RU2544849C1 - Method of purifying perfluorodecalin - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes crystallising perfluorodecalin in two steps: at the first step, crystallisation is carried out while reducing the temperature to minus 17°C - minus 18°C at a rate of 1-2°C per minute while stirring; the mass is held at a temperature of minus 17°C - minus 18°C for 30-35 minutes, filtered and dried and the obtained crystals are separated; the crystals are then melted at ambient temperature; at the second step crystallisation is repeated at the same conditions, but while reducing temperature to minus 15°C. The product obtained using the present method has purity higher than 99 wt %.

EFFECT: high purity of the finished product.

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Description

The invention relates to organic chemistry, and in particular to methods for producing perfluorinated cyclic compounds, in particular perfluorodecalin (hereinafter PFD), free of fluorinated impurities.

PFD can be used as a gas transfer medium, coolant, and dielectric. PFD dissolves oxygen well and is therefore used as an intraoperative drug in ophthalmology. This product is also widely used in cosmetology. PFD is a component of the blood substitute drug - perfluorane.

In industry, PFDs are obtained through exhaustive fluorination of naphthalene with cobalt trifluoride. The obtained raw PFD undergoes alkaline purification, rectifies and is isolated with a content of about 93% of the target commercial product.

The commercial product - PFD is a mixture of cis and trans isomers in a percentage ratio of 45-50: 50-55 with a boiling point in the range 142-143 ° C. Along with PFD, during fluorination of naphthalene, a significant amount of destructive fluorination products is formed, as well as perfluorinated isomers containing perfluoroalkylcyclohexanes with a total number of carbon atoms equal to 10, as in PFD: C ₆ F ₁₀ (CF ₃ ) C ₃ F ₇ , C ₆ F ₁₀ (C ₂ F ₅ ) ₂ , C ₆ F ₁₁ C ₄ F ₉ and others (more than 25 products in total).

In addition, the product obtained as a result of fluorination contains the following boiling impurities:

perfluoromethylcyclohexane, T bale 76.3 ° C,

perfluoroethylcyclohexane, T bp 101 ° C),

perfluorobutylcyclopentane and perfluorobicyclo- [4,3,1] nonane (C ₉ F ₁₆ ) with T bale 125 - 128 ° C,
C10F16 - Hexafluorobicyclo [4.4.0] decen-1, 6, T bp 126 ° C
C10F15H - Pentadecafluorocyclo-3H- [4.4.0] decen-1, 6, T bp 139 ° C,

 and boiling impurities close to PFD: pentadecafluorocyclo-3H- [4,4,0] decane (C10F17H with T bale 149 ° C), various high-boiling under-fluorinated naphthalenes of the general formula C10FxH18-x with T bale 155-160 ° C.

These impurities increase electrical conductivity and increase the toxicity of the finished product.

One of the main requirements for the product is that the amount of hydrogen-containing impurities in terms of fluoride ion should not exceed 3 · 10 ^-5 wt.%. Similar requirements apply when using PFD in perfume ointments and fluids for skin care and treatment, as well as in ophthalmic surgery.

Currently, the purity of the manufactured industrial product - PFD according to TU 95-1233-92 is 93.0 wt.%, However, due to increased demands on the quality of the product, there is a need to increase its purity to 99 wt.%.

The known method (LP, t.69, issue 1, s.116, 1996) purification of PFD using adsorbents, which consists in the fact that the rectified PFD obtained after treatment with an aqueous-alcoholic alkali solution with a fluoride ion content of 2 · 10 ^{- 4} mol / l, passed through adsorbents - silica gel and activated carbon. The product thus purified has a fluoride ion content of (1-3) · 10 ^-5 mol / l, i.e. a tenfold decrease in hydrogen-containing impurities occurs, but the amount of perfluorinated impurities remains almost unchanged. Also, due to the exceptional chemical inertness of PFD and impurities, it turned out to be impossible to concentrate PFD by chemical methods - oxidation, reduction, hydrolysis or esterification of impurities.

The authors of the invention carried out experiments on separation by distillation contained in the commodity PPD isomers that have similar boiling points (141 ± 5 ° C).

 The proximity of the boiling points of PFD and isomers, as well as their tendency to form azeotropes, make it difficult to isolate concentrated PFD by distillation. Using a highly efficient column (40 theoretical plates), it is possible to increase the concentration of PFD from 94.6 to 96.5 wt.% In the amount of 10% of the loaded PFD.

The objective of the invention was to provide a method for producing high purity PFD - not less than 99 wt.% Of the target product with a fluoride ion content of not more than 3 · 10 ^-5 mg / L.

