst mass of aluminum hydroxide gel, pseudo-boehmite • Ί

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The structure is treated with a suspension, which consists of a strong organic acid and dispersed metal salts at the rate of 0.5–12 wt.% of active oxide or a mixture thereof. Acid (formic, acetic, oxalic) is injected with suspension in such quantity (as a rule, not more than 7 weight, ”from ACO ^ in the sample) so that ^{- the} viscosity of the formable mass does not exceed 30-35 Pe. If, after adding the calculated amount of suspension, the viscosity of the mass does not reach 10 10-35 Pz (preferably 20-25)

, several (2-3) portions of acid are successively introduced. After the suspension is introduced into the hydroxide gel, the mass is thoroughly mixed for 20-40 minutes. \

To speed up the interaction of sour! With pseudoboehmite gel, the mass can be 'heated up to 30-35 ° C.

Next, the liquid catalyst mass, stirred to a fluid state, is subjected to a hydrocarbon-ammonia molding. To do this, the mass flow through the molding cylinder, in the Day of which filters are installed with through holes of 1-5 mm. The resulting droplets enter the neutralization column and, after successively passing through two layers of liquid — hydrocarbon (gasoline, clarified kerosene) and ammonia — are transferred to heat treatment (drying, calcination) .Time; stay molded granules in the neutralization column must be at least 3 minutes By changing the concentration of ammonia solution in the column, as well as the concentration and nature of the salt of the active component, it is possible to obtain catalysts with different structures. but the strength characteristics (see table. 1). Calcined catalyst granules 40 under these hydrocarbon-ammonia forming conditions (nozzle size, A1 concentration _and 0 ^ in mass) will have a size of 0.23.5 mm in diameter. 45

Abrasion resistance in the airlift for all samples 95-100%.

After exiting the neutralization column, the catalyst beads are heat treated. Drying of food is carried out in a tubular furnace for 0.5-1.0 h at 100-115 ° С and a current of dry air supplied with a bulk velocity of 5000-10 000 4 ^-1 , calcined at 600 ° С for 2 hours. __

Example 1. Prepare 100g · ^e spherical granules of the catalyst, containing 5.3 wt.% Co ^ C ^, 0.5 wt.%

Cu and 94.2 wt.% ACO ^. *

471 g of aluminum hydroxide gel with pseudo-boehmite structure with moisture 40

80 wt.% are treated with 31 mp of 15% acetic acid (density 1,019 g / cm ¹ ), in which 1.14 g of copper acetate and 3.23 g of cobalt oxalate are suspended (calculated on the anhydrous).

7 '', h *

. salt The mass is thoroughly mixed for 40 min while heating to 30-40 ° C, 4 ml of acid are additionally introduced for 0.5 h and, after reaching a mass of viscosity 15-20 Pz, it is subjected to 5 hydrocarbon-ammonia molding. The concentration of ACO ^ in the mass of 240 g / l.

The neutralization is carried out in a column filled with a 22% ammonia solution for 3 minutes, and the heat treatment is carried out under the following conditions; drying in a stream of dry air with a space velocity of 8000 h * ’, temperature 105 ° C for 0.5 h, calcining at 600 ° C for 2 h.

Characteristics of the structural strength properties and activity of the catalysts are given in table. 2

Example 2: Prepare 100 g of spherical catalyst granules containing b wt.% CuO, 2 wt.%

“Θ CC4O4, 2.0 wt.% Νΐ0 ^ 2.8 wt.% MpOd, and 88 wt.% A1 _g 0 /.

196 c of aluminum hydroxide gel of a pseudo-boehmite structure with a humidity of 55 wt.% Is treated with 28.1 ml of 9% 25 oxalic acid (density

1.04.2 g / cm ³ ), in which 11.43 g of copper oxalate ⁴ , 0.734 g of cobalt oxalate are suspended; 3.93 g of nickel oxalate and 4.62 g of manganese oxalate. The mass is thoroughly mixed for 30 minutes, while heating to 4 0-4 5® C, while ^{4 is} additionally injected with 6 mg of 9% oxalic acid, and after reaching a mass of 25-30 Pz, its hydrocarbon-ammonia form is applied. The concentration of A1 _g 0 ^ in the paste 380 g / l.

Neutralization is carried out in a column filled with a 16% ammonia solution for 4.0 minutes. The heat treatment is carried out under the following conditions: drying in a stream of air with a bulk velocity of 5000 h ' ¹ and a temperature of 100®.C for 1.0 h, and calcining at 6OO ° C for 2 h.

The characteristics of the structural strength properties and catalyst activity in the oxidation of CO are given in Table. 2

Example 3. Prepare 100 g of spherical catalyst granules containing 7.3 wt.% N10, 1.7 wt.% ^:

CuO and 91 wt.% A1 _g O ^.

