JP5692340B2 - Method for defoaming anionic surfactant-containing liquid and method for cleaning hexafluoropropylene oxide - Google Patents

Description

  The present invention relates to a method for defoaming an anionic surfactant-containing liquid, and more particularly to a method for suppressing foaming in an aqueous liquid containing an anionic surfactant. The present invention also relates to a method for cleaning hexafluoropropylene oxide to which such an antifoaming method is applied, and more particularly to a method for cleaning a composition containing hexafluoropropylene oxide and a carbonyl fluoride oligomer. Furthermore, the present invention also relates to a method for producing hexafluoropropylene using such a cleaning method.

  An anionic surfactant ionizes in water to become an organic anion, and has an action of reducing the surface tension of water. Compounds that act as anionic surfactants can be generated by a variety of reactions. For example, a carbonyl fluoride oligomer by-produced in the method for producing hexafluoropropylene oxide also acts as an anionic surfactant in water.

  Hexafluoropropylene oxide is an important compound in the production of fluorine-containing compounds, for example, used as a raw material for perfluorovinyl ether. Further, the oligomer of hexafluoropropylene oxide is used as a lubricating oil or a heat medium.

  As a method for producing hexafluoropropylene oxide (hereinafter also referred to as HFPO), a method is known in which hexafluoropropylene (hereinafter also referred to as HFP) is oxidized with oxygen to obtain HFPO (see Patent Documents 1 and 2). about).

In such a HFPO production method, carbonyl fluoride (COF ₂ ) is by-produced in addition to the target substance HFPO (see Patent Document 1). Furthermore, in this HFPO production method, carbonyl fluoride (COF ₂ ) is polymerized, and a carbonyl fluoride oligomer is also produced as a by-product (see Patent Document 2). Therefore, a by-product such as a carbonyl fluoride oligomer is separated from the reaction product containing HFPO to obtain a product HFPO.

Japanese Examined Patent Publication No. 45-11683 JP-A-6-107650

  Conventionally, it has been known that when an anionic surfactant is present, foaming can occur in a gas / liquid colloid, and as a detergent, an emulsifier, a dispersing agent, etc., using an action such as foaming (foaming) It is used. However, it may not be desirable for foaming to occur in an alkaline aqueous liquid containing an anionic surfactant. If severe foaming occurs when processing a liquid containing a compound that acts as an anionic surfactant, there is a problem that the processing operation cannot be carried out suitably.

  An example of such a case is deoxidation treatment. Generally, deoxidation treatment of a gas containing an acid component is performed by a cleaning operation in which a gas to be treated is sufficiently brought into contact with an alkaline aqueous liquid (usually an alkaline aqueous solution).

  In the method for producing HFPO, a composition containing HFPO produced by a reaction from HFP and a carbonyl fluoride oligomer is subjected to a deoxidation treatment. More specifically, the composition is alkaline in a gas phase state (gas). After washing with an aqueous liquid, an acid component such as a carbonyl fluoride oligomer is separated into an alkaline aqueous liquid (so an alkaline aqueous liquid can be used to remove a compound derived from a carbonyl fluoride oligomer or the like after deoxidation treatment). It is conceivable to obtain an aqueous liquid containing in the form of a metal salt (more specifically, ionized ions) and a gaseous substance containing HFPO as a target substance (hereinafter also simply referred to as a HFPO cleaning method).

  In such a HFPO cleaning method, the alkaline aqueous liquid generated by the deoxidation treatment contains a compound derived from a carbonyl fluoride oligomer in the form of an alkali metal salt, and the alkali metal salt acts as an anionic surfactant. It has been found by the present inventors that severe bubbling is caused by contact with gas. In a cleaning device such as a deoxidation tower, if bubbles are left as they are and the cleaning operation is carried out continuously, bubbles overflow to the take-out line of the gaseous matter containing HFPO after the deoxidation treatment. There is a problem that the aqueous liquid (and hence the carbonyl fluoride oligomer) is mixed in HFPO), and the pressure loss of the cleaning device is excessively increased due to foaming, which causes a load on the cleaning device. In order to avoid such a problem, it is necessary to reduce the processing speed of the washing operation. As a result, the ability to deoxidize the above composition containing HFPO and carbonyl fluoride oligomer, etc. Compared to the case where a simple gas composition is subjected to deoxidation treatment, the gas composition is remarkably reduced.

