WO1996040371A1

WO1996040371A1 - The use of bis(difluoromethyl)ether as a fire extinguishant

Info

Publication number: WO1996040371A1
Application number: PCT/US1996/008187
Authority: WO
Inventors: Gerald J. O'neill
Original assignee: Hampshire Chemical Corp.
Priority date: 1995-06-07
Filing date: 1996-05-31
Publication date: 1996-12-19
Also published as: ES2128279T1; EP0841967A1; CA2220431A1; BR9609407A; CN1199349A; AU6147596A; TW349874B; DE841967T1; MX9709476A; JPH11506648A; ZA964268B; EP0841967A4; AU699193B2

Abstract

Bis(difluoromethyl)ether as a fire extinguishant. Bis(difluoromethyl)ether is non-flammable, non-chlorofluorocarbon containing compound having an atmospheric life of only 2,8 years, and has zero ozone depletion potential.

Description

THE USE OF BIS(DIFLϋOROMETHYL)ETHER AS A FIRE EXTINGUISHANT

BACKGROUND OF THE INVENTION

The Halons, particularly 1301 (CF₃Br) and 1211 (CF₂ClBr) , have been used successfully for many years as fire and explosion suppressants. Halon 1301 is generally used in "total flood" applications in which the agent is discharged from a fixed automated system to uniformly fill a space to extinguish a fire or to provide inertion. The agent concentration required for fire suppression is the most important performance parameter in this application.

Halon 1211 is usually used in "streaming" applications in which the halon is discharged from a portable, manual extinguisher to provide localized fire suppression. Both the extinguishment concentration and the discharge characteristics of "streaming" agents are important in determining fire extinguishment capacity.

The vapor pressure of Halon 1301 is 234 psia, and that of Halon 1211 is 40 psia at room temperature. Either system can be pressurized for faster discharge, if needed.

The Halons contain chlorofluorocarbons, and thus have been subject to the same restraints as other compounds of that class in view of their potential to deplete the ozone. Halon 1211 has an atmospheric life of 15 years and an ozone depletion 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 to the atmosphere, they undergo phσtolitically catalyzed deomposition and the halogen atoms then catalyze the decomposition of ozone. Suitable substitutes must meet certain requirements. There should be hydrogen in the molecule in order to facilitate photolytic degradation in the troposphere, but preferably the molecule should contain no halogen other than fluorine. Acceptable substitutes would exhibit fire suppressant efficiency, low residue levels, non- conductivity, negligible ODP, low global warming potential (GWP) , non-corrosiveness, materials compatibility, stability under long term storage, and low toxicity.

It is therefore an object of the present invention to provide a fire extinguishant that does not suffer from the drawbacks of conventional extinguishants.

It is a further object of the present invention to provide a method of extinguishing fires while minimizing the potential for ozone depletion.

SUMMARY 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 extinguishant. 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 zero ozone depletion potential. The ether behaves well as a fire extinguishant.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a schematic view of apparatus used to test fire extinguishing concentrations.

DETAILED DESCRIPTION OF THE INVENTION

Bis(difluoromethyl)ether can be prepared by a variety of processes conventional in the art. For example, it can be prepared by chlorination of dimethyl ether followed by isolation and fluorination of bis(dichloromethyl)ether. A preferred approach avoids the unstable complex mixture of chlorinated ethers, some of which are carcinogens, by employing methyl difluoromethyl ether as a starting material. The methyl difluoromethyl ether is chlorinated to give a chlorinated reaction mixture including at least one compound of the formula CF₂H0CH₃_-C1_Z, wherein z is 1, 2 or 3, which compound can be readily separated from the chlorinated reaction mixture. The chlorination of methyldifluoromethyl ether would generally form only three derivatives, i.e., z=l, z=2 and z=3. The dichloromethyl difluoromethyl ether (z=2) can be readily 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 produced also may be separated from the chlorination reaction product and fluorinated. Alternatively, the chlorination reaction product itself may be fluorinated (without prior separation) as follows.*

