JPS5910329A - Method for removing fluorinated hydrocarbon - Google Patents

Abstract

PURPOSE:To remove fluorinated hydrocarbon contained in a gas or liquid easily and almost quantitatively, by bringing it into contact with a liquid ammonia soln. of an alkali metal. CONSTITUTION:To remove the fluorinated hydrocarbon from a gas, the gas to be treated freed of O2, CO2, H2O, etc. in advance is passed through a liquid ammonia dissolving a metallic sodium or the like alkali metal, and to bring them into gas-liquid contact. To remove fluorinated hydrocarbon dissolved in the liquid, a liquid ammonia soln. of the alkali metal and the liquid freed of water, alcohols, organic acids, etc. in advance are brought into liquid-liquid contact. The ammonia remaining in the gas and the liquid after the treatment is removed by cooling or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing fluorinated hydrocarbons from gases or liquids containing them.

As is well known, 70 ton 11 (cal@F), Freon 12 (
OOJ*h), Freon 13 (OOJ?s), Freon 14 (OF4), Freon 21 (0HOJ,F), Freon 22 (oHo11!I*), Freon 113 (OO
1mFOOJI? ), 70n114 (OOJIF snow o
Fluorinated hydrocarbons such as alh, ) are usually chemically stable and are resistant to most metals and acids at temperatures below 200°C.
It doesn't react.

Further, the above-mentioned fluorinated hydrocarbons decompose at temperatures above 200° C., for example in flames, although they do not decompose completely, and the resulting products are highly erodible. The hydrogenated hydrocarbons are solids (e.g. polytetrafluoroethylene, graphite, etc.)
Although it is possible to adsorb fluorinated hydrocarbons, the amount of adsorption is extremely low, and there is no known method for efficiently and quantitatively removing fluorinated hydrocarbons.

However, in recent years, it has been proposed that fluorinated hydrocarbons accumulate in the stratosphere and destroy the ozone layer that exists in the stratosphere, raising concerns about their impact on living things on Earth. As a result, the use of fluorinated hydrocarbons in aerosols has become problematic. Furthermore, the above-mentioned fluorinated hydrocarbons are used for semiconductor manufacturing and other purposes, and consumption is expected to increase in the future. Therefore, the release of fluorinated hydrocarbons into the atmosphere must be suppressed as much as possible. The present invention has been made to meet the demands of society based on such circumstances.

As is well known, alkaline earth metals (for example, lithium, sodium, potassium, etc.) in Group 1 A of the weekly rate table are dissolved in liquid ammonia (hereinafter referred to as liquid ammonium).

These solutions contain alkali metal; M
dissociates into alkali metal cations and electrons.

M−M+10e−(NH8):c・・・・・・・・・(1
) The above #5 liquid is blue regardless of the type of alkali metal, and when the concentration of alkali metal is high, the color changes from reddish brown to gold quickly. This is a combination of the above-mentioned dissociated electrons and ammonia molecules f! It is said that this is due to the color of (NH,), Zj. The father solution exhibits high electrical conductivity. At the same time, chemically, it is known to have an extremely high reducing power as an electron donor.

From the above viewpoint, the present inventors have discovered that by bringing fluorinated hydrocarbons, which have conventionally been considered extremely difficult to remove due to their chemical stability, into contact with a liquid solution of an alkali metal, a reaction can be achieved extremely rapidly. It was discovered that fluorides of alkali metals were produced.

For example, OF4+4na (liquid NHs bath U) = e + 41J
alF...+2), all the fluorine atoms in the fluorinated hydrocarbon molecule become alkali metal fluorides.

It's a trench, aaA, F+4Na (1 body NH, 1 melt) = c+3Na
In a fluorinated hydrocarbon in which other halogen atoms are present, such as Cl+NaF (3), all the halogen atoms become halogenides of alkali metals. However, 0 on the right side in formulas 2) and (3) does not necessarily represent only carbon.

The above reaction conditions are not critical. There is no major difference in the solubility of liquid solutions of each alkali metal at room temperature (under pressure) or at low temperatures (at normal pressure), and their ability to remove fluorinated hydrocarbons remains the same, so it can be used depending on the purpose. pressure,
Temperature conditions can be selected.

In particular, metallic sodium is cheap and easy to use, and its liquid solution has excellent stability. In addition, instead of directly dissolving metallic sodium in liquid ammonium, a liquid ammonium solution of a sodium salt such as sodium chloride or sodium bromide that dissolves well in liquid ammonium is prepared, and this is electrolyzed in an electrolytic cell with a diaphragm. ,
It is also possible to use a liquid solution of an alkali metal formed in the cathode chamber.

When removing fluorinated hydrocarbons contained in gas,
O@, 00, 1110, etc. contained in the gas react with the liquid ammonium solution of metallic sodium, so they must be removed as the gas ages. The gas from which these harmful impurities have been removed is passed through a liquid ammonium solution in which the alkali metal is dissolved. At this time, a stirring device or a disperser (e.g. glass,
It is necessary to increase the gas-liquid contact area by dispersing the above-mentioned gas as fine particles in the liquid washing liquid through a porous blowing plate made of carbon, etc.) or an absorption tower. Note that hydrogen, nitrogen, etc. are inert to the above solution, and there is no problem even if they are present.

