JP5900130B2 - How to use fluoroalkyl iodide - Google Patents

Description

  The present invention relates to a method for using a fluoroalkyl iodide, and more particularly, an unnecessary chain length by recovering hydrofluoric acid or calcium fluoride from a fluoroalkyl iodide obtained by a telomerization reaction. The present invention relates to a method for effectively using the fluoroalkyl iodide.

  Fluoroalkyl iodides are very useful compounds as functional materials and organic synthetic intermediates such as water and oil repellents and emulsifiers, and are mainly produced by telomerization reaction using tetrafluoroethylene as a raw material. .

  The telomerization reaction is a reaction in which taxonogen is added to telogen by applying heat or light in the presence of an appropriate catalyst to obtain a polymer having a low degree of polymerization, that is, a telomer.

  However, since the telomerization reaction is a kind of polymerization reaction, the crude product is always obtained with a distribution in carbon number. Therefore, a certain amount of fluoroalkyl iodide telomers obtained by the telomerization reaction is always in the state of long-chain telomers with little industrial utility value, and the resources can be recycled from the viewpoint of effective utilization of rare resources and reduction of manufacturing costs. Is required.

  For example, it is possible to recover fluorine atoms as hydrofluoric acid by burning fluoroalkyl iodide in the presence of oxygen and water. However, if the combustion process is performed without separating fluorine and iodine atoms from fluoroalkyl iodide, hydrofluoric acid, hydroiodic acid and iodine are produced at the same time. Is expected. Further, when hydrofluoric acid is to be recovered from the mixed acid obtained by this method, separate purification is required, and the process becomes complicated.

  In addition, as a method for recycling long-chain telomers, a fluoroalkyl iodide having 4 to 6 carbon atoms is mixed with a fluoroalkyl iodide having 6 or more carbon atoms and subjected to a heat treatment to obtain a fluoroalkyl iodide having 4 to 6 carbon atoms. A method for obtaining a dye has been reported (see Patent Document 1 below). However, according to this method, a telomer compound having a low selectivity of the target short-chain fluoroalkyl iodide and a distribution in the number of carbon atoms can be obtained, and further, perfluorocarbon, iodine and the like are generated as by-products. For this reason, a separate process for separating and purifying the desired fluoroalkyl iodide is required. However, separation and purification are complicated because perfluorocarbons having a distribution in the number of carbon atoms are mixed as in the case of the telomer compound. Moreover, since iodine and perfluorocarbon having a high carbon number (particularly 12 or more carbon atoms) are solid at room temperature, they solidify in the production facility and cause clogging of the apparatus and piping. Furthermore, at 450 ° C. to 495 ° C., which is a temperature range suitable for the implementation of this method, iodine has a very significant corrosiveness to metal materials, which is a concern in the maintenance of production facilities.

  In addition, a method of recovering iodide (Rf-I) as a hydride (Rf-H) by reacting a fluoroalkyl iodide with hydrogen has been proposed (see Patent Document 2 below). However, this method has a problem that the lifetime of the equipment is shortened because iodine and hydrogen iodide by-produced at a high temperature must be handled in the same manner as the thermal decomposition of telomer. In addition, if the reaction temperature is lowered in order to suppress the production of perfluorocarbons due to side reactions and the decomposition of the perfluoroalkyl chain, the conversion rate of the reaction will decrease, so that the separation and purification of the desired compound will be required separately. The process becomes complicated.

  On the other hand, a method of obtaining 1H-perfluoroalkane and alkali metal iodide by reacting perfluoroalkyl iodide and alkali metal hydroxide in the presence of methanol has also been reported (see Patent Document 3 below). . According to this method, perfluoroalkyl iodide can be converted into 1H-perfluoroalkane and alkali metal iodide, but it is necessary to use alkali metal hydroxide in a large excess relative to perfluoroalkyl iodide. Therefore, the alkali metal iodide recovered after the reaction is obtained as a mixture with a large amount of alkali metal hydroxide. For this reason, in the subsequent collection and reuse, a separate purification step is required, and it is difficult to say that it is efficient. Further, when a fluoroalkyl iodide and an alkali metal hydroxide are reacted by this method, 1H-perfluoroalkane is generated by the donation of proton from methanol, and formaldehyde is by-produced at the same time. For this reason, in this method, since methanol is consumed for each batch of reaction, it is necessary to replenish, and separation and purification are required when recovering and reusing methanol after reaction. Moreover, since formaldehyde is an easily polymerizable substance, it can be polymerized in the production facility and cause blockage or contamination of the facility.

  As described above, the method described in Patent Document 1 cannot completely reuse an unnecessary chain length of fluoroalkyl iodide. Further, in the method described in Patent Document 2 or Patent Document 3, if the product 1H-perfluoroalkane (Rf-H) has no application, the fluorine atom cannot be recycled.

