JPH0525671A - Electrolytically fluorinating method - Google Patents

Abstract

PURPOSE:To improve the productivity of a desired fluorinated product by increasing an electrode area to increase an electrolytic current. CONSTITUTION:This method consists in executing the electrolytic fluorination of an org. compd. having a carbon-hydrogen bond in an electrolytic cell 1 by circulating an electrolytic bath liquid contg. the org. compd. having the carbon- hydrogen between this electrolytic cell 1 and a circulating cell 2. The electrolytic cell 1 installed with electrode groups 3, 3', 3'' is connected in series and the electrolytic fluorination is executed by maintaining the temp. difference in the flow direction of the electrolytic bath liquid in the respective electrode groups 3, 3', 3'' at <=5 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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]

2. Description of the Related Art Electrolytic fluorination methods for electrochemically fluorinating organic compounds are well known. For example, JP-A-47-18775 discloses that the organic compound is fluorinated while circulating an electrolytic bath solution containing the organic compound between the electrolytic bath and the circulation bath.

[0003]

When electrolytically fluorinating industrially, it is desired to increase the production amount in one electrolytic fluorinating apparatus consisting of an electrolytic cell and a circulation tank to improve the production efficiency. The present inventors conducted various experiments such as increasing the current density and increasing the electrode area for the purpose of increasing the production amount in one electrolytic fluorination apparatus.

As a result, when the current density is increased,
Problems such as a decrease in the yield of the desired fluorinated product and instability of the electrolytic voltage have occurred. In addition, when the number of electrode pairs is increased or the size of each electrode is increased to increase the electrode area, the problems such as a significant decrease in the yield of the desired fluorinated product and a sharp increase in voltage are still present. There has occurred.

[0005]

In view of the above-mentioned problems, the present inventors have studied a method for increasing the production amount. As a result, a plurality of electrode groups should be installed in the flow direction of the electrolytic bath solution that circulates between the electrolytic bath and the circulation bath, and the temperature difference in the flow direction of the electrolytic bath liquid in each electrode group should be below a certain value. As a result, they have found that the above objects can be achieved, and have completed the present invention.

That is, according to the present invention, an electrolytic bath solution containing an organic compound having a carbon-hydrogen bond is circulated between an electrolytic cell and a circulation tank, and an organic compound having a carbon-hydrogen bond is produced in the electrolytic cell. In the electrolytic fluorination method, a plurality of electrode groups are installed along the flow direction of the electrolytic bath solution, and the electrolytic fluorination is performed by setting the temperature difference in the flow direction of the electrolytic bath solution in each electrode group to 5 ° C or less. Is an electrolytic fluorination method.

In the present invention, electrolytic fluorination is carried out by dissolving or dispersing a raw material organic compound having a carbon-hydrogen bond in anhydrous hydrofluoric acid.

As the organic compound having a carbon-hydrogen bond, any organic compound having a hydrogen atom directly bonded to a carbon atom can be used without particular limitation. For example, hydrocarbons such as aliphatic hydrocarbons and aromatic hydrocarbons that have hitherto been known as targets for electrolytic fluorination; linear or cyclic aliphatic primary amines, secondary amines, tertiary amines,
Amines such as aromatic amines; linear or cyclic aliphatic ethers, aromatic ethers, polyethers and other ethers;
Alcohols such as linear or cyclic aliphatic alcohols and aromatic alcohols; phenols; ketones; aldehydes; linear or cyclic aliphatic carboxylic acids, aromatic carboxylic acids, etc., and carboxylic acids derived from these Chloride,
Carboxylic acid halides such as carboxylic acid fluorides, carboxylic acids such as acid anhydrides and esters, and their derivatives; Aliphatic sulfonic acids, aromatic sulfonic acids, and sulfonic acids such as sulfonic acid chlorides and sulfonic acid fluorides. Examples thereof include sulfonic acids such as halides or esters and derivatives thereof; sulfur-containing compounds such as thioethers.

Of these, an organic compound having a nitrogen atom, an oxygen atom or a sulfur atom in the molecule is preferable in view of the solubility in anhydrous hydrofluoric acid used for electrolytic fluorination. Of course, it goes without saying that an organic compound in which a part of hydrogen atoms of the above-mentioned organic compound is replaced with a halogen atom such as a fluorine atom can also be used as the organic compound in the present invention.

