Mixture flash point

Note that many original contributions are presented in this book (on mixture flash points and autoignition temperatures). 

Liquid Mixtures Flash point temperatures for mixtures of liquids can be estimated if only one component is flammable and the flash point temperature of the flammable component is known. In this case the flash point temperature is estimated by determining the temperature at which the vapor pressure of the flammable component in the mixture is equal to the pure component vapor pressure at its flash point. Estimation of flash point temperatures for mixtures of several flammable components can be done by a similar procedure, but it is recommended that the flash point temperature be measured experimentally. 

Solvent-laden air (SLA), 70 95 Solvent mixtures flash point of, 23 116 viscosity of, 23 99 Solvent Orange 107, 60, 63, 7 colorant for plastics, 7 374t Solvent polarity/hydrophobicity probing, polymethine dyes in, 20 517 Solvent polarity/temperature, in initiating systems, 74 268 Solvent power, 23 89 Solvent preparation, for Grignard reactions, 72 823 Solvent properties... 

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. 

Flash point is an important solvent blend performance property. Mixture flash points cannot be predicted using linear mixing rules, and to date no literature describing a satisfactory method of predicting flash... 

If values of Ti can be predicted for each component at various temperatures, a trial-and-error procedure might be used to converge on the mixture flash point. 

As a first approach to utilizing this flashing index calculation technique, component flashing indexes were defined as the reciprocal of the component vapor pressure at the flash point. Mixture flash points were then computed by trial-and-error as the temperature at which... 

When non-combustible components are present in a mixture, their presence in the vapor space does not contribute to the support of combustion at the flash point. In such cases, Mv is calculated as the mean molecular weight of only the flammable components present in the vapor phase. This approach of course ignores the likely effects of different noncombustible components on mixture flash points but nevertheless provides an effective model. 

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. 

Compotmd or Mixture Flash Point (Closed Container), °C ... 

Flash point. The flash point of a liquid is the lowest temperature at which it gives off enough vapor to form an ignitable mixture with air. The flash point generally increases with increasing pressure. 

The flash point measures the tendency of a petroleum material to form a flammable mixture with air. It is one of the properties to be considered when evaluating the flammability of a petroleum cut. 

Calculating the flash point starting from the mixture s composition is not very accurate however an estimation can be obtained if 7) is determined as-the temperature for which the following relation holds true [ 9 )... 

It should be noted finally that adding gasoline to diesel fuel which was sometimes recommended in the past to improve cold behavior conflicts with the flash point specifications and presents a serious safety problem owing to the presence of a flammable mixture in the fuel tank airspace. Adding a kerosene that begins to boil at 150°C does not have the Scune disadvantage from this point of view. 

Carbon disulphide should never be used if any alternative solvent is available, as it has a dangerously low flash-point, and its vapours form exceedingly explosive mixtures with air. Ether as a solvent for recrystallisation is much safer than carbon disulphide, but again should be avoided whenever possible, partly on account of the danger of fires, and partly because the filtered solution tends to creep up the walls of the containing vessel and there deposit solid matter by complete evaporation instead of preferential crystallisation. 

Properties of the principal hydrocarbons found in commercial hexane are shown in Table 9. The flash point of / -hexane is —21.7 °C and the autoignition temperature is 225°C. The explosive limits of hexane vapor in air are 1.1—7.5%. Above 2°C the equiUbrium mixture of hexane and air above the Hquid is too rich to fall within these limits (42). 

The lower flammable limit (LEL) or lower explosive limit (LEL) is the minimum concentration of vapor in air below which a flame is not propagated when an ignition source is present (61—64). Below this concentration, the mixture is considered too lean to bum. The lower flammable limit and the flash point of a flammable Hquid are closely related by the Hquid s vapor pressure characteristics. 

The amyl alcohols are readily flammable substances / fZ-amyl alcohol is the most flammable (closed cup flash point, 19 °C). Their vapors can form explosive mixtures with air (Table 6) (5,139—147). 

Flash Point. As a liquid is heated, its vapor pressure and, consequendy, its evaporation rate increase. Although a hquid does not really bum, its vapor mixed with atmospheric oxygen does. The minimum temperature at which there is sufficient vapor generated to allow ignition of the air—vapor mixture near the surface of the hquid is called the dash point. Although evaporation occurs below the dash point, there is insufficient vapor generated to form an igrhtable mixture below that point. 

