Low conductivity heat transfer fluid with vapor phase corrosion inhibition

Abstract

An improved Battery Electric Vehicle heat transfer fluids is made diluting a heat transfer fluid concentrate comprising greater than or equal to 85 weight percent of a freezing point depressant; 20 to 80 ppm of calcium ions; an azole compound; 100 to 250 ppm of an inorganic phosphate; and a polyelectrolyte polymer dispersant, wherein the heat transfer fluid concentrate has a pH of 7 to 9.0 and the weight ratio of polyelectrolyte polymer dispersant to calcium ions is 1 to 3 and the weight ratio of inorganic phosphate to calcium is 2 to 4. For use this concentrate is preferably diluted with deionized water usually 50 / 50. The addition of N-methyl-imidazole provides protection against vapor phase corrosion particularly for ferrous metals.

Description

Low Conductivity Heat Transfer Fluid with Vapor Phase Corrosion InhibitionCross-reference to Prior Applications

[0001] N / AU.S. Government Support

[0002] N / ABackground of the InventionArea of the ArtThe current invention is in the art of low electrical conductivity cooling fluids for use in Battery Electric Vehicles and discloses a novel fluid composition that provides vapor phase corrosion protection for ferrous metals.Description of the Background Art

[0001] The automotive industry currently is shifting away from internal combustion engine vehicles and towards Battery Electric Vehicles (BEV). Modern electric vehicles generally require a low electrical conductivity heat transfer fluid of generally less than 100 uS / cm to provide long-lasting, year-round protection of their cooling systems. Lowering the electrical conductivity of coolants reduces the risk of discharge during a short circuit, and therefore, reduces the risk of a thermal runaway of BEV battery packs. Following the shift towards BEV and safety concerns have prompted Chinese lawmakers to introduce the GB29743.2 standard. In short, the GB29743.2 standard mandates a significant reduction in the electrical conductivity of coolants and enhanced corrosion protection to enhance battery safety and prevent leaks from corrosion and material incompatibility. Conventional coolant compositions, such as those used in internal combustion engines, cannot be used with battery systems unless there is complete electrical insulation of the cooling channels, because these conventional compositions have an undesirably high electrical conductivity due to salts and ionizable compounds used as corrosion inhibitors. The presence of significant numbers of positive and negative ions in a solution provides a path for a "stray electrical current” if the system is damaged; such stray currents must be limited to ensure safety. First, stray currents may cause electrical shock hazards to the operator. Second, such stray currents may generate highly explosive hydrogen gas in the cooling system through hydrolysis.

[0002] Heat transfer fluids must provide efficient heat transfer to control and maintain cooling system temperature for efficient battery and electronic system operation and to prevent system failures due to coolant freezing or over-heating. An additional key requirement of a heat transfer fluid is that it provides corrosion protection to all cooling system metals over a wide range of temperature and operating conditions. Aluminum corrosion protection for battery packs, water pumps, heat exchangers and other components made from aluminum or aluminum alloys is particularly important. Beyond metal protection, corrosion protection helps the heat transfer fluid to fulfill its primary function of transferring excess heat from the heat-generating components to the radiator for dissipation.

[0003] EP 1485444 B1 describes an aqueous heat-transfer fluid with a low electrical conductivity for use in a fuel cell comprising a water-soluble alcoholic anti-freeze agent, a triazole, an amine and / or amine phosphate.

[0004] US 7,201 ,982 B2 describes fuel cell coolant compositions with a low electrical conductivity comprising one or more carboxylic acids or salts thereof.

[0005] US 9,567,507 B2 US and 10,557,070 B2 describe heat-transfer fluids for preventing corrosion in heat-transfer systems comprising carboxylic acid salts, H3PO4, divalent metal cations, and polyelectrolyte polymers.

[0006] US 5366651 and US 5723061 describe heat-transfer fluids comprising carboxylic acid salts and imidazole derivatives for preventing corrosion. The imidazole derivate provides additional pH-, and oxidation / high temperature stability.