As the anhydrous hydrofluoric acid used in the present invention, commercially available anhydrous hydrofluoric acid is used as it is, or if necessary, a known method such as electrolysis at a low current density in advance with a small amount of water contained therein. It is used after being removed by.

In the present invention, electrolytic fluorination is carried out while circulating the electrolytic bath liquid between the electrolytic bath and the circulation bath.
In this case, the electrolytic reaction can be stabilized by circulating the electrolytic bath solution so as to flow substantially parallel to the electrode surface inside the electrolytic cell. By doing so, the resinous products generated by the electrode reaction, nickel fluoride and the like can be smoothly removed from the electrode surface, and the raw material organic compound can be smoothly supplied to the electrode reaction site. In order to perform stable electrolysis for a long period of time, the linear velocity of the electrolytic bath solution on the electrode surface is 1.5 cm / sec or more, preferably 2.
5 cm / sec or more, more preferably 4 cm / sec or more.

The electrolytic fluorination in the present invention may be carried out by either a batch method or a continuous method. In particular, an organic compound as a raw material and anhydrous hydrofluoric acid are electrolyzed continuously or intermittently, respectively. Replenish into the bath solution to carry out the reaction continuously for a long time while maintaining the concentration and composition of the raw material organic compounds and various fluorinated organic compounds as intermediate products in the electrolysis bath solution in a substantially steady state. The continuous type is preferable. At this time, the total concentration of the organic compounds as raw materials and various fluorinated organic compounds as intermediate products is generally 2 to
It is preferably selected so as to fall within the range of 40% by weight, and more preferably 3 to 30% by weight.

The fluorinated product containing the perfluoroorganic compound, which is the target product produced by the electrolytic reaction, does not dissolve in the electrolytic bath liquid and has a larger specific gravity than the electrolytic bath liquid. For this reason, as a method for separating and extracting this from the electrolytic bath solution, a method in which the circulation tank itself also has a function of a settling tank to settle the fluorinated product, and this is continuously or periodically extracted Is preferably adopted.

One of the major features of the present invention is to provide a plurality of electrode groups along the flow direction of the electrolytic bath solution. The electrode group in the present invention refers to a group of electrodes in which an anode and a cathode are arranged so as to face each other with a certain distance between the electrodes. In this case, a large number of anodes and cathodes may be alternately arranged to form a group, and a pair of facing anodes and cathodes may be arranged in a spiral or wavy form to form a group. Alternatively, the other electrode plate may be inserted between one electrode plate of one of the anodes or cathodes arranged adjacent to each other in a wavy manner,
Cathodes and anodes may be arranged alternately to form a group.

In the present invention, a plurality of the above electrode groups are arranged along the flow direction of the electrolytic bath liquid. Specifically, as shown in FIG. 1, the electrolytic cell 1 and the circulation tank 2 form a closed circuit, and the electrode groups 3, 3 ′ and 3 ″ in the electrolytic cell 1 have a flow direction of the electrolytic bath solution. In this case, between the electrode groups and the wall surface in a direction perpendicular to the flow of the electrolytic bath solution of each electrode group so that most of the electrolytic bath solution passes between the electrodes of each electrode group. Most of the electrolytic bath solution that has passed through the electrode group 3 passes through the electrode group 3 ', and most of the electrolytic bath solution that has passed through the electrode group 3'passes through the electrode group 3 "without providing a gap. Each electrode group is arranged so that

The electrode area can be increased by arranging a plurality of electrode groups in parallel in the flow direction of the electrolytic bath solution, but in this case, it is difficult to uniformly supply the electrolytic bath solution to each electrode group. In addition, in order to do so, there is a problem that the circulation amount of the electrolytic bath solution must be increased, and therefore the circulation tank must be enlarged, which is not preferable in the present invention.

In the present invention, as a specific method of providing a plurality of electrode groups along the flow direction of the electrolytic bath solution, for example, as shown in FIG. Examples of the method include a method of providing a plurality of electrode groups along the line, a method of connecting in series electrolytic cells having one electrode group as shown in FIG. 2, and a method of combining the above two methods.