WO2011 / 256312 A1 USP6525231 Japanese Patent No. 2559312

  The present invention has been made in view of the current state of the prior art described above, and the main purpose thereof is a telomer having an unnecessary chain length generated when a fluoroalkyl iodide is produced using a telomerization reaction, in particular, An object of the present invention is to provide a method capable of effectively reusing a long-chain telomer without requiring a complicated separation operation and without adversely affecting the apparatus.

  The inventor has conducted extensive research to achieve the above-described object. As a result, fluoroalkyl iodides of various chain lengths were treated, and ethylene was added to this to form an ethylene adduct, followed by alkali metal hydroxide and / or alkali metal alkoxide in the presence of a lower alcohol. According to the method of reacting and olefinating, and then heat treating the olefin product in an oxygen-containing atmosphere to generate hydrogen fluoride and absorbing it into water to form hydrofluoric acid, It was found that fluorine atoms can be recovered almost completely as hydrofluoric acid. In addition, in this method, iodine contained in the fluoroalkyl iodide to be treated can be almost completely removed by the dehydroiodination reaction of the ethylene adduct. Concerns such as corrosion and deterioration of equipment due to hydrogen fluoride and contamination of iodine atoms in the regenerated hydrogen fluoride can be eliminated. The hydrofluoric acid obtained by this method has a high purity, and without requiring a complicated purification step, fluorine atoms can be fluorinated by reacting with calcium ions to separate the calcium fluoride into a solid and liquid. It can be recovered with good yield as calcium fluoride. Calcium fluoride obtained by this method can be effectively used as a raw material for various fluorine compounds, and effectively uses fluoroalkyl iodides with unnecessary chain lengths, especially long-chain telomers with little industrial utility value. It becomes possible to do. The present invention has been completed based on these novel findings.

That is, this invention provides the utilization method of the following fluoroalkyl iodide.
Item 1. General formula (1): R _f (CF ₂ CF ₂ ) _n I (wherein Rf is a C 1-10 fluoroalkyl group, characterized in that it comprises the following steps (i) to (iii): And n is an integer of 1 or more).
(I) A fluoroalkyl iodide represented by the general formula (1): R _f (CF ₂ CF ₂ ) _n I (wherein Rf and n are the same as above) is reacted with ethylene to give a general formula (2 ): R _f (CF ₂ CF ₂ ) _n CH ₂ CH ₂ I (wherein Rf and n are the same as above), an ethylene adduct,
(Ii) The ethylene adduct represented by the general formula (2) obtained in the step (i) is at least selected from the group consisting of an alkali metal hydroxide and an alkali metal alkoxide in the presence of a lower alcohol. is reacted with one alkali metal compound, the general formula _{(3): R f (CF} 2 CF 2) ( wherein, Rf and n are as defined above) _n CH = CH ₂ step for an olefin compound represented by the ,
(Iii) A step of heating the olefin product represented by the general formula (3) obtained in the step (ii) to generate hydrogen fluoride and absorbing it into water to obtain hydrofluoric acid.
Item 2. Item 2. The method according to Item 1, wherein the fluoroalkyl iodide represented by the general formula (1) has 8 or more carbon atoms.
Item 3. Item 1 or 2 wherein the lower alcohol used in step (ii) is at least one selected from the group consisting of methanol and ethanol, the alkali metal hydroxide is sodium hydroxide, and the alkali metal alkoxide is sodium methoxide. The method described in 1.
Item 4. Item 4. A method for using a fluoroalkyl iodide, characterized in that hydrofluoric acid obtained by any one of items 1 to 3 is reacted with calcium ions and recovered as calcium fluoride.

  Hereinafter, the method of the present invention will be specifically described.

(1) Object to be treated The object to be treated of the method of the present invention is represented by the general formula (1): R _f (CF ₂ CF ₂ ) _n I (wherein Rf is a fluoroalkyl group having 1 to 10 carbon atoms, n is an integer of 1 or more).

The fluoroalkyl iodide represented by the general formula (1) can be obtained, for example, by a telomerization reaction between a fluoroalkyl iodide represented by R _f -I and tetrafluoroethylene. In R _f -I, R _f is a fluoroalkyl group having 1 to 10 carbon atoms, preferably a fluoroalkyl group having 1 to 8 carbon atoms, more preferably a fluoroalkyl group having 1 to 5 carbon atoms. . R _f is preferably a perfluoroalkyl group.

Specific examples of R _f -I include trifluoromethyl iodide, pentafluoroethyl iodide, perfluoroisopropyl iodide, perfluoro-n-butyl iodide, and the like. Of these, pentafluoroethyl iodide is often used for the telomerization reaction of tetrafluoroethylene.