[0007] There is an ongoing need for heat transfer fluids for BEVs having good heat transfer and corrosion protection under low conductivity coolant requirements of less than 200 uS / cm. While heat transfer, freezing, and boil-over protection are readily achievable through the proper selection of a freezing point depressants, good corrosion protection is often associated with a high concentration of ionic corrosion inhibitors which add a high level of electrical conductivity. Therefore, a low conductivity coolant with low electrical conductivity of less than 200 pS / cm, more specifically less than 100 pS / cm is very difficult to achieve when excellent corrosion protection under corrosive condition, e.g. in the presence of corrosive anions like chloride, fluoride and / or sulfate, is required. Furthermore, when systems are tested and then drained of the heat transfer fluid before shipping, corrosion may occur unless the remaining traces of heat transfer fluid provide vapor phase corrosion inhibition.Summary of the Invention

[0008] The present inventors have found that the requirements for improved BEV heat transfer fluids can be met by a heat transfer fluid concentrate comprising greater than or equal to 85 weight percent of a freezing point depressant; 20 to 80 ppm of calcium ions; an azole compound; 100 to 250 ppm of an inorganic phosphate; and a polyelectrolyte polymer, wherein the heat transfer fluid concentrate has a pH of 7 to 9.0 and the weight ratio of polyelectrolyte polymer to calcium ions is 1 to 3 and the weight ratio of inorganic phosphate to calcium is 2 to 4. Coolants for automotive applications are generally produced as concentrates with the various components dissolved in MEG (monoethylene glycol), usually around 95%. For use this concentrate is diluted with water usually 50 / 50. In such a case all concentrations will be halved while the ratios stay the same in the diluted product The heat transfer fluid concentrate is diluted with water, ideally with demineralized water, to form a heat transfer fluid comprising less than 65 weight percent of the freezing point depressant.

[0009] According to the disclosed invention, a heat transfer fluid concentrate can be diluted to make a heat transfer fluid with vapor phase inhibition, particularly for ferrous metals when a preferred amine or amine combinations, e.g., 1 ,3-diazoles, in particular N-Methyl-imidazole (NMI) or combination of amines when 1 ,3-diazoles are present as disclosed below, is used. The composition may be used for a cooling circuit which includes a battery and requires an electrical conductivity of less than 200 uS / cm. Due to the low conductivity requirements amines are preferably used as pH adjusting reagent. When silicate is present in the heat transfer composition, a non-ionic, stabilized organic silicate based on organic silicate esters should be used. These compositions afford heat transfer fluids compliant with GB-standard 29743.2.Description of the Figures

[0010] Fig. 1 shows a photograph of, left to right, aluminum, steel and copper coupons corrosion tested in coolant fluid containing 0.05 wt. % DMAMP + 0.17 wt. % 3-AO;

[0011] Fig. 2 shows a photograph of, left to right, aluminum, steel and copper coupons corrosion tested in coolant fluid containing 0.2 wt. % 3-AO;

[0012] Fig. 3 shows a photograph of, left to right, aluminum, steel and copper coupons corrosion tested in coolant fluid containing 0.05 wt. % DMAMP + 0.17 wt. % 3-AO + 0.06 wt. % NMI;

[0013] Fig. 4 shows a photograph of, left to right, aluminum, steel and copper coupons corrosion tested in coolant fluid containing 0.2 wt. % 3-AO + 0.07 wt. % NMI;

[0014] Fig. 5 shows a photograph of left to right, aluminum, cast iron and steel coupons corrosion tested in commercially available coolant 1 ;

[0015] Fig. 6 shows a photograph of left to right, aluminum, cast iron and steel coupons corrosion tested in commercial coolant 1 to which 0.035 wt. % N-methyl-imidazole was simply added to the commercially available coolant 1 prior to testing;

[0016] Fig. 7 shows a photograph of left to right, aluminum, cast iron and steel coupons corrosion tested in commercially available coolant 2; and

[0017] Fig. 8 shows a photograph of left to right, aluminum, cast iron and steel coupons corrosion tested in commercially available coolant 2 to which 0.035 wt. % N-methyl- imidazole was simply added to the commercial coolant 2 prior to testing.Detailed Description of the Invention

[0018] The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventors of carrying out their invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the general principles of the present invention have been defined herein specifically to provide an improved heat transfer fluid that provides vapor phase corrosion protection.

[0019] Disclosed herein are heat transfer fluid concentrate and heat transfer fluid compositions made by dilution of the concentrate that demonstrate a synergistic effect between the components of the composition. In a heat transfer fluid comprising ethylene glycol, water, inorganic phosphate, and an azole compound the synergistic effect is observed between alkaline earth metal ions, phosphate, and a polyelectrolyte polymer, as shown in the corrosion tests presented here. The optimal performance is observed when the ratio of polyelectrolyte polymer to calcium ion (both as ppm and wt. %) in the heat transfer fluid concentrate is between 1 and 3. The results show that adding 20-80 ppm of calcium ions can ensure good corrosion performance. The effect of calcium ions in a phosphate containing heat transfer fluid is particularly surprising. The highly insoluble nature of various calcium phosphate salts in aqueous solutions at pHs between 7.0 and 9.0 would lead one of skill in the art to predict poor solubility due tothermodynamic considerations. In this specific case the high insolubility of calcium phosphate combined with the dispersion ability of the polymer affords excellent corrosion protection. To achieve excellent corrosion protection at a low electrical conductivity the ratio of phosphate to calcium must be between 2 and 4. The effect of calcium ions in the phosphate containing heat transfer fluid is particularly surprising because corrosion protection even with corrosive water, e.g. in the presence of anions like chloride, fluoride and sulfate, is achieved while still maintaining a low electrical conductivity.