According to the present invention, it is possible to install a plurality of electrode groups, for example, 2 to 10 pieces, usually 3 to 6 pieces, in one electrolytic fluorination apparatus, the electrode groups having the sizes currently used in industry. Therefore, the electrode area can be significantly increased.
In this case, it is generally preferable that the size of each electrode plate constituting one electrode group, the number of pairs of negative and positive electrodes, etc. be selected from the following ranges because stable electrolytic fluorination can be carried out. The electrode length in the flow direction of the electrolytic bath solution is 30 to 150 c.
m, preferably 40 to 120 cm, the number of pairs of negative and positive electrodes is 1 to 2
50 pairs, 25 to 25 when performing electrolytic fluorination on an industrial scale
The distance between 250 pairs and negative and positive electrodes is in the range of 0.5 to 7 mm, preferably 1 to 4 mm.

As the material of the electrode used in the present invention, known materials can be used without any limitation. Nickel or a nickel alloy is usually used for the anode, and iron, stainless steel, copper or the like is used for the cathode in addition to nickel or its alloy.

In the present invention, a plurality of electrode groups are installed along the flow direction of the electrolytic bath solution, and the direction of the electrolytic bath solution flowing between the electrode pairs in the electrode group is vertical upward, vertical downward, horizontal direction, etc. Not limited. However, in order to flow the electrolytic bath solution uniformly between each pair of electrodes, the vertical direction, particularly the vertical upward direction is preferably adopted.

When a plurality of electrolytic cells are connected in series, a pump is installed as necessary to move the electrolytic bath solution between the electrolytic cells. Alternatively, it is possible to move the electrolytic bath liquid between the electrolytic cells by utilizing the difference in heads by sequentially lowering the installation positions of the electrolytic cells.

Another major feature of the present invention is that the temperature difference in the flow direction of the electrolytic bath solution in each electrode group is maintained at 5 ° C. or less for electrolysis. The temperature of the electrolytic bath liquid in the electrode group rises from the inlet to the outlet of the electrolytic bath liquid due to the heat generated by the electrolytic fluorination reaction. By controlling this temperature difference, stable electrolysis can be performed for a long period of time, and the desired fluorinated product can be obtained in good yield. When the above temperature difference is 5 ° C. or more, the temperature distribution on one electrode surface becomes large and the difference in current density becomes abnormally large, which causes a sharp increase in voltage and an extreme yield of the target fluorinated product. A decrease occurs and it becomes impossible to continue the electrolysis. This phenomenon is not seen in the conventional salt electrolysis or the like, and is the first time that the present inventors found out. When the temperature difference is 4 ° C. or less, more preferably 3 ° C. or less, better results can be obtained.

This temperature difference is determined by factors such as current density, electrolysis voltage, length in the direction of flow of the electrolytic bath solution, distance between the electrodes, and linear velocity of the electrolytic bath solution on the electrodes. Therefore, while referring to the results of the electrolysis characteristics obtained by experiments using a relatively small electrolytic cell and other factors, the electrolysis conditions were selected and the temperature difference of the electrolytic bath solution in each electrode group under those conditions was kept below the above value. The electrolytic fluorination apparatus may be designed so that

There is an upper limit to the temperature difference of the electrolytic bath solution in each electrode group as described above. However, the temperature difference of the electrolytic bath liquid between the first electrode group and the last electrode group is
The operation is not particularly limited, and the operation may be performed within an allowable temperature difference range depending on the type of the organic compound as the raw material. When an organic compound having a narrow allowable temperature difference is used as a raw material, a cooling device such as a cooler may be installed between the electrodes to prevent the temperature rise of the electrolytic bath solution. ..

Regarding the method of energizing a plurality of electrode groups, a large number of rectifiers can be installed and supplied separately, but one rectifier is used to connect the negative and positive terminals of each electrode group in series or in parallel. It is also possible to energize with. Although the conditions in each electrode group installed along the flow direction of the electrolytic bath solution are strictly different, each electrode group is electrically connected in series and energized with a constant current using one rectifier. By doing so, stable electrolysis is possible, which has great significance both economically and in terms of operation management.

The electrolysis conditions for the electrolytic fluorination vary depending on the kind of the organic compound as the raw material, but usually the temperature is -15 to 25.
C, current density 0.5 to 6 A / dm ² , voltage between negative and positive electrodes 4 to
It is good to adopt from the range of 8V. The pressure in the electrolytic cell is
Usually normal pressure, but can be somewhat pressurized.

