WO2010008951A1

WO2010008951A1 - Corrosion-inhibited propyleneglycol/glycerin compositions

Info

Publication number: WO2010008951A1
Application number: PCT/US2009/049666
Authority: WO
Inventors: Kevin Connor; John Cuthbert
Original assignee: Dow Global Technologies Inc.
Priority date: 2008-07-16
Filing date: 2009-07-06
Publication date: 2010-01-21

Abstract

Anti-freeze concentrates include propylene glycol, a specified amount of glycerin and a corrosion inhibitor. Anti-freeze solutions result from dilution of a concentrate with at least 50 weight percent water, based upon total solution weight. The anti-freeze solutions have lower viscosity than an antifreeze solution prepared with the same weight percent water but lacking any glycerin. The anti-freeze solutions have freezing point properties (e.g. freezing point depression) and corrosion resistant properties (e.g. corrosion of cast iron) comparable to the antifreeze solution prepared with the same weight percent water but lacking any glycerin.

Description

CORROSION-INHIBITED PROPYLENEGLYCOL/GLYCERIN COMPOSITIONS

This application is a non-provisional application claiming priority from the U.S. Provisional Patent Application No. 61/081,064, filed on July 16, 2008, entitled "CORROSION-INHIBITED PROPYLENEGLYCOL/GLYCERIN COMPOSITIONS," the teachings of which are incorporated by reference herein, as if reproduced in full hereinbelow.

This invention relates generally to compositions of matter suitable for use as an antifreeze fluid or as a heat transfer fluid. In some embodiments, this invention more particularly relates to a composition of matter, especially an anti-freeze concentrate composition that includes propylene glycol, an amount of glycerin and at least one corrosion inhibitor as well as an anti-freeze composition that includes propylene glycol, an amount of glycerin, at least one corrosion inhibitor, and water. In some embodiments, the propylene glycol and glycerin are present in certain amounts relative to each other and water is present in an amount of at least 50 percent by weight (wt%), based upon total composition weight.

A variety of end use applications (e.g. plumbing systems, fire water sprinkler systems, and heat transfer systems such as those used for internal combustion engine cooling, hydronic heating and cooling of buildings, and heating of various natural gas streams) employ an anti-freeze composition. A typical end use application involves use of an anti-freeze composition to protect water conveying or water containing equipment from damage caused by the formation of ice during exposure to freezing temperatures. As water changes state from liquid to solid as a result of freezing, its volume increases by approximately 10 percent (%). When water freezes inside piping or another confined space, the volume increase may result in generation of sufficient pressure to overcome or exceed yield strength (burst pressure) of materials (e.g. carbon steel, copper, polyethylene (PE) or polyvinyl chloride (PVC) used to form the piping or other confined space.

In an effort to prevent or substantially limit formation of solid ice, anti-freeze compositions often include a freezing point depressant, more preferably a water-soluble freezing point depressant. Illustrative water-soluble freezing point depressants include low molecular weight (e.g. less than 100 grams per mole (g/mol) for freezing point depressants other than salts and less than about 110 g/mol for salts used as freezing point depressants) salts, alcohols, or glycols. More specific examples include aqueous solutions of a salt such as sodium chloride, calcium chloride or potassium formate, as well as one or more of methanol, ethanol, isopropanol, ethylene glycol, propylene glycol and glycerin.

An anti-freeze composition desirably has a number of attributes including, without limitation, relatively low cost (e.g. less than one (1) dollar per pound (US$/lb), minimal, preferably no toxicity, little and preferably no flammability, as little as possible and preferably no corrosivity, low and preferably no adverse environmental impact, and easy pumpability or at least flow-ability at low fluid temperatures (e.g. within a range of from -40 degrees centigrade (⁰C) to 0 ⁰C). Based upon information and belief, no current, commercial anti-freeze composition has all of the aforementioned attributes. SaIt- containing or salt-based freezing point depressants such as chloride or formate brines readily corrode common metals such as steels, cast iron and copper alloys. Such corrosivity limits widespread use of such salt-containing freezing point depressants and anti-freeze compositions including the same. Most, if not all, anti-freeze composition formulators consider alcohol-based freezing point depressants such as methanol, ethanol and isopropanol to be flammable and subject to catching fire even when mixed with water. Ethylene glycol is relatively toxic, at least in comparison to salt-containing freezing point depressants and propylene glycol-based freezing point depressants. Such relative toxicity results in prohibitions against use of ethylene glycol in applications involving food processing or where contact with ground or potable waters is a possibility. Propylene glycol and glycerin are viscous and difficult to pump at low fluid temperatures (i.e. within a range of from -40 ⁰C to -15 ⁰C). In addition, glycerin degrades quite readily compared to ethylene glycol or propylene glycol and glycerin degradation compounds contribute to excessive corrosion of common metals.

