JP3115423B2 - Method for producing fluorine compound - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrolytic fluorination method for electrochemically fluorinating an organic compound between an anode and a cathode in an electrolytic bath solution.

[0002]

BACKGROUND OF THE INVENTION The electrolytic fluorination method is well known as a method for completely fluorinating organic compounds. This method has an advantage that a completely fluorinated product corresponding to the organic compound as a raw material can be obtained by a relatively simple apparatus. On the other hand, since the cleavage and decomposition of the organic compound of the raw material are apt to occur, fluorinated by-products other than the intended fluorine compound are easily produced as by-products, and the amount of the intended fluorine compound is a raw material with respect to the amount of the intended fluorine compound obtained. A considerable excess of hydrogen fluoride had to be used. Hydrogen fluoride is relatively expensive, which has been a major economic problem.

[0003]

In view of the above problems, the present inventors have conducted various studies for the purpose of reducing the amount of hydrogen fluoride used as a raw material. As a result, the mixture of fluorinated by-products and hydrogen produced as a by-product in electrolytic fluorination can be successfully burned, and hydrogen fluoride produced by combustion does not require special purification or the like, and is used as a raw material for electrolytic fluorination. The present invention was completed by finding that it can be reused.

That is, according to the present invention, an organic compound having a carbon-hydrogen bond in a molecule is electrolytically fluorinated to obtain a desired fluorine compound, a by-product fluorinated by-product, and hydrogen. A method for producing a fluorine compound, characterized in that hydrogen fluoride produced by burning a mixture of the above is used as a raw material for electrolytic fluorination.

In the present invention, electrolytic fluorination involves dissolving or dispersing an organic compound having a carbon-hydrogen bond in a molecule in anhydrous hydrofluoric acid (a solution obtained by liquefying hydrogen fluoride at a reduced temperature). It is carried out by applying a current between the anode and the cathode.

As the organic compound having a carbon-hydrogen bond used for electrolytic fluorination, any organic compound having a hydrogen atom directly bonded to a carbon atom can be used without any particular limitation. For example, hydrocarbons such as aliphatic hydrocarbons and aromatic hydrocarbons which have hitherto been known as objects of electrolytic fluorination; linear or cyclic aliphatic primary amines, secondary amines, tertiary amines, aromatics Amines such as amines; linear or cyclic ethers such as aliphatic ethers, aromatic ethers and polyethers; linear or cyclic alcohols such as aliphatic alcohols and aromatic alcohols; phenols; linear or cyclic Carboxylic acids such as aliphatic carboxylic acids, aromatic carboxylic acids and the like, and carboxylic acid chlorides and the like derived therefrom; carboxylic acids such as acid anhydrides and esters; and derivatives thereof; ketones; aldehydes;
Examples thereof include sulfonic acid halides such as aliphatic sulfonic acid, aromatic sulfonic acid and sulfonic acid chloride derived therefrom, sulfonic acids such as esters, and derivatives thereof; and sulfur-containing compounds such as thioethers.

Among these, organic compounds having a nitrogen atom, an oxygen atom and a sulfur atom in the molecule are preferable in consideration of the solubility in hydrofluoric anhydride used in electrolytic fluorination. In addition, it is more preferable that the target perfluorinated compound is liquid and phase-separates from the electrolytic bath solution and settles. For this purpose, the number of carbon atoms of the raw material organic compound is 5 to 5. The number is preferably 40, more preferably 8 to 28.

As the hydrofluoric anhydride used in the present invention, a commercially available hydrofluoric anhydride may be used as it is, or if necessary, a known method such as electrolysis at a low current density may be performed by preliminarily removing a small amount of contained water. Used after removal by method.

[0009] Hydrofluoric anhydride or hydrogen fluoride and the above-mentioned raw material organic compound are supplied to the electrolytic cell separately or mixed, and the supply of the organic compound and hydrofluoric anhydride or hydrogen fluoride is performed. The ratio is preferably selected so that the concentration of the organic compound in the electrolytic cell is in the range of 1 to 40% by weight.

The materials of the electrodes used in the present invention include:
Known ones can be used without any limitation. Nickel or a nickel alloy is usually used as the anode, and iron, stainless steel, copper, or the like is used as the cathode in addition to nickel or its alloy. Generally, the distance between the negative and positive electrodes is preferably about 0.5 to 5 mm. In addition,
As the material of the electrolytic cell, the material of the cathode can be used as it is, and a fluorine-based resin can also be used.

