IL28400A - Gelled methyl bromide fumigants - Google Patents

Description

Gelled Methyl Bromide Fumigants DEAD SEA WORKS LIMITED and J· GAEL DAWSON 0:26946 • Th·e invention concerns■ fumigant compo-sitions ■ comprising as fumigant methyl bromide or a mixture containing methyl bromide., The invention also concerns methods of fumigating spaces, bulk storage or soil by Introducin fumigant compositions of the invention into the area to be fumigated.

There are know fumigant compositions used for fumigating grain and for other applications are those consisting of ethylene dibromide and methyl bromide, which exhibit a synergistic effect making them superior to that of either fumigant compound alone. However, methyl bromide has a boiling point of about 4°C. Therefore, when such fumigant mixtures are employed in fumigating grain stored in large, round, silo- ype bins, for example, by applying the fumigant mixture from the top of the bin, the methyl bromide component evaporates on its way to the bottom of the bin and is thus lost with the result that good distribution of fumigant vapors throughout the grain mass to be fumigated is not achieved and the synergistic action of the fumigant mixture is not observed.

Ef orts hitherto made to retard or inhibit the volatilization of methyl bromide in fumlgants have not proven, satisfactory.

The present invention provides fumigant compositions with which these difficulties are not experienced and the volatilization of volatile fumlgants Is effectively retarded.

The invention consists in stable, gelled methyl bromide fumigant compositions comprising a colloidal silica carried-having a particle size of about 0.007 to 0.020 micron.

It Is found that from such a gelled fumlgant composition the methyl bromide is slowly released into the space where it . is needed.

In a preferred embodiment of the invention the composition comprises a mixture of methyl bromide and ethylene dibromide as fumigants.

Pyrogenic colloidal silica, i,,e... one prepared by vapor phase thermal decomposition, has been found especially satisfactory for use in the present invention, e.g. that sold under the trade designation ,,Cab-0-Sil" (marketed b Minerals & Chemipals Division, Cabot Corporation). This has the following properties* Silica content (moisture-free) basis . . 99.9$ Free moisture (105°C) 1.5* : Particle size range 0.007-0.020 micron Specific gravity '■' 2.2 Refractive index .46 ; Bulking value 0.0943 kg/l. pH (4$ aqueous suspension) 3.6-4.2 Colour : " ' - ■ White Of course, other kinds of finely divided silica having similar properties may also be used in carrying ou the invention. in preparin gelled fumigant compositions in accordanc with the inventio i colloidal silica of the kind defined above and a methyl bromide or a volatile fumigant mixture comprising methyl bromide are mixed and agitated in a container "whereby a gelled fumigant composition is readily produced. The gelled fumigant composition is then preferably maintained under pressure until ready for use. When the gelled composition is exposed to the atmosphere, the volatile fumigant or fumigant mixture is slowly released.

While the amount of said colloidal silica in the gelled fumigant compositions varies with the particular volatile fumigant or fumigant mixture being gelled, in general between approximately 2$ and approximately 10J& by weight of said colloidal silica should be included to form a gelled fumigant of the desired consistency. Preferably, 3-5% by weight of said colloidal silica is included to produce gels having a consistency comparable to that of toothpaste, The invention is illustrated by the following Examples to which it is not limited: Example 1 A gelled fumigant composition was prepared as follows; Weighed amounts of a fumigant mixture of 70% by weight of ethylene dibromide and 30% of methyl bromide and colloidal silica of the kind marketed under the trade designation "Cab-O-Sil H5" by Minerals & Chemicals Division, Cabot Corporation were introduced into a half-litre glass jar and agitated to produce a gelled fumigant composition having the following percentage by weight composition: Component Percentage toy Weight iFumlgant 98$ Colloidal silica gelling agent 2$ The gelled fumigant composition was quite fluid in nature. The fumigant and colloidal silica mixed readily and required little agitation. , Example 2 In the manner described in Example 1 a gelled fumigant composition having the following composition was preparedι Component Percentage by Weight Fumigant (as in Example 1) 97# Colloidal silica gelling agent This gelled fumigant composition was of a thicker consistency than that of Example 1 and retained liquid properties to a lesser degree.

