NO314312B1 - Defrosting agents and agents that protect against ice formation for aircraft - Google Patents

Abstract

The invention relates to a novel unthickened deicing agent and antiicing agent for aircraft which essentially comprises glycols and water as principal components, at least one nonionic surfactant from the group consisting of fatty alcohols and low-molecular-weight alkoxylates thereof and preferably a further anionic surfactant from the group consisting of alkali metal alkylarylsulphonates, corrosion inhibitors and optionally pH regulators. The new agent has a relatively long holdover time and therefore combines the advantages of unthickened and thickened aircraft deicing agents.

Description

De-icing agents and agents that protect against the formation of ice for aircraft (hereinafter for the sake of brevity referred to as de-icing agents or de-icing liquids) are used to remove ice, snow and/or frost from specific aircraft surfaces and to prevent such deposits on these surfaces. The period of time in which the de-icing fluid provides protection against the re-formation of ice, snow and/or frost on the aircraft is referred to as the re-icing protection period or Eoldovertime.

In GB-A 1,026,150, a de-icing liquid is described which essentially consists of glycol and water as main components and of a relatively small amount of a tertiary amine from the group of ethoxylated fatty amines and at least one corrosion inhibitor. US-A 3,412,030 also refers to the reinforcing effect of water-soluble surfactants when thawing or melting snow and ice.

US-A 4,585,571 describes a deicing agent which essentially consists of glycol as the main component and a combination of three special surfactants, and more specifically an anionic surfactant from the group of fatty acid diamines, a hydrophilic surfactant from the group of mono- or polyalcohol amines and an anionic hydrophilic surfactant from the group of sulfated or sulfonated compounds as a coupling agent for the hydrophobic residues in the fatty acid diamine and the hydrophilic alcohol amine. Although this de-icing fluid should exhibit a longer-lasting protection against re-formation, it is however not fully satisfactory, among other things due to the complicated surfactant system.

In a number of publications in the area of anti-icing and anti-icing fluids for aircraft, which, among other things, concern the increase of the holdover time, thickeners are therefore recommended because it is obviously convinced that an increased holdover time can only be achieved by with the help of thickeners, see e.g. US-A 4,358,389, DE-A-31 42 059 (Derwent-Referat AN 44404K/19), US-A 4,744,913 and EP-B 0,360,183 (Derwent-Referat AN 90/092789/13). The thickening agents mentioned here therefore essentially consist of glycol and water, at least one thickening agent, e.g. from the group of polyacrylates, at least one surfactant, e.g. from the group of alkylarylsulfonates and oxalkylated alcohols, corrosion inhibitors and possibly pH-value regulators. These thickened release agents, i.e. pseudoplastic liquids with a non-Newtonian flow behavior, are distinguished compared to the non-thickened ones by a significantly longer protection time against renewed ice formation.

In the "Recommendations for De-/Anti-Icing of Aircraft on the Ground" (issue March 1993) from the Association of European Airlines (AEA) two types of aircraft de-icing fluids are specified. AEA-Type-I liquids essentially consist of glycol, water and corrosion inhibitors as well as possibly surfactants and pH-value regulators, and AEA-Type-II liquids also contain a thickening agent. AEA-Type-I deicing fluids are also the so-called "Military Specification Fluids" with sodium di-(2-ethylhexyl)-sulfosuccinate as surfactant.

The most important technical properties of aircraft de-icing agents are the longest possible protection against renewed ice formation on the airfoils before take-off under extreme weather conditions and good runoff of the de-icing agent from the fuselage and airfoils when the aircraft takes off. Furthermore, the properties of the de-icing fluids must not be affected by storage at temperatures up to 100<*>C and by shearing of the fluids by pumping and spray nozzles. While the thickened release agents now largely meet the requirements in terms of Holdovertime, compared to non-thickened, they generally flow off the bearing surfaces more slowly. Due to their polymeric thickening agent, Type II deicers are also significantly more sensitive to shearing and heat, so that their use requires technically complex spray devices. In contrast, non-thickened Type-1 deicers are generally shear- and temperature-insensitive and flow off the bearing surfaces more quickly at start-up. However, they show the significant disadvantage of a shorter protection time against renewed ice formation. In the test methods described in the aforementioned AEA Recommendations regarding the determination of Holdovertime, namely in the "Water Spray Endurance Test" (which simulates freezing rain) and in the "High Humldlty Endurance Test" (which simulates frost formation), it is therefore required for Type- In liquids only at least 3 minutes or 20 minutes protection time, for Type-II liquids, however, under the same conditions at least 30 minutes or 240 minutes.