  Therefore, in the above HFPO cleaning method, it is necessary to adjust the processing speed of the cleaning operation at a low level so that foaming does not occur or is suppressed to an acceptable level even when foaming occurs. Cannot be implemented efficiently.

  An object of the present invention is to provide a method for defoaming an anionic surfactant-containing liquid, which can suppress foaming in an alkaline aqueous liquid containing an anionic surfactant. Another object of the present invention is to provide a cleaning method for hexafluoropropylene oxide, which can be stably and continuously performed efficiently. Furthermore, the objective of this invention is providing the manufacturing method of hexafluoropropylene using this washing | cleaning method.

  According to one aspect of the present invention, there is provided a method for defoaming an alkaline aqueous liquid containing an anionic surfactant, wherein the alkaline aqueous liquid has a pH of 14 or more. The

  Foaming due to an anionic surfactant is difficult to suppress with an antifoaming agent as commonly used. On the other hand, as a result of intensive studies, the present inventors have found that by setting the pH of the aqueous phase to 14 or more, foaming caused by the above compounds can be effectively suppressed, and the present invention has been completed. It was.

  In the defoaming method of the present invention, by setting the pH of the alkaline aqueous liquid to 14 or more, foaming caused by an anionic surfactant (more specifically, a compound acting as an anionic surfactant) is effective. Can be suppressed. In the present invention, “defoaming” means that foaming can be suppressed (or reduced) as compared with general processing conditions (for example, pH 7 to 12 which are conventional deoxidation processing conditions).

In one embodiment of the present invention, the anionic surfactant is represented by the following general formula (Y):
CF ₃ O (CF ₂ O) _n —R ′ (Y)
(In the formula, —R ′ represents —COOM, —OCOOM or —CF ₂ COOM, M represents an alkali metal, and n represents an integer of 0 to 50.)
The compound represented by these is included. The compound represented by the general formula (Y) acts as an anionic surfactant and causes very intense foaming by contact with a gas. Can not. However, according to the present invention, bubbling due to the compound represented by the general formula (Y) can be effectively suppressed by setting the pH of the alkaline aqueous liquid to 14 or more.

According to another aspect of the present invention, a method for cleaning hexafluoropropylene oxide, comprising:
Hexafluoropropylene oxide and the following general formula (X):
_{CF 3 O (CF 2 O)} n -R ··· (X)
(Wherein, -R is -COF, indicates -OCOF or _-CF 2 COF, n is an integer of 0 to 50.)
There is provided a method of washing a composition containing the compound represented by formula (1) with an alkaline aqueous liquid having a pH of 14 or higher.

  The compound represented by the general formula (X) corresponds to the above-mentioned carbonyl fluoride oligomer. Such a compound may exist in the form of a compound represented by the general formula (Y) (more specifically, ionized ions) in an alkaline aqueous liquid. Therefore, the cleaning method of the present invention is an application of the defoaming method of the present invention. According to the cleaning method of the present invention, foaming caused by the compound represented by the general formula (X) is effective. The cleaning operation can be carried out stably and continuously efficiently.

According to another aspect of the present invention, there is provided a process for producing hexafluoropropylene oxide,
a) Oxidation of hexafluoropropylene with oxygen to produce hexafluoropropylene oxide and the following general formula (X):
_{CF 3 O (CF 2 O)} n -R ··· (X)
(Wherein, -R is -COF, indicates -OCOF or _-CF 2 COF, n is an integer of 0 to 50.)
And b) separating the compound represented by the general formula (X) into an alkaline aqueous liquid by washing the composition with an alkaline aqueous liquid having a pH of 14 or higher. And the manufacturing method including the process of obtaining the gaseous substance containing hexafluoropropylene oxide is provided.

  The manufacturing method of the present invention uses the above-described cleaning method of the present invention, and can achieve the same effects.

In a preferred embodiment of the above washing method and production method of the present invention, the alkaline aqueous liquid contains at least one of potassium hydroxide and sodium hydroxide. Since potassium hydroxide and sodium hydroxide are strong alkalis, HF can be trapped in an aqueous liquid as F ⁻ by a neutralization reaction in a relatively small amount, particularly when potassium hydroxide is used. Since the solubility of potassium fluoride is as large as 92.3 (g / 100 g-water) (18 ° C.), precipitation as a fluoride can be effectively avoided. Such an embodiment is particularly suitable when an alkaline aqueous liquid is recycled. In addition, potassium hydroxide and sodium hydroxide are relatively inexpensive and easily available, and thus can be suitably used industrially. Potassium hydroxide and sodium hydroxide may be contained in the alkaline aqueous liquid alone or in combination.

