GB2039454A - Powder for fire extinguishers - Google Patents

Abstract

A method for producing a powdery fire extinguishant comprising monoammonium phosphate and/or ammonium sulphate as main raw materials, in which method a polysiloxane having an active hydrogen and a solvent are included with the raw materials which are then subjected to the steps consisting of mixing; a solvent-vaporization and removal; and heating in the presence of an oxygen-containing gas. An organotin compound is for preference also included with the raw materials. The method is best effected in apparatus provided by the invention and having a mixing and kneading chamber 1; a solvent-vaporizing chamber 2; a heating reaction chamber 3; a raw material-feeding port 4; a solvent-vaporizing pipe 5; a port 6 for discharging powdery fire extinguishant; a rotating shaft 7; stirring blades (rotor) 8; partition walls 9 and 10, partition plates 11; heaters (jacket) 12 and 13; and a transfer opening 14. <IMAGE>

Description

SPECIFICATION Powder for fire extinguishers The present invention relates to powder for fire extinguishers, and in particular to such powders which are prepared using monoammonium phosphate and/or ammonium sulphate.

Extinguishant powders, particularly the so-called ABC powders prepared from monoammonium phosphate, can be used effectively against most fires, electric or otherwise, and have met with broad acceptance in recent years. In order to maintain their effectiveness, it is important that such powders should have good moisture resistance so that they do not deteriorate with time. Additionally, the powders should possess good particle fluidity in order that they can be discharged from an extinguisher without difficulty. To these ends, the conventional powders for fire extinguishers have been made by mixing finely powdered silicic an hydride (otherwise known as white carbon), a silicone resin and/or other ingredients, with the main raw material, monoammonium phosphate and/or ammonium sulphate.

However the products from there simple mixing methods are not entirely satisfactory.

According to the present invention there is provided a method for producing a powdery fire extinguishant comprising monoammonium phosphate and/or ammonium sulphate as main raw materials, in which method a polysiloxane having an active hydrogen and a solvent are included in the raw materials which are then subjected to the steps consisting of mixing; solvent-vaporization and removal; and heating in the presence of an oxygen-containing gas.

The method can be carried out as a batch process using a batch mixer, or, more preferably, the method is carried out as a continuous process. In this latter respect, a continuous process preferably comprises feeding the ingredients in fixed amounts to a mixing step where mixing and kneading are carried out at room temperature, thereafter continuously feeding the resulting material to a solvent-vaporizing and removal step where the material is heated with stirring and the solvent is removed by vaporization, and finally feeding the resultant material to a heating step where a heat treatment is carried out in the presence ofthe oxygen-containing gas.

Continuous processes in accordance with the present invention are conveniently effected in sectional apparatus providing respective sections in which the steps of mixing, evaporating, and heating can be independently and continuously performed on material passing through the apparatus.

In a particularly preferred embodiment, the method of the invention is carried out using apparatus also forming the subject of this invention, this apparatus comprising a mixing and kneading part having a feed port for raw materials; a solvent vaporizing part with heater and vaporization pipe; and a heating reaction part with a heater and fire extinguishant discharging port.

It is preferable to employ an apparatus of high efficiency, making the retention time shorter yet allowing a sufficient time for the various steps.

The ingredients employed by the present invention for preparing extinguishant powders comprise monoammonium phosphate and/or ammonium sulphate as the main raw material, together with a polysiloxane and other optionai ingredients. The polysiloxane has an active hydrogen and is, for example, a poly(alkylhydrogensiloxane) such as poly(methylhydrogensiloxane) or a copolymer of an alkylhydrogensiloxane with a copolymerizable monomeric siloxane, such as the copolymer formed by copolymerization of dimethylsiloxane with methylhydrogensiloxane. While the amount is not critical it is preferred to use 0.2 to 3% polysiloxane, based on the main raw material (quoted percentages of raw materials are by weight).

In order to improve the particle fluidity of the product, it is greatly preferred to include as an ingredient an organotin compound. Suitable organotin compounds include those of the general formula

(where R' and R2 are the same or different and each represent an alkyl group, usually the same alkyl group, and R3 and R4 are the same or different and each represent an oxycarbonylalkyl group derived from a monocarboxylic fatty acid, usually the same group, or R3 and R4 together represent a di - (oxycarbonylalkylene group derived from a dicarboxylic fatty acid). R' and R2 are suitably each butyl, and R3 and R4 can for example each be stearate or octoate groups or together form a maleate group. Thus, typical organotin compounds (I) include dibutyltin distea rate, dibutyltin dioctoate and dibutyltin maleate.