  In the fluoroalkyl iodide telomer represented by the general formula (1) to be treated by the method of the present invention, the polymerization degree n is an integer of 1 or more, and is usually in the range of about 2 to 12. For example, a long chain telomer having 8 or more carbon atoms can be effectively treated. Usually, in the method of the present invention, a mixture of fluoroalkyl iodide telomers having different values of polymerization degree n can be treated.

(2) Treatment method According to the method of the present invention, the fluoroalkyl iodide represented by the above general formula (1) is treated, and the treatment is performed according to the following steps, whereby the fluoroalkyl iodide in the fluoroalkyl iodide is treated. Fluorine atoms can be recovered as hydrofluoric acid.
(I) a step of reacting the fluoroalkyl iodide represented by the general formula (1) with ethylene to form an ethylene adduct,
(Ii) The ethylene adduct represented by the general formula (2) obtained in the step (i) is at least selected from the group consisting of an alkali metal hydroxide and an alkali metal alkoxide in the presence of a lower alcohol. is reacted with one alkali metal compound, the general formula _{(3): R f (CF} 2 CF 2) ( wherein, Rf and n are as defined above) _n CH = CH ₂ step for an olefin compound represented by the ,
(Iii) A step of heating the olefin product obtained in step (ii) to generate hydrogen fluoride and absorbing it into water to form hydrofluoric acid.

  Hydrofluoric acid recovered by the above-mentioned method is a substance useful for semiconductor etching and glass processing, and further, it can be effectively used as a raw material for various fluorine compounds by processing by the method described below. Available calcium fluoride (fluorite) can be easily obtained.

  Hereinafter, each process described above will be described in detail.

(I) The ethylene addition step <br/> ethylene addition step, the general formula _{(1): R f (CF} 2 CF 2) n I ( wherein, Rf is selected from the group consisting a fluoroalkyl group having 1 to 10 carbon atoms, n is an integer greater than or equal to 1), and ethylene is added to the fluoroalkyl iodide represented by the general formula (2): R _f (CF ₂ CF ₂ ) _n CH ₂ CH ₂ I (wherein Rf and n is the same as described above).

  This step can be carried out under conditions generally employed in ethylene addition reactions. Specifically, ethylene addition may be carried out at a reaction temperature of 50 to 200 ° C., for example 70 to 120 ° C., and a reaction pressure of 0.01 to 3 MPa, for example 0.1 to 1 MPa. The reaction time is generally 0.5 to 4 hours. The reaction pressure is the pressure generated by the injected ethylene.

  It is preferable that the usage-amount of ethylene shall be about 1-1.2 mol with respect to 1 mol of fluoroalkyl iodides represented with General formula (1).

  The ethylene addition reaction is preferably carried out in the presence of a catalyst that generates radicals. As a catalyst, an azo compound, an organic peroxide, etc. can be used, for example. As the azo compound, for example, α, α'-azobisisobutyronitrile can be used. Examples of the organic peroxide that can be used include diacyl peroxides such as benzoyl peroxide, dialkyl peroxides such as t-butyl peroxide, and peroxymonocarbonates such as t-butyl percarbonate. The amount of the catalyst is preferably about 0.005 to 0.02 mol with respect to 1 mol of the fluoroalkyl iodide represented by the general formula (1).

  In addition, by performing the ethylene addition reaction in the presence of a metal copper catalyst, a high conversion can be achieved, and a monoethylene adduct can be produced with a high selectivity. Moreover, since the metal copper catalyst is a solid catalyst, there is an advantage that it can be easily separated from the product and can be reused.

  The metal copper catalyst is not particularly limited as long as it is copper of a single metal. The metal copper catalyst is preferably in the form of a powder having a large contact area with the starting material on the surface of the metal copper from the viewpoint of catalytic activity. As an average particle diameter of powdery copper, what is necessary is just to be about 0.1-300 micrometers, for example, and about 30-150 micrometers is preferable. The amount of the metal copper catalyst used may be, for example, about 0.1 to 90% by weight, and about 0.5 to 10% by weight with respect to the weight of the fluoroalkyl iodide represented by the general formula (1). preferable.

  The metal copper catalyst may be a metal copper supported on a carrier. The carrier that can be used is not particularly limited as long as it does not adversely affect the activity of the metal copper catalyst, and examples thereof include metal oxides. Specifically, a single metal metal oxide selected from the group consisting of zinc oxide, iron oxide, copper oxide, titanium oxide, zirconium oxide, cerium oxide, aluminum oxide, and silicon oxide, or zinc, iron, copper, Examples thereof include composite oxides of two or more metals selected from the group consisting of titanium, zirconium, cerium, aluminum, and silicon. The shape of the carrier supporting metal copper is not particularly limited, but a powder is preferable from the viewpoint of catalytic activity. A known method may be used as a method for immobilizing metallic copper on the carrier.

