TWI637781B - Catalyzed ceramic candle filter and method of cleaning process off- or exhaust gases - Google Patents

Abstract

The present invention relates to a ceramic core filter and the use of the filter in particulate matter in the form of soot, ash, metals and metal compounds, together with hydrocarbons and nitrogen oxides, in the presence of process vent gas or engine consuming gas, The filter comprises a combined SCR and oxidation catalyst disposed on the dispersion side of the filter and in the wall; and a palladium-containing catalyst disposed on the permeate side and in the wall of the filter facing the permeate side.

Description

Catalytic ceramic core filter and method for cleaning process discharge or gas consumption

The present invention relates to a ceramic core filter and a method of cleaning a process for discharging or consuming gas. More specifically, the present invention provides a catalytic ceramic core filter for removing dust and particulate matter from process exhaust gases or engine-consuming gases and harmful components contained therein. Catalytic ceramic core filters are particularly useful for cleaning processes or feedstock gases from industrial processes involving combustion (eg, production of minerals, glass, cement, waste incineration) or from coal-fired boilers and engines.

Ceramic filters in the form of a filter heart are used in many industries for self-contained gas removal of particulate matter. It is one of the most efficient types of dust collectors available, and can achieve a collection efficiency of greater than 99% with respect to the particles. The filter can be made from a variety of ceramic materials, including ceramic fibers made from alkali and alkaline earth metal silicates or aluminosilicates.

The high particle removal efficiency of the ceramic core filter is due in part to the dust layer formed on the surface of the heart filter and in part due to the core filter composition and porosity. In order to provide sufficient filtration activity and acceptable low pressure drop through the filter, conventional ceramic core filters have a porosity between 70% and 90%. For sufficient stability and mechanical strength, the wall thickness of their filters should be in the range of 10-20 mm.

Particle-containing process gas generally having a concentration depending on local regulations must be lowered a plurality of kinds of pollutants, such as NO _X, volatile organic compounds _{(VOC), SO 2, CO} , NH 3, dioxin and furan. Several conventional methods are available for this purpose.

By contact with the catalyst can be effectively reduced as NO _X, VOC, gaseous pollutants dioxin and furan of. Certain words, catalysts based on vanadium oxide catalyst used for reduction of NO _X, in which by fixing by NH ₃ selective reduction and automatic application of NO _X.

This combined catalyst by the oxidation of NH ₃ and reaction with SCR activity are both removed with hydrocarbons (VOC) and in the NO _x.

Vanadium oxide is also known as an active oxidation catalyst. Compared to the noble metal catalyst (e.g. Pd catalyst), vanadium oxide catalyst is less selective and the amount of CO produced during the oxidation reaction in a CO ₂ formation. It is not possible to oxidize CO to CO ₂ at a feasible reaction rate by contact with a vanadium oxide catalyst, but requires the presence of a noble metal catalyst such as Pd.

It has been found that the provision of a very small amount of palladium to the inner surface of the vanadium oxide catalyzed heart filter, i.e., the permeate surface or the wall portion facing the permeate surface, results in a lower slip of ammonia and carbon monoxide from the filter.

In accordance with the findings, the present invention provides a ceramic core filter suitable for use in the removal of particulate matter in the form of soot, ash, metals and metal compounds present in process exhaust gases or engine exhaust gases, together with hydrocarbons and nitrogen oxides, The filter comprises at least a combined SCR and oxidation catalyst disposed on the dispersed side and/or in the wall of the filter; and palladium disposed on the permeate side of the filter and/or in the wall of the filter facing the permeate side catalyst.

As used herein, the terms "dispersed side" and "permeate side" refer to the flow side of the filter facing the unfiltered gas-consuming filter and the flow side facing the filtered discharge or gas.

