JPS6018607B2 - Method for manufacturing graphite articles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new and improved method for producing dense graphite bodies.

In particular, the present invention relates to fabricating core elements by forming highly dense graphite bodies that are relatively non-porous and mechanically strong. Traditionally, graphite products are made by extruding or molding a graphitizable mixture of graphite or carbon particles and a binder Pittach into the desired shape.

The molding is then fired, cooled, impregnated with additional pitch, and fired again. This impregnation can be repeated several times to obtain the desired final density. Finally, the impregnated article is heated to a temperature sufficient to cause graphitization.

For the production of nuclear fuel element components, the availability of refractory bodies made of graphite and having consistent physical properties is particularly important.

This is particularly true for applications requiring graphite with low concentrations of impurities, especially sulfur. Sulfur is believed to pose several problems.

If sulfur is present, it is necessary to conduct the graphitization at high temperatures, such as 3000 qC, to remove the sulfur from the article being graphitized. 2600-220 if sulfur is not present
Temperatures as low as 0°C can be used. Sulfur is considered to have a catalytic effect on the progress of graphitization. As a result, as sulfur moves through the article at high temperatures, it causes graphitization variations along its path. This in turn creates localized areas of stress in the graphitized article. Petroleum coke has long been an available product of the petroleum industry and is produced by various known methods.

The feedstock for producing petroleum pitch is a refinery hydrocarbon stream having a low aromatic hydrocarbon concentration. That is, the feedstock oil can be a decant oil or a solvent extract of the decant oil. Various methods are used to process these pitch source oils into pitch. All of these processes begin by rectifying the pitch stock to remove low boiling oils. In the thermal pitch method, the high-boiling crab fraction is further heated to condense and polymerize the aromatic compounds present into polynuclear aromatic hydrocarbons. The product thus obtained usually has a weight of 54.5 to 143.3 qo (130 to 2900 F).
It is a high-grade pitch with a softening point of . In another method, air oxidation, pitch is produced by blowing air into a heated high-boiling fraction. Hydrocarbons obtained by air blowing are not normally used in the production of synthetic graphite bodies.

This is because air blowing imparts undesirable softening point-coking properties and softening point-viscosity relationships that make graphitized pitch more difficult and expensive to produce. It is an object of the present invention to provide a method for producing a consistent quality dense graphite body from a consistent quality carbon precursor (pitch).

Another object of the invention is to vary the temperature of graphitization within a desired range;
The object of the present invention is to provide a method for producing a graphite body that can be maintained at a temperature lower than that required to remove sulfur impurities.

``That is, the present invention provides a first portion of thermally unoxidized petroleum pitch having a softening point of 130 to 29 pF and a sulfur content of 2.5% by weight or less. [b'] The granular petroleum coke obtained in the above step 'a' is converted into granular petroleum coke, and the granular petroleum coke obtained in the above step 'a' is mixed with the second part of the hot anointed petroleum pitch of the above step [a] and the first part.
A molding paste is formed by mixing 10 to 4 parts by weight of the second part per 10 parts by weight of the second part; {
d - The article obtained in the above step 'cl' is calcined to evaporate the volatile components of the pitch, and the calcined article of 'c' the above step 'd} is heated to a third temperature of the hot unoxidized petroleum pitch of the above step 'a'. The impregnated and fired article produced in step 'c' above is heated to a temperature of at least 2200°C to convert it into graphite, and the impregnation and firing of steps 'e' and '0' above are desired. A method for producing a high density graphite article of consistent quality with low sulfur content, characterized in that the method is repeated until a density of .

The invention is based on the sole use of hot petroleum pitch and petroleum coke derived from said petroleum pitch as ingredients for producing graphite sheath articles. The petroleum pitch used in the present invention is hot petroleum pitch currently available as a petroleum refinery product.

