JP2002058964A - Diesel particulate removing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel particulate filter(DPF) which collects PM (particulate matter) in combustion gases discharged from a diesel engine vehicle and burns the PM stably at low temperature by increasing the combustibility of the PM, consequently attains improvement in efficiency of removal of the PM and long service life of the DPM. SOLUTION: The device collects PM in combustion gases discharged from diesel engine vehicles, then removes the PM by combustion, and is provided with a filter depositing molybdenum compounds thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel particulate filter (Diesel Particulate Filter, hereinafter abbreviated as "DPF").
Particulate matter (particulate matter, hereinafter abbreviated as “PM”) in the combustion gas discharged from diesel engine vehicles is collected by a filter, burned at low temperature, and its removal efficiency is increased and longer. The present invention relates to a DPF that can have a long life.

[0002]

2. Description of the Related Art Diesel engine vehicles have better fuel efficiency than gasoline engine vehicles, are effective in reducing carbon dioxide, and have the advantage that light oil used as fuel oil is lower in cost than gasoline. is there. However, PM contained in the combustion gas discharged from diesel vehicles has recently been widely considered due to the problem of environmental pollution. This PM is a fine burnt of fuel oil such as soot, and is known to have an adverse effect on the respiratory system when it enters the human body. Therefore, reduction of PM in exhaust gas is the biggest issue for diesel vehicles. Therefore, in Japan, new regulations aimed at achieving in 2005 require manufacturers to reduce PM emissions to one-third of the current regulations.
We are considering obligating diesel vehicles running in Tokyo to have a DPF by around 2003, and it is highly likely that they will spread to other local governments.

[0003] Under these circumstances, efficient and practical DPFs are being actively developed. Currently, several types of DPFs, specifically (1) an alternate regeneration DPF,
(2) Continuous regeneration type DPF by NO ₂ oxidation method, (3)
A continuous regeneration type DPF using a catalytic oxidation method and (4) an intermittent regeneration type DPF have been proposed. The alternate regeneration type DPF of the above (1) is a switching type that alternately performs collection and regeneration by using two filter units in which both sides of a silicon carbide fiber nonwoven fabric are sandwiched between a wire mesh heater and a protective wire mesh. This DPF can handle the current diesel oil with a high sulfur content, but requires a large current to burn PM.
In addition to the necessity of mounting a dedicated large-capacity generator, there is a problem that the filter may be damaged by rapid combustion.

[0004] (2) The continuous regeneration type DPF using the NO ₂ oxidation method uses a porous ceramic made of cordierite having a wall flow honeycomb structure as a filter.
By the oxidation catalyst provided on the upstream side, to oxidize NOx to NO _2, by using a strong oxidizing power of this NO _2, a continuous regeneration type apparatus for burning PM collected in the filter at low temperatures. However, in this method, the activity of the oxidation catalyst is degraded due to the sulfur content in the exhaust gas, and the function of the oxidation catalyst is not sufficiently exhibited. Therefore, it is necessary to reduce the sulfur content in the fuel oil. There is a problem that it is difficult.
The continuous regeneration type DPF of the catalytic oxidation method (3) uses a porous ceramic filter made of cordierite having a wall-flow honeycomb structure coated with two kinds of metal catalysts, and does not require a heating device such as a heater. P collected by the filter only by the action of
This is a continuous regeneration type device for burning M. In this scheme,
The metal catalyst is relatively insensitive to the sulfur content in the exhaust gas, and thus can be applied to existing diesel oil. However, the metal catalyst is more susceptible to phosphorus, and the lower the sulfur content, the higher the performance. Further, since a certain ratio or more is required for traveling in which the exhaust gas temperature becomes about 300 ° C. or more, it is difficult to apply the method to a vehicle or a passenger car traveling at low speed for a long time.

(4) The intermittent regeneration type DPF uses a porous ceramic filter made of silicon carbide having a wall flow honeycomb structure, captures PM, injects fuel at the time of regeneration, raises the temperature of exhaust gas, and generates an oxidation catalyst. Oxidizes hydrocarbons and carbon monoxide to further raise the temperature and burn PM. In this method, a cerium compound is added to the fuel oil to reduce the amount of PM generated. Although this method can be applied to existing light oil, it requires a power supply for regeneration, and has a problem that cerium oxide remains after PM combustion and deposits on a filter, thereby shortening the life of the DPF. As described above, all of the DPFs currently under development have advantages and disadvantages, and are not always satisfactory. Industrially, DPF
It is important to exhibit the function effectively and to prolong its life, and for that purpose, it is important to burn PM stably at a temperature as low as possible.

