RU2118941C1 - Method of production of oxidized graphite - Google Patents

Abstract

FIELD: technology of carbon-graphite materials. SUBSTANCE: to natural graphite fuming HNO₃ (mass ratio of HNO₃ : graphite = (0.37-0.75):1) or a mixture consisting of 2-4 mas. p. p. fuming and 1 p. 58% HNO₃ (mass ratio mixture : graphite = (0.75-2.2):1) is added. It is possible to add preliminary 0.025 mas. p. urea/1 mas. p. graphite. Evolved gases are removed continuously. Hydrolysis and washing out are carried out at water feeding by countercurrent method to compound that is incorporated in graphite. Stirring is carried out by pulsating method. Mass ratio water : compound to be incorporated in graphite = (5-7):1. Drying the oxidized graphite is carried out at 80 C and below. Expansion degree of oxidized graphite is 230-500. Invention can be used for production of cellular graphite and graphite foil. EFFECT: improved method of production, decreased consumption of acid and acid effluence. 3 cl, 1 tbl, 2 ex

Description

 The invention relates to the technology of carbon-graphite materials, in particular to the production of oxidized graphite, which can be used as a component of flame retardant materials, as well as to obtain penografit, used for the manufacture of flexible graphite foil.

A known method of producing oxidized graphite, which consists in dispersing graphite in 60 - 95 wt.% HNO ₃ taken in a 3 - 5-fold excess and adding small portions of KMnO ₄ taken in a 4 - 20-fold excess, heating the mixture to 60 ^o C for 2 hours, centrifugation, washing with water to pH 6, wetting with anticorrosive agents and drying at T <100 ^o C. Heat treatment at 1000 ^o C produce penografite with a bulk density of 12 g / l [Japanese application N 55-80711 / 80, C 01 B 31/04, 1980].

 The disadvantages of this method are the high cost of reagents and a low degree of expansion of oxidized graphite.

A known method of producing oxidized graphite, which consists in processing graphite powder of steaming (100%) HNO ₃ with a mass ratio of graphite to acid of 1: 4, separating the resulting graphite nitrate from excess acid, repeatedly washing the product and drying. Heat treatment of oxidized graphite produces penografite with a bulk density of ~ 5 g / l. [US Patent N 3260632, C 06 B 1/04, 1966].

The disadvantage of this method is the high consumption of HNO ₃ , as well as the large amount of water required for washing, and a significant amount of acidic waste.

A known method for producing oxidized graphite, comprising treating graphite powder in a flow tube reactor with nitric acid vapors with a concentration of at least 85 wt.% (100%) or a mixture thereof with a carrier gas (air, oxygen, helium) at a rate of smoking HNO ₃ 0, 4 to 4 g per 1 g of graphite at 20 to 50 ^o C for 1 to 4 hours, subsequent processing with acetic acid, washing with water, filtering and drying. As a result, oxidized graphite is obtained with a low foaming start temperature and a degree of expansion of ~ 300 [A.S. USSR N 1805632, C 01 B 31/04, 1990].

 The disadvantage of this method is the complex hardware design of the process and its multi-stage.

A known method of producing oxidized graphite by sequential processing of 1 g of graphite powder of 2.5 - 10 ml of HNO ₃ (d = 1.51 g / cm ³ ) for 16 hours, glacial acetic acid, water, filtration and drying. The resulting oxidized graphite has a low foaming start temperature and an expansion ratio of 200 - 300 ^o C [A.S. USSR N 1614350, C 01 B 31/04].

The disadvantage of this method is the high consumption of HNO ₃ and the duration of the chemical treatment.

The closest is a method for producing oxidized graphite, which includes treating graphite powder with steaming HNO ₃ with a constant redox potential of 0.92-0.97 for 30 minutes at a mass ratio of HNO ₃ : graphite = 4: 1, followed by hydrolysis of the compound incorporating into graphite with cold water, washing and drying at T <80 ^o C. The result is oxidized graphite with a degree of expansion of ~ 165 [PCT, application N WO 96/339949, C 01 B 31/04, 1996].

The disadvantage of this method is the high consumption of steaming HNO ₃ and the associated large amounts of water and acidic waste. In addition, oxidized graphite has an insufficiently high degree of expansion.

 An object of the invention is to increase the environmental process and reduce material costs.

The problem is solved in that in a method for producing oxidized graphite, which includes treating natural graphite with fuming nitric acid to form a compound for incorporation into graphite, hydrolyzing, washing and drying oxidized graphite at a temperature of not more than 80 ^o C, the treatment is carried out with a mass ratio of fuming nitric acid to graphite 0.37 - 0.75: 1 or a mixture of steaming nitric acid and 58 wt.% nitric acid with a mass ratio of graphite 0.75 - 2.2: 1 with continuous removal of the resulting gases, hydrolysis and washing are carried out at feed water in a countercurrent to the intercalation compound in graphite with pulsating mixing of the intercalation compound in graphite and water with a mass ratio of water to graphite 5-7: 1. The problem is also achieved by the fact that the mass ratio of steaming HNO ₃ to 58% HNO ₃ is 2-4 : 1 and urea is added to the mixture at a specific flow rate of 0.025 parts by weight. urea per 1 wt.h. graphite.

