Antifreeze properties

Many chemicals when added to water cause a freezing point depression, as shown in Table 1, and thus are termed antifreezes. The antifreeze properties of these chemicals vary widely as a function of their coUigative, or concentrative, properties. The reduction in freeze point depends both on the chemical itself and the concentration of the chemical in water. The freeze point depression increases as the antifreeze chemical is added to the water, until a characteristic concentration is achieved. Further addition of the antifreeze chemical to water will either result in insolubility or serve to increase the freezing point of the mixture, as illustrated in Figure 1. 

But diethylene glycol is not glycerin or propylene glycol, both of which are nontoxic toothpaste ingredients that also have antifreeze properties, in addition to the emulsifying and moisturizing properties that are useful in toothpastes, cosmetics, baby wipes, bubble baths, medicines, flavorings, and shampoos. 

Propanediol. In its racemic form, 1,2-propanediol is a petroleum-based high-volume chemical with an aimual production of over 500,0001, mostly used to manufacture the unsaturated polyester resins, yet also featuring excellent antifreeze properties. Enantiomerically pure (/ )-1,2-propanediol accumulates along two different pathways via DAHP (3-deoxy-D-flrahmo-heptulosonic acid 7-phosphate) and methylglyoxal, which then is reduced with either... 

In the winter months, significant benefits are derived from the use of concretes that contain cold-weather accelerating (CWA) admixtures with antifreeze properties. The economic benefits are derived from their ability... 

Aqueous solutions of propylene glycol display excellent antifreeze properties and are therefore valuable as low temperature heat-transfer fluids. For applications involving indirect food contact, heat-transfer fluids formulated with the USP grade product are preferred, since there could be inadvertent contact with a food product. These fluids are commonly used in the brewing and dairy industries as well as in refrigerated display cases in retail grocery stores. 

Antifreeze properties include low freezing point and excellent compatibility. 

Study of antifreezing properties of different-length segments of the polypeptide chains—determination of the minimum lengths of polymers required. 

The levels of bound water and the extended conformation of a glycoprotein found in the Antarctic fish, Dissostichus mawsoni, are responsible for the antifreeze properties of the glycoprotein. ... 

Proteins with specific antifreeze properties were first characterized in winter flounder (Pseiidopleiironectes americanus) and shorthorn sculpin (Yang et al., 1988). The simplest of these proteins, Type I from the winter flounder, are alanine-rich, amphiphilic, a-helices about 3-5 kD in size (Davies and Hew, 1990). 

The coUigative properties of antifreeze chemicals may also result in boiling point elevation. As the chemical is added to water, the boiling point of the mixture increases. Unlike the freeze depression, the boiling elevation does not experience a maximum the boiling point versus concentration curve is a smooth curve that achieves its maximum at the 100% antifreeze level. The boiling point elevation can be another important characteristic for antifreeze fluids in certain heat-transfer appHcations. 

Besides freeze protection, antifreezes provide many other performance properties that enhance the operation of a heat-transfer system. Because the internal combustion engine is by far the largest antifreeze appHcation, and ethylene glycol is the predorninant antifreeze in use, the following focus on the performance properties of an ethylene glycol-based antifreeze and their relationship to engine cooling. 

Corrosion Inhibition. Another important property of antifreeze solutions is the corrosion protection they provide. Most cooling systems contain varied materials of constmction including multiple metals, elastomeric materials, and rigid polymeric materials. The antifreeze chosen must contain corrosion inhibitors that are compatible with all the materials in a system. Additionally, the fluid and its corrosion inhibitor package must be suitable for the operating temperatures and conditions of the system. 

Metal- Working and Hydraulic Fluids. In the preparation of fluids for metal-working and hydrauflcs, the trend has been to replace organic-based materials with aqueous-based materials. Neodecanoic acid has found apphcation in these newer fluids as a corrosion inhibitor and a viscosity improver. For example, neodecanoic acid is used in an aqueous hydrauflc fluid concentrate for corrosion inhibition and improved antiwear properties (101), in the preparation of a thickened aqueous hydrauflc fluid to reduce viscosity loss (102), and in a water-soluble metal working oil to reduce corrosion (103). In a similar vein, neodecanoic acid has been used in antifreeze concentrates for corrosion inhibition (104). 

Miscellaneous Derivatives. Fimehc acid is used as an intermediate in some pharmaceuticals and in aroma chemicals ethylene brassylate is a synthetic musk (114). Salts of the diacids have shown utUity as surfactants and as corrosion inhibitors. The alkaline, ammonium, or organoamine salts of glutaric acid (115) or C-5—C-16 diacids (116) are useflil as noncorrosive components for antifreeze formulations, as are methylene azelaic acid and its alkah metal salt (117). Salts derived from C-21 diacids are used primarily as surfactants and find apphcation in detergents, fabric softeners, metal working fluids, and lubricants (118). The salts of the unsaturated C-20 diacid also exhibit anticorrosion properties, and the sodium salts of the branched C-20 diacids have the abUity to complex heavy metals from dilute aqueous solutions (88). 

QUENCH LIQUID SELECTION The choice of the appropriate quench liquid depends on a number of fac tors. Water is usually the first quench hquid to consider, since it is nontoxic, nonflammable, compatible with many effluent vapors, and has excellent thermal properties. If water is selected as the quench liquid, the tank should oe located indoors, if possible, to avoid freezing problems. If the tank has to be located outdoors in a cold climate, the addition of antifreeze is preferable to heat-tracing the tank, since overheating the tank can occur from tracing, thus reducing its effectiveness. 

In all circumstances it is important to ensure that the inhibitor is chemically compatible with the liquid to which it is added. Chromates, for example, cannot be used in glycol antifreeze solutions since oxidation of glycol by chromate will reduce this to the trivalent state which has no inhibitive properties. 

The key feature of ethylene glycol (EG) is the hydroxyl group, -OH, one on each of the two carbon atoms. The hydroxyls are responsible for its reactivity EG is a monomer used in the production of polyester polymers. The hydroxyls also give EG its most important physical property its solubility in water. That, linked with its low freeze point, makes EG suitable as an antifreeze and as a deicer. When EG is sprayed on ice, it combines with the water crystals and lowers the freeze point. This causes the mixture to melt and effectively keeps it in the liquid state. 

End uses. Its a little curious that the two major end uses for EG are so different. One is -a consumer product the other is a feedstock for more complicated chemistry. The reasons have to do with two separate properties of EG, one physical property, one chemical property. Because of EG s low freezing point, it is the main ingredient in automotive antifreeze. Because it is so chemically reactive, it is used as a monomer in making polyester polymers and PET, the plastic in the ubiquitous water and drink bottles. 

Together, antifreeze, PET, and polyester polymers account for about 98% of the ethylene glycol produced in the United States. It is also used sometimes as a deicer for aircraft surfaces. The two hydroxyl groups in the EG molecule also make EG suitable for the manufacture of surfactants and in latex paints. Other applications include hydraulic brake fluid, the manufacture of alkyd resins for surface coatings, and stabilizers for water dispersions of urea-formaldehyde and melamine-formaldehyde The hygroscopic properties (absorbs moisture from the air) make EG useful as a humectant for textile fibers, paper, leather, and adhesives treatment. 

There is one use to which levulinic acid can immediately be put. We have found that its sodium salt has ideal properties for an antifreeze agent. It has definite advantages over ethylene glycol for this purpose. It is a solid and is therefore more easily marketed than the liquid glycol. It is less corrosive to the iron parts of internal combustion engines than is tap water itself and has no detrimental effect on the rubber connections used in engines. 

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