Example 3 In the manner described in Example 1 a gelled fumigant composition having the following composition was preparedί Component Percentage by Weight Fumigant (as in Example 1) 96$ Colloidal silica gelling agent # This gelled fumigant composition was still more viscous that that of Example 2 and had a consistency approximating that of toothpaste.

Example 4 In the manner described in Example 1 a gelled fumigant composition having the following composition was Fumigant (as in Example 1) 95 Colloidal silica gelling agen , 5% This composition was more viscous than the compositions of Examples 1-3..

Example 5 In the manner described in Example 1 a gelled fumigant composition having the following composition was prepared: Component Percentage by Weight Fumigant (as in Example 1) 9 # Colloidal silica gelling agent 6$ This composition was rather thick with the gel clumping together into large masses.

Example 6 In the manner described in Example 1 a gelled fumigant composition having the following composition was prepared: Component Percentage by Weight Fumigant (as in- Example 1) 92 Colloidal silica gelling agent 8$ The composition formed a thick gel which was difficult to stir.

Example 7 The process was carried out as in Example 1 but the gelling agent was finely divided silica marketed under the trade designation "Si-O-Llte" by Malllnckrodt Chemical Works. This is a bulky silica of very fine particle size. A gelled fumigant composition was obtained having the Component Percentage by Weight Fumigant (as in Example 1) 90$ Finely divided silica 10$ S is composition had a consistency comparable to that of the composition of Example 3; Example 8 In the manner described in Example 1 a composition was prepared from the same colloidal silica as in Example 1 while the fumigant consisted of 7·2# by weight of ethylene dibromide, 29.2$ of ethylene dichloride and 63·6 o carbon tetrachloride. A gelled fumlgant composition was obtained having the following composition: Component Percentage by Weight Pumigant 96fi Colloidal silica gelling agent 4$ This composition had a consistency comparable to that of the composition of Example 3.

Example 9 In the manner described i Example 1 a composition was prepared from the same colloidal silica as in Example 1 the while/fumigant consisted of 70.2# by weight of ethylene dichloride and 29.8$ of carbon tetrachloride. A gelled fumigant composition was obtained having the following compositio ; Component Percentage by Weight Fumigant 95f* Colloidal silica gelling agent 5$ This composition had a consistency comparable to that of the composition of Example 3* Example 10 In the manner described in Example 1 a composition was prepared from the same colloidal silica as in Example 1 while the fumigant consisted of 83.5 by weight of carbon tetrachloride and 16.5$ of carbon bisulfide. A gelled fumigant composition was obtained having the following composition: Component Percentage by Weight Fumigant 95.5$ Colloidal silica gelling agent 4. $ This composition had a consistency comparable to that of the composition of Example 3.

Example 11 In the manner described in Example 1 a composition was prepared from the same colloidal silica as in Example 1 while the fumigant consisted of 76.5 by weight of carbon tetrachloride, 10.0# of carbon bisulfide, 10.0JS of ethylene dlchloride and 3 * 5% of ethylene dibromide. A gelled fumigant composition was obtained having the following composition: Component Percentage by Weight Fumigant 9 .5 Colloidal silica gelling agent 4*5 This composition had a consistency comparable to that of the composition of Example 3* Example 12 In the manner described in Example 1 a composition was prepared from the same colloidal silica as in Example 1 while the fumigant consisted of 78.8$ by weight of carbon tetrachloride, 19.2$ of carbon bisulfide, 1.0$ of sulfur pomponent Percentage by Weight Fumigant 95.5 Colloidal silica gelling agent « $ This composition had a consistenc comparable to that of the composition of Example 3· Bxample 15 The: gelled fumigant composition of Example 2 wa employed in the test work described in this and the following Examples except Example 18. The fumigant composition was prepared in a 22.5-liter cylinder, and the cylinder was then 2 pressurized to 8 kg/cm with compressed air. An automatic cylinder filler was used for this, purpose with only the air solenoid in operation. Λ switch automatically shut the air pressure off when it reached the predetermined 8 kg/cm .

The cylinder was equipped with an oversized positive action mm valve with attached standplpe. Approximately 1 m of 8.5/ outer diameter polyethylene tubin was attached to the valve on the oyllnder. At the end of the polyethylene tubing, a Hoke mm valve was Installed and to this valve 1 m of 8-,pouter diameter copper tubing was attached..

