Pure component 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. 

Flash points can be estimated for multicomponent mixtures if only one component is flammable and if the flash point 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 points of mixtures cannot simply be deduced fi-om the data of the pure components. This is due to the quite complex relationship which describes the vapour pressure behaviour of mixtures. Only for the comparatively simple case of binary mixtures, algorithms are known which allow the caleulation of the flash-point with satisfying accuracy [e.g. 33]. 

For safety reasons numerous attempts have been made to raise the flash point of solvent mixtures [14.84]. Azeotropes having a lower flash point than those of the pure components can be formed on mixing solvents use of solvent mixtures to raise the flash point is therefore extremely problematic. The flash point of toluene can, for example, be significantly raised above 21 °C by adding chlorinated hydrocarbons [14.85], [14.86]. However, the flash point is first lowered instead of raised if dichloro-methane is added. Non-flammability is achieved only above a minimum addition of dichloromethane. 

However, small traces of toluene in mixed xylenes cause the mixture to have a flash point lower than the weighted average of its main components and the reproducibility of the test method means that a flash point of at least 24 C is normally required for satisfactory operation. In recovery operations, the effect of -butanol (pure flash point 35 C) and ethyl Cellosolve (pure flash point 40 °C), but which both... 

Flash point values quoted in the literature, in general, are for pure solvents. The presence of contaminants can have a significant effect on the flash point, particularly if the contaminant is relatively more volatile. For example, pure ethylene glycol has a flash point of 111°C. However, the flash point is reduced to 29°C when acetaldehyde at a level of only 2% is present. Similarly, when handling solvent mixtures, a small change in the composition can have a significant effect on the flash point. Thus, whenever possible, flash points should be measured when it is known or suspected that more than one component will be present. 

It is possible to estimate the flash point of a multicomponent mixture provided only one of the components is flammable and its flash point and vapour pressure/temperature relationship is known [5]. The flash point temperature of the mixture is estimated by determining the temperature of the mixture at which the vapour pressure of the flammable component in the mixture, obtained using Raoult s Law, is equal to its vapour pressure at its flash point. Thus to determine the flash point of a mixture of 75% methanol and 25% water by weight, it is necessary to know the flash point of methanol (11°C) and that its vapour at this temperature is 53 mmHg. The mole fraction, a, of the flammable component in the mixture is needed (in this case the mole fraction of methanol is 0.63) in order to apply Raoult s Law. This is used to calculate the vapour pressure (Psat) of pure methanol based on the partial pressure (p) required at the flash point ... 

Azeotropes. One solvent may form azeotropes with another solvent due to molecular association. This physical principle can be exploited in several ways. The most important in solvent applications is the possibility of reducing the boiling temperature (some azeotropes have lower boiling point) therefore an applied product such as a coating may lose its solvents and dry faster. The formation of such azeotrope also lowers flash point by which it increases hazards in product use. The formation of an azeotrope is frequently used to remove water from a material or a solvent. It affects the results of a distillation since azeotrope formation makes it difficult to obtain pure components from a mixture by distillation. Azeotrope formation can be suppressed by lowering the boiling point (distillation under vacuum). One benefit of azeotropic distillation is the reduction in the heat required to evaporate solvents. 

Vapor pressure data, P, of pure components are important in calculations relating to vapor-liquid phase equilibria, e.g., in the simplest case to predict the pressure in a closed vessel containing a specific liquid or mixture of liquids. P data are required for bubble point and most dew point computations. These values are used in flash calculations involving mass transfer operations. Clearly the design of pressure requirements for storage equipment requires knowledge of the vapor pressure of the components as does the design of appropriate pressure relief... 

In this chapter, we describe an algorithm for predicting feasible splits for continuous single-feed RD that is not limited by the number of reactions or components. The method described here uses minimal information to determine the feasibility of reactive columns phase equilibrium between the components in the mixture, a reaction rate model, and feed state specification. This is based on a bifurcation analysis of the fixed points for a co-current flash cascade model. Unstable nodes ( light species ) and stable nodes ( heavy species ) in the flash cascade model are candidate distillate and bottom products, respectively, from a RD column. Therefore, we focus our attention on those splits that are equivalent to the direct and indirect sharp splits in non-RD. One of the products in these sharp splits will be a pure component, an azeotrope, or a kinetic pinch point the other product will be in material balance with the first. 

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