Conveniently from 0 to 0.5% organotin compound based on the main raw material is added, with 0.005 to 0.5% being preferred.

Further ingredients which may be employed include silicic anhydride and/or pigment. 0 to 5% silicic anhydride based on the main raw material is a particularly suitable amount, more particularly 0.5 to 5%. Trace amounts, if any, of pigment are normally appropriate.

It is preferred that each ingredient is in powdered form with a size of 80 mesh or less.

In the present method, the ingredients are intimately mixed with an organic solvent. Solvents with a relatively IQw boiling point are preferred, especially halogenated hydrocarbons. Examples of the preferred solvents are perchloroethylene and trichloroethylene. The amount of solvent is variable, but is conveniently from 5 to 20% based on the main raw materials (monoammonium phosphate and/or ammonium sulphate).

For the mixing step, it is preferable to mix the ingredients together while compressing them at room temperature, usually employing a mixer or a kneader. Machines capable of uniformly mixing a small amount of liquid with fine powder are preferable, particularly those having blades such as of the oar, paddle or ribbon type fixed on to a twin worm and capable of applying a high compression force to the mixture.

Solvent is evaporated from the intimate mixture, preferably using a relatively low temperature. In particular, it is preferable to carry out the vaporization step with stirring at 70"C or lower. As for the kind of machine employed, a kiln type and a paddle type is preferable in which heat transfer is possible from stirring blades in addition to transfer to the wall of the machine.

Subsequent to the solvent evaporation, the resultant residue is heated in an oxygen-containing gas, typically air or oxygen itself.

Heating when the ingredients do not include an organotin compound is preferably carried out at a temperature of 70-200"C, for an average retention time of 2 hours or longer, preferably at 70-1450C for 3-20 hours, with stirring, in a flow method manner.

When the ingredients do include an organotin compound the heating treatment is preferably carried out at a temperature of 40-200"C, preferably 70-145"C, for 0.5-2 hours, with stirring. In the cases where the main raw material is monoammonium phosphate, the temperature is 1500C or lower, pref erably, 70-1450C.

As mentioned, in a production method of the present invention, the mixing, vaporization and heating treatments may be carried out in a batch mixer. As one alternative, mixing, vaporization and heating may be compartmentalized and independently and continuously carried out.

For continuous production, apparatus of the present invention consists, for example, of a mixing and kneading chamber, a solvent-vaporizing chamber and a heating reaction chamber. Each ofthese chambers is furnished with at least two mixing rotors and partition plates for partitioning the mixing rotors. The mixing and kneading chamber, the solvent-vaporizing chamber and the heating reaction chamber are independent, and they communicate with the succeeding chamber by way of an opening or pipe.Thus, as examples, one can have an apparatus wherein the respective chambers are independent from each other, such as a mixer, a solvent-vaporizer and a heating reactor independent from each other; an apparatus wherein a mixing and kneading chamber and a solvent-vaporizing chamber as well as a solvent-vaporizing chamber and a heating reaction chamber are contacted with each other by way of a partition wall, respectively and are so integrated that the rotors of the respective chambers are rotated by a common shaft; or an apparatus wherein a solvent-vaporizing chamber is contacted with a heating reaction chamber by way of a partition wall, and the two chambers are so integrated that the rotors of the respective chambers are rotated by a common shaft and the mixing and kneading chamber is separate.

The location of the opening or pipe through which the mixing and kneading chamber communicates to the solvent-vaporizing chamber is not particularly critical, but the opening or pipe is preferably arranged to be where the raw materials are retained, ie. at the lower part of the rotating shaft. The shape of the rotors in the apparatus of the present invention has no particular limitation. For example, ribbon oar and paddle type blades, etc, are mentioned. The number of the rotors of the respective chambers may be decided in accordance with necessity. The partition plates provided between the rotors prevent the short pass of raw materials and increase the kneading effect, and may be furnished as appropriate with openings, if necessary.The mixing and kneading chamber is furnished with a raw materialfeeding port, the solvent-vaporizing chamber with a heater and a vaporizing pipe for removing the vapour of solvent and the heating reaction chamber with a heater and a discharging port for the product, the powdery fire extinguishant. As for the heater, any type may be employed, but a jacket is preferable. For the heating reaction, an air-blowing-in port may be provided, and its location may be anywhere in the apparatus of the present invention.

