JPS63242324A - Exhaust gas purifying method - Google Patents

Abstract

PURPOSE:To efficiently remove NOX, by adding an alkali metal compound to fuel and supporting a catalyst containing one or more kind of a transition metal containing the Group IIB and Sn by a heat resistant filter and using fine carbon particles in the exhaust gas as a reducing agent. CONSTITUTION:Fuel is sent to a diesel engine while an alkali metal compound such as KOH is added to the fuel and burnt to generate exhaust gas which is, in turn, passed through a heat resistant filter supporting one or more kind of a catalyst selected from Sn and a transition metal containing the Group IIB such as Ce, Ni, Mn, Th, Cu, Zn, Sn or the like and NOX is reduced and removed by the fine carbon particles contained in the exhaust gas.

Description

[Detailed description of the invention] B. Industrial application fields The present invention relates to an exhaust gas purification method.

BACKGROUND OF THE INVENTION In recent years, particulate matter (mainly composed of solid carbon particles and liquid or solid high molecular weight hydrocarbon particles) in the exhaust gas of diesel engines has become a problem in terms of environmental health. Hereinafter, such fine particles are referred to as carbon-based fine particles.These carbon-based fine particles have an average particle size of approximately 0.1 to 1 μm, and are easily suspended in the atmosphere and easily taken into the human body through breathing. This is because clinical test results have confirmed that it also contains carcinogenic substances.

Methods for removing these fine particles can be roughly divided into the following two methods.
Two methods are being considered. One is to capture particulates by filtering exhaust gas using a heat-resistant filter.
When the pressure loss increases due to this, the filter is regenerated by burning the captured particles using a burner, electric heater, etc.

Examples include monoliths. Another method is to have a heat-resistant filter carrying a catalyst material carry out a combustion operation as well as a filtration operation, thereby reducing the frequency of the above-mentioned particulate combustion and filter regeneration, or reducing the frequency of the above-mentioned particulate combustion and filter regeneration to the extent that regeneration is not necessary. This is a method of increasing combustion activity.

Furthermore, in these methods, attempts have been made to lower the ignition temperature of particulates by increasing the combustible components in the exhaust gas or adding a carbon oxidation promoter to the fuel.

In the former case, it is believed that the higher the particle removal effect, the faster the pressure drop will rise, the more frequently the regeneration will be required, and the more reliable the regeneration will be, which will also be economically disadvantageous.

On the other hand, the latter method is considered to be a much better method if there is a catalyst that can maintain catalytic activity under the exhaust conditions (gas composition and temperature) of diesel engine exhaust gas. However, the exhaust gas temperature of a diesel engine is much lower than that of a gasoline engine, and since light oil is used as fuel, the amount of SO2 in the exhaust gas is also large.

A regeneration method that successfully ignites and burns the accumulated particulates under such exhaust gas conditions and does not cause secondary pollution has not yet been established.

For example, particulate combustion reactions in heat-resistant filters carrying only base metals typically occur at temperatures above about 350°C.

In most cases during normal operation, the exhaust gas temperature is below this temperature and no combustion reaction occurs, and the particulates are temporarily captured by the catalyst-supported filter, and then when the temperature rises, the filter is regenerated by a process in which it burns out. In this case, the pressure loss increases rapidly until the predetermined temperature is reached, and the frequency of combustion regeneration using a burner, electric heater, etc. increases, making it impractical. Furthermore, when a catalyst containing noble metals is used, the combustion reaction of fine particles is more likely to occur at a lower temperature, and the increase in pressure loss becomes more gradual. However, at the same time, 802 in the exhaust gas also oxidizes, producing extremely harmful SO3 and sulfuric acid mist, resulting in secondary pollution.

As described above, a method for efficiently removing particulates from exhaust gas from diesel engines, etc., has not yet been found, and furthermore, nitrogen oxides from exhaust gas whose oxygen concentration varies over a wide range from several percent to 13%. Removal is extremely difficult and remains a major problem.

Object of the Invention The present invention efficiently burns and removes carbon-based particulates contained in exhaust gas emitted from diesel engines, etc., which is relatively low temperature and has a large change in oxygen concentration, and at the same time effectively removes nitrogen oxides. The purpose of this project is to provide an exhaust gas purification method that can remove

28 Structure of the invention, that is, the present invention adds one or more alkali metal compounds to the fuel, and one or more alkali metal compounds selected from the group consisting of a transition metal including an nB group element of the periodic table and tin. The present invention relates to an exhaust gas purification method for reducing nitrogen oxides in exhaust gas using carbon-based fine particles in exhaust gas as a reducing agent using an exhaust gas purifying material in which a catalyst containing at least ft or more is supported on a heat-resistant filter.

Water 2 Functions and Effects of the Invention As a result of intensive research, the present inventor has determined that one or more types selected from the group consisting of transition metals including group B elements of the periodic table and tin can be used as nitrogen oxide removers. is supported on a heat-resistant filter, one or more alkali metal compounds are added to the fuel, and carbon-based fine particles in the exhaust gas are used as a reducing agent to reduce nitrogen oxides in the exhaust gas even at relatively low temperatures. , and succeeded in effectively removing both carbon-based particulates and nitrogen oxides in exhaust gas.

When the alkali metal component added to the fuel and the transition metal and tin on the heat-resistant filter coexist with carbon-based fine particles, their synergistic effect effectively reduces nitrogen oxides in the exhaust gas, reducing the amount of exhaust gas. It is considered that it is effectively purified. At the same time, carbon-based fine particles are also consumed as reducing agents and oxidized as C'02, disappearing, and are prevented from accumulating on the heat-resistant filter more than necessary. This eliminates the need to often perform filter regeneration as described above, which involves burning and removing carbon-based particulates.

