RU2388686C1 - Method of obtaining metal oxides - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used to obtain highly pure metal oxides. The method involves reacting dispersed liquid droplet forms of metal compounds with an oxidising agent. To obtain lead oxide, aluminium oxide or their mixture as starting compounds, an alkyl compound - tetraethyl lead, alcoholate compound - aluminum isopropylate or their mixture are used respectively, where the said compounds are mixed with an organic diluent - isooctane. The oxidising agent used is a gas mixture of oxygen and ozone. The reaction is carried out at temperature 1500 - 2300°C. The amount of oxidising agent is not more than 4 times greater than the stoichiometric amount and ozone content of the gaseous mixture ranges from 25 to 90 vol %.

EFFECT: invention increases degree of purity of synthesised metal oxides, simplifies their synthesis method and increases output.

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Description

The invention relates to the field of synthesis technologies for inorganic materials, in particular to the production of metal oxides or their mixtures from liquid alkyl or alcoholate metal compounds, for example zinc oxide from dimethylzinc or aluminum oxide from aluminum isopropylate. Metal oxides are widely used in electronics as part of semiconductor, ferromagnetic and phosphor materials, they are used in fiber optics, chemical catalysis, and other branches of technology.

The material used for these purposes has high demands on purity, phase and particle size distribution, bulk density, specific surface. To obtain oxides with the necessary physicochemical properties, in particular, alkyl and alcoholate compounds of the corresponding metals or their mixtures are used, existing (at least for some time) in liquid form under normal conditions.

A known method for producing lead oxides (AC SU 828632, IPC C01G 21/02, published: BI No. 14, date of publication: 15.04.87). The method consists in oxidizing with oxygen the liquid atomized lead compound. The oxidation is carried out by burning reagents in the temperature range from 1200 to 2000 ° C.

A method is implemented, for example, by pouring 100 ml of tetraethyl lead (C ₂ H ₅ ) ₄ Pb into the installation tank with an impurity content of 10 ^-5 to 10 ^-6 % (mass). 120 l / min of oxygen are supplied through the peripheral channels of the burner. At the base of the central channel of the burner, a zone of reduced pressure is created, due to this, liquid tetraethyl lead is sucked from the tank and sprayed in a stream of oxygen. The mixture is ignited with an electric igniter. In this case, 100 ml of tetraethyl lead is burned in the reactor at 1200 ° C for 12 minutes, resulting in 100 g of a mixture of lead oxides with a particle size of 5 to 11 μm, which are captured by a filter system. The mixture of oxides is transferred either to lead red oxide by calcination in the temperature range from 500 to 600 ° C, or to lead lead by calcination in the temperature range from 680 to 800 ° C in an oxidizing atmosphere. The productivity of the process is 500 g / hour. The yield of oxides reaches 100% of the theoretical yield (apparently, after calcination).

The disadvantages of this method are:

- contamination of the final product with soot, the occurrence and existence of which is determined by the relatively low (under the conditions of the above example) value of the average weight of the flame of the oxygen burner, which realizes (at the flame boundary under conditions of a slight lack of oxygen) at temperatures below about 350 ° C elemental carbon formation;

- the complexity of the method due to the presence of additional technological operations - calcination of a mixture of lead oxides in an oxidizing environment in the temperature range from 500 to 800 ° C, providing soot burning and oxidation of metallic lead;

- the need to use (in order to reduce the content of impurities) a practically nine-fold excess of the oxidizing agent (oxygen - α _ok > 4) supplied to the burner (in the synthesis of lead oxides with a high degree of oxidation), which reduces the weighted average flame temperature to 1200 ° C and reduces productivity method by reducing the concentration of tetraethyl lead in the flame torch. Moreover, α _ok = v / v ₀ , where v is the actually supplied number of moles

oxidizer, av ₀ is the stoichiometric coefficient for oxygen, which ensures the complete oxidation of the fuel (C, H ₂ , CO) supplied to the burner to carbon dioxide and water;

- the practical impossibility of synthesizing the product in one stage with a condensed impurity content of 0.01 ppm even under the conditions of a weighted average flame temperature in the region of 2000 ° C by reducing the oxygen excess coefficient to values close to unity. The reason for this effect is hidden in the lack of chemical activity of oxygen.

