WO1980001883A1

WO1980001883A1 - Fire-fighting concentrates

Info

Publication number: WO1980001883A1
Application number: PCT/US1980/000111
Authority: WO
Inventors: P Chiesa
Original assignee: Philadelphia Suburban Corp
Priority date: 1979-03-06
Filing date: 1980-01-23
Publication date: 1980-09-18
Also published as: EP0024416A1; FI800440A; AU5568480A; JPS56500080A; EP0024416A4

Abstract

Fire-fighting foam effective against burning hydrophilic or polar liquids like lower alcohols, ketones, etc. is made from concentrate containing thixotropic thickener dissolved in large amount, yet has a tolerable viscosity so that it can be poured or pumped. Heteropolysaccharide-7 or chain-shortened modifications of it are particularly suitable for this purpose. The concentrate can also be made suitable for fighting fires on hydrophobic liquids by adding surfactants that cause aqueous film formation over such liquids. Solution of polysaccharide thickeners is speeded and higher concentrations made practical by including in the concentrate urea, thiourea, ammonium cyanate or ammonium thiocyanate. Slurrying the polysaccharide in liquid amides such as N-methyl-pyrollidone-2 or dimethylformamide and then pouring the slurry in water also conveniently dissolves the polysaccharides in high concentrations. The liquid amide can be diluted with up to 3 times its weight of a glycol, polyglycol, or a monoalkyl ether of such glycol or polyglycol, the diluent having not over 10 carbons in its molecule. Magnesium salts can be dissolved in concentrate to improve fire extinguishing action when diluted with fresh water.

Description

FIRE-FIGHTING CONCENTRATES

The present invention relates primarily to the fighting of fires on hydrophilic liquids.

Among the objects of the present invention is the provision of novel compositions with which to fight such fires, as well as novel techniques for making such compositions.

These as well as further objects of the present invention are discussed in the following description of several of its exemplifications.

The fighting of fires on hydrophilic liquids such as isopropyl alcohol, acetone, and the like, is more awkward than the fighting of fires on hydrophobic liquids. Aqueous foams are considered the most desirable materials for fighting fires on large bodies of flammable liquids, and applicant's earlier patent applications show that the presence of a thixotropic polysaccharide in dissolved condition in the aqueous liquid from which the foam is prepared, causes the foam to gel and become a bubble-containing mat when it contacts the hydrophilic liquid. Such mat floats on the burning liquid and protects the foam above it so that the fire is fairly rapidly extinguished. Because the foams are generated by foaming an aqueous concentrate that is diluted with many times its volume of water, the concentration of the thixotropic polysaccharide in the diluted solution is quite small so that it is difficult to develop a very good, stable mat formation. Moreover it is not too practical to merely dissolve a very high concentration of the thixotropic polysaccharide in the aqueous concentrate, inasmuch as this generally produces a concentrate that is too stiff a gel to be rapidly diluted to foaming dilution or to be suitable for use with the proportioning foamers that have been developed. The solution of the thixotropic polysaccharide in the concentrate is colloidal in nature and the concentrate resembles a broken-up gel although it is pourable as well as pumpable and is readily inducted into the suction inlet of a venturi-type proportional diluter.

According to the present invention, very desirable fire-fighting concentrates are in the form of colloidal solutions essentially in water, containing high concentrations of thixotropic polysaccharide thickener. So long as the concentrate is pourable, the higher the concentration of the polysaccharide thickener the greater the fire-fighting effectiveness and the more the concentrate can be diluted with water to make the fire-fighting foam. More dilution means less concentrate and less concentrate storage is needed to provide the same quantity of diluted liquid. Particularly desirable thixotropic polysaccharides are heteropolysaccharide-7 described in U. S. Patent 3,915,800, as well as somewhat degraded forms of heteropolysaccharide-7. Among other advantages these polysaccharides yield more effective foams when the concentrates are diluted with sea water, as compared to fresh water.

Some working examples illustrate the present invention. Example 1

The following ingredients are combined:

Water 9 , 240 ml .

Chlorinated metaxylenol 3 . 6 g .

Urea 93 g .

