JPS59157045A - Dehydration of hexafluoroacetone hydrate - Google Patents

Abstract

PURPOSE:To purify hexafluoroacetone via a hydrate, safely, in high recovery, by contacting hydrated hexafluoroacetone with a molecular sieve as a dehydration agent. CONSTITUTION:A hydrate of hexafluoroacetone (especially preferably a hydrate containing about 70-75% of hexafluoroacetone) is dehydrated by contacting with a molecular sieve preferably at about 120-150 deg.C. Althoug the one-pass yield of the process is about 60-70%, the residue is merely adsorbed to the water-absorbent in the form of hydrate, and consequently, it can be recovered by the regeneration of the water-absorbent by thermal dehydration. The regenerated dehydration agent can be used repeatedly. USE:Monomer for the production of fluorine-containing polymers, synthetic intermediate of pharmaceuticals, agricultural chemicals, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method for dehydrating hexafluoroacetone hydrate. More specifically, hexafluoroacetone water solution which recovers hexafluoroacetone with a good recovery rate.
Concerning methods of dehydrating things.

Hexafluoroacetone is an important raw material compound as a monomer for the production of fluorine-containing polymers, an intermediate for synthesizing pharmaceuticals and agricultural chemicals, and a raw material for the synthesis of bisphenol AF, which is used as a crosslinking agent for fluororubber. It is.

Hexafluoroacetone is synthesized by various methods, such as isomerization of hexafluoropropylene oxide, reaction of hexachloroacetone with hydrogen fluoride, oxidation of octafluoroisobutylene, and reaction of hexafluoropropylene with oxygen. This is done by reactions such as

In the cholera synthesis method, hexafluoroacetone, which is obtained by isomerizing hexafluoropropylene oxide or reacting hexafluoropropylene with oxygen, contains low-boiling compounds that are by-produced during the isomerization reaction and products that are produced by decomposition. Although the former can be removed by distillation, a small amount of the latter cannot be avoided. Further, unsubstituted chloride and acidic compounds are inevitably mixed into hexafluoroacetone obtained by the reaction of hexachloroacetone and hydrogen fluoride.

Furthermore, in the case of hexafluoroacetone obtained by oxidizing octafluoroisobutylene, since the reaction system is aqueous, hexafluoroacetone is obtained in the form of water FII, and the manganese dioxide used as an oxidizing agent must be disposed of. There are also problems with processing.

Hexafluoroacetone synthesized in this way is
Must be purified prior to use. As one of the purification methods, the extractive distillation method was published in JP-A-53-'71,00.
As proposed in Publication No. 6, depending on the synthesis method, hexafluoropropylene or hexafluoropropylene oxide may be mixed into the product, and since these compounds have similar boiling points to hexafluoroacetone, they can be removed by distillation. Complete separation is difficult. Furthermore, since hexafluoroacetone has strong interactions with other compounds, it is difficult to separate it from low-boiling compounds and intoxicating compounds.

Separately, JP-A-57-81,433 proposes a method of preparing hexafluoroacetone hydrate and dehydrating it with a dehydrating agent such as concentrated sulfuric acid, sulfuric anhydride, or phosphorus pentoxide. In the case of this method, there is a problem that hexafluoroacetate reacts with these dehydrating agents, decomposes, or dissolves, making the recovery rate poor, and there is also a danger in handling. exist.

The present inventors have conducted extensive research in search of a method for safely purifying hexafluoroacetone via hydrate with high recovery rate, and have found that the use of molecular sheep as a dehydrating agent is extremely effective. I discovered something.

Therefore, the present invention relates to a method for dehydrating hexafluoroacetone hydrate, and the dehydration of hexafluoroacetone hydrate is carried out by bringing it into contact with a molecular sheep.

The monohydrate of hexafluoroacetone, ton, is not a mere mixture of hexafluoroacetone and water or an adsorbate of water, but is produced according to the following equilibrium equation, and the equilibrium is significantly shifted to the right, with a melting point of 52°C. It is a solid.

(CF3)2CO+H20(CF3)2C(OH)2This monohydrate of hexafluoroacetone is a highly hygroscopic solid that is very easy to promote, and is difficult to handle. It:
Therefore, in the present invention, the hexafluoroacetone concentration is not low and it is easy to handle as a hydrate with mi, ν0 of about 70 to 75%, and the hydrate is dehydrated. .

Dehydration is carried out in a reaction vessel containing molecular sheep.
Hexafluoroacetone hydrate is added dropwise, and after the completion of the dropwise addition, the reaction vessel is heated to a liquid temperature of about 120 to 150°C to evaporate it as anhydrous hexafluoroacetone. This is done by directing it to a sheep-packed column and drying it. Also,
It is also possible to set the liquid temperature to Y1100°±10°C culmability and guide the vapor of evaporated fuhekifluoroacetone hydrate to a molecular sheep packed column for dehydration.

In the method of dehydrating hexafluoroacetone hydrate using molecular sheep, which is carried out in this way, molecular sheep, which is itself a stable and safe substance, is used as a dehydrating agent, so the operation is easy. It can be done safely, and the recovery rate in one treatment is about 60-70%. It is only adsorbed on the molecular sheep as water > U, so when the molecular sheep is heated and dehydrated, it is recovered as hexafluoroacetone hydrate and regenerated again. It has many great advantages such as ease of use.

Next, the present invention will be explained with reference to examples.

EXAMPLE A glass column and a dropping funnel each having a diameter of 50 mm and a length of 1 m are attached to a 1101-volume Sepa 2-pu flask. Then, a 1/8 inch x 10 mm pellet-shaped molecular sheep was packed into a flask with a 35kfJ and a tower with Lookkg, and a 0-drop funnel was added.
When the entire drop is finished at 7'C, gradually heat the flask with a mantle heater. Anhydrous hexafluoroacetone (boiling point -27°C) is generated, which is cooled and collected in a dry ice-methanol cooled trub installed via a rubber article at the top of the column. During this time, the liquid temperature is maintained at about 120-150°C.

rs 11 ko of hexafluoroacetone is recovered as anhydride, with a recovery rate of 635%.

The used molecular sieve is regenerated at 200° C. under reduced pressure and used again. At this time, the remaining hexafluoroacetone hydrate adsorbed on the molecular sieve was also recovered, so the recovery rate of 635% actually became 912%.

Comparative Example A four-eye flask with a capacity of 11 is equipped with a stirrer, a dropping funnel, a thermometer, and a gas outlet.

300 g of concentrated sulfuric acid is charged into this flask, and 100 g of a hydrate containing 700% hexafluoroacetone is slowly dropped from the dropping funnel so that gas is continuously generated at 40 to 50°C.

The generated gas passes through a drying tube filled with a 1/8 inch x IQllll pellet-shaped molecular sieve.
It was collected in a corrugated tube trap cooled with dry ice-methanol. 3"z1 g of hexafluoroacetone was recovered as anhydride, with a recovery rate of 530%.

agent Patent attorney Toshio Yoshida

Claims (1)

[Scope of Claims] A method for dehydrating hexafluoroacetone hydrate, which comprises bringing the hexafluoroacetone hydrate into contact with a molecular sheep. The method for dehydrating a single hexafluoroacetone hydrate according to claim 11J, wherein a hydrate containing about 70 to 75% of 2-hexafluoroacetone is used. A method for dehydrating hexafluoroacetone hydrate according to claim 1, wherein the hexafluoroacetone hydrate is contacted with a molecular sieve at a temperature of about 120 to 150°C.