JPH04361621A - Carbon fiber for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain the subject carbon fiber capable of readily removing nitrogen oxides from exhaust gases containing oxygen at a high concentration from moving units such as the exhaust gases from diesel automobiles by baking raw yarn of infusibilized pitch-based carbon fiber within a specific temperature range in an inert gas atmosphere. CONSTITUTION:Isotropic or anisotropic pitch (1) is melt spun (2) to provide pitch-based fiber, which is then infusibilized (3) in an oxidizing atmosphere at 150-400 deg.C. Raw yarn of the resultant infusibilized pitch-based fiber is then baked (4) at 600-800 deg.C temperature in an inert gas atmosphere of >=95% purity to afford carbon fiber. Thereby, the objective carbon fiber (5), useful for removing nitrogen oxides and suitable for removing the nitrogen oxides from exhaust gases, especially the exhaust gases from diesel engines is obtained. Furthermore, although pores are formed between crystallites by production and growth of the crystallites of carbon at >=600 deg.C baking temperature to increase the pores participating in decomposition of the nitrogen oxides, shrinkage of the carbon fiber starts at >=700 deg.C and the diameter of the formed pores is reduced. As a result, performance of removing the nitrogen oxides reaches the maximum at 700 deg.C baking temperature.

Description

[Detailed description of the invention]

0001

[Industrial application field] Removal of nitrogen oxides from exhaust gas,
In particular, the present invention relates to carbon fibers for removing nitrogen oxides, which are suitable for removing nitrogen oxides from diesel engine exhaust gas.

0002

[Prior Art] Conventionally, nitrogen oxides are removed using the following reaction equation ( Nitrogen oxide removal (Catalyst Course, Vol. 7, P. 253, Kodansha), NOx + NH3 + O2 → N2 + H2O
...(1)

Nitrogen oxide removal using the following reaction equation (2 equations) using a three-way catalyst for small-scale treatment of mobile objects such as gasoline engine automobiles (Catalyst Lecture, Vol. 9, P. .195, Kodansha) exists. NOx+CO+hydrocarbon → N2+CO2+H2
O...(2)

In addition, pitch-based carbon fibers are generally produced by infusible spun pitch, which is carbonized at 800 to 1200°C in an inert gas atmosphere, then heated to 1500°C.
Manufactured by graphitizing at ~3000℃ (Revised Introduction to Carbon Materials, p. 204, Carbon Materials Society of Japan)
.

Removal of nitrogen oxides by carbon fibers is shown by the following reaction formula (Equation 3) using carbon in the carbon fibers as a reducing agent. NOx+C → N2+CO+CO2 ・・
・(3)

[0006]

[Problems to be Solved by the Invention] However, when ammonia is used to remove nitrogen oxides from the exhaust gas of diesel automobiles, it is difficult to handle due to the toxicity of ammonia and is not suitable for moving objects.When using a three-way catalyst, however, does not work under high oxygen concentrations such as diesel car exhaust gas.

Carbon fibers produced by conventional methods have poor reactivity with NOx and have low nitrogen oxide removal efficiency.

An object of the present invention is to provide carbon fibers for removing nitrogen oxides that are suitable for removing nitrogen oxides from the exhaust gas of moving vehicles containing high concentration of oxygen, such as diesel automobile exhaust gas.

[0009]

[Means for Solving the Problems] The carbon fiber for removing nitrogen oxides of the present invention is produced by firing infusible pitch-based carbon fiber yarn at a temperature of 600°C or more and less than 800°C in an inert gas atmosphere. It is characterized by being made of carbon fiber. The present invention can significantly improve the nitrogen oxide removal performance.

0010

[Operation] The present invention will be explained in detail below with reference to the drawings.

FIG. 2 shows an example of the manufacturing process of the carbon fiber of the present invention. In Figure 2, (1) isotropic or anisotropic pitch is (2) melt-spun, (3) infusible in an oxidizing atmosphere at 150 to 400°C, and (4) purity is 95% or more. The carbon fiber of the present invention can be obtained by firing in an inert gas atmosphere at a temperature of 600°C or higher and lower than 800°C.

FIG. 1 shows the results of a nitrogen oxide removal test conducted by the present inventors using the carbon fiber obtained in the present invention.