A known method of producing zinc oxide by oxidation of dimethylzinc or diethylzinc (patent RU 2154027 C1, IPC C01G 9/02, published: BI No. 22, publication date: 10.08.2000). The method consists in diluting dimethylzinc or diethylzinc with an organic diluent in a ratio of 1: (1: 4) by volume before spraying them in an oxygen medium to produce an aerosol and burning it.

The method is as follows: in a supply tank, a solution of dimethylzinc or diethylzinc in hexane, heptane or octane is prepared in a ratio from the interval 1: (1-4), that is, from 1: 1 to 1: 4. The mixture is prepared in an inert gas atmosphere, eliminating the contact of alkyl compounds with oxygen and air moisture. The mixture from the supply tank is fed to a multi-channel nozzle of the burner introduced into the tubular reactor. The nozzle sprays the feed mixture in an oxygen medium to an aerosol state. The aerosol mixture in the reactor ignites from the igniter introduced into it and burns with the formation of finely dispersed zinc oxide, which is captured at the outlet by a filter system, and gaseous products of combustion (carbon dioxide and water vapor) are discharged into the atmosphere.

This known method, which consists in the oxidation by oxygen of dimethylzinc or diethylzinc, is selected as a prototype of the present invention as the closest to it in purpose, technical essence and the achieved effect.

The disadvantages of the prototype are:

- the final product is contaminated with soot micro-impurities and even (in the general case) with a pure metal of an alkyl-forming or alcohol-forming compound, the thermodynamics of the appearance and existence of which are determined on the whole by the value of the oxidizer excess coefficient α _ok , the relatively low average weight of the flame of the oxygen burner and its fuzziness. The blurriness of the flame during the synthesis of zinc oxide implements at its borders quite wide spatial areas with temperatures below 1000 ° C. In these areas, a certain amount of dimethylzinc or diethylzinc diluted with liquid fuel dies with the appearance of a visible amount of condensed impurity polluting the final product;

- the presence of an additional technological operation (to obtain high-purity zinc oxide with an impurity content of up to 0.01 ppm) - heat treatment of zinc oxide in oxygen, which ensures the burning of soot and the oxidation of metal (zinc) when it appears. An additional process operation complicates the process;

- the need to use the coefficient of excess of the oxidizing agent α _ok > 4 (in order to reduce the content of impurities) by burning it in an oxygen burner, which increases oxygen consumption, reduces the temperature of the flame, reduces the productivity of the method.

The main disadvantages of the prototype are characterized by almost all technological processes associated with the interaction of fuel and oxygen by burning them in a burner (regardless of the method for further quenching of the condensed products of this interaction). The disadvantages are associated with relatively small values of the average weighted temperatures of the flame and its transverse temperature gradient, which mainly depend on the relative concentration and chemical activity of oxygen. The application of the additional heat treatment operation of condensed synthesis products or its absence is associated with specific purity requirements for the content of impurities in the final high-purity product.

The task of the invention is to increase the purity of the synthesized metal oxides or their mixtures while simplifying the method and increasing its productivity.

Using the present invention, the following technical result is achieved: the content in the condensed products of the synthesis of elemental carbon or pure metal of alkyl or alcoholate compounds does not exceed 0.01 ppm for each of them, while the synthesis is carried out in one stage (i.e., the operation of heat treatment of condensed synthesis products in an oxidizing environment). At the same time, the productivity of the process increases.

This problem is solved, and the technical result is achieved by the fact that in the method of producing metal oxides by the interaction of dispersed liquid-drop forms of metal compounds with an oxidizing reagent according to the invention, for the production of lead oxide, aluminum oxide or mixtures thereof, respectively, an alkyl compound — tetraethyl lead, alcoholate — is used as metal compounds - aluminum isopropylate or a mixture thereof, which is mixed with an organic diluent, isooctane, as an oxidizing agent and a gas mixture of oxygen with ozone is used, the interaction is carried out in the temperature range from 1500 to 2300 ° C, while the amount of oxidizing reagent exceeds the stoichiometric not more than 4 times, and the ozone content in the gas mixture is from 25 to 90 vol.%.