This pitch is usually 54.4-143.3℃ (130-2
It has a softening point of 900F). Also, available oxidized petroleum pitch does not form part of this invention. The physical properties of several types of hot petroleum pitch that can be used in the present invention are shown in the table below. Softening
Point.

0, (T, R&B) 76.7 (170) 148.
9 (300) 115.6 (240) Flookfield viscosity/cpsl90.600 (3750F) 3
0 390 140176.70○
(3500P) 45 780
275162800 (325F) 86
1600 700 Cokeability value (A
sTMD-2416) 38 63
51 Benzene insoluble matter Weight% 4
28 5 quinoline insoluble matter
0 0.5 0 specific gravity 250
/2500 (77T/770F) 1.19
1.24 1.22 Sulfur
Weight% 1.3 1.3 1.3 Average molecular weight 380 5
30 487 Carbon Weight% 92.4 94.0 93
．． 1 hydrogen 5.
7 4.4 5.4 The petroleum coke used in the present invention is made from the same pitch used as the binder pitch.

The above-mentioned 7670 (170T) and 115 are ○ (240
Typical physical properties of petroleum needle coke made from a pitch sample having a softening point of 0F) are shown in the table below. pitch softening point,
.

0 (〇F, R&B) 76.7 (170) 115.6
(240) Carbon yield weight% (1) 49
60×-ray diffraction intermediate layer spacing
3.360 3.358Lc
520 860La
510 1000 Coke microstructure Needle-like structure 77 83 Microisotropic structure
23 17 (1) The technique of producing 280,000 carbonized needle coke from petroleum pitch in a sealed graphite board under an argon atmosphere does not form part of the present invention and is widely known in the industry.

In making graphite articles, powder or granular coke made from hot petroleum pitch and 10 to 4 parts by weight of hot petroleum pitch per 10 parts by weight of coke are placed in a suitable mixer.

Mixing is carried out for 20 to 120 minutes at a temperature of 70 to 20 pi, depending on the melting point of the binder pitch. The resulting mixture is then compressed or extruded into the desired shape and fired at a temperature of about 600 to 100 pi for 5 to 60 days to carbonize the binder. The resulting article is impregnated with an additional amount of the same pitch originally used under conditions of temperature and pressure sufficient to allow the liquid pitch to penetrate into the pores of the article. Next, this impregnated article is again coated with 600-100%
Firing at a temperature of 0.0 psi for a period sufficient to carbonize the additional pitch. This impregnation and heating step is repeated as many times as necessary. Finally, the article is heated to a temperature of 2200°C or higher, such as from 2800 to 3000 qo, preferably from 2200 to
Graphitize the fired article by heating to 26000C. In this way, a graphite article is obtained that is significantly less likely to crack and fracture at high temperatures when used, for example, in nuclear energy. If a hot petroleum pitch with a low impurity content, especially a low sulfur content, is used as a binder, the articles produced by graphitizing the coke obtained from the pitch will naturally have a low sulfur content.

The articles thus obtained are particularly useful for thermonuclear applications. The hot petroleum pitch to be used in this invention is about 54.4 to 143.30
(130-2900F), but especially about 7
6.7-115. A pitch having a softening point of C (170-2400F) is preferred.

The densification of the article, which is the objective of the multi-stage pitch impregnation-firing step, can also be achieved by isostatic pressing of the green article after shaping and before subsequent calcining-graphitization.

EXAMPLE Hereinafter, an example of manufacturing a graphite rice cake article of the present invention will be explained based on FIG.

In FIG. 1, petroleum pitch commercially available as A240 pitch is used as the raw material supply source 1.

