Volatilization, rapid

The Henry s law constant value of 2.Ox 10 atm-m /mol at 20°C suggests that trichloroethylene partitions rapidly to the atmosphere from surface water. The major route of removal of trichloroethylene from water is volatilization (EPA 1985c). Laboratory studies have demonstrated that trichloroethylene volatilizes rapidly from water (Chodola et al. 1989 Dilling 1977 Okouchi 1986 Roberts and Dandliker 1983). Dilling et al. (1975) reported the experimental half-life with respect to volatilization of 1 mg/L trichloroethylene from water to be an average of 21 minutes at approximately 25 °C in an open container. Although volatilization is rapid, actual volatilization rates are dependent upon temperature, water movement and depth, associated air movement, and other factors. A mathematical model based on Pick s diffusion law has been developed to describe trichloroethylene volatilization from quiescent water, and the rate constant was found to be inversely proportional to the square of the water depth (Peng et al. 1994). 

Simple models are used to Identify the dominant fate or transport path of a material near the terrestrial-atmospheric Interface. The models are based on partitioning and fugacity concepts as well as first-order transformation kinetics and second-order transport kinetics. Along with a consideration of the chemical and biological transformations, this approach determines if the material is likely to volatilize rapidly, leach downward, or move up and down in the soil profile in response to precipitation and evapotranspiration. This determination can be useful for preliminary risk assessments or for choosing the appropriate more complete terrestrial and atmospheric models for a study of environmental fate. The models are illustrated using a set of pesticides with widely different behavior patterns. 

Volatilization volatilizes rapidly from water and land (Howard 1989). 

The dominant fate process for chloroform in surface waters is volatilization. Chloroform present in surface water is expected to volatilize rapidly to the atmosphere. An experimental half-disappearance range of 18-25 minutes has been measured for volatilization of chloroform from a 1 ppm solution with a depth of 6.5 cm that was stirred with a shallow pitch propeller at 200 rpm at 25 °C under still air ( 0.2 mph air currents) (Dilling 1977 Dilling et al. 1975). Using the Henry s law constant, a half-life of 3.5 hours was calculated for volatilization from a model river 1 meter deep flowing at 1 meter/second, with a wind velocity of 3 m/second, and neglecting adsorption to sediment (Lyman et al. 1982). A half-life of 44 hours was estimated for volatilization from a model pond using EXAMS (1988). 

The separation of disaccharides and higher oligomers is not essentially different from the separation of monosaccharides, except that the volatility rapidly decreases with increasing molecular weight. Oligosaccharides may be transformed into volatile derivatives, commonly the trimethylsilyl ethers, either directly or after reduction. Other derivatives, such as trifluoroacetates, have been used, but the acetates have low volatility. Oligosaccharides are not usually converted into their methyl glycosides prior to trimethylsilylation. Detailed examples are listed in Table VII (see p. 130). 

The berry or the small fruits consist of strawberry, raspberry, blackberry, black currant, blueberry, cranberry and elderberry. The volatiles responsible for the flavour of small fruits are esters, alcohols, ketones, aldehydes, terpenoids, furanones and sulfur compounds (Table 7.3, Figs. 7.1-7.7). As fruit ripen, the concentration of aroma volatiles rapidly increases, closely following pigment formation [43]. 

Ammonium Bicarbonate occurs as white crystals or as a crystalline powder. It volatilizes rapidly at 60°, dissociating into ammonia, carbon dioxide, and water, but it is quite stable at room temperature. One gram dissolves in about 6 mL of water. It is insoluble in alcohol. 

If released to ambient air, acetonitrile will remain in the vapor phase where it will be degraded through reaction with photochemically produced hydroxyl radicals. The half-life of acetonitrile in ambient air has been estimated to be 620 days. If released to soil, acetonitrile is expected to volatilize rapidly. Biodegradation in soil is not expected to be a major degradation pathway. If released to water, acetonitrile is not likely to adsorb to soil and sediment particles. Acetonitrile is expected to be removed from water bodies through volatilization as the chemical hydrolysis and bioaccumulation potential for this chemical are low. 

Rasmussen et al. 1983). 1,1,1 -Trichloroethane removed by rain water would be expected to re-volatilize rapidly to the atmosphere. Because of its long half-life of 4 years in the atmosphere (see Section 5.3.2.1), tropospheric 1,1,1-trichloroethane will be transported to the stratosphere, where it will participate in the destruction of the ozone layer. It will also undergo long-distance transport from its sources of emissions to other remote and rural sites. This is confirmed by the detection of this synthetic chemical in forest areas of Northern and Southern Europe and in remote sites (Ciccioli et al. 1993). 

PROBABLE FATE photolysis not important except as photooxidation, C-Cl bond can photolyze slowly oxidation