The simplification of the process is achieved by the fact that in the known method for producing metal oxide (zinc) by reacting alkyl and (or) alcoholate metal compounds or mixtures thereof (dimethylzinc or diethylzinc) with an oxidizing reagent, a gas mixture of oxygen with ozone is used as the latter. This reagent converts dimethylzinc or diethylzinc to high-purity zinc oxide, and, for example, aluminum isopropylate and tetraethyl lead to high-purity aluminum and lead oxides in a single stage according to the reactions, respectively:

Combustion reactions of diluents, for example, isooctane in oxygen and ozone:

These reactions are accompanied by the release of a significant amount of heat, which allows them to be realized in the combustion mode. From reactions 1-8, it can be seen that, in comparison with the prototype, the introduction of ozone into the oxidizing reagent noticeably increases the heat balance of the flame plume. The consequences of this are an increase in the weighted average temperature of the flame plume, an increase in the temperature gradient in its cross section (leading to a decrease in the degree of blurriness of the flame), ceteris paribus, its geometric dimensions (core diameter and total flame length) are reduced. Due to the greater reactivity of ozone, the temperature of the flame core increases. Theoretical estimates show that the use of pure ozone (in reactions 5–8) in comparison with oxygen (in reactions 1–4) raises the maximum attainable flame temperatures (adiabatic conditions) by an average of about 25%. Moreover, due to the greater reactivity of ozone, reaction rates increase. Under these conditions, while the coefficient of excess of the oxidizing agent decreases, the degree of blurriness of the flame plume narrows. The number of alkyl or alcoholate compounds falling into the narrowed (in comparison with the prototype) region of the flame, in which the conditions for the synthesis of elemental carbon or pure metal of the corresponding compound can be realized, is reduced, which realizes the achievement of the claimed technical result - synthesis of high-purity metal oxides or their mixtures in one stage.

To intensify the combustion process, it is carried out by spraying liquid alkyl and alcoholate metal compounds or their mixtures in a gaseous mixture of oxygen with ozone. Moreover, the amount of oxidizing reagent exceeds the stoichiometric not more than 4 times, which increases the productivity of the method by increasing the mass flow rate of liquid alkyl and alcoholate metal compounds or their mixtures in the central channel of the oxygen-ozone burner, which, in turn, is controlled by the value of the reduced pressure at its base. The mass flow rate of the liquid increases with a decrease in pressure in the base zone of the central channel of the burner, which decreases with increasing flame temperature and the rate of outflow of the oxidizing reagent. In this case, the flame temperature increases with decreasing oxidizer excess coefficient α _approx .

An increase in the excess coefficient of the oxidizing reagent more than 4 leads to a noticeable decrease in the maximum possible temperature of the oxygen-ozone flame (for the case of the maximum ozone content in the oxidizing reagent) of the burner due to heating of its excess without significantly affecting the quality of the synthesized metal oxides (the amount of condensed impurities remains at the level 0.01 ppm), the performance of the process decreases. Maintaining the value of the coefficient of excess oxidizer α _ok ≤1 has neither economic nor technical meaning.

The use of the ozone content in the gas mixture of the oxidizing reagent in the range from 25 to 90 vol.% Above is limited by the current level of technology - a microwave generator of 100% high purity ozone with the required performance is technically difficult to build because of the high chemical activity of ozone (converted to oxygen before use ) or because of economic inexpediency.

The lower ozone limit is dictated by the required degree of a possible increase in the minimum value of the average weighted temperature of the flame plume (providing an impurity content of not higher than 0.01 ppm for individual metal alkyl and alcoholate compounds), which is realized with a minimum oxidant excess ratio close to unity.

Maintaining the weighted average temperature of the torch flame of the burner above about 2300 ° C (with a minimum coefficient of excess oxidizing agent close to unity) even with the use of pure ozone and the absence of organic diluents is difficult from the practical side due to heat dissipation in the external environment.

Supporting the weighted average temperature of the torch of the flame of the burner not lower than 1500 ° C enables the combustion of almost all known liquid-drop forms of mixtures of alkyl and (or) alcoholate metal compounds or their mixtures without precipitation of hardware-visible amounts of condensable impurities.

The introduction into the composition of liquid droplet forms of metal alkyl and alcohol compounds or their mixtures of organic diluents that do not noticeably lower or increase their combustion temperature (balanced by the calorific value, see reactions 9 and 10) provides such a technical effect as reducing the concentration of metal compounds in the flare flame, and hence their content in narrower (in comparison with the prototype) areas in which the synthesis of condensable impurities is still possible, which ensures the solution of the problem and is achieved e technical result.

For the practical implementation of the method, the installation shown in the patent taken as a prototype (patent RU 2154027 C1, IPC C01G 9/02, published: BI No. 22, publication date: 10.08.2000) is taken as the basis. In contrast to the prototype, an external source of gaseous ozone of excess pressure is additionally connected to the oxygen channel of the burner with the possibility of fine-tuning its flow rate in order to supply an oxygen mixture with ozone of the appropriate amount and concentration to the burner.