Stabilized tetrachloroethylene, as provided commercially, can be used in the presence of air, water, and light, in contact with common materials of constmction, at temperatures up to about 140°C. It resists hydrolysis at temperatures up to 150°C (2). However, the unstabilized compound, in the presence of water for prolonged periods, slowly hydrolyzes to yield trichloroacetic acid [76-03-9] and hydrochloric acid. In the absence of catalysts, air, or moisture, tetrachloroethylene is stable to about 500°C. Although it does not have a flash point or form flammable mixtures in air or oxygen, thermal decomposition results in the formation of hydrogen chloride and phosgene [75-44-5] (3). 

Flash Point. As fuel oil is heated, vapors are produced which at a certain temperature "flash" when ignited by an external ignition source. The flash point is the lowest temperature at which vapor, given off from a Hquid, is in sufficient quantity to enable ignition to take place. The flash point is in effect a measure of the volatiHty of the fuel. The measurement of flash point for pure Hquids is relatively straightforward. However, the measured value may depend slightly on the method used, especially for Hquid mixtures, since the composition of the vapor evolved can vary with the heating rate. Special... 

Flammability. Since almost all ethers bum in air, an assessment of their potential ha2ards depends on flash points and ignition temperatures. The flash point of a Hquid is the lowest temperature at which vapors are given off in sufficient quantities for the vapor—air mixture above the surface of the... 

The flash point is the lowest temperature at which a liquid gives off sufficient vapor to form an ignitable mixture with air near the surface of the liquid or within the vessel used. ASTM test methods include procedures using a closed cup (ASTM D56, ASTM DOS, and ASTM D3828), which is preferred, and an open cup (ASTM D92 and ASTM D1310). When several values are available, the lowest temperature is usually taken in order to assure safe operation of the process. 

An alternate method for flash point prediction is the method of Gmehling and Rasmussen and depends on the lower flammabihty limit (discussed later). Vapor pressure as a function of temperature is also required. The method is generally not as accurate as the preceding method as flammability limit errors are propagated. The authors have also extended the method to defined mixtures of organics. 

The upper and lower flammabihty limits are the boundary-line mixtures of vapor or gas with air, which, if ignited, will just propagate flame and are given in terms of percent by volume of gas or vapor in the air. Each of these limits also has a temperature at ch the flammabihty limits are reached. The temperature corresponding to the lower-hmit partial vapor pressure should equal the flash point. The... 

Dowtheim J (Dow Corning Coi poration). A mixture of isomers of an alkylated aromatic recommended temperature range —70°C to 300°C noncorrosive toward steel, common metals and alloys combustible material flash point 58°C low toxic prolonged and repeated exposure to vapors should be limited 10 ppm for daily exposures of eight hours. 

The equilibrium vapor pressure of a flammable hquid at its closed-cup flash point about equ s its LFL in percent by volume. Thus, the vapor pressure of toluene at its closed-cup flash point (4.4°C or 40°F) of 1.2 percent (1.2 kPa) is close to its LFL of 1.1 percent. The composite LFL of a mixture may be estimated by Le Cnatelier s Rule ... 

The equilibrium vapor pressure above a confined liquid depends only on temperature. The fraction of the total pressure exerted by vapor pressure determines the composition of the vapor-air mixture. Thus when the total pressure is reduced, for example at high elevations or in vacuum tmcks, the vapor concentration in air increases. Since flash points are reported at a... 

Small concentrations of volatile components in a liquid mixture may accumulate in the vapor space of a container over time and appreciably reduce the flash point relative to the reported closed-cup value. This may be the result of degassing, chemical reaction or other mechanism. An example is bitumen [162]. Similarly, if a tank truck is not cleaned between deliveries of gasoline and a high flash point liquid such as kerosene or diesel oil, the mixture might generate a flammable atmosphere both in the tmck tank and the receiving tank. Contamination at the thousand ppm level may create hazards (5-1.4.3 and 5-2.5.4). Solids containing upward of about 0.2 wt% flammable solvent need to be evaluated for flammable vapor formation in containers (6-1.3.2). 

In view of the above adverse effects a safety factor should be applied where flammability is assessed using flash point. For pure liquids in containers the vapor should be considered potentially flammable if the liquid temperature is upward of at least 5°C below the reported flash point. For mixtures whose composition is less certain, such as petroleum mixtures, the safety factor should be about 15°C relative to the flash point [55]. Where combinations of adverse effects are identified the safety factors should be increased accordingly. A simple but very conservative approach is to assume that all liquids having a flash point <141°F may produce a flammable atmosphere under some ambient conditions, even where no mist or froth production is involved. A more practical approach is to assume that liquids handled in air at least 5-15°C below their closed cup flash points will not present ignition risks unless... 

---