  According to the present invention, bubbling due to an anionic surfactant can be effectively suppressed by setting the pH of an alkaline aqueous liquid containing an anionic surfactant to 14 or more. If this invention is applied to the cleaning method, the cleaning operation can be carried out stably and continuously efficiently.

It is the schematic for demonstrating the washing | cleaning method of the hexafluoropropylene oxide in one embodiment of this invention.

(Embodiment 1)
The present embodiment relates to a method for defoaming an anionic surfactant-containing water of the present invention.

  First, an alkaline aqueous liquid containing an anionic surfactant, which is a defoaming target, will be described.

Examples of the anionic surfactant include the following general formula (Y):
CF ₃ O (CF ₂ O) _n —R ′ (Y)
(In the formula, —R ′ represents —COOM, —OCOOM or —CF ₂ COOM, M represents an alkali metal, preferably potassium or sodium, and n represents an integer of 0 to 50, preferably 0 to 15. Show.)
The compound represented by these may be sufficient.

  The compound represented by the general formula (Y) can exist in the form of ions ionized in an aqueous liquid, and among these, an organic anion can act as a surfactant. The compound represented by the general formula (Y) may be any compound as long as it can form the compound represented by the general formula (Y) in an alkaline aqueous liquid. For example, the compound represented by the general formula (Y) in the alkaline aqueous liquid may be obtained by adding the compound itself to the aqueous liquid and dissolving it. For example, the compound represented by the general formula (Y) in the alkaline aqueous liquid is dissolved by adding the compound represented by the general formula (X) described later in Embodiment 2 to the aqueous liquid containing alkali metal ions. It may be caused by doing. Therefore, the alkali metal (M) in the general formula (Y) may be an alkali metal originally contained in the compound or an alkali metal ion contained in the aqueous liquid.

The alkaline aqueous liquid may contain at least one alkaline substance such as an alkali metal hydroxide, an alkaline earth metal hydroxide, and ammonia in an aqueous medium. The alkali metal hydroxide may be used such as potassium hydroxide, a etc. sodium hydroxide. As the alkaline earth metal hydroxide, calcium hydroxide, barium hydroxide or the like can be used. As other alkaline substances, potassium carbonate, sodium carbonate, potassium hydrogen carbonate, sodium hydrogen carbonate can be used. These may be used in at least one kind, and among these, it is preferable to use either or both of potassium hydroxide and sodium hydroxide. Alkali metal hydroxides and alkaline earth metal hydroxides can be used in the form of aqueous solutions. Ammonia can be used in the form of aqueous ammonia.

  Next, the pH of the alkaline aqueous liquid will be described.

  In order to exert the defoaming effect, the pH of the alkaline aqueous liquid needs to be 14 or more. Specifically, the pH of the aqueous phase is adjusted by the alkali concentration (concentration of the alkaline substance) in the alkaline aqueous liquid.

  If the pH of the aqueous phase is 14 or more, an antifoaming effect can be obtained, but if it is too high, the consumption of alkaline substances increases, which is not preferable. From such a viewpoint, the pH may be set to 15 or less, for example.

  The pH is adjusted in advance before the anionic surfactant is present in the alkaline aqueous liquid (in other words, the anionic surfactant is added to the alkaline aqueous liquid that has been previously adjusted to pH 14 or higher). Is effective in suppressing foaming. However, the present embodiment is not limited to this, and the pH of the aqueous phase is adjusted to 14 or more by adding an alkaline substance or an alkaline aqueous solution containing an alkaline substance to an aqueous liquid containing an anionic surfactant and having a pH of less than 14. May be.

  The content of the anionic surfactant in the alkaline aqueous liquid is not particularly limited, but may be, for example, about 1 ppm by weight or more, specifically about 10 ppm by weight to 10% by weight (all are based on the whole).

  According to this embodiment, the foaming resulting from the said compound can be suppressed effectively by making pH of an alkaline aqueous liquid 14 or more.