The task of the invention therefore consists in finding an AEA-Type-I deicing agent which is simply structured and exhibits an extended Holdovertime. The new de-icing fluid must therefore combine the advantages of Type-I and Type-II fluids, without having their negative properties. They must also be designed so that the used liquid can be easily processed and reused.

The de-icing agent and protective agent against renewed icing for aircraft, According to the present invention, based on glycols and water consists essentially of

a) 60 to 97 wt-9É, of at least one glycol from the group of alkylene glycols with 2 to 3 C atoms and oxalkylene glycols with 4 to 6 C atoms, b) 0.01 to 1 wt-#, of at least one non-ionic surfactant from the group of fatty alcohols and the fatty alcohols with a lower molecular weight alkoxylated fatty alcohols with 1 to 10 alkoxide units, preferably 1 to 8 alkoxide units, c) 0.01 to 0.8 wt-Sé, of at least one corrosion inhibitor and

d) water as residue to 100 weight-#, where weight percentages are indicated on the basis of the weight of the agent.

It was further found that an even higher value for Holdovertime can be achieved when a combination of the specified non-ionic surfactant b) and an anionic surfactant b') from the group of alkali metal alkylaryl sulphonates is used as surfactant components in an amount of likewise 0, 01 to 1 wt-5É, preferably 0.1 to 0.5 wt-£. The two surfactant compounds b) and b'), whereby the surfactant b') above all acts as a dispersant, are preferably used in a weight ratio of approx. 1 : (0.5 to 1) and particularly preferred in a weight ratio of approx. 1:1.

Component a) of the liquid according to the invention is preferably ethylene glycol, propylene glycol (1,2-propylene glycol or 1,3-propylene glycol), diethylene glycol, dipropylene glycol or a mixture of two or more of these glycols, whereby propylene glycols are particularly preferred. The glycols above all serve to reduce the freezing point and constitute, alongside water, the main components of the liquid.

Component b) is a fatty alcohol, i.e. an alcohol with 6 to 24 C atoms in the alkyl residue, preferably 8 to 18 C atoms, or an alkoxylate thereof with 1 to 10 C atoms, preferably 1 to 8 C atoms, of a low molecular weight alkylene oxide in an alkylated fatty alcohol. The low molecular weight alkylene oxide is preferably ethylene oxide, propylene oxide or a mixture thereof, whereby ethylene oxide is preferred. The aforementioned alkyl residue in fatty alcohol can be straight-chain or branched, whereby the straight chain is preferred, and saturated or unsaturated with preferably 1 to 3 double bonds. Examples include: Octyl, decyl, dodecyl, isotridecyl and stearyl alcohol, further oleyl, coconut alkyl and tallow alkyl alcohol. The components b) can also be a mixture of the mentioned fatty alcohols and/or fatty alcohol alkoxylates, such as a fatty alcohol mixture with a C₁-alkyl residue and <C>14-alkyl residue (<C>i2/<C>14-fatty alcohol) .

Component b') is preferably a potassium and/or sodium alkylaryl sulfonate with one or more, preferably one or two sulfonate groups (SO3K or SC^Na groups), one or more, preferably one or two alkyl groups with 5 to 18 C -atoms, preferably 12 to 18 C atoms, and one or more, preferably one or two benzene rings. Alkali metal (potassium and/or sodium) alkylbenzene sulfonates with 12 to 18 C atoms in the alkyl group are preferred. Since the preparation of alkylarylsulphonates is also based on hydrocarbon mixtures, which are for example formed as fractions by crude oil extraction, the alkyl group can also form such mixtures. Thereby, the number of carbon atoms is preferably 12 to 18 (ie an average number of 15).

The components c) comprise corrosion inhibitors, which are usable for liquids based on glycols and water. Suitable corrosion inhibitors are alkali metal phosphates, lower alkyl phosphates such as ethyl phosphate, dimethyl phosphate, isopropyl phosphate and the like, lmldazoles such as 1H-imidazole, methylimidazole, benzimldazole and the like and triazoles such as benzotriazole and tolyltriazole, whereby the triazoles are preferred.

Component d) is water. Completely desalinated water is preferably used.

The pH value for AEA-Type-I de-icing liquids should be 6.5 to 10, preferably 7 to 9. If the liquid according to the invention does not of itself exhibit such a value, it can easily be set using suitable pH regulators. In general, a basic compound must be added to the liquid. Suitable basic compounds are those from the group of alkali metal hydroxides, such as NaOH and KOH, alkylamines such as butylamine, hexylamine, octylamine and isononylamine and the alkanolamines such as mono-, di- and triethanolamine. The alkali metal hydroxides are preferred.