(30% in water) 357 ml. Heteropolysaccharide- 7 122 g.

(30% in water) 675 ml. 30% aqueous solution of equimolecular mixture of sodium decylsulfate and sodium octylsulfate 795 ml. Monobutyl ether of diethylene glycol 300 ml.

(40 weight percent in 1:1 isopropanol- water mixture by volume) 213 ml. (CF₃)₂CF(CF₂)_nCOO^-+NH₃C₂H₅ where 20% of the n is 2, 30% of the n is 4, 30% of the n is 6, and 20% of the n is 8 102 g.

MgSO₄ 204 g.

The heteropolysaccharide-7 is difficult to dissolve directly in water in the above-specified amount, and it is preferred to begin by mixing together the first five ingredients, using only 12 ml. of the fourth ingredient (the C₉-substituted imidazoline) and adding the fifth in small portions with stirring, followed by pumping this pre-mix through a recirculating pump until smooth. The remaining ingredients are then added and the resulting mixture thoroughly mixed. Its pH should be about 7.1 to 8, and if necessary it is adjusted to that pH with acetic acid or ammonia. Upon completion of the stirring associated with the mixing, the product rapidly sets up to gel-like character, but is pourable and easily liquefied by a little agitation. With a bit of stirring it flows fairly easily. Under the influence of a suction of several inches of mercury produced at the intake of a venturi jet, the set-up product flows smoothly up into such a suction intake.

When the foregoing concentrate is diluted with ten times its volume of water it is readily foamed with air to produce a very effective fire-fighting foam having an expansion of 6 to 8. When foamed with the apparatus of U. S. Patent 2,868,301 the foam can be projected a substantial distance. Projected onto a burning liquid as hydrophilic or as polar as ethanol or acetone, the majority of foam thus applied is not broken but some forms a gel-like mat that does not dissolve in such liquid rapidly enough to significantly diminish the spreading of the projected foam over the burning surface and the extinguishing of the fire by the foam. The formation of the mat involves gelation of the liquid contained in the foam and loss of water from the gelled liquid to the hydrophilic liquid through syneresis, and takes place so rapidly that the foam bubbles are trapped in the mat causing it to float on the hydrophilic liquid. This action takes place with about equal effectiveness when the diluting water is tap water or sea water or any combination of these two waters, and resulting diluates have about the same fire-fighting effectiveness.

Also when used to fight fires on hydrophobic liquids, the foregoing foam shows about the same good results as the well-known foams that do not contain thixotropic polysaccharide. Example 2

The formulation of Example 1 is modified in two respects. Instead of the 122 grams of heteropolysaccharide-7, there is added 138 grams of degraded form of that polysaccharide, and instead of 102 grams of the ethylammonium salt of the perfluorinated mixed acids, 100 grams of the free mixed acids

CF₃(CH₂)_mCOOH are used, where 40% of the m is 4, 35% of the m is 6, and

25% of the m is 8. The degraded form of the polysaccharide is prepared by adding a little HCl to the fermentation broth in which it is formed to bring its pH to 6.5, and then heating the acidified broth to 90ºC for thirty minutes. The degraded product is then recovered by the same technique used to recover the undegraded material.

Other hydrolysis techniques can be used to degrade the fermentation product if desired. Alternatively degradation can be effected by heat alone or by oxidative attack. Thus a one-hour boiling of the fermentation broth causes degradation, or the fermentation broth can be treated with 1/20 its volume of 30% H₂O₂ at 70ºC for 30 minutes, and a similar degradation can be effected with 1/10 its volume of acidified 2% potassium permanganate at 50ºC. The degradation is not major and the degraded product is still quite insoluble in lower alcohols so that the recovery technique does not have to be modified. It is estimated that the degrading step shortens the polymer chains about twenty to thirty percent and has no other significant effect. The viscosity of a 1% aqueous solution of the polymer at low shear is generally reduced about 1/3, and this is the important result that is desired. Because of the viscosity reduction the formulation of Example 2 contains more of the polysaccharide and when diluted and foamed it is somewhat more effective in extinguishing fires on hydrophilic liquids. Thus when a typical concentrate of Example 2 has its viscosity measured with a Brookfield LVF viscometer using a No. 4 spindle, it gives the following readings at the designated spindle speeds:

