RU2019502C1 - Method for removal of impurity of non-diamond carbon and device for its realization - Google Patents

Abstract

FIELD: production of powder of synthetic diamonds. SUBSTANCE: ozone- air mixture for oxidizing of graphite is passed through charge of artificial diamonds, in addition to that charge is heated till 120-400 C. Device except container for charge and heater has generator of ozone-air mixture and additional container for charge coupled with the first container and having clear opening for gas which is bigger that the first container. Device is provided additionally with heater for additional container. EFFECT: simplified process and ecological clean owing to preparation and utilization of ozone as graphite oxidant in single technological process. 3 cl, 1 dwg

Description

 The invention relates to chemical technology and can be used in enterprises manufacturing synthetic diamond powders.

A method is known diamond separation from the diamond-bearing material of non-diamond carbon being mixed with 40-60% aqueous solution of nitrite or nitrate of an alkali metal chlorate (oxidizing agent) and the subsequent heat treatment at a temperature of 500-550 ^{° C} for 1-1.5 hours.

 The diamond-containing material is loaded into a stainless steel pan. Then the mixture is moistened with an aqueous solution of an oxidizing agent for impregnation of porous graphite, mixed and leveled with a layer with a height of not more than 5-10 mm.

Thereafter, baking with diamond-bearing mixture and oxidant is placed in a preheated to 500-550 ^{° C} air atmosphere furnace and heated for several hours. At the end of the process, the baking tray with diamonds is removed from the oven and cooled. Then carry out the dissolution of the residues of the oxidizing agent with water, washing and drying the selected diamonds.

 Hence, a device that implements the known method comprises a vessel for placing diamond-containing material impregnated with an oxidizing agent solution, a vessel for preparing an oxidizing agent solution, a heater and a device for washing the separated diamonds from the oxidizing agent residues.

 The disadvantage of this method is the need for disposal of the vapor of the oxidizing agent from the furnace and the residual oxidizing agent when washing the isolated diamonds.

Furthermore, the required high temperature heat treatment limits the applicability of the method in the case of, e.g., batch treatment comprising ultrafine diamond fraction, since they already start to oxidize at 400 ° ^C.

 The aim of the invention, both for the method and the device for its implementation, is to simplify the process of removing non-diamond carbon from a mixture of artificial diamonds and increase its environmental cleanliness.

This object is achieved in that, in a method for removing impurities from a blend of non-diamond carbon oxidation artificial diamond oxidation is performed by passing ozone through the charge-air mixture while heating the charge to 120-400 ^{° C} until complete burnout of non-diamond carbon.

 A device for implementing the proposed method, containing a vessel for placing a charge and a heater, is equipped with an ozone-air mixture generator and an additional vessel for placing a mixture connected to the first vessel and having a gas passage larger than the first vessel. In addition, the device is equipped with an additional vessel heater.

 When blowing the ozone-air mixture through the mixture, a certain amount of it is carried away by the gas stream and carried out of the reaction zone. Therefore, a filter was introduced into the device to catch the blown particles, made in the form of a vessel filled with the same charge, but the gas passage through the gas section of this vessel is larger than the passage section of the reaction vessel vessel so that the gas flow in the filter cross section is laminar and does not lead to the removal of charge particles from the filter.

 As graphite burns out in the reaction chamber of the first vessel, the amount of residual ozone at the inlet of the filter increases. Therefore, it is advisable to heat the filter mixture in order to ensure the complete utilization of residual ozone from the reaction chamber of the first vessel using the oxidizing process in the filter.

 Heating the charge activates the oxidation reaction, which significantly (tens to thousands of times) accelerates this process. However, the heating temperature of the charge should be set below the temperature that provides the activation energy of diamond particles, which leads to the selective oxidation of graphite, the activation energy of which is less. Heating at the same time provides a more efficient utilization of ozone, since its decomposition and conversion into oxygen depends on temperature and accelerates with its growth.

 The oxidizing agent (ozone) used can be prepared using known devices from the air and disposed of in a single technological process for removing graphite from a charge without using additional materials and substances. And after graphite removal, no additional operation is required to remove the oxidizing agent from the charge.

 The present invention allows for any degree of dispersion of the diamond charge to establish the upper limit of its heating, at which the diamond is not yet oxidized, but graphite burns out.

 The invention is illustrated in figure 1, which shows a schematic mutual arrangement of elements of a device that implements the proposed method.

 The vessel 1, filled with a charge of 2 artificial diamonds, is placed in the heat field of the heater 3. An ozone-air mixture from the ozonizer 4 is supplied to the inlet of the vessel 1. The sensor of the temperature meter 5 is located in the mass of the charge and allows you to control the temperature of its heating.

 The output of the vessel 1 is connected to the input of the vessel 6 filled with the charge 7. The vessel 6 is also located in the thermal field of the heater 8, and the sensor of the temperature meter 9 is located in the mass of the charge.

 When passing through the charge of the vessel 1 of the ozone-air mixture, graphite is oxidized and its mixing. Oxidation products (carbon dioxide), residual ozone and a certain amount of charge are carried out by a gas stream from vessel 1 to vessel 6.