CF₂H0CH₂C1 > CF^OCH_jF (I)

(II)

CF₂H0CC1₂F CF₂H0CC1₃ ζ- > CF₂H0CC1F₂

CF₂HOCF₃ (III)

The methyl difluoromethyl ether which is regarded as the starting material for the process of the present invention is a known compound which may be prepared in the manner reported by Hine and Porter in their aforementioned article published in the Journal of the American Chemical Society. Specifically, difluoromethyl methyl ether is produced by reaction of sodium methoxide (NaOMe) with chlorodifluoromethane (CF₂HC1) , which reaction may be represented as follows:

CF₂HC1 + CH₃ONa > CF₂HOCH₃ + NaCl

Briefly, the method involves forming an alcohol solution of sodium methoxide and bubbling the chlorodifluoromethane slowly into the reaction mixture to obtain the methyldifluoromethyl ether as a residue in the reaction mixture. Some product is entrained with unreacted CF₂HC1 and can be separated from it in a distillation operation.

The starting ether, CHF₂OCH₃, also might be prepared by first reacting NaOH with CH₃0H, in effect making CH₃ONa, and then reacting it with CF₂HC1. However, water is also formed in the NaOH/CH₃OH reaction. The effect 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:

CHF₂OCH₃ > CF₂H0CH₃._ZC1_Z + zHCl (wherein z = 1 , 2 , or 3)

CF₂H0CH₃__ZC1_Z > CF₂HOCH₃._zCl₂z.-y_yF-,y

(wherein z = 1, 2, or 3 y = 1, 2, or 3 y ≤ z) The formation of CF₂H0CH₃._ZC1₂ wherein z = 3 in the above reaction scheme can be inhibited or even eliminated upon the addition of an oxygen source, preferably air, to the vapor phase reaction medium. Rather than inhibiting the three chlorination products equally, the addition of oxygen surprisinglypreferentially inhibits the formation of CF₂H0CC1₃. Any oxygen source not deleterious to the production of the desired compounds could be used, including oxygen-containing compounds which liberate oxygen in situ .

The oxygen should be present in an amount effective for the desired inhibition. In the case of air, preferably the air is added in an amount from 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 air. Preferably the oxygen source is added to the reaction medium for as long as the chlorine gas is flowing.

It has been found that CHF₂OCH₃ may be suitably chlorinated by liquefying the CHF₂OCH₃ and reacting it with chlorine gas while irradiating with a source of visible light. Alternatively, one may use other light sources such as ultraviolet light or heat, a catalyst or a free radical initiator to aid in the reaction. The chlorination products of CHF₂OCH₃ can be readily separated prior to fluorination or the reaction mixture can be fluorinated without separation to give an admixture of CF₂H0CC1₂F, CF₂H0CF₂C1, CF^OCK_jF, CFjHOCFHCl, CF₂HOCF₂H. All separations may be effected by fractional distillation. A preferred method of chlorinating the CHF₂OCH₃ is to maintain the CHF₂OCH₃ in a vapor phase and react it with chlorine gas while subjecting the chlorination reaction to a source of light, 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 procedure, the chlorinated reaction product is reacted with anhydrous hydrogen fluoride (HF) , which reaction may be represented as follows:

2CF₂H0CC1₃ + 3HF > CF₂H0CFC1₂ + CF₂H0CF₂C1 + 3HC1

Utilizing the above reaction with hydrogen fluoride has resulted in a yield as high as 78% CF₂H0CF₂C1 with a small amount of CF₂H0CFC1₂. This was an unexpected result since HF by itself does not normally replace a halogen such as chlorine, except perhaps at very high temperatures, but instead fluorinates by continuous regeneration of a fluorinating agent such as SbCl₅._yF_y, such as SbF₃, or SbF₃Cl₂. Apparently, the difluoromethoxy group activates the chlorine on the alpha- carbon atom, allowing it to react readily with HF.