[0020] The heat transfer fluids according to the present invention can be free of carboxylic acids, nitrites, and borates. Any nitrate content of the fluids should be less than 100 ppm by weight based on the total weight of the heat transfer fluid. The freezing point depressant can be an alcohol or mixture of alcohols. Said components are monomeric to tetrameric 1 ,2-ethylene glycols, 1 ,2-propylene glycols or, more rarely, 1 ,3- propylene glycols, preferably monomeric to trimeric 1 ,2-ethylene glycols or 1 ,2- propylene glycols, particularly preferably monomeric or dimeric 1 ,2-ethylene glycols, very particularly preferably monomeric 1 ,2-ethylene glycol, and in each case the mixtures thereof. In addition, glycerol or glycerol oligomers are possible components. In addition, 1 ,3-propandiol is a possible component. Preferred alkylene glycol components or derivatives are particularly monoethylene glycol, di-ethylene glycol, triethylene glycol, tetraethylene glycol and mixtures thereof, but additionally also monopropylene glycol, dipropylene glycol and mixtures thereof. Particular preference is given to monoethylene glycol alone or mixtures of monoethylene glycol as main component, i.e. with a content in the mixture of more than 50% by weight, in particular of more than 80% by weight, especially of more than 95% by weight, with other alkylene glycols or derivatives of alkylene glycols.

[0021] In the heat transfer fluid concentrate the freezing point depressant can be present in an amount greater than or equal to 85 weight percent (wt. %) and less than or equal to 99.8 wt. %, assuming a 50:50 dilution. Those of skill in the art will recognize that the concentration of freezing point depressant depends on the climactic conditions the fluid will be used in. That said, it is economically sensible to ship a concentrate with as little water as possible.

[0022] The inorganic phosphate can be phosphoric acid. In the heat transfer fluid concentrate, the inorganic phosphate can be present in an amount of 0.010 wt. % to0.040 wt. %, based on the total weight of the heat transfer fluid concentrate. The phosphoric acid concentration should be more than about 0.011% to work and must be less than about 0.025% to fulfill the electrical conductivity goal of 100 pS / cm. The concentration of phosphoric acids depends on the application. The concentration of phosphoric acid is primarily defined by the conductivity requirement (e.g., 100 pS / cm).

[0023] The heat transfer fluid additive composition comprises an azole as a corrosion inhibitor for copper metal and copper containing alloys (e.g., brass). Exemplary azoles include benzotriazole, tolyltriazole, methyl benzotriazole (e.g., 4-methyl benzotriazole and 5-methylbenzotriazole), butylbenzotriazole, and other alkyl benzotriazoles (e.g., the alkyl group contains from 2 to 20 carbon atoms), mercaptobenzothiazole, thiazole substituted thiazoles, imidazole and substituted imidazoles, benzimidazole and substituted benzimidazoles, indazole and substituted indazoles, and tetrahydrotolyltriazole. Combinations of two or more of the foregoing azoles may also be used and such combinations of azoles are included in the term ‘azole'.

[0024] In the heat transfer fluid concentrate, the azole compound can be present in an amount of 0.01 wt. % to 3 wt. %, based on the total weight of the heat transfer fluid concentrate assuming a 50:50 dilution of the concentrate in making a working solution. Within this range, the azole compound can be present in an amount greater than or equal to 0.05 wt. %, or, more specifically, greater than or equal to 0.1 wt. %. Also, within this range, the azole compound can be present in an amount less than or equal to 2 wt. %, or, more specifically, less than or equal to 1 wt. %.