In this experiment and the experiments described in the following Examples, grain was introduced into a vertical bin using a conventional belt and tripper,. The r¾te of flow of the grain was determined prior to initiating fumigation for the purpose of determining at what intervals to apply the gelled fumigant composition to arrive at the : desired dosage per 35»000 liters of grain.

In preparation for the fumigation, the cylinder containin the gelled fumigant composition was placed on the copper tubing was inserted into the manhole. In applying the gelled fumigant composition, the valve on the cylinder containing the composition was opened first and then the Hoke valve was opened and the scales observed until the predetermined dosage of gelled fumigant composition was dispersed. It was observed that it took from five to eight seconds to disperse 0.5 kg. of gelled fumigant composition. The valvfc on the cylinder remained open during the entire fumigation operation and the fumigant composition was dispersed by employing the Hoke valve only. In some of the teste described, care was exercised not to apply the gelled fumigant composition directly on the grain stream. In other tests, the gelled fumigant composition was applied directly on the grain stream. The intervals between applications of the fumigant composition were timed with a stop watch The gelled fumigant composition was applied at 17,500 liters intervals in order to distribute the fumigant composition evenly throughout the grain mass. In all but one of the fumigation operations, the first and last 35,000 liters of grain entering the test bin were given twice the amount of umigant composition as the remainder of the grain received* During the fumigation operations, grain was take from the belt using a 10-liters bucket, A small amount of grain from each of these buckets was placed in a sample bag for the purpose of obtaining bromine residue and percent moisture of the grain. These samples were taken every ,000 litersf Grain temperatures were obtained by using a Radson thermocouple grain temperature probe, The probe was inserted into each bucket of grain removed from the belt. These temperatures were averaged to arrive at an average prefumigation grain temperature* After completing the fumigation operation, all samples in the bags were thoroughly mixed and processed through a grain separator to obtain two composite samples. These samples were used to determine the percentage of moisture in the grain and to obtain prefumigation bromine residues of the grain; Plastic test boxes containing as test insects five Confused Flour Beetle adults, or five Granary Weevil adults,' or five Confused Flour Beetle adults plus five Granary Weevil adults, were employed in the test worki.

A small amount of lour was added to each test box to prevent starvation" of the inseots during the exposure period. Two test boxes per 35,000 liters of grain were used. The test boxes were perforated with a small hole to aid in the entry of oxygen and fumigant composition vapors. The test boxes were placed inside oloth bags to aid in their recovery from the belts in the event the grain could not be run over a coarse separator or a scalper.

Caution was exercised not to apply the test boxes and fumigant composition too close together so that the fumigant composition would come directly in contact with the test boxes.

Upon completion of each fumigation operation, the manhole cover on top of the bin was sealed with masking tape and a warning sign attaohed. Also, any accessible air vents - - I After a predetermined exposvire period, the fumigated grain was transferred from the fumigated bin to another bin. At this time, the test boxes were removed directly from the belt, or, If possible, from a coarse separator or scalper. As the test boxes were being removed, temperatures of the grain were again taken in the manner described above when obtaining the before-fumigation temperatures. Also, two composite samples for the purpose of obtaining poat-fumigation grain moisture and inorganic, as well as total, bromine residues were gathered in the same manner as employed in obtaining the pre-fumigatio information.

The test insects in each test box were counted immediately upon removal from the bin and again after 24 hours. They were recorded as "live", "moribund" or "dead". "Moribund" may be defined as an affected Inseot, ranging from a slight twitching of the antenna or legs to more vigorous kicking. In any case, the insect is immobile. One or more control test boxes were retained from each fumigation as a check. These insects were held at room temperature during the exposure period and oounted along with the other test insects recovered from the fumigated bins.

In the first test, a fumigation was carried out with 0.9 kg of the gelled fumigant composition of Example 2 per 35,000 liters of grain. The first and last 35,000 liters received a dosage of 2 kg. Fumigation was conducted in a round concrete bin, 42 m deep and 6 m i diameter, with a capacity of 1,300,000 liters. The grain of the wheat were introduced into the bin. The wheat was weighed over a scale and emptied into the bin in 70,000 liter drafts. The temperature of the grain at the time of fumigation was 25°C and the moisture content was 13«7$.

The atmospheric temperature was 15.5°0. 33 Test boxes were added to the grain as it went into the bin, and all but six of these test boxes were recovered at the end of a 14-day exposure period, Ths insects employed in this fumigation as test inaects were Granary , Weevil adults, with five of the Insects in each test box.

