RU2182556C1 - Method of obtaining nitrogen trifluoride - Google Patents

Abstract

FIELD: inorganic chemistry; method of obtaining nitrogen trifluoride. SUBSTANCE: nitrogen trifluoride is used chemical industry as fluorinating agent and as oxidant for fuel. In electronic industry, it is used as gas in dry etching processes which leaves no sediment; it is also used in vapor-phase settling chemical apparatus. Proposed method consists in fluorination of ammonium polyfluoride salt NH₄F•xHF, where "x" is more than 0-1.3 and may be equal to 1.3; starting salt is used in mixture with sorbent sorbing hydrogen fluoride formed in the course of synthesis; sorbent is just fluoride of metals MeF, where Me is metal of group I of periodic Table, preferably NaF, KF and LF. RbF and CsF may be also used because there is little point in using it from the economical standpoint. Process of obtaining nitrogen trifluoride is performed at temperature of from 20 to 125 C. EFFECT: simplification of process; complete use of starting salt NH₄F•xHF; possibility of withdrawing hydrogen fluoride at simultaneous removal of heat. 5 cl, 1 dwg, 1 tbl, 1 ex

Description

 The invention relates to the field of inorganic chemistry, and in particular to methods for producing nitrogen trifluoride.

 Nitrogen trifluoride is used in the chemical industry as a fluorinating agent and as an oxidizing agent for fuel. In the electronics industry, it is used in dry etching processes as a non-sedimenting gas; its use is also known in chemical vapor deposition apparatuses.

There are 3 main technologies for producing nitrogen trifluoride:
1. Electrolysis of the melt of ammonium bifluoride [US Pat. US 3235474, CL 204/63, op. 10/02/1961].

2. Liquid phase fluorination of a melt of ammonium bifluoride at 130-160 ^o C and 0.2-0.4 MPa [US Pat. USA 4091091, cl. 423/406, op. 05/23/1978].

 3. Fluorination of solid complex ammonium fluorides and metals. The invention relates to this area.

A known method of fluorination of solid complex ammonium fluorides and metals of the General formula (NH ₄ ) _x MF _y and (NH ₄ ) _x MM ¹ F _y , where x = 1-3, y = 4-7, M = Fe, Al, Ti and other metals, M ¹ = Li, Na, K [US Pat. USA 4543242, C 01 B 21 / 83B, 09.24.1985].

 The process can be organized in a continuous mode, with the supply of fluorine diluted with an inert gas (nitrogen, argon). Complex ammonium fluorides are used in the form of particles of a certain size, which ensures a stable reaction. The fluorine reaction yield reaches 80-85%.

 The disadvantage of this method is the high cost of the original complex ammonium fluorides and metals, as well as the need for disposal of the resulting metal fluorides.

The closest technical solution is the method [US Pat. Japan 3232710, cl. C 01 B 21/083, application. 02/06/1990, op. 10.16.1991]. According to this method, nitrogen trifluoride is obtained by the reaction of fluorine with a mixture of metal fluorides and ammonium salts in a mass ratio of 2: 1. The reaction is carried out at a temperature of 50-450 ^o With dilution with fluorine nitrogen supplied to the reactor.

As the metal fluoride in this invention, for example, fluorides K, Na, Cu, Ca, Zn, Al, Sn, Pb, Mn, Ni, Co, Fe and others can be used, however, the best result is achieved using NaF, CaF ₂ , FeF ₃ .

As the inorganic ammonium salt in the present invention, (NH ₄ ) ₂ SO ₄ , (NH ₄ ) ₂ CO ₂ , NH ₄ NO ₂ , NH ₄ F, NH ₄ CI, NH ₄ Br, NH ₄ I and others can be used.

 The ratio of the components of the metal fluoride and inorganic ammonium salt can be arbitrary, however, it is desirable that the reaction be carried out with an excess of metal fluoride, the weight ratio of metal fluoride and inorganic ammonium salt was approximately 2: 1.

The reaction temperature may be close to or above room temperature. From the point of view of the reaction rate, it is desirable that the temperature is more than 50 ^° C. To prevent decomposition of the resulting NF _3, it is desirable that the temperature is less than 450 ^° C. Taking into account a number of production factors (reaction rate, heat consumption and others), it is desirable so that the reaction temperature is 100 ~ 200 ^o C.

 A disadvantage of the production method is the formation of liquid ammonium polyfluorides, which are obtained as a result of the interaction of ammonium salts with hydrogen fluoride formed as a by-product. The formation of a liquid phase can lead to clogging of the reactor and increased corrosion of the equipment. High temperatures of the process sharply increase the contribution of side reactions occurring with the formation of nitrogen, which significantly reduces the yield of the target product - nitrogen trifluoride.

The challenge facing the invention is the development of a method that allows full use of the starting salt NH ₄ F • xHF, to remove the resulting hydrogen fluoride, while removing heat of the reaction.

 The solution to this problem allows us to simplify the production process of nitrogen trifluoride, to achieve high efficiency of its production and greatly facilitates the solution of the problem of recycling by-products.

This problem is solved by reacting an acid salt of ammonium polyfluoride of the formula NH ₄ F • xHF in the solid phase, where x is greater than 0 to 1.3, and x may be 1.3. The starting salt is used in a mixture with a sorbent capable of sorbing hydrogen fluoride resulting from the synthesis. The sorbent is a metal fluoride of the formula MeF, where Me is a metal of group I of the Periodic table, preferably NaF, KF, LiF. RbF and CsF can also be used, but their use is not economically feasible. The process of obtaining nitrogen trifluoride is carried out at 20 - 125 ^o With and the mass ratio of the sorbent: NH ₄ F • xHF from 2 to 100.