  The content of the metallic copper in the metallic copper catalyst in which metallic copper is supported on the carrier may be about 0.01 to 50% by weight, and about 0.1 to 20% by weight with respect to the total amount of the catalyst. Is preferred.

  The amount of the metallic copper catalyst in which metallic copper is supported on a carrier may be, for example, about 0.1 to 90% by weight with respect to the weight of the fluoroalkyl iodide represented by the general formula (1). Is about 0.5 to 10% by weight.

  In addition, another metal may be added to the copper metal catalyst in order to increase the activity of the catalyst. For example, titanium, chromium, iron, cobalt, nickel, tin and the like are exemplified. Of these, tin is preferred. The amount of other metals to be added may be, for example, about 0.1 to 90% by weight, preferably about 10 to 30% by weight, based on the weight of the metal copper catalyst. The other metal is preferably in powder form from the viewpoint of catalytic activity.

  In the case of using a metal copper catalyst, the ethylene addition reaction may be performed by reacting the fluoroalkyl iodide represented by the general formula (1) with ethylene under pressure of ethylene gas in the presence of the metal copper catalyst. The pressure of ethylene gas should just be about 0.01-3 MPa, for example, Preferably it is about 0.1-1 MPa. The usage-amount of ethylene gas should just be about 1-1.2 mol with respect to 1 mol of fluoroalkyl iodides represented with General formula (1).

  In the ethylene addition reaction, for example, a fluoroalkyl iodide represented by the general formula (1) and a metal copper catalyst are put in a pressure heating vessel such as an autoclave, if necessary, and the inside of the vessel is degassed and reacted with a heater. After heating up to temperature, it can carry out by introduce | transducing ethylene gas in a container and stirring for a fixed time at the same temperature. The reaction temperature may be, for example, about 50 to 200 ° C., and preferably about 70 to 120 ° C. from the viewpoint of safety and reaction rate.

  In the ethylene addition reaction, when ethylene is consumed, the internal pressure of the reaction decreases and the reaction rate decreases. Therefore, it is preferable to supply ethylene successively to keep the internal pressure constant.

  The reaction time of the ethylene addition reaction may vary depending on the reaction conditions, but is usually about 0.5 to 4 hours, and the end point of the reaction may be the point at which no ethylene pressure drop is observed.

(Ii) Olefination step In the olefination step, in the presence of a lower alcohol, the general formula (2) obtained in the above step (i): R _f (CF ₂ CF ₂ ) _n CH ₂ CH ₂ I (wherein , Rf and n are the same as described above) and at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal alkoxides are reacted to give a general formula (3 ): R _f (CF ₂ CF ₂ ) _n CH═CH ₂ (wherein Rf and n are the same as above).

  As the alkali metal hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, or the like can be used. Of these, sodium hydroxide is preferred because it is particularly inexpensive and available.

  As the alkali metal alkoxide, thium methoxide, lithium ethoxide, sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, or the like can be used. Among these, sodium methoxide, which is widely distributed at a relatively low cost, is preferable.

  The alkali metal hydroxide and alkali metal alkoxide can be used singly or in combination of two or more.

  The amount of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal alkoxides is 1 to 1 mol per 1 mol of the ethylene adduct represented by the general formula (2) as the total amount. The amount is preferably about 1.5 mol, more preferably about 1 to 1.2 mol.

  The olefination reaction needs to be performed in the presence of a lower alcohol. As the lower alcohol, a lower alcohol having about 1 to 4 carbon atoms is preferable, and methanol, ethanol and the like are particularly preferable. In particular, it can be obtained at a low cost, and since it does not have an azeotropic composition with water, it is easy to recover, and further, the amount of dissolved olefinate is small and the yield after separation is good. In this respect, methanol is preferable. A lower alcohol can be used individually by 1 type or in mixture of 2 or more types.

Regarding the amount of the lower alcohol used, the total amount of at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal alkoxides is 1.5 mol to 1 liter of lower alcohol. The amount is preferably in the range of 4 mol, and more preferably in the range of 2 to 3 mol. General formula (3) generated after the reaction by using a lower alcohol so that the concentration of the alkali metal compound falls within the specific range described above: R _f (CF ₂ CF ₂ ) _n CH═CH ₂ (where Rf And n are the same as described above) are separated from the alcohol and clearly separated into two layers of an olefinate layer and an alcohol layer. Thereby, a high purity olefination thing can be collect | recovered only by liquid-separating an olefination thing layer and an alcohol layer. Further, since the amount of olefinated product dissolved in the alcohol layer is very small, the yield of olefinated product is greatly improved.

  The olefination step may be performed in the presence of water. However, if the amount of water is too much with respect to the lower alcohol, the reaction rate is lowered, and there is a risk of hindering the recovery of the lower alcohol after the reaction. For this reason, it is preferable that it is 45 volume parts or less with respect to 100 volume parts of lower alcohol, and it is especially preferable that it is 11.5 volume parts or less.

