RU2355632C1 - Method of thermally expanded graphite production - Google Patents

Abstract

FIELD: fire safety.

SUBSTANCE: invention relates to natural graphite processing and can be used to produce heat and fire protective materials. The original graphite is treated with the mixture of nitric and sulfuric acids, washed and dried. Then petroleum asphalt in the amount of 5-20 wt % is introduced to the oxidised graphite and the latter is thermally treated in the air.

EFFECT: invention allows for the increase of the expansion coefficient and simplification of the thermally expanded graphite manufacturing technique.

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Description

The invention relates to a technology for processing natural graphite, in particular, to the production of thermally expanded graphite, which can be used as a component of heat-protective and fire-retardant materials, as well as composite materials.

A known method of producing thermally expanded graphite, comprising treating natural graphite with a mixture of concentrated nitric and sulfuric acids, wherein nitric acid is used in the form of melange containing 7.5-15 wt.% Sulfuric acid, 3.5 wt.% Water, the rest is nitric acid, the mass ratio of melange to sulfuric acid is 1-2.3 in terms of anhydrous acids. Next, the resulting mixture is washed, dried and subjected to heat treatment in air at a temperature of 1000 ° C for 10 seconds. The obtained thermally expanded graphite has a bulk density in the range of 3-5 g / l (RU 2090498, publ. 09/20/1997).

The disadvantage of this method is the allocation during the heat treatment of sulfuric acid or products of its partial or complete decomposition.

It is known to use petroleum bitumen and coal tar pitch mixed with graphite in the manufacture of electrodes and structural materials (WO 02078945, publ. 10.10.2007, RU 2134656, publ. 08.20.1999).

However, in this case, coke-forming organic residues (petroleum bitumen and coal tar pitch) are used as a binder and do not lead to thermal expansion of graphite.

The closest in physical essence and final result to the proposed method is a method for producing thermally expanded graphite, comprising treating the initial graphite powder with a mixture of sulfuric acid with an oxidizing agent - nitric acid or potassium dichromate, subsequent drying and heat treatment of oxidized graphite in the presence of gaseous ammonia (SU 1813711, publ. 05/07/93).

The disadvantage of this method is the need for conducting the heat treatment process in an atmosphere of ammonia, due to the need to use a large amount of sulfuric acid. In addition, the disadvantage of this method is the high bulk density of the obtained thermally expanded graphite (low expansion coefficient).

The objective of the invention is to increase the expansion coefficient and simplify the technology for thermally expanded graphite.

The problem is solved in that in the method for producing thermally expanded graphite, comprising treating the initial graphite with a mixture of nitric and sulfuric acids, subsequent washing, drying and heat treatment of the oxidized graphite, according to the invention, oil bitumen in the amount of 5-20 wt.% Is introduced into the oxidized graphite and conduct heat treatment in air.

Comparative analysis with the prototype shows that the common features with the proposed invention are:

- processing of the original graphite with a mixture of nitric acid with sulfuric;

- subsequent washing to pH 7;

- product drying;

- heat treatment of oxidized graphite.

Distinctive features of the prototype are:

- before heat treatment in oxidized graphite is additionally introduced petroleum bitumen in an amount of 5-20 wt.%;

- heat treatment is carried out in air (in the prototype in an atmosphere of ammonia). Thanks to these distinguishing features, it was possible to simplify the technology for producing thermally expanded graphite, as well as to increase the expansion coefficient of graphite.

The essence of the problem is to achieve the maximum expansion of the interlayer space of graphite at the oxidation stage, but at the same time to avoid premature delamination of graphite, which reduces the overall efficiency of the process.

To solve the aforementioned problem, it was proposed to use, after oxidation with acids, a material such as petroleum bitumen, which is capable of melting with slight heating (105-130 ° C), passing into a liquid state with further heating, while penetrating into the voids formed in the first stage of graphite oxidation nitric acid.

All these characteristics of petroleum bitumen make it possible to significantly expand the interlayer space of graphite during its heat treatment and, accordingly, to obtain thermally expanded graphite with a high coefficient of expansion and a specific surface area higher than that of thermally expanded graphites obtained by other methods.

The invention is supported by specific examples.

Example 1. 100 g of powder of natural flake graphite brand GAK-3 of the Kyshtym field (GOST 10273-79) is placed in a reactor, stirred, add 100 cm ³ (90% HNO ₃ + 10% H ₂ SO ₄ ) and continue stirring the reaction mixture in within 10 minutes The reaction mixture is washed with distilled water to pH 7. The final product is dried at (100-105) ° C to constant weight. Oxidized graphite is heat treated at 800 ° C for 3 minutes in an atmosphere of ammonia. The characteristics of the obtained graphite are presented in the table. This example corresponds to the prototype.

Example 2. 100 g of graphite powder is treated with an oxidizing mixture in the same manner as in Example 1. Next, 5% of the Achinsk oil refinery petroleum bitumen (GOST 22245-90) is added and the mixture is mixed for 10 minutes. Heat treatment is carried out at 800 ° C for 3 minutes in air. Characteristics of thermally expanded graphite are given in the table. A slight increase in specific surface area compared with the prototype. This experience corresponds to the claimed method.

Example 3. The process is carried out analogously to example 2. The difference is that add 10% of oil bitumen. Characteristics of thermally expanded graphite are given in the table. A significant increase in Cp and specific surface area was noted compared to the prototype. This experience corresponds to the claimed method.

Example 4. The process is carried out analogously to example 2. The difference is that add 20% of oil bitumen. Characteristics of thermally expanded graphite are given in the table. The sample has higher performance than the prototype. This experience corresponds to the claimed method.

Example 5. The process is carried out analogously to example 2. The difference is that add 30% of oil bitumen. Characteristics of thermally expanded graphite are given in the table. A decrease in thermally expanded graphite in comparison with previous samples was noted, which proves the inappropriateness of using such a high concentration of bitumen.

INFLUENCE OF OIL BITUMEN ADDITIVES ON THE COEFFICIENT EXPANSIONS AND QUALITY OF SPECIFIC SURFACE THERMAL EXTENDED GRAPHITE Table No. p / p The content of petroleum bitumen in oxidized graphite,% Coefficient of thermal expansion Specific surface, m ² / g 1 (prototype) 0 146 36 2 5 146 38 3 10 190 81 four twenty 150 78 5 thirty one hundred 77

As can be seen from the table, the introduction of from 5 to 20% of petroleum bitumen in oxidized graphite provides improved characteristics of thermally expanded graphite in comparison with the prototype. With an optimum bitumen concentration of 10%, an increase in the Cp of thermally expanded graphite by 30% and a specific surface by 125% was achieved.

Thus, the inventive method can significantly increase the coefficient of thermal expansion, the specific surface of the obtained thermally expanded graphite, as well as simplify the technology for its production.

Claims (1)

A method of producing thermally expanded graphite, comprising treating the initial graphite with a mixture of nitric and sulfuric acids, subsequent washing, drying and heat treatment of oxidized graphite, characterized in that before heat treatment, 5-20 wt.% Petroleum bitumen is added to the oxidized graphite, and heat treatment is carried out on in the air.