By adoption of the preferred forms of the present invention in which the mixing of the raw materials with a solvent, the solvent-vaporizing treatment and the heating treatment are sectioned and separately carried out, a balance of the times of the respective treatments can be maintained; particularly the time of the heating reaction can be varied as desired, whereby it is possible continuously to produce a product having a constant quality.Furthermore, the solvent vaporization and the heating reaction can be carried out by separate steps and the reaction time made longer, whereby the reaction of the polysiloxane with oxygen in the heating reaction step, or the reaction of the raw material mixture with the polysiloxane, can be uniformly carried out, thereby to be able to impart moisture resistance and freeflow properties at a lower temperature and with uniformity, and thus stabilize the quality of product.

Still further, the preferred methods of the present invention have the great advantages that large hoppers for containing either raw materials after milling or fire extinguishant prior to sieving are unnecessary, thereby allowing smaller apparatus. As for the heating equipment, supply of only the heat quantity sufficient for the raw materials fed is usually needed and hence a small capacity may be sufficient.

The resulting extinguishant typically has a superior emission property and does not change in performance even after lengthy storage. These advantages are particularly attainable when an organotin compound is included into the raw materials. A further advantage of this invention attainable when using an organotin compound is that moisture resistance and flec-flow properties can be imparted to the powder in a short time, thus representing a saving in the volume capacity of the reactor used for the continuous production process of the invention.

The present invention is illustrated by the following non-limiting examples.

Example 7 A 500 I capacity batch mixer having a heating jacket heated by way of a heating medium and a main shaft having ribbon type stirring blades fixed thereonto was employed. With the mixer rotating at 40 rpm, the raw materials given in Table 1 were introduced and then mixed together for one hour.There after the temperature was elevated and perc hioroethylene was vaporized at 600C, followed by - further elevating the temperature and carrying out baking at 1000Cto prepare a powdery fire exting5 uishant Table 1

Ingredient Weight (Kg) Monoammonium phosphate 200 Fine powder of silicic anhydride 6 Methylhydropolysiloxane 4 Perchloroethylene 30 Red pigment trace Dibutylin dioctoate 0.01 The relationship between the baking time and the properties of the resulting powdery fire extinguishant were as shown in Table 2.

Example 2 Example 1 was repeated except the amount of dibutyltin dioctoate was changed to 0.1 Kg. The results were as shown in Table 2.

Example 3 Example 1 was repeated except that dibutyltin dioctoate was not employed. The results were as shown in Table 2.

Table2

Baking Property Example time*3 (min.) 1 2 3 0 Rate of moisture absorption*1 0.31 0.13 Angle of repose ( ) 38 34 Light-duty bulk density*1 0.82 0.90 Residual amount of emission (9)*2 168 88 30 Rate of moisture absorption*1 0.28 0.10 Angle of repose ( ) 34 32 Light-duty bulk density*1 0.86 0.91 Residual amount of emission (9)*2 62 39 60 Rate of moisture absorption*1 0.22 0.10 Angle of repose ( ) 33 33 Light-duty bulk density*l 0.92 0.93 Residual amount of emission (9)*2 34 34 120 Rate of moisture absorption*1 0.16 0.08 0.20 Angle of repose ( ) 33 33 38 Light-duty bulk density*1 0.93 0.93 0.79 Residual amount of emission (9) *2 33 32 183 180 Rate of moisture absorption*1 0.16 0.08 0.24 Angle of repose ( ) 33 32 36 Light-duty bulk density*1 0.93 0.93 0.82 Residual amount of emission (g)*2 *2 36 32 162 240 Rate of moisture absorption*1 0.12 0.08 0.19 Angle of repose ( ) 32 32 36 Light-duty bulk density*1 0.93 0.93 0.84 Residualamountofemission(g)*1 33 36 165 *1 According to Japanese minor regulations for inspection offire-extinguishant agents of fire extinguisher *1.5 Kg vessel employed *3 Time after arrival at 100"C Example 4 Example 1 was repeated except that the baking temperature was changed to 140"C. The results were as shown in Table 3.

Example 5 Example 4 was repeated except that the amount of dibutyltin dioctoate was changed to 0.1 kg. The results were as shown in Table 3.

Example 6 Example 4 was repeated except that dibutyltin dioctoate was not employed. The results were as shown in Table 3.

