WO1999013018A1

WO1999013018A1 - Deicing composition

Info

Publication number: WO1999013018A1
Application number: PCT/IL1998/000432
Authority: WO
Inventors: Shaul Zolotov; Margarita Genis; Izhak Haliva
Original assignee: Dead Sea Works Ltd.
Priority date: 1997-09-08
Filing date: 1998-09-07
Publication date: 1999-03-18
Also published as: IL121719A0; IL121719A

Abstract

A composition for melting ice and snow and for preventing the formation of ice on roads, comprising an inner layer containing a secondary ice melting agent and an outer layer containing a primary ice melting agent, wherein said primary ice melting agent has been melt-coated onto said secondary ice melting agent.

Description

DEICING COMPOSITION

Field of the Invention

The present invention relates to compositions for melting, loosening or

preventing the formation of ice on roads, streets, sidewalks and the like.

Background of the Invention

The formation of ice on roads can present a safety hazard, as a well as a

potential economic impediment, in climates where road ice formation can

occur during part or all of the year. Chemical means are known in the art

and widely used for preventing the formation of ice on roads, or for aiding in

the removal of ice from roads, e.g. by melting or loosening ice.

The ideal choice of chemical agent to be employed depends on a combination

of factors, including the conditions under which the agent will be

employed-e.g. temperature, type of surface to be treated, and whether ice is

already present or not~and the inherent properties of the chemical agent.

The impact of the chemical agent on the enviroment must also be taken into

consideration.

The aforementioned inherent properties can be classified into three groups:

the ability of the agent to melt ice, i.e the volume of melt water which can be produced during a given time by application of a given amount of deicer at a

specified rate; the ability of the agent to penetrate ice, i.e. its ability to melt

ice when operating in a downward mode; and the ability of the agent to

loosen ice from the road surface, or its undercutting ability, i.e. its ability to

melt ice at the interface between a layer of ice and a pavement or road

substrate. A given ice-melting agent may not be efficient in all three

capacities.

Chemical deicers may be used in combination, and with other materials, to

meet different needs. For example, a solution of 30-32 wt.% CaC in water,

so-called "liquid" calcium chloride, is often used in combination with sodium

chloride (sometimes referred to, in its crude form, as "rock salt"), or with

abrasives such as sand. It has been known to spray rock salt with liquid

CaC prior to application of the rock salt; this method reduces the amount

of rock salt required for application at low temperatures (~ -7°C or less).

US 5,599,475 describes a process for the preparation of sodum chloride

coated with calcium chloride powder or particles, whereby the sodium

chloride is coated with an adhering solution (usually water or water with

some potassium acetate mixed in, optionally containing calcium chloride as

well), and then dry calcium chloride is mixed in with the NaCl which has

been treated with the adhering solution. Various drawbacks exist in the methods known in the art. By their nature,

preventive measures must be taken prior to, or shortly after, the onset of ice

formation; the ability of the agent to be applied to prevent ice formation, as

well as the temperature and surface to be treated, will dictate how much

material need be applied, and whether the material must be applied in

advance of ice formation, or how soon after commencement of ice formation

the agent may be applied. If, however, the weather forecast is erroneous,

and no freezing is forthcoming, a deicing agent applied prior to the fall of

precipitation will be wasted. If the potency of the agent could be in

increased, this would enable a longer wait prior to application of the agent,

so that the accuracy of weather forecasts could be verified or invalidated,

thus sparing unnecessary applications of the agents.

Furthermore, increasing the efficacy, and/or lengthening the duration of

efficacy, of the chemical agent would enable application of a smaller amount

of agent, thus saving money and creating less impact on the environment.

It is an object of the invention to provide a deicing composition with good

penetrating, melting and undercutting abilities.

It is another object of the invention to provide a deicing composition which

can act quickly. It is a further object of the invention to provide a deicing composition which,

by virtue of the aforesaid properties, can decrease the total amount of

deicing agent necessary to melt, loosen, or prevent the formation of ice on

roads relative to the total amount of deicing agent required in techniques

known in the art.

It is still another object of the invention to provide a process for the

preparation of compositions of the invention.

Other objects, purposes and advantages of the invention will become

apparent as the description proceeds.

Summary of the Invention

The improved deicing composition according to the invention comprises (a)

an inner layer containing a secondary ice melting agent, and (b) an outer

layer containing a primary ice melting agent, wherein said primary ice

melting agent has been melt-coated onto said secondary ice melting agent.

Throughout this description, by "secondary melting agent" is meant

potassium chloride or sodium chloride. "Primary melting agent" will be

understood to refer to calcium chloride complexed with water or magnesium

chloride complexed with water; each molecule of CaC or MgCb will have

from two to six molecules of water complexed around it. By "melted primary melting agent" is meant a primary melting agent

which, when part of the composition of the invention, is either in a melted

state or was in a melted state immediately prior to formation of the

composition of the invention.