 Since the cross section of the vessel 6 is larger than the vessel 1, the gas flow turbulence decreases, it becomes laminar and passes through the charge 9. In this case, the particles of the charge removed from the vessel 1 are delayed by the microporous filter structure, and the residual ozone either completely reacts with graphite, or, decomposing, turns into oxygen.

 The gas stream from the vessel 6 through the outlet opens to the atmosphere.

 A criterion for the end of the process can be, for example, a change in the color of the charge in vessel 1 from black (in the initial state, diamond particles are shrouded by particles of graphite) to gray (color of particles of synthetic diamond).

 PRI me R. The mixture of ultrafine diamonds (UDD), dried and crushed to lumps, the size of which does not exceed 1 mm, is loaded into vessels 1 and 6. The amount of charge loaded into vessel 1 is pre-weighed.

 Vessel 6 is loaded with the amount of UDD charge not less than vessel 1. The mass of the charge in vessel 6 can be used repeatedly and after some number of cycles of use can be sent to vessel 1.

 Previously, by any known method, the percentage of graphite in the UDD mixture should be measured.

Then the charge in the vessels are heated to 120-250 ^{° C} and blown therethrough nainayut ozone-air mixture, maintaining the temperature.

 The upper temperature value is limited by the permissible degree of burnout of diamond-like fractions of the charge, and the lower one is limited by the sluggishness of the reaction flow or by the need to burn out impurities in the mixture of plastic masses.

 The purge time depends on the amount of charge, the percentage of graphite in it, the concentration of ozone in the mixture and the speed of the ozone-air flow (selected experimentally and laid the foundation for the technology for a specific composition of the charge, depending on the characteristics of the equipment).

 The ozone concentration and the ozone-air flow rate are the structural parameters of the device, therefore, the requirements for them are more convenient to characterize the amount of ozone required for the implementation of the cleaning process. For example, we have 1 kg of UDD blend with 10% graphite content (i.e. 100 g).

= 800 (г) ,
100 - Х где 12 - атомная масса графита, участвующего в реакции;
96 - атомная масса озона участвующего в реакции;
100 - количество графита, которое необходимо окислить, в граммах;
Х - требуемое количество озона, в граммах.From the reaction and interaction of ozone with graphite,
2О ₃ + С = СО ₂ + 2О ₂ ,
it is seen that for the oxidation of one graphite atom it is necessary to have two ozone molecules at the output of the ozonizer. From here, on the basis of the known relations, we calculate the amount of ozone necessary for the oxidation of 100 g of graphite:
12 - 96 X =

= 800 (g),
100 - X where 12 is the atomic mass of graphite involved in the reaction;
96 - atomic mass of ozone involved in the reaction;
100 - the amount of graphite to be oxidized, in grams;
X is the required amount of ozone, in grams.

 Assume that the ozone concentration at the ozonizer outlet is 20 g / m3 (this value is in the zone of optimal energy efficiency for the production of ozone from the air). Then 800 (g) must be passed through the UDD charge: 20 (g / cu.m) = 40 (cu.m) of the ozone-air mixture. At a speed of passing it through a charge of 0.5-1 cubic meters per hour (such a speed seems extremely reasonable, since an increase in the flow rate complicates the task of filtering UDD particles carried away from the reaction chamber), the whole process will take 80-40 hours.

The total energy costs for ozone production in modern ozonizers are approximately 20-25 kWh / kg. Hence, the cost of energy costs for the production of ozone for the oxidation of 100 g of graphite (at a price of 4 kopecks per 1 kWh of electricity) will be
20 (kWh / kg) 0.8 (kg) 4 (kop / kWh) =
= 64 (cop),
In a real process, it is necessary to take into account that part of ozone is destroyed with conversion to oxygen without participation in the oxidation of graphite, so the required amount of ozone will be greater. The increase coefficient depends on the specific design characteristics of the device, in particular on the length of the pipeline connecting the ozonizer and the reaction chamber, its temperature, etc., and the required degree of purification.

 The following can be said about the degree of purification of the UDD charge from graphite.

 As indicated in the prototype, the effective removal of graphite is associated with the effective impregnation of graphite with an oxidizing agent throughout the volume (we are talking about ensuring the access of an oxidizing agent to each graphite molecule). When using an aqueous solution of an oxidizing agent, the residual amount of graphite does not exceed 0.4%. The “impregnating” ability of the oxidizing agent in the gas phase is significantly higher than in the liquid phase, therefore, the degree of purification of the charge should be no worse than by the prototype method.

Claims (3)

1. The method of removing impurities of non-diamond carbon from a mixture of artificial diamonds by oxidation, characterized in that, in order to simplify the process and increase its environmental purity, the oxidation is carried out by passing an ozone-air mixture through the mixture with simultaneous heating to 120 - 400 ^o C until the non-diamond carbon is completely burned out.  2. A device for removing non-diamond carbon impurities from a charge of artificial diamonds, containing a vessel for placing the charge and a heater, characterized in that, in order to simplify the process and increase its environmental cleanliness, it is equipped with an ozone-air mixture generator and an additional vessel for placing the charge connected to the first vessel and having a gas section larger than the first vessel.  3. The device according to claim 2, characterized in that it is equipped with a heater for an additional vessel.

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