Table3

Baking Property Example time (min.) 4 5 6 0 Rate of moisture absorption*1 0.27 0.10 Angle of repose ( ) 36 31 Light-duty bulk density*1 0.89 0.92 Residual amount of emission (9)*2 77 36 30 Rate of moisture absorption*' 0.22 0.08 Angle of repose ( ) 36 32 Light-duty bulk density*' 0.90 0.93 Residual amount of emission (9)*2 62 39 60 Rate of moisture absorption*1 0.20 0.07 0.30 Angle of repose e) 34 31 39 Light-duty bulk density*1 0.91 0.94 0.85 Residual amount of emission (9)*2 38 31 114 120 Rate of moisture absorption*1 0.15 0.08 0.22 Angle of repose ( ) 34 30 38 Light-duty bulk density*' 0.90 0.93 0.88 Residual amount of emission (9)*2 32 32 93 180 Rate of moisture absorption*1 0.11 0.06 0.12 Angle of repose ( ) 35 30 34 Light-duty bulk density* 0.92 0.95 0.91 Residual amount of emission (g)*2 34 33 48 *4 Time after arrival at 1400C Example 7 A powdery extinguishant was produced employing a continuous production apparatus separated into a mixer(100 I capacity), a solvent vaporizer (250 I capacity) and a baking chamber (a mixer of 1 m3 volume, having ribbon-type stirring blades fixed onto its rotating main shaft and having partition plates provided therebetween, and also having two chambers inside it; ; rpm, 40). At a temperature for the mixer of room temperature, forthe solventvaporizer of 50"C and for the baking chamber of 140"C, raw materials were fed at the rates shown in Table 4 and production was continuously carried out for 3 weeks: Table4

Raw Material Rate (kg/hr) Monoammonium phosphate 300 Fine powder of silicic an hydride 9 Methylhydropolysiloxane 6 Perchloroethylene 50 Red pigment trace Dibutyltin octoate 0.1 A powdery extinguishant was obtained at a rate of 315 kg/hr. Its properties after one, two and three weeks were as shown in Table 5.

Table5

Example 7 After After After one week 2 weeks 3 weeks Rate of moisture absorption*1 0.04 0.06 0.06 Angle of repose (") 31 29 305 Light-duty bulk density*l 0.935 0.93 0.93 Residual amount of emission (9)*2 32 30 32 For the remaining examples an apparatus in accordance with the invention was employed. This apparatus is shown in the accompanying drawing, in which: The figure is a cross-section of an apparatus for producing a powdery fire extinguishant.

The inside of a 4 m3 capacity mixer having a rotatable main shaft 7 with stirring blades 8 fixed thereonto was sectioned into three chambers, viz a mixing and kneading chamber 1, a solvent-vaporizing chamber2 and a heating reaction chamber3. Sectioning was by means of partition walls 9 and 10, with partition plates 11 were provided between the stirring blades of the respective chambers. An opening 15 for transferring raw material was provided above the partition wall 10, between the mixing and kneading chamber 1 and the solvent-vaporizing chamber 1. An opening 14 was also provided at the lower part of the partition wall, between the solvent-vaporizing chamber2 and the heating reaction chamber 3.A feed port 4 was fixed on to the mixing and kneading chamber 1, a vaporization pipe 5 for removing vapor was fixed to the solventvaporizing chamber 2, and a discharge port 6 was fixed on the heating reaction chamber. Furthermore, on the outer walls of the solvent-vaporizing chamber 2 and the heating reaction chamber 3 were fixed heating jackets 12 and 13 capable of feeding heat at 15000 Kcal/hr.

Example 8 A powdery fire extinguishant was produced employing the described apparatus, the temperatures of the solvent-vaporizing chamber and the heating reaction chamber being set to 50"C and 140"C, respectively, and the stirring blades being rotated at a rate of 40 times per minute. Raw materials were supplied through the raw material feeding port at the rates shown in Table 6 and the extinguishant was produced continuouslyfor3 weeks. Perchloroethylene was quantitatively removed at a rate of 50 Kg/hr.

Table6

Raw Materials Rate (Kg/hr).

Monoammonium phosphate 300 Fine powder of silicic an hydride 9 Methylhydropolysiloxane 6 Perchloroethylene 50 Red pigment trace The resulting powdery fire extinguishant was obtained at a rate of 315 Kg/hr. Test results after 1,2 and 3 weeks were as shown in the following Table 8.