Spindle Speed in Viscosity

Revolutions per Minute in Centipoises

0.3 142,000

0.6 95,000

1.5 53,600

3.0 32,000

6.0 17,700

12.0 9,450

30.0 4,200

60.0 2,330

Because the 60 rpm viscosity is below 3000 centipoises, such a concentrate is well suited for use with standard proportioning foamers. Because of the high content of the polysaccharide, over 1.1% by weight of the concentrate, it can be diluted with more than 10 times its volume of water and still do a very good job of extinguishing fires. A typical fire test gives the following results on a burning batch of 60 gallons 99% isopropyl alcohol in a round pan providing a 40 square foot surface.

Preburn time 3 minutes Dilution with 16 2/3 its volume of tap water (6%)

Application rate 0.15 gallons of diluate per minute per square foot of surface

Expansion 8.8 Control 2 minutes 20 seconds

Extinguishment 2 minutes 50 seconds Sealability (the application of the foam is continued for 1 minute after extinguishment) 11 minutes 30 seconds

A feature of heteropolysaccharide-7 as well as of the thixotropic polysaccharides into which it can be degraded, is that they are more effective in extinguishing fires on hydrophilic liquids when they are used with sea water, as compared to their use with fresh water. This appears to be largely due to the presence of magnesium ions in sea water, and the addition of magnesium ions in the foregoing formulations in a proportion of at least about 1/6 the weight of the polysaccharide, shortens their fire extinguishing times when they are diluted with fresh water. It has no significant effect on the fire extinguishing when sea water is the diluent.

Increasing the magnesium ion content to about 1/3 the weight of the polysaccharide heightens the improvement, but further increases in magnesium ion content do not further add significantly to the effectiveness.

Adding too much magnesium ion can also produce problems such as the precipitation of magnesium compound when the concentrate is subjected to very low temperatures. Such precipitation could interfere with the use of the concentrate in standard proportioning foamers in extremely cold weather. Magnesium sulfate in a proportion of about 1.3 to about 1.7 times the weight of the polysaccharide is a preferred choice and gives magnesium ions in a proportion of about 1/4 to about 1/3 the weight of the polysaccharide. However, magnesium chloride, nitrate, and/or acetate can be substituted for some or all of the magnesium sulfate, if desired. Other metallic ions such as of calcium, chromium and the others listed in U. S. Patent 3,915,800 (Table VII) can be substituted for the magnesium but are not as good at equalizing the effects of sea water and fresh water dilution.

The urea in the foregoing examples speeds up the solution of the polysaccharide in the water. For the degraded forms of heteropolysaccharide-7 the optimum urea content of the water in which the polysaccharide is to be dissolved is not as high as for the undegraded heteropolysaccharide-7. From about 1/2% to about 5% urea in the water, by weight, is a preferred range of concentration regardless of the type of heteropolysaccharide-7, and the same concentration is suitable for other viscosity-increasing thickeners such as scleroglucan, mannan gum, etc. The increase in polysaccharide dissolution rate makes itself felt however, even with lesser concentrations of urea, and its effect is not changed much over wide variations in the amount of polysaccharide being dissolved. The urea also helps reduce the freezing point of the concentrate, as mentioned in British Patent Specification 1,126,027. As little as 1/2% urea based on the weight of the concentrate produces a noticeable improvement, particularly when the concentrate also contains at least about 2% of a glycol or an etherified glycol freezing point depressant. The urea can be partially or completely replaced by thiourea or even ammonium thiocyanate or ammonium cyanate, without much change in effectiveness. All of these additives rapidly dissolve in water to greatly improve its solvent action on the polysaccharide, even when the additive and the polysaccharide are added to the water simultaneously. The stabilizing effect of urea as noted in German Auslegeschrift

1,169,302 for protein hydrolyzates, is not noticeable with the polysaccharides of the present invention.

