SU1765114A1 - Method of expanded graphite production - Google Patents

Abstract

The invention relates to methods for producing thermally split graphite (TRG). The goal is to reduce the sulfur content. The essence of the method is that the graphite bisulfate is treated with 5-10% aqueous ammonia solution for 10-20 minutes, followed by washing it with water, drying and heat treatment. The proposed method allows to reduce the sulfur content in the TWG to 0.0008% w / w and thereby improve its consumer properties. 1 tab.

Description

The invention relates to non-metallic elements, in particular to methods for cleaning thermally expanded graphite (TRG), used to make plastic thermally and thermally conductive gasket elements resistant to corrosive media and used in the chemical industry, cryogenic technology and other engineering fields.

It is known that the determining parameter influencing the corrosion resistance of articles from TRGs is the presence of impurities, in particular sulfur. Therefore, upon receipt of TRG, reduction of sulfur in the final product is relevant.

As a prototype, a method was chosen for purifying a graphite compound by treating graphite bisulfate (C24 + HS04 nHaS04) with water at a temperature above 100 ° C in an autoclave or with an aqueous solution of nitric acid or nitrates at 30 ° C for several hours. Then, the graphite bisulfate treated in this way was washed with water, dried at 80 ° C for 4 hours, and thermally treated at 1000 ° C.

The obtained TRG had a pH of 3.5 draw water and the sulfur content in the TWG was reduced to 0.0025 May. %

The disadvantage of this method is not high enough purification of the TRG from sulfur.

The purpose of the invention is to reduce the sulfur content in the TWG.

This goal is achieved by the fact that in a known method of purification of a graphite compound, which involves the processing of graphite bisulfate with an aqueous solution, according to the method of treatment, a 5 to 10% aqueous solution of ammonia is carried out for 10 to 20 minutes.

Graphite bisulphate obtained from natural graphite of the Zavalevskoye deposit GAK-2 (GOST 18191-78) with a particle size of 50–250 µm by electrochemical anodic oxidation in a solution of sulfuric acid was taken as the starting material. Electrolyte solutions were prepared on the basis of technical sulfuric acid (GOST 2184-77). Electrochemical processing of graphite was carried out in an electrochemical cell with separated

SP

with

 "

SL

cathode and anode chambers. A titanium plate, a platinum anode, served as the cathode. A stabilized power source LIPS 35-1 was used as a direct current source. The value was measured using a combined device Sch 4300.

For the preparation of an aqueous solution of ammonia, an analytical grade analytical grade ammonia was used with a concentration of 25% (GOST 3760-79) containing not more than 0.0003 wt.% Sulfur.

The process of obtaining graphite bisulfate included the following operations: dosage of powdered graphite in a solution of sulfuric acid; electrochemical treatment of graphite in a solution of sulfuric acid in the anode chamber of the electrolyzer until the moment of obtaining blue graphite bisulfate; filtration and washing of graphite bisulfate with water.

Then, the intercalated graphite compound was treated with an aqueous ammonia solution according to the method. After that, the product was washed with water to a pH of 6.5 - 7, the product was dried in an oven at 80 ° C for several hours. The heat treatment of the dried product was carried out in an electric furnace at a temperature of 1000 ° C for 1 min (this refers to the residence time of the loaded mass of graphite bisulfate in the hot zone of the furnace). Then TRG was removed from the furnace and cooled in air. After that, the bulk density value of TEG was determined by the method described in GOST 14922-77 and the sulfur content according to GOST 8606-72.

The determination of total sulfur content in TEG was carried out as follows.