In this embodiment, the case where the compound represented by the said general formula (Y) is used as an anionic surfactant was demonstrated. However, the anionic surfactant that can be used in the defoaming method of the present invention is not limited to the compound represented by the general formula (Y), and various anionic surfactants can be used.
Other anionic surfactants include, for example, the following alkali metals and (alkyl) ammonium salts of hydrocarbon compounds (see JP-T-2007-523777):
1) Alkyl sulfate and alkyl sulfonates such as sodium dodecyl sulfate and potassium dodecane sulfonate;
2) Sulfates of linear or branched aliphatic alcohols and polyethoxylated derivatives of carboxylic acids;
3) alkyl benzene sulfonates and sulfates or alkyl naphthalene sulfonates and sulfates, such as sodium lauryl benzene sulfonate;
4) Ethoxylated and polyethoxylated alkyl and aralkyl alcohol carboxylic acid esters;
5) glycinates such as alkyl sarcosine and alkyl glycinate;
6) Sulfosuccinates, including dialkyl sulphosuccinates;
7) isethionic acid derivatives;
8) N-acyl taurine derivatives such as N-methyl-N-oleyl taurine sodium;
9) Amine oxides, including alkyl and alkylamidoalkyldialkylamine oxides; and 10) Alkyl phosphate mono- or di-esters, such as ethoxylated dodecyl alcohol phosphates, sodium salts.
In addition, as another anionic surfactant, for example, in the case of fluorine-containing compounds, the following may be mentioned (see JP-A-2005-290350):
・ The following general formula (1)
_{Y- (CF 2) x1 - (} CH 2) y1 -A (1)
(In the formula, Y represents H or F. x1 represents an integer of 4 to 13, y1 represents an integer of 0 to _3. A represents —SO ₃ M or —COOM, and M represents , H, NH ₄ , Li, Na, or K)), an anionic compound having no ether oxygen, and the following general formula (2)
_{F (CF 2) x2 O (} CFXCF 2 O) y2 -CFX-A (2)
(In the formula, x2 represents an integer of 1 to 5, y2 represents an integer of 0 to 10. X represents F or CF ₃ , A represents —SO ₃ M or —COOM, M Represents an H, NH ₄ , Li, Na, or K) anionic compound having an ether oxygen.
In addition, any appropriate anionic surfactant can be used in the defoaming method of the present invention at least one or more.

(Embodiment 2)
In the present embodiment, the method for cleaning hexafluoropropylene oxide of the present invention and the method for producing hexafluoropropylene oxide using the same will be described in detail with reference to FIG.

・ Process a)
First, hexafluoropropylene oxide (HFPO) and the following general formula (X):
_{CF 3 O (CF 2 O)} n -R ··· (X)
(Wherein, -R is -COF, indicates -OCOF or _-CF 2 COF, n is an integer of 0 to 50.)
The composition containing the compound represented by this is prepared.

  Such a composition is not limited to the cleaning method of the present invention, but can be obtained through a reaction step of oxidizing hexafluoropropylene (HFP) with oxygen.

Specifically, HFP and oxygen (O ₂ ) are supplied to a reactor (not shown) charged with a solvent in advance, and HFP is oxidized with oxygen (liquid phase reaction) in the reactor to generate HFPO.

  Examples of the solvent include saturated halogen carbon inert to the oxidation reaction, such as 1,1,2-trichloro-1,2,2-trifluoroethane, trichlorofluoromethane, perfluoro (dimethylcyclobutane), carbon tetrachloride and the like. Can be used.

In the oxidation reaction, in addition to HFPO which is a target substance of the production method of the present invention, the following general formula (X):
_{CF 3 O (CF 2 O)} n -R ··· (X)
(Wherein, -R is -COF, indicates -OCOF or _-CF 2 COF, n is an integer of 0 to 50, preferably an integer of 0 to 15.)
(Hereinafter also referred to as oligomer represented by the general formula (X)) is by-produced.

  The oligomer represented by the general formula (X) may be one type of compound, but it may be usually a mixture of a plurality of types of compounds having different terminal groups -R and / or n numbers.

In the general formula (X), the bond between _two adjacent CF ₂ O repeating units is
—CF ₂ —O—CF ₂ —O—
—CF ₂ —O—O—CF ₂ —
_{-O-CF 2} -CF ₂ -O-
—O—CF ₂ —O—CF ₂ —
Any of them may be used. In the case of —CF ₂ —O—CF ₂ —O— and —O—CF ₂ —O—CF ₂ —, an ether bond is formed, and in the case of —CF ₂ —O—O—CF ₂ — An ether bond is formed.

The ratio of the ether peroxide bond in the oligomer represented by the general formula (X) is preferably such that the active oxygen concentration measured by the iodometric titration method is 0.01 to 25% by weight. As long as the oligomer represented by the general formula (X) satisfies this condition, the general formula (X) end groups in the -R is -COF, there is no limit for the proportion of the compound is -OCOF or _-CF 2 COF.

