RU2177905C2 - Method of preparing oxidized graphite - Google Patents

Abstract

FIELD: chemical industry, more particularly preparation of antifire, sealing and constructional materials. SUBSTANCE: reactor is poured with sulfuric acid. Hydrogen peroxide is fed under sulfuric acid layer under vigorous stirring and cooling. Graphite is charged, 30-35 min later the resulting oxidized graphite is diluted with water and washed under the following conditions: Vgr/Vw= 1/10-1/8 ; d st/D -0.4; d st/4 0.5 wherein Vgr and Vw are volumes of oxidized graphite and water; D are diameters of stirrer and capacities of suspension diluent; h st, H are heights of stirrer and layer of aqueous graphite suspension. Washing operation is carried out for 8-7 min, suspension is maintained for 5-7 min, filtered and dried at 100-110 C. Bulk density of oxidized graphite varies from 8.1 to 41.2 g/l. K_swel= 8-34 varies from 8 to 34. Method is ecologically clean and no toxic flows are present. EFFECT: more efficient preparation method. 1 dwg, 1 tbl

Description

 The invention relates to the production of oxidized (intercalated) graphite, which can be used as a structural material and in various compositions: intumescent fireproof materials for fire-fighting purposes (for the protection of metal and wooden coatings of aircraft, spacecraft, armored vehicles, cable lines, computer equipment, etc. etc.), fire-resistant system of rigid heat-insulating polyurethane foam for the construction industry, as various sealing materials, work melting at high temperatures and pressures.

Typical tests showed that the packing of thermally expanding graphite proved to be highly reliable components for any environment and are operable at operating temperatures of ~ 500 ^o C and a pressure of 300 kgf / cm ² .

 A known method of producing oxidized graphite (K. E. Makhorin, A. P. Kozhan, V. V. Veselov "Expansion of natural graphite treated with sulfuric acid" // Journal "Chemical Technology", 1985, 2, p. 3-6) .

 This method uses the treatment of graphite with concentrated sulfuric acid in a mixture with potassium bichromate, ammonium persulfate or nitric acid for one hour, then the suspension is diluted with water, followed by filtration of the graphite from the excess oxidizer and drying to a moisture content of 40-50%.

 The disadvantages of this method are the use as an oxidizing agent of a 2% potassium dichromate solution, which is harmful to the human body and irritates the mucous membranes of the eyes, respiratory tract, in addition, it affects the gastrointestinal tract and can cause severe poisoning of the body. Further heat treatment of graphite leads to the release of vapors with residues of potassium dichromate, there is a need for additional purification of water and air from oxidizing agents. The output is a high humidity graphite after drying and, in General, the method gives a low yield.

 The well-known "Method for producing oxidized graphite" by a. from. 1781984, class From 01 to 31/04, 1990

 This method involves the preliminary processing of graphite with hydrogen peroxide, followed by treatment with chromic anhydride, concentrated sulfuric acid, urea and magnesium oxide.

 The disadvantage of this method is the complex processing scheme of graphite and the use of chromic anhydride as an oxidizing agent. In fact, it is a poison that affects the vital organs of a person. There is a difficulty in regulating the temperature in the pre-treatment reactor; there is an additional operation of graphite reloading from the drying reactor.

 Closest to the proposed technical solution is the "Method for producing oxidized graphite" according to patent 2057065, class. 6 C 01 B 31/04, 1996

 This method includes processing the crushed crystalline graphite with sulfuric acid and hydrogen peroxide as an oxidizing agent, filling graphite, holding the reaction mass, diluting, filtering and washing with water the reacted mass.

 Hydrogen peroxide and sulfuric acid are mixed in a ratio of 1: (6-20) wt. including feeding hydrogen peroxide under a layer of sulfuric acid, intensively mixing and continuously cooling until a homogeneous mixture is formed, then graphite is poured in a ratio of 1: (2-3) wt. including sulfuric acid, withstand the reacting mass with continuous stirring for 10-20 minutes, after which the reacted mass is fed to the filtration. In this method, the mixing of hydrogen peroxide and sulfuric acid and the oxidation of graphite are carried out while sparging the air.

 The disadvantages of this method are the complexity of the design of the apparatus for providing bubbler air, the possible evaporation of a liquid by a stream of bubbler air, high energy consumption, as well as the supply of hydrogen peroxide under pressure.

 The objective of the present invention is to obtain high-quality oxidized graphite in an environmentally friendly, waste-free production. The quality of graphite is controlled by the main output parameters, the coefficient of swelling.

 The problem is solved as follows.

In the known method for producing oxidized graphite, comprising treating graphite with sulfuric acid and hydrogen peroxide as an oxidizing agent, wherein hydrogen peroxide is fed under a layer of sulfuric acid with vigorous stirring and cooling, filling graphite, diluting, filtering, washing and drying the reacted mass, the graphite is oxidized for 30-35 minutes, and when washing in a diluent suspension, the following conditions are met:
V _g / V _in = 1 / 10-1 / 8;
d _m / D ~ 0.4;
h _m / N ~ 0.5,
where V _g , V _in - volumes of oxidized graphite and water;
d _m , D - diameters of the mixer and the capacity of the diluent suspension;
h _m , N - the height of the mixer and the layer of water-graphite suspension,
moreover, after washing, exposure is carried out at a ratio of washing time and exposure time of 1: 1, and oxidized graphite is dried at a temperature of 100-110 ^o C.

