FR2482420A1 - Vaporising insecticide or insect repellent from cellulose support - by combustion of a fuel to provide the necessary heat - Google Patents

Abstract

In a method for vaporising an insecticide or insect repellant (I) absorbed onto a cellulose support, the heat of vaporisation is provided by burning a fuel. Either a natural flame or catalytic combustion is used and the heat of vaporisation gives a temp of about 140 deg C. Particularly, (I) in incorporated into an absorbant pellet, each pellet contg 40 mg bioalethrim (Ia); 90 mg solvent; 17mg butylated hydroxytoluene (BHT), 1mg dye and 7mg perfume. Also new is a burner for this process using catalytic combustion of a liquefied gaseous fuel. This comprises a fiel reservoir fitted with a pipe and a manually-operated valve to control the fuel supply. Above the pipe is the catalyst and mounted above this is the (I)-contg pellet. (I) can now be vapourised without needing a fixed electrical energy source, and the burner can be made portable.

Description

 The present invention relates to a burner for vaporizing an insect repellant or insecticide, as well as to a method for operating this burner.

 It is known that certain active substances, such as for example pyrethrins and synthetic pyrethroids have an insect repellant or insecticidal action if they are dispersed in the air in the form of vapors by evaporating them by heating at sufficient temperatures.

The above method has been used until now to eliminate insects, and in particular mosquitoes, from places of habitation,
In known evaporation devices, the necessary heat is supplied by the transformation of electrical energy into heat using electric heating elements. The invention relates to a method and an apparatus which use the thermal energy produced by combustion, which gives a device independent of stationary energy sources.

 It is possible to use fuels of various types, for example gasolines or other petroleum-derived hydrocarbons such as butane, propane or other gases or their mixtures derived from petroleum or other sources. , which may be contained in the liquid state in a container or a tank.

 Thanks to combustion, the required temperature is obtained on a surface which provides heat to the active substance at its core, which is advantageously supported in heat exchange relation with this surface.

The emission of vapors is proportional to the amount of energy exchanged.

The fuels can be charged in the combustion zone either in the gaseous state, under pressure, or in the liquid state, by capillarity or by gravity.

 By modifying the quantity of fuel loaded, the desired temperature is obtained and therefore the desired vaporization effect.

 The emission of the active substance takes place as soon as the heat generated, once it has overcome the thermal inertia of the materials participating in the heat exchange, brings the active substance to the vaporization temperature.

 Combustion can take place in various ways and at various temperatures.

The simplest example is that of natural combustion, in the presence of a visible flame.

There is also what is called catalytic combustion in the presence of catalysts, generally formed from mixtures of platinum salts on supports of inert fibrous mineral materials such as mineral wool, in which catalytic combustion or catalytic oxidation with splitting of the molecules of the gaseous fuel takes place in the absence of any visible flame and at temperatures which are much lower than those of natural combustion.

The catalytic combustion makes the combustion continue independently of the presence of air currents In fact the increase of the air content in the combustion zone is not annoying and can even have a favorable influence on the reaction of oxidation.

 By using this type of combustion, it is therefore possible to obtain the emission of active substance even in the open air, without the need to use complicated flame protection devices.

In addition, due to the relatively low combustion temperature, any accidental contact of flammable liquid with the appliance does not cause their ignition.

 In order to limit the fluctuations in emission of the active substance, it is possible to protect the heating surface so as to maintain, even in the presence of drafts, a sufficiently constant temperature.

 In the case of combustion at high heat, it is on the contrary absolutely necessary to use a suitable screen so as to ensure the continuity of combustion, the diffusion into the air of the active substance, the correct mixing of the air and gas and exhaust gas evacuation.

 The advantage of using combustion heat is to be freed from any fixed source of energy.

In fact, the usual electrically heated burner is dependent on the transmission of energy by wires, while a device according to the invention.
Vention is portable, since it requires no connection to external energy sources
The device according to the invention can thus operate anywhere, even to replace conventional devices.

The burner according to the invention comprises a container intended to contain mixtures of liquefied combustible gases, a nozzle for distributing the gaseous fuel leaving the container, a flow valve which controls the gas stream leaving the nozzle, a catalytic element placed above of the nozzle and an element for supporting the tablet to be vaporized disposed above the catalytic element.