The produced HFPO and the oligomer represented by the general formula (X) can be extracted from the reactor, for example, in a gas phase. The extracted gas phase is usually HFPO, an oligomer represented by the general formula (X), unreacted HFP, by-produced acetyl fluoride (CF ₃ COF), hexafluoroacetone (CF ₃ COCF _3). ) And carbonyl fluoride (COF ₂ ) and the like.

The reaction conditions can be appropriately set according to the reactor and solvent to be used so that the final HFPO recovery amount becomes large. For example, the reaction conditions may be as follows, but this embodiment is limited to this. is not.
The reactor is charged with 30 to 50% of the solvent, and HFP is charged with 1 to 40%, preferably 5 to 35% of the solvent, and heated to 90 to 150 ° C.
The reaction is carried out by dispensing oxygen gas at a partial pressure of 0.02 to 0.5 MPa (gauge pressure), preferably 0.05 to 0.1 MPa (gauge pressure). The total amount of oxygen charged can be determined by analyzing the conversion rate of HFP as a raw material, but is approximately 1.3 to 1.7 times the theoretical amount.
Further, the total reaction pressure at this time varies depending on the solvent species, the HFP feed ratio, the temperature conditions, and the like, and is not particularly specified, but is generally 1.5 to 4 MPa (gauge pressure).
The reaction time (average residence time) is, for example, 1 to 10 hours.

  Such a reaction operation can be carried out either batchwise or continuously in a closed vessel. The reactor is preferably a metal container capable of stirring and heating the liquid.

In addition to HFPO and the oligomer represented by the general formula (X), the gas phase extracted from the reactor is unreacted HFP, by-produced acetyl fluoride (CF ₃ COF), hexafluoroacetone (CF ₃ COCF ₃ ). And carbonyl fluoride (COF ₂ ) and the like, and may be appropriately subjected to a conventional separation operation (eg, distillation, evaporation, etc.). Of these, at least the oligomer represented by HFPO and general formula (X) may be contained in the composition subjected to step b), and before step b), HFPO and / or general formula ( The oligomer represented by X) may be partially separated.

  By the above, the composition containing the oligomer represented by HFPO and general formula (X) is obtained.

-Process b)
Next, in order to deoxidize the composition obtained above, a cleaning operation is performed by applying the cleaning method of the present invention. Specifically, the above-obtained composition is washed with an alkaline aqueous liquid having a pH of 14 or higher, usually an aqueous alkaline solution (hereinafter simply referred to as an aqueous alkaline solution in order to simplify the explanation in this embodiment). . As a result, acid components (such as oligomers represented by the general formula (X) and hexafluoroacetone) are removed from the composition, and HFPO is washed by paying attention to HFPO which is a target substance of the production method of the present invention. .

  Such a washing operation can be carried out either batchwise or continuously, but can be carried out continuously using, for example, the washing apparatus 11 shown in FIG. The cleaning device 11 includes a deoxidation tower 10 and its attached equipment. The deoxidation tower 10 includes a tower part 10a and a can part 10b connected to the lower part thereof, and the tower part 10a is preferably filled with any appropriate packing. The accessory equipment includes the illustrated composition supply line 1, alkaline aqueous solution supply line 3, gaseous matter discharge line 5, pump 7, alkaline aqueous solution discharge line 9a, waste liquid line 9b, circulation line 9c, and the like.

  Referring to FIG. 1, the composition obtained in step a) is in a gas phase (gas) from composition supply line 1 to tower section 10a of deoxidation tower 10, preferably at the supply port located therebelow. Supply more.

  On the other hand, the alkaline aqueous solution is supplied from the alkaline aqueous solution supply line 3 to the tower portion 10a of the deoxidation tower 10, preferably from the supply port located above.

  As the alkaline aqueous solution, an alkaline aqueous liquid as described above in Embodiment 1 can be used. For example, at least one alkaline substance such as an alkali metal hydroxide, an alkaline earth metal hydroxide, or ammonia is contained in the aqueous medium. Can be included.

  The pH of the aqueous alkali solution to be supplied (or the alkali concentration, more specifically, the concentration of the alkaline substance in the aqueous alkali solution) may vary depending on the amount of gas to be treated, etc. The pH of the aqueous alkaline solution in contact with the aqueous solution is selected to be 14 or higher.