The present invention further provides a method of removing particulate matter in the form of soot, ash, metals, and metal compounds, together with hydrocarbons and nitrogen oxides, present in a process vent gas or engine consuming gas, comprising the steps of: providing nitrogen-containing reduction The process of the agent vents the gas or the engine consumes gas or adds a nitrogen-containing reductant to the exhaust or consumes the gas; causes the exhaust gas to pass through the ceramic core filter and captures the particulate matter; and reduces the particles trapped on the dispersed side of the filter The amount of soot in the material, by oxidation to reduce the amount of hydrocarbons in the exhaust or spent gas, and to bring the nitrogen-containing reducing agent into contact with the combined SCR and oxidation catalyst disposed on the dispersed side of the filter and/or in the wall Reducing the amount of nitrogen oxides by selective catalytic reduction (SCR) of nitrogen oxides; and passing the gas through the walls of the filter and by means of a filter disposed on the permeate side of the filter and/or facing the permeate side The palladium-containing catalyst contact in the wall reduces the amount of carbon monoxide and ammonia in the gas passing through the filter wall.

Preferably, the combined SCR and oxidation catalyst comprises vanadium oxide and titanium dioxide.

More preferably, the palladium-containing catalyst further comprises vanadium oxide and titanium dioxide.

The term "a vanadium oxide" or "vanadium oxide" means: vanadium (II) oxide (vanadium monoxide), VO; or vanadium (III) oxide (vanadium sesquioxide or vanadium trioxide), V ₂ O ₃ ; Vanadium (IV) oxide (vanadium dioxide), VO ₂ ; or vanadium oxide (V) (vanadium pentoxide), V ₂ O ₅ .

Preferably, the vanadium oxide used in the present invention comprises or consists of vanadium oxide (V) (vanadium pentoxide, V ₂ O ₅ ).

The term "titania" refers to titanium dioxide (TiO ₂ ).

The catalytically active form of palladium is palladium in a metal and/or oxidized form.

The abbreviations V/Ti and Pd/V/Ti shall mean catalysts composed of vanadium oxide and titanium dioxide, respectively, and catalysts composed of palladium, vanadium oxide and titanium dioxide.

It is also preferred that the vanadium oxide/titanium dioxide catalyst is additionally dispersed on the permeate side of the filter together with the palladium-containing catalyst.

Preferably, the palladium-containing catalyst contains palladium in an amount between 20 and 1000 ppm per filter.

These catalysts are preferred for the following reasons. Pd/V/Ti catalysts have i) dual functionality (removing NOx and removing VOCs (volatile organic compounds)); ii) S-tolerance; and iii) with other catalyst compositions (eg Pt-based catalysts) ) compared to lower SO ₂ oxidation activity.

For example, when the ammonia-containing gas and the VOC process gas pass through the dispersed side on which the vanadium oxide-based catalyst is supported, the NH ₃ -SCR of NOx is removed before the ammonia gas contacts the permeate side. During the passage through the dispersion side, a certain amount of CO is formed by incomplete oxidation of the VOC after direct contact with the V/Ti catalyst. With only the permeate side of the filter and / or a wall with a Pd catalyst or a supported Pd / V / Ti catalyst, followed by the balance of CO and VOC is effective to oxidize CO _2. In this way, a minimum load of expensive palladium in the wall and/or on the permeate side of the filter can be achieved.

As a further advantage, when a Pd/V/Ti catalyst is used, the catalytic filter core is sulfur resistant, i.e., does not undergo sulfur deactivation. Pd / V / Ti catalyst additionally reduces the amount of SO ₃ is formed by the oxidation of the SO _2. If H ₂ S is also present in the process gas entering the filter, it will also be oxidized to SO ₂ via both the V/Ti and Pd/V/Ti catalysts.

In the case of high temperature ceramic filters, several types of fibers are available for their production. These may, for example, be composed of ceria-aluminate, calcium-magnesium-citrate, calcium-citrate fibers or mixtures thereof.

Other preferred ceramic fibers comprise biosoluble fibers selected from the group of calcium-magnesium-tellurates.

The catalytically active material is obtained by impregnating the dispersion side and the filter wall with a slurry containing a catalytically active material in the form of fine particles of titanium dioxide and a precursor of the active material (ie, a vanadium salt), and using a palladium salt solution or titanium dioxide fine particles and vanadium and The slurry of the palladium salt is impregnated on the permeate side and applied to the ceramic filter. After impregnation, the filter is subsequently dried and heated to the temperature required to decompose all of the precursors and activate the catalyst.

Example 1

The following examples illustrate the performance obtainable by a ceramic core filter prepared from a calcium magnesium-silicate fiber having a wall thickness of 3 m and a wall thickness of 20 mm. The filter was coated with a V/Ti catalyst in the wall containing 1.26 wt% V and 2.36 wt% Ti, based on the total weight of the filter. The coated filter had a porosity of 83%. The toluene oxidation of the filter was tested in an inlet gas containing 40 ppm anhydrous toluene, 19 vol% O ₂ , 8 vol% H ₂ O.

Toluene oxidation on V/Ti coated filter

As apparent from the above table, 85% toluene was converted at 240 °C. The CO emissions at the same temperature are equal to 35 ppm, wet.

Example 2

The following examples illustrate the CO oxidation performance of the ceramic core filter of Example 1 additionally coated with 36 ppm Pd. A gas containing about 150 ppm wet CO, 19% O ₂ and 8% H ₂ O was tested.

At 240 ° C, 97% CO is oxidized to CO ₂ .

By combining the potency of the ceramic centrate filters reported in Examples 1 and 2, it is possible to draw the following conclusion: only by catalyzing the V/Ti catalyst on the dispersed side and passing Pd/V on the permeate side The /Ti catalyst catalyzed heart filter emits 1 ppm CO.

Claims (12)

A ceramic core filter suitable for removing particulate matter in the form of soot, ash, metals and metal compounds present in a process vent gas or engine consuming gas together with hydrocarbons and nitrogen oxides, the filter comprising at least a configuration a combined SCR and oxidation catalyst on and/or within the wall of the filter; and a palladium-containing catalyst disposed on the permeate side of the filter and in the wall of the filter facing the permeate side. The ceramic centroid filter of claim 1, wherein the combined SCR and oxidation catalyst comprises vanadium oxide and titanium dioxide. The ceramic centroid filter of claim 1 or 2, wherein the palladium-containing catalyst further comprises vanadium oxide and titanium dioxide. A ceramic centrate filter according to claim 1 or 2, wherein the palladium-containing catalyst contains palladium in an amount between 20 and 1000 ppm per weight of the filter. The ceramic centrifugal filter of claim 1 or 2, wherein the ceramic material of the filter is selected from the group consisting of ceria-aluminate, calcium-magnesium-citrate, calcium-citrate a group of fibers or mixtures thereof. A ceramic centroid filter according to claim 5, wherein the ceramic material of the filter consists of a biosoluble fiber selected from the group consisting of calcium magnesium citrate. A method of removing particulate matter in the form of soot, ash, metals, and metal compounds, together with hydrocarbons and nitrogen oxides, present in a process vent gas or engine consuming gas, comprising the steps of: providing a process discharge containing a nitrogen-containing reductant Gas or engine consumes gas or returns the nitrogen The raw agent is added to the process to discharge or consume gas; the discharged or consumed gas is transferred to the ceramic core filter and the particulate matter is captured on the dispersed side of the filter; the capture on the dispersed side of the filter is reduced The amount of soot in the particulate matter and contacting the nitrogen-containing reducing agent with the combined SCR and oxidation catalyst disposed on the dispersed side and/or the wall of the filter to reduce the hydrocarbons in the gas or the gas by oxidation And reducing the amount of the nitrogen oxides by selective catalytic reduction (SCR) of nitrogen oxides; and passing the gas through the wall of the filter and by being disposed on the permeate side of the filter The palladium-containing catalyst contact in the wall of the filter above and/or facing the permeate side reduces the amount of carbon monoxide and ammonia in the gas passing through the filter wall. The method of claim 7, wherein the combined SCR and oxidation catalyst comprises vanadium oxide and titanium dioxide. The method of claim 7 or 8, wherein the palladium-containing catalyst further comprises vanadium oxide and titanium dioxide. The method of claim 7 or 8, wherein the palladium-containing catalyst contains palladium in an amount between 20 and 1000 ppm per weight of the filter. The method of claim 7 or 8, wherein the ceramic material of the filter is selected from the group consisting of ceria-aluminate, calcium-magnesium-citrate, calcium-citrate fiber or a mixture thereof . The method of claim 7 or 8, wherein the ceramic material of the filter comprises a biosoluble fiber selected from the group consisting of calcium magnesium citrate.