  The specific method for carrying out the olefination step is not particularly limited, but an example of the treatment method is as follows.

  First, a reaction vessel is charged with at least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal alkoxides, a lower alcohol, and an ethylene adduct represented by the general formula (2). I do. At this time, if necessary, the reaction solution may be heated and stirred.

  At least one alkali metal compound selected from the group consisting of alkali metal hydroxides and alkali metal alkoxides may be added to the lower alcohol at the same time as the ethylene adduct, or before the addition of the ethylene adduct, the lower alcohol It may be dissolved in

  Although reaction temperature is not specifically limited, When reaction rate, safety | security, and economical efficiency are considered, it is about 0-200 degreeC normally, Preferably what is necessary is just to be about 20-160 degreeC.

  The pressure during the reaction is not particularly limited, and the reaction can usually be performed under normal pressure or increased pressure.

  About reaction time, what is necessary is usually just about 1 to 10 hours.

  By the above-mentioned method, the olefination product represented by the general formula (3) can be obtained. By allowing the obtained reaction solution to stand, the reaction solution is separated into two layers of a layer containing the target olefin compound and an alcohol layer. By collecting the lower olefin product layer by liquid separation, a high-purity olefin product can be obtained. Moreover, since the olefination substance which melt | dissolves in an alcohol layer is very few, an olefination substance can be obtained with a high yield.

(Iii) Heat treatment step In the heat treatment step, the olefin product obtained in the above step (ii) is heated to form hydrogen fluoride by thermal decomposition, and absorbed in water to form hydrofluoric acid. In this process, there is no generation of hydrogen iodide and iodine that occurs when the fluoroalkylidide telomer is directly heated and decomposed, and the equipment is corroded and deteriorated by hydrogen iodide and iodine, and the hydrofluoric acid formed Problems such as mixing of iodine atoms inside can be solved.

  The heat treatment process may be performed under conditions where hydrogen fluoride is generated, and can be performed in a known fluorocarbon destruction facility. As the CFC destruction facility, for example, a submerged combustion method facility, a plasma method facility, a catalyst method facility, a superheated steam reaction method facility, or the like can be used. For example, in a submerged combustion method facility, fuel, air as an oxygen source, an incinerator capable of heat treatment by introducing an object to be heat treated and steam for hydrolyzing it, and generated by blowing combustion gas into water It can process with the equipment provided with the cooling can and / or an absorption can which absorb and collect | recover an acid content in water. Hydrofluoric acid can be recovered as an acid component by introducing the olefin compound as a treatment target.

  Hereinafter, the heat treatment method using the submerged combustion method will be described more specifically.

  As the operating condition of the incinerator, combustion is insufficient when the temperature is low, and damage to the furnace becomes severe when the temperature is high, so the temperature in the furnace is 800 ° C or higher and 1600 ° C or lower, preferably 1000 ° C or higher and 1400 ° C or lower. That's fine. Although there is no restriction | limiting in particular in the pressure in a furnace, what is necessary is just to make it atmospheric pressure vicinity from the ease of an operation | movement, for example, what is necessary is just about -0.05-0.1 MPaG.

  The residence time of the olefin product in the incinerator is usually 1 second or longer, and preferably 2 seconds or longer.

  As an object to be treated, the olefinated product obtained in the above step (ii) can be used alone, and heat treatment can be performed simultaneously with other fluorine compounds. The fluorine compound that can be heat-treated at the same time is not particularly limited as long as it is a compound having fluorine in the molecule and can be supplied into the furnace. However, when recovering hydrofluoric acid with high purity, the constituent elements of the compound are A compound containing two or more elements selected from the group consisting of C, F, H, and O is desirable.

  In addition, when a chlorine-containing compound is treated simultaneously with the olefin compound, hydrochloric acid is contained in the recovered hydrofluoric acid, so a separate purification step is required to recover hydrofluoric acid with high purity. When the obtained hydrofluoric acid is treated in the step (iv) described later to obtain calcium fluoride, a purification step is required even when the calcium fluoride forming step is performed from hydrofluoric acid containing hydrochloric acid. Therefore, calcium fluoride can be recovered with high purity.

  City gas, heavy oil, etc. can be used as fuel. The amount of fuel to be introduced is not particularly limited, but an amount in which the operating temperature in the furnace becomes a temperature in the above range is necessary.

  The introduction of air is to supply the fluorine compound to be processed simultaneously with the above olefinated product and oxygen necessary for complete combustion of the fuel, and the introduction amount thereof is usually about 1 to 3 as the air ratio. What is necessary is just about 1-2. If the air ratio is large, the flame becomes unstable and causes misfire, and if the air ratio is small, incomplete combustion occurs. The air ratio is the ratio of the amount of air actually used to the theoretical amount of air when burning combustibles (processing object and fuel).