It is known that PFD freezes at -10 ° C, while the perfluorinated impurities included in the commercial product have a freezing temperature below minus 30 ° C, which allows the PFD to be purified by crystallization. However, as the authors found, with rapid cooling of the mass, precipitated PFD crystals “capture” impurities, reducing the crystallization efficiency. Therefore, in order to efficiently concentrate PFD, it is necessary to create a new approach to crystallization in such a way that, when choosing the temperature and crystallization rate, the maximum concentration of PFD in the crystals is achieved and mass flow is maintained.

The problem is solved by carrying out crystallization with stirring in two stages, with a decrease in temperature at a certain speed to the desired value, filtration and drying of the obtained crystals.

The essence of the invention lies in the fact that a method has been developed for the purification of perfluorodecalin obtained by fluorination of naphthalene, characterized in that crystallization of perfluorodecalin in two stages is carried out:

1 - first, crystallization is carried out with a decrease in temperature to minus 17 - minus 18 ° C at a speed of 1-2 ° C per minute with stirring, then the mass is kept at a temperature of minus 17 - minus 18 ° C for 30-35 minutes, filtered, dried and the resulting crystals are separated, then they are melted at ambient temperature,

2 - then the crystallization is repeated, as in stage 1, with a decrease in temperature to minus 15 ° C at the same speed with stirring and aging under the same conditions, after which it is filtered and dried, as described above.

After the first stage of crystallization, the PPD content in the resulting product is 97.2-98.2 wt.%.

PFD obtained as a result of the second crystallization, contains 99.0-99.3% of the target product.

The method is as follows:

Stage 1: the obtained raw PFD with a basic substance content of about 94-95 wt.% Is placed in a stainless steel apparatus with an anchor low-speed mixer - mixing helps to reduce "fur coat" (this term means the settling of crystals on the surface of the apparatus). The device has a cooling jacket and a bottom drain. To reduce "fur coat" cooling the reaction mass is carried out at a speed of 1-2 ° C per hour. Step cooling will prevent instant freezing ("setting") of the solution into the polycrystalline mass and the associated risk of breakdown of the mixer. In the case of "setting" the mixer is turned off, a warmer coolant (about -5 ° C) is supplied to the shirt, as a result of which the mass melts, then the mixer is switched on again and cooling continues. The speed of the mixer is chosen so as to prevent cracking of the crystals.

Then the resulting mass is maintained to minus 17-18 ° C for 30-35 minutes.

After that, the mixture from the crystallizer is transferred to a filter reactor, which is a steel apparatus with a jacket and a false bottom, on which a layer of filter cloth, for example belting (possibly several layers), is laid.

 A coolant with a crystallization temperature is fed into the jacket of this apparatus. Nitrogen or dry air is supplied to the top of the apparatus to prevent ice from settling on the crystals. A vacuum pump is attached to the apparatus for efficient suction of the mother liquor into the receiver. The crystals are dried by blowing with chilled nitrogen or dry air, the drying time is determined by analysis of the crystals.

Filtration is carried out at a temperature of minus 17-18 ° C.

After drying of the crystals, the mother liquor merges, and the molten crystals are transferred to the receiver. PFD crystals are molten by supplying a refrigerant with a temperature of more than -5 ° C to the filter-reactor jacket.

Then the separated crystals are melted and subjected to recrystallization under the same conditions, but bringing the temperature of the stirred mass to -15 ° C, after which the mass is kept for 30 minutes and transferred to the filter. Filtration is carried out at a temperature of -15 ° C.

Filtration is carried out until the mother liquor is stopped (30-40 minutes) and additionally in a stream of nitrogen for another 1-1.5 hours. The obtained crystals are unloaded and analyzed by GLC on a Crystal-2000M instrument for the content of the target product and fluoride ion (not more than 3 · 10 ^-5 mg / l).

Examples of experiments

Example 1

100 g of the original PFD with a basic substance content of 93.2 wt.%, Loaded into a cylindrical apparatus made of Pyrex glass, equipped with a cooling jacket and slow speed mixer made of fluoroplast-4, cooled from room temperature to -18 ° C at a rate of 2 ° C / min, after which the mass is held for 30 minutes and then filtered at -18 ° C. The crystals are dried by purging with nitrogen cooled to -18 ° C with a dew point of -43 ° C. The obtained crystals (70 g) contain 97.5 wt.% PFD, and 88.1 wt.% PFD is contained in the isolated mother liquor (mother liquor). The crystals are subjected to the second stage of crystallization with cooling at 1 ° C with slow stirring to a temperature of -15 ° C as described above. The resulting PFD (70 g) contains 99.2 wt.% Of the target product. A mother liquor with a concentration of 95% is used to obtain PFD with a concentration of 97 wt.%.

