Cooling agents for cooling systems in fuel cell drives containing azole derivatives

(22) Filed on: June 6, 2002 (51) Int.Cl.

C09K 5/20 (2006.01) (86) Date and number of the international application:

2006-06-06, PCT / EP02 / 06194 (87) International application publication date and number:

2002-12-19, WO02 / 101848 PCT Gazette No. 51/02

Patent Office of the Republic of Poland

<td colspan="2">Antifreeze concentrate for cell cooling systems ₍₅₄₎ fuel, ready-to-use water cooling composition prepared therefrom, application⁽⁵⁴⁾ a five-membered heterocyclic azole derivative together with orthosilicates and the use of antifreeze concentrate</td>

<td>(30) Priority: 2001-06-13, DE, 10128530.2</td><td>(73) The right holder of the patent: BASF AKTIENGESELLSCHAFT, Ludwigshafen, DE (72) Inventor (s): Bernd Wenderoth, Birkenau, DE</td>

<td>(43) Application was announced:</td><td>Stefan Dambach, Haβloch, DE</td>

<td>February 21, 2005 BUP 04/05</td><td>Ladislaus Meszaros, Mutterstadt, DE Uwe Fidorra, Wachenheim, DE</td>

<td>(45) The grant of the patent was announced:</td><td></td>

<td>April 30, 2009 WUP 04/09</td><td>(74) Representative: Agnieszka Marszałek, SULIMA-GRABOWSKA-SIERZPUTOWSKA, Biuro Patenty i Znaków Towarowych Sp. J.</td>

⁽⁵⁷⁾ The invention relates to an antifreeze concentrate for fuel cell drive cooling systems, which produces ready-to-use aqueous cooling compositions with a conductivity of 50 μS / cm or less, based on alkylene glycols or their derivatives, and containing one or more five-membered compounds. heterocyclic azole derivatives with 2 or 3 heteroatoms selected from the group consisting of nitrogen and sulfur, which contain at most one sulfur atom and may be fused to an aromatic or saturated six-membered ring, the total content of azole derivatives in the antifreeze concentrate being 0.05-5 wt.%, characterized by additionally containing orthosilicates in an amount to ensure 2-2000 wt ppm silicon in the prepared ready-to-use aqueous cooling composition. The invention also relates to a ready-to-use water cooling composition for fuel cell propulsion cooling systems prepared by diluting the above antifreeze concentrate with deionized water, and the use of the above-defined five-membered azole heterocyclic compound together with orthosilicates to prepare an antifreeze concentrate.

PL 201 392 B1

Description of the invention

The subject of the invention is an antifreeze concentrate for cooling systems of drives powered by fuel cells, in particular in motor vehicles, based on alkylene glycols or their derivatives and containing certain azole derivatives as corrosion inhibitors, a ready-to-use water cooling composition for cooling systems of drives powered by fuel cells fuel, use of a five-membered azole derivative heterocyclic with orthosilicates; and use of an antifreeze concentrate for fuel cell powered drive cooling systems.

Fuel cells for use in motor vehicles in motion have to function even at low ambient temperatures down to about -40 ° C. The anti-freeze cooling circuit therefore plays a very important role.

The use of typical protective compositions for coolers used in internal combustion engines in fuel cells is not possible without complete electrical insulation of the cooling pipes. This is due to the high electrical conductivity of these compositions as a result of the presence of salts and ionizable compounds in them; they act as corrosion inhibitors but adversely affect the operation of the fuel cell.

DE-A 19802490 (1) describes fuel cells with an anti-freeze cooling circuit in which a mixture of paraffin isomers with a freezing point below -40 ° C was used as a cooling fluid. However, a disadvantage of this type of coolant is its flammability.

EP-A 1009050 (2) describes an automotive fuel cell system which uses air as a coolant. The disadvantage of this solution is its inferior thermal conductivity compared to that of a liquid coolant.

