FR2460891A1 - Preventing dust generation from lead oxide - by adding polyethylene glycol - Google Patents

Abstract

Dust generation from lead oxide is prevented by adding polyethylene glycol (PEG). For minium the PEG has a mol. wt. of 200-400 and amt. used is 0.2-1 wt. %. For litharge the PEG has a mol. wt. of 300-400 and amt. used is 0.75-1.25 wt. %. The lead oxide powder is easily wetted by water and can be granulated.

Description

 The present invention relates to lead compounds which do not form dust.

 It has been known for a long time that powdered lead compounds are a health hazard due to their tendency to generate toxic dust when injected.

planb oxide, in the form of minium or litharge, is used for the production of lead glass and the present applicant has for some time supplied glass manufacturers with a substance known as minium of quality D, containing 0.3% by weight of mineral oil. The incorporation of this proportion of mineral oil has been found to be effective in wetting the minium, that is to say reducing its tendency to generate dust, to an acceptable degree, without altering the free flow characteristics of the powder.

 Recently, however, a technique has been developed for producing glass masses in a central location and supplying such masses to glass manufacturers for melting and manufacturing. The process involved in preparing such masses consists in dry mixing the constituents of the glass, i.e. 1w minium-, sand, potash and possibly other substances, spraying the mixture with water and to put it in the form of substantially spherical granules.

 Although grade D minimum effectively eliminates the health hazards of dust, it cannot be used satisfactorily for mass production by this process, since the oil causes disturbance when wetting pulverulent mixture during the stage of formation of the granules.

The present invention results from research undertaken by the applicant with the aim of finding a replacement humidifying additive for minium and for litharge which effectively solves the problem of the formation of dust without, however, preventing the effective formation of granules.

The Applicant has carried out research into the effect of many water-miscible humidifier additives, but has found that, contrary to what might be expected, many additives have been shown to be ineffective for various reasons. The additive must not have a boiling point that is too low to ensure that it does not evaporate during storage and that it does not cease to effectively humidify the dust formed during the production of the masses. of glass. It must not be toxic or produce a sticky mixture with the minium rather than a free flowing powder. Nor should it be too hygroscopic.

 During the performance of these experiments, the weight loss, in the form of dust, of the mixture of minium and additive was determined by placing a sample of 50 g of the said mixture on a sintered glass disc with a diameter of 42 mm sealed in a glass tube, sending an ascending air flow through the disc and the tube at a rate of 20 liters per minute, collecting and weighing any dust released by the mixture on a Soxhlet cartridge placed 670 mm above the disc, and expressing the dust loss as a percentage reduction in the weight of the mixture per minute.

 Untreated minium gives, in accordance with this test, a dust loss of between 1.3% and 4.6% while untreated litharge gives a loss of 5 to 10%, a loss at most equal to 0.5% can be considered acceptable. The loss due to dust, in the case of the above grade D minium, is less than $ 0.1.

 The Applicant has carried out tests on emulsifiable oils, which have been found to be effective in reducing the tendency to form dust, but which do not give an improvement in the grade O grade during the granule formation stage. . The Applicant has also carried out tests with water-miscible organic liquids and it has been found that some of these increase the tendency to form dust instead of decreasing it. The use of ethylene glycol seemed promising since, immediately after addition of this compound, the loss due to dust was negligible. However, after exposure to air for only 24 hours, the dust loss was 3.15%, which is completely unacceptable.Another portion of the same mixture was kept in a tightly closed bottle and tested at different intervals. According to these tests, the dust loss remained constant for six days and then began to rise on the fourteenth day to a tolerable value. However, after thirty-three days, this loss rose to a totally unacceptable value, equal to 6.2%.

Glycerol was then tested, but it was quickly found that it also lost its dust inhibiting properties. Diethylene glycol monobutyl ether and 2-butoxyethanol have been shown to increase the dust formation rate of minium.

 The Applicant has finally succeeded in obtaining the desired result by using polyethylene glycol. This substance not only ensures a low rate of dust production after prolonged storage, but also gives a mixture which is easily wetted by water.

The table below gives the results obtained by carrying out the test described above with samples of minium to which 0.5> by weight of commercially available polyethylene glycols having molecular weights of 200, 300 and 400 have been added. , the dust loss being expressed as the percentage reduction in sample weight per minute
Number of days of exposure $ 0.5 0.5% 0.5%
PEG 200 PEG 300 PEG 4M test bench)
6 0.04 0.03 0.02
12 0.05 0.03 0.08
19 0.05 0.02 0.05
26 0.05 0.06 0.06
38 0.10 0.06 0.0g
95 0.10 0.08 0.12
123 0.32 0.20 0.36
131 0.24 0.30 0.54
186 - 0.22
PEG = Polyethylene glycol
Although the test samples show a significant, although not serious, loss of dust after prolonged exposure to thin air, identical samples of minium to which were added $ 0.5 by weight of PEG 200, PEG 300 and PEG 400 have been found, after storage for one year in airtight bottles, to give excellent results, the losses due to dust being 0.16 respectively; 0.04 and 0.02.