The conditions for the electrolytic fluorination are appropriately selected from known ranges, but are usually employed at a temperature of -15 to 20 ° C., a current density of 0.1 to 8 A / dm ² , and a voltage between the negative and positive electrodes of 4 to 10 V. Is done. In general, it is preferable to stir or circulate the electrolytic solution or to blow an inert gas into the electrolytic solution from the viewpoint of improving the current efficiency and stabilizing the voltage between the negative electrode and the anode. In some cases, a circulation tank is provided, and the electrolytic bath solution is circulated between the tank and the electrolytic tank. The electrolytic fluorination reaction can be performed in a batch system,
In addition, a continuous system in which the concentration of the raw material organic compound or various fluorinated intermediates in the electrolytic bath is maintained in a substantially steady state while the raw material organic compound and hydrofluoric anhydride are supplied constantly or intermittently. It is also possible to do with.

In the electrolytic fluorination reaction, the target fluorine compound is usually separated from the electrolytic bath solution and settles in the electrolytic bath or the lower part of the circulation bath. Therefore, this may be extracted from the lower part of the electrolytic bath or the circulation bath to remove partially mixed hydrofluoric anhydride. If necessary, it can be purified by distillation or other known methods. Furthermore, the compound in which a trace amount of hydrogen atoms partially contaminated remains may be fluorinated by any method in order to completely fluorinate the compound.

[0013] The hydrogen gas generated at the cathode is discharged through a reflux condenser for collecting hydrogen fluoride that escapes along with the hydrogen gas. When the molecular weight of the target fluorine compound is low and the boiling point is low, the target fluorine compound is discharged from the electrolytic cell along with the hydrogen gas generated at the cathode, and thus may be collected by a low-temperature trap. Even useful fluorinated by-products, which are decomposed as by-products, can be separated and recovered from hydrogen gas by a low-temperature trap.

A feature of the present invention resides in that hydrogen fluoride produced by burning a mixture of hydrogen and a fluorinated by-product by-produced by electrolytic fluorination is used as a raw material for electrolytic fluorination. As a method for recovering hydrogen fluoride from fluorinated by-products, the present inventors have proposed a reduction reaction using coexisting hydrogen gas, a hydrolysis reaction performed by supplying water and heating, and supplying oxygen. Then, a combustion reaction for reacting hydrogen and oxygen, an ultraviolet treatment method, a plasma treatment method and the like were examined. In addition, the recovery of fluorine as calcium fluoride was also studied. For example, an experiment was conducted on the reaction of calcium oxide with fluorinated by-products at high temperatures. As a result, it was found that the combustion reaction was relatively excellent among them.

The fluorinated by-product in the present invention includes:
A fluorinated substance which is decomposed by electrolytic fluorination to have a low molecular weight and is discharged from the electrolytic cell as a gas accompanying hydrogen gas can be mainly used. In addition, fluorinated substances other than the intended fluorine compound among fluorinated substances settled in the lower part of the electrolytic cell or the circulation tank can be used as fluorinated by-products.

In the combustion reaction of the fluorinated by-product in the present invention, hydrogen gas co-produced as a by-product in the electrolytic fluorination reaction can be used. In other words, hydrogen reacts with fluorinated by-products together with oxygen, and is converted into carbon dioxide, hydrogen fluoride, and the like. As the hydrogen gas required for this reaction, hydrogen gas by-produced in the electrolytic fluorination reaction is usually sufficient, but in some cases, it may be replenished from outside.

The supply amount of oxygen or air is selected from a wide range. If the amount of oxygen is insufficient, soot is likely to be generated. Therefore, it is preferable to supply oxygen so that soot is not generated much and oxygen remains in the combustion gas. Generally,
Supplying a sufficient excess of oxygen and burning in a state close to complete combustion is advantageous because the amount of hydrogen fluoride generated by combustion increases.

The combustion of fluorinated by-products may be carried out by supplying hydrocarbons, aromatic compounds, alcohols, ethers and other combustibles together with oxygen or air. In particular, when the utilization rate of hydrogen gas cannot be increased, it is preferable to use the combustibles described above. When an organic chlorine compound is added as a combustible substance, hydrogen chloride is also generated at the same time, so that the separation may be performed when hydrogen fluoride is recovered. In some cases, water is added. Depending on the conditions of these additions, a reduction reaction, a hydrolysis reaction, and the like partially progress in addition to the combustion / combustion decomposition reaction.

[0019] The combustion temperature is usually selected from the range of 400 to 1900 ° C. By using known catalysts such as various metals, metal oxides, ceramics, and activated carbon, the combustion temperature can be reduced to, for example, 200 to 300 ° C. The residence time in the combustion furnace is preferably selected from the range of 0.05 to 50 seconds. As a material of the combustion furnace, a metal, a refractory brick, or the like that can withstand generated hydrogen fluoride at a high temperature is used. It may be diluted with excess nitrogen gas, air or the like in order to dilute the generated hydrogen fluoride and reduce the corrosiveness to the combustion furnace. The type of the combustion furnace is not limited as long as it is a known type, and for example, a rotary kiln can be suitably used.