 In the composition of the solid salt of ammonium polyfluoride x can take values from a value greater than 0 to a value less than or equal to 1.3.

Upon fluorination of compounds of the formula NH ₄ F • xHF in the solid phase per 1 mol of the desired reaction product NF ₃ , (4 + х) mol of HF is formed.

The resulting hydrogen fluoride is sorbed by metal fluorides (mainly Group I metals of the periodic table, for example, LiF, NaF, KF), and polyhydrofluorides of the corresponding metals are formed. Sorption is carried out to a molar ratio of hydrogen fluoride: metal fluoride from 1: 1 to 1: 100, using a specially prepared metal fluoride. Before the metal fluoride is fed into the reactor, it is activated by heating to a temperature of about 350 ^{° C.} , removing volatile impurities and moisture from it.

 Metal fluoride can be used in powder, tablet or granular form. The size of the particles, granules or tablets is not critical for the reaction.

Such metal fluoride allows multiple cycles of sorption-desorption of hydrogen fluoride. To carry out desorption, the saturated sorbent is placed in the stripper and the temperature is gradually raised at a rate of 25-100 ^o C / h, eventually bringing it to 350 ^o C. A very slow rise in temperature is not technologically feasible, and a quick one can destroy the structure of the pelletized or granular material. Hydrogen fluoride formed as a result of desorption can be used in the synthesis of fluorine compounds.

 Fluorine can be fed into the reaction zone both with diluted inert gas (for example, nitrogen, argon or helium), and without dilution.

 The process is carried out on the installation shown in the drawing.

 The installation consists of a mixer 1, a reactor 2, a phase separator 3 and a stripper 4.

In the mixer 1 serves the initial salt NH ₄ F • xHF, where x is more than 0 to 1.3, and x may be equal to 1.3, and pre-activated metal fluoride of group I. The reagents are mixed in a predetermined ratio to a homogeneous mass, and from the mixer are sent to the reactor 2 with a diameter of 40 mm, a length of 500 mm, made of nickel. Fluorine gas or a mixture of fluorine with an inert gas is fed into this reactor. In the reactor at 20 - 125 ^o With the process of fluorination. From the reactor, the reaction mixture is fed to phase separator 3, where gaseous and solid products are separated. Gaseous products are collected in the receiver, then from there they are sent to the separation stage, where the target product is separated (not shown in the diagram).

Solid products, mainly metal fluorides adsorbing HF, are sent to stripper 4, where they are desorbed and / or activated at 350 ^° C. The separated hydrogen fluoride is condensed and collected in a receiver (not shown), and the metal fluorides are returned to the mixing stage .

 The process can be organized in both periodic and continuous mode. The examples given illustrate but do not limit the scope of the present invention.

 The invention is illustrated by the examples presented in the table.

Example 1. Into mixer 1, 70 g of NH ₄ F • xHF are fed, where x = 0.01, and 700 g of NaF. Before this, sodium fluoride, not used in the process, is pre-activated in stripper 4, raising the temperature by 25 ^o C per hour. Bringing the temperature to 350 ^o With, maintain the sodium fluoride at this temperature for 5 hours. These reagents are fed to the mixer in the ratio of NaF: NH ₄ F • xHF = 10, and mix them to a homogeneous mass. The particle size of the solid reagents was about 200 μm.

Solid reactants are fed into the reactor 2 from the mixer at a speed of 385 g / h, and gaseous fluorine at a speed of 110 g / h. The temperature in the reactor is maintained at 80 ^° C. The resulting reaction mixture from the reactor is taken out to phase separator 3, where gaseous products are separated from solids. Gaseous products are passed through a trap of acidic impurities (not shown in the diagram) and collected in a receiver.

Chromatographic analysis of gaseous products showed the following composition, vol.%: NF ₃ - 87%, N ₂ - 11.0%, other products (CF ₄ , N ₂ F ₂ , N ₂ F ₄ ) - 2.0%.

The solid phase, consisting of NH ₄ F • xHF, where x is less than or equal to 1, is fed to the HF desorption step, which is carried out at 350 ^° C. The desorption time is 30 hours. After desorption, the NaF is cooled to 20-60 ^{° C.} and sent to mixer 1. Hydrogen fluoride is condensed in a trap (not shown in the diagram) and sent to neutralization.

 In the remaining examples (2-11), the activation and desorption stages were carried out as described in example 1.

 Examples of other experiments are given in the table.

 Carrying out the process under the stated conditions allows full use of the starting salt, ammonium polyfluoride, to rationally remove hydrogen fluoride, while simultaneously removing the heat of reaction.

Claims (5)

1. A method of producing nitrogen trifluoride by fluorination of a solid phase ammonium salt, characterized in that the acid salt of ammonium polyfluoride of the formula NH ₄ F • xHF is fluorinated, where x exceeds 0 but does not exceed 1.3, and the process is carried out in the presence of a hydrogen fluoride sorbent with a sorbent mass ratio : NH ₄ F • xHF from 2 to 100 and a temperature of 20 - 125 ^o C.  2. The method according to p. 1, characterized in that as the sorbent of hydrogen fluoride use compounds of the formula MeF, where Me is a metal of group 1 of the Periodic system of elements or a mixture of these metals.  3. The method according to p. 1 or 2, characterized in that, as the sorbent, it is preferable to use NaF, LiF, KF or a mixture thereof. 4. The method according to any one of paragraphs. 1-4, characterized in that the recirculation of the sorbent after desorption of hydrogen fluoride from it at temperatures up to 350 ^o C. 5. The method according to any one of paragraphs. 1-5, characterized in that before feeding into the reactor, the sorbent is activated by stepwise heating to 350 ^o C.

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