JPH05286875A - Method for removing stabilizer in trichloroethylene - Google Patents

Abstract

PURPOSE:To remove a stabilizer which is an aromatic compound having a hydroxyl group from trichloroethylene by bringing trichloroethylene into contact with a molecular sieve. CONSTITUTION:A stabilizer of an aromatic compound (e.g. phenol) having a hydroxyl group in trichloroethylene (trichlene) is removed by bringing the stabilizer into contact with a molecular sieve in a liquid phase. Trichlene is a raw material for producing 1,1,1,2-tetrafluoroethane useful as a substitute refrigerant for chlorofluorocarbon 12 widely used as a refrigerant for a car air conditioner and refrigerant which lately becomes a problem by breakage of ozone layer, etc. By the objective method, lowering of activity of a catalyst used in reaction of trichlene with HF can be prevented and the operation is made easy and industrially practicable, in comparison with a stabilizer removing method by fractional distillation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has been attracting attention as an alternative refrigerant to Freon-12, which is widely used as a refrigerant for car air conditioners, refrigerators and the like, which has recently become a problem due to ozone depletion. , 2-tetrafluoroethane (CF ₃
-Trichlorethylene (hereinafter, CHCl = C) used as a manufacturing raw material such as CH ₂ F or HFC-134a)
Cl ₂ or trichlene)).

[0002]

2. Description of the Related Art A method for producing trichlene is produced by, for example, a chlorination reaction of ethylene and chlorine, a thermal decomposition and a purification step. Stabilizers are added to ensure stability in the manufacturing process, and stability is generally required depending on the application, and it is common for stabilizers to be added in the range of several hundred to several thousand ppm.
Most of the uses are for metal cleaning or solvents,
There was almost no use as an organic fluorine compound raw material.

On the other hand, in order to produce HFC-134a,
A method of reacting trichlene and HF has been considered. This reaction cannot be achieved in a single step and the reaction conditions are different. 2
It is carried out by the reaction of the stage. First, a reaction of the first stage in which trichlene and HF are reacted to produce 1,1,1-trifluoro-2-chloroethane (hereinafter referred to as CF ₃ CH ₂ Cl or HCFC-133a), and HCFC-133
A second stage reaction is used in which a and HF are reacted to produce HFC-134a. These first-stage and second-stage reactions are represented by the following equations (1) and (2).

CCl ₂ = CHCl + 3HF → CF ₃ CH ₂ Cl + 2HCl (1) CF ₃ CH ₂ Cl + HF → CF ₃ CH ₂ F + HCl (2) The above reaction is carried out in the gas phase in the presence of, for example, an alumina-chromia catalyst. The reaction conditions are different. In the reaction of the formula (1), the pressure is 4 kg / cm ² G, the temperature is 250 ° C.,
In the reaction of HF / trichlene molar ratio 6, formula (2), pressure 4 kg / cm ² G, temperature 350 ° C., HF / HC
It is carried out at a molar ratio of FC-133a of 4.

In this step, particularly, the stabilizer in trichlene, which is one of the reaction raw materials of the formula (1), causes deterioration of catalytic activity and is preferably not contained. However, when a stabilizer is not contained in trichlene, trichlene lacks stability and side reactions such as generation of acid components proceed, so that tens of pp is included in trichlene as a raw material for an organic fluorine compound.
It contains a stabilizer for suppressing the generation of acid components due to the decomposition of m.

Examples of the stabilizer include aromatic compounds having a hydroxyl group, such as phenol and cresol. As a conventional removal method, fractional distillation and the like are known.

[0007]

However, the method of removing the stabilizer by fractional distillation has a problem that the operation is complicated and the apparatus requires a large amount of money. In view of the above circumstances, the present inventors have made earnest studies to develop a method for removing a stabilizer in trichlene which is easy to operate and industrially practical, and the stabilizer is obtained by bringing trichlene into contact with molecular sieves. It was found that it can be removed.

[0008]

As a method for producing CF ₃ .CH ₂ F, a method of reacting trichlene with HF is known. The reaction is, for example, in the presence of an alumina-crussia catalyst, pressure 4 kg / cm ² G, temperature 250 ° C., HF /
It is carried out in the gas phase under the reaction conditions of a trichlene molar ratio of 6. A stabilizer is contained in trichlene, which is one of the reaction raw materials, for the above-mentioned reason, and it is desirable that even a small amount of this stabilizer causes deterioration of catalytic activity and is not contained. Therefore, a removal method by fractional distillation or the like is known, but there is a problem that the operation is complicated and the apparatus requires a large amount of cost.