[0025] The alkaline earth metal ions are derived from an alkaline earth metal compound that can produce alkaline earth metal ions upon dissolving. The alkaline earth metal compound can be an inorganic alkaline earth metal compound such as calcium nitrate, calcium sulfate, calcium molybdate, calcium tungstate, calcium vanadate, calcium perchlorate, or a combination thereof. The alkaline earth metal compound is soluble in the heat transfer fluid. Soluble, as used herein, is defined as dissolving such that no particulate matter is visible to the naked eye. The alkaline earth metal compound can also be an alkaline earth metal salt formed between alkaline earth metal ions and an organic acid containing one or more carboxylic acid groups, such as calcium benzoate, calcium polyacrylate, calcium polymaleate, calcium lactate, calcium citrate, calcium tartrate, calcium gluconate, calcium glycolate, calcium succinate, calcium acetate, calcium adipate, calcium oxalate, calcium malonate, calcium formate, calcium acetate,calcium propionate, a calcium salt of an aliphatic tri-carboxylic acid or aliphatic tetracarboxylic acid, and combinations of the foregoing calcium compounds. The alkaline earth metal ions can also be derived from alkaline earth metal oxides and / or alkaline earth metal hydroxides. Deriving the alkaline earth metal ions from hydroxides and / or oxides as opposed to acetates or nitrates, avoids the presence of potentially corrosive acetate ions or nitrosamine-forming nitrate in the heat transfer fluid concentrate and any heat transfer fluid derived therefrom. In some embodiments the alkaline earth metal compound may be an alkaline earth metal salt formed between alkaline earth metal ions and a phosphonate or a phosphinate, such as calcium-PBTC salts, calcium-HEDP salts, calcium-HPA salts, calcium phopshonosuccinic acid salts, calcium-PSO salts (where PSO is a mono-, bis-, and oligomeric phosphinosuccinic acid adduct mixtures), and / or the like, hydrates of the salts, or combinations thereof.

[0026] In the heat transfer fluid concentrate, the alkaline earth metal compound is present in an amount such that the heat transfer fluid has an alkaline earth metal ion concentration of 20 to 80 parts per million by weight (ppm) of the heat transfer fluid concentrate. Within this range, alkaline earth metal ion concentration can be greater than or equal to 20 ppm, or, more specifically, greater than or equal to 25 ppm. Also, within this range, the alkaline earth metal ion concentration can be less than or equal to 70 ppm, or, more specifically, less than or equal to 60 ppm.

[0027] Heat transfer fluid concentrates in accordance with the present teachings further include one or more water-soluble (polyelectrolyte) polymers (average molecular weight of 500 to 20000 Daltons) derived from a polymerizable monomer (monomeric unit). Exemplary polymers include polyacrylates, acrylate-based polymers, copolymers, terpolymers, such as acrylate / acrylamide copolymers, polymethacrylates, polymaleic acids or maleic anhydride polymers, maleic acid-based polymers, their copolymers and terpolymers, modified acrylamide-based polymers, including polyacrylamides, acrylamide-based copolymers and terpolymers. In general, water-soluble polymers suitable for use include homo-polymers, copolymers, terpolymer and inter-polymers having (1) at least one monomeric unit containing C3 to C16 monoethylenically unsaturated mono- or dicarboxylic acids or their salts; or (2) at least one monomeric unit containing C3 to C16 monoethylenically unsaturated mono- or dicarboxylic acid derivatives such as amides, nitriles, carboxylate esters, and acid anhydrides, and combination thereof; or (3) at least one monomeric unit containing unsaturated ethers,unsaturated alcohols, unsaturated sulfonic acids or salts, unsaturated phosphonic acids or salts, unsaturated phosphinic acids or salts, and / or the like, and combinations thereof.

[0028] Representative monocarboxylic acids suitable for use in water-soluble polymers include but are not limited to acrylic acid, methacrylic acid, ethyl acrylic acid, vinylacetic acid, allylacetic acid, and cratonic acid. Representative monocarboxylic acid esters include but are not limited to butyl acrylate, diethylaminoethyl acrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, methyl acrylate, methyl methacrylate, tertia, and vinyl acetate.

[0029] Representative dicarboxylic acids include but are not limited to maleic acid, itaconic acid, fumaric acid, citaconic acid, mesaconic acid, and methylenemalonic acid.

[0030] Representative amides include but are not limited to acrylamide (or 2- propenamide), methacrylamide, N,N-dimethylacrylamide (or N,N-dimethyl-2- propenamide), ethyl acrylamide, propyl acrylamide, N-t-butylacrylamide, vinyl acetamide, sulfomethylacrylamide, 2-hydroxy-3-sulfopropyl acrylamide, N-Vinyl pyrrolidone (a cyclic amide), 2-vinylpyridene, carboxymethylacrylamide.

[0031] The inventive formulations all require the presence of effective amounts of a water-soluble (polyelectrolyte) polymer (also referred to as “polymeric dispersant” or “polymeric polyelectrolyte dispersant”). In some embodiments, this water-soluble polymer contains at least one monomeric unit selected from the group consisting of allylhydroxypropylsulfonate, AMPS or 2-acrylamido-2-methylpropane sulfonic acid, polyethyleneglycol monomethacrylate, vinyl sulfonic acid, styrene sulfonic acid, methallyl sulfonic acid, allyloxybenzenesulfonic acid, allylalcohol, allyl phosphonic acid, 3-allyloxy-2-hydroxy propane sulfonic acid, polyethylene glycol monomethacrylate, an alkoxylated allyl alcohol sulfonate, and / or the like, and combinations thereof.