United States Patent (USP) 71, 948 (Baker) teaches use of salted water, glycerin, or their equivalents to prevent freezing in transmitting and diffusing heat through ordinary pipes, tubes or radiators.

USP 1,687,094 (Iserman) discloses a composition of matter for depressing the freezing point of water or an aqueous solution. The composition comprises a soluble amide (e.g. formamide) and glycerin, or a soluble amide, glycerin and diacetone alcohol. USP 1,711,324 (Osterlund) describes anti-freeze compositions that comprise sodium glycerol-phosphate and glycerin. USP 1,742,349 (Haag et al.) provides teachings relative to anti-freeze mixtures that consist of water, glycerin and glucose.

USP 1,752,145 (Calcott et al.) discloses a non-corrosive mixture comprising an aqueous solution of a polyhydric alcohol and a higher fatty acid (e.g. stearic acid, oleic acid and palmitic acid) that is substantially soluble in water.

USP 1,754,457 (Calcott et al.) teaches a non-corrosive aqueous solution of a polyhydric alcohol, or a mixture of polyhydric alcohols and monohydric alcohols, containing a primary aromatic diamine. The solution optionally includes a higher fatty acid and/or a secondary diaromatic amine. European Patent Application (EP) 1 010 740 Al (Schwarz et al.) discusses concentrated cooling liquids that comprise 80 wt% to 95 wt% of glycerin, 1 to 12 wt% of water and 2.0 wt% to 5.0 wt% of an additive such as a corrosion inhibitor, a stabilizing additive or a pH adjustment additive. EP' 740 also discusses diluted cooling liquids that comprise water in volume proportions of one part of the concentrated liquid to 0.01 parts to 10 parts of water.

USP 4,131,250 (Binckley) provides teachings relative to a means for preventing accumulation of ice on a helicopter main rotor blade using a freezing point depressant fluid. The freezing point depressant fluid comprises, for example, a glycerin- alcohol mixture.

British Patent Publication (UK) 2 050 398 (Sewell) relates to polyethylene glycol (EG) based de-icing and anti-icing compositions. The compositions comprise EG and a low molecular weight alcohol, possibly in paste form. The compositions may also include one or more of shellac, polyvinyl acetate, a liquid detergent or a water-insoluble plasticizer.

USP 7,387,748 (Pellet et al.) describes an improved antifreeze coolant composition that has a pH of from about 7.8 to 11.1 and consisting of water and a glycol in a weight ratio of about 95:5 to 5:95 respectively, and about 0.01 wt% to about 5 wt% of at least one additive selected from a group of hydroxy benzoic acids and their alkali metal salts. Pellet et al. notes that most glycol coolant formulations will contain a ratio of water to glycol which varies from about 60:40 to about 40:60 respectively. The glycol is, per the claims, at least one of eight glycols, two of which are propylene glycol and glycerin. Sapienza et al., in a series of patents and patent publications, one of which is United

States Patent Application Publication (USPAP) 2003/0168625, presents teachings related to "environmentally benign anti-icing or deicing fluids". The fluids may contain, for example, glycerin, an organic acid salt and water. An alternate fluid includes a hydroxyl-containing organic compound such as a hydrocarbyl aldoside or a glycol, a carbonate salt and water. Suitable glycols include glycerin, ethylene glycol and propylene glycol.

US 5,993,684 (Back et al.) teaches a method and compositions for reducing or removing ice formation from surfaces. The compositions consist essentially of one or more polyhydric alcohols and one or more non-potassium, low carbon percentage organic compounds and, optionally, one or more non-potassium, non-halide inorganic compounds and/or monohydric alcohols.

US 5,708,068 (Carder et al.) teaches glycol- and/or glycerin-based "universal" aircraft fluids that comprise an aqueous glycol and/or glycerin thickened with a polymeric thickener and/or its salt.