Alternatively, the HF may be diluted with an organic solvent, preferably a dipolar aprotic solvent such as methyl pyrrolidone, in order to reduce fragmentation of the fluorinated material, resulting in higher yields of desired product with less by-product generation. Other sources of fluorine for the fluorination step include metal fluorides that can form salts of the HF₂ ^Θ anion, such as KHF₂, NaHF₂, LiHF₂, NH₄HF₂, etc., and pyridine salts of HF and NaF and KF in suitable solvents.

The resultant fluorinated products may be separated by distillation or by the process as taught in U.S. Patent 4,025,567 or U.S. Patent 3,887,439 which are incorporated herein by reference in their entirety.

The Bis(difluoroomethyl)ether thus produced has been found to be effective as a fire extinguishant at a minimum concentration of about 11.7 volume percent in air. In order to increase the rate of expulsion and/or dispersion, the bis(difluoromethyl)ether can be used in conjuction with inert gases, such as nitrogen, carbon dioxide, CF₃H, etc. Carbon dioxide is especially preferred, since it exhibits some degree of solubility in the ether.

The present invention will now be further illustrated by the following examples.

EXAMPLE 1 a) Preparation of CF₂H0CH₃

A 25 wt % solution of sodium methoxide in methanol (1533.lg) containing 7.1 moles of sodium methoxide was placed in a 4 liter jacketed autoclave fitted with a temperature sensor, a pressure gauge and a dipleg. The vessel was cooled to 0 to 5°C and chlorodifluoromethane (318.2g, 3.70 moles) added over a period of 2.5 hours with agitation. When the addition of gas had been completed, the autoclave was slowly warmed to about 60°C while venting gaseous products through the water-cooled condenser-into a collection trap cooled to about - 70°C.

When all volatile material had been collected unreacted CHF₂C1 was removed at -20°C and the remaining CF₂HOCH₃ transferred to a metal cylinder. The recovered difluoromethyl methyl ether (150.Og, 1.83 moles) represented a yield of 49.4% based on CF₂HC1. b) Chlorination of CF₂HOCH₃

Chlorine and CF₂HOCH₃ in a gaseous phase are passed through separate condensers cooled to 0°C and then the gas streams combine and pass into one arm of a U-shaped reactor, irradiated with visible light or UV. Both arms of the reactor are jacketed and cooled with water.

There is an outlet at the bottom of the U to which is attached a product collection flask. A Dewar-type condenser cooled to -50°C is attached to the outlet of the second arm of the U-tube and, in turn, it is connected in series with a cold trap to collect unreacted chlorine and an NaOH scrubber to remove HC1. The reaction is normally carried out at atmospheric pressure, but higher or lower pressure can be used. Temperature should not be allowed to rise much above 50°C in the reactor to avoid attack on the glass.

In practice, the apparatus is flushed with nitrogen and then chlorine and CHF₂OCH₃ are fed to the reactor at rates such that the ratio of the flow of chlorine to that of the ether is maintained at about 2.5:1 for optimum results, i.e., yield of CF₂H0CHC1₂. A predominant amount of any one of the three products can be obtained by changing the ratio of the gas flows .

After the passage of 2.3 moles of chlorine and 0.9 moles of CHF₂OCH₃, 136.6g of product were recovered. GC analysis of the product mixture showed CF₂H0CH₂C1 10.0%, CF₂H0CHC1₂ 62.4%, and CF₂H0CC1₃22.2%. c) Fluorination of CHF₂0CHC1₂ with HF

The chlorinated CHF₂OCH₃ (40.Og) containing 46.1% CF₂H0CHC1₂ in a stainless steel cylinder was then cooled in ice before adding anhydrous HF (30.Og). The cylinder was closed with a valve and pressure gauge and then was placed in a water bath at 60°C for 3 hours. The cylinder was then vented through a NaOH scrubber and volatile products collected in a trap cooled at -70°C. The weight of product recovered from the trap was 16.8g. It contained 71.8% CF₂HOCF₂H by GC analysis, corresponding to a yield of 83.8% of CF₂H0CF₂H.

