Preparation of high purity thermoexfoliated graphite by electrochemical method

Carbon materials with a graphite-like structure have the highest thermal stability in a non-oxidizing environment, sufficient structural strength, are easily processed, etc., and therefore they are widely used in various fields of technology. There are two methods of obtaining such materials: pyrolysis or carbonization of hydrocarbons and processing of natural graphite, so-called “thermo-expanded graphite technology” (TRG), which consists of successive reactions of intercalation, hydrolysis and heat treatment of natural graphite, leads to modification of the surface of TRG particles and provides the ability to their pressing and rolling on rollers to form dense materials. Natural graphite with a carbon content of 99.0–99.5 % by mass is used for the production of TRG, from which sealing materials are obtained for the equipment of enterprises of general industrial purpose: the fuel and energy complex, the petrochemical industry, utilities, etc. In the equipment of nuclear power plants, materials from TRG, of so-called “atomic purity”, are used, in which the carbon content must be at least 99.85 % by mass. Therefore, the purpose of the work is to obtain thermally expanded graphite of high purity by the method of electrochemical oxidation and further purification of flotation-enriched graphite. The production process took place in two stages: electrochemical intercalation of graphite with concentrated sulfuric acid followed by hydrolysis, and chemical further purification using ammonium bifluoride and Trilon B as cleaning reagents. Combining into one process of electrochemical oxidation of graphite and its further purification allows obtaining high purity TRG with a carbon content of 99.94–99.96 % by mass. In order to find the regularities of the interaction of Trilon B with metal ions included in the composition of graphite impurities, quantum chemical modeling of these processes was carried out. The energy effect of the interaction of the iron (III) cation is greater in absolute value (–969.1 kJ/mol) than for the case with the aluminum cation (–748.3 kJ/mol) both in the aqueous medium and in the adsorbed state on the surface of the graphene plane (–816.9 for Fe3+ and –621.2 kJ/mol for Al3+). Regardless of the nature of the cation, its interaction with Trilon B is thermodynamically more likely in an aqueous solution than in an adsorbed state on the surface of a graphene-like plane.