The diethylene glycol monobutyl ether in the above examples can also be omitted, although it helps boost the expansion obtainable when the concentrate is foamed, and also helps shorten the time required to extinguish a fire, particularly on hydrophilic liquids. Only about 2 to 5% of such additive based on the total weight of the concentrate is all that is needed for this purpose. This additive also helps reduce the freezing point of the concentrate, but this is not important. The concentrates of the present invention are freeze-thaw stable so that they are not damaged by freezing, and as they cool to freezing temperature their gel-like condition becomes too stiff before they actually freeze. They should accordingly be stored for use at temperatures no lower than about 35ºF, unless the concentrates are to be pumped through a diluting apparatus by a positive displacement pump. It will be further noted that the dissolved magnesium salt significantly reduces the freezing point of the concentrates, whether or not other freeze-preventing additives are used. Additives such as ethylene glycol and hexylene glycol can be used in place of some or all of the diethylene glycol monobutyl ether, if desired, but are not preferred inasmuch as they are considered toxic to marine life and fire-fighting liquids can eventually run off into streams. However any glycol, polyglycol or monoalkyl ether of such glycol or polyglycol having not over 10 carbons in its molecule will improve the pourability of the concentrate.

The silicone surfactant and/or the fluorocarbon surfactant can also be omitted if desired. As noted in applicant's earlier applications, their presence makes the formulations, after dilution and foaming, extremely effective in extinguishing fires on hydrophobic liquids such as gasoline, so that these formulations can be used for fighting fires involving either type of liquid with excellent results. The silicone surfactant and the fluorocarbon surfactant cause aqueous films to form over burning hydrophobic liquids, and this greatly assists the fighting of fires on such liquids. However, either of these two aqueous film formers can be reduced in quantity or entirely eliminated, and good aqueous film formation generally effected by increasing the concentration of the other. Also as pointed out in applicant's earlier applications other fluorocarbon surfactants and other silicone surfactants can be used to provide the aqueous film formation. For such result the diluted concentrate should have a surface tension of 19 or less dynes per centimeter, preferably 18 dynes or less. Higher surface tensions do not cause significant aqueous film formation. The omission of all fluorocarbon surfactant from the foregoing formulations also lowers the effectiveness with which they fight fires on hydro philic liquids. At least about 0.4% fluorocarbon surfactant, or better still 0.6% is particularly desired to give such increased effectiveness to concentrates that are subject to a 6% dilution before foaming.

The formulation of Example 2 with its relatively high concentration of thixotropic polysaccharide does a very good job of extinguishing fires on hydrophilic liquids, even when diluted with 16 2/3 times its volume of fresh or sea water. On the other hand the formulation of Example 1 is best used when diluted with only about 10 times its volume of fresh or sea water.

The formulations of both examples do not include the resinous film-formers normally used in foam concentrates as described in applicant's earlier applications. Such film-formers can be added as for instance in concentrations that add about 1/2% to about 1 1/2% solids based on the total weight of the concentrate. A particularly good resinous film-former is the reaction product of 3-dimethylaminopropylamine-1 with an equivalent amount of ethylenemaleicanhydride copolymer, described in Example I of British Patent 1,381,953 and column 8 of U. S. Patent 3,957,687.

The chlorinated metaxylenol of the formulations of the present examples is a biocide that prevents the growth of mold, bacteria, etc. in the concentrates. Other biocides or preservatives, such as methyl parahydroxybenzoate or any of these designated in the prior applications can be used instead of or combined with the chlorinated metaxylenol, preferably in a total concentration of 0.01 to about 0.3% by weight of the concentrate. When the concentrate is made by a sequence of steps extending over a number of hours, as for instance when the polysaccharide solution in the water is prepared and stirred or permitted to stand overnight before the remaining ingredients are added, the preservative should be added in the first stage of the preparation.

The formulations of Examples 1 and 2 not only have fluorocarbon and silicone surfactants in small amounts but they also have additional surfactants that are not of the fluorocarbon or silicone types and are in larger amounts to impart the desired foamability to the compositions. Those foamability-improving surfactants are largely of the type that have a hydrophilic moiety weighing at least 80% more than the lipophylic moiety, and thus follow the teachings of applicant's earlier U. S. Patent 3,849,315.