The introduction of the steam is for the purpose of suppressing the generation of nitrogen oxides by increasing the temperature in the furnace, by hydrolyzing the F atoms of the burned fluorine compound into hydrogen fluoride. The amount of introduction is not particularly limited, but even if an excess amount is introduced, the effect is not changed, and it causes corrosion due to condensation, and is generally about 10 kg / hr with respect to 100 Nm ³ / h of air.

  According to the above method, the fluorine atom of the olefin compound can be decomposed into hydrogen fluoride with very high efficiency by heat treatment.

  The heat-treated high-temperature gas containing hydrogen fluoride can be recovered as hydrofluoric acid by blowing it into a large amount of water and quenching it to absorb an acid component such as hydrogen fluoride in water.

  The amount of water that absorbs hydrogen fluoride depends on the amount of combustion, but if the concentration of recovered hydrofluoric acid is low, the treatment efficiency is poor, and if the concentration is high, it causes corrosion. An amount of water is used in which the concentration of hydrofluoric acid is 1 to 20% by weight, preferably 3 to 10% by weight.

(Iv) Calcium fluoride forming step In the calcium fluoride forming step, the pH of the hydrofluoric acid recovered in the step (iii) is adjusted in the presence of calcium ions to form calcium fluoride (CaF ₂ ). Since the hydrofluoric acid recovered in the step (iii) has a low impurity content, high-purity calcium fluoride can be obtained without performing a step for removing the impurities.

  In addition, even if other fluoride ions such as chloride ion, bromide ion, and iodide ion are contained as impurities in hydrofluoric acid, the solubility of each calcium salt in water is higher than the solubility of calcium fluoride. Is sufficiently high, calcium fluoride can be obtained with high purity by reacting with calcium ions.

  The calcium fluoride forming step may be performed under the condition that calcium fluoride is formed by the reaction. Usually, calcium fluoride is precipitated by adjusting hydrofluoric acid to pH 5 to 8.5 and reacting with calcium ions, and solid-liquid separation may be performed.

  The concentration of hydrofluoric acid is not particularly limited, but it may be usually about 1 to 20% by weight.

  Examples of calcium salts that can be used include calcium chloride, calcium hydroxide, calcium oxide, calcium carbonate, and calcium sulfate. Among these, calcium chloride is preferable because of its high solubility in water. When calcium chloride is used, it is supplied in the form of an aqueous solution. The concentration of the aqueous solution of calcium chloride is not particularly limited, but can be about 1 to 30% by weight.

  The necessary abundance of calcium ions may be about 0.5 to 1.5 mol per mol of fluorine ions.

  As the pH adjuster, sodium hydroxide, sodium carbonate, calcium hydroxide and the like can be used when the reaction solution is acidic. Among them, calcium hydroxide is preferable because it can be used as a calcium ion source. When calcium hydroxide is used, it can be supplied to the reaction system in the form of a powder or an aqueous solution, but is preferably supplied as a slurry suspended in water. In the slurry, the calcium hydroxide particles are dispersed in a concentrated calcium hydroxide aqueous solution. The slurry concentration of calcium hydroxide is not particularly limited, but can be about 1 to 30% by weight. In addition, hydrochloric acid, sulfuric acid, and the like can be used when the reaction solution is shaken alkaline, but hydrochloric acid is desirable because of the high solubility of the calcium salt. By adjusting the pH range by adding such a pH adjuster, a precipitate is generated. The precipitate is calcium fluoride.

  In order to improve the sedimentation and separation of the calcium fluoride precipitate, it is preferable to add an inorganic flocculant and / or an organic flocculant to the reaction liquid to cause aggregation. As the inorganic flocculant, sulfuric acid, polyaluminum chloride, sulfuric acid band and the like can be used. As the organic flocculant, a polymer flocculant or the like can be used.

  The amount of the flocculant added is preferably 0.5% by weight or less with respect to the total amount of the reaction liquid because it causes a decrease in the purity of the calcium fluoride to be recovered.

  The calcium fluoride precipitate obtained by the reaction with calcium ions can be separated using a known solid-liquid separation means. For example, it can be separated using a clarifier or thickener.

  The solid content obtained by solid-liquid separation can be dehydrated by a known means such as a filter press or a screw decanter.

  In order to increase the purity of the dehydrated solid, it is desirable to perform washing, and since impurities are inorganic solids, it is preferable to perform water washing.

  The solid obtained by the washing step can be dried using various drying means. For example, various drying means such as hot air drying, vacuum drying, air blowing, spin drying, and radiation heating drying can be used. For example, by performing hot air drying, a calcium fluoride solid with moisture reduced to about 15 wt% or less can be obtained.