WO 00/17951 (3) describes a fuel cell cooling system in which a 1: 1 mixture of pure monoethylene glycol and water is used as the cooling medium without any additives. Since, due to the absence of corrosion inhibitors, the metals present in the cooling system would not be protected against it at all, the cooling circuit includes an ion exchange unit in order to keep the coolant clean and to ensure its low conductivity over a long period of time; this prevents short circuits and corrosion. Suitable ion exchangers for this purpose are anionic resins, e.g. strongly alkaline resins containing hydroxyl groups, as well as cationic resins, e.g. containing sulfonic acid functional groups as well as other filter systems, e.g. activated carbon filters.

The construction and operation of a fuel cell for cars, in particular a fuel cell containing an electronically conductive electrolytic membrane ("PEM fuel cell", "polymer electrolytic membrane fuel cell") is described in e.g. (3), where the metal in the cooling circuit (in the cooler) preferably aluminum is used.

DE-A 10063951 (4) describes cooling fluids for cooling systems of fuel cell driven systems containing orthosilicates as corrosion inhibitors.

The use of azole derivatives, such as benzimidazole, benzotriazole or tolutriazole, as corrosion inhibitors in protective compositions for coolers, intended for use in typical combustion engines powered by gasoline or diesel oil, has been known for some time, e.g. from the work of G. Reinhard et al., "Aktiver Korrosionschutz in waβrigen Medien" pp. 87-98, expert Verlag 1995 (ISBN 3-8169-1265-6).

However, the use of this type of azole derivatives in cooling fluids for cooling systems in drives powered by fuel cells has not been described so far.

The main problem to be solved in the cooling systems of fuel cell drives is to maintain the low electrical conductivity of the coolant in order to ensure safe and trouble-free operation of the fuel cell and to prevent short circuits and corrosion in the long term.

It has surprisingly been found that in a cooling system based on alkylene glycol and water, in particular with an integrated ion exchanger according to (3), the low electrical conductivity period can be significantly extended by adding a small amount of azole derivatives. Practically, this means advantageously extending the period of time after which the coolant in the fuel cell drive must be replaced, which is of particular interest to the automotive industry.

PL 201 392 B1

The above observations allowed for the development of an antifreeze concentrate for the cooling systems of drives powered by fuel cells, from which ready-to-use water cooling compositions are obtained with a conductivity of at most 50 μS / cm, based on alkylene glycols or their derivatives, and containing one or more five-membered heterocyclic compounds which are azole derivatives of 2 or 3 heteroatoms selected from the group consisting of nitrogen and sulfur, which contain at most one sulfur atom and may be fused to an aromatic or saturated six-membered ring, the total amount of azole derivatives in the antifreeze concentrate it is 0.05-5 wt.%, which is characterized by that it additionally contains orthosilicates in an amount to provide 2-2000 wt. ppm. silicon in the prepared ready-to-use aqueous cooling composition.

Preferably, the anticoagulant concentrate according to the invention comprises as the azole derivatives benzimidazole, benzotriazole, tolutriazole and / or hydrogenated tolutriazole.

Preferably, the antifreeze concentrate according to the invention comprises monoethylene glycol as the alkylene glycol.

The invention also relates to a ready-to-use aqueous cooling composition for fuel cell drive cooling systems containing (a) 10-90 wt. % alkylene glycols or derivatives thereof, (b) 90-10 wt. % of water, and (c) 0.005-5 wt. of the azole derivatives, produced by dilution with deionized water of the above defined antifreeze concentrate, which is further characterized in that it additionally comprises orthosilicates in an amount to provide 2-2000 wt. silicon.

The invention also relates to the use of a five-membered azole derivative heterocyclic compound with 2 or 3 heteroatoms selected from the group consisting of nitrogen and sulfur which contains at most one sulfur atom and may be fused with an aromatic or saturated six-membered ring, together with orthosilicates, for the preparation of a fluid concentrate. antifreeze for use in cooling systems of drives powered by fuel cells, especially in motor vehicles, based on alkylene glycols or their derivatives.