The foamed compositions of the present invention do a very good job of extinguishing fires when applied by projection from foam-delivering nozzles, either portable or fixed as for example on towers, or from line-proportioning foamers, or foam chambers. In each case standard equipment can be used without modification.

The formulation of Example 2 meets all commercial standards when used to extinguish fires after dilution with 16 2/3 times its volume of fresh or sea water, which is a standard dilution provided by standard foaming equipment. At this dilution it is preferred to apply it to fires on the following liquids at the designated rates in gallons of diluted liquid per minute per square foot of surface on the burning liquid, using a fixed applicator such as a foam chamber:

Methanol .16

Isopropanol .20 n-Propanol .10 n-Bufanol .10 t-Butyl Alcohol .35

Isodecanol .10 SDA-1-200 PF (Ethanol) .16

Ethyl Acetate .10 n-Propyl Acetate .10

Butyl Acetate .10 Methyl Amyl Acetate .10

Methyl Acrylate .10

Acetone .20

Methyl Ethyl Ketone .20

Methyl Isobutyl Ketone .10 Propionaldehyde .10

Hexane .10

Heptane .10

Automotive Gasoline .10

Lactol Spirits (Naphtha Solvent) .10 Mineral Spirits (Petroleum Spirit) .10

Toluene .10

Petroleum Distillate .10

Methyl Cellosolve .10

The foregoing application rates are preferably increased by about one-fourth when using movable discharge nozzles to spread the applied foam and speed the extinguishment. However, it is not desirable to increase the rate of application to t-butyl alcohol (on which fires are always difficult to extinguish) or to have a movable nozzle application rate less than about 0.16 gallons per minute per square foot.

The formulations of Examples 1 and 2 can be applied when diluted with 10 times their volume of fresh or sea water. The preferred application rates of the Example 2 formulation when so diluted are about one-fifth less than listed above, except that application rates lower than about 0.10 gallons per minute per square foot are not desirable whether from fixed or movable foam applicators. Also the tenfold dilution is not recommended for fires on hydrophobic liquids where the 16 2/3 dilution has been a time-honored and widespread standard proven to be highly effective and built into standard fire-fighting equipment,

The formulations of the present invention can be further varied. Thus the formulation of Example 2 can use the fluorinated surfactant of

Example 1, or major variations can be made such as shown in the following exemplifications: Example 3

In this example some of the heteropolysaccharide-7 is replaced by xanthan gum and good results are obtained, although there is some loss of burnback resistance. The formulation is water 6155 ml urea 62 g . the degraded heteropolysaccharide-7 of Example 2 41 g. xanthan gum 41 g . o-phenoxy phenol 5 . 8 g . the C₉ substituted imidazoline surfactant solution of

Example 1 460 mls. the mixed alcohol sulfates solution of Example 1 530 mls. the silicone surfactant solution of Example 1 142 mls. the fluorinated surfactant of Example 1 68 g. acetic acid 35 mls.

The formulation of Example 3 can also be modified by the addition of 0.3% tris-hydroxymethyl aminomethane, about 0.07% of the disodium salt of nitrilotriacetic acid, and about 3% butyl carbitol, based on the total weight of concentrate.

Other very effective mixtures of perfluorocarboxylic acids useful for the formulations of the present invention, are those in which by weight about 55 to about 70% is C₈, about 14 to about 23% is C₁₀, about 6 to about 9% is C₁₂, about 2 to about 7% is C₁₄, and any balance is C₆. Such a mixture in a concentration of 30 grams/gallon in a formulation also having 25 grams/gallon of the silicone surfactant solution of Example 1 and 600 mis./gallon of the mixed imidazolines of Example 1, 150 mis./gallon of 30% solution of the corresponding C₁₁-substituted imidazoline surfactant, 295 mis./gallon of propylene glycol monobutyl ether and 268 mis./gallon of butyl cellosolve, makes a very effective fire extinguisher whether or not the heteroρolysaccharide-7 is added to it.