  Through the above steps, the fluorine atom of hydrofluoric acid can be recovered as a calcium fluoride solid with a yield of 90% or more. Moreover, this method makes it possible to recover calcium fluoride having a solid content of calcium fluoride of 90% by weight or more.

  By the above method, the fluoroalkyl iodide telomer having an unnecessary chain length obtained by the telomerization reaction can be recovered as calcium fluoride at a high recovery rate. Calcium fluoride recovered by this method can be effectively used as a raw material for producing a fluorine compound.

  According to the method of the present invention, fluorine atoms can be recovered in a very high yield as hydrofluoric acid from telomers with unnecessary chain length contained in the fluoroalkyl iodide obtained by telomerization reaction. Hydrofluoric acid obtained by this method is a useful substance that can be used, for example, as an etching agent for semiconductors or a processing agent for glass.

  Moreover, in the method of the present invention, since iodine can be almost completely removed in the olefination step, hydrogen iodide and iodine are not generated in the heat treatment step, and the equipment is corroded, deteriorated or regenerated hydrogen fluoride. There are no problems such as mixing of iodine atoms inside.

  Furthermore, the hydrofluoric acid recovered by the method of the present invention is highly pure and highly useful as a raw material for producing a fluorine compound with a high recovery rate by a relatively simple method without requiring complicated purification steps. It can be recovered as calcium fluoride (fluorite).

  Therefore, according to the method of the present invention, it is possible to effectively use an unnecessary chain length telomer contained in a fluoroalkyl iodide obtained by a telomerization reaction, which is extremely remarkable such as effective utilization of rare resources and production cost reduction. Effects are achieved.

  Hereinafter, in order to show the effectiveness of each process of the processing method of the present invention, the present invention will be described in detail by giving an example of each process.

Example 1: Ethylene addition step In a 200 ml Hastelloy autoclave, 130.8 g of 1-iodoperfluorooctane (n-C ₈ F ₁₇ I) and 2.66 g of copper powder were added, deaerated, and heated to 80 ° C. Then, ethylene was introduced to adjust the internal pressure of the autoclave to 0.1 MPa. Ethylene was introduced while maintaining the internal pressure at 0.1 MPa, and the end of the reaction was defined as the point at which no pressure drop of ethylene was observed. The reaction time was 120 minutes. As a result of analysis by gas chromatography after cooling the reaction mixture, the conversion of 1-iodoperfluorooctane was 99.7%, and the selectivity of the produced ethylene adduct (ethylene monomolecular adduct) was 99.9. % Or more.

Example 2: Olefination process A 200 mL eggplant flask equipped with a Dimroth condenser was charged with 89.7 mmol of 98% sodium hydroxide and 45 ml of methanol and stirred at 50 ° C until the sodium hydroxide was dissolved. . After dissolution of sodium hydroxide, 50.02 g of 1H, 1H, 2H, 2H-1-iodoperfluorodecane was added, and the mixture was further stirred at 50 ° C. for 2 hours.

  After heating and stirring were stopped and the mixture was allowed to stand, the two-layer solution was separated, and 36.18 g of the lower layer was recovered as 1H, 1H, 2H-perfluorodecene. As a result of analysis by gas chromatography, the purity was 99.99 GC%. Further, the weight of the separated methanol layer was 50.72 g.

Example 3: Olefination process
Into a 100 mL shaking autoclave, charge 29.9 g of 1H, 1H, 2H, 2H-1-iodoperfluorodecane, 53.9 mmol of 98% sodium hydroxide, and 26.9 ml of methanol. Stir for hours.

  After heating and stirring were stopped and the mixture was allowed to stand, the two-layer solution was separated, and 22.52 g of the lower layer was recovered as 1H, 1H, 2H-perfluorodecene. As a result of analysis by gas chromatography, the purity was 99.99 GC%. Further, the weight of the separated methanol layer was 31.34 g.

Example 4: Olefination process
In a 100 mL shaking autoclave, a mixture of 1-iodo-2- (perfluoroalkyl) ethane in which n is 3 or 4 in the formula: C ₂ F ₅ (CF ₂ CF ₂ ) _n CH ₂ CH ₂ I 30.03 g, 52.0 mmol of 98% sodium hydroxide and 26.9 ml of methanol were added, and the mixture was immersed in an oil bath at 80 ° C. and stirred for 2 hours.

  Heating and stirring were stopped and the mixture was allowed to stand, and the two-layer solution was separated to recover 22.97 g of the lower layer as perfluoroalkylethylene. Table 1 shows the composition of the raw material and the conversion rate of the reaction by gas chromatography analysis. Further, the weight of the separated methanol layer was 29.08 g.