 The container for the mixture of combustible gases may be integral with an assembly supporting the catalyst and the pellets and supplying the gas, in which case the container is conveniently provided with a filling valve which is intended to receive the means for delivering the gas produced on the bomb for recharging a cigarette lighter of a known type.

 As a variant, the container can be separated from the assembly supporting the catalyst and the gas discharge tablets, in which case this assembly is provided with means for retaining a container which is for example similar to the means provided on the accessories for hot dishes of camping.

Other characteristics and advantages of the invention will appear during the description which follows with reference to the appended drawings, given solely by way of examples, in which
Figure 1 is a side view of the burner according to the invention.

 FIG. 2 is a side view of the same burner taken at 900 with respect to FIG. 1.

Figure 3 is a plan view of the burner of Figure 1.

FIG. 4 is a plan view corresponding to that of FIG. 3, the metal strip carrying the pellet and the cylindrical case carrying the catalyst being removed, and
Figure 5 is a side view of a variant burner according to the invention, the container intended to contain the mixture of liquefied gas being separable from the assembly intended to deliver gas.

 Referring to Figures 1 to 4 of the drawings, the burner comprises a cylindrical container 1 serving as a base, surmounted by an assembly comprising a partially cylindrical carcass and a vertical upright 3 which is opposite it delimiting between them a space intended to receive the element for debiting and regulating the flow of gaseous fuel.

The assembly intended to deliver and regulate the flow of gaseous fuel comprises an intermediate nozzle 4 controlled by a flow valve 104, which is actuated by an opening device comprising a sink 5 intended to lift the nozzle and consisting of a metal rod which is flattened and bored in an intermediate position so as to allow the passage and the embedding of the part forming a stop formed on the external face of the nozzle 4. The marks 6 and 106 d- sign two vertical uprights, which serve as a guide.

for the lever 5 for lifting the nozzle and which are integral with the burner casing. The reference 7 designates the cylindrical element intended to operate the lever 5. The cylinder 7 rests on the plane from which the vertical uprights 6 and 106 start and rotates so that these uprights are inscribed in this cylinder. On the upper inner face of the cylinder 7 are formed two diametrically opposite inclined planes 8, which serve as a stop and guide means for the ends of the lever 5. From the cylinder 7 leaves radially outward a control lever 9 integral with the cylinder 7. When one acts on the lever 9, the cylinder 7 rotates, the ends of the lever 5 are forced to rise towards the upper dead center constituted by a horizontal zone 108.

Thus the nozzle, against which the intermediate bore of the lever 5 abuts, is lifted. The pressure exerted by a compression spring (not shown) which, in the closed position of the valve, acts on a packing arranged at the base of the nozzle and is pressed on the bore in order to put the container in communication and the nozzle is therefore released so that gas flows out of the nozzle 4. At the base of the cylinder, on the inner face, is formed a notch 10 which cooperates with a stop groove 210 formed in the outer face a metal ring 110, which is integral with the uprights 6, 106, so as to constitute the end of travel stop for the opening of the flow valve.

 The reference II designates a filling valve which is intended to receive means for supplying gas provided on the most conventional filling bombs with lighters in order to fill the container 1.

The reference 12 designates a metal strip which bridges the upper edge of the carcass 2 and the upright 3. The strip is provided in its center with an opening through which passes the cylinder 13 carrying the catalyst 14. This catalyst is constituted by a support made of asbestos or an inert material, if necessary reinforced with steel wire, on which are finely ground platinum salts. The catalyst 14 is carried by the strip 12 at the level of the maximum upward movement of the mouth of the nozzle so as to have immediate and direct contact of the gas with the catalyst itself. The cylinder 13 is provided at its top with a receptacle 15 intended to support the tablet (not shown) containing the insecticide or insect repellant substance which can be vaporized.

The operation of the device is as follows.

The lever 9 is rotated counterclockwise until the lever is locked and can no longer rotate. A flame source (such as a match, a gas lighter, but not a piezoelectric discharge lighter) is brought near the catalyst 14. Combustion occurs almost instantaneously without any flame.

 In order to ensure that the burner has been correctly lit, you can blow lightly on the surface of the catalyst and observe the brightness of a few hundred incandescent points.

