Vapor pressure and volatilization

The preceding definition is applicable to other characteristics such as MON, vapor pressure and volatility characteristics such as E70 and El00. 

Substances with high vapor pressure evaporate rapidly. Those with low vapor pressure evaporate slowly. The impact of vapor pressure on the rate of evaporation makes vapor pressure a very important property in considering the tactical use and duration of effectiveness of chemical agents. A potential chemical agent is valuable for employment when it has a reasonable vapor pressure. One with exceptionally high vapor pressure is of limited use. It vaporizes and dissipates too quickly. Examples are arsine and carbon monoxide. On the other hand, mechanical or thermal means may effectively aerosolize and disseminate solid and liquid agents of very low vapor pressure. Vapor pressure and volatility are related. Translated into volatility, vapor pressure is most understandable and useful. 

By limiting the amount of hydrocarbons that are lower boiling than the main component, the vapor pressure control is reinforced. Tests are available for vapor pressnre 100°F (38°C) (ASTM D1267) and at 113°F (45°C) (IP 161). The limitation on the amonnt of higher-boiling hydrocarbons supports the volatility clause. The vapor pressure and volatility specifications will often be met automatically if the hydrocarbon composition is correct. 

The amount of ethylene is limited because it is necessary to restrict the amount of unsaturated components so as to avoid the formation of deposits caused by the polymerization of the olefin(s). In addition, ethylene [boiling point —104°C (—155°F)] is more volatile than ethane [boiling point —88°C (—127°F)], and therefore a product with a substantial proportion of ethylene will have a higher vapor pressure and volatility than one that is predominantly ethane. Butadiene is also undesirable because it may also produce polymeric products that form deposits and cause blockage of lines. 

Soil. The major soil metabolite is 2,6-dichlorobenzamide which degrades to 2,6-dichloro-benzoic acid. The estimated half-lives ranged from 1 to 12 months (Hartley and Kidd, 1987). Under field conditions, dichlobenil persists from 2 to 12 months (Ashton and Monaco, 1991). The disappearance of dichlobenil from a hydrosol and pond water was primarily due to volatilization and biodegradation. The times required for 50 and 90% dissipation of the herbicide from a hydrosol were approximately 20 and 50 d, respectively (Rice et al., 1974). Dichlobenil has a high vapor pressure and volatilization should be an important process. Williams and Eagle (1979) found... 

Grover, R., Spencer, W.F., Farmer, W., Shoup, T.D. (1978) Triallate vapor pressure and volatilization from glass surfaces. Weed Sci. 26, 505-508. 

The vapor pressure and volatility of mustard gas are low, as showm by the following tabulation ... 

The butanols and their methyl and ethyl ethers have several advantages as oxygenates over methanol and ethanol in gasoline blends. Their energy contents are closer to those of gasoline the compatibility and miscibility problems with petroleum fuels are nil excessive vapor pressure and volatility problems do not occur and they are water tolerant and can be transported in gasoline blends by pipeline without danger of phase separation due to moisture absorption. Fermentation processes (Weizmann process) have been developed for simultaneous production of 1-butanol, 2-propanol, acetone, and ethanol from... 

Volatility is expressed in terms of the temperature at which 95% of the sample is evaporated and presents a measure of the least volatile component present (ASTM D-1837). Vapor pressure (IP 410) is, therefore, a measure of the most extreme low-temperature conditions under which initial vaporization can take place. By setting limits on vapor pressure and volatility jointly the specification serves to ensure essentially single-component products for the butane and propane grades (ASTM D-1267, ASTM D-2598, IP 410). By combining vapor pressure/volatility limits with specific gravity for propane-butane mixtures, essentially two-component systems are ensured. 

