MXPA97009476A - The use of bis (difluoromethyl) eter as an extinguisher of fu - Google Patents

Abstract

Bis (difluoromethyl) ether is described as a fire extinguisher. Bis (difluoromethyl) ether is a non-flammable compound, which does not contain chlorofluorocarbons, which has an atmospheric life of only 2.8 years, and has a potential for ozone depletion.

Description

THE USE OF BIS (DIFLUOROMETHYL) ETHER AS A FIRE EXTINGUISHER BACKGROUND OF THE INVENTION Halons, particularly 1301 (CF3Br) and 1211 (CF2ClBr), have been used successfully for many years as fire and explosion suppressors, halon 1301 is generally used in "flow or total flood" applications in which agent is discharged from a fixed automatic system to uniformly fill a space to extinguish a fire or to provide inactivation. The agent concentration required for fire suppression is the most important operating parameter in this application. Halon 1211 is usually used in "current propagation" applications in which the halon is discharged from a portable, portable fire extinguisher to provide localized fire suppression. The extinction concentration and the discharge characteristics of the "current propagating" agents are important in the determination of fire extinguishing capacity.

REF: 26183 The steam pressure of halon 1301 is 16. 45 kg / cm2 (234 psia), and that of halon 1211 is 2. 81 kg / cm2 (40 psia) at room temperature.

Any system can be pressurized for faster discharge, if necessary. Halons contain chlorofluorocarbons, and have thus been subject to the same restrictions as other compounds of that class, in view of their potential to destroy ozone. Halon 1211 has an atmospheric life of 15 years and an ozone destruction potential (ODP) of 3.0. Halon 1301 has an atmospheric life of 110 years and an ODP of 10.0. When these compounds are released into the atmosphere, they undergo photolytically catalyzed decomposition, and the halogen atoms then catalyze the decomposition of ozone. Appropriate substitutes must meet certain requirements. There must be hydrogen in the molecule in order to facilitate catalytic degradation in the troposphere, but preferably the molecule must not contain halogen other than fluorine. Acceptable substitutes could show fire suppressive efficiency, low residual levels, no conductivity, negligible ODP, low global warming potential (GWP), no corrosivity, compatibility with materials, stability under long-term storage, and low toxicity. Therefore, an object of the present invention is to provide a fire extinguisher that does not suffer from the drawbacks of conventional extinguishers. A further object of the present invention is to provide a method for extinguishing fires, while minimizing the potential for ozone destruction.

BRIEF DESCRIPTION OF THE INVENTION The problems of the prior art have been overcome by the present invention, which provides a non-chlorofluorocarbon compound as a fire extinguisher. More specifically, the present inventor has found that bis (difluoromethyl) ether is non-flammable, has an atmospheric life of only 2.8 years, and has ozone destruction potential of zero. The ether behaves well as a fire extinguisher.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a view of the apparatus used to test fire extinguishing concentrations.