Furthermore, the invention relates to the use of the above defined antifreeze concentrate for the preparation of a ready-to-use aqueous cooling composition having a conductivity of 50 μS / cm or less for use in cooling systems of fuel cell drives, especially motor vehicles.

Preferably, the anti-freeze concentrates according to the invention contain 0.075-2.5 wt.%, In particular 0.1-1 wt.%. such azole derivatives.

Five-membered heterocyclic compounds of this type (azole derivatives) usually contain two nitrogen atoms as heteroatoms and do not contain a sulfur atom, or contain three nitrogen atoms and contain no sulfur or contain one nitrogen atom and one sulfur atom.

Preferred groups of such azole derivatives are fused imidazoles and fused 1,2,3-triazoles of general formula (I) or (II),

<img file="PL201392B1_D0001.tif" />

HH (I) (II) wherein the variable R represents a hydrogen atom or a C1-C10 alkyl atom, especially methyl or ethyl, and the variable X represents a nitrogen atom or a CH group. Typical examples of azole derivatives of general formula (I) are benzimidazole (X = CH, R = H), benzotriazole (X = N, R = H) and tolutriazole (tolyltriazole) (X = N, R = CH3). A typical example of an azole derivative of general formula (II) is hydrogenated 1,2,3-tolutriazole (tolyltriazole) (X = N, R = CH3).

PL 201 392 B1

Another group of preferred such azole derivatives are the benzothiazoles of general formula (III)

<img file="PL201392B1_D0002.tif" />

wherein the variable R is as defined above and the variable R 'represents a hydrogen atom, C1-C10 alkyl, in particular methyl or ethyl, or a mercaptan group (-SH). A typical example of an azole derivative of general formula (III) is 2-mercaptobenzothiazole.

Another preferred group are the non-condensed azole derivatives of general formula (IV)

<img file="PL201392B1_D0003.tif" />

AND

Η (IV) where X and Y together represent two nitrogen atoms or one nitrogen atom and one CH group, e.g. 1H-1,2,4-triazole (X = Y = N) or imidazole (X = N, Y = CH).

As mentioned above, particularly preferred azole derivatives for use in the anticoagulant concentrates of the invention are benzimidazole, benzotriazole, tolutriazole, hydrogenated tolutriazole or mixtures thereof.

Such azole derivatives are commercially available or can be obtained by known methods. The hydrogenated benzotriazoles and the hydrogenated tolutriazole can be obtained as described in DE-A 1948794 (5); they are also commercially available.

As mentioned above, in addition to the above-mentioned azole derivatives, the anticoagulant concentrates according to the invention additionally contain orthosilicates as described in (4). Typical examples of orthosilicates of this type are tetraalkoxysilanes such as, for example, tetraethoxysilane. The antifreeze concentrates contain a total of 0.05-5 wt. the above azole derivatives; they are prepared into ready-to-use aqueous cooling compositions having a silicon content of 2 - 2000 ppm by weight, more preferably 25 - 500 ppm by weight. silicon.

By diluting the antifreeze concentrates according to the invention with deionized water, ready-to-use aqueous cooling compositions are obtained with a conductivity of at most 50 μS / cm, which contain:

% (a) 10-90 wt. % alkylene glycols or derivatives thereof, (b) 90-10 wt. % of water, (c) 0.005-5, in particular 0.0075-2.5 and especially 0.01-1 wt. azole derivatives; and (d) orthosilicates.

The proportion of all components is added up to 100% by weight.

As noted above, the ready-to-use aqueous cooling compositions for fuel cell drive cooling systems according to the invention comprise:

% (a) 10-90 wt. % alkylene glycols or derivatives thereof, (b) 90-10 wt. % of water, (c) 0.005-5, in particular 0.0075-2.5 and especially 0.01-1 wt. azole derivatives and (d) orthosilicates, and are obtained by diluting antifreeze concentrates with deionized water.

The proportion of all components is added up to 100% by weight.