In some embodiments, this invention is an antifreeze composition, the composition comprising propylene glycol, glycerin, water and at least one corrosion inhibitor, the water being present in an amount within a range of from 50 percent by weight (wt%) to 90 wt%, the propylene glycol and the glycerin being present in a combined amount within a range of from 10 wt% to 50 wt%, the amounts of water, propylene glycol and glycerin combining to equal 100 percent by weight, with all percentages by weight being based upon combined weight of water, propylene glycol and glycerin, the propylene glycol and the glycerin being present in a weight ratio of glycerin to propylene glycol that falls within a range of from 0.05:1 to 1:1, and the corrosion inhibitor being present in an amount within a range of from 0.5 part by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin (phr) to 5 phr, the antifreeze composition having a viscosity at a temperature of 25 degrees centigrade that is less than that of a composition comprising the same amount of water, an amount of propylene glycol equal to the combined weight of propylene glycol and glycerin present in the antifreeze composition, and the same amount and type of corrosion inhibitor, the antifreeze composition also having a freeze point temperature that is less than or equal to the freeze point temperature of a composition comprising the same volume of water, a volume of propylene glycol equal to the combined volume of propylene glycol and glycerin present in the antifreeze composition, and the same amount and type of corrosion inhibitor, and the antifreeze composition further having a metal corrosion weight loss for each metal selected from a group consisting of copper, solder, brass, cast iron, steel, and aluminum, as determined in accord with ASTM D1384, that differs from metal corrosion weight loss for each of the same metals using a composition comprising the same amount of water, an amount of propylene glycol equal to the combined weight of propylene glycol and glycerin present in the antifreeze composition, and the same amount and type of corrosion inhibitor by no more than five (5) milligrams (mg). In other embodiments, this invention is a concentrate composition suitable for use in preparing the anti-freeze compositions of this invention. The concentrate composition comprises propylene glycol, glycerin and at least one corrosion inhibitor and, preferably very little (e.g. less than 10 wt%, based upon total concentrate weight), and more preferably from greater than 0 wt% to less than 3 wt%. Skilled artisans understand that a water content of 0 wt%, while possible, is impractical when one wants to include any corrosion inhibitor that is both substantially insoluble in a glycol such as PG but soluble, often highly soluble in water. In other words, the concentrate composition includes water in an amount sufficient to facilitate addition of glycol-insoluble corrosion inhibitors.

When ranges are stated herein, as in a range of from 2 to 10, both end points of the range (e.g. 2 and 10) and each numerical value, whether such value is a rational number or an irrational number, are included within the range unless otherwise specifically excluded.

References to the Periodic Table of the Elements herein shall refer to the Periodic Table of the Elements, published and copyrighted by CRC Press, Inc., 2003. Also, any references to a Group or Groups shall be to the Group or Groups reflected in this Periodic Table of the Elements using the IUPAC system for numbering groups.

The term "comprising" and derivatives thereof does not exclude the presence of any additional component, step or procedure, whether or not the same is disclosed herein. In order to avoid any doubt, all compositions claimed herein through use of the term "comprising" may include any additional additive, adjuvant, or compound whether polymeric or otherwise, unless stated to the contrary. In contrast, the term, "consisting essentially of" excludes from the scope of any succeeding recitation any other component, step or procedure, excepting those that are not essential to operability. The term "consisting of" excludes any component, step or procedure not specifically delineated or listed. The term "or", unless stated otherwise, refers to the listed members individually as well as in any combination.

Expressions of temperature may be in terms either of degrees Fahrenheit (⁰F) together with its equivalent in ⁰C or, more typically, simply in ⁰C. Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percents are based on weight.

For purposes of United States patent practice, the contents of any patent, patent application, or publication referenced herein are hereby incorporated by reference in their entirety (or the equivalent US version thereof is so incorporated by reference) especially with respect to the disclosure of synthetic techniques, definitions (to the extent not inconsistent with any definitions provided herein) and general knowledge in the art.

Descriptions and examples serve to illustrate, rather than define or limit, this invention in any way and do not constitute an exhaustive or all-inclusive listing of all possible embodiments of this invention. To those skilled in the art, other embodiments within the scope of appended claims will be apparent, from consideration of the specification and/or practice of the invention as disclosed herein. Such other embodiments may include one or more of, for example, selections of specific formulation components or amounts thereof within the broadest definitions provided; and processing or fabrication conditions.