Example 71 A jacket was fixed also to the outer wall of the mixing and kneading chamber of the apparatus; the partition walls and the partition plates were removed; the discharge port for fire extinguishant was closed; the stirring blades were rotated at a rate of 40 times/min; and the raw materials of Table 7 were introduced: Table 7

Raw Material Amount (Kg) Monoammonium phosphate 2,000 Fine powder of silicic anhydride 60 Methylhydropolysiloxane 40 Perchloroethylene 333 Red pigment trace Mixing was carried out for one hour, and then the same heat quantity as in Example 8 was supplied.

Perchloroethylene was vaporized over 5 hours and then heat treatment was carried out for 3 hours. This procedure was repeated 3 times. The results were as shown in the Table 8. After initiation of temperature elevation, the amount of solvent vaporized varied to a large extent, and at the time of the most violent vaporization, the amount was about 300 kg per hour.

Tables

Example 9 Example 10 After After After Aiter After one week 2 weeks 3 weeks twice thrice - Mixing and kneading 3.5 3.5 3.5 1 1 Time of Solvent removal 3.5 3.5 3.5 5 5 Steps Heating reaction (hr) Total 14 14 14 9 9 Produc- Kglbatch 2,100 2,100 tion Kglhr 315 315 315 capacity Kglday 7,560 7,560 7,560 5,600 5,600 Number of steps required (per day) 3 3 3 6 6 Powdery Rate of moisture absorption*1 (%) 0.05 0.04 0.05 0.10 0.08 fire Angle of repose (") 31 30 31 36 34 extin- Light-duty bulk density*1 0.93 0.93 0.93 0.90 0.93 guishant Residual amount of emission (g)*2 32 35 30 48 44

Claims (15)

1. A method for producing a powdery fire extinguishant comprising monoammonium phosphate and/or ammonium sulphate as main raw materials, in which method a polysiloxane having an active hydrogen and a solvent are included with the raw materials which are then subjected to the steps consisting of mixing; solvent-vaporization and removal; and heating in the presence of an oxygen-containing gas.

2. A method according to Claim 1, wherein the production steps are sectioned into a mixing and kneading step, a solvent-vaporizing and removing step, and a heating reaction step, each of the steps being effected independently and the sequence of steps being carried out continuously in a flow system.

3. A method according to Claim 1 or Claim 2, wherein an organotin compound is included with the raw materials.

4. A method according to Claim 3 wherein the organotin compound is a compound expressed by the general formula

(wherein R' and R2 each represent an alkyl group; R3 and R4 each represent a fatty acid residue, or R3 and R4 together represent a dibasic fatty acid residue).

5. A method according to any preceding Claim, wherein the mixing step is carried out by compression mixing at room temperature.

6. A method according to any preceding Claim, wherein the solvent-vaporizing and removing step is carried out by stirring at 70"C or lower.

7. A method according to any preceding Claim, wherein said heating reaction step is carried out at a temperature of 70 to 200"C.

8. A production method according to any one of Claims 1 to 6, wherein the main raw material is monoammonium phosphate and the temperature forthe heating step is 70 to 145"C.

9. An apparatus for continuously producing a powdery fire extinguishant, the apparatus comprising a mixing and kneading part having a feed port for raw materials; a solvent-vaporizing part with heater and vaporization pipe; and a heating reaction part with a heater and fire extinguishant discharge port.

10. Apparatus according to Claim 9 comprising a mixing and kneading chamber, a solvent-vaporizing chamber and a heating reaction chamber, each of these chambers being furnished with at least two mixing rotors and partition plates between the mixing rotors, and said mixing and kneading chamber and said solvent-vaporizing chamber and also said solvent-vaporizing chamber and said heating reaction chamber communicating through a respective opening.

11. Apparatus according to Claim 10, wherein the respective rotors of said solvent-vaporizing chamber and said heating reaction chamber are rotated by means of a common shaft.

12. Apparatus according to Claim 10 or Claim 11, wherein said solvent-vaporizing chamber shares with said reaction chamber a common partition wall through which extends an opening from the solvent-vaporizing chamber to the heating reaction chamber, the opening being located where materials will be retained.

13. Apparatus according to Claim 10, 11 or 12, wherein the mixing and kneading chamber and the solvent-vaporizing chamber, and also the solventvaporizing chamber and the heating reaction chamber each share a respective partition wall and form a unified structure so that the rotors of the respective chambers can be rotated by means of a common shaft.

14. Apparatus according to any one of Claims 10 to 13, wherein the partition plates have a throughopening.

15. Apparatus according to any one of Claims 9 to 14, wherein an opening is provided for blowing in of air into the apparatus.