[0032] The water-soluble polyelectrolyte polymer can be selected from the following commercially available polymers: (1) polymers available from BASF under the SOKALAN and TAMOL brands; (2) polymers available from Dow under the Acumer brand; (3) polymers available from Nouyron under the AQUATREAT brand; (4) polymers available from Italmatch under the Belclene brand.

[0033] In the heat transfer fluid concentrate (and the heat transfer flu id made by diluting the concentrate), the amount of polymeric polyelectrolyte dispersant is chosen basedon the amount of the alkaline earth metal ions present. The ratio of polyelectrolyte polymer to alkaline earth metal ions must be greater than 1.0 and less than 3.0. Within this range, the ratio can be greater than or equal to 1 .0 or, preferably, greater than or equal to 1.5. The ratio is determined using the amount (the weight) of polymeric dispersant dissolved in the concentrate.

[0034] The heat transfer fluid concentrate also comprises a pH-adjusting, neutralizing amine. Exemplary amines include primary and tertiary amino alcohols such as triethanolamine (TEA), 2-amino-2-methyl-1 -propanol (AMP), diethylethanolamine (DEAE), dimethylethanolamine (DMAE), 3-methoxy-propylamine (MOPA), 2- dimethylamino-2-methyl-1 -propanol (DMAMP), 1-amino-2-propanol, 3-aminooctan-4-ol (3-AO), 2-(2-aminoethoxy)ethanol, and the like. The concentrate can also comprise ethoxylated N-alkyl-amines (fatty amines) and amine ethoxylates. The concentrate composition can also contain unsubstituted oralkyl-substituted 1 ,3-diazoles (imidazole). The imidazole derivative is not particularly limited; for example, imidazole, alkyl- or arylsubstituted imidazole, and a condensed imidazole may be used. In some embodiments N-alkyl-substituted 1 -methylimidazole (NMI) is preferred. The concentrate composition can also contain a pyridine compound. The pyridine compound is not particularly limited; for example, pyridine, alkyl-substituted pyridine, or a condensed pyridine, like quinoline, may be used. The amount of the amine strongly depends on the pKa of the amine and its indirect influence on conductivity. Amines with a pKa close to 7-8 can be less than or equal to 2.0% by weight, or, more specifically, less than or equal to 1 .0% by weight, or, more specifically, less than or equal to 0.50% by weight. Weak amines, amines with a pKa smaller than 8, show the ability to increase the reserve alkalinity of the heat transfer fluid while not affecting significantly the electrical conductivity and pH. Table 2 shows an example of N-methyl-imidazole's (NMI) influence on reserve alkalinity, pH and electrical conductivity on formulation 5. NMI was added to the finished composition already containing TEA.

[0035] Imidazole contained in the heat transfer fluid concentrate not only improves the reserve alkalinity and stabilizes the pH but also shows improved vapor phase corrosion protection on steel without staining aluminum. The effect of imidazole is particularly surprising as corrosion protection and vapor phase corrosion protection on steel is often achieved with strong, strongly basic amines. Whereas N-methyl-imidazole has a pKa of 7.4, and therefore, shows only weak basic properties.

[0036] The heat transfer fluid concentrate can further comprise phosphonocarboxylates as metal chelators and anti-scale agents. Exemplary phosphonocarboxylates include phosphonosuccinic acid, 1 -phosphono- 1 ,2, 3, 4-tetracarboxybutane, and 1-phosphono- 1 ,2,3,4,5,6-hexacarboxyhexane, 1 -hydroxy-1 , 1-diphosphonic acid, amino- trimethylphosphonic acid, 2-phosphonobutan-1 ,2,4-tricarboxylic acid, 1-phosphono-1- hydroxy acetic acid, and others. While not necessary, phosphonocarboxylates in the range of 1-150 ppm, based on the total weight of the heat transfer fluid, improve performance (e.g., decreased elution of flux residue).

[0037] The heat transfer fluid concentrate may further comprise phosphinocarboxylates as metal chelators and anti-scale agents. Exemplary phosphinocarboxylates include phosphinosuccinic acid and water-soluble salts, phosphinobis(succinic acid) and water- soluble salts and phosphinosuccinic acid oligomer and water-soluble salts. In the heat transfer fluid, the phosphinocarboxylate can be present in an amount of 0 to 150 ppm, based on the total weight of the heat transfer fluid.