Anti-freeze compositions used in at least some embodiments of this invention comprise a mixture of propylene glycol (PG) and glycerin that is diluted with water in an amount of at least 50 wt%, based upon total composition weight. Such compositions have a lower viscosity than that of an anti-freeze composition containing the same amount of water and an amount of PG that equals weight percentage of the mixture of propylene glycol and glycerin. In some embodiments more fully described below, anti-freeze compositions of this invention that include a controlled amount of glycerin (e.g. in a weight ratio of glycerin to PG of less than 1: 1, preferably within a range of from 0.1: 1 to 0.5:1, and more preferably within a range of from 0.2: 1 to 0.4:1) and a water content of at least 50 wt%, based upon total composition weight, have a lower viscosity but comparable or near equivalent antifreeze properties and corrosion-resistance properties relative to an anti-freeze composition containing the same amount of water and an amount of PG that equals the volume percentage of the mixture of PG and glycerin.

Other than containing only a small amount water as noted above, concentrates used to prepare such anti-freeze compositions contain the same components and component ratios as the anti-freeze compositions. Anti-freeze compositions of the present invention have utility in all conventional anti-freeze and heat transfer fluid applications. They have particular utility in anti-freeze applications such as plumbing anti-freeze used for winterization of recreational vehicles (RVs), food industry applications as secondary coolants used for refrigeration or freezing purposes, and various other Low Temperature Thermal Fluid (LTTF) applications.

Skilled artisans understand that pure glycerin has a higher viscosity than pure PG. Skilled artisans also understand that, when diluted with water, glycerin decreases in viscosity more substantially and more rapidly than propylene glycol. See Table 1 below for viscosity data (in centipoises (cps)) relative to pure glycerin and pure propylene glycol as well as mixtures of either glycerin or PG with various amounts of water. In particular, Table 1 shows that glycerin-water solutions with a water content of at least 50 wt%, based on total solution weight, have a lower viscosity than solutions of PG-water with the same water content.

Table 1 : Viscosity of Propylene Glycol and Glycerin with increasing water content at

25 ⁰C

Table 2 below illustrates a discovery that, up to a ratio of glycerin to propylene glycol that is less than or equal to 1:1, mixtures of glycerin and propylene glycol with a water content of at least 50 wt%, based upon total mixture weight, have a lower viscosity than a composition that contains propylene glycol rather than a mixture of propylene glycol and glycerin at the same water content. While mixtures of glycerin and propylene glycol with a ratio in excess of 1 : 1 may be used in at least some of the end use applications noted above (e.g. RV antifreeze), reductions in viscosity that follow substitution of some glycerin for an equal volume (or weight) of propylene glycol, tend to shrink in magnitude with increasing glycerin content.

Table 2: Effect of Glycerin Ratio on viscosity reduction versus water content

One typically prepares anti-freeze compositions as a volumetric mixture of a freezing point depressant with water. Glycerin has a higher molecular weight than PG. This tends to make glycerin less efficient than PG in depressing the freezing point of water. Glycerin also has a higher density than PG, a factor that offsets at least some of lowered freezing point depression efficiency as long as one compares volumetric mixtures of glycerin. As such, replacing some propylene glycol with an equal volume of glycerin means that a given volume of a mixture of propylene glycol and glycerin has a greater mass than an equal volume of propylene glycol when each is used as a freezing point depressant. Notwithstanding the higher molecular weight or greater mass of a mixture of glycerin and propylene glycol relative to an equal volume of propylene glycol, Table 3 below shows that a glycerin to propylene glycol ratio of from greater than 0.0:1 to 1.0:1 or less in glycerin/propylene glycol water solutions causes a reduction in anti-freezing properties, relative to PG water solutions, of less than 1%.

Table 3 : The effect of glycerin ratio on the molarity of anti-freezing mixtures

Glycerin has a number of characteristics that favor its use as a substitute for a portion of propylene glycol in a propylene glycol/water solution used in an anti-freeze end use application. First, glycerin exhibits toxicity, flammability and environmental impact comparable to that of propylene glycol. As such, mixtures of glycerin and propylene glycol should merit a rating of "non-toxic, non-flammable and environmentally benign" just as propylene glycol does. As both glycerin and propylene glycol merit a classification of

"Generally Regarded as Safe" (GRAS) by FDA and an approval for use as direct food additives, mixtures of the glycerin and propylene glycol could also be used as direct food additives. Neither glycerin nor propylene glycol has a measurable flash point when mixed with at least 15 wt% water. As such, the anti-freeze compositions of various embodiments of this invention should pose no risk of ignition into flames or supporting a fire. Propylene glycol and glycerin are both considered to be readily bio-degradable and can be produced from bio-renewable sources.