  When the cleaning apparatus 11 shown in FIG. 1 is used, specifically, the pH of an alkaline aqueous solution (which is an alkaline aqueous solution after washing and is considered to have the lowest pH) discharged from the can 10b through the alkaline aqueous solution discharge line 9a. The pH of the alkaline aqueous solution can be maintained and managed so that the value becomes 14 or more. The pH can be adjusted by adjusting the supply amount of the composition to the cleaning device 11, the supply amount of the alkaline aqueous solution, the pH (or alkali concentration) of the alkaline aqueous solution to be supplied, etc. alone or in combination.

The composition and the aqueous alkali solution supplied to the deoxidation tower 10 are sufficiently in contact with each other inside, and in the illustrated embodiment, they are in countercurrent contact while flowing through the tower portion 10a. The composition after contact is discharged as a gaseous matter through the gaseous matter discharge line 5 from an outlet located preferably above the tower 10a. On the other hand, the alkaline aqueous solution after contact, after being received by being connected to the lower portion of the column portion 10a can portion 10b, by the pump 7, is discharged through the can portion 1 0 b from an aqueous alkaline solution discharge line 9a.

  While the composition and the aqueous alkaline solution are in contact, the acid component in the composition moves into the aqueous alkaline solution. In other words, the aqueous solution of the composition becomes HFPO by focusing on the target substance of the production method of the present invention. Will be washed). During this time, the pH of the aqueous alkaline solution that is the liquid phase is maintained at 14 or higher. The composition after cleaning, that is, the gaseous matter discharged through the gaseous matter discharge line 5 contains HFPO.

  In this washing operation, since the pH of the alkaline aqueous solution is 14 or more, foaming due to the oligomer represented by the general formula (X) is effectively suppressed in the tower portion 10a and the can portion 10b of the deoxidation tower 10. Can do. Therefore, an alkaline aqueous solution (and consequently an oligomer represented by the general formula (X) and / or the general formula (Y)) is mixed in the gaseous matter after washing, or the pressure loss of the deoxidation tower 10 increases due to foaming. Can be prevented. As a result, the processing speed of the cleaning operation can be increased, and the process can be carried out stably and continuously efficiently.

In this washing operation, the pH of the liquid phase may be 14 or more. Such pH maintenance can be easily performed by measuring the pH of the aqueous alkaline solution (aqueous phase) using a commercially available pH meter. The actual measured value of the pH measured with the pH meter is generally equal to the theoretical value of pH obtained from the molar concentration of the alkaline substance measured by neutralization titration if the pH is 14 or less. However, some commercially available pH measuring devices can display a value of pH 14 or higher, but it is known that the error increases at pH 14 or higher. Therefore, in order to obtain an accurate pH value at pH 14 or more, it is preferable to obtain a theoretical pH value by neutralization titration.

Further, if the pH of the alkaline aqueous solution is 14 or more, HF and CO ₂ produced by hydrolysis of the oligomer can be further trapped in the alkaline aqueous solution by a neutralization reaction, and F ⁻ and CO ₃ ² respectively. ^- as can be separated in an alkaline aqueous solution (Thus, it is possible to improve the HFPO purity gaseous product is discharged through the gaseous product discharge line 5).

The alkaline aqueous solution is preferably an aqueous solution of potassium hydroxide and / or sodium hydroxide. The compound represented by the general formula (X) can generate HF by hydrolysis, and the fluorine ions can form fluorides with alkali metal ions in the aqueous liquid. Potassium fluoride and sodium fluoride have higher solubility than other fluorides. Therefore, when an aqueous solution of potassium hydroxide and / or sodium hydroxide is used as the alkaline aqueous liquid, HF can be sufficiently trapped in the aqueous liquid as F ⁻ by a neutralization reaction and precipitated as fluoride. Can be effectively avoided. In particular, since potassium fluoride has higher solubility than sodium fluoride, a higher effect can be obtained when a potassium hydroxide aqueous solution is used.

  The upper limit value of the pH of the aqueous alkaline solution may be appropriately set within a range not impairing the object of the present invention, and may be, for example, pH 15 or less. By setting the pH to 15 or less, it can be handled in a liquid state. For example, when an alkaline aqueous solution containing potassium hydroxide (potassium hydroxide aqueous solution) is used, an alkali concentration (potassium hydroxide concentration) of 48% by weight can be easily obtained on the market. Is 15 or less.