The vapor pressures and volatilities of the various chemical threat agents are particularly relevant to their detection as airborne vapors. The volatility of sarin is comparable to that of water or volatile organic compounds such as limo-nene and cyclohexanone (24,000 to 28,000 mg m-3). In contrast, VX has a low volatility, on the order of long-chain aliphatic waxes (for example, the volatility of docosane [C22H46] is about 17 mg m-3). TICs of concern as threat agents typically have higher vapor pressures than many other chemical threat agents they could be attractive to attackers because they can be dispersed more easily than compounds with low vapor pressure. 

D. Zudkevitch, A. K. S. Murthy, J Gmehling. Thermodynamic aspects of reformulation of automotive fuels, Part 1. The effects of oxygenates on the vapor pressures and volatilities of gasolines. J. Hydrocarbon Processing, 93-100, June 1995. 

Vapor pressure and volatility Less than nitroglycerine. Nitro isobutyl glycerine trinitrate is little volatile at room temperature without odor. It is slightly volatile at 30 °C with odor of tar and acridity. The volatility is increased at elevated temperature. It is obviously volatile at 50 °C. Its volatility at 25 °C is 0.127 x 10 mg/ cm/day. The relationship of the volatility of nitro isobutyl glycerine trinitrate and temperature is shown in Fig. 5.19 and its vapor pressures are listed in Table 5.49. 

Vapor pressure and volatility about 1/2 of nitroglycerine Hygroscopicity 0.04 % in the relative humidity of 65 %... 

In normal applications of extractive distillation (i.e., pinched, closeboiling, or azeotropic systems), the relative volatilities between the light and heavy key components will be unity or close to unity. Assuming an ideal vapor phase and subcritical components, the relative volatility between the light and heavy keys of the desired separation can be written as the produc t of the ratios of the pure-component vapor pressures and activity-coefficient ratios whether the solvent is present or not ... 

As mentioned earlier the ease or difficulty of separating two products depends on the difference in their vapor pressures or volatilities. There are situations in the refining industry in which it is desirable to recover a single valuable compound in high purity from a mixture with other hydrocarbons which have boiling points so close to the more valuable product that separation by conventional distillation is a practical impossibility. Two techniques which may be applied to these situations are azeotropic distillation and extractive distillation. Both methods depend upon the addition to the system of a third component which increases the relative volatility of the constituents to be separated. 

Vapor Pressure and Relative Volatility of Various Components... 

Vapor pressure, which is the tendency of a liquid to release vapors to the surrounding area, goes down as MW increases but goes up as temperatures rise. By definition, the more volatile a liquid, the higher its vapor pressure and the lower its boiling point. Examples are ... 

This procedure is commonly used to calculate vapor pressures and activities for volatile mixtures. For example, it was used to determine the vapor pressures for the (ethanol + water) system shown in Figure 6.7. 

The vapor of an ideal mixture of two volatile liquids is richer than the liquid in the more volatile component. The contribution of each component to the total vapor pressure and its mole fraction in the vapor can be calculated by combining Raoulfs law and Dalton s law. 

Spencer WF, Shoup TD, death MM, et al. 1979. Vapor pressures and relative volatility of ethyl and methyl parathion. J Agric Food Chem 27 273-278. 

The following physico-chemical properties of the analyte(s) are important in method development considerations vapor pressure, ultraviolet (UV) absorption spectrum, solubility in water and in solvents, dissociation constant(s), n-octanol/water partition coefficient, stability vs hydrolysis and possible thermal, photo- or chemical degradation. These valuable data enable the analytical chemist to develop the most promising analytical approach, drawing from the literature and from his or her experience with related analytical problems, as exemplified below. Gas chromatography (GC) methods, for example, require a measurable vapor pressure and a certain thermal stability as the analytes move as vaporized molecules within the mobile phase. On the other hand, compounds that have a high vapor pressure will require careful extract concentration by evaporation of volatile solvents. 

Water-soluble volatile compounds may be involved, but vapor pressure and vapor density are not significant considerations in deep-well injection Greater than ambient temperatures. 

As previously discussed according to Henry s Law, as water solubility decreases and vapor pressure increases volatility will increase. Therefore a chemical like tetrachlorobiphenyl will have a... 

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