[0013] For each carbon fiber fired at a temperature of about 500 to 1500°C in an inert atmosphere with a nitrogen concentration of 99.99% or more, SV: 2187 hr-1 using 1000 ppm of nitrogen monoxide and a standard gas of blank nitrogen. ,400
The nitrogen oxide removal performance was evaluated at ℃.

As shown in FIG. 2, the nitrogen oxide removal rate of carbon fibers fired at a firing temperature of 600° C. or higher and lower than 800° C. is high.

[0015] Even if the firing temperature is between 600°C and above and below 800°C, around 700°C is preferable.

The reason for this is that at temperatures above 600°C, pores are formed between the crystallites due to the generation and growth of carbon crystallites, and the number of pores involved in the decomposition of nitrogen oxides increases, while at temperatures above 700°C, carbon due to heat treatment increases. The fibers begin to shrink, and the pore diameters of the formed pores become smaller, reducing the number of pores involved in the decomposition of nitrogen oxides.

[0017] Due to the interaction between the increase in the number of pores involved in the decomposition of nitrogen oxides due to the generation and growth of carbon crystallites and the decrease in the number of pores involved in the decomposition of nitrogen oxides due to shrinkage of the carbon fibers due to heat treatment. Nitrogen oxide removal performance at 70% firing temperature
It has a maximum value at 0℃.

[0018] Below 600°C, pores between crystallites are not formed due to the generation and growth of carbon crystallites, and there are almost no pores involved in the decomposition of nitrogen oxides, so the decomposition of nitrogen oxides occurs on the carbon fiber surface. Since most of the reactions occur in

[0019] At temperatures above 800°C, the pore diameter of the formed pores becomes smaller and the number of pores involved in the decomposition of nitrogen oxides decreases. Oxide removal performance decreases.

[0020] In the present invention, the infusible fiber is heated to 600°C or higher.
It is characterized by firing at a relatively low temperature of less than 800°C.

[0021]

[Example] Table 1 shows a comparison of various nitrogen oxide removal methods for diesel engine exhaust gas.

Here, carbon fibers A and B are the carbon fibers of the present invention, and carbon fiber A is a pitch fiber that is made infusible and then treated with nitrogen 99.9%.
Carbon fibers are carbon fibers fired at 700°C for 1 minute in an inert atmosphere containing 9% or more nitrogen, and carbon fiber B is a carbon fiber fired at 620°C for 1 minute in an inert atmosphere containing 99% nitrogen after infusible pitch fibers. It is.

Further, as a comparative example, conventional carbon fiber C is a carbon fiber obtained by infusibleizing pitch fibers and then firing them at 1500° C. for 1 minute in an inert atmosphere containing 99.99% nitrogen.

[0024]

[Table 1]

[0025] Nitrogen oxides are sufficiently removed from the carbon fiber of the present invention.

The carbon fibers A and B of the present invention exhibit much higher nitrogen oxide removal performance than the conventional carbon fiber C, and have a nitrogen oxide removal performance of 700
Carbon fiber A fired at °C shows the highest nitrogen oxide removal performance.

Carbon fiber B fired at 620° C. shows a high nitrogen oxide removal performance that is practically effective. Carbon fiber A is
The performance was almost the same as when ammonia was used as the reducing agent.

On the other hand, under the present experimental conditions, the three-way catalyst hardly removes nitrogen oxides.

[0029]

[Effects of the Invention] When the carbon fiber of the present invention is used for removing nitrogen oxides, the following effects can be obtained. (1) Nitrogen oxides can be removed even if oxygen is present in the exhaust gas. (2) Since no toxic substances such as ammonia are used, it is easy to mount on a mobile vehicle. (3) Exhibits extremely high nitrogen oxide removal performance compared to conventional carbon fibers.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between firing temperature and nitrogen oxide removal rate.

FIG. 2 is a diagram showing the manufacturing process of the carbon fiber of the present invention.

Claims (1)

[Claims] 1. Carbon for removing nitrogen oxides, which is carbon fiber obtained by firing infusible pitch-based carbon fiber yarn at a temperature of 600°C or higher and lower than 800°C in an inert gas atmosphere. fiber.