DETAILED DESCRIPTION OF THE INVENTION The bis (difluoromethyl) ether can be prepared by a variety of conventional processes in the art. For example, it can be prepared by chlorination of dimethyl ether, followed by isolation and fluorination of bis (difluoromethyl) ether. A preferred method avoids the complex unstable mixture of chlorinated ethers, some of which are carcinogenic, by the use of methyl difluoromethyl ether as an initial material. The methyl difluoromethyl ether is chlorinated to give a chlorinated reaction mixture which includes at least one compound of the formula CF2H0CH3-2C1Z, wherein z is 1, 2 or 3, which compound can be easily separated from the chlorinated reaction mixture. The chlorination of methyl difluoromethyl ether could in general form only three derivatives, for example, z = 1, z = 2, and z = 3. The ether Dichloromethyl difluoromethyl (Z = 2) can be easily separated from the chlorinated reaction mixture, and is then fluorinated, with or without such separation, to form the bis (difluoromethyl) ether. The production of CF2H0CC13 (z = 3) can be inhibited, and any product can also be separated from the chlorination reaction product, and be fluorinated. Alternatively, the chlorination reaction product itself can be fluorinated (without prior separation) as follows: CF2H0CH2C1 CF2H0CH2F (I) Methyl difluoromethyl ether, which is considered as "the starting material for the process of the present invention, is a known compound that can be prepared in the manner reported by Hiñe and Porter in their previously mentioned article, published in the Journal of the American Chemical Society. Specifically, difluoromethyl methyl ether is produced by the reaction of sodium methoxide (NaOMe) with chlorodifluoromethane (CF2HC1), which reaction can be represented as follows: CF2HC1 + CH3ONa > CF2HOCH3 + NaCl In summary, the method involves the formation of an alcoholic solution of sodium methoxide and the bubbling of chlorodifluoromethane slowly into the reaction mixture, to obtain the methyl difluoromethyl ether as a residue in the reaction mixture. Some of the product is entrained with the unreacted CF2HC1, and can be separated from it in a distillation operation. The initial ether, CHF2OCH3, can also be prepared firstly by the reaction of sodium hydroxide with methanol, effectively constituting CH3ONa, and then reacting it with CF2HC1. However, water is also formed in the NaOH / CH3OH reaction. The effect that water has on the subsequent reaction to form CHF2OCH3 is to reduce the yield of CHF2OCH3. The chlorination and fluorination steps of this invention can be represented as follows: ZC12 CHF2OCH3 > F2H0CH3.ZC1Z + zHCl (where z = 1, 2, or 3) F CF2HOCH3_zlz > CF2H0CH3-zClz-yFy (where z = 1, 2, or 3 Y - 1, 2, or 3, and < z) The formation of CF2H0CH3_ZC1Z where z = 3 in the above reaction scheme, can be inhibited or even eliminated after the addition of an oxygen source, preferably air, to the reaction medium in the vapor phase. Instead of inhibiting the three chlorination products equally, the addition of oxygen preferentially inhibits, surprisingly, the formation of CF2H0CC13. Any oxygen source that is not harmful to the production of the desired compounds could also be used, including oxygen-containing compounds which release oxygen in itself.

The oxygen must be present in an effective amount for the desired inhibition. In the case of air, air is preferably added in an amount of about 1.5 to about 5.5% of the total gas flow. Those skilled in the art will recognize that where pure oxygen is used, the amounts will be about 1/5 that of the air. Preferably, the oxygen source is added to the reaction medium as long as the chlorine gas is flowing. It has been found that CHF2OCH3 can be suitably chlorinated by liquefaction of CHF2OCH3 and reacted with chlorine gas while being irradiated with a visible light source. Alternatively, other light sources such as ultraviolet light or heat, a catalyst or a free radical initiator can be used to aid the reaction. The chlorination products of CHF2OCH3 can be easily separated before fluorination, or the reaction mixture can be fluorinated without separation to give a mixture of CF2H0CC12F, CF2H0CF2C1, CF2HOCH2F, CF2H0CFHC1, CF2HOCF2H. All separations can be effected by fractional distillation.

A preferred method of chlorination of CHF2OCH3 is to maintain CHF2OCH3 in a vapor phase, and to react it with chlorine gas, while subjecting the chlorination reaction to a light source, preferably visible or ultraviolet light. Alternatively, other reaction aids such as a catalyst, heat or a free radical initiator may be used instead of light in the chlorination reaction. In the preferred fluorination process, the chlorinated reaction product is reacted with anhydrous hydrogen fluoride (HF), which reaction can be represented as follows: 2CF2H0CC13 + 3HF > CF2H0CFC12 + CF2H0CF2C1 + 3HC1 Using the above reaction with hydrogen fluoride, it has resulted in a yield as high as 78% CF2H0CF2C1 with a small amount of CF2H0CFC12. This was an unexpected result, since the HF by itself does not normally replace a halogen such as chlorine, except perhaps at very high temperatures, but rather performs the fluorination by continuous regeneration of a fluorinating agent such as SbCl5- yFy, such as SbF3, or SbF3Cl2. Apparently, the difluoromethoxy group activates chlorine on the alpha carbon atom, allowing it to react easily with HF. Alternatively, the HF can be diluted with an organic solvent, preferably a dipolar aprotic solvent such as methylpyrrolidone, in order to reduce the fragmentation of the fluorinated material, resulting in higher yields of the desired product, with less generation of by-products. Other sources of fluorine for the fluorination step include metal fluorides which can form salts of the HF2 anion, such as KHF2, NaHF2, LiHF2, NH4HF2, etc., and pyridine salts of HF and NaF and KF, in suitable solvents. The resulting fluorinated products can be separated by distillation or by the process as shown in U.S. Patent No. 4,025,567 or U.S. Patent No. 3,887,439, which are incorporated by reference herein in their entirety. Bis (difluoromethyl) ether produced in this way, it has been found to be effective as a fire extinguisher at a minimum concentration of approximately 11.7 volume percent in air, in order to increase the rate of ejection and / or dispersion, bis (difluoromethyl) ether can be used in conjunction with inert gases, such as nitrogen, carbon dioxide, CF3H, etc. Carbon dioxide is especially preferred, since it shows some degree of solubility in the ether. The present invention will now be illustrated by the following examples.