Skilled artisans know that aqueous solutions of glycols (e.g. PG) and glycerin oxidize and form acidic degradation compounds like formic, glycolic or lactic acids as well as various aldehydes. They also know that such solutions undergo a decrease in pH over time. In order to counter adverse effects, pH decrease or both, skilled practioners typically add at least one of a corrosion inhibitor and a buffering compound to the aqueous solutions. Dipotassium phosphate represents a commonly-added, acid-neutralizing compound that at least partially protects common metals like carbon steel, cast iron, solders and even copper alloys from corrosion. Skilled artisans further know that degradation reactions for glycerin tend to be far more facile than degradation reactions for propylene glycol such that corrosion inhibitors and pH buffering components like dipotassium phosphate are less effective in solutions based upon glycerin as sole freezing point depressant relative to solutions based on PG as sole freezing point depressant.

The anti-freeze compositions of various embodiments of this invention have a lower thermal oxidative degradation rate, as shown by a lower reduction in pH and a lower weight loss, than 100 % glycerin. See Table 4 below for data related to pH and weight loss for carbon steel and cast iron, with weight loss being determined in accord with American Society for Testing and Materials (ASTM) D 1384-05 (Corrosion Test for Engine Coolants in Glassware Corrosion, current edition approved June 1, 2005). All Table 4 solutions contain 0.5wt% dipotassium phosphate as a corrosion inhibitor. The % values shown in Table 4 represent wt%, based upon combined weight of PG and glycerol in a concentrate prior to dilution of the concentrate in accord with ASTM D 1384-05. Table 4: The effect of propylene glycol addition on glycerin degradation and corrosivity

As shown in Table 4, 100 wt% glycerin (in this instance USP Grade glycerin) has a corrosion rate for cast iron and carbon steel that is more than 100 times as severe as that for 100wt% PG. The severity is consistent with the drop in pH of 100% glycerin relative to the drop in pH for 100% PG. With a lower grade of glycerin, e.g. crude, unrefined by-product glycerin from bio-diesel production, impurities such as chlorides and acid salts should increase severity of the degradation. The data in Table 4 show that a 50/50 wt/wt mixture of glycerin and PG has an unexpectedly low corrosion weight loss relative to pure glycerin. From this data, one may conclude that PG has both a dilutive effect upon glycerin and a possible inhibitive effect upon glycerin degradation. Although not shown in Table 4, as concentration of PG relative to glycerin increases (i.e. 75 wt% PG and 25 wt% glycerin), corrosion performance approaches that of PG alone.

Degradation compounds of glycerin and propylene glycol tend to be acidic in nature. Accordingly, the pH of anti-freezing compositions based upon either of glycerin and propylene glycol or, in embodiments of this invention, a mixture of glycerin and propylene glycol normally decreases with time particularly when subjected to the conditions of ASTM D 1384-05. As a general rule, glycerin degradation reactions tend to be more facile than propylene glycol degradation reactions. On that basis, many of the corrosion inhibitors and pH buffering compounds that function acceptably well in solutions of propylene glycol either have limited effectiveness or are totally ineffective in solutions of glycerin. As shown in Table 5 below, the anti-freeze compositions of various embodiments of this invention have a surprisingly acceptable corrosivity performance notwithstanding the presence of glycerin in mixtures of glycerin and propylene glycol with a glycerin to propylene glycol ratio of greater than 0:1 but less than 0.5:1. ASTM D1384-05 specifies dilution of a concentrate with water to form a solution that contains 33-1/3 volume percent (vol%) concentrate components and 67-2/3 vol% water, each vol% being based on total volume of water and concentrate. Each concentrate contains 2.0 wt% of dipotassium phosphate as a corrosion inhibitor. This provides the solution with a dipotassium phosphate content of about 0.67 wt%, based upon solution weight

Table 5: Effect of glycerin ratio on corrosion weight loss and solution pH

The data in Table 5 show that, aqueous solutions with glycerin to propylene glycol ratios of 0.45:1, 0.26: 1 and 0.12:1 have corrosion weight loss and pH buffering performance comparable to that of aqueous solutions of propylene glycol.

