Note: Descriptions are shown in the official language in which they were submitted.
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DE-ICING AND ANTI-FREEZING COMPOSITION
Present invention relates to a de-icing and anti-freezing
composition which is non-corrosive, environmentally safe and which
is readily applicable using existing snow removal vehicles.
BACKGROUND OF THE INVENTION
Common salt (sodium chloride) has been used as a road de-icer
throughout the world due to its availability in virtually unlimited
quantities, low cost and ease of application. In colder climates,
salt may be combined or completely replaced with calcium chloride,
which further lowers the freezing point of water. Adverse impact of
sodium chloride on the environment - corrosion of vehicles and road
structures, damage of the road surfaces and surrounding concrete
and brickwork as well as the detrimental action on ground water and
plants - rises the overall societal costs of its implementation.
U.S. Environmental Protection Agency, for example, has estimated
that overall costs amount to 14 times the direct cost of salt,
while the Ontario Ministry of Transportation deems the overall cost
to be 10-20 greater. This situation has, in the past 10-15 years,
motivated researchers to investigate alternative de-icing
materials.
Due to the fact that common industrial salt and some other
alkali metal and alkaline earth metal chlorides are considerably
cheaper than almost any alternative chemical, attempts were made at
retaining sodium chloride as the major component of a de-icing
composition while at the same time minimizing its adverse action.
Studies were conducted on a number of anti-corrosion
additives, which were aimed at either changing the pH of a de-icing
composition (buffers such as phosphates, borates, etc.), enhancing
its penetration properties, or retaining the salt in a slurry which
would be plowed from the road surface instead of forming a
solution. U.S. patents Nos. 4,668,416 and 4,824,588, for example,
propose the use of lignosulfonates as penetration enhancing
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additives, while U.S. patent No. 5,135,674 proposes the use of
hydroxyethyl cellulose as a gelling agent. While additives could be
beneficial in laboratory conditions and even offer some short-
period advantages in the road tests, the problem of chlorides as
principal agents causing corrosion and other environmental damage
remains unsolved. Therefore, the research on additives has in most
instances been abandoned.
Organic materials have been subject of extensive studies, as
their corrosive action is more favourable and often negligible
compared to industrial salt. Of particular interest were
compositions containing lower alcohols, glycols and urea. Although
non-corrosive, lower alcohols are highly volatile and could be
toxic. The fire danger must be taken into consideration as well.
Glycols have been extensively used as anti-freezing agents in
vehicle cooling systems, but should not be released into the
environment in large quantities due to extremely low
biodegradability.
While being inferior to common salt below -10C, urea also
poses serious environmental problems, especially after being washed
into rivers and lakes - its degradation product is ammonia which is
toxic to the fish even in low concentrations, while its fertiliser
properties may lead to eutrophication.
Compositions comprising mixtures of alkali metal chlorides and
organic materials mentioned above have also been proposed (see e.g.
U.S. patent No. 4,960,531), but they are not likely to have better
environmental properties than their constituents.
Major research effort in the past few years has therefore been
oriented towards developing de-icers comprising alkali metal and/or
alkaline earth metal salts of carboxylic acids. Organic acids in
the free acid form were discussed as well (see e.g. Canadian Patent
No. 1,179,840).
Among carboxylic acid salts, calcium magnesium acetate (CMA)
appears to be the most promising de-icing material. Results of
extensive road tests performed in Germany, Scandinavian countries,
U.S.A. and Canada have proved CMA to be an efficient alternative to
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industrial salt. Subject of a number of patent and non-patent
references, CMA was also extensively investigated and marketed as
a component of a special applications de-icer by author of the
present invention (Yugoslav Patent Application P-1683/89). Apart
from high costs (which would probably be reduced in the case of
large-scale production), CMA seems to be less efficient than salt
at the temperatures below -5C.
High costs of organic chemicals have caused some researchers
to investigate the possibilities of using certain waste materials
as de-icers. U.S. Patent 4,430,240 proposes the use of waste
polysaccharide sources (e.g. sawdust), while U.S. Patent No.
4,676,918 describes a composition containing waste concentrate of
alcohol distilling industry. Canadian Patent No. 1,260,696 utilizes
"black liquor", waste effluent resulting from pulping operations.