[0027]

According to the method of the present invention, it is possible to perform electrolytic fluorination with one electrolytic fluorination apparatus at an electrolytic current that is 2 to 10 times that of the conventional one. Moreover, electrolysis can be stably continued for a long period of time. In addition, although the fluorinated product produced by electrolytic fluorination in the previous electrode group was expected to decompose when passing through the latter electrode group, the desired fluorinated product was obtained in good yield. Can be obtained at As a result, the amount of the target fluorinated product that can be produced by one electrolytic fluorination device can be improved.

In this case, since it is not necessary to increase the circulation flow rate of the electrolytic bath solution of the electrolytic fluorination apparatus, the fluorinated product can be sufficiently separated from the electrolytic bath solution with the same capacity as the conventional circulation tank. It is possible, and there is no need to make the circulation tank extra large or to install a special device. Therefore, the effect of the present invention in terms of economy or labor saving of operation management is very large.

[0029]

EXAMPLES Examples and comparative examples are shown below for illustrating the present invention further in detail, but the present invention is not limited to these examples.

Example 1 Three cathodes and two anodes made of nickel (4 pairs of negative anodes)
Electrode groups (electrode dimensions; width 60c
m, height 70 cm, thickness 2 mm, distance between poles: 1.8 m
m) was electrolytically fluorinated with tributylamine using a Monel electrolytic cell in which three groups were installed at intervals of 2 cm in the vertical direction (hereinafter, three electrode groups were sequentially arranged from the bottom to the first). Called the electrode group, the second electrode group, and the third electrode group).

First, a Monel circulation tank (inner diameter 24 cm,
25 liters of anhydrous hydrofluoric acid and tributylamine were fed so that the concentration of tributylamine was 6% by weight. This mixed solution was supplied from the lower part of the electrolytic cell using a pump so that the linear velocity between the negative and positive electrodes was 4.5 cm / sec (circulation flow rate 195c
m ³ / sec), the electrolysis was started while returning to the circulation tank due to overflow from the upper part of the third electrode group. The cathode and anode terminals of each electrode group were connected in series, and a current was made to flow from the first electrode group to the third electrode group using one rectifier. The current was gradually increased, and after 60 hours, the energization amount was set to 400 A (electrolytic current value: 1200 A). At this time, the temperature of the mixed liquid flowing into the electrolytic cell was adjusted to −4 ° C. by a cooler installed in front of the electrolytic cell inlet of the circulation line.

The hydrogen gas generated by electrolysis was discharged through a -40 ° C. reflux condenser provided in the upper part of the electrolytic cell.
During the reaction, anhydrous hydrofluoric acid was continuously supplied so as to keep the amount of the electrolytic bath solution constant. Shortly after the start of electrolysis, the supply of tributylamine to the circulation tank was started so that the concentration of all amines in the electrolytic bath solution was maintained at a steady state of about 12% by weight.

The fluorinated product containing the perfluoro compound was intermittently withdrawn from the lower part of the circulation tank. 40 this
After refluxing for 120 hours in an equal volume mixture of a caustic soda aqueous solution and diisobutylamine by weight, washing with water,
It was dried and distilled to obtain perfluorotributylamine.

When electrolysis was continued for 120 days, both voltage and yield were very stable. The average electrolysis results during this period (however, after the energization amount reached 400 A) are shown below; the yield of perfluorotributylamine 4.67.
kg / day, supply amount of tributylamine 3.54 kg /
Day, yield of perfluorotributylamine 36.4
%, Voltage between negative and positive electrodes 5.32 V (first electrode group) 5.21
V (second electrode group) 5.18V (third electrode group), temperature of electrolytic bath solution in each electrode group -4.0 to -1.7 ° C (first electrode group), -1.7 to- 0.5 ° C (second electrode group),-
0.5-3.0 degreeC (3rd electrode group).