In view of the above circumstances, the inventors of the present invention have made earnest studies to develop a method for removing a stabilizer in trichlene which is easy to operate, inexpensive, and industrially practical. As a result, the trichlene is brought into contact with the molecular sieves. It was found that the stabilizer can be removed by. The molecular sieves used in the present invention preferably have a pore diameter of 2.5 to 4Å, which gives an advantage that water can be removed at the same time as the stabilizer in trichlene.

In order to bring trichlene into contact with the molecular sieve in the liquid phase, a known method such as a batch system or a continuous system can be used, but industrially, the trichlene is continuously circulated with the molecular sieve as a fixed bed. The liquid-based space velocity (LHSV) is appropriately selected depending on the concentration of the stabilizer and the amount of trichlene to be treated, but a range of ¹ to 30 Hr ^-1 is usually used. In addition, in order to industrially remove the stabilizer in trichlene, the removal tower should be 2
Purification can be continuously carried out by a known method in which a column is provided and this is switched. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0011]

【Example】

Raw Material Example 1: Commercially available trichlene (containing a stabilizer) was purified by fractional distillation. Stabilizer (phenol) to this 300
When analyzed by gas chromatography such that the weight of the product was adjusted to ppm by weight (all the following analyzes are performed by gas chromatography), the phenol content was 300 ppm by weight.

Example 1 Zeolite (Molecular Sieves 3A, manufactured by Union Showa Co., Ltd.) was added to a glass container having an internal volume of 2 liters in an amount of 20.
0 ml was filled, and 1.8 liter of the trichlene of the raw material example 1 was filled in a liquid form. After stirring occasionally, 2 hours later, a part of the liquid phase was sampled and analyzed, and no phenol was detected.

Example 2 A glass container having an inner volume of 2 liters was filled with 200 ml of zeolite (Molecular Sieves 4A manufactured by Union Showa Co., Ltd.) different from that of Example 1, and 1.8 liters of trichlene of the raw material example 1 were filled. Filled in liquid form. Stir occasionally, 2
After a lapse of time, a part of the liquid phase was collected and analyzed, and no phenol was detected.

Raw Material Example 2: Trichlorene with a small stabilizer content was prepared and analyzed by the same method as in Raw Material Example 1, and the phenol content was 15 ppm by weight.

Example 3 4.8 liters of Molecular Sieves 3A was filled in a SUS container having an internal volume of 5 liters, and trichlene of Example 2 was continuously supplied at a flow rate of 10 liters / hr. 100 hours, 200 hours, and 400 hours after the start of the supply, the outlet liquid was collected and analyzed, but no phenol was detected.

Example 4 The reaction represented by the reaction formula (1) was carried out by continuously introducing trichlene and HF from which the stabilizer was completely removed by the method of Example 2. In the presence of an alumina-chromia catalyst, the reaction temperature is 250 ° C., the HF / trichlene molar ratio is 6, and the reaction conditions are SV1000Hr ^−1.
The conversion of trichlene after Hr was 99.5% and the conversion of trichlene after 300 Hr was 99.4%, and the catalyst activity did not decrease.

Comparative Example 1 The trichlene and HF of the raw material example 1 were continuously supplied to the reactor to carry out the reaction represented by the reaction formula (1). In the presence of an alumina-chromia catalyst, the reaction temperature is 250 ° C., the molar ratio of HF / trichlene is 6, and the reaction condition of SV1000Hr ⁻¹ is 29.5 hr after the reaction is started.
After 0 hr, the conversion of trichlene was 80.4%, and the catalytic activity was lowered. From this, it is clear that the stabilizer is the cause of the decrease in catalytic activity.

[0018]

INDUSTRIAL APPLICABILITY As described above, the method for removing a stabilizer in trichlene according to the present invention can maintain the catalytic activity for a very long period of time, and hence CF ₃ .CH _{3 which will be} important as a substitute for CFC-12 in the future. it is very large to contribute to the field of manufacturing ₂ F.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hidetoshi Nakayama 5-1 Ogimachi, Kawasaki-ku, Kawasaki-shi, Kanagawa Showa Denko Chemicals Laboratory

Claims (1)

[Claims] 1. A method for removing a stabilizer in trichlorethylene, which comprises removing the stabilizer which is an aromatic compound having a hydroxyl group in trichlorethylene by using molecular sieves.