NOVEL COOLANT WITH LOW ELECTRICAL CONDUCTIVITY

Abstract

Coolants with low electrical conductivity and the corresponding coolant concentrates are made. A method is developed for circulating the coolants in 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 1,2-propylene glycol or derivatives thereof, (B) water, (C) at least one azole derivative, (D) optionally at least one ester of orthosilicic acid or alkoxy alkylsilane, (G) at least one silicophosphonate, and (H) optionally at least one further coolant additive wherein the electrical conductivity is at most 50 ?S/cm.

2. The coolant according to claim 1, wherein component (A) is at least one selected from the group consisting of 1,2-propylene glycol, polymers of 1,2-propylene glycol, oligomers of 1,2-propylene glycol, monoalkyl ethers of 1,2-propylene glycol, monoalkyl ethers of polymers of 1,2-propylene glycol, monoalkyl ethers of oligomers of 1,2-propylene glycol, dialkyl ethers of 1,2-propylene glycol, dialkyl ethers of polymers of 1,2-propylene glycol, and dialkyl ethers of oligomers of 1,2-propylene glycol.

3. The coolant according to claim 1, wherein the content of 1,2-propylene glycol in component (A) is at least 50% by weight among other derivatives of 1,2-propylene glycol.

4. The coolant according to claim 1, wherein the coolant optionally comprises one or more alkylene glycols and derivatives thereof other than 1,2-propylene glycol and its derivatives, wherein the content of 1,2-propylene glycol and its derivatives in the mixture of all alkylene glycols and derivatives thereof is at least 50% by weight.

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

6. The coolant according to claim 1, comprising, as the ester of orthosilicic acid (D), orthosilicic acid tetra ethyl ester or orthosilicic acid tetra methyl ester.

7. The coolant according to claim 1, wherein component (G) is of formula (V) ##STR00005## where R.sup.5 is a bivalent organic residue, and R.sup.6 and R.sup.7 are independently of another C.sub.1- to C.sub.4-alkyl.

8. The coolant according to claim 1, comprising at least one compound (D) and at least one compound (G).

9. The coolant according to claim 1, comprising at least one compound (G) and no compound (D).

10. The coolant according to claim 1, comprising at least one compound (D) and no compound (G), wherein the coolant comprises only 1,2-propylene glycol or derivatives thereof without other alkylene glycols or derivatives thereof than 1,2-propylene glycol.

11. The coolant according to claim 1, wherein the coolant does not contain any carboxylic acids.

12. The coolant according to claim 1, comprising: (A) 1,2-propylene glycol or derivatives thereof: 10 to 90 wt %, (B) water: 10 to 90 wt %, (C) at least one azole derivative: 0.01 to 1 wt %, (D) optionally at least one ester of orthosilicic acid or alkoxy alkylsilane: if present 0.01 to 1 wt %, (G) at least one silicophosphonate: 0 to 1 wt %, and (H) optionally at least one further coolant additive: 0 to 0.5 wt % for each further coolant additive, with the proviso that the sum of all components always add up to 100 wt %.

13. A coolant concentrate, comprising: (A) 1,2-propylene glycol or derivatives thereof: 50 to 99.9 wt %, (B) water: 0 to 10 wt %, (C) at least one azole derivative: 0.02 to 1 wt %, (D) optionally at least one ester of orthosilicic acid or alkoxy alkylsilane: if present 0.02 to 1 wt %, (G) at least one silicophosphonate: 0 to 1 wt %, and (H) optionally at least one further coolant additive: 0 to 0.5 wt % for each further coolant additive, with the proviso that the sum of all components always add up to 100 wt %.

14. A method of cooling 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, the method comprising: circulating the coolant according to claim 1 within cooling systems of said vehicles.

15. A method of cooling in systems comprising a heat exchanger comprising aluminum components, the method comprising: circulating a coolant within said systems, wherein the coolant comprises: (A) at least one 1,2-propylene glycol or derivatives thereof, (B) water, (C) at least one azole derivative, (D) optionally at least one ester of orthosilicic acid or alkoxy alkylsilane, (G) optionally at least one silicophosphonate, and (H) optionally at least one further coolant additive, wherein at least one of the components (D) and (G) is present, and wherein the electrical conductivity is at most 50 ?S/cm.