In addition, when removing fluorinated hydrocarbons contained in the liquid, water, alcohols, organic acids, oxygen-containing compounds, and other substances that react with the alkali metal liquid must be removed in advance. It is necessary to keep it.

In general, liquid ammonium dissolves in petroleum-based hydrocarbons or saturated aromatic hydrocarbons in only a small amount, so it exists in two separate layers: a liquid ammonium solution of an alkali metal and a petroleum-based solution containing fluorinated hydrocarbons. Hydrocarbons or saturated aromatic hydrocarbons are vigorously stirred, and a liquid solution having a low specific gravity is introduced into the hydrocarbon containing the fluorinated hydrocarbon to form an emulsion and liquid-liquid contact is carried out to produce the fluorinated hydrocarbon. can be removed.

After the fluorinated hydrocarbon contained in the gas or liquid is treated with a liquid alkali metal solution as described above, the gas or liquid contains ammonia at a concentration depending on the treatment temperature and pressure. This can be easily removed by known methods such as cooling, compression and cooling, other physical adsorption, chemical neutralization, washing with acid, washing with water, etc.

As described above, the method for removing fluorinated hydrocarbons according to the present invention removes almost all fluorinated hydrocarbons by washing the gas or liquid containing the fluorinated hydrocarbons with a liquid solution containing an alkali metal. Hydrocarbons can be easily removed.

Next, the method of the present invention will be specifically explained with reference to Examples.

[Example-1] 9460 cc of a liquid solution containing metallic sodium 509 was put into a container, and while being kept at -33°C and stirred with a stirrer at 3000 revolutions per minute, 2.5% carbon tetrafluoride (OF4) was added. Containing nitrogen gas was passed through at a flow rate of 1O1 per minute. The exhaust gas was returned to the absorption bottle after condensing the accompanying ammonia gas using a reflux condenser at -70°C. Carbon tetrafluoride in the exhaust gas was below Q, lpp.

[Example-2] Put 223 cc of liquid ammonium bath liquid containing 23 g of metallic sodium into a cylindrical vertical absorption tower, place a rotary atomizer in this liquid ammonium liquid, and rotate the rotor of this rotary atomizer at 3000191. At the same time, below this rotor, dichlorodifluoromethane (acl, y,) o
, 30 minutes at a speed of 1077g1r containing a ton of water. The temperature of the liquid is room temperature (25℃) and the vapor pressure is 9K.
It is y/i. The exhaust gas was cooled to -33° C. through a condenser, and the entrained ammonia was refluxed to the absorption tower. ool, F in the exhaust gas! was not detected.

[Example-3] Liquid weak solution W containing 150 g of metallic potassium as an absorption liquid
i, 600 g was placed in an absorption tower equipped with the same rotary atomizer as in Example-2 and maintained at -33°C, and hydrogen gas containing 5% chlorodifluoromethane (aaolFt) was introduced from below the rotor at a flow rate of 1017 min. did. When the exhaust gas was discharged through a reflux condenser at -70°C, 0HOA'F' was found in the exhaust gas! The concentration was below 0.1 pIm.

Example A cathode chamber of a pressure-resistant electrolytic cell equipped with a stirring blade was used as a container for the absorption liquid. The electrolytic cell is provided with a porous plate made of sintered glass particles as a diaphragm, and a cathode made of a metal aluminum plate and an anode made of graphite are provided across the diaphragm.

In the above electrolytic cell, pre-dried sodium bromide IJum 100
An electrolytic solution containing 0 g dissolved in liquid ammonium 35009 was added, and this was electrolyzed by passing DC 7 V and 190 AH at 30° C. and 11 kg/l. 15 minutes after the start of current application, 0.5 t of trichlorofluoromethane (OFOlm), 0.5 t of dichlorodifluoromethane (OF, cl, ) 2. Nitrogen gas containing 1.2% OqA, chlorotrifluoromethane (oFs CI ) was blown into the cathode chamber at a rate of 101/min for 30 minutes with vigorous stirring. The gas discharged from the cathode chamber was passed through a cold trap at -33°C to remove entrained ammonia.

The total amount of fluorinated hydrocarbons in the exhaust gas was 0.13-.

[Example-5] Trichlorofluoromethane (oval,) t, 5 qA
A treatment solution prepared by dissolving 100 cc of mineral oil containing 100 cc of sodium metal 2II in 10 g of liquid ammonium was placed in a pressurized distillation vessel equipped with a stirrer and stirred at room temperature at 3000 ml to react.

After the reaction, the reaction product was washed with water in the presence of liquid sodium chloride to remove ammonia and generated salts (sodium fluoride, sodium chloride, etc.).

2I - No fluorinated hydrogen fluoride was detected in the separated mineral oil.

Applicant Showa Denko Co., Ltd.

Claims (1)

[Claims] Alkali metal liquid ammonia #! A method for removing fluorinated hydrocarbons, which comprises bringing a liquid into contact with a gas or liquid containing a fluorinated hydrocarbon.