A weighed portion of thermally expanded graphite 1 g was mixed with a mixture of Eshka in the ratio 1: 4. The contents were thoroughly mixed and the leveled surface was additionally covered with 2 g of Eshk's mixture. The crucible with the mixture was placed in a muffle furnace, which was gradually heated and kept for 3 hours at 815 ± 25 ° C. After sintering the mixture, the crucible was cooled. The contents of the crucible were transferred to a glass (150 cm), the crucible was thoroughly washed with hot water. The contents of the glass were filtered through a de-salt filter (red ribbon) into a glass (600 cm) and the filter cake was washed at least 5 times with hot water. The solution was neutralized with 20% HCl with methyl red indicator, and then an additional 1 cm of 20% HCl was added. Then the solution was boiled for 5 min. 10 cm of BaCl2 solution was added to the boiling solution over a period of 20 seconds with constant stirring and the solution was kept in

for 30 minutes at a temperature close to the boiling point. After precipitating barium sulphate and clarifying the solution the next day, it was filtered through

tight filter. The filter cake was further washed with hot water.

The wet filter with the precipitate was placed in a pre-weighed crucible and dried. The crucible was then calcined for 20 minutes at a temperature of 815 ± 25 ° C. After removing the crucible from the muffle and cooling it for room temperature, weighed it

Mass fraction of sulfur in the analytical

the sample (Ztrg) in percent was calculated by the formula

ZTRG (mi 2l ° -1374- 100%,

20

GPTRG

where mi is the mass of barium sulphate obtained in the analysis, g;

that is the mass of barium sulphate obtained by (idle) control experiment,

g,

0.1374 is the conversion factor for the mass of BaSO to the mass of sulfur;

GPTRG - the mass of the sample of thermally expanded graphite.

The arithmetic average of the results of three parallel determinations was taken as the final result.

The preparation of intercalated graphite compound (ISG) was carried out according to a known method. GAK-2 graphite powder with a total weight of 400 g was loaded into the anode chamber of the electrolyzer. The cell contained 800 ml of 50% sulfuric acid. In this electrolyte was performed

anodic oxidation of graphite with a specific consumption of the amount of 504 Cl / g of graphite. After changing the color of graphite to blue, which indicated the production of graphite bisulfate of approximate composition C24 + HS04X

xnH2S04, the electrolyzer was de-energized, the ISH was washed with water to pH 4.

For all specific examples, portions of the intercalated graphite compound obtained as described above were taken.

The invention is illustrated by examples of a specific embodiment, and the results of determining the sulfur content in the TWG are given in the table.

Example 1. 40 g of ISH is added to 40 g.

ml of 10% aqueous solution of ammonia and periodically stirred for 15 minutes Then the product was washed with water, dried and subjected to heat treatment at 1000 ° C. The bulk density of the obtained TEG was 0.0065 g / cm3, the sulfur content was 0.00085 wt.%.

In the other examples, the procedure was as described in Example 1, the concentration of the aqueous ammonia solution and the duration of the treatment vary. When the concentration of the aqueous solution of ammonia is less than 5 wt.% (Example 3), the goal is not achieved, the sulfur content is the same as in the prototype.

When using a 15% ammonia solution (example 4), the sulfur content remains almost unchanged compared to the prototype, and at a solution concentration of 20 wt.% (Example 5), the sulfur content is even higher than that of the prototype,

It was established by additional experiments that an increase in the temperature of an aqueous solution of ammonia does not affect the achievement of the set goal, therefore, it is not an essential feature.

If the processing time is lower than the claimed interval (Example 8), then the goal is not achieved. With a treatment time of more than 20 minutes (Examples 9 and 10), the sulfur content in the TWG does not decrease. Therefore, to increase the processing time over 20 minutes is impractical.

Thus, the inventive method allows to reduce the sulfur content in the TWG to 0.0008 wt.% And, accordingly, improve the consumer properties of the TWG.

Claims (1)

Invention Formula A method of producing expanded graphite, which includes purifying graphite compounds by treating graphite bisulfate with an aqueous reagent solution, washing it with water, drying and heat treating, characterized in that ammonia is used as a reagent to reduce the sulfur content and the treatment is carried out with 5-10% ammonia solution for 10-20 minutes.