 The invention consequently provides a form of minium giving little dust, which is easily wetted by water, this form being constituted by a mixture of minium and from 0.2 to 1%, preferably 0.6%, in weight, of a polyethylene glycol having an average molecular weight of 200 to 400.

 The Applicant has found that, if the content of polyethylene glycol is less than 0.2%, the loss due to dust is too high, while if this content is increased beyond 1%, the mixture tends to form a dough and stops flowing freely.

 The mixture of minium and polyethylene glycol can easily be prepared in a conventional mixer.

In practice, the above-mentioned mixture of minium and polyethylene glycol can be supplied for transport in a sealed container where it is introduced in bulk or it can be stored in bulk in a hopper. Storage with a high thickness in a hopper corresponds, as regards the tendency to an increased loss due to dust, to conditions intermediate between those resulting from exposure to the atmosphere on the test bench and those resulting from air-protected storage. Of course, exposure to the atmosphere leads to a maximum risk of loss of polyethylene glycol by evaporation and absorption of moisture due to the hygroscopicity of the polyethylene glycol. The fact that the mixture passes the test The aforementioned therefore gives absolute assurance that this mixture will not produce a harmful quantity of dust during its subsequent use for the production of glass masses.

The Applicant has also found that polyethylene glycol produces a humidifying effect on the litharge, although a larger amount of polyethylene glycol and a higher molecular weight polyethylene glycol are required, since it is It is more difficult to reduce the tendency to form dust from the litharge than that of minium. This is demonstrated by the following results obtained by carrying out the aforementioned tests (in ç:
Number of days of exposure 0.5% of 1.0% of
to the PEG 200 test bench PEG 200
1 3.0 0.3
2 2.0
3 2.2
6 1.1 1.4
B 2.6 0.6
14 2.9 2.1
21 3.5
28 3.2
35 5.4
Number of exposure days $ 0.5 0.75% 1.0% of bench test PEG 300 PEG 300 PEG 300
1 0.7 0.7 0.5
2 0.6
3 0.8 0.3
4
6 1.2 0.5 0.4
8 0.8 0.6
10 0.5
14 0.8 0.5
Samples stored in vials
Number of days 14 10 14
Dust loss 0.3 0.3 0.08
Number of days $ 0.5 0.75% 0.9% 1.0% exposure PEG 400 PEG 400 PEG 400 PEG 400 on the test bench
1 0.5 0.44 0.22
2 0.5 0.24
4 0.30
5 0.20
6 0.7 0.48
7 0.14
8 0.7 0.22
10 0.48
13 0.18
Number of days 0.5% of 0.75 46 of 0.9% of 1.0% of exposure PEG 400 PEG 400 PEG 400 PEG 400 on the test bench
14 0.9
20 0.28
21 0.9
27 0.22
28 0.5
35 1.1 0.30
43 0.38
44 0.8
Samples stored in vials
Number of days 44 43
Dust loss 0.34 0.08
These results show that PEG 200 is not suitable even in an amount of 1% by weight. However, a content of 0.75 * by weight of PEG 300 or PEG 400 gives a loss of dust which is just to an acceptable degree.
PEG 400, the upper limit of the added amount for which the mixture becomes - unduly co-llant is 1.5 q6 by weight, this ~~ limit being consequently- higher in the case of the litharge than in the case of minium.

 Consequently, the invention also relates to a form of litharge which gives little dust, which is easily wetted with water and which consists of a mixture of litharge and from 0.75 to 1.25% by weight of a polyethylene. -glycol- having a molecular weight of 300 to 400.

 It goes without saying that the present invention is in no way limited to the embodiments described which have simply been given by way of illustration. Consequently, all means equivalent to the means or embodiments described, modifications or variants of these means or embodiments also form part of the present invention as defined by the claims below.

Claims (2)

 1. A form of minium giving little dust and easily wetted by water, characterized in that it consists of a mixture of minium and from 0.2% to 1% by weight of a polyethylene glycol having a weight average molecular from 200 to 400. 2. A form of litharge giving little dust and easily wetted with water, characterized in that it is constituted by a mixture of litharge and from 0.75 to 1.25% by weight of a polyethylene glycol having an average molecular weight 200 to 400.