Instead of degrading the normal polymeric chains of heteropolysaccharide-7 their formation by fermentation can be stopped when it has proceeded about half to three-quarters the extent practiced to produce the undegraded heteropolysaccharide-7. This early termination lowers the yield but also produces a shorter polymer that can be considered a degraded form of heteropolysaccharide-7 in accordance with the present invention. The undegraded polymer seems to resist degradation by high-shear stirring.

As shown in applicant's earlier applications, non-thixotropic thickeners for aqueous systems can also be used in small amounts in the formulation of the present invention. Thus, locust bean gum can be used in an amount about 1/3 that of the thixotropic polysaccharide. Some thickeners such as guar gum and its derivatives impart to the concentrates a freezethaw instability that is not desired.

N-methyl pyrrolidone-2 and other liquid amides such as dimethyl formamide, and organic compounds containing a nitrogen atom in the molecule, such as acetonitrile and triethylamine, have special solubilizing effects on thixotropic polysaccharides and reduce the viscosity of the concentrate in which they are present, N-methyl pyrollidone-2 is preferred for this purpose because of its effectiveness and low toxicity. However, it has an adverse effect on fire fighting with heteropolysaccharide-7 or its degraded forms, and is best used with scleroglucan as the thixotropic polysaccharide.

These solubility modifiers can be used in very small amounts to enable the simple and inexpensive manufacture of concentrates containing as much as 1.5% or more of the thixotropic polysaccharide by weight. This is shown in the following example. Example 4

A very concentrated slurry of degraded heteropolysaccharide-7 is prepared by slowly stirring 590 grams of this polysaccharide in dry powder form into an anhydrous solution of 300 milliliters N-methyl-pyrollidone-2 in 850 milliliters of butyl carbitol. Only a few minutes of vigorous agitation is needed to obtain a milky slurry that pours readily and is highly effective in dissolving in water to make aqueous fire-fighting concentrates having large contents of the polysaccharide. This dissolving action is also speeded up by the presence in the water of the urea or thiourea or ammonium cyanate or ammonium thiocyanate, and the slurry dissolves very rapidly in such a solution.

Thus the foregoing slurry is poured slowly, with agitation into a previously prepared solution in 30.5 liters tap water of 480 grams urea and 40 ml. of 30% commercial grade imidazoline di-carboxylate having the attached C₉H₁₉ group as in Example 1. This solution preferably also contains a small amount of preservative such as 111 grams of p-phenoxy phenol. Stirring is continued for about 3 hours after the slurry is completely introduced and the container in which the slurry was prepared is washed with 150 ml. of butyl carbitol , the washings being poured into the solution to make sure all the heteropolysaccharide-7 is transferred. The resulting batch is permitted to stand overnight, following which about two more hours of stirring leaves it as a very smooth colloidal solution free of undissolved solid and of lumps, and ready to receive the remaining ingredients. A separately prepared mixture of 476 grams of the fluorocarbon surfactant of Example 1, 424 ml. of the silicone surfactant of Example 1, 1.15 liters of the foregoing imidazoline dicarboxylate, 2.2-5 liters of 30% commercial grade second imidazoline dicarboxylate of Example 1, 3.05 liters of the mixed sodium decylsulfate and octylsulfate of Example 1, is then poured into the colloidal solution, the resulting mixture stirred for about a half hour and 545 grams of magnesium sulfate added. About one hour of stirring at this point brings the combination into its final form ready for use. For storage, its pH is best adjusted to 7.4±0.1 with acetic acid, and 57 grams of 30% aqueous formaldehyde added. About 10 gallons of very effective concentrate is thus produced. Because it contains a little over 1.5% thixotropic polysaccharide it is more effective than the concentrate of Example 1 in fighting fires on hydrophilic liquids.

It is also helpful to buffer this concentrate as by the addition of some tris-hydroxymethyl aminomethane in a quantity of 1/8 to 1/2% by weight, unless the silicone surfactant is omitted.

The concentrates of the present invention can be stored in mild steel containers that have their interiors uncoated, or in plastic containers. No serious corrosion of the mild steel is produced after many months of storage in such a container. They can be used very effectively to fight non-polar liquid fires in tanks by introducing the foamed diluted concentrate below the liquid surface in the tank. This so-called sub-surface introduction technique is particularly desirable in tanks of gasoline or other petroleum products, and is not suitable for fighting fires on polar, that is hydrophilic, liquids.