[0038] The heat transfer fluid concentrate may further comprise a non-ionic organic silicate to provide corrosion protection for aluminum. Suitable non-ionic organic silicates are silicate esters of the type of Si(OR)4 , in which R can be an alkyl-, aryl-, or hydroxyalkyl group between C1 and C36. Organic silicate esters can be stabilized by organosilanes such as Silquest Y-5560 or Silan AF-1 , sodium-(trihydroxysilyl) propymethylphosphonate such as Xiameter® Q 1-6083, alkaline metal aminophosphonates, or organic phosphosilicones of the type (Oi sSiCSHe)- P(O)(ONa)(OC2Hs). Organic silicate can be present in an amount less than or equal to 600 ppm although optimum results are achieved with a silicate concentration of less than or equal to 300 ppm expressed as total silicon.

[0039] The heat transfer fluid concentrate (and hence the heat transfer fluid) may optionally comprise one or more antifoaming agents (defoamers), dispersants, surfactants, colorants and other coolant additives. Exemplary surfactants include fatty acid esters, such as sorbitan fatty acid esters, polyalkylene glycols, polyalkylene glycol esters, copolymers of ethylene oxide (EO) and propylene oxide (PO), polyoxyalkylene derivatives of a sorbitan fatty acid ester, alkoxylated alcohols, and mixtures thereof.

[0040] The heat transfer fluid concentrate can be diluted, typically with water, to form a heat transfer fluid. The water used for dilution can be deionized water, purified water or distilled water. In the heat transfer fluid, the freezing point depressant is present in anamount of 30 wt. % to less than 70 wt. %, based on the total weight of the heat transfer fluid. Within this range, the amount of the freezing point depressant can be greater than or equal to 40 wt.%, but less than 65 wt. % based on the total weight of the heat transfer fluid. There is a danger of vehicle overheating with freezing point depressants above 65 wt. % so that higher values are used only in extremely cold climates (e.g., Alaska).

[0041] The pH of the heat transfer fluid concentrate is 7 to 9.5 at room temperature. Within this range, the pH can be greater than or equal to 7.5 and less than or equal to 8.5. The narrower range is preferred due to improved steel corrosion performance, improved reserve alkalinity (buffer capability), and electrical conductivity limitations.

[0042] In the present embodiment a method for producing the coolant concentrate is not particularly limited and a common method for producing a coolant can be used. For example, the coolant concentrate can be produced by uniformly stirring and mixing phosphoric acid, water, polymer, alkaline earth metal salts, and triazole into the freeze point depressant. When these components have dissolved the amine is added, and as necessary, the further additives are then added.

[0043] The coolant composition of the present embodiment has sufficiently high metal corrosion prevention even under corrosive conditions, e.g. in the presence of anions like chloride, fluoride, and sulfate, and, for example, aluminum, steel, brass, and copper corrosion prevention are all less than 5mg / coupon or 1 mg / cm2 and the metal coupons do not show discoloration. The corrosion protection of the coolant composition can be measured directly using the coolant concentrate diluted with corrosive water as a test solution in accordance with ASTM D1384 (Corrosion Test for Engine Coolants in Glassware) and ASTM D4340 (Corrosion of Cast Aluminum Alloys in Engine Coolants Under Heat-Rejecting Conditions). For ASTM D1384 solder and cast iron were omitted. Corrosion evaluation of only aluminum, steel, brass, and copper was regarded as favorable because solder and cast iron are generally not used in modern cooling circuits that include batteries. ASTM 4340 was performed as published by ASTM D15.

[0044] The coolant composition of the present embodiment has sufficiently high vapor phase corrosion prevention, and, for example, aluminum, steel, and copper coupons do not show discoloration or visual rust on the metal coupon exposed to air following immersion in the coolant. The corrosion protection of the coolant composition can be measured directly using the coolant composition as a 50 wt.% in glycol test solution in accordance with ASTM D1384. The metal coupons were half immersed in the test fluidat 70°C in a closed container and visually evaluated after five days for discoloration and rust, including the steel spacer (used to ensure electric continuity between aluminum and steel).

[0045] The coolant composition can be generally used as a coolant, and, since the coolant composition of the present embodiment simultaneously achieves low electrical conductivity and high corrosion prevention, the coolant composition of some embodiments is used as a coolant for a cooling circuit for HEVs, PHEVs, EVs, and FCVs, or as a coolant for a cooling circuit including a battery of EVs or FCVs.