At this instant, a tablet is placed in the receptacle 15 with coverslip
FIG. 5 illustrates a burner similar to that of FIGS. 1 to 4 in which the container 5 of fuel in the form of liquefied gas is of the type with a non-refillable cartridge for disposal, and is fixed to the case 2 in itself known, by being retained using bars 201.

In order to verify the effectiveness of the process and the apparatus according to the invention, the emission diagrams for the various insecticidal compositions absorbed on known cellulosic tablets have been drawn, using the burner according to the invention.

 The fuel used was a mixture of liquefied petroleum gas composed mainly of propane, isobutane and normal butane.

The various temperatures were obtained by modifying the fuel loading.

 In the case of catalytic combustion, to which the following emission effects refer, the temperatures range from room temperature to about 2000C. It goes without saying that the test temperatures were chosen from a more limited range corresponding to the average temperature values obtained in electric heating burners, that is to say from 1200 to 1300C.

 The temperatures mentioned above refer to the surface of the heating element and have been measured and controlled using an instantaneous electronic thermometer for detecting the temperature of the surfaces.

 Ignition is always carried out using a match on the surface of the catalyst plate inserted in the loading device.

The insecticide composition used for the tests was absorbed on pellets using a technique which allows precise measurement of the substances used.

This measurement technique consists in depositing the desired quantity of insecticidal liquid composition using a microsyringe on a microscope plate having an area equal to that of the pellets to be impregnated, this plate being glued to a similar plate of larger dimensions. . The drop of substance deposited in the middle of the plate of smaller dimensions is then spread over the entire surface of the plate by correctly tilting the two plates. The absorbent tablet is then gently placed on the plate with a light pressure, so as to make it absorb all the liquid, the difference between the known initial weight of the two plates plus the drop of liquid and the final weight of the two plates after absorption, the amount absorbed is easily obtained
The pellets thus prepared are ready to be introduced into the heated burner at the temperature desired for the experiment. The emission of the active substance and sometimes of other constituents of the composition as a function of time is calculated by quantitatively determining the residual amounts of pellets at various heating times.

This determination of the residues is carried out by extracting pellets of the residual constituents with the aid of suitable solvents and determining them quantitatively by analytical methods of gas chromatography according to the method of the internal standard.

EXAMPLE 1
The following insecticide composition is used:
Bio-aletrine (active substance) 69 mg
Piperonyl butylate (solvent and agent 49 mg
synergy) Butyl-hydroxy-toluene (ber) 49 mg dye 1 mg
Perfume 7 mg
The above composition is chosen as being a typical insecticide composition, the essential constituents of which are the active substance having an in secticidal action, a solvent (having a synergistic action) serving as a vehicle, an antioxidant serving as stabilizer for the active substance which breaks down easily by oxidation, in particular in the presence of light, a dye which plays the role of chromatic indicator and a perfume. The tablet is subjected to heating in the burner according to the invention at 1200C, for a total of 12 hours. The emission values mentioned in Table 1 below have been determined by expressing them in mg of residual active substance from the tablets.
TABLE 1 mg of BHT Bioaletrine Butylate residue after piperonyl
1 hour 67 48.5 24
2 hours 65 48 8
4 "63 46 O-
6 "60 45
8 "58 44 - 10" 55 41.5 -
Starting value 69 45 49
EXAMPLE 2
The same composition as that of Example 1 is subjected to heating at the temperature of 1500C. The emission values given in Table 2 are obtained.
TABLE 2 mg of BHT Bioaletrine Butylate residue after piperonyl
1 hour 61 45 0
2 hours 54 42
4 "39 38.5
6 "25 36
8 "10 35
10 "0 32
Starting value 69 49 49
EXAMPLE 3
The same composition as that of Example 1 is subjected to heating at a temperature of 18000. The emission values given in Table 3 below are obtained.
TABLE 3 mg of BHT Bioaletrine Butylate residue after piperonyl
(in hours)
1 39 43 0
2 15 40
4 0 36
6 - 31
8 - 25
10 - 21
Starting value 69 49 49
From the results of experiments 1, 2 and 3, we can deduce the following
a) The temperatures of 12000 and 18000 are respectively too low and too high with an insufficient emission of active substance in the first case and with an excess of emission in the second, so that the pellets are exhausted after approximately 4 hours. Assuming that an emission period of 8 to 10 hours is the best, a temperature between 150 and 14,000 is best. It can also be observed that the emission of bioaletrine is substantially linear.

 b) The emission of piperonyl butoxide is very slow and reaches 50% after approximately 10 hours at the highest temperature of 18000. This seems to exclude that the supposed synergistic action of this substance is real.

 c) The emission of BHT takes place very quickly, in approximately 3 hours at 1200C, in one hour at 1500C and in half an hour at 180 C.

