JPS6333892B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention deals with sulfur oxides (hereinafter abbreviated as SOx) and nitrogen oxides (hereinafter abbreviated as Nox) contained in various types of combustion exhaust gas, including exhaust gas from sulfur-containing fuel combustion equipment such as boilers. ) and its catalyst. Currently, SOx and NOx are components of combustion exhaust gas that cause air pollution, and measures to purify them are
It is being developed in various areas. The main countermeasures against this problem are the lime plaster method for desulfurization and the catalytic reduction method for denitrification, but these are each independent processes. In addition, the reason why this single purification method was adopted is that exhaust gas that requires desulfurization has a large negative effect on the denitrification catalyst, making it difficult to carry out the denitration process, and conversely, the combustion exhaust gas that can undergo the denitrification process is so-called clean gas. In that case, desulfurization was not necessary. By the way, in these days of tight petroleum supplies, the use of coal fuel and heavy oil is being considered due to the diversification of energy sources. When these coals and heavy oils are burned, the concentrations of NOx and SOx in the exhaust gas are high, so it is necessary to purify both. Further, the current state of the conventional denitrification and desulfurization methods using different methods and equipment for both requires complicated peripheral equipment and deteriorates economic efficiency, so that they have not been put into practical use. Under these circumstances, if desulfurization and denitrification (hereinafter abbreviated as desulfurization/nitrification) could be performed simultaneously using a single method and device, the contribution to society would be of great value. Dry desulfurization attempts have already been announced, but they have not been put into practical use due to the following problems. First, regarding desulfurization, a method using an iron oxide (Fe ₂ O ₃ ) catalyst is publicly known, and the principle is (1) and (2).
It is shown by the formula. Fe ₂ O ₃ +3SO ₃ Fe ₂ (SO ₄ ) ₃ ...(1) Fe ₂ O ₃ +3SO ₂ +3/2O ₂ Fe ₂ (SO ₄ ) ₃ ...(2) Alumina (Al ₂ O) is used as a support for this catalyst. ₃ ) has been reported (Special Publication No. 52-43615), but SOx
The problem is that the reaction with Al ₂ (SO ₄ ) causes conversion to Al 2 (SO 4 ), resulting in a subsequent decrease in activity. As an improved method, there is a catalyst (Japanese Patent Laid-Open No. 49-97794) in which titania is coated on alumina, but as mentioned above, the problem of sulfation of alumina cannot be avoided. The present inventors searched for a carrier material that has SOx resistance and high catalytic performance and found that anatase type titania (TiO ₂ ) is excellent. As announced at the Catalyst Discussion Group (Professor Murakami, Nagoya Institute of Technology in 1971), this is a carrier with low activity, and in order to put this TiO ₂ carrier to practical use, the following two problems must be met. Ta. The first problem is the thermal stability of _TiO2 . As mentioned earlier, the crystal form of the active TiO ₂ support is anatase type, but Fe ₂ O ₃ on the catalyst _is
When it becomes (SO ₄ ) ₃ , the purification effect of SOx disappears, so regeneration treatment is necessary. Known methods for this regeneration include the leftward reactions of equations (1) and (2) by heating, and the reduction reaction by Co and H ₂ . This reaction results in 600
The catalyst is exposed to high temperatures above ℃ and has high activity.
The problem is that TiO ₂ converts to rutile form and loses its activity at such high temperatures, so it cannot be recycled and used repeatedly. Yet another problem is
Unlike the conventional carrier Al ₂ O ₃ , TiO ₂ has extremely poor formability, making it difficult to hold it in catalyst shapes such as pellets or honeycombs. From these facts, it is easy to understand why the above-mentioned patent application for coating TiO ₂ was filed. In this respect, the catalyst of the present invention is made of thermally stabilized TiO ₂
This invention relates to simultaneous desulfurization, characterized by a carrier. The features and advantages of the present invention will be described below using experimental examples. Experimental Example The test conditions for the desulfurized nitrogen of the present invention are shown in Table 1, and the test gas properties are shown in Table 2.