  The acid component separated in the alkaline aqueous solution includes an oligomer represented by the general formula (X) and hexafluoroacetone when present. The oligomer represented by the general formula (X) is dissolved in the alkaline aqueous solution in the form of the compound represented by the general formula (Y) described in Embodiment 1 (more specifically, ionized ions). Hexafluoroacetone dissolves in an aqueous alkaline solution as a trihydrate.

  Therefore, the alkaline aqueous solution discharged (after washing) through the alkaline aqueous solution discharge line 9a includes the compound represented by the general formula (Y) derived from the oligomer represented by the general formula (X) and hexafluoro if present. Acetone is included.

  The aqueous alkali solution discharged from the deoxidation tower 10 in this way is discarded after being subjected to any post-treatment as necessary through the waste liquid line 9b. Generally, it is discarded after neutralization. Since hexafluoroacetone trihydrate is stable in a neutral state, neutralize the alkaline aqueous solution after washing, and then separate hexafluoroacetone trihydrate (for example, by extraction, membrane separation, adsorption, etc.). ) It may be taken out stably and used for any purpose.

In addition, since the alkaline aqueous solution discharged as described above may still have a cleaning effect, a part of the alkaline aqueous solution is returned to the tower portion 10a of the deoxidation tower 10 through the circulation line 9c, and passed through the alkaline aqueous solution supply line 3. It may be used together with a newly supplied alkaline aqueous solution. Thereby, the consumption of alkali can be reduced.

In particular, when an aqueous solution of potassium hydroxide and / or sodium hydroxide is used as the alkaline aqueous solution, HF can be sufficiently trapped in the aqueous liquid as F ⁻ by a neutralization reaction as described above. Since precipitation as a chemical compound can be effectively avoided, the alkaline aqueous solution can be circulated at a higher rate. From this viewpoint, it is more preferable to use an aqueous potassium hydroxide solution.

  However, when a sodium hydroxide aqueous solution is used as the alkaline aqueous solution, there is another advantage. Sodium hydroxide is less expensive than potassium hydroxide, and is manufactured by salt electrolysis from seawater. Therefore, sodium hydroxide is hardly affected by market conditions and can be obtained and used stably.

The cleaning conditions can be appropriately set according to the type of the cleaning apparatus used and the alkaline aqueous solution so that the final HFPO recovery amount becomes large. For example, the cleaning conditions may be as follows, but this embodiment is not limited thereto. Is not to be done.
The composition is supplied to the deoxidation tower 10 in a gas phase state, for example, at 0 to 50 ° C. and 0 to 0.6 MPa (gauge pressure).
An aqueous alkali solution is supplied to the deoxidation tower 10 in a liquid state, for example, at 0 to 30 ° C.
The ratio of the aqueous alkali solution circulating in the deoxidation tower 10 is not particularly limited, and may be, for example, 0 to 5000 times the supply flow rate of the aqueous alkali solution newly supplied from the outside.
The supply flow rate of the alkaline aqueous solution may be 2 to 20 L / hr with respect to the supply flow rate of 1 m ³ / hr of the composition.
Although the gaseous matter discharged | emitted from the deoxidation tower 10 depends on each calorie | heat amount of the composition supplied, aqueous alkali solution, the pressure loss of the deoxidation tower 10, etc., for example, 0-50 degreeC and 0-0.6 MPa (Gauge pressure).
The discharged alkaline aqueous solution is, for example, 0 to 50 ° C., although it depends on the amount of heat of the supplied composition and alkaline aqueous solution, the pressure loss of the deoxidation tower 10, and the like.
PH of the alkaline aqueous solution being washed (more specifically, an alkaline aqueous solution comprising an alkaline aqueous solution supplied from the outside and a circulated alkaline aqueous solution in contact with the composition supplied in the gas phase. The pH of the alkaline aqueous solution (or liquid phase), which may be considered to be substantially equal to the pH of the alkaline aqueous solution after washing, may be 14 or more, for example, may be 14 or more and 15 or less.

  Thus, HFPO, more specifically, a composition containing HFPO and the oligomer represented by the general formula (X) is washed, and HFPO is produced in the form of a gaseous substance after washing. The content of HFPO in the obtained gaseous product is, for example, 80 mol% or more, typically 90 to 100 mol%.

(Example)
According to the above-mentioned step a), HFP is oxidized with oxygen to produce HFPO, and COF ₂ , CF ₃ COF, etc. are appropriately removed from the resulting gas phase by a conventional method to obtain composition P It was.