According to the proposed method, when processing graphite, the mass ratio of steaming HNO ₃ to graphite is 0.37 - 0.75: 1, preferably 0.57: 1. It is impractical to reduce the consumption of HNO ₃ <0.37: 1, since it leads to incomplete oxidation of graphite , the formation of a mixture of higher steps of the interstitial compound and a decrease in the quality of oxidized graphite. An increase in the ratio> 0.75: 1 is also impractical, since it leads not only to an increase in the consumption of acid, but also to a non-flowing product, which negatively affects the processability. It is preferable to use the stoichiometric amount of HNO ³ necessary for the formation of stage II graphite nitrate according to the equation:
48C + 5HNO ₃ __ → C $\genfrac{}{}{0ex}{}{\text{+}}{\text{48}}$ NO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$ • 3HNO ₃ + H ₂ O + NO ₂ ↑
NO ₂ is released as a reaction by-product, which in a closed volume inhibits the reaction process and degrades the quality of oxidized graphite. As our experimental studies have shown, the degree of expansion of oxidized graphite obtained in a confined space decreases by a factor of 2–5 compared with the product obtained by continuously removing the formed nitrogen oxides.

You can use an oxidizing mixture based on steaming HNO ₃ and concentrated HNO ₃ for graphite treatment with a mass ratio of graphite of 0.75 - 2.2: 1 and a mass ratio of steaming HNO ₃ to 58 wt.% HNO ₃ = 2 - 4: 1. The indicated ratios are selected mainly from technological considerations and are associated with the possibility of using reactors of any type: when deviating from these ratios, the reaction mass becomes non-fluid; in addition, it is possible to obtain heterogeneous products as a result of the reaction or the consumption of reagents increases, which is undesirable. The ratio of acids in the oxidizing mixture, equal to 2 - 4: 1, is optimal, since an increase in the content of 58 wt.% Acid leads to a decrease in the degree of expansion of oxidized graphite, and a decrease in the content of 58 wt.% HNO ₃ only slightly improves the characteristics of oxidized graphite.

Уменьшение удельного расхода мочевины нецелесообразно, так как в этом случае малое количество окислов азота поглощается, а увеличение количества CO(NH₂)₂ > 0,025 мас.ч./мас.ч. графита отрицательно влияет на свойства окисленного графита: степень расширения окисленного графита падает в 1,5 - 2 раза.To increase the environmental friendliness of the process and reduce the amount of nitrogen oxides emitted, it is advisable to add urea to the oxidation mixture in an amount of 0.025 parts by weight / 1 part by weight. graphite. Urea binds nitrogen oxides according to the equations below:
2CO (NH ₂ ) ₂ + 3NO ₂ __ → 3,5N ₂ + 2CO ₂ + 4H ₂ O
4CO (NH ₂ ) ₂ + 3NO ₂ + 4HNO ₃ ___ → 3,5N ₂ + 4NH ₄ NO ₃

A decrease in the specific consumption of urea is impractical, since in this case a small amount of nitrogen oxides is absorbed, and an increase in the amount of CO (NH ₂ ) ₂ > 0.025 parts by weight / part by weight. graphite adversely affects the properties of oxidized graphite: the degree of expansion of oxidized graphite drops by 1.5 - 2 times.

The hydrolysis and washing operation is recommended to be carried out in countercurrent mode and combined in one stage, which is possible when selecting suitable equipment with a specific water flow rate of 5 to 7 parts by weight. per 1 part by weight graphite. An increase in the consumption of H ₂ O is impractical, since it leads to an increase in the volume of acidic waste and adversely affects the degree of expansion of oxidized graphite. Reducing water consumption is also impractical, since it leads to the production of oxidized graphite with a high content of residual nitric acid, which is released during drying and storage, which affects the ecology of the working area and the environment.

 In the proposed method, hydrolysis and washing operations are combined and carried out in a counterflow mode; Such a process of hydrolysis and washing is based on the laws of diffusion mass transfer, does not depend on the degree of condensation of the sample, and is determined primarily by the efficiency of the interaction of the phases — graphite nitrate and washing water in a vertical stream. With countercurrent movement of phases and a certain speed of the upward flow of water, favorable conditions are created for washing the oxidized graphite. In addition, the reciprocating effects of the pulsator are superimposed on the vertical flow of the interacting phases.

 The upward velocity of the washing liquid may be in the range of 1.5 - 8 m / h, a decrease in the linear velocity is undesirable, as it leads to an increase in washing time, a decrease in the productivity of the process and the quality of the oxidized product; an increase in speed is also impractical, since it leads to the production of an incompletely washed “acidic” product with pH <1 and unstable characteristics.