While the usage of non-toxic waste materials is environmentally
sound and should be encouraged whenever possible, uniformity of
composition and purity might be difficult to attain and the
available amounts may not be sufficient for large-scale
applications such as road de-icing.
The de-icing composition of the present invention comprises
alkali metal lactates, which are cited as possible components of a
complex mixture in the Canadian Patent No. 1,260,696 (referred to
as "pseudolactates"). The mixture of U.S. Patent 4,430,240 contains
alkaline earth metal lactates. However, the present invention
features a defined mixture wherein lactates are used as a major
component in admixture with specific amounts of an alpha-thioacid
and calcium chloride, to provide an anti-freezing and de-icing
composition with greatly enhanced properties.
OBJECTS OF THE INVENTION
The principal object of the present invention is to provide a
de-icing and anti-freezing composition which is superior to the
prior art compositions in respect to various disadvantages
discussed above, particularly the corrosive action on metals and
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road surfaces as well as the environmental impact such compositions
exert both directly on plants surrounding roads and other surfaces,
and indirectly through sewer systems and ground water.
The further object of the present invention is to provide an
environmentally safe de-icing and anti-freezing composition which
can be applied at costs comparable to overall direct, societal and
environmental costs of applying traditional industrial salt based
de-icers.
Another object of the present invention is to provide a de-
icing and anti-freezing composition which is easy to produce, store
and handle and which can be applied using existing snow and ice
removal systems.
Yet another object of the present invention is to provide a
de-icing and anti-freezing composition which is efficient at the
temperatures lower than temperatures permitting an efficient use of
industrial salt and/or CMA based de-icers.
Other objects and advantages of the present invention will
become apparent from the detailed description of the invention and
the preferred embodiments thereof.
DETAILED DESCRIPTION OF THE INVENTION
The inventor has carried out a comprehensive study of a wide
range of organic materials in order to provide municipal
authorities with an efficient, non-corrosive, ecologically safe and
yet economically acceptable replacement for industrial salt based
de-icers. The present invention is based upon the unexpected
discovery that small amounts of an alpha-thioacid of formula
R-CH(SH)-COOH wherein R denotes hydrogen atom or a lower alkyl
group, and calcium chloride, when mixed with alkali metal lactates,
provide compositions with greatly enhanced de-icing and anti-
freezing properties.
Initial studies have identified alkali metal lactates aspotential constituents of a de-icing and anti-freezing composition.
Sodium lactate is a preferred member of this group. The results
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were promising at temperatures slightly below 0C (down to
approximately -5C), but performance at lower temperatures was slow
and often unreliable.
After numerous trials, it was established that addition of
small amounts of an alpha-thioacid significantly broadens the
temperature range of application. While the exact mechanism of
alpha-thioacid action was not investigated, it is believed that SH
group disruption of hydrogen bonding plays a significant part.
Calcium chloride was introduced to promote faster penetration
and to improve overall performance of the composition at extremely
low temperatures (below -20C). Attempts to find environmentally
more appropriate replacement, which would be efficient in aqueous
systems, were not sucessful. However, as the adverse environmental
impact of chlorides is well known, effort was made to minimize the
amount of CaCl2.
Depending upon the prices of raw materials, in might be
beneficial to manufacture the composition of the present invention
starting from lactic acid and corresponding alkali metal carbonate.
The process involves a simple one-step procedure which will be
obvious to a person skilled in the art.
Storing and handling large amounts of aqueous/organic liquid
compositions may generally give rise to two problems - excessive
foaming and microbial growth in barrels, tanks and other storage
vessels. The composition of the present invention is not an
exception. According to the invention, the problem of foaming is
solved by supplementing the liquid composition with 0.2 to 0.8% v/v
of a defoamer, preferably low temperature resistant silicone-based
defoamer.
Microbial growth, on the other hand, requires no particular
attention - any sludge formed will be simply skimmed off the
surface of the liquid.
The liquid composition of the present invention, therefore,
comprises an aqueous solution of from about 25 to 50% w/v of an
alkali metal lactate, from about 2 to 4% v/v of an alpha-thioacid
of formula R-CH(SH)-COOH wherein R denotes hydrogen atom or a
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Cl3alkyl group, from about 0.2 to 0.8% w/v of calcium chloride, and
from about 0.2 to 0.8% v/v of silicone-based defoamer. Preferred
alkali metal lactate is sodium lactate, while preferred alpha-
thioacid is thiolactic acid.