The components of the composition P were analyzed by a Fourier transform infrared spectrophotometer (FT-IR), a nuclear magnetic resonance spectrum ( ¹⁹ F-NMR, ¹³ C-NMR) and gas chromatography. The results are shown in Table 1. The composition P contained HFPO and the oligomer represented by the above general formula (X), and also contained a trace amount of hexafluoroacetone (CF ₃ COCF ₃ ).

Next, this composition P was washed using the washing apparatus 11 shown in FIG. 1, and a washing liquid sample Q after washing was collected. The washing operation was carried out without adding an antifoaming agent, and the specific conditions were as follows.
The above-mentioned composition P is continuously supplied from the composition supply line 1 to the deoxidation tower 10 of the cleaning apparatus 11 shown in FIG. 1 from the composition supply line 1, and an aqueous potassium hydroxide solution is supplied as an alkaline aqueous solution. The gaseous matter and the alkaline aqueous solution after washing were continuously discharged from the gaseous matter discharge line 5 and the alkaline aqueous solution discharge line 9a, respectively. The alkaline aqueous solution supplied from the alkaline aqueous solution supply line 3 was set to about 15 ° C. and an alkali concentration of 5.4 mol / L (pH = 14.7 (theoretical value)). The ratio of the alkaline aqueous solution circulated to the deoxidation tower 10 from the circulation line 9 c was 1000 times the alkaline flow rate supplied from the alkaline aqueous solution supply line 3. The aqueous alkali solution obtained from the waste liquid line 9b had a temperature of about 20 ° C. and an alkali concentration of 2.9 mol / L (pH = 14.4 (theoretical value)).
Under such conditions, the alkaline aqueous solution obtained from the waste liquid line 9b was collected as a cleaning liquid sample Q.

  The collected cleaning liquid sample Q contained 1% by weight of the oligomer represented by the general formula (Y).

  During the washing operation, the deoxidation tower 10 was sufficiently defoamed (suppressed), and could be continuously operated without any problem. Therefore, it was confirmed that foaming can be prevented by setting the pH of the alkaline aqueous solution to 14 or more.

(Comparative example)
The washing operation was performed in the same manner as in the above example except that the alkaline aqueous solution supplied from the alkaline aqueous solution supply line 3 was about 15 ° C. and the alkali concentration was 2.9 mol / L (pH = 14.4 (theoretical value)). Carried out. In this comparative example, the alkaline aqueous solution obtained from the waste liquid line 9b had a temperature of about 20 ° C. and an alkali concentration of 0.6 mol / L (pH = about 13.8).

  While carrying out the washing operation, intense bubbling was observed in the deoxidation tower 10, and the operation had to be stopped one hour after the start of washing.

  The antifoaming method of the present invention can be widely used to suppress foaming of an anionic surfactant-containing liquid. The hexafluoropropylene oxide obtained by the washing method and the production method of the present invention can be used as a raw material for perfluorovinyl ether, for example.

DESCRIPTION OF SYMBOLS 1 Composition supply line 3 Alkaline aqueous solution supply line 5 Gaseous material discharge line 7 Pump 9a Alkaline aqueous solution discharge line 9b Waste liquid line 9c Circulation line 10 Deoxidation tower 10a Tower part 10b Can part 11 Cleaning apparatus

Claims (3)

A method for cleaning hexafluoropropylene oxide, comprising:
Hexafluoropropylene oxide and the following general formula (X):
_{CF 3 O (CF 2 O)} n -R ··· (X)
(Wherein, -R is -COF, indicates -OCOF or _-CF 2 COF, n is an integer of 0 to 50.)
A method comprising washing a composition containing the compound represented by formula (1) with an alkaline aqueous liquid having a pH of 14 or higher. A method for producing hexafluoropropylene oxide, comprising:
a) Oxidation of hexafluoropropylene with oxygen to produce hexafluoropropylene oxide and the following general formula (X):
_{CF 3 O (CF 2 O)} n -R ··· (X)
(Wherein, -R is -COF, indicates -OCOF or _-CF 2 COF, n is an integer of 0 to 50.)
And b) separating the compound represented by the general formula (X) into an alkaline aqueous liquid by washing the composition with an alkaline aqueous liquid having a pH of 14 or higher. And a method for producing a gaseous product containing hexafluoropropylene oxide. The method according to claim 1 or 2 , wherein the alkaline aqueous liquid contains at least one of potassium hydroxide and sodium hydroxide.

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