When the test boxes were recovered, the temperature of the grain was 25°C and the moisture content was 13»85$.

The immediate count of the insects revealed no "live", 2,3% "moribund" and 97.7$ "dead". There was no change from the above count after 24 hours. The control insects were all "live" in both of these counts. The pre-fumiga ion wheat samples contained 98.4 p.p.m. total bromine and 79.8 p.p.m. inorganic bromine. The post-* fumigation samples contained 100.1 p. .m. total bromine and 79.9 p.p.m. Inorganic bromine.

Example 14 Example 13 was repeated with 1.4 kg. of the, gelled fumigant composition of Example 2 per 35,000 liters. The test bin was a round concrete bin, 33 m deep and 3.75 m in diameter. This bin had a capacity of 500,000 liters of grain. The grain fumigated was 1961' Kansas iSfo. 1 Hard Wheat and 460,000 liters of this wheat were introduced into the bin. The grain temperature at the time the fumigation was conducted averaged 11°0. In this particular bin, the first dosage of the fumigant composition. 27 Test boxes were introduced into the bin and of these 25 were recovered after a seven-day exposure period. Each of the test boxes contained 5 Oonfused Flour Beetle adults as the test insects.

Immediate count of the test insects upon expiration of the exposure period revealed no "live", 25. $ "moribund" and 74.4$ "dead". The 24-hour count showed 2 "moribund" · and 6$ "dead"* The control test box showed all of the insects to be alive in both counts. Pre-fumigation samples showed that the wheat contained 100^1 p.p.m. total bromine and 71.9 Ρ·Ρ·πι· inorganic bromine whereas the post-fumigation samples showed 100.1 p.p.m. total bromine and 74.6 p.p.m. inorganic bromine.

Example 15 Example 13 was repeated using 1.4 kg. of the gelled fumigant composition of Example per 35»000 liters. The test bin was a round concrete bin, 42 m deep and 6 m in diameter, with a capacity of 1,300,000 liters. The grain fumigated was Ho. 3 New Crop Red Garlic Soft Wheat, and 1,200,000 liters were introduced into the bin in 70,000 liters drafts. Temperature of the wheat at the time of fumigation averaged 22°C with a 13.6$ moisture content. The first and last 35*000 liters of wheat were given a double dosage of 2.7 kg. of the gelled fumigant composition.

A total of 70 test boxes were Introduced into the bin and 60 of these were recovered after an exposure period of nine days. The test boxes each contained 5 Oonfused Flour - - Ά k · Beetle adults and 5 Granary Weevil adults. The temperature of the wheat at the time the boxes were removed therefrom was 21.5°C and atmospheric temperature was 7.2°0.

The immediate count, as well as the 24-hour count, showed 7$ of the Confused Plour Beetles and 19$ of the Granary Weevils to be "live". 19$ of the Confused Piour Beetles and 3$ of the Granary Weevils were "moribund". 74$ of the Confused Flour Beetles and 78$ of the Granary Weevils were "dead". The total results were thus 13$ "live", 11$ "moribund" and 76$ "dead". Samples of the wheat taken prior to fumigation oontained 42.6 p. .m. total bromine, and 24.1 p. .m. inorganic bromine, whereas post-fumigation samples of the wheat showed 53.4 p.p.m. total bromine and 29*4 p.p.m. inorganic bromine^ In this particular fumigation operation, the wind velocity was rather high, creating an updraft in the bin. During the fumigation, strong fumigant vapors were noticed coming from the top of the bin from time to time. ffxample 16 Example 13 was repeated with 1.4 kg. of the gelled fumigant composition of Example 2 per 35,000 liters. The grain fumigated was No. 1 Dark Northern Spring Wheat , and the test bin was a round concrete bin 33 m.deep and 3.75 m in diameter with, a capacity of 500,000 liters. 385,000 liters of wheat were introduced into the bin. The temperature of the wheat at the time of fumigation was 17.5°C and the moisture content was 10.98$. The first and last 35,000 liters of wheat entering the bin were given a double dosage of 2.7 kg. of the fumigant composition.