The ready-to-use aqueous cooling compositions according to the invention have an initial electrical conductivity not exceeding 50 µS / cm, in particular 25 µS / cm, more preferably 10 µS / cm, especially 5 µS / cm. The conductivity is kept so low over a long period of operation of the fuel cell drive for several weeks or months, especially when using a cooling system having an integrated ion exchanger in the fuel cell drive.

The pH of the ready-to-use aqueous cooling compositions according to the invention drops significantly more slowly during their service life than in the case of cooling fluids to which no azole derivatives have been added. The pH of freshly prepared cooling compositions according to the invention is typically 4.5-7 and drops to a value of 3.5 over an extended period of operation. The deionized water used for dilution may be pure distilled or double-distilled water, or deionized water, e.g. by an ion exchanger.

In ready-to-use aqueous cooling compositions, the preferred weight ratio of alkylene glycol or its derivatives to water is from 20:80 to 80:20, especially from 25:75 to 75:25, preferably from 65:35 to 35:65. mainly from 60:40 to 40:60. The alkylene glycol component or its derivatives which can be used is, in particular, monoethylene glycol, but also monopropylene glycol, polyglycols, glycol ethers or glycerin, in each case alone or in the form of mixtures. As mentioned above, it is particularly preferred to use monoethylene glycol alone or in a mixture in which it is the main component, so that its content in the mixture exceeds 50% by weight, in particular exceeds 80% by weight, especially above 95% by weight, with the other ingredients being other alkylene glycols or their derivatives.

The antifreeze concentrates of the invention from which the aqueous cooling compositions described above are obtained are prepared by dissolving azole derivatives in alkylene glycols or derivatives thereof, either anhydrous or with a low water content (e.g. up to 10, especially up to 5 wt.%).

The cooling compositions according to the invention can also be used in a fuel cell system as described in DE-A 10104771 (6), in which the coolant is additionally subjected to electrochemical deionization to prevent corrosion.

Examples

The invention is described in more detail in the following examples without limiting its scope.

In the tests described below, the suitability of the cooling compositions according to the invention in fuel cell drives was tested in comparison with the cooling composition described in document (3) and with other compositions.

Study description:

Five aluminum samples (aluminum vacuum brazed with the symbol EN-AW 3005, on which on one side 10% by weight of EN-AW 4045 was brazed; dimensions 58 x 26 x 0.35 mm, with a hole with a diameter of 7 mm) were weighed , connected with a non-conductive plastic screw with a washer and Teflon discs, placed on two Teflon stands in a 1 liter beaker with ground glass and glass lid. Then 1000 ml of the test liquid were added. During the tests presented in Table 1, a small bag of material containing 2.5 g of the ion exchanger (AMBERJET mixed ion exchange resin bed) was suspended in the liquid.^® UP 6040 RESIN, from Rohm + Haas). The tests presented in Table 2 were carried out without the use of an ion exchanger. The beaker was sealed with a glass lid and heated to 88 ° C while vigorously stirring the liquid using a magnetic stirrer. The electrical conductivity was measured before the start of the tests and at intervals of several weeks, in a previously collected fluid sample (LF 530 conductometer from WTW / Weilheim). After completion of the tests, the aluminum samples were visually inspected and after etching with an aqueous solution of chromic acid and phosphoric acid, they were subjected to gravimetric tests in accordance with ASTM D 1384-94.

PL 201 392 B1

The results are summarized in Tables 1 and 2.

Table 1: Tests conducted in the presence of an ion exchanger

<td>Composition of the fluid</td><td>Example</td><td>Example 1</td><td>Example 2</td><td>Example 3</td><td>Example 4</td><td>Example 5:</td>

<td>cooling</td><td>comparative</td><td>(compare-</td><td>(compare-</td><td>(compare-</td><td>(compare-</td><td>60 vol.%</td>

<td></td><td>(according to</td><td>whether):</td><td>whether):</td><td>whether):</td><td>whether):</td><td>MEG</td>

<td></td><td>WO</td><td>60 vol.%</td><td>60 vol.%</td><td>60 vol.%</td><td>60 vol.%</td><td>40 vol.%</td>

