Hydrocarbon solvents flash point

Flash points of mixtures of oxygenated and hydrocarbon solvents cannot be predicted simply. A computer based method is proposed which exhibits satisfactory prediction of such Tag Open Cup flash points. Individual solvent flash point indexes are defined as an inverse function of the component s heat of combustion and vapor pressure at its flash point. Mixture flash points are then computed by trial and error as the temperature at which the sum of weighted component indexes equals 1.0. Solution nonidealities are accounted for by component activity coefficients calculated by a multicomponent extension of the Van Laar equations. Flash points predicted by the proposed method are compared with experimental data for 60 solvent mixtures. Confidence limits of 95% for differences between experimental and predicted flash points are +8.0-+3.0°F. 

The flash point of a solvent mixture is not identical to that of its most flammable component. When solvents with widely differing hydrogen bond parameters are mixed (e.g., alcohol hydrocarbon), tbe flash point is significantly reduced. On the other hand, the flash point of a mixture of chemically related solvents lies between those of the individual components [14.87]-[14.89]. Methods have been developed for calculating the flash point of solvent mixtures and solutions, activity coefficients are used to account for nonideal behavior [14.90]. 

Xylenes for solvent purposes consist of a mixture of three dimethylbenzene isomers, ortho-, meta- and para-xylene, and ethylbenzene. The physical properties quoted are for a typical mixture and the only property that is significantly altered by the ratio of the isomers is the flash point of the mixture. This can be significant in the UK and other countries where legislation primarily aimed at the safe storage of petrol regulates the storage and handling of hydrocarbons with flash points of less than 73 °F (22.8 °C) by the Abel method. 

Tetrahydronaphthalene [119-64-2] (Tetralin) is a water-white Hquid that is insoluble in water, slightly soluble in methyl alcohol, and completely soluble in other monohydric alcohols, ethyl ether, and most other organic solvents. It is a powerhil solvent for oils, resins, waxes, mbber, asphalt, and aromatic hydrocarbons, eg, naphthalene and anthracene. Its high flash point and low vapor pressure make it usehil in the manufacture of paints, lacquers, and varnishes for cleaning printing ink from rollers and type in the manufacture of shoe creams and floor waxes as a solvent in the textile industry and for the removal of naphthalene deposits in gas-distribution systems (25). The commercial product typically has a tetrahydronaphthalene content of >97 wt%, with some decahydronaphthalene and naphthalene as the principal impurities. 

Ref L). Used as a solvent and as a flash point retarder for hydrocarbons and higher boiling solvents... 

When more organic solvent power is needed, nonazeotropic mixtures of PFCs and HCs are also available. They are formulated to take advantage of the inerting ability of the PFCs and therefore do not have flash points. Although most hydrocarbons do not exhibit appreciable solubility in PFCs, numerous useful PFC/HC combinations do exist. Some PFC/HC mixtures exhibit complete miscibility and are thus limited only by flash points and flammability. To develop a mixture, the HC solvent(s) can be selected to provide the required solvency properties and substrate compatibility, then an appropriate PFC inerting solvent can be selected. Table 6.6 lists PFC/HC mixtures that have no flash point at the indicated concentrations. Some of these mixtures, or their recipes, are being offered on an experimental basis for evaluation purposes. 

One useful blend currently being employed as a very effective silicone solvent on an industrial scale is a mixture of 80 vol % hydrocarbon heptane and 20 vol % perfluoropentane, called 1.-12808 (see Table 6.7). 1.-12808 is useful for applying silicone lubricants to numerous medical devices, such as needles, IV spikes, blood filters, and catheters. This mixture shows no flash point and no explosion limits in air. The presence of the more volatile PFC, relative to the HC,... 

Tag open cup-apparatus for determining the flash point of hydrocarbon liquids, usually solvents, having flash points between -17.8° and 168°C (0° to 325°F), under test methods prescribed in ASTM D 1310. The test sample is heated in an open cup at a slow, constant rate. A small flame is passed over the cup at specified intervals. The lowest temperature at which the vapors above the sample briefly ignite is the flash point. See Cleveland open cup. 