Example 5: Olefination process
In a 100 mL shaking autoclave, 1-iodo-2- (perfluoroalkyl) ethane in which n is in the range of 3 to 11 in the formula: C ₂ F ₅ (CF ₂ CF ₂ ) _n CH ₂ CH ₂ I 30.00 g, 98% sodium hydroxide 48.6 mmol, and methanol 24.3 ml were added, immersed in an oil bath at 150 ° C. and stirred for 2 hours.

  Heating and stirring were stopped and the mixture was allowed to stand, and the resulting two-layered white solution was separated to recover 21.21 g of the lower layer as perfluoroalkylethylene. Table 1 shows the composition of the raw material and the conversion rate of the reaction by gas chromatography analysis. Further, the weight of the separated methanol layer was 28.50 g.

Example 6: absorption cooling cans heat treatment incineration gases, heat treatment using a cylindrical vertical liquid combustion furnace of 3m ³ submerged combustion system having a waste gas treatment facility, and wastewater treatment equipment was performed. An incinerator operating at 1250 ° C. with a city gas introduction rate of 34 kg / h, a steam introduction rate of 63 kg / h, and an air introduction rate of 980 Nm ³ / h was introduced into 1H, 1H, 2H-perfluorodecene ( A fluorine-containing compound containing C ₈ F ₁₇ CH═CH ₂ ) was introduced at 47 kg / h. The main component of the fluorine-containing compound was a fluorine-containing ether mixture represented by the composition formula C ₅ F ₈ H ₄ O that is liquid at room temperature with an HFC mixed gas such as HFC32 and HFC125. The residence time at this time was 2.3 seconds. The heat-treated gas was rapidly cooled through the cooling water with an absorption cooling can, whereby the cooling water could be recovered as hydrofluoric acid, and the recovery rate as hydrogen fluoride was 99.9% or more. The gas that passed through the cooling water was released into the atmosphere through a detoxification tower containing sodium hydroxide. When the exhaust gas was analyzed by gas chromatography, the decomposition rate of the fluorine compound was 99.99% or more.

Example 7: Calcium fluoride formation step 50 g of 5 wt% hydrofluoric acid was charged into a 1 L PFA flask. Separately, 556 g of a 1% by weight slurry of calcium hydroxide dispersed in water with a beaker was added dropwise with a dropper over 15 minutes under stirring at room temperature. Next, 6 g of 10% by weight sulfuric acid was added. The pH of the reaction solution after the dropping was 8. While stirring, 6 g of a polymer flocculant diluted to 0.1% by weight with water was added and further stirred for 5 minutes.

  The reaction solution was subjected to suction filtration using a Kiriyama funnel to separate the solid. The obtained solid was washed with 100 g of water and filtered with a Kiriyama funnel twice. The solid washed with water was dried at 110 ° C. for 2 hours with a constant temperature dryer. After cooling to room temperature, 5.3 g of calcium fluoride white solid was obtained. As a result of analysis by an infrared moisture meter, the water content was 1% by weight. As a result of atomic absorption and F ion analysis, the purity of calcium fluoride in the solid content was 93%. Impurities were calcium sulfate and calcium carbonate. The yield of calcium fluoride from hydrofluoric acid was 99%.

Claims (4)

General formula (1): R _f (CF ₂ CF ₂ ) _n I (wherein Rf is a C 1-10 fluoroalkyl group, characterized in that it comprises the following steps (i) to (iii): And n is an integer of 1 or more).
(I) A fluoroalkyl iodide represented by the general formula (1): R _f (CF ₂ CF ₂ ) _n I (wherein Rf and n are the same as above) is reacted with ethylene to give a general formula (2 ): R _f (CF ₂ CF ₂ ) _n CH ₂ CH ₂ I (wherein Rf and n are the same as above), an ethylene adduct,
(Ii) The ethylene adduct represented by the general formula (2) obtained in the step (i) is at least selected from the group consisting of an alkali metal hydroxide and an alkali metal alkoxide in the presence of a lower alcohol. is reacted with one alkali metal compound, the general formula _{(3): R f (CF} 2 CF 2) ( wherein, Rf and n are as defined above) _n CH = CH ₂ step for an olefin compound represented by the ,
(Iii) A step of heating the olefin product represented by the general formula (3) obtained in the step (ii) to generate hydrogen fluoride and absorbing it into water to obtain hydrofluoric acid. The method according to claim 1, wherein the fluoroalkyl iodide represented by the general formula (1) has 8 or more carbon atoms. The lower alcohol used in step (ii) is at least one selected from the group consisting of methanol and ethanol, the alkali metal hydroxide is sodium hydroxide, and the alkali metal alkoxide is sodium methoxide. 2. The method according to 2. A method for using a fluoroalkyl iodide, characterized in that hydrofluoric acid obtained by the method according to any one of claims 1 to 3 is reacted with calcium ions and recovered as calcium fluoride.