[0046] Below, the present disclosure will now be described in more detail by specifically selected examples. However, the technical scope is not limited to these examples. Electrical conductivity, pH, RA, and metal corrosion according to the ASTM 4340 with corrosive water (100 ppm chloride) was evaluated by standard methods. Table 1 (split into Table 1a — comparative sample 1 and 2 and compositions 1-7 and Table 1b — compositions 8-15) shows the formulations and results of compositions 1 to 15 and comparative samples 1 to 2. Note that composition 11 is identical to composition 10 with the addition of NMI; composition 13 is identical to composition 12 with the addition of NMI; and composition 15 is identical to composition 5 with the addition of NMI. Only the key reagent variations are listed. All compositions contain 0.05 wt.% benzotriazole, 0.05 wt.% tolyltriazole, and 3.0 wt.% water. The quantity of mono ethylene glycol is adjusted to reach 100 wt. %.

[0047] For the tests shown in Figs. 1-4 three metal coupons (aluminum, steel, and copper) were assembled according to ASTM 1384. Steel spacers were used to allow electrical conductivity between the aluminum and steel coupons. Copper was electrically insulated from the steel with a Teflon spacer. The metal coupon assembly was fully immersed in the 50% coolant formulation (working fluid produced by a 50:50 dilution of the concentrate with deionized water) for two hours at 70°C in a closed polypropylene container. Afterwards a portion of the coolant was poured out so that the coupons were only half immersed in the coolant and the test was continued for five days at 70°C. After completion of the test the coupons and spacers were visually inspected for corrosion. Formulations without NMI showed corrosion (rust and discoloration) right on the line between liquid and air interphase. The solutions without NMI also showed a deeper yellowish color or some precipitation. The spacers also were not corroded with formulations with NMI.

[0048] Fig. 1 shows a photograph of the test results for Formulation 10 which included DMAP and 3-AO but no NMI. Note the rust / discoloration on the line marking the liquid air interface; this is most apparent on the steel coupon. Also, the test liquid (not photographed) showed a yellowish color with some precipitates.

[0049] Fig. 2 shows a photograph of the test results for a test of Formulation 12 which included 3-AO but no NMI. Note the rust / discoloration on the line marking the liquid air interface. Also, the test liquid showed (not photographed) a yellowish color with some precipitates.

[0050] Fig. 3 shows a photograph of the test results for Formulation 11 which included DMAP, 3-AO and NMI. The coupons are shiny and there is no rust / discoloration on the line marking the liquid air interface. The test liquid (not photographed) was not discolored and was free of precipitates.

[0051] Fig. 4 shows a photograph of the test results for Formulation 13 which included 3-AO and NMI. The coupons are shiny and there is no rust / discoloration on the line marking the liquid air interface. The test liquid (not photographed) was not discolored and was free of precipitates.

[0052] As shown in Table 1 , the test coolant compositions which contain a polyelectrolyte polymer, an alkaline earth metal, and phosphate ion show excellent metal corrosion protection with corrosive water while having a low electrical conductivity. According to comparative sample 1-2 compositions without polymer or without polymer and alkaline earth metal show poor corrosion protection. Alkaline earth metals are critical to afford corrosion protection. These compositions show that not only the presence of alkaline earth metals is sufficient to achieve corrosion protection with corrosive water, but also the ratio of polymer to alkaline earth metal and the ratio to phosphate ion to calcium is critical. Both ratios need to be in a defined, narrow window to achieve corrosion protection. Coolant compositions with a low conductivity are sensitive to neutralizing reagents. Amines with a low pKa, specifically with a pKa of less than 8.0, afford overall a lower electrical conductivity and a lower pH. This effect is observed in compositions with TEA and N-methyl-imidazole (NMI). TEA'S and NMI's pKas are less than 8. Exemplary composition 5 in Table 2 shows that when amines with a pKa of less than 8.0, or, more specifically less than 7.5, are used, the reserve alkalinity (RA) can be increased without having a significant impact on electrical conductivity and pH. A higher reserve alkalinity will afford an improved longevity of the heat transfer fluidduring operation and allow a more stable pH during operation. When amines are used with a high pKa value of > 8.5 it is recommended to use exactly the amount of amine needed to deprotonate two acidic protons of phosphoric acid. In In such a case the strong amine is best combined with an additional weak amine with a pKa value of < 8.0. This approach will specifically afford heat transfer fluids with an electrical conductivity below 100 pS / cm. It was also surprisingly found that compositions with N-methyl- imidazole showed improved vapor phase corrosion on steel when added to the original composition as shown in Table 3.Table 1 b

[0053] Table 2: Influence of N-methyl-imidazole on reserve alkalinity and pH.

[0054] Table 3: Influence of N-methyl-imidazole on vapor phase corrosion inhibition.