The hydrogen fluoride produced by the combustion reaction can be recovered, for example, by passing the combustion gas at about 100 ° C. through a sodium fluoride tube, preferably a tube filled with porous sodium fluoride pellets, to obtain acid fluoride. It is preferable to fix by fixing as sodium and then heating to about 300 ° C. to release hydrogen fluoride and regenerate sodium fluoride. Alternatively, the trap may be collected by a low-temperature trap. In this case, the trap may be filled with anhydrous hydrofluoric acid or a liquid or oily perfluorinated compound and absorbed therein. Separation of these completely fluorinated products and hydrogen fluoride is easy, and even if the separation is insufficient and some of the completely fluorinated products are mixed in the electrolytic fluorination step, the influence on the electrolytic fluorination reaction is small. In addition, what remains in the exhaust gas without being recovered by the hydrogen fluoride generated by combustion may be removed from the exhaust gas by a known detoxification method.

The recovered hydrogen fluoride is reused as a raw material for electrolytic fluorination after simple distillation or the like, if necessary. Thereby, the amount of newly supplied hydrogen fluoride can be significantly reduced. The recovered hydrogen fluoride and the newly supplied hydrogen fluoride are supplied to an electrolytic cell or a circulation tank separately or in advance by mixing them.
In the electrolytic fluorination reaction, trace impurities in anhydrous hydrofluoric acid may have a serious adverse effect on the electrolytic reaction,
It is surprising that the hydrogen fluoride recovered by the present invention can be suitably used as a raw material for electrolytic fluorination without special purification.

[0022]

According to the method of the present invention, although it depends on the type of the organic compound as the raw material and the conditions of the electrolytic fluorination reaction, the amount of the hydrogen fluoride as the raw material is compared with the case where the present invention is not carried out. 15% or more, usually 25% or more, and particularly preferably 35% or more under preferable conditions.

[0023]

EXAMPLES The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

EXAMPLE An electrolytic fluorination of triethylamine was carried out in a Monel electrolytic cell (inner diameter 11c) having a reflux condenser (-55 ° C.) at the top.
m, height 25 cm) by continuous operation.
The negative anode was a total of 15 nickel plates (65 mm × 96 mm, 1 m thick) alternately arranged with a distance between the electrodes of 1.3 mm.
m), and the effective area was 8 dm ² each.

After supplying 1500 g of anhydrous hydrofluoric acid and 160 g of triethylamine to the electrolytic cell, electrolysis was started at a current value of 24 A. The temperature of the electrolysis was kept at -10 ° C by adjusting the temperature of the refrigerant cooling the electrolytic cell. Thereafter, the amounts of hydrogen fluoride and triethylamine continuously supplied to the electrolytic cell were adjusted to control the total amine concentration of the electrolytic solution to about 13% when the composition of the electrolytic solution became steady.

After the electrolytic reaction reaches a steady state, air is added at a rate of 90 L / hour (room temperature) to a mixed gas of hydrogen and fluorinated by-product discharged from the reflux condenser, and the mixture is heated at a temperature of about 1550 ° C. 3.6 cm inside diameter, length about 40
cm (the residence time was about 10 seconds). Hydrogen fluoride was recovered by cooling the combustion decomposition gas coming out of the electric furnace to −40 ° C., and was continuously supplied to the electrolytic cell.

At this time, the supply amount of triethylamine to the electrolytic cell was about 66 g per day, and the supply amount of hydrogen fluoride supplied separately from the recovered hydrogen fluoride was 168 g on average per day. The fluorine compound which had phase-separated and settled at the lower part of the electrolytic cell was collected from the outlet once a day, washed with water and dried, and then subjected to weight measurement and composition analysis. According to this, an average of 185 g of a fluorine compound was obtained per day, and the amount of perfluorotriethylamine contained therein was 62.7% (corresponding to 116 g). The voltage between the anode and the cathode was about 5.5V.

COMPARATIVE EXAMPLE The same electrolysis apparatus and the same electrolysis conditions (temperature, current value, total temperature) as those of the embodiment were used except that the fluorinated by-product discharged along with the hydrogen gas was not burned. (Amine concentration) for electrolytic fluorination of triethylamine.

In this case, the average supply amounts of triethylamine and hydrogen fluoride per day were 66.5 g and 27, respectively.
It was 0 g. The average daily yield of the fluorine compound obtained from the lower part of the electrolytic cell is 179 g, and the amount of perfluorotriethylamine contained therein is 59.8% on average.
(Equivalent to 107 g). The voltage between negative and positive electrodes is 5.5V
Met.

Claims (1)

(57) [Claims] An organic compound having a carbon-hydrogen bond in a molecule is electrolytically fluorinated to obtain a desired fluorine compound, a by-product fluorinated by-product and hydrogen, and combust a mixture of the fluorinated by-product and hydrogen. A method for producing a fluorine compound, comprising using hydrogen fluoride produced as a raw material for electrolytic fluorination.