The alkali metal component is added to the fuel as an alkali metal compound so that the additive is dissolved or suspended in the fuel.

In this way, with the <17/) Shioryu S It is also effectively purified.

F. Example The present invention will be explained in detail below.

The above-mentioned "transition metals that also include elements of group nB of the periodic table" include:
Examples include cobalt, manganese, iron, nickel, zinc, copper, cerium, lanthanum, and thorium. In addition, when two or more selected from the group consisting of the above transition metals and tin are contained in the catalyst, that is, when these are used in plurality such as cerium-manganese, thorium-nickel, etc., The ignition temperature of the carbon-based particles is lowered, and the combustion (oxidation) and removal of the carbon-based fine particles becomes more efficient, and therefore the reduction and removal of nitrogen oxides is also performed more efficiently.

Further, the ignition effect of the catalyst filter is improved if it is heat-treated at 450°C to 500°C in an inert gas or vacuum prior to its use.

In addition to impregnating the heat-resistant filter with transition metals and tin, it is also subjected to a drying process. It is also possible to add a heat-resistant filter to a solution of an alkali ferrocyanide or the like and carry out a drying process to support the alkali and Fe at the same time.

"Heat-resistant filters" must have the necessary collection performance and allowable pressure loss, and are usually made of alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina, etc., which are used as carriers. titania,
Examples include, but are not limited to, ceramic fibers, ceramic foams, ceramic monoliths, etc. made of silica-titania, silica-zirconia, titania-zirconia, etc., and metal wire meshes.

The above-mentioned "catalyst" does not need to be directly supported on the heat-resistant filter; it is sufficient that it is indirectly supported on the heat-resistant filter via a commonly used carrier such as the above-mentioned alumina, silica, titania, etc. It's also practical.

To add an alkali metal component to the fuel, it is preferable to add an alkali metal compound such as sodium hydroxide (NaOH) or potassium hydroxide (KOH).

Next, specific examples of the present invention will be described.

Titania was supported on a commercially available cordierite ceramic (ceramic whose main components are magnesia, alumina and silica) monolith (bulk density 0.37 g/cl, porosity 86.0%, volume 2.0 l). Impregnated with cerium, nickel and manganese. Prior to use, this catalyst-supported ceramic monolith was dried at 150°C for 4 hours and fired at 800-900°C for 3 hours (Example 1).

From now on, such exhaust gas purification materials will be used as Ce/Ni/
It is written like M n.

In the same manner as above, T h / Cu / Z n exhaust gas purification material (Example 2), Ce exhaust gas purification material (Example 3)
and Ce/Sn exhaust gas purification material (Example 4) was manufactured.

Regarding the exhaust gas purification materials of Examples 1 to 4, 100 ppm of potassium hydroxide (KOH) was added to the fuel, and changes in back pressure were continuously measured using a single-cylinder diesel engine with a displacement of 510 cc. An evaluation test was conducted. At this time, the engine speed is 15 (fOrpn).

It is operated at 90% load, and the exhaust gas temperature is 350℃ at this time.
The oxygen concentration was 3%. Figure 1 shows back pressure changes with respect to engine operating time.

In addition, regarding the above exhaust gas purification materials, each of the N2 of NOx
6 conversion rate (NO x removal rate) at exhaust gas temperature of 250 to 45
Measurement was carried out continuously at 0°C by chemiluminescence method. Figure 2 shows the NO and c removal rates after 60 minutes of operation at each exhaust gas temperature.

For comparison, an evaluation test was conducted regarding back pressure changes using the same ceramic monolith as in Examples 1 to 4 and without supporting a catalyst in the same manner as in the above Examples (Comparative Example 1). Also,
Using Ce/Ni/Mn exhaust gas purification materials,
A similar test was conducted without adding an alkali metal component to the fuel (Comparative Example 2). These results are also shown in FIG.

As is clear from the results in Figure 1, when the ceramic monolith (exhaust gas purification material) of Comparative Example 1 is used, carbon-based fine particles are MHIed into the filter, and after 60 minutes of operation, the back pressure is more than 6 times the initial level. In Comparative Example 2, the increase is about 5 times, but when the exhaust gas purifying materials of Examples 1 to 4 are used, the back pressure increase after 60 minutes of operation is about 2 and a half times at the highest. Moreover, almost no increase in back pressure was observed after 60 minutes of operation. In this way, when the exhaust gas purifying material of the example is used, particulates in the exhaust gas of a diesel engine can be efficiently burned and removed.

Furthermore, when the exhaust gas purification materials of Examples 1 to 4 were used, a good NO8 removal effect was obtained as is clear from FIG. 2, and the No. removal rate was 4.
Reach 0%. Furthermore, the No-c removal effect can be seen even at a very low exhaust gas temperature of 250°C.

From FIG. 1 and FIG. 2, when using the exhaust gas purifying materials of Examples 1 to 4, it is possible to continue operating the engine while effectively purifying exhaust gas for a long time without performing filter regeneration. will be understood.

In addition, in the above-mentioned Examples 1 to 4, generation of SO3 and sulfuric acid mist was not substantially observed.

[Brief explanation of the drawing]

The drawings all show examples of the present invention. Figure 1 is a graph showing the relationship between engine operating time and back pressure, and Figure 2 is a graph showing the relationship between engine operating time and back pressure. It is a graph showing the relationship with the nitrogen oxide removal rate.

Claims (1)

[Claims] 1. One or more types of alkali metal compounds are added to the fuel, and a catalyst containing at least one type or two or more types selected from the group consisting of tin and transition metals including group IIB elements of the periodic table is used in the heat-resistant filter. An exhaust gas purification method that uses a supported exhaust gas purification material to reduce nitrogen oxides in exhaust gas by using carbon-based fine particles in the exhaust gas as a reducing agent.