The inventor's idea was to develop a multi-purpose product
which can be used both for de-icing of roads and other traffic
surfaces such as airport runways, pathways, etc., and for
protecting various surfaces (lower parts of cars, trucks,
streetcars, as well as aircraft surfaces, open decks, etc.) against
the formation of ice.
The liquid composition in its original, undiluted form, may be
conveniently used as an anti-freezing agent. It could be applied to
the surface to be protected in any convenient way, for example by
spraying.
For de-icing purposes, the liquid composition of the present
invention is sprayed onto the road surface in the amount of l liter
per 10-16 m2. The benefit of using a liquid form of the composition
is in the ability to achieve uniform application at high vehicle
speed of up to 50 km/h.
Alternatively, the composition of the present invention may be
prepared in the solid de-icer/stone aggregate form, suitable for
use in the same way as known salt/stone aggregate, CMA/stone
aggregate or similar mixtures. Examples of suitable stone aggregate
include limestone, perlite, basalt, etc. having particle size of
from about 0.3 to 10 mm, preferably from about 1 to 4 mm.
Mixing could be performed in any convenient manner, for
example in a concrete mixer. According to the invention, the
mixture could be supplemented with small quantities of hydrated
lime and crystalline sugar in order to achieve better wetting
properties and the stability of the composition.
The preferred solid composition of the present invention
comprises 1 m3 of said stone aggregate in admixture with about 90
to 130 liters of above liquid composition. This quantity may be
supplemented with about 1 kg of hydrated lime and about 0.5 kg of
crystalline sugar.
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The following non-limiting Examples describe some of the
preferred embodiments of the present invention.
Example 1
A sample of liquid composition according to the invention is
obtained by diluting 60 litres of industrial grade sodium lactate
solution (60% w/v) with 40 litres of water. 3 litres of thiolactic
acid are mixed with the solution.
In a separate vessel, 0.5 kg of crystalline calcium chloride
(in the form of monohydrate) is dissolved in 5 litres of water and
the solution obtained is mixed with the above lactate/thiolactic
acid solution.
The final liquid composition is obtained by adding a 30%
solution of silicone-based defoamer (e.g. Antifoam 1430 supplied by
Dow Corning) and contains, in the volume of 108.5 litres, the
following:
Sodium lactate 33.18% w/v
Thiolactic acid 2.76% v/v
Calcium chloride 0.39% w/v
Defoamer 0.16% v/v
The liquid composition of this example, when sprayed in the
amount of 1 litre per 10-16 m2, readily penetrates the snow and
leaves the surface, after plowing, wet and free from ice. In the
absence of rain it remains active for 5-10 days, while in the
conditions of rain or heavy snowfall the application should be
repeated each 2-4 days. When the temperatures throughout the day
remain lower than -16C, composition should be sprayed in the
amount of 1 litre per 6 m2 of surface.
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Example 2
23.62 kg sodium carbonate monohydrate (Na2CO3 x H20) are
dissolved in 36.5 litres of lactic acid (80%) and 20 litres of
water, and the mixture obtained is stirred at ambient temperature
overnight. The resulting solution is allowed to settle and any
insoluble material is separated.
The volume is adjusted to 100 litres with water and resulting
solution is treated in the same manner as in Example 1 (3 litres of
thiolactic acid, 5 litres of 10% w/v CaCl2, 0.5 litres of 30%
defoamer), so as to obtain 108.5 litres of liquid composition
according to the invention.
Example 3
1 m3 of crushed limestone aggregate (particle size 1-4 mm) is
mixed with 108.5 litres of liquid composition of Example 1 or 2,
for example in a concrete mixer. The mix is supplemented with 1 kg
of hydrated lime and 0.5 kg of crystalline suggar.
The composition obtained is used as a replacement for
conventional salt/abrasive mixtures and can be efficiently employed
in essentially same manner and quantities to achieve improved skid
resistance and disbonding of ice from the road surfaces.
While specific embodiments of the invention have been
discussed in the detailled description and Examples, it should be
apparent that many modifications can be made without departing from
the spirit and scope of the invention. Accordingly, the invention
is limited only by the scope of the claims appended hereto.