The weight ratio of glycerin to propylene glycol preferably falls within a range of from 0.1:1 to 0.5:1. The weight ratio of glycerin to propylene glycol more preferably within a range of from 0.2:1 to 0.4:1. In some, preferably all, embodiments of this invention, the corrosion inhibitor is at least one inhibitor selected from a group consisting of a water-soluble, alkali metal phosphate, an alkali metal or ammonium hydroxide-neutralized aliphatic monocarboxylic acid having from eight to 14 carbon atoms and a pH within a range of from 7 to 10, an alkali metal or ammonium hydroxide-neutralized aliphatic dicarboxylic acid having from eight to 14 carbon atoms and a pH within a range of from 7 to 10, an aromatic or substituted aromatic monocarboxylic acid that has from seven to 14 carbon atoms or its alkali metal salt or ammonium salt, an alkali metal borate, an alkali metal silicate, an alkali metal molybdate, an alkali metal nitrate, and an alkali metal nitrite.

In some embodiments of this invention, the corrosion inhibitor is dipotassium phosphate. The dipotassium phosphate is preferably present in an amount within a range of from 1.5 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin to 4 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin.

In other embodiments of this invention, the corrosion inhibitor is a combination of dipotassium phosphate and sebacic acid, each of the dipotassium phosphate and the sebacic acid being present in an amount of at least 0.5 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin, and the composition further comprises an amount of alkali metal hydroxide sufficient to neutralize at least a portion of acid moieties of the sebacic acid and provide the composition with a pH within a range of from 7.8 to 8.4. In yet other embodiments of this invention, the corrosion inhibitor is sebacic acid, the sebacic acid being present in an amount within a range of from 1.5 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin to 4 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin, and the composition further comprises an amount of alkali metal hydroxide sufficient to neutralize at least a portion of acid moieties of the sebacic acid and provide the composition with a pH within a range of from 7.8 to 8.4.

Glycerin suitable for use in compositions of various embodiments of this invention may be obtained from any source and is preferably either synthetic or vegetable oil-based (also known as "bio-renewable"). All other factors being equal, bio-renewability makes vegetable oil-based glycerin a particularly preferred material for use in compositions of this invention. While Unites States Pharmaceutical (USP) grade glycerin yields particularly satisfactory results in any of a variety of end use applications, one may also use lesser grades of glycerin, such as industrial grade glycerin, in some less demanding applications such as those where there is essentially no likelihood of contact between the compositions and food or potable water. In addition, sources of glycerin with an assay of less than 99.5% may be used provided the source consists only of glycerin and water.

Propylene glycol, like glycerin, need not be obtained from any particular source or process. As such, the propylene glycol may be derived via catalytic hydrogenation of vegetable based glycerin (also known as "bio-renewable propylene glycol"). The propylene glycol may also be sourced from recycled or reclaimed post-consumer or industrially-use propylene glycol streams. As with glycerin, one may also use propylene glycol grades that do not meet USP requirements provided that the anti-freezing composition has no more than a possibility of incidental contact with food or potable water. In addition, one may use a source of propylene glycol with an assay substantially less than 99.5% as long as the source consists only of propylene glycol and water.

Some sources of water yield more preferred results than others base, at least in part, upon impurity type and level Water grades that do not meet ASTM Dl 193, Type I specifications, for example ASTM Dl 193, Type IV water, tend to include impurities such as chlorides or sulfates that lead to an increase in corrosion or other impurities such as calcium or magnesium, at least some of which react directly with many corrosion inhibitors or sources of alkalinity to form insoluble scales. When preparing anti-freezing compositions of some embodiments of this invention, a preferred technique involves initial preparation of a concentrate that consists of propylene glycol, glycerin and no more than a minor fraction (e.g. less than 5 wt%) of water desired for compositions of this invention. The concentrate also preferably consists of one or more corrosion inhibitors and/or pH buffering components. Dilution of the concentrate with a suitable volume of water readily facilitates preparation of anti-freezing compositions of various embodiments of this invention. If desired, one may modify an existing anti-freezing composition that consists of propylene glycol, water and a corrosion inhibitor by adding thereto an amount of glycerin sufficient to provide a weight ratio of glycerin to propylene glycol that falls within a range of from 0.05:1 to 1: 1. If the existing anti-freezing composition contains less than 50 percent by weight of water, based upon total composition weight, one may also modify the existing anti-freezing composition by adding water sufficient water to increase the water content to at least 50 percent by weight, preferably in conjunction with addition of the aforementioned amount of glycerin. Skilled artisans recognize that one may add water in an amount sufficient to increase the water content to at least 50 weight percent in a single aliquot or multiple aliquots and in one or more of before, at the same time as, or after addition of the glycerin.

