Method for preparing a catalyzed fabric filter and a catalyzed fabric filter

Abstract

A catalyzed fabric filter substrate and a method of preparing the substrate comprising the steps of a) providing a fabric filter substrate b) providing an aqueous impregnation liquid comprising an aqueous hydrosol of one or more catalyst metal precursor compounds dispersed on nanoparticles of an oxidic metal carrier, a surfactant and a dispersing agent selected from the group of primary amines; c) impregnating the fabric filter substrate with the impregnation liquid; and d) drying and thermal activating the impregnated fabric filter substrate at a temperature below 300? C. to convert the one or more metal compounds of the catalyst precursor to their catalytically active form.

Claims

1. A method for preparing a catalyzed fabric filter comprising the steps of a) providing a fabric filter substrate b) providing an aqueous impregnation liquid comprising an aqueous hydrosol of one or more catalyst metal precursor compounds dispersed on nanoparticles of an oxidic metal carrier, a dispersing agent comprising one or more primary amines and a surfactant; c) impregnating the fabric filter substrate with the impregnation liquid; and d) drying and thermally activating the impregnated fabric filter substrate at a temperature below 300? C. to convert the one or more metal compounds of the catalyst precursor to their catalytically active form.

2. The method of claim 1, wherein the thermally activation of the impregnated fabric substrate is performed prior to or subsequent to installation of the impregnated fabric substrate in a filtration unit.

3. The method of claim 1, wherein the fabric filter substrate consists of woven or non-woven glass fibres coated with a polymeric material.

4. The method of claim 3, wherein the polymeric material consists of polytetrafluoroethylene.

5. The method of claim 1, wherein the one or more catalyst metal precursor compounds comprise ammonium metavanadate, ammonium metatungstate, ammonium heptamolybdate, palladium nitrate, tetraammineplatinum(II) hydrogen carbonate or mixtures thereof.

6. The method of claim 1, wherein the catalytically active form of the one or more catalyst metal precursor compounds comprises one or more of vanadium oxide, tungsten oxide, molybdenum oxide, palladium and platinum in the oxidic and/or metallic form.

7. The method of claim 6, wherein the catalytically active form of the one or more catalyst metal precursor compounds consists of vanadium pentoxide and palladium in metallic and/or oxidic form.

8. The method of claim 1, wherein the oxidic metal carrier comprises oxides of titanium, aluminum, cerium, zirconium or mixtures and compounds thereof.

9. The method of claim 8, wherein the oxidic metal carrier consists of nanoparticles of titanium oxide with a particle size of between 10 and 150 nm.

10. The method of claim 1, wherein the dispersing agent comprises a primary amine selected from one or more of the group consisting of mono methyl amine, mono ethyl amine, mono propyl amine and mono butyl amine.

11. The method of claim 10, wherein the dispersing agent consists of mono ethyl amine.

12. The method of claim 1, wherein the dispersing agent is added to the impregnation liquid in an amount resulting in a pH value above 7 of the impregnation liquid.

13. The method of claim 1, wherein the catalyzed fabric substrate comprises from about 5 to about 8% by weight of catalytically active material.

14. The method of claim 1, wherein the aqueous impregnation liquid is prepared by the steps of i) adding the one or more catalyst metal precursor compounds and the oxidic metal carrier to water and continuously adding an acid to the liquid to maintain the pH of the liquid at a value where the surface charge of the one or more catalyst precursor metal compound is negative and the Zeta potential of the oxidic metal carrier is positive; ii) adsorbing the at the one or more catalyst metal precursor compound onto the surface of the oxidic metal carrier; iii) adding the dispersing agent to the thus prepared liquid in an amount to obtain a pH value above 7 of the thus prepared impregnation liquid; and subsequently iv) if palladium and/or platinum are present in the impregnation liquid, adding a solution comprising a salt of palladium and/or platinum to the impregnation liquid prepared in step (iii).

15. The method of claim 14, wherein the pH value in step (i) and (ii) is maintained between 4.0 and 4.3.

16. The method of claim 1, wherein the one or more catalyst precursor metal compounds are ammonium metavanadate and palladium nitrate.

Description

EXAMPLE 1

(1) Preparation of a Ammonium Vanadate/Titania Containing Impregnation Liquid 1. 37.26 kg demineralized water is mixed with 3.11 kg NH.sub.4VO.sub.3. 2. 29.62 kg of a slurry of pearl milled TiO2 (LOI=18 wt % TiO.sub.2) is added under continuous stirring. The NH.sub.4VO.sub.3/TiO.sub.2-ratio is 0.58. 3. The pH is monitored and increases continuously. 4. The pH is adjusted with concentrated nitric acid in the interval of 4.0-4.3. 5. After a few hours the pH of the liquid remains constant and the liquid is left under constant stirring for at least 24 hours. However, the pH needs adjustment every 3 hours.

(2) The resulting liquid has a red color and a yield point (Q?2-4 Pa). 6. 1.84 kg Ethylamine (70% in water) is added (or until pH?9.2-9.5).

(3) The liquid becomes ivory white and very fluid (Q<1 and ??1 mPas).

(4) Fabric filter bags made of glass fibres coated with Teflon? are impregnated with the liquid. These filter bags are extremely hydrophobic and considerable amounts of surfactant are needed for successful impregnation. 7. 1.96 kg Softanol-90 surfactant is added. 8. Wetting tests are performed by adding a few drops of the liquid to the filter bag material.

(5) If the wetting tests fails, additional Softanol-90 must be added.

EXAMPLE 2

(6) Preparation of a Palladium/Ammonium Vanadate/Titania Containing Impregnation Liquid

(7) In this example 3635 wt ppm Pd per amount titania in the impregnation liquid was added to the impregnation liquid by the steps described below. Palladium was available as an aqueous solution of Pd(NO.sub.3).sub.2 containing 16.9 wt % Pd. 1. The desired amount of Pd was calculated; 3635 ppm*4.64*10.sup.3 g/10.sup.6 ppm=16.87 g Pd A 16.9 wt % Pd solution was available and 16.37 g Pd/0.169=99.8 g solution was extracted. 2. The Pd solution was diluted with 3 kg water to a Pd solution containing 0.54% by weight Pd. 3. An impregnation liquid was then prepared by the same procedure described in Example 1, with the exception that 3 kg less water have been added to the impregnation liquid and the pearl milled slurry contained 20.65% by weight of TiO.sub.2. 4. The entire amount of the palladium solution prepared in step 2 was added to the impregnation liquid prepared in step 3 after pH adjustments with mono ethylamine. The Pd solution was added drop wise by means of a funnel. During addition of the Pd solution, the liquid was continuously stirred. 5. Softanol-90 surfactant was finally added and the wetting test was performed.