<td></td><td> 00/17951):</td><td>MEG</td><td>MEG</td><td>MEG</td><td>MEG</td><td>water</td>

<td></td><td>60 vol.%</td><td>40 vol.%</td><td>40 vol.%</td><td>40 vol.%</td><td>40 vol.%</td><td>0.05 wt.%</td>

<td></td><td>MEG</td><td>water</td><td>water</td><td>water</td><td>water</td><td>benzotriazole,</td>

<td></td><td>40 vol.%</td><td>0.1 wt.%</td><td>0.1 wt.%</td><td>0.1 wt.%</td><td>0.1 wt.%</td><td>371 ppm</td>

<td></td><td>water</td><td>benzimi-</td><td>benzotriazole</td><td>tolutriazole</td><td>hydrogenated</td><td>wt.</td>

<td></td><td></td><td>dazol</td><td></td><td></td><td>one</td><td>tetraethoxy-</td>

<td></td><td></td><td></td><td></td><td></td><td>tolutriazole</td><td>silane</td>

<td>Conductivity electric [mS / cm] Beginning research:</td><td> 2,0</td><td> 4,9</td><td> 3,3</td><td> 3,1</td><td> 1,1</td><td> 1,9</td>

<td>After 7 days:</td><td> 2,3</td><td> 4,2</td><td> 1,5</td><td> 1,5</td><td> 0,8</td><td> 1,5</td>

<td>After 35 days: After</td><td> ---</td><td> 7,6</td><td> 4,1</td><td> 10,2</td><td> ---</td><td> 2,5</td>

<td>42 days:</td><td> 36,2</td><td> ---</td><td> 3,9</td><td> ---</td><td> 3,5</td><td> 3,3</td>

<td>After 56 days:</td><td> ---</td><td> ---</td><td> 7,8</td><td> ---</td><td> ---</td><td> 5,5</td>

<td>PH value Beginning research:</td><td> 6,9</td><td> 7,5</td><td> 5,0</td><td> 5,5</td><td> 6,6</td><td> 5,5</td>

<td>End research:</td><td> 2,9</td><td> 6,5</td><td> 3,8</td><td> 3,9</td><td> 4,0</td><td> 3,7</td>

<td>Look</td><td>Slightly</td><td>Mat</td><td>Mat</td><td>Mat</td><td>Mat</td><td>Mat</td>

<td>aluminum samples after testing:</td><td>mat</td><td></td><td></td><td></td><td></td><td></td>

<td>Mass change [mg / cm²]</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>after digestion: 1</td><td> -0,05</td><td> -0,07</td><td> -0,06</td><td> -0,01</td><td> -0,04</td><td> -0,03</td>

<td> 2</td><td> -0,04</td><td> -0,06</td><td> -0,06</td><td> -0,01</td><td> -0,05</td><td> -0,04</td>

<td> 3</td><td> -0,04</td><td> -0,06</td><td> -0,06</td><td> -0,01</td><td> -0,05</td><td> -0,02</td>

<td> 4</td><td> -0,04</td><td> -0,06</td><td> -0,06</td><td> -0,01</td><td> -0,05</td><td> -0,03</td>

<td> 5</td><td> -0,03</td><td> -0,07</td><td> -0,06</td><td> -0,01</td><td> -0,05</td><td> -0,03</td>

<td>Average in samples:</td><td> -0,04</td><td> -0,06</td><td> -0,06</td><td> -0,01</td><td> -0,05</td><td> -0,03</td>

<td>Look</td><td>Yellowish,</td><td>Brownish,</td><td>Colorless,</td><td>Colorless,</td><td>Colorless,</td><td>Colorless,</td>

<td>solution after testing</td><td>transparent</td><td>transparent</td><td>transparent</td><td>transparent</td><td>transparent</td><td>transparent</td>

In a mixture of monoethyl glycol (= MEG) and water, a volume ratio of 60:40 corresponds to a weight ratio of 62.5: 37.5.