The following examples illustrate, but do not limit, the present invention. All parts and percentages are based upon weight, unless otherwise stated. All temperatures are in ⁰C. Examples (Ex) of the present invention are designated by Arabic numerals and Comparative Examples (Comp Ex or CEx) are designated by capital alphabetic letters. Unless otherwise stated herein, "room temperature" and "ambient temperature" are nominally 25°C.

Measure viscosity using a Brookfield digital dynamic viscometer according to the procedure described in ASTM D2196-05 (Standard Test Materials for Rheological Properties of Non-Newtonian Materials by Rotational (Brookfield type) Viscometer) using spindle #18 and # 31.

Evaluate corrosion protection performance of six common metals (copper, solder, brass, steel, cast iron and aluminum) using ASTM D 1384-05. In accord with ASTM D

1384, immerse a coupon bundle of a single one of the six common metals in 750 milliliters

(mL) of a test solution that is maintained at a temperature of 88 ⁰C +/- 1 ⁰C for 336 hours.

Aerate the test solutions with instrument grade air through a one quarter inch (0.64 centimeter (cm)) gas dispersion tube at a flow rate of 100 cubic centimeters per minute (cc/min). Prepare each test coolant by diluting LTTF concentrate with sufficient synthetic corrosive water to give a solution with approximately 33.3 % by volume of propylene glycol.

Determine solution pH in accord with ASTM D 1287 (pH of Engine Coolants and Antirusts). Comp Ex A: Anti-freezing concentrate composition having a glycerin to PG ratio of zero

In a 1.0 Liter volumetric flask, stir 960.0 g of propylene glycol at a moderate (200 revolutions per minute (rpm)) speed while slowly (at a rate of 10 mL of solution every 15 seconds) adding to the propylene glycol 40.0 g of a 50 wt% solution of dipotassium phosphate in water sufficient to yield a concentrate with a propylene glycol content of 96 wt%, based upon total concentrate weight. Continue stirring until the concentrate has a visually uniform appearance.

Evaluate the concentrate for pH change and corrosion protection performance using procedures described above and summarize test results in Table 6 below.

Volumetrically titrate the concentrate with water to provide a dilute solution that has a water content of 30 volume percent (vol%), based upon total dilute solution volume. Evaluate the dilute solution for viscosity and anti-freezing characteristics and summarize test results in Table 7 below.

Volumetrically titrate the concentrate with water to provide a dilute solution that has a water content of 37 vol%, based upon total dilute solution volume. Evaluate the dilute solution for viscosity and anti-freezing characteristics and summarize test results in Table 8 below. Example 1: Anti-freezing concentrate composition having a glycerin to PG ratio of 0.26: 1

Replicate Comp Ex A, but add sufficient glycerin to yield a concentrate that contains 76 wt% propylene glycol, 20 wt% glycerin and 4 wt% of the aqueous dipotassium phosphate solution.

Volumetrically titrate the concentrate with water to provide a dilute solution that has a water content of 37 vol%, based upon total dilute solution volume. Evaluate the dilute solution for viscosity and anti-freezing characteristics and summarize test results in Table 6 below.

Table 6: Comparison of Corrosion and Degradation properties

Table 7: Properties of 30 vol% solutions of Anti-freezing Concentrates

Table 8: Properties of 37 vol% solutions of Anti-freezing Concentrates

The data in Tables 7 and 8 show that addition of glycerin (Ex 1 versus Comp Ex A) produces a viscosity reduction of approximately 5% at a 30 vol% concentration and temperature of 0 ⁰C or -10 ⁰C, and over 6% and over 7%, respectively, at temperatures of 0 0C or -10 ⁰C for a 37 vol% concentration. The viscosity reductions accompany only a minor change in either solute molarity or freeze point. Ex 2

Replicate Ex 1 but add the glycerin to the concentrate of Comp Ex A in an amount sufficient to provide a modified concentrate that has a glycerin content of 20 wt%, based upon total weight of the modified concentrate. The resulting solution has, as shown in Table 9 below, a composition very much like that of Ex 1 above. Given the near identical composition, the composition of Ex 2 should provide freezing point and corrosion resistance properties nearly identical to those of Ex 1.

