CATALYZED CERAMIC CANDLE FILTER AND METHOD FOR CLEANING OF OFF- OR EXHAUST GASES

Abstract

Ceramic candle filter and use of the filter in the removal of particulate matter in form of soot, ash, metals and metal compounds, together with hydrocarbons and nitrogen oxides being present in process off-gas or engine exhaust gas, the filter comprises a combined SCR and oxidation catalyst arranged at least on the dispersion side and/or within wall of the filter, the combined SCR and oxidation catalyst comprises palladium, a vanadium oxide and titania.

Claims

1. A ceramic candle filter suitable for the removal of particulate matter in form of soot, ash, metals and metal compounds, together with hydrocarbons and nitrogen oxides being present in process off-gas or engine exhaust gas, the filter comprises a combined SCR and oxidation catalyst arranged at least on the dispersion side and/or within wall of the filter, the combined SCR and oxidation catalyst comprises palladium, a vanadium oxide and titania.

2. The ceramic candle filter of claim 1, wherein the catalyst contains palladium in an amount of between 20 and 1000 ppm/weight of the filter.

3. The ceramic candle filter according to claim 1, wherein the ceramic material of the filter is selected from the group of silica-aluminate, calcium-magnesium-silicates, calcium-silicates fibers, or a mixture thereof.

4. The ceramic candle filter according to claim 1, wherein the ceramic material of the filter consists of bio-soluble fibres selected from the group of calcium-magnesium-silicates.

5. A method for the removal of particulate matter in form of soot, ash, metals and metal compounds, together with hydrocarbons and nitrogen oxides being present in process off-gas or engine exhaust gas, comprising the steps of providing a process off-gas or engine exhaust gas containing a nitrogenous reductant or adding the nitrogenous reductant to the off- or exhaust gas; passing the off-gas or the exhaust through a ceramic candle filter and capturing the particulate matter; and reducing amounts of soot in the particulate matter captured on the at least one particulate filter and reducing amounts of nitrogen oxides and hydrocarbons in the off- or exhaust gas by oxidation of the hydrocarbons and by selective catalytic reduction (SCR) of the nitrogen oxides with the nitrogenous reductant in contact with a combined SCR and oxidation catalyst being arranged on the dispersion side and/or within wall of the filter, wherein the combined SCR and oxidation catalyst comprises palladium, a vanadium oxide and titania.

6. The method according to claim 5, wherein wherein combined oxidation and SCR catalyst contains palladium in an amount of between 20 and 1000 ppm/weight of the filter.

7. The method of claim 5, wherein the ceramic material of the filter is selected from silica-aluminate, calcium-magnesium-silicates, calcium-silicates fibers, or a mixture thereof.

8. The method according to claim 5, wherein the ceramic material of the filter comprises bio-soluble fibres selected from the group of calcium-magnesium-silicates.

Description

[0010] The invention provides additionally a method for the removal of particulate matter in form of soot, ash, metals and metal compounds, together with hydrocarbons and nitrogen oxides being present in process off-gas or engine exhaust gas, comprising the steps of [0011] providing a process off-gas or engine exhaust gas containing a nitrogenous reductant or adding the nitrogenous reductant to the off- or exhaust gas; [0012] passing the off-gas or the exhaust through a ceramic candle filter and capturing the particulate matter; and [0013] reducing amounts of soot in the particulate matter captured on the at least one particulate filter and reducing amounts of nitrogen oxides and hydrocarbons in the off- or exhaust gas by oxidation of the hydrocarbons and by selective catalytic reduction (SCR) of the nitrogen oxides with the nitrogenous reductant in contact with a combined SCR and oxidation catalyst being arranged on the dispersion side and/or within wall of the filter, wherein the combined SCR and oxidation catalyst comprises palladium, a vanadium oxide and titania.

[0014] The term “a vanadium oxide” or “vanadium oxide” refers to: [0015] Vanadium(II)oxide (vanadium monoxide), VO; or [0016] vanadium(III)oxide (vanadium sesquioxide or trioxide), V.sub.2O.sub.3; or [0017] vanadium(IV)oxide (vanadium dioxide), VO.sub.2; or [0018] vanadium(V)oxide (vanadium pentoxide), V.sub.2O.sub.5.

[0019] Preferably, vanadium oxide for use in the invention comprises or consists of vanadium(V)oxide (vanadium pentoxide), V.sub.2O.sub.5.

[0020] The term “titania” refers to titanium dioxide (TiO.sub.2).

[0021] The catalytically active form of palladium is palladium in the metallic and/or oxidic form.

[0022] The shortage Pd/V/Ti shall mean a catalyst consisting of palladium, a vanadium oxide and titania.

[0023] The Pd/V/Ti catalyst has i) dual functionality (removal of NOx and removal of VOC, volatile organic compounds); ii) a S-tolerance; and iii) a lower SO.sub.2 oxidation activity compared to other catalyst compositions, e.g. Pt-based catalysts.

[0024] When employing a Pd/V/Ti catalyst the catalyzed filter candles are sulfur resistant, i.e. not subjected to sulfur deactivation. The Pd/V/Ti catalyst additionally reduces the amount of SO.sub.3 formed by oxidation of SO.sub.2. If H.sub.2S is also present in the process gas entering the filter, it will also be oxidized to SO.sub.2 on the Pd/V/Ti catalyst.

[0025] The catalytically active material may be applied on the ceramic filter by impregnation with a slurry containing the catalytically active material in form of titania microparticles and the precursors of the active materials, i.e. salts of vanadium and palladium. Once impregnated, the filter is subsequently dried and heated up to the required temperature for the decomposition of all precursors and activation of the catalyst.

[0026] Compared to monolithic formed filters or wall flow filters, the effective gas contact between the palladium metal particles and reactants in gas is much higher, which results in a much reduced amount of palladium necessary to obtain a reasonable oxidation activity.

[0027] Typically, the catalyst employed in the invention the catalyst contains palladium in an amount of between 20 and 1000 ppm/weight of the filter, preferably less than 200 ppm/weight.

[0028] In the case of high temperature ceramic filters several types of fibers may be used for their production. These can be constituted e.g. by silica-aluminate and calcium-silicates fibers, or a mixture thereof.

[0029] Other preferred ceramic fibres comprise bio-soluble fibres selected from the group of calcium-magnesium-silicates.