16. The coolant according to claim 1, wherein the electrical conductivity is at most 20 ?S/cm.

Description

EXAMPLES

[0124] The invention is illustrated in the following examples, but without it being restricted thereto.

[0125] Coolant compositions were prepared by mixing the constituents as listed in Table 1 (all amounts given in weight %) and electrical conductivity according to ASTM D 1125 at 25? C. [?S/cm] was determined.

TABLE-US-00001 TABLE 1 Raw material Ex 1 Ex 2 (Comp) 1,2-Propylene glycol 50.0 Monoethylene glycol 50.0 Pure water (distilled) 49.8 49.8 Benzotriazole 0.1 0.1 Tetraethoxysilane 0.1 0.1 Total 100 100

[0126] The coolants according to Table 1 were tested as follows and the electrical conductivity according to ASTM D 1125 at 25? C. [?S/cm] determined.

[0127] The coolants were stored for a period of 21 days at a temperature of 25? C. in commercially available heat exchangers, predominantly made of aluminium by using a soldering method comprising a fluoroaluminate soldering flux.

[0128] Electrical conductivity of the coolants was determined before the test, and samples of the stored coolants at the start and at the end of the test were analysed.

[0129] Immediately after filling the electrical conductivity of the coolants increased due to residual traces of fluoroaluminate solder in the system.

TABLE-US-00002 Test 1 Electrical Conductivity [?S/cm] Ex 1 Ex 2 (Comp) Before Test 0.7 0.9 After Fill before Test 36.0 67.4 After Test 69.3 215

TABLE-US-00003 Test 2 (repetition) Electrical Conductivity [?S/cm] Ex 1 Ex 2 (Comp) Before Test 0.9 3.3 After Fill before Test 9.9 17.0 After Test 63.6 192.8

[0130] It can easily be seen that the coolant according to the present invention based on 1,2-propylene glycol does not only exhibit a lower electrical conductivity than an analogous coolant based on monoethylene glycol, but retains this advantageous property throughout the test.

Examples 3 to 5

[0131] The formulations according to Table 2a were submitted to a corrosion test of an aluminium specimen according to ASTM D4340 for 168 hours. pH-value was determined before and after the test and the and electrical conductivity (ASTM D 1125) was measured. The results are given in Table 2b.

TABLE-US-00004 TABLE 2a Raw material Ex 3 Ex 4 Ex 5 1,2-Propylene glycol 50.0 50.0 50.0 Pure water (distilled) 49.8 49.8 49.7 Benzotriazole 0.1 0.1 0.1 Tetraethoxysilane 0.1 0.1 Silicophosphonate * 0.1 0.1 Total 100 100 100 * Silicophosphonate (Formula (V), R5 = 1,3-propylene, R.sup.6, R.sup.7 = methyl and ethyl (statistical mixture), sodium salt)

TABLE-US-00005 TABLE 2b Ex 3 Ex 4 Ex 5 Corrosion [mg/cm.sup.2] ?0.01 ?0.01 ?0.01 Electrical conductivity 0.6 37.3 36.9 before test [?S/cm] pH-value before test 5.35 7.74 7.75 pH-value after test 6.49 7.24 7.53

[0132] It can easily be seen that the change in pH is lowest for the composition according to Example 5 comprising both a silicophosphonate as well as tetraethoxysilane indicating a higher stability of the composition under corrosion conditions.

[0133] The composition according to Example 3 with no silicophosphonate present exhibits the lowest electrical conductivity due to the absence of ionic compounds.

[0134] The corrosion of aluminium is well inhibited by all compositions. For comparison: A formulation of 50 wt % ethylene glycol and 50 wt % water (see e.g. WO 00/17951) yields a corrosion of cast aluminium in a corrosion test according to ASTM D1384 (88? C., 336 h) of ?0.3 mg/cm.sup.2 and a change in the pH-value from 5.9 (before test) to 4.0 (after test) showing the excellent corrosion inhibition of the coolants according to the present invention and their stability under test conditions. Furthermore, the electrical conductivity of the ethylene glycol/water composition increases from 0.5 to 728 ?S/cm during this test which is not acceptable for a use in cooling systems of vehicles with electric engines, fuel cells or hybrid engines.