[0055] In addition, the influence of N-methyl-imidazole was evaluated by modifying commercially available heat transfer fluids. Three metal coupons (left to right in the figures: aluminum, cast iron, and steel) were assembled according to ASTM 1384. Steelspacers were used to allow electrical conductivity between each metal coupon. The metal coupon arrangement was fully immersed in the 50% coolant formulation (50:50 dilution of the commercially available concentrate) for two hours at 70°C in a closed polypropylene container. Afterwards a portion of the coolant was poured out so that the coupons were only half immersed in the coolant and the test was continued for five days at 70°C. After completion of the test the coupons and spacers were visually inspected for corrosion. Cast iron was included because cast iron is extremely difficult to protect from corrosion in the vapor phase.

[0056] Fig. 5 shows that commercial coolant 1 provided good corrosion protection to immersed aluminum and steel with more limited corrosion protection for cast iron. The coolant provided good vapor phase corrosion protection to aluminum and steel but poor vapor phase protection to cast iron. Fig. 6 shows an identical experiment to which 0.035 wt. N-methyl-imidazole was added to the coolant in advance. In this instance, good, immersed corrosion protection was provided to all metals although the vapor phase protection for cast iron was still not optimal.

[0057] Fig. 7 shows that commercial coolant 2 provided good corrosion protection to immersed aluminum and steel with more limited corrosion protection for cast iron. The coolant provided good vapor phase corrosion protection to aluminum and steel but poor (but somewhat better than coolant 1) vapor phase protection to cast iron. Fig. 8 shows an identical experiment to which 0.035 wt. N-methyl-imidazole was added to the coolant in advance. In this instance, good immersed and vapor phase corrosion protection was provided to all metals.

[0058] The following claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope of the invention. The illustrated embodiment has been set forth only for the purposes of example and that should not be taken as limiting the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims

What is claimed is:

1. A concentrate for diluting to a heat transfer fluid having low electrical conductivity of less than 200 pS / cm and providing vapor phase corrosion inhibition comprising: greater than or equal to 85 weight percent of an alcohol for lowering the freezing point; a triazole for corrosion protection; an amine for pH adjustment; a polymeric polyelectrolyte dispersant; a phosphate; and an alkaline earth metal salt wherein a ratio of the polymeric polyelectrolyte dispersant concentration to the alkaline earth metal concentration is between 1 and 3, wherein a ratio of the phosphate concentration to the alkaline earth meal concentration is between 2 and 4 and wherein 1-Methyl- Imidazole is added to enhance vapor phase corrosion inhibition.

2. The concentrate for diluting to a heat transfer fluid of Claim 1 , wherein the alcohol is selected from the group consisting of ethylene glycol, 1 ,2- propylene glycol, 1 ,3-propandiol, 1-4-butandiol, glycerol, and a combination thereof.

3. The concentrate for diluting to a heat transfer fluid of Claim 1 , wherein the phosphate concentration is between 100 and 250 ppm.

4. The concentrate for diluting to a heat transfer fluid of Claim 1 , wherein the alkaline earth metal salt concentration is between 20 and 80 ppm.

5. The concentrate for diluting to a heat transfer fluid of Claim 1 , wherein the amine is a primary or a tertiary water-soluble amino alcohol, an unsubstituted or alkyl-substituted 1 ,3-diazole, an N-alkyl-amine ethoxylate, and / or mixtures thereof.

6. The concentrate for diluting to a heat transfer fluid of Claim 1 , wherein at least one amine has a pKa of less than 8.0.

7. The concentrate for diluting to a heat transfer fluid of Claim 1 , wherein the pH is between pH 7 and pH 9.

8. The concentrate for diluting to a heat transfer fluid of Claim 1 further comprising one or more of a coloring agent, a denaturant, a bittering agent, an antifoam agent, a wetting agent, a stabilized non-ionic organic silicate, and an antioxidant.

9. The concentrate for diluting to a heat transfer fluid of Claim 1 , wherein the heat transfer fluid prepared from the concentrate has an electrical conductivity of less than 175 pS / cm.

10. The concentrate for diluting to a heat transfer fluid of Claim 9 wherein the ready-to-use heat transfer fluid prepared from the concentrate has an electrical conductivity of less than 150 pS / cm.

11. The concentrate for diluting to a heat transfer fluid of Claim 10 wherein the ready-to-use heat transfer fluid prepared from the composition has an electrical conductivity of less than 100 pS / cm.

12. Use of a heat transfer fluid to any of the above claims cooling systems of vehicles with combustion engines, vehicles with electric engines, vehicles with hybrid engines with a combination of combustion engines with electric engines or a combination of combustion engines with fuel cells.

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