The invention also comprises a process for the preparation of a composition

for melting ice or preventing the formation of ice on roads, comprising the

steps of (a) forming a first layer containing a secondary ice melting agent;

and (b) forming a second layer on top of said first layer, said second layer

containing a primary ice melting agent which has been melt-coated onto

said secondary ice melting agent.

Brief Description of the Figures

Fig. 1 compares the rate of ice penetration ability at -10°C of NaCl and a

composition of the invention containing NaCl coated with MgCl2*(H2O)6,

26% by weight (Salmag 26).

Fig. 2 compares the rate of ice penetration ability at 14°C of NaCl and a

composition of the invention containing NaCl coated with 50% MgCl2*(H2O)6

(Salmag 50). Detailed Description of Preferred Embodiments

The composition according to the invention may comprise from about

30wt.% to about 92 wt.% secondary ice melting agent, and from about 8

wt.% to about 70 wt.% primary ice melting agent. The secondary melting

agent is selected from potassium chloride or sodium chloride. The primary

melting agent agent is selected from calcium chloride complexed with water

or magnesium chloride complexed with water; each molecule of CaC or

MgC will have from two to six molecules of water complexed around it.

Other ingredients, such as abrasives, may be incorporated into the

composition of the invention if desired, although this is not necessary. The

relative amounts by weight of secondary ice melting agent and primary ice

melting agent may be varied in accordance with intended conditions for use,

but will usually fall in the range of from about 11:1 to 1:2.

Preferably, the composition is in pelletized or spheronized form, with pellets

(spheres) of a size between about 2 and about 11 mm average diameter

(although pellets (spheres) with sizes larger or smaller than this may in

principle be obtained); more preferably, the size of the pellets (spheres) is

between about 2 and about 5 mm average diameter. The radius of the inner

layer is preferably _from about 1 to about 4 mm. The thickness of the outer

layer is preferably between 0.5 and 3 mm. It is known (see, e.g., "Handbook of Test Methods for Evaluating Chemical

Deicers", Strategic Highway Research Program, National Research Council,

Washington, D.C., 1992, and protocol SHRP H-205.1 therein for measuring

ice-melting ability) that the ice-melting properties of NaCl and CaC are

similar at -3.9°C, but at -15°C CaC is a markedly better ice-melter.

Similarly, while the ice undercutting ability (cm² ice undercut/g deicer

applied, determined by protocol SHRP H-205.5, ibid.) of CaC is better then

NaCl at -3.9°C, at -15°C CaC is noticeably better at ice -undercutting.

One of the advantages of the present invention is that the compositions of

the invention combine properties of both the primary ice melting agent and

the secondary ice melting agent. Thus, as shown in Fig. 1, a composition

according to the present invention, containing sodium chloride coated with

magnesium chloride, initially acts more quickly than NaCl alone

(approximately twice as effective over the first 30 minutes), and over the

next several hours closely approximates the efficacy of NaCl alone

(approximately 80% as effective as NaCl). Melting ability was determined

using the aforementioned protocol SHRP H-205.1.

The compositions of the invention may be used in conjunction with other

methods, e.g. dispersion of abrasives on road surfaces or incorporation of

abrasives into the compositions of the invention. As stated, the amounts of material to apply will depend on a variety of

conditions, including but not limited to the surrounding temperature,

amount of ice to be melted or prevented from forming, nature of the surface

to be treated, density of traffic on the surface to be treated, and the size of

the pellets used.

The compositions of the invention may be formed by any convenient method

known in the art. For example, the compositions may be prepared by

drum-coating NaCl granules with magnesium chloride, although other

methods of forming the compositions of the invention, particularly other

methods of melt-coating the primary ice-melting agent onto the secondary

ice melting agent, can readily be envisioned by practitioners skilled in the

art, and are contemplated within the scope of the invention. Unlike the

compositions and process disclosed in US 5,599,475, the compositions of the

present invention are formed by coating the secondary ice melting agent

with melted primary ice melting agent, without the use of additional

adhering components and the like. The outer coating is essentially

homogeneous, as it is not composed of powder or particles which are glued

onto a foreign surface, as is done in prior art materials.