In example 5 according to the invention, the orthosilicate was added in such an amount that the silicon content of the cooling liquid was 50 ppm by weight.

The results presented in Table 1 show a very low electrical conductivity, below μS / cm, even after 42 days without interruption in Examples 2 and 4 (comparative), while in the case of an additive-free fluid according to WO 00/17951 (3) it increased to almost 40 μS / cm, and the parameters of the fluid significantly worsened. Even after testing continuously for 56 days, in some cases the electrical conductivity was still maintained

PL 201 392 B1 levels well below 8 µS / cm in Example 2 (comparative) and Example 5 according to the invention.

In none of the cases the samples of aluminum corroded to any significant extent.

Table 2: Tests without ion exchanger

<td>Composition fluid cooling</td><td>Example 1: (comparative) 60 vol.% MEG 40 vol.% water 0.1 wt.% benzotriazole</td><td>Example 2: 60 vol.% MEG 40 vol.% water 0.1 wt.% benzotriazole 742 wt ppm tetraethoxysilane</td><td>Example 3 (comparative): 60 vol.% MEG 40 vol.% water 0.1 wt.% hydrogenated tolutriazole</td>

<td>Conductivity [pS / cm] Start of research:</td><td> 3,2</td><td> 3,2</td><td> 2,1</td>

<td>After 7 days:</td><td> 5,0</td><td> 5,6</td><td> ---</td>

<td>After 14 days:</td><td> 5,8</td><td> 5,2</td><td> 5,8</td>

<td>After 28 days:</td><td> 8,2</td><td> 6,9</td><td> ---</td>

<td>After 35 days:</td><td> 11,2</td><td> 6,9</td><td> 8,6</td>

<td>After 42 days:</td><td> 13,1</td><td> 7,9</td><td> 9,3</td>

<td>After 49 days:</td><td> 16,1</td><td> 7,6</td><td> 9,7</td>

<td>After 56 days:</td><td> ---</td><td> 7,8</td><td> ---</td>

<td>After 63 days:</td><td> ---</td><td> 7,1</td><td> ---</td>

<td>After 77 days:</td><td> ---</td><td> 6,6</td><td> 17,5</td>

<td>PH value Start research</td><td> 5,0</td><td> 5,0</td><td> 5,2</td>

<td>Completion of the research:</td><td> 3,6</td><td> 4,9</td><td> 3,4</td>

<td>The appearance of aluminum samples after the tests:</td><td>Almost no change</td><td>Almost no change</td><td>Mat</td>

<td>Mass change [mg / cm²] after digestion:</td><td></td><td></td><td></td>

<td> 1</td><td> -0,01</td><td> 0,00</td><td> -0,02</td>

<td> 2</td><td> 0,00</td><td> 0,00</td><td> -0,02</td>

<td> 3</td><td> 0,00</td><td> 0,00</td><td> -0,04</td>

<td> 4</td><td> 0,00</td><td> 0,00</td><td> -0,04</td>

<td> 5</td><td> 0,00</td><td> 0,00</td><td> -0,04</td>

<td>Average in samples:</td><td> 0,00</td><td> 0,00</td><td> -0,03</td>

<td>Appearance of the solution</td><td>Colorless,</td><td>Colorless,</td><td>Colorless,</td>

<td>after the end of the research</td><td>transparent</td><td>transparent</td><td>transparent</td>

In a mixture of monoethyl glycol (= MEG) and water, a volume ratio of 60:40 corresponds to a weight ratio of 62.5: 37.5.

In Example 2 of the invention, the orthosilicate was added in such an amount that the silicon content of the cooling fluid was 100 ppm by weight.

The results in Table 2 show a very low electrical conductivity of well below 10 µS / cm even after 77 days of continuous testing in Example 2 of the invention; the electrical conductivity after 77 days was well below 20 µS / cm in Example 3 (comparative).

Also in these tests, corrosion of the aluminum samples did not occur or was insignificant.