605 g of aluminum hydroxide gel with a pseudo-boehmite structure with a moisture content of 85% by weight is processed, 35.2 ml of 10% by weight of formic acid (density 1.023 g / cm ^g ), in which 17.25 g of nickel acetate are suspended (calculated on anhydrous salt) - 3.28 g of copper formate. The mass is thoroughly mixed for 40 min while heating to 30-40 ° C, then additionally two portions of acid are added in 0.2 ml each and after reaching a viscosity mass of 30-35 Pz it is subjected to

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carbon ammonia form. Concentration A, _and 0 _? in the paste 220 g / l;

Neutralization is carried out in a column filled with a solution of ammonia with a concentration of 18 wt.%, For

3.3 min Heat treatment is carried out under the following conditions: drying in a stream of dry air at a volumetric rate of 1000 h ~ * and a temperature of 115 ° C for 1.0 h, and calcining at 600 ° C for 2 h.

The characteristics of the structural strength properties and catalyst activity in the oxidation of CO are given in Table. 2

Example 4. YuOg spherical catalyst granules are prepared containing 15 wt.% SOpo ₄ , 0.5 wt.%

N10, 4.8 wt.% CuO and 89.3 wt.% AC 0 _g .

255 g of aluminum hydroxide gel of peevdobemitic structure with a moisture content of 65% by weight is treated with 26.6 ml of 10% by weight of 20 acetic acid (density 1.012 g / cm ⁵ ), in which 3.34 g of cobalt formate, 1.18 g of nickel acetate and 10.9 g of acetate, IU; di (calculated on anhydrous salts). 25

The mass is thoroughly mixed for 30 minutes while being heated to 30-35 ° C, after which three additional portions of acid are added in 0.3 ml each, after reaching a mass of viscosity 25-30 Pz, it is subjected to a hydrocarbon-ammonia-30 formation. The concentration of Al ₂ 0 ₃ in the mass of 350 g / l.

Neutralization is carried out in a column filled with 25% ammonia solution for 3 minutes. Heat treatment 35 is carried out under the following conditions: drying in a stream of dry air with a space velocity of 6,000 hours "* and a temperature of 100 ° C for 40 minutes, calcining at € 00 ° C for 2 hours. 40

The characteristics of the structural strength properties and catalyst activity in the oxidation of CO are given in Table. 2

Example 5. Prepare 45

100 g of spherical catalyst granules containing 9.5 wt.% N10;

0.5 wt.% Co ^ O ^ and 90 wt.% A1 _g 0-3.

250 g of aluminum hydroxide gel of peevdobemitite structure with a moisture content __

75.7 wt.% is treated with 37.7 ml ** 8.0 wt.% of formic acid (density 1.147 g / cm ⁵ ), in which 18.65 g of nickel oxalate and 0.308 g of cobalt formate are suspended.

The mass is thoroughly mixed for 25 minutes, two additional portions of acid, 0.5 ml each, are added; after reaching a mass of a viscosity of 20-25 Pz, it is subjected to its hydrocarbon-ammonia molding. A1 concentration _a 0 ^ ¢ 0

in bulk - 260 g / l.

Neutralization is carried out in a column,

* filled with 19% ammonia solution, for 3.8 minutes Heat treatment is carried out under the following conditions: sush- <

ku in a stream of dry air with a space velocity of 9000 h ' ¹ and ^ temperature.

1 ° C for 50 minutes, and calcination at 600 ° C for 2 hours.

Structural characteristics, etc. properties and activity of the catalyst in. CO oxidation reactions are given in Table. 2

Example b. UOH of spherical granules containing .0 6.8 wt.% CuO and 93.2 wt.% A1 _g O ^ are prepared.

233 g of aluminum hydroxide gel

The peevdobemitic structure with a humidity of 60 wt.% is treated with '49 ml of 8% acetic acid (density 1.009 g / cm ⁵ ), in which 15.55 g of copper acetate are suspended. The mass is thoroughly mixed for 40 min while heating to 50 ° C and after reaching a mass of viscosity of 25-30 Pz it is subjected to its hydrocarbon ammonia molding. The concentration of A1 ₂ Au in the mass of 320 g / l.

Neutralization is carried out in a column filled with a 15% ammonia solution for 4 minutes. Heat treatment 25 is carried out under the following conditions: drying in a stream of dry air with a bulk velocity of 7000 h "[and a temperature of 110 ® C for 0.5 h, and calcining at 600 ° C for 2 h.

“The characteristics of the structural strength properties and the activity of the catalyst in the reaction of CO oxidation are given in Table. 2

Example 7. UOg are prepared of spherical catalyst granules containing 6.5 wt.% Co $ 0d, 5.5 wt.% Ρε ^, Οο, and 88 wt.% A1 _g 0 ₅ .

308 g of aluminum hydroxide gel of peevdoboehmite structure with a humidity of 70 wt.% Is treated with 42.3 ml of 6% 40 oxalic acid (density

1.027 g / cm ⁵ ), in which 11 g of cobalt oxalate and 4.95 g of oxalate iron are suspended. "; In the mass of 280 g / l.

Neutralization is carried out in a column filled with a 21% ammonia Ka solution for 3.5 minutes. The heat treatment is carried out under the following conditions: drying in a stream of dry air with. a bulk velocity of 6000 h ' ¹ and a temperature of 105 ° C for 40 min, and calcination at 600 ° C for 2 h.