Table 9

Claims

WHAT IS CLAIMED IS:

1. An antifreeze composition, the composition comprising propylene glycol, glycerin, water and at least one corrosion inhibitor, the water being present in an amount within a range of from 50 percent by weight to 90 percent by weight, the propylene glycol and the glycerin being present in a combined amount within a range of from 10 percent by weight to 50 percent by weight, the amounts of water, propylene glycol and glycerin combining to equal 100 percent by weight, with all percentages by weight being based upon combined weight of water, propylene glycol and glycerin, the propylene glycol and the glycerin being present in a weight ratio of glycerin to propylene glycol that falls within a range of from 0.05:1 to 1:1, and the corrosion inhibitor being present in an amount within a range of from 0.5 part by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin (phr) to 5 phr, the antifreeze composition having a viscosity at a temperature of 25 degrees centigrade that is less than that of a composition comprising the same amount of water, an amount of propylene glycol equal to the combined weight of propylene glycol and glycerin present in the antifreeze composition, and the same amount and type of corrosion inhibitor, the antifreeze composition also having a freeze point temperature that is less than or equal to the freeze point temperature of a composition comprising the same volume of water, a volume of propylene glycol equal to the combined volume of propylene glycol and glycerin present in the antifreeze composition, and the same amount and type of corrosion inhibitor, and the antifreeze composition further having a metal corrosion weight loss for each metal selected from a group consisting of copper, solder, brass, cast iron, steel, and aluminum, as determined in accord with ASTM D1384, that differs from metal corrosion weight loss for each of the same metals using a composition comprising the same amount of water, an amount of propylene glycol equal to the combined weight of propylene glycol and glycerin present in the antifreeze composition, and the same amount and type of corrosion inhibitor by no more than 5 milligrams.

2. The antifreeze composition of Claim 1, wherein the weight ratio of glycerin to propylene glycol falls within a range of from 0.1:1 to 0.5:1.

3. The antifreeze composition of Claim 1, wherein the weight ratio of glycerin to propylene glycol falls within a range of from 0.2: 1 to 0.4: 1.

4. The antifreeze composition of any of Claims 1 through 3, wherein the corrosion inhibitor is at least one inhibitor selected from a group consisting of a water- soluble, alkali metal phosphate, an alkali metal or ammonium hydroxide-neutralized aliphatic monocarboxylic acid having from eight to 14 carbon atoms and a pH within a range of from 7 to 10, an alkali metal or ammonium hydroxide-neutralized aliphatic dicarboxylic acid having from eight to 14 carbon atoms and a pH within a range of from 7 to 10, an aromatic or substituted aromatic monocarboxylic acid that has from seven to 14 carbon atoms or its alkali metal salt or ammonium salt, an alkali metal borate, an alkali metal silicate, an alkali metal molybdate, an alkali metal nitrate, and an alkali metal nitrite.

5. The antifreeze composition of Claim 4, wherein the corrosion inhibitor is dipotassium phosphate.

6. The antifreeze composition of Claim 5, wherein the dipotassium phosphate is present in an amount within a range of from 1.5 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin to 4 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin.

7. The antifreeze composition of Claim 4, wherein the corrosion inhibitor is a combination of dipotassium phosphate and sebacic acid, each of the dipotassium phosphate and the sebacic acid being present in an amount of at least 0.5 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin, and the composition further comprises an amount of alkali metal hydroxide sufficient to neutralize at least a portion of acid moieties of the sebacic acid and provide the composition with a pH within a range of from 7.8 to 8.4.

8. The antifreeze composition of Claim 4, wherein the corrosion inhibitor is sebacic acid, the sebacic acid being present in an amount within a range of from 1.5 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin to 4 parts by weight per 100 parts by weight of combined weights of water, propylene glycol and glycerin, and the composition further comprises an amount of alkali metal hydroxide sufficient to neutralize at least a portion of acid moieties of the sebacic acid and provide the composition with a pH within a range of from 7.8 to 8.4.