The foregoing characteristics and advantages of the invention will be better

understood through the following illustrative and non-limitative examples

of preferred embodiments thereof. Example 1

Drum coating of NaCl crystals

NaCl crystals of 5 mm average diameter (0.12 - 0.15 g each) were placed in a

revolving drum and heated to about 150°C. At the same time, a weighed

amount (about 25 wt.% relative to NaCl) of MgC hexahydrate flakes were

heated at 160°C until molten. The clear molten liquid was carefully poured

into the revolving drum containing the rock salt crystals, using a baffle to

help mix the components. Visual inspection indicated that the NaCl

crystals became coated almost immediately. The heat source was removed

and the coated crystals were allowed to cool while mixing was continued.

After a few minutes the coated particles stopped adhering to one another,

and were allowed to continue to cool in the rotating drum. The particles

obtained contained an average of about 74 wt.% NaCl, about 26 wt.%

MgCl₂*6H₂O.

In a similar fashion, smaller NaCl particles were coated with MgCk. The

ratio of sodium chloride to magnesium chloride in the coated particles was

approximately the same as when 5 mm NaCl was used. Example 3 Ice Penetration Test

This example was conducted in accordance with SHRP H-205.3 ("Handbook of Test Methods for Evaluating Chemical Deicers", Strategic Highway Research Program, National Research Council, Washington, D.C., 1992). The ice penetration abilities (at -10°C) of pellets of NaCl and MgCk-coated

NaCl (Salmag 26), prepared as per Example 1, were compared. The results are plotted in Fig. 1. These results confirm that the coated material behaves initially in a manner similar to the behavior of the coating material, but over the course of several hours behave in a manner more

similar to the core material.

A similar test was conducted to compare the rate of ice penetration ability

at 14°C of NaCl and a composition of the invention containing NaCl coated

with 50% MgCl₂*(H2θ)₆ (Salmag 50). The results are plotted in Fig. 2.

Example 4 Preparation of CaCb-coated NaCl

To CaCl₂*2H₂θ was added water to obtain CaCl2»4H2θ. This slurry was

then heated until a clear liquid was obtained at 45°C. This was then added

to a revolving drum, also heated to 45°C and containing NaCl (15-50 wt.% relative to CaCl2^#4H2θ), and the temperature of the drum and its contents was then raised to 175°C. The coated particles obtained were allowed to

cool. The coated particles contained, on average, about 75 wt.% NaCl and

about 25 wt.% CaCk complexed with water. The coated particles so

obtained behave similarly to the particles of Example 1 in the de-icing tests

described above.

The foregoing description and examples have been provided for illustrative

purposes only, and are not intended to limit the invention in any way. It

will be apparent that many modifications, variations and adaptations may

be made to the invention by persons skilled in the art, without departing

from the spirit of the invention or exceeding the scope of the claims.

Claims

1. A composition for melting ice and snow and for preventing the formation of ice on roads, comprising an inner layer containing a_secondary ice melting agent and an outer layer containing a primary ice melting agent, wherein said primary ice melting agent has been melt-coated onto said secondary ice melting agent.

2. Composition according to claim 1, wherein the primary melting agent

is selected from calcium chloride, magnesium chloride, and hydrates of calcium chloride and magnesium chloride, and their mixtures.

3. Composition according to claim 1 or claim 2, wherein the secondary melting agent is sodium chloride.

4. Composition according to any of claims 1 to 3, wherein the composition is in pelletized form.

5. Composition according to claim 4, wherein the pellets are between about 2 mm and 11 mm average diameter.

6. Composition according to claim 5, wherein the radius of the inner layer is between about 1 and 4 mm.

7. Composition according to claim 6, wherein the primary melting agent

is magnesium chloride, or a hydrate thereof, and the thickness of the outer

layer is between about 0.5 and 3 mm.

8. Composition according to claim 6, wherein the primary melting agent

is calcium chloride, or a hydrate thereof, and the thickness of the outer layer

is between about 0.05 and 0.3 mm.

9. Composition according to any one of claims 1 to 8 wherein the

secondary melting agent constitutes between about 30 wt.% and about 92

wt.% of the composition.

10. Composition according to any one of claims 1 to 9 wherein the

primary ice melting agent comprises between about 8 wt.% and about 70

wt.% of the composition.

11. Composition according to claim 1 wherein the weight ratio of

secondary ice melting agent to primary ice melting agent is in the range of

from about 11:1 to about 1:2.

12. A process for the preparation of a composition for melting ice or snow

or for preventing the formation of ice on roads, comprising the steps of (a)

providing a core material consisting essentially of a secondary ice melting agent; (b) coating said core material with a coating consisting essentially of a melted primary ice melting agent; and (c) allowing the coating on the core material to cool so as to provide an essentially homogeneous outer coating.

13. Process according to claim 12, wherein the coating comprises a

material selected from calcium chloride, magnesium chloride, hydrates of calcium chloride and magnesium chloride, and their mixtures.

14. Process according to claim 12 or claim 13, wherein the core material

comprises sodium chloride.