NOVEL COOLANT WITH LOW ELECTRICAL CONDUCTIVITY

Abstract

Coolants with low electrical conductivity and corresponding coolant concentrates are useful for cooling systems of vehicles with electric engines, fuel cells, or hybrid engines with a combination of combustion engines with electric engines or a combination of combustion engines with fuel cells.

Claims

1: A coolant, comprising: (A) at least one glycol, (B) water, (C) at least one azole derivative, (D) at least one ester of orthosilicic acid or alkoxy alkylsilane, (E) at least one tertiary amine bearing at least one 2-hydroxyethyl- or 2-hydroxypropyl-group, (F) at least one monocarboxylic acid, (G) optionally, at least one silicophosphonate, and (H) optionally, at least one further coolant additive, wherein a molar ratio between the at least one tertiary amine (E) and the at least one monocarboxylic acid (F) is from 1:0.1 to 1:0.6, and components (C) to (H) are present in amounts so that the coolant exhibits an electrical conductivity of less than 50 S/cm.

2: The coolant according to claim 1, wherein the at least one glycol (A) is selected from the group consisting of monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, monopropylene glycol, dipropylene glycol, 1,3-propanediol, a higher poly alkylene glycol, an alkylene glycol ether, and glycerol.

3: The coolant according to claim 1, wherein the at least one azole derivative (C) is selected from the group consisting of benzimidazole, benzotriazole, tolutriazole, hydrogenated tolutriazole, (2-benzothiazylthio) acetic acid, and (2-benzothiazylthio) propionic acid.

4: The coolant according to claim 1, wherein the at least one ester of orthosilicic acid (D) is orthosilicic acid tetra ethyl ester or orthosilicic acid tetra methyl ester.

5: The coolant according to claim 1, wherein the at least one tertiary amine (E) is selected from the group consisting of a compound of the general formula (I) ##STR00007## wherein R.sup.2 and R.sup.3 independently of another each are a linear or branched alkyl substituent comprising 1 to 18 carbon atoms, or together form a five- or six-membered ring including the nitrogen atom, X.sub.i is CH.sub.2CH.sub.2O, CH.sub.2CH(CH.sub.3)O or CH(CH.sub.3)CH.sub.2O, and n is a positive integer from 1 to 5, a compound of the general formula (II) ##STR00008## wherein R.sup.4 is a linear or branched alkyl substituent comprising 1 to 18 carbon atoms, each Xi for i=1 to p and 1 to q, is independently selected from the group consisting of CH.sub.2CH.sub.2O, CH.sub.2CH(CH.sub.3)O, and CH(CH.sub.3)CH.sub.2O, and p and q independently of another are a positive integer from 1 to 5, and a tertiary amine bearing three 2-hydroxyethyl- or 2-hydroxypropyl-groups.

6: The coolant according to claim 5, wherein the at least one tertiary amine (E) is of the general formula (I), and is at least one selected from the group consisting of dimethyl ethanolamine, dimethyl propanolamine, diethyl ethanolamine, diethyl propanolamine, di-n-butyl ethanolamine, di-n-butyl propanolamine, N-hydroxyethyl pyrrolidine, N-hydroxyethyl piperidine, and N-hydroxyethyl morpholine.

7: The coolant according to claim 5, wherein the at least one tertiary amine (E) is of the general formula (II), and is a bis(2-hydroxyethyl) amine or bis(2-hydroxypropyl) amine bearing as substituent R.sup.4 n-hexylamine, 2-methylpentylamine, n heptylamine, 2-heptylamine, isoheptylamine, 1-methylhexylamine, n-octylamine, 2 ethylhexylamine, 2-aminooctane, 6-methyl-2-heptylamine, n-nonylamine, isononylamine, n decylamine and 2-propylheptylamine or a mixture thereof.

8: The coolant according to claim 5, wherein the at least one tertiary amine (E) is the tertiary amine bearing three 2-hydroxyethyl- or 2-hydroxypropyl-groups, and is selected from the group consisting of triethanolamine and tripropanolamine.

9: The coolant according to claim 1, wherein the at least one monocarboxylic acid (F) is aliphatic, aromatic or cycloaliphatic.

10: The coolant according to claim 1, wherein the at least one monocarboxylic acid (F) is linear or branched.

11: The coolant according to claim 1, wherein the at least one monocarboxylic acid (F) is selected from the group consisting of 2-ethylhexanoic acid and isononanoic acid.

12: The coolant according to claim 1, wherein no carboxylic acids with a functionality of more than 1 are present.

13: The coolant according to claim 1, wherein a water content is not more than 5 wt %.

14: A method of cooling a vehicle, the method comprising: adding the coolant according to claim 1 into a cooling system of a vehicle with an electric engine, fuel cell, or hybrid engine with a combination of a combustion engine with an electric engine or a combination of a combustion engine with a fuel cell.

15: The coolant according to claim 1, wherein components (C) to (H) are present in amounts so that the coolant exhibits an electrical conductivity of less than 45 S/cm.

16: The coolant according to claim 5, wherein in the compound of the general formula (I), R.sup.2 and R.sup.3 are independently of another a linear alkyl substituent comprising 6 to 12 carbon atoms.

17: The coolant according to claim 5, wherein in the compound of the general formula (I), n is 1.

18: The coolant according to claim 5, wherein in the compound of the general formula (II), R.sup.4 is a linear alkyl substituent comprising 6 to 12 carbon atoms.