The production of the de-icing agent and the protective agent against renewed ice formation According to the invention takes place by mixing the individual (known and commercially available) components in any order, which can for example be done in a container equipped with stirrers.

The deicing agent according to the invention exhibits all the advantages of unthickened deicing fluids and furthermore has a Holdovertime that is significantly above the value required for AEA-Type-I fluids. It therefore combines both the advantages of non-thickened and pre-thickened liquids. This is an unexpected result. Until recently, the professional community obviously assumed that a longer holding time with liquids based on glycols and water can only be achieved with the help of thickeners.

In the application for de-icing and preservation of the aircraft fleets to be treated, the de-icing agent is used either as such, i.e. concentrated, or diluted with water, preferably 1 ratio of 1:1. The application of the de-icing agent to the surfaces to be treated can be carried out by spraying with the usual devices , such as spray nozzles and the like.

The invention shall be described in more detail by means of examples and comparative examples.

Example 1:

A de-icing agent and protective agent against renewed ice formation was produced according to the invention by mixing the following components (concentrate): This de-icing agent has a pH value of 9. The holdover time was determined according to the "AEA Water Spray Endurance Test" (test 1) and according to "AEA High Humidity Endurance Test" (test 2), and more specifically for the concentrated formulation and the formulation diluted with - water 1 : 1. The values are summarized below:

Comparison example 1:

Example 1 was repeated, however excluding the ethoxylated fatty alcohol. The following components were thus mixed:

The test of the agent with a pH value of 9 took place as in Example 1:

Example 2:

In this example, according to the invention, the following components were mixed:

The test of the agent with a pH value of 9 took place as in Example 1:

Comparison example 2:

Example 2 was repeated, however excluding the ethoxylated fatty alcohol. The following components were thus mixed:

The test of the agent with a pH value of 9 took place as in Example 1:

Example 3:

A de-icing agent and protective agent against renewed ice formation according to the invention was produced by mixing the following components:

This deicing solution has a pH value of 9. It was tested by only the most important test 1:

Example 4:

In this example according to the invention, the components below were mixed:

This deicing solution has a pH value of 9. It was only tested in the most important test 1:

Claims (8)

1. De-icing agent and anti-icing agent for aircraft, based on glycols and water, which essentially consists of a) 60 to 97 weight-* of at least one glycol from the group of alkylene glycols with 2 to 3 C atoms and oxalkylene glycols with 4 to 6 C atoms, b) 0.01 to 1 weight-* of at least one nonionic surfactant from the group of fatty alcohols and those with a lower molecular weight alkoxide, the fatty alcohols with 1 to 10 alkoxide units, c) 0, 01 to 0.8 weight-* of at least one corrosion inhibitor and d) water as a residue to 100 weight-*, where weight percentages are indicated on the basis of the weight of the agent. 2. Agent according to claim 1, which essentially consists of a) 60 to 97 weight-* of at least one glycol from the group of alkylene glycols with 2 to 3 C atoms and oxalkylene glycols with 4 to 6 C atoms, b) 0, 01 to 1 weight-* of at least one non-ionic surfactant from the group of fatty alcohols and those with a lower molecular weight alkoxide, the fatty alcohols with 1 to 10 alkoxide units, b') 0.01 to 1 weight-* of at least anionic surfactant from the group of alkali metal alkylarylsulfonates, c) 0.01 to 0.8 weight-* of at least one corrosion inhibitor and d) water remaining to 100 weight-*. 3. Agent according to claim 1, which contains the components a) to d) in the quantities indicated below: a) 80 to 95 weight-*, b) 0.1 to 0.5 weight-*, c) 0.03 to 0.5 weight-* and d) water as residue to 100 weight-*. 4. Agent according to claim 2, which contains the components a) to d) in the quantities indicated below: a) 80 to 95 weight-*, b) 0.1 to 0.5 weight-*, b' ) 0.1 to 0, 5 weight-*, c) 0.03 to 0.5 weight-* and d) water as residue to 100 weight-*. 5. Agent according to claim 2 or 4, where the component b') is an anionic surfactant from the group of alkali metal alkylbenzene sulfonates with 12 to 18 C atoms in the alkyl group. 6. Agent according to claims 1 to 5, where component b) is a nonionic surfactant from the group of Cg to C18 fatty alcohols and Cg to C18 fatty alcohols ethoxylated with 1 to 8 ethylene oxide units. 7. Agent according to claims 1 to 6, where component c) is a corrosion inhibitor from the group of alkali metal phosphates, lower alkyl phosphates, imldazoles and triazoles. 8. Agent according to claims 1 to 7, where the agent has a pH value of 7 to 9.