Example 2

 100 g of the starting PPD with a basic substance content of 93.2 wt.% Crystallize as described in example 1, but the cooling rate is 1 ° C per minute in both cycles. After the first crystallization cycle, the product (70 g) contains 97.5 wt.%. After the second crystallization cycle, 70 g of product with a purity of 99.2 wt.% Were obtained.

Example 3

PFD with a concentration of 93.2 wt.% Crystallize in the same way as in examples 1-2, but the cooling rate is 0.5 ° C per minute. Obtained 70 g of PFD with a concentration of 97.5 wt.% After the first crystallization and 70 g with a concentration of 99.2 wt.% After the second. Thus, a decrease in the cooling rate does not lead to a cleaner product.

Example 4

PFD with a concentration of 93.2 wt.% Crystallize, as described in examples 1-3, but the cooling rate is 2.5 ° C per min. Received 70 g of PFD with a concentration of 96.7 wt.% After the first crystallization and 70 g of PFD with a concentration of 98.5 wt.%. Thus, accelerated cooling reduces the purity of the product.

Example 5

The crystallization of PFD with a concentration of 93.2.0 wt.% Is carried out as described in examples 1-4, but at a rate of 3.0 ° C / min. Obtained 70 g of PFD after the first crystallization with a concentration of 96.3 wt.% And 70 g after the second with a concentration of 98.2 wt.%. Thus, accelerated cooling reduces the purity of the product.

Example 6

In a crystallizer apparatus made of steel 12Kh18N10T, with a capacity of 100 l, equipped with a cooling jacket with an adjustable cooling temperature, an anchor stirrer (the anchor stirrer provides satisfactory mass and heat transfer and minimizes the crushing of crystals), as well as with a bottom drain, load 160 kg of PFD with concentration of 93.8 wt.%. When the stirrer is working, a coolant is fed into the apparatus jacket, the mass is cooled at a speed of 1.5-2 ° C / min to -17 ° C and kept at this temperature for 1.5 hours. After that, the mass is transferred through the lower drain to a filter, which is a device made of 12X18H10T steel with a cooling jacket and a false bottom with a diameter of 1000 mm, on which a filter cloth - belting is laid. The temperature of the refrigerant entering the filter jacket is -17 ° C. Nitrogen with a dew point of -43 ° C, cooled to -17 ° C, is fed to the top of the filter to prevent condensation of air moisture on the PFD crystals.

A vacuum pump is connected to the apparatus for efficient suction of the mother liquor from the crystalline mass. After the mother liquor is completely separated (the vacuum worsens), the crystals are “dried” in a stream of nitrogen cooled to -17 ° C for an hour, then the mother liquor is discharged into the mother liquor receiver. The drain pipe is purged with nitrogen at a temperature of + 20 ° C for an hour, after which a coolant with a temperature of + 18 ° C is fed into the filter jacket, the PFD crystals melt and are collected in an amount of 110 kg in a PFD receiver-accumulator with a concentration of 97%. The mass of the mother liquor is 50 kg, the PFD content in it is 88.2 wt.%, The mass of PFD is 97.6 wt.%. The mother liquor can be recrystallized at a lower temperature or used as a dielectric.

PFD with a concentration of 97.6 wt.% In the amount of 160 kg is loaded into a purified crystallizer and crystallization is carried out as described above, but at -15 ° C. Received PFD (110 kg) with a purity of 99.3 wt.%. A mother liquor in an amount of 50 kg with a concentration of 95.4 wt.% Is used to obtain PFD with a concentration of 97 wt.%.

As follows from the results of the above examples, the problem has been solved: a purification method has been developed to obtain the target product of high purity - at least 99 wt.% PFD and the required fluoride ion value.

Claims (1)

1. The method of purification of perfluorodecalin obtained by fluorination of naphthalene, characterized in that the crystallization of perfluorodecalin in two stages:
- at the first stage, crystallization is carried out with a decrease in temperature to minus 17 - minus 18 ° C at a speed of 1-2 ° C per minute with stirring, the mass is kept at a temperature of minus 17 - minus 18 ° C for 30-35 minutes, filtered, dried and the resulting crystals are separated, then they are melted at ambient temperature,
- at the second stage, crystallization is repeated under the same conditions, but with a decrease in temperature to minus 15 ° C.