,J 22 Test boxes were introduced into the bin and of these 16 were recovered. Bach test box contained 10 Confused Flour Beetle adults. An eight-day exposure period was used. The temperature of the wheat at the time the test boxes were removed therefrom was 13°C and the atmospheric temperature was 8..5°0.

The immediate count revealed 37.6$ "live", 1.8$ "moribund" and 60,7 "dead". The 24-hour count showed 30$ "live", 5.6 "moribund" and 64.4$ "dead". Two control boxes held at room temperature throughout the exposure period contained all "live" Confused Flour Beetles in both counts. Example j Example 13 was repeated with 1.8 kg. of the gelled fumigant composition of Example 2 per 35»000 liters. The grain fumigated was No. 1 Dark Hard Kansas Wheat which had been in storage for two years, and the test bin was a round concrete structure, 33 m deep and 3.75 m in diameter and with a capacity of 500,000 liters. The temperature of the wheat at the time of fumigation was 21.5°C, and the moisture content was 11.5$. The first and last 35»000 liters of wheat entering the bin were given a double dosage of 3.6.'kgof the fumigant composition. 23 Test boxes were introduced into the bin, and all of these were recovered. Each test box contained 5 Confused Flour Beetle adults, and an exposure period of 13 days was used. The temperature of the wheat at the time the test boxes were removed therefrom was 15,5°0 and the atmospheric temperature was 8.5°C.

The immediate count revealed no "live", 0.7 ''moribund" and 98,3 "dead". There was no change in this count after 24 hours· Two control boxes held at room temperature throughout the exposure period contained all "live" Confused Flour Beetles in both counts. Samples of wheat taken prior to fumigation contained 42.6 p. .m. total bromine and 34.6 p. .m. inorganic bromine , whereas post-fumigation samples of the wheat contained 58.7 p.p.m. total bromine and 45*4 p»p*m* inorganic bromine. xample 18 Example 13 was repeated except that the fumigant composition employed was an ungelled liquid fumigant composition consisting of 70$ by weight of ethylene dibromide and 30 by weight of methyl bromide, The dosage applied was 1.65 kg. per 35»000 liters of grain, and the test bin was a round concrete bin 42 m deep and 6 m in diamete with a capacity of 1,300,000 liters of grain.

However, only 770,000 liters Of grain were Introduced into the bin and fumigated, lhe grain fumigated was 1961 Ho, 2 Tello Hard Wheat, The average temperature of the wheat at the time of fumigation was 15°0 and the moisture content was 13$. The first and last 35,000 liters of wheat entering the bin were given a double dosage of fumigant composition. 44 Test boxes were introduced into the bin, and 42 of these were recovered. Bach test box contained 10 Confused Flour Beetle adults as the test insects, and a exposure period of 12 days was used.

The immediate count as well as the 24-hour count showed 42,4$ "live", 9.8$ "moribund" and 47.8$ "dead".

The grain had natural infestation of insects ~ and when removing the test boxes, samples were sieved out to determine the effect of the fumigant composition on the natural infestation. It was found that all insects sieved from the wheat were "live".

In the foregoing teste, the temperature of the grain being fumigated ranged from 11 C to .a maximum of 25 C» Grain fumigation is normally carried out wit the grain temperature above 15.5°C (e.g., in the range between 26.5 and 32°C), and it is known that at grain temperatures below 15»5°C, increased dosages of fumigant composition must be utilized in order to achieve effective fumigation. Accordingly, based on the foregoing test results, a higher percentage of mortality among test insects would be expected. to occur with the same dosages at grain temperatures in the normal fumigation range of above 15.'5°0.

The foregoing Examples show that the compositions of the invention achieve the desired advantageous results.

Claims (2)

1. gelled methyl bromide fumigant compositions comprising a colloidal carrier having a particle size of about to compositions according to Claim comprising between approximately and by weight of a fumigan mixture comprising methyl bromide and between approximately and of said silica Fumigant compositions according to Claim comprising approximately by weight of said mixture and imately of said silica Fumigant compositions according to Claim 2 wherein said fumigant mixture comprises methyl bromide and ethylene Fumigant compositions according to

2. Claim 2 or wherein the fumigant mixture consists essentially of approximately by weight of ethylene dibromide and approximately of methyl bromide A method of fumigating which comprises introducing into an area to be a gelled fumigant composition according to any of Claims 1 to For the Applicants COM AND insufficientOCRQuality