This pitch has an average sulfur content of 1.3% and an average density of 1.3%.
22/cc, softening point is average 115. is 0 (2400F
)Met. The present invention preferably uses this pitch as the sole carbon source for the various purposes described below.
A portion of this A240 (hot unoxidized petroleum) pitch was coked in a conventional delayed coking device 2 to produce unrefined (green) petroleum coke particles. In the roasting apparatus 3, the petroleum coke was roasted in a rotary hearth heating furnace or rotary kiln using a conventional technique. This technology includes, for example, M. W. Process technology, i.e. 198
4Ko September issue “Hydrocarbon Brossing” 145
The "MW" rotary hearth furnace described on page 1 is used. The resulting coke had a sulfur content of 1.0% by weight and a density of 2.1.
It was evening/fairy tale. The coke was then pulverized in a pulverizer and classifier 4 to a relatively uniform particle size with an average particle height of about 300 to 1000 microns.

The crushed coke is sent to mixer 5 where an additional amount of A240 pitch is mixed. This additional pitch is the same as the raw material for crushed coke and is supplied from raw material supply source 1. The amount to be added is sufficient to turn the crushed coke into a paste. Here, about 35 parts by weight was used per 100 parts by weight of the raw material. The paste produced in the mixer 5 is molded in a molding device 6 using conventional techniques.

The molded article is fired hard in the open 7 at a suitable temperature, but is somewhat porous due to the release of volatile substances during firing.

At this stage the sulfur content is 0. Mother weight%, density is 1.4/
It was cc. Each hard fired molded article is further processed under pressure in an impregnation device 8 using conventional vacuum impregnation techniques.
Impregnate with sufficient amount to impregnate additional A240 pitch from source 1.

Next, the impregnated molded product is returned to the open chamber 7 and further fired. This reconstitution and impregnation is carried out to achieve the desired density, e.g.
Continue until it reaches 7 to 1.9 evenings/cc. The molded product having a desired density is graphitized in an open state 9 at a temperature in the range of 2,200 to 3,000 CO for a sufficient time, for example, several days in the case of a large-scale product, by a conventional method. The graphitized article has an average pore size of about 0.1-0.3 microns and a tensile strength of about 140
．． 6k9/ground (2000 pounds/square inch), sulfur content less than 0.1% by weight, density approximately 1.7-1.9 kg/c
c (generally slightly smaller than the final finished product because it always volatilizes in a small amount during graphitization), electrical resistivity is approximately 2.2×
It was 10-4 ohm skin (5.6 x 10-4 ohm inches). The graphite articles thus obtained were sufficiently dense and low in sulfur that they could be used in many applications, including as discharge mine poles as well as core components of nuclear reactors.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of manufacturing a graphite article by the method of the present invention. 1... Raw material supply source, 2... Delayed coking device,
3... Time baking device, 4... Grinding and classification device, 5... Mixer, 6... Molding device, 7, 9... Open, 8...
・Impregnation equipment. Figure 1

Claims (1)

[Claims] 1 (a) 54.4 to 143.3°C (130 to 290°
(b) granular petroleum coke obtained in step (a) above; is mixed with the second part of the heated unoxidized petroleum pitch of step (a) above in a ratio of 10 to 40 parts by weight of the second part per 100 parts by weight of the first part to form a molding paste, and (c ) Molding the paste obtained in step (b) above into an article of desired shape,
(d) baking the article obtained in step (c) above to evaporate the volatile components of the pitch; (e) converting the baked article of step (d) above into the heated unoxidized petroleum pitch of step (a). (f) heating the impregnated fired article produced in step (e) above to a temperature of at least 2200°C to convert it to graphite; (g) performing steps (e) and (f) above; Method 2 for producing high-density graphite articles of low sulfur content and consistent quality characterized by repeating impregnation and calcination until the desired density is achieved.
2. The method of claim 1, wherein a hot petroleum pitch having a softening point of 170 DEG to 240 DEG F. is used. 3. The method of claim 1, wherein the impregnated fired article is heated to a temperature of about 2200-2600C. 4. The method of claim 1, wherein after step (e) and before step (f) the impregnated fired article is fired and impregnated again into the fourth portion of the heated unoxidized petroleum pitch of step (d). 5. The method of claim 1, wherein the impregnated fired article is heated to a temperature of about 2800-3000°C.