The characteristics of the structural strength properties and catalyst activity in the oxidation of CO are given in Table. 2

¢ 0 Example 8. UOg is prepared

spherical catalyst granules containing 7.9% by weight of C03O4, 4.1% by weight of Μησ and 88.0% by weight of A1 ₂ 0z ·

352 g of aluminum hydroxide gel of peevdoboehmite structure with moisture

eleven

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75 wt.% Is treated with 26.5 ml of 16 wt.% Formic acid (density 1.039 g / cm *), in which 8.27 g of cobalt oxalate and 7.2 manganese oxalate are suited.

The mass is thoroughly mixed for 20 minutes, after reaching a viscosity of 25-30 Pz, its mass is subjected to its hydrocarbon-ammonia molding. The concentration of A1 ₂ 0 _g in the mass of 255 g / l.

Neutralization is carried out in a column filled with a 20% ammonia solution for 3.0 minutes. The heat treatment is carried out under the following conditions: drying in a stream of dry air with a bulk velocity of 7500 h ' ^l and temperature

(0

110 ° C for 1 hour, and calcination at 600 ° C for 2 hours.

Characteristics structurally firmly ^STNYH properties and catalytic activity in CO oxidation reaction are shown in Table. 2

The catalytic activity of the synthesized samples is determined in the re- action of oxidation of CO, the main component, industrial and flue gases. The determination is carried out on a flow-through installation in the temperature range of SO-BOO ^ C, the CO concentration in the gas-air mixture is 1-2 vol.% And the space velocity is 5.0 - 10 'h " ^1. The catalyst volume of the fraction is 0.75 mm 4 cm *. Data activity is also listed in Table 2.

Table 1

Change of structural and strength properties of catalyst granules (Neutralization time 5 min, 300 g A1 ₂ 0 ^ / l)

Active Concentration Total Radius Specific Strength oxide assets- ammonia pore volume pore surface on handing out foot ka in cm ^ / cm * BUT ness pouring oxide Neutra m / g®. kg / cm ⁷ la liziruyu- , ςχ ·. ’· .._ < weight.% hereby dissolve re, weight,% · · · · - - * - - - -r - - - ——————————— - - - - - - - - -. B - ^ .———————— ί—— —— - - - - - - - 0.5 ' 18 : . '· 0.68 89 195: 310 Cu 12 18 • 0.57 56 235 340 0.5 15 0.48 86-112 170 330 ^! · ^? · Gzzyyyyyyy - - ----- ------- 2 25 0.65 48 225 300 ^Co ° + 12 25 0.57 41 '· " 250 285 2 17 0.54 56-66 215 305 - - - - * - "- - - - _ - - ———————————— - - ——— - - - - —— —— - ——— - - - - - - - - - - - - - - - - ——— - - - - - --------- .... .... ^ ... ...... four 15 0.43 Not one - 160 290 /’.-· "·. Λ / ·; · .-; - ·. ... · '· ""? ' dear · - ···· · Not one PUP ten 15 0.38 dear 165 300 * ί b 20 0.49 66-82 190 . 335 - - - - ———————— ———————————— ————————— ——————————— —————————— ... - .. .... .... ...... NU 0.5 22 - 0.61 56 255 340

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___; . ' _ Table 2

Structural and strength properties of the activity of the granules

catalysts

Catalysis Total Radius Specific Strength Activity Fore by pore volume pore surface for example cm* BUT ness at once Isti Tempera Power cm% m ^g / g davl- early tour, transform the knowledge. weight. % ° С hunt kg / cm ⁴ WITH, vol.% one 0.44 75-9-2 175 270 91 180/242 32.4 / 98.3 2 0.58 56 230 ' 280 90 200/250 90.3 / 100 3 0.40 98-112 165 295 94 200/250 97.1 / 100 . four 0.60 42 260 355 91 180/240 39.4 / 99.0 five 0.39 108-122 200 330 94 200/240 99.7 / 100 '' ⁶ 0.58 63 220 270 98 250/290 86.5 / 100 7 0.38 not one 150 360 96 240/280 44 / 98.7 eight • g 0.52 35 285 300 95 200/240 98.6 / 100

Claims (1)

Claim The method of preparation of the granular catalyst for the oxidation of carbon monoxide to carbon dioxide, which includes mixing the hydrated oxygen compound adiumium with the compounds of the active components, ammonia hydrocarbon forming the resulting mass and heat treatment of spherical granules, which, the purpose of obtaining a catalyst with increased mechanical strength and improve the sanitary conditions of its production, as the aluminum compound, use aluminum hydroxide gel 'pseudo-boehmite steel structures with a humidity of 55-85 wt.%, which is treated with a suspension consisting of formates, or acetates, or oxalates, Mn, Co, N1, Cu, D, or from their mixture in an amount of 0.5-12 wt.% or their mixtures and acids with the same anion with a concentration of 3-7 wt.%, and molding of the mass is carried out in a hydrocarbon-ammonia liquid with a concentration of 15-25 wt.%%.