Example 1

100 ml of tetraethyl lead (C ₂ H ₅ ) ₄ Pb with an impurity content of 10 ⁻⁵ to 10 ⁻⁶ wt.% Are poured into the supply capacity of the installation. About 95 l / min of a gas mixture of oxygen and ozone with a volume content of ozone of 27% is supplied through the peripheral channels of the burner. At the base of the central channel of the burner, a zone of reduced pressure is created, due to this, liquid tetraethyl lead is sucked from the supply tank and sprayed in the stream of the oxidizing reagent with an excess coefficient α _ok ≈ 3.7. The mixture is ignited with an electric igniter. In this case, 100 ml (C ₂ H ₅ ) ₄ Pb burns in the reactor at a weighted average flame temperature of 1700 ° C for 5.5 minutes, resulting in approximately 122 g of fine crystalline lead oxide with a particle size of from 0.5 to 4, 5 microns, which are captured by a filter system.

The productivity of the process is 1331 g / hour. The yield of lead oxide reaches 100% of the theoretical yield. Elemental carbon and metallic lead are not detected by hardware, i.e., are at a level less than 0.01 ppm.

Example 2

A high-purity mixture of the following composition is prepared in the unit’s supply tank: 100 ml of tetraethyl lead (C ₂ H ₅ ) ₄ Pb are mixed with 100 ml of aluminum isopropylate (C ₃ H ₇ O-i) ₃ Al and 200 ml of isooctane (trimethylpentane). The preparation of the mixture is carried out in an inert gas atmosphere, excluding its contact with oxygen and air moisture.

135 l / min of a gas mixture of oxygen with ozone with a volume content of ozone of 80% is supplied through the peripheral channels of the burner. At the base of the central channel of the burner, a zone of reduced pressure is created, due to this, the prepared liquid mixture is sucked from the supply tank and sprayed in the stream of the oxidizing reagent with an excess coefficient α _ok ≈2. The mixture is ignited with an electric igniter. In this case, 400 ml of the mixture burns in the reactor at a weighted average flame temperature of 2200 ° C for 5.2 minutes, resulting in approximately 148 g of a mechanical mixture of fine crystalline lead oxide and α-alumina with a particle size of 0.25 to 2, 5 microns, which are captured by a filter system.

The performance of the process by the total mass of metal oxides is 1707 g / h. The yield of lead oxide and corundum reaches 100% of the theoretical yield. Elemental carbon, metallic lead, and aluminum are not detected by hardware, i.e., are at a level less than 0.01 ppm.

Example 3

High purity 100 ml of aluminum isopropylate is mixed with 100 ml of isooctane in the supply capacity of the installation. 85 l / min of a gas mixture of oxygen with ozone with a volume content of ozone of 80% is supplied through the peripheral channels of the burner. At the base of the central channel of the burner, a zone of reduced pressure is created, due to this, the prepared mixture is sprayed in the stream of the oxidizing reagent with an excess coefficient α _ok ≈2. The mixture is ignited with an electric igniter. In this case, 200 ml of the mixture burns in the reactor at a weighted average flame temperature of 2100 ° C for 5.5 minutes, resulting in approximately 26 g of α-alumina with a particle size of 0.25 to 1.7 μm, which are captured by the system filters.

The productivity of the process is 284 g / hour. The yield of alumina reaches 100% of the theoretical yield. Elemental carbon and metallic aluminum are not detected by hardware.

In addition to the simultaneous synthesis of mechanical mixtures of several metal oxides, the invention fundamentally allows the synthesis of fine crystalline forms of individual complex oxides of various sizes under certain specific conditions.

Claims (1)

A method of producing metal oxides by reacting dispersed liquid-drop forms of metal compounds with an oxidizing reagent, characterized in that for the production of lead oxide, aluminum oxide or mixtures thereof, the metal compounds are, respectively, an alkyl compound - tetraethyl lead, an alcoholate compound - aluminum isopropylate, or a mixture thereof which are mixed with an organic diluent - isooctane, a gas mixture of oxygen with ozone is used as an oxidizing reagent, the interaction is carried out in the temperature range from 1500 to 2300 ° C, while the amount of oxidizing reagent exceeds the stoichiometric not more than 4 times, and the ozone content in the gas mixture is from 25 to 90 vol.%.