[0006]

SUMMARY OF THE INVENTION Under such circumstances, the present invention captures PM in a combustion gas discharged from a diesel engine vehicle with a filter, enhances the flammability of the PM, and stably cools the PM. It is an object of the present invention to provide a DPF that can be burned at a high temperature to increase its removal efficiency and extend its life.

[0007]

Means for Solving the Problems As a result of intensive studies to develop a DPF having the above-mentioned excellent functions, the present inventor has found that a molybdenum compound is supported on a filter, and the DPF is collected by the filter. It enhances the flammability of PM and makes it possible to burn at low temperatures.Moreover, this effect is exhibited stably without being affected by other components in the exhaust gas, for example, sulfur compounds and phosphorus compounds. It has been found that it can be achieved. The present invention has been completed based on such findings. That is, the present invention is a device for collecting, burning and removing PM in combustion gas discharged from a diesel engine vehicle, wherein the device is equipped with a filter supporting a molybdenum compound. DPF
Is provided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A DPF with a DPF according to the present invention is provided with a filter carrying a molybdenum compound on the surface thereof. ) And heteropolymolybdic acid such as phosphomolybdic acid and silicomolybdic acid. Molybdenum sulfide can also be used because it changes into an oxide in the use environment. MoO ₃ or phosphomolybdic acid is particularly preferred. These molybdenum compounds may be used alone or in a combination of two or more.

Further, in the present invention, the molybdenum compound can coexist with a conventionally used noble metal catalyst or other metal oxide catalyst. On the other hand, the material and shape of the filter for supporting the molybdenum compound are not particularly limited, and any one can be appropriately selected from those conventionally known for DPF. Examples of the filter include a ceramic fiber such as cordierite or silicon carbide, or a cylindrical pleated filter formed of a nonwoven fabric of metal fiber, a porous ceramic filter having a wall flow honeycomb structure formed of cordierite or silicon carbide, or the like. Can be. By supporting the molybdenum compound on the surface of these filters, the PM collected by the filter can be stably burned at a low temperature without being affected by other components in the exhaust gas, for example, sulfur compounds and phosphorus compounds. Therefore, the PM removal efficiency can be increased and the life of the DPF can be extended. Examples of a method of supporting the molybdenum compound on the filter include, for example, a method of preparing a solution or dispersion of the molybdenum compound, immersing the filter in the solution, air-drying, and then drying in a heating furnace. it can. .

[0010]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Examples Carbon black [PM manufactured by Mitsubishi Chemical Corporation "MA"
100 ") and 10 parts by weight of a molybdenum compound powder shown in Table 1 as a catalytic substance was mixed with 100 parts by weight of the mixture, and the combustion temperature of the mixture was set to DT-TG.
A (differential thermal-thermogravimetric analysis) was used to measure the temperature in air at a rate of 10 ° C./min. The results are shown in Table 1. COMPARATIVE EXAMPLE As a catalyst substance, powders of various metal compounds shown in Table 1 were used and carried out in the same manner as in the examples. The combustion temperature of only carbon black was measured in the same manner as in the example. Table 1 shows the results.

[0011]

[Table 1]

As is apparent from Table 1, the presence of the molybdenum compound can lower the PM combustion temperature.

[0013]

The DPF of the present invention is equipped with a filter supporting a molybdenum compound. The filter collects PM in the combustion gas discharged from the diesel vehicle and stably burns the fuel at a low temperature. As a result, the removal effect can be enhanced and the service life can be extended.

Claims (2)

[Claims] 1. A device for collecting, combusting and removing particulate matter in a combustion gas discharged from a diesel engine vehicle, wherein the device is provided with a filter supporting a molybdenum compound. Diesel particulate removal equipment. 2. The diesel particulate removing apparatus according to claim 1, wherein the molybdenum compound supported on the filter is at least one selected from molybdenum oxide, molybdic acids, heteropolymolybdic acid, and molybdenum sulfide.