Comparative Example 1 The electrolytic cell shown in Example 1 had a width of 60 cm and a height of 210 c.
m, 2 mm thick nickel-made two anodes and three cathodes were alternately installed with the distance between the electrodes being 1.8 mm, and the circulating tank, cooler and the like used in Example 1 were used as they were,
Similarly, electrolytic fluorination of tributylamine was performed. The current was increased in the same manner as in Example 1 except that the energized current after 50 hours from the start of energization was 1200 A (the current density was the same as in Example 1). The conditions such as the circulation flow rate are the same as those in the first embodiment. The temperatures at the electrolytic cell inlet and outlet of the electrolytic bath solution at the time when the energizing current reached 1200 A were −4 ° C. and 3.2 ° C., respectively. Thereafter, the voltage between the negative and positive electrodes gradually increased, and the voltages after 5 days and 10 days were 5.35 V and 5.73 V, respectively. After 20 days, the voltage exceeded 6.8 V, and the yield of perfluorotributylamine at this point was extremely low at 20% or less,
For this reason, the electrolysis had to be stopped.

Example 2 Tripentylamine was electrolytically fluorinated using the electrolytic fluorination apparatus shown below. The circulation tank, the cooler, etc. are the same as those shown in the first embodiment, but as the electrolysis tank, the same three electrode groups as those shown in the first embodiment are installed. What connected the tank along the flow of the electrolytic bath liquid was used. In this case, the electrolysis baths are placed 50 cm lower from the first electrolyzer (sequentially referred to as the first electrolyzer, the second electrolyzer, and the third electrolyzer), and supplied from the bottom of each electrolyzer. The liquid was allowed to overflow at the top of each electrode group and flow to the next electrolytic cell with a head difference. While supplying hydrofluoric acid anhydride and tripentylamine to the circulation tank so that the concentration of total amine in the electrolytic bath liquid (25 liters) would be 13% by weight, it was also supplied to the lower part of the first electrolytic tank by a pump. While controlling the temperature of the electrolytic bath solution to −3 ° C., electrolysis was performed while circulating the electrolytic bath solution at a rate such that the linear velocity between the electrodes was 9 cm (circulating flow rate 390 cm ³ /
Seconds). As a method of energizing, the negative and positive terminals of the electrode group of each electrolytic cell were connected in series, and a current of 500 A was passed using one rectifier (electrolytic current value 1500 A).

The hydrogen gas generated by electrolysis was discharged through a -45 ° C. reflux condenser provided at the top of each electrolytic cell. The fluorinated product containing perfluorotripentylamine was withdrawn from the lower part of the circulation tank and treated in the same manner as in Example 1 to obtain perfluorotripentylamine.

Electrolysis was continued for 90 days after the energizing current reached 500 A, and the voltage and yield were very stable. The average electrolysis results during this period were as follows; Yield of perfluorotripentylamine 4.67 kg /
Supply amount of tripentylamine 4.28 kg / day,
Yield 30.2%, voltage between cathode and anode 5.67V (first electrolytic cell), 5.58V (second electrolytic cell), 5.52V (third)
Electrolyte bath), temperature of electrolytic bath liquid in each electrode group −3.0 to
-1.4 ° C (first electrolyzer), -1.4 to 0.3 ° C (second
Electrolytic bath), 0.1 to 1.9 ° C (third electrolytic bath).

[Brief description of drawings]

FIG. 1 is a schematic view showing a typical embodiment of an electrolytic fluorination apparatus used in the electrolytic fluorination method of the present invention.

FIG. 2 is a schematic view showing another embodiment of the electrolytic fluorination apparatus used in the electrolytic fluorination method of the present invention.

[Explanation of symbols]

 1, 1'and 1 "electrolysis tank 2 circulation tank 3, 3'and 3" electrode group

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Shirai 1-1, Mikage-cho, Tokuyama-shi, Yamaguchi Prefecture Tokuyama Soda Stock Company

Claims (1)

Claim: What is claimed is: 1. An electrolytic bath solution containing an organic compound having a carbon-hydrogen bond is circulated between an electrolytic cell and a circulation tank, and an organic compound having a carbon-hydrogen bond is provided in the electrolytic cell. In the method for performing electrolytic fluorination of a compound, a plurality of electrode groups are installed along the flow direction of the electrolytic bath solution, and the temperature difference in the flow direction of the electrolytic bath solution in each electrode group is set to 5 ° C. or less to perform the electrolytic fluorination. An electrolytic fluorination method characterized by carrying out.