When conducted on a larger scale (e.g., 5 gallons) , almost quantitative yields of CF₂HOCF₂H (based on CF₂H0CHC1₂) were obtained.

EXAMPLE 2

The chlorination apparatus consisted of two vertical lengths of jacketed glass tubing, 4 feet long by 2 inches I.D., connected at the lower ends in a U-tube fashion by a short length of unjacketed 2 inch I.D. tubing. A drain tube led from the lowest point of the U-tube arrangement so that product could be collected as it formed and removed continuously from the apparatus or alternatively allowed to accumulate in a receiver. Three 150 watt incandescent flood lamps were arranged along the length of each tube.

The gases were fed into the upper end of one arm of the U-tube arrangement. Flow rates were measured by calibrated mass flowmeters. A low temperature condenser on the outlet of the second arm of the U-tube returned unreacted E-152a and chlorine to the illuminated reaction zone. Hydrogen chloride by-product and air passed through the condenser into a water scrubber where the hydrogen chloride was removed.

A mixture of methanol and water, cooled to 0 to 5°C was circulated through the cooling jackets of the apparatus.

In a typical run, coolant at a temperature of 0 to 5°C is circulated through the cooling jackets, the flood lamps were turned on and dry ice placed in the low temperature condenser. Chlorine was introduced into the apparatus first, followed by difluoromethyl ether and air in the desired ratios. Product was removed at intervals from the receiver and washed with saturated NaHC0₃ solution to remove HC1. Since the reaction was continuous, it could proceed for any length of time desired. At the end of the reaction, gas flows were stopped and product allowed to drain from the vertical reactor tubes into the receiver.

The results are tabulated in Table 1 below. Examples 6- 29-1 to 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 diminishing amounts, in accordance with the present invention. TABLE

w c* Product Distπbution in Total

The extinguishing concentra ion of Bis(difluoromethyl)ether was determined using the I.C.I, cup burner method, which is a standard test. The apparatus is shown in Figure 1, and consisted of a 8.5 cm by 53 cm tall outer chimney through which air was passed at 40L/min from a glass bead distributor at its base. An inner fuel cup burner with a 3.1 cm O.D. and a 2.15 cm I.D. was positioned 30.5 cm below the top edge of the chimney. Bis(difluoromethyl)ether was added to the air stream prior to entering the glass bead distributor. The air flow rate was maintained at 40L/min for the trial. Air and bis (difluoromethyl) ether flow rates were measured using rotameters.

The test was conducted by adjusting the extended fuel reservoir to bring the liquid (heptane) level in the cup burner to just even with the base of a ground glass lip on the burner cup. With the air flow maintained at 40L/min, the fuel in the cup burner was ignited. Bis(difluoromethyl)ether was gradually added to the air stream until the flame was extinguished. The bis- (difluoromethyl)ether totameter reading was then recorded. The extinguishing concentration of the ether was calculatedd as a percentage of the combined flow of the ether and air. Reference agents Halon 1301 and HFC-227ea were tested similarly. Several runs were made with each test material, and the average values of the extinguishing concentration were as follows:

Test Material Extinguishing Concentration (Vol. %) Halon 1301 2.5 ± 0.1

HFC-227ea 6.3 ± 0.1

Bis(difluoromethyl)ether 11.7 ± 0.3

Claims

What is claimed is:

1. A fire extinguishant, comprising a fire extinguishing effective amount of bis(difluoromethyl)ether.

2. The fire extinguishant of claim 1, further comprising an inert gas.

3. The fire extinguishant of claim 2, wherein said inert gas is selected from the group consisting of nitrogen, carbon dioxide and CHF₃.

4. A method of extinguishing fires, comprising applying to said fire a fire extinguishing effective amount of bis(difluoromethyl)ether.

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