 Example 1

. Затем продукт подают в приемное устройство вертикальной пульсационной колонны, расположенное в ее верхнем торце. С противоположной стороны колонны (т.е. снизу) с определенной скоростью подают холодную воду в количестве, обеспечивающем массовое отношение воды к графиту 5 : 1. Одновременно сжатым воздухом от пульсатора на столб промывочной воды накладывается возвратно-поступательное воздействие. Окисленный графит движется вниз, постепенно освобождаясь от кислоты, а промывные воды вверх и уходят с верхнего слива. Отмытый окисленный графит разгружается в нижней части колонны, потом отфильтровывается до влажности ≈ 30 мас. %. Время пребывания пробы в колонне (т.е. время гидролиза и промывки) составляет 30 мин. Полученный продукт сушится при температуре 70^oC в течение 15 мин в печи с инертным теплоносителем. В результате получают 22,1 г окисленного графита с влажностью 1% и степенью расширения 480. Степень расширения определяется как объем (см³), занимаемый 1 г окисленного графита после его термообработки при 900^oC.In a reactor equipped with a fluoroplastic mixer with nozzles throughout the reactor volume and a gas suction system, 20 g of natural graphite are placed and 7.6 ml of steaming HNO ₃ (d = 1.51 g / cm ³ ) is added. The mass ratio of acid: graphite is 0.57: 1. The synthesis of the intercalation compound is carried out at room temperature, stirring with constant removal of the resulting gases for 1 hour. The evolved gases are drawn in vacuum through a system of absorbers at a rate of ≈ 1.5 l / min. As a result of the reaction, a free-flowing product is obtained - stage II graphite nitrate with an identity period of I _c = 11.20

. Then the product is fed into the receiver of the vertical pulsation column located in its upper end. On the opposite side of the column (ie, from below), cold water is supplied at a certain speed in an amount that provides a mass ratio of water to graphite of 5: 1. At the same time, the reciprocating effect is applied to the wash water column with compressed air from the pulsator. Oxidized graphite moves downward, gradually freeing itself from acid, and washings upward and leave the upper drain. Washed oxidized graphite is unloaded at the bottom of the column, then filtered to a moisture content of ≈ 30 wt. % The residence time of the sample in the column (i.e., the hydrolysis and washing time) is 30 minutes. The resulting product is dried at a temperature of 70 ^o C for 15 minutes in an oven with an inert coolant. The result is 22.1 g of oxidized graphite with a moisture content of 1% and a degree of expansion of 480. The degree of expansion is defined as the volume (cm ³ ) occupied by 1 g of oxidized graphite after heat treatment at 900 ^o C.

 Example 2

и 14,55

. После гидролиза, промывки и сушки получают 21,7 г окисленного графита со степенью расширения 300.20 ml of HNO ₃ (d = 1.51 g / cm ³ ) and 7.35 ml of 58% HNO ₃ (d = 1.36 g / cm ³ ) are poured into the same reactor; 0.5 g of urea is added with mixing of acids and 20 g of natural graphite. The synthesis is carried out at room temperature, with constant stirring and removal of the resulting gases for 60 minutes. Further, as in example 1, but the mass ratio of water to graphite is 7: 1. The mass ratio of the oxidizing mixture to graphite is 2: 1; the mass ratio of steaming HNO ₃ 58% HNO ₃ = 3: 1. The urea consumption of 0.025 g per 1 g of graphite. As a result of oxidative treatment, a mixture of graphite nitrate of the II and III stages with I _c = 11.20

and 14.55

. After hydrolysis, washing and drying, 21.7 g of oxidized graphite with a degree of expansion of 300 are obtained.

 The results obtained by the proposed method are summarized in table.

 Thus, the proposed method can significantly reduce material costs (acid, water), significantly reduce the amount of acidic waste, and also significantly improve the quality of the final product. The undoubted advantage of the method is its environmental friendliness and manufacturability due to the low consumption of nitric acid, removal and absorption of exhaust gases and hydrolysis and washing operations in one stage.

Claims (3)

1. A method of producing oxidized graphite, comprising treating natural graphite with fuming nitric acid to form an incorporation compound in graphite, hydrolyzing, washing and drying oxidized graphite at a temperature of not more than 80 ^o C, characterized in that the treatment is carried out with a mass ratio of fuming nitric acid to graphite 0.37-0.75: 1 or a mixture of steaming nitric acid and 58 wt.% Nitric acid with a mass ratio of graphite of 0.75-2.2: 1 with continuous removal of the resulting gases, hydrolysis and washing are carried out when the water is supplied countercurrently to the connection of the introduction of graphite with pulsating mixing of the connection of the introduction of graphite and water with a mass ratio of water to graphite 5-7: 1.  2. The method according to p. 1, characterized in that the mass ratio of steaming nitric acid to 58 wt.% Nitric acid is 2-4: 1.  3. The method according to claims 1 and 2, characterized in that urea is added to the mixture of steaming nitric acid and 58 wt.% Nitric acid at a specific flow rate of 0.025 wt. urea per 1 wt.h. graphite.

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