 Thus, the hydrodynamic process is determined by the type of mixing device, the speed of the reactor stirrer, the temperature of the washing water, the mixing time and holding time after mixing.

 The method uses only hydrogen peroxide and sulfuric acid.

 The method is as follows.

 Sulfuric acid or oleum is pumped from storage tank 2 to the measuring tank 4 using a vacuum pump 7, then by gravity to the synthesis reactor 5. Hydrogen peroxide from the storage tank 1 by gravity is supplied to the measuring tank 8, then volumetric dosing of hydrogen peroxide to the synthesis reactor 5 is carried out A funnel 3 with a portion of graphite is mounted on the reactor 5.

 Graphite oxidation is carried out in synthesis reactor 5.

A dose of sulfuric acid is poured into the synthesis reactor 5 from the measurer 4, the reactor stirrer is turned on, and the dose of hydrogen peroxide is supplied under a sulfuric acid stream from the measurer 8 using a tube under a layer of sulfuric acid, eliminating overheating of the medium due to the automatic supply of cold water with a temperature of 5-25 to the jacket of the reactor ^o C. The loading of graphite is carried out with the stirrer open by opening the gate on the funnel 3. The temperature of the reaction mixture should be in the range of 25-55 ^o С. The oxidation process in the reactor lasts 30-35 min with a constantly working stirrer. Next, the oxidized graphite from the synthesis reactor with the help of compressed air is transferred to the lower part of the diluent of suspension 6 with the mixer turned on, and the required amount of drinking water is poured into it. To maintain the temperature of dilution of the suspension within 40-60 ^o C, cold water with a temperature of 5-25 ^o C is fed into the jacket, the contents of the diluent are cooled with stirring to a temperature of 25-30 ^o C. Washing of oxidized graphite in the diluent is carried out with the stirrer operating for 5 -7 min, after which the diluent mixer stops. The extract is held for 5-7 minutes and then the mass of oxidized graphite is fed by a vacuum pump 9 to the filtration. The oxidized graphite remaining on the vacuum filter 10 is washed with drinking water from acid residues supplied in portions until the pH of the aqueous extract of graphite reaches 3.5-7, then graphite with a moisture content of not more than 40% is sent to dryer 11. The oxidized graphite is dried to a moisture content of not more than 5% at a temperature of 100-110 ^o C, after which graphite goes to packaging. Water, after filtration and pressing graphite by pumps 13, 14, enters a tank for collecting acidic water 12, into which, with the mixer turned on, a portion of lime paste is loaded. The resulting gypsum suspension is mixed for 5-7 minutes, and then poured using a pump 14 onto the filter 15. After filtration, the gypsum with a moisture content of 30% is fed to the packaging.

 Synthesis reactor 5 has fixed values of D, H, etc.

 From the experimental work (see table) it can be seen that the expansion coefficient varies from 8 to 34 units, depending on the type of mixing device, the speed of the mixers, and the composition of the oxidizing mixture.

 To optimize the washing regime, a series of experimental and computational works was carried out. Experimental work was carried out to verify the adequacy of the calculated hydrodynamic model of the process based on mathematical modeling of the Navier-Stokes equations for a Newtonian fluid by the finite element method.

The results were obtained on a “model” and confirmed in a full-scale experiment for a non-standard mixing apparatus with an anchor mixer when generally fulfilling dimensionless conditions:
d _m / D ~ 0.4;
h _m / N ~ 0.5,
where d _m is the diameter of the mixer;
D is the diameter of the capacity of the diluent;
h _m is the height of the mixer;
H is the height of the layer of water-graphite mixture.

Fulfillment of the conditions that determine the hydrodynamics of the mixing process during the washing of graphite allows us to obtain a rather high value of the coefficient of swelling (K _sp = 32-34) from all technological factors:
To _vsp - (Re, V _g , V _in , t ^o _cm , t _per , t _vyd , d _m / D, h _m / N),
where V _g ; V _in - the volumes of the graphite mixture and water, respectively;
t ^o _cm - temperature of the mixture;
t _lane is the mixing time;
t _vyd - the exposure time after mixing.

The best results were achieved with:
t ^o _cm = 20-40 ^o C,
t _vyd ≥5-7 min
t _pe ≥5-7 min,
V _g / V _in = 1 / 10-1 / 8
Fulfillment of the latter conditions allowed us to further increase the amount of swelling of oxidized graphite to
K _pop = 32-34
The established ratios for the technological phase of graphite washing are implemented at a pilot plant for the production of intercalated graphite with a capacity of 120 tons / year, at Perm Plant named after S. M. Kirov.

Claims (1)

A method of producing oxidized graphite, comprising treating graphite with sulfuric acid and hydrogen peroxide as an oxidizing agent, wherein hydrogen peroxide is fed under a layer of sulfuric acid with vigorous stirring and cooling, filling graphite, diluting, filtering, washing and drying the reacted mass, characterized in that the oxidation process graphite is carried out for 30-35 minutes, and when washing in a diluent suspension, the following conditions are met:
V _g / V _in = 1 / 10-1 / 8,
d _m / D ~ 0.4,
h _m / N ~ 0.5,
where V _g , V _in - volumes of oxidized graphite and water;
d _m , D - diameters of the mixer and the capacity of the diluent suspension;
h _m , N - the height of the mixer and the layer of water-graphite suspension,
moreover, after washing, exposure is carried out at a ratio of washing time and exposure time of 1: 1, and oxidized graphite is dried at a temperature of 100-110 ^o C.

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