As shown above, burning tertiary butyl alcohol is more difficult to extinguish with the compositions of the present invention than most other hydrophilic liquids generally ericountered in firefighting. Organic compounds containing a nitrogen atom in the molecule, such as those referred to above as having solubility-increasing effects, are similarly quite difficult to extinguish and require substantial foam application rates.

Where facilities for storing the concentrates are limited, as for example in an off-shore oil well rig, the water content of the concentrates can be reduced. Thus a concentrate very effective for use after dilution to 100 times its volume, has the following formulation: Example 5 a mixture of C₆ to C₁₂ perfluorocarboxylic acids having at least

55% C_8, about 5% C₆ about 10% C₇ about 10% C₉ about 10% C₁₀ about 5% C₁₁ and about 5% C₁₂

0 .0436 pounds The silicone surfactant combination of Example 1 but in the form of 50 weight % solution in 1:1 isopropanol-water mixture by volume

0.031 gallons a 30% by weight solution in water of equal parts of the imidazoline surfactants of Example 1

0 .518 gallons a 30% by weight solution in water of the imidazoline surfactant

0.195 gallons Monobutyl ether of diethylene glycol

0.261 gallons Water to make 1 gallon acetic acid or 50% caustic soda as needed to adjust pH to about 7.4 This formulation does not contain thixotropic polysaccharide and is highly effective for extinguishing fires on hydrophobic liquids like the petroleum recovered by off-shore rigs. Its proportion of fluorinated surfactant to silicone surfactant is quite low, about 1:2.5 on a 100% active basis, inasmuch as the solubility of the fluorinated surfactant in the concentrate is limited. This proportion can range from about 3:5 to about 1:3 and still provide excellent results.

Larger proportions of fluorinated surfactant can be used, but since it is very expensive, reduced amounts are desirable, particularly with the high content of butyl carbitol or any other of the above-mentioned glycols, polyglycols, or monoalkyl ether of such glycols or polyglycols, having not over 10 carbons in their molecule, Such glycol or glycol ether content of at least 1 3/4 pounds per gallon helps provide the desired fire extinguishing action and also reduces the solubility in the concentrate of some of the most effective perfluorinated surfactants such as perfluorooctanoic acid salts. A glycol or glycol ether content of more than 2 1/8 pounds per gallon is not needed.

Perfluorocarboxylic acids can be used in the formulation without first converting them to salts. Although substantially less water-soluble than their salts, these acids readily dissolve in the silicone surfactant ingredient which is supplied as a 50% by weight solution in a water-methanol mixture. Once dissolved in that ingredient the perfluorinated acids do not precipitate out upon addition of the remaining ingredients. Any of the other fluorinated surfactants referred to in applicant's earlier patent applications can be used in place of the perfluorocarboxylic acids of Example 5, but these perfluoro acids are particularly inexpensive and thus more desirable. While the perfluorooctanoic acid is preferred, it appears to be less expensive to provide a mixture of this acid with its homologs imasmuch as such mixtures can be most economically manufactured. These same considerations apply to the silicone surfactant of Example 5, which surfactant can also be replaced by any of those referred to in applicant's earlier applications.

Similar considerations also apply to the imidazoline surfactants except that when these are manufactured by different processes they are sometimes more poisonous to fish. Such undesired side-effect appears to be due to by-products or contaminants introduced by the manufacture, inasmuch as carefully purified surfactants of this type have sharply reduced toxicity to fish. It is accordingly helpful to compare such surfactants with corresponding surfactants from other sources, if low fish toxicity is desired. The burn-back resistance of the composition of Example 5 does not have to be too high when used to extinguish fires on off-shore oil rigs. Such resistance can be increased however by adding to the concentrate sufficient sorbitol to provide in the diluted foamed fire fighting mixture a sorbitol content of at least about 0.2% by weight, preferably about 0.3 to 0.4%.