EXAMPLE 1 a) Preparation of CF2HOCH3 A 25 wt% solution of sodium methoxide in methanol (1533.1 g) containing 7.1 moles of sodium methoxide was placed in a lined 4 liter autoclave equipped with a temperature sensor, pressure gauge and an immersion foot . The vessel was cooled to 0-5 ° C and chlorodifluoromethane (318.2 g, 3.70 mol) was added over a period of 2.5 hours, with stirring. When the addition of the gas had been completed, the autoclave was slowly heated to about 60 ° C, while the gaseous products were vented through from the condenser cooled with water, to a collection trap cooled to approximately -70 ° C. When all volatile material had been collected, the unreacted CHF2C1 was removed at -20 ° C and the remaining CF2HOCH3 was transferred to a metal cylinder. The recovered difluoromethyl methyl ether (150.0 g, 1.83 mol) represented a yield of 49.4% based on CF2HC1. b) Chlorination of CF2HOCH3 The chlorine and CF2HOCH3 in a gas phase, are passed through separate condensers, cooled to 0 ° C, and then the gas streams are combined and passed inside an arm of a U-shaped reactor, irradiated with visible light or ultraviolet. Both arms of the reactor are lined and cooled with water. There is an outlet at the bottom of the U, to which a product collection flask is attached. A Dewar condenser cooled to -50 ° C, is coupled to the outlet of the second arm of the U-shaped tube and, in turn, is connected in series with a cold trap to collect unreacted chlorine and a NaOH purifier to eliminate HCl. The The reaction is normally carried out at atmospheric pressure, but higher or lower pressure can be used. The temperature should not be allowed to rise well above 50 ° C in the reactor, to avoid the attack on the glass. In practice, the apparatus is flushed with nitrogen, and then chlorine and CHF2OCH3 are fed to the reactor, at speeds such that the ratio of the chlorine flow to that of the ether, is maintained at about 2.5: 1, for optimum results, for example, the yield of CF2H0CHC12. A predominant amount of any of the three products can be obtained by changing the proportion of gaseous flows. After passage of 2.3 moles of chlorine and 0.9 moles of CHF2OCH3, 136.6 g of the product were recovered. GC analysis of the product mixture showed 10.0% CF2H0CH2C1, 62.4% CF2H0CHC12, and 22.2% CF2H0CC13. c) Fluorination of CHF20CHC12 with HF Chlorinated CHF2OCH3 (40.0 g) containing 46. 1% CF2H0CHC12 in a stainless steel cylinder, was then cooled in ice before add anhydrous HF (30.0 g). The cylinder was closed with a valve and pressure gauge, and then placed in a 60 ° C water bath for 3 hours. The cylinder was then vented through a sodium hydroxide scrubber and the volatile products were collected in a trap cooled to -70 ° C. The weight of the product recovered from the trap was 16.8 g. This contained 71.8% of CF2HOCF2H by GC analysis, corresponding to a yield of 83.8% of CF2HOCF2H. When conducted on a larger scale (eg, 18.9 liters (5 gallons)), quasi-quantitative yields of CF2HOCF2H (based on CF2H0CHC12) were obtained.

