Flash point prediction

The method of Shebeko et al. " is the preferred flash point prediction method. The formula of the compound, the system pressure, and vapor pressure data for the compound must be available or estimable. Equation (2-174) is the basic equation. 

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. 

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. 

For the calculated data the corresponding limits were +8.0° to 1.8°F (earlier experimental vs. calculated flash points) and +8.0° to +3.0°F (redetermined experimental vs. calculated flash points). These limits further indicate the skew in the calculated data and show that a conservative, or low, flash point prediction is more likely than a high prediction. 

The use of ANN is highly developed due their great advantage compared with traditional computing systems. ANNs have a flexible structiue, capable to make a nonlinear mapping between input and output data sets. In fact, multilayer perceptrons, one of the more extended neural network architectures, are imiversal approximators for complex problems [12]. The apphcation of this is reflected in the hteratiue devoted to prediction of many physical and chemical parameters, such as nanofluids density [14], density of binary mixtures of ionic hquids [15], electrical percolation temperatiue [16], molecular diffusivity of nonelectrolytes [17], vegetable oils viscosity [18], esters flash point prediction [12], polarity parameter in binary mixed solvents systems [19], etc. 

Flash points, lower and upper flammability limits, and autoignition temperatures are the three properties used to indicate safe operating limits of temperature when processing organic materials. Prediction methods are somewhat erratic, but, together with comparisons with reliable experimental values for families or similar compounds, they are valuable in setting a conservative value for each of the properties. The DIPPR compilation includes evaluated values for over 1000 common organics. Detailed examples of most of the methods discussed are available in Danner and Daubert."... 

The partial pressure of LEL ethanol is 0.0327 atm. The temperature that produces a vapor pressure of 0.0327 atm is I l C. which is our predicted flash point. This is close to the reported 13°C. 

Lenoir, I. M., Predict Flash Points Accurately, Hydro. Proc. Tan. (1975), p. 95. 

The direct deposition of excess calcite method should be used in predicting the utilization period in cases where the flash point temperature of the well is known and the saturation ratio at this condition is above 1.72. 

Predictive hazard evaluation procedures may be required when new and different processes, designs, equipment, or procedures are being contemplated. The Dow Fire and Explosion Index provides a direct method to estimate the risks in a chemical process based upon flammability and reactivity characteristics of the chemicals, general process hazards (as exothermic reactions, indoor storage of flammable liquids, etc.) and special hazards (as operation above the flash point, operation above the auto-ignition point, quantity of flammable liquid, etc.). Proper description of this index is best found in the 57-page Dows Fire and Explosion Index, Hazard Classification Guide, 5 th ed., AIChE, New York, 1981. 

Flash points, lower and upper flammability limits, and autoignition temperature are important properties for determining safe operating limits when processing organic componnds. As with any property, experimental valnes are preferable to predicted values, and prediction techniques for these properties are only modestly accurate. 

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... 

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. 

The flash point of a multicomponent system cannot be determined by summing a simple fraction of the flash points of the individual components. If, however, the component flash points were defined by some temperature dependent property which might then be calculated for a multicomponent system, the flash point of that system might be predicted. 

An early approach to predicting TCC flash points for hydrocarbon mixtures used this concept by estimating flash point as the temperature at which mixture vapor pressure reached about 10 mm Hg (3). Other workers (4) have found both the product of vapor pressure at the flash point and molecular weight to be constant for a number of hydrocarbon fractions. The TCC flash point for hydrocarbon blends was predicted as the temperature at which... 

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. 

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. 

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. 

The U. S. Department of Transportation has announced (9) that future labeling regulations for flammable liquids may be based on their TCC flash points. If this change is made, the empirical calculation technique proposed here is expected to be equally applicable to predicting TCC data if the closed cup flash points of the individual solvents are substituted in basic calculation data. No attempts have yet been made to predict closed cup data, but one might expect that the vapor space in the closed cup would be more easily simulated than that in the open cup tester. 

Flash points of systems containing dissolved solids have not been considered in the present treatment. A more universal model would be necessary to quantify solvent-solute interactions and to predict flash point modification by solutes. Such a model would be valuable in screening total solvent-solute formulations. 

---