19: The coolant according to claim 5, wherein in the compound of the general formula (II), p and q are 1.

20: The coolant according to claim 9, wherein the at least one monocarboxylic acid (F) is aliphatic with 5 to 14 carbon atoms.

Description

EXAMPLES

[0122] The invention is illustrated in the following examples, but without it being restricted thereto.

[0123] Coolant compositions were prepared by mixing the constituents as listed in Table 1 (all amounts given in weight %) and the features and physical parameters as pointed out in Table 1 were determined as follows:

TABLE-US-00001 Appearance Visual Water, % DIN 51777 Density at 20 C., g/cm3 DIN 51757 pH as-is ASTM D 1287 Reserve alkalinity of 10 mL, mL 0.1 mol/L HCl ASTM D 1121 Refractive index at 20 C. DIN 51423 Conductivity at 25 C., S/cm ASTM D 1125

[0124] Examples 2, 4, 5, and 6 are for comparative purposes, Examples 1, 3, 7, and 8 are according to the invention.

[0125] The coolants were brought to a slightly alkaline pH-value using different bases in order to ensure a sufficient reserve alkalinity which is necessary to buffer acidic degradation products of the coolant.

[0126] It can easily be seen that the use of the strong bases potassium and sodium hydroxide (Comparative Examples 4 and 5) in order to achieve the target pH-value due to their full dissociation raise the electrical conductivity to an unacceptable high value.

[0127] Using di isopropyl amine as base (Comparative Example 2) lowers the electrical conductivity, however, it still remains above the critical value of 50 S/cm. This critical value is achieved only the bases (E) according to the invention (octyl diethanol amine in Example 3 and preferably triethanolamine in Example 1).

[0128] Variation of the carboxylic acids shows that use of the dicarboxylic acid sebacic acid (Comparative Example 6) leaves the electrical conductivity above the critical value of 50 S/cm. The aromatic monocarboxylic acid benzoic acid (Example 8) yields good values with the aliphatic monocarboxylic acids ethylhexanoic acid (Example 7) and especially isononanoic acid (Example 1) being most preferred.

TABLE-US-00002 TABLE 1 Ex 2 Ex 4 Ex 5 Ex 6 Raw material Ex 1 (Comp) Ex 3 (Comp) (Comp) (Comp) Ex 7 Ex 8 Monoethylene glycol 49.89 49.92 49.86 49.91 49.93 49.88 49.89 49.89 Pure water (distilled) 49.81 49.81 49.81 49.81 49.81 49.81 49.81 49.81 Tolutriazole 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Tetraethoxysilane 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Triethanol amine (85%) 0.08 0.08 0.08 0.08 Isononanoic acid 0.02 0.02 0.02 0.02 0.02 Di isopropyl amine 0.05 Octyl diethanol amine 0.11 Potassium hydroxide 0.06 (KOH), 48% Sodium hydroxide 0.04 (NaOH), 50% Sebacic acid 0.03 Ethylhexanoic acid 0.02 Benzoic acid 0.02 Total 100 100 100 100 100 100 100 100 Appearance clear, clear, clear, clear, clear, clear, clear, clear, color- color- color- color- color- color- color- color- less less less less less less less less Water, % 50.3 50.5 50.3 49.8 48.5 50.7 50.1 50.1 Density at 20 C., g/cm3 1.065 1.065 1.065 1.065 1.065 1.065 1.065 1.065 pH as-is 7.7 8.2 8.2 8.6 8.6 7.3 7.7 7.8 Reserve alkalinity of 10 0.4 0.4 0.5 0.5 0.4 0.3 0.5 0.4 mL, mL 0.1 mol/L HCl Refractive index at 20 C. 1.384 1.384 1.384 1.383 1.384 1.384 1.384 1.384 Electr. Conductivity, S/cm 40 54 50 166 135 73 41 43

Corrosion Examples

[0129] The coolant compositions of Example 1 and the composition of Example 1 further comprising 0.01 wt % of a silicophosphonate (Formula (V), R.sup.5=1,3-propylene, R.sup.6, R.sup.7=methyl and ethyl (statistical mixture), sodium salt) were compared in corrosion tests according to ASTM D 1384 at 88 C.

[0130] Values for pH, reserve alkalinity, electrical conductivity, and silicon content were determined before and after the corrosion test.

TABLE-US-00003 Ex. 1 + 0.01% Sample silicophosphonate Weight change, mg/cm.sup.2 Ex. 1 (38% in water) Copper 0.06 0.04 Steel H-II 0.02 0.02 Steel 1.4301 0.05 0.07 Cast aluminum G-ALSi6Cu4 0 0.01 pH before test 7.82 7.74 pH after test 7.64 7.71 pH change, % 2% 0% RA before test (mL 0.1 mol/L HCl) 0.45 0.46 RA before test (mL 0.1 mol/L HCl) 0.38 0.41 RA change, % 16% 11% Conductivity before test (S/cm) 39.2 41.2 Conductivity after test (S/cm) 51.5 51.5 Conductivity change, % 31% 25% Si calculated before test (ppm) 135 140 Si after test (ppm) 42 70 Si change (%) 69% 50%

[0131] While the results of the corrosion test and pH-value are comparable within the accuracy of measurement, the drop of reserve alkalinity and loss of silicon content is less distinctive in the presence of the silicophosphonate than in its absence.

[0132] It is, therefore, preferred that the coolants contain at least one silicophosphonate which reduces the consumption of tetraethoxysilane which acts as an inhibitor of aluminium corrosion.