Allyl alcohol (2-propen-l-ol, CH2=CHCH2OH, boiling point 96.9°, density 0.8520, flash point 25°C) is the simplest unsaturated alcohol and is a colorless corrosive liquid with a pungent odor. The vapor can cause severe irritation and injury to eyes, nose, throat, and lungs. Allyl alcohol is miscible with water and miscible with many polar organic solvents and aromatic hydrocarbons, but is not miscible with //-hexane. It forms an azeotropic mixture with water and a ternary azeotropic mixture with water and organic solvents. 

Krytox seems like a product from heaven, as many of its attributes are spectacular. It is a fluorinated grease and is therefore impervious to hydrocarbon- and water-based solvents. It cannot bum, so it has no flash point and can be exposed directly to oxygen, even at high pressures. It can be used over the widest temperature range of all the greases and works equally well with stopcocks as with joints. It has remarkable stability characteristics and can withstand long-term abuse. Best of all, Krytox greases are nontoxic. 

Hydrocarbon Solvents. Most hydrocarbon solvents are mixtures. Few commercial hydrocarbon solvents are single compounds. Toluene is an exception. Hydrocarbon solvents are usually purchased and suppHed on specification. The most important specification properties are distillation range, solvency as expressed by aniline cloud point and Kauri-Butanol (KB) value, specific gravity, and flash point. Composition requirements such as aromatic content and benzene concentration are also important in many appHcations. 

Agricultural Products. Pesticides are frequently applied as emulsifiable concentrates. The active insecticide or herbicide is dissolved in a hydrocarbon solvent which also contains an emulsifier. Hydrocarbon solvent selection is critical for this application. It can seriously impact the efficacy of the formulation. The solvent should have adequate solvency for the pesticide, promote good dispersion when diluted with water, and have a flash point high enough to rniriinii2e flammability hazards. When used in herbicide formulas, low solvent phytotoxicity is important to avoid crop damage. Hydrocarbon solvents used in post-harvest application require special testing to ensure that polycyclic aromatics are absent. 

Another cleaning application involving solvents is the degreasing of metal parts and other objects in manufacturing plants and automotive repair facilities. Mineral oils and other high flash point hydrocarbon solvents are used in these applications. 

The flash point most often quoted for oxygenated solvents is the Taghabue (Tag) Open Cup or TOC flash point while for hydrocarbons the Tag Closed Cup or TCC flash point is more commonly used. When hydrocarbon and oxygenated solvents are mixed together, the TOC flash point is generally the one chosen to characterize the blend. The main concern here will be that of predicting TOC flash points for solvent blends from the flash points of the individual components. 

For hydrocarbon fractions there are established correlations between TCC flash point and boiling range (6,7). In the present work a review of TOC flash point data for oxygenated solvents shows a relatively good correlation (standard deviation of 5%) between log (component vapor pressure at 25°C) and flash point. Correlation between flash point and boiling point proved to be less satisfactory. 

Vapor pressure at the flash point and the product of molecular weight and vapor pressure at the flash point were computed for 40 oxygenated solvents. Vapor pressure at the flash point varied between 7 and 58 mm Hg while the product of vapor pressure and molecular weight varied between 800 and 4200. Thus, some of the above methods of predicting flash points of mixed hydrocarbons appear unlikely to be effective for systems containing oxygenated solvents with their attendant non-ideal behavior. 

The accuracy of predicting mixture flash points depends strongly on the validity of the pure component flash point data which are used in the calculation procedure. There is, for example, little published data for TOC flash points of hydrocarbons. Some of the accepted TOC flash point data for oxygenated solvents were unreliable, e.g., the TOC flash point acetone is often quoted as 15°F this was redetermined in the present work at — 20°F. Component flash points shown in Table III were generally taken from published flash point data and were not checked experimentally. 

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