EXAMPLE 2 The chlorination apparatus consisted of two vertical lengths of lined glass tubing, with a length of 1.22 meters (4 feet) by 5 cm (2 inches) in internal diameter, connected at the lower ends in a U-shaped tube, by a short length of unlined tubing 5 cm (2 inches) in internal diameter. A drain tube led from the bottom point of the pipe arrangement into U-shape, so that the product could be collected as it formed, and continuously withdrawn from the apparatus or alternatively allowed to accumulate in a receiver. Three incandescent flood lamps of 150 watts were accommodated along the length of each tube. The gases were fed to the upper end of an arm of the U-shaped tube arrangement. Flow rates were measured by calibrated mass flowmeters. A low temperature condenser on the outlet of the second arm of the U-shaped tube returned the unreacted E-152a and the chlorine to the illuminated reaction zone. The by-product hydrogen chloride and air were passed through the condenser to a water scrubber, where the hydrogen chloride was removed. A mixture of methanol and water, cooled to 0-5 ° C, was circulated through the cooling liners of the apparatus. In a typical run, the refrigerant at a temperature of 0 to 5 ° C was circulated through the cooling liners, the flood lamps were turned on and dry ice was placed in the low temperature condenser. Chlorine was introduced within the first apparatus, followed by the difluoromethyl ether and air in the desired proportions. The product was removed at intervals from the receptor, and washed with saturated sodium hydrogen carbonate solution, to remove the HCl. Since the reaction was continuous, it could proceed for any desired length of time. At the end of the reaction, the gaseous flows were stopped and the product was allowed to drain from the vertical reactor tubes, towards the receiver. The results are reported in Table 1 below. Examples 6-29-1 through 6-29-7 show the distribution of products normally obtained without the addition of air to the gas stream. Examples 7-7-3 through 7-8-6 show the effect of the addition of air in decreasing amounts according to the present invention. < AC < EXAMPLE 3 The extinction concentration of bis (difluoromethyl) ether was determined using the cup burner method I.C.I., which is a standard test. The apparatus is shown in Figure 1, and consisted of an external chimney 8.5 cm by 53 cm high through which air is passed at 40 liters / minute from a distributor, glass spheres at its base. An internal fuel cup burner with an outer diameter of 3.1 cm and an inner diameter of 2.15 cm, was placed 30.5 cm below the upper edge of the chimney. Bis (difluoromethyl) ether was added to the airstream before introducing the glass spheres distributor. The air flow rate was maintained at 40 liters / minute for the test. The air flow velocities of the bis (difluoromethyl) ether were measured using rotameters. The test was conducted by adjusting the extended fuel tank, to bring the liquid (heptane) to a level in the cup burner to be just level with the base of a flange of the glass spheres on the burner cup. With the air flow maintained at 40 liters / minute, the fuel in the cup burner was ignited. Bis (difluoromethyl) ether was gradually added to the air stream until the flame was extinguished. The rotameter reading for bis (difluoromethyl) ether was then recorded. The extinction concentration of the ether was calculated as a percentage of the combined flow of ether and air. The halon 1301 and HFC-227ea reference agents were similarly tested. Several runs were made with each test material, and the average values of the extinction concentration were as follows: Test Material Extinction Concentration (vol.%) Halon 1301 2.5 ± 0.1 HFC-227ea 6.3 ± 0.1 Bis (difluoromethyl) ether 11.7 ± 0.3 It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (5)

REINVINDICATIONS

1. A fire extinguisher, characterized in that it comprises an effective amount for fire extinction, of bis (difluoromethyl) ether.

2. The fire extinguisher according to claim 1, further characterized in that it comprises an inert gas.

3. The fire extinguisher according to claim 2, characterized in that the inert gas is selected from the group consisting of nitrogen, carbon dioxide and CHF34.

A method for extinguishing fires, characterized in that it comprises the application to fire of an effective quantity of fire extinguisher of bis (difluoromethyl) ether.

5. The method according to claim 4, characterized in that the effective amount of fire extinguishing is such that the minimum concentration of bis (difluoromethyl) ether in air is 11.7 volume percent.