The following example shows such use of sorbitol in a concentrate intended for dilution to 6% (with 16 2/3 times its volume of water): Example 6

The perfluorocarboxylic acid mixture of Example 5

0.0728 lbs. The silicone surfactant solution of Example 5

0.0084 gallons The 30% solution of the C₇H₁₅ and C₉H₁₉ substituted imidazolines of Example 5

0.1686 gallons The 30% solution of the C₁₁H₂₃ substituted imidazoline of Example 5

0.0145 gallons Butyl carbitol

0.0305 gallons 70% by weight sorbitol solution in water

0.0645 gallons adjust pH to

7.4 ± 0.2 water to make

1 gallon In some cases burn-back resistance may be more important than rapid extinguishment of a fire. For such an objective the formulation of Example 6 can be modified by incorporating in it 0,132 gallons of the 10% by weight solution of the above-noted reaction product of 3-dimethylamino-propylamine-1 with an equivalent amount of ethylene-maleic anhydride copolymer. Such incorporation is effected without increasing the total, volume of the concentrate, and in the interest of economy the C₇H₁₅ and C₉H₁₉- substituted imidazolines can be replaced by an additional 0.086 gallons of the C₁₁H₂₃-substituted imidazoline.

The butyl carbitol content can also be increased to 0.106 gallons to further improve burn-back resistance.

For dilution of any of the foregoing concentrates with sea water it is also helpful to use the perfluoroalkyl amino carboxylic acids of U. S. Patent 4,038,195, in place of the simple perfluoro carboxylic acids. Of the various silicone surfactants disclosed in applicant's earlier applications, there is no significant advantage in any of them, and so the preference is to use the least expensive. Thus the first silicone surfactant described in column 1 of U. S. Patent 3,957,657 can be substituted for the silicone surfactants of any of the foregoing examples.

Film forming polymers can also be added to the concentrates of Example 5, and while the reaction product of 3-dimethylamino-propylamine-1 with the ethylene-maleic anhydride copolymer is very effective for this purpose, others such as water soluble gums and even polyacrylic acid can be used instead.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims

WHAT IS CLAIMED;

1, In the process of dissolving a thixotropic polysaccharide in water, the improvement according to which the rate of solution is speeded by incorporating in the water at least one member of the class consisting of urea, thiourea, ammonium thiocyanate and ammonium cyanate, such incorporation being in an amount from about 1/2 to about 5% of the water.

2. The combination of claim 1 in which urea is the solution-speeding member incorporated in the water.

3. The combination of claim 1 in which the thixotropic polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heterσpolysaccharide-7.

4. In the process of dissolving a thixotropic polysaccharide in water, the steps of first slurrying the polysaccharide in essentially water-free N-methyl-pyrollidone-2, to form a milky slurry essentially free of coarse particles and having from about 1/3 to about 3 times as much N-methyl-pyrollidone-2 as polysaccharide, by weight, then stirring the slurry into an excess of water.

5. The combination of claim 4 in which the water into which the slurry is stirred, contains dissolved in it a solubilizer selected from the class consisting of urea, thiourea, ammonium cyanate and ammonium thiocyanate, in an amount from about 1/2 to about 5% of the weight of the water.

6. The combination of claim 4 in which the slurrying is in N-methyl-pyrollidone-2 diluted with up to about 3 times its weight of a glycol, a polyglycol, or a monoalkyl ethyl of such glycol or polyglycol, the diluent having not over 10 carbon atoms in its molecule.

7. The combination of claim 4 in which the concentration of the polysaccharide in the final aqueous solution is at least about 1.5% by weight.

8. The combination of claim 4 in which the thixotropic polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7.

9. In a pourable liquid fire-fighting concentrate that contains a colloidally-dissolved thixotropic polysaccharide which causes it to form a gel mat when diluted with water and contacted with polar organic liquids, the improvement according to which the concentrate contains at least about 1.5% by weight of the colloidally-dissolved polysaccharide.

10. The combination of claim 9 in which the colloidally-dissolved polysaccharide was dissolved in the concentrate from a slurry in N-methyl-pyrollidone-2.

11. The combination of claim 9 in which the thixotropic polysaccharide is selected from the class consisting of heteropolysaccharide-7 and degraded forms of heteropolysaccharide-7.