 To better define the characteristics of the emission of the active substance, and to obtain a linear or constant emission as a function of time during the entire heating period, which is very important in order to obtain an effective and continuous insecticidal effect, a series of tests is carried out using different amounts of active substance (bioaletrine) in a typical basic composition.

The tests were carried out at the temperature of 1400C chosen according to the above discussion.

EXAMPLE 4
We use the following composition
Bioaletrine 70 mg
Solvent 61 mg
BHT 17 mg
Dye 1 mg
Perfume 7 mg
The tests are carried out at the temperature of 1400C according to the method described in the previous examples, which gives a linear emission curve for Bioaletrine. The emission is almost constant and continues at the rate of approximately 3 mg per hour.

 The solvent used in this series of tests consists of esters of branched fatty acids.

EXAMPLE 5
We use the following composition
Bioaletrine 55 mg
Solvent 75 mg 17-mg
Dye 1 mg
Perfume. 7 mg
A linear curve is also obtained in this case parallel to that of Example 4. The amount of active substance emitted per hour is approximately 3 mg.

EXAMPLE 6
We use the following composition
Bioaletrine 40 mg
Solvent 90 mg
BHT 17 mg
Dye 1 mg
Perfume 7 mg
In this case too, a continuous emission is obtained at the rate of approximately 3 mg per hour.

It is deduced from the above that it is possible to determine the optimum amount of active substance necessary to maintain an insecticidal effect over a given period in advance. This is for example the case, for a period of 10 hours, and retaining a certain margin of safety, an amount of 40 mg of Bioaletrine is required in each lozenge.

Claims (10)

1) A method of vaporizing an insecticide or insect repellent active substance absorbed on a cellulosic support, characterized in that the heat of vaporization is provided by the combustion of a fuel. 2) Method according to claim 1, characterized in that the combustion is a natural flame combustion. 3) Method according to claim 1, characterized in that the combustion is a catalytic combustion. 4) Process according to claim 1, characterized in that the heat of vaporization gives a temperature of the order of 1400C. 5) Process according to claim 1, characterized in that it consists in incorporating the active substance into insecticidal tablets formed from an absorbent cellulosic support containing, in the absorbed state, a composition containing 40 mg of bioaletrine, 90 mg of a solvent, 17 mg of butyl-hydroxy-.toluene, 1 mg of a colorant and 7 mg of a perfume. 6) vaporization burner for carrying out the process according to claim 1 by vaporizing -an active substance, absorbed in a suitable support, by catalytic combustion of a liquefied gaseous fuel, characterized in that it comprises a tank intended to contain a fuel in the form of liquefied gas, a nozzle intended to distribute the gaseous fuel from the tank, a manually controlled valve> interposed between the tank and the nozzle in order to master the flow of gaseous fuel going to the nozzle, a catalyst carries above from the nozzle and means for supporting above the catalyst a pellet containing in the absorbed state the vaporizable active substance. 7) Burner according to claim 6, characterized in that the catalyst comprises a support including asbestos or inert material reinforced by-steel wires on which are deposited finely divided platinum salts. 8) Burner according to one of claims 6 or 7, characterized in that the valve is controlled by means of a cylindrical body mounted coaxially with the nozzle and able to rotate about its axis, this cylindrical body being provided at the end upper of inclined plane surfaces similar to cams cooperating with a transverse bar connected to the nozzle, the latter being connected to the control valve, and elastic means are provided to constantly stress the nozzle and the valve which is axially connected to it in a direction in which the passage for the gas stream is closed, while by rotating the cylindrical element in one direction, the axial lifting of the nozzle is controlled by the bar against the action of the elastic means , which establishes communication between the tank and the nozzle. 9) Burner according to one of the preceding claims, characterized in that the tank is in one piece with the carcass of the burner and is provided with a filling valve for the liquefied gaseous fuel. 10) Burner according to one of claims 6 to 8, characterized in that the tank is not in one piece with the carcass of the burner and can. be secured in a removable manner.