【table】

【table】

[Table] (1) Experiment 1 Titanyl sulfate was neutralized with aqueous ammonia to form a precipitate, which was overseparated and calcined at 400°C. To this TiO ₂ powder, an aqueous solution of alumina hydroxide equivalent to 5% Al ₂ O ₃ was added, formed into particles with a particle size of 2 to 4 mm, and fired at 600° C. for 3 hours to obtain a carrier. This carrier was impregnated with an aqueous solution of ferrous nitrate to a concentration of 10% as Fe ₂ O ₃ and fired at 500°C for 3 hours to form a catalyst. The following results were obtained. (2) Experiment 2 Titanyl sulfate was neutralized with aqueous ammonia to form a precipitate, which was overseparated and calcined at 400°C. Here, 7% by weight of a solution of tungstic acid dissolved in methylamine as WO ₃ was added to the produced TiO ₂ and fired at 700° C. to obtain a thermally stabilized TiO ₂ -WO ₃ powder. Next, add alumina hydroxide to this powder with Al ₂ O ₃ for 5 minutes.
It was added in an amount equivalent to % by weight, formed into particles with a particle size of 2 to 4 mm, and fired at 600°C for 3 hours to obtain a carrier. The obtained carrier was treated in the same manner as in Experiment 1.
Using Fe ₂ O ₃ as a catalyst, evaluation was performed under the conditions shown in Tables 1 and 2, and the results shown in Table 3 were obtained. (3) Experiment 3 Commercially available activated alumina (Sumitomo Chemical KHA) was sieved to a particle size of 2 to 4 mm, and this was used as a carrier to support 10% Fe ₂ O ₃ in the same manner as in Experiment 1 to serve as a catalyst.
The performance of this catalyst was evaluated under the conditions shown in Tables 1 and 2, and the results shown in Table 3 were obtained.

[Table] As can be seen from this result, the effect of desulfurization was higher in the case of the present invention using a TiO ₂ -WO ₃ carrier (Experiment No. 2) than with Al ₂ O ₃ or TiO ₂ alone. It can be seen that he is excellent. (4) Experiment 4 In the catalyst used in Experiments 1 to 3, Fe ₂ O ₃
is converted to Fe ₂ (SO ₄ ) ₃ . In order to confirm whether these catalysts can be regenerated, each was heated at a temperature of 700°C for 3 hours and regenerated by thermal decomposition.
The performance of the catalyst was evaluated again under the test conditions shown in Tables 1 and 2, and the results are shown in Table 4. As can be seen from the results, the catalyst using the TiO ₂ -WO ₃ carrier in the example of the present invention showed almost no deterioration, while the other catalysts showed significant deterioration in desulfurization and desulfurization performance.

[Table] (5) Experiment 5 In Experiment 2, the amount of WO ₃ added was 0, 5, 1,
0, 3.0, 5.0, and 9.0% by weight of Fe 2 O 5 were added as trial carriers, and in the same manner as in Experiment 1, 10% by weight of Fe ₂ O ₅ was supported to prepare a catalyst. Each of these was subjected to accelerated deterioration treatment at a high temperature of 700°C for 3 hours, and the denitrification performance was evaluated under the test conditions shown in Tables 1 and 2. The results obtained here are the degree of deterioration of the denitrification performance after accelerated deterioration treatment relative to the denitrification performance before accelerated deterioration treatment ([denitrification rate before treatment - denitrification rate after treatment] ÷ denitrification rate before treatment)
It is expressed in Table 5.

[Table] As you can see from this result, the amount of WO ₃ added is 3
% or more, it can be understood that the degree of deterioration is small and there is no problem in practical use. Furthermore, since WO ₃ is expensive, it is preferable to limit the maximum usage amount to 7wt%. (6) Experiment 6 In Experiment 2, the amount of aqueous solution of alumina hydroxide added was 1, 3, 5, 7, 9 as Al ₂ O _3.
Prototype carriers containing each weight percent were prepared, and the carrier particles having a particle size of 3 mm were sieved, and the compressive strength of each carrier was measured. The results are shown in Table 6. Note that this intensity value is the average value of 100 samples.

[Table] As you can see from this value, the amount of Al ₂ O ₃ added is 3
% or more, the strength is sufficient for practical use. Further increasing the amount of Al ₂ O ₃ will increase the strength somewhat, but will reduce the catalyst performance and increase the amount of Al _{2 O 3} during use.
This is not preferable because it increases the production of (SO ₄ ) ₃ and leads to catalyst deterioration. Therefore, the preferred composition of the catalyst carrier according to the present invention is 85 to 94, 7 to 3, and 8 to 3 in weight percent ratio of titania, tungsten oxide, and alumina. Silica hydroxide (silica sol manufactured by Nissan Chemical) was used as a substitute for Al ₂ O ₃ , but the caking strength of TiO ₂ could not be obtained. In addition, tests on aluminosilicate showed that it was effective as a binder, but the silicate component only had the effect of diluting the catalyst composition, and that only Al ₂ O ₃ had a caking effect. I think that there is. As shown in the above tests, the present invention provides an extremely excellent method and catalyst for simultaneous desulfurization.

Claims (1)

[Claims] 1 Titanium oxide thermally stabilized with tungsten oxide is caked with alumina to form a carrier, and a catalyst with iron oxide supported on this carrier removes sulfur oxides and nitrogen oxides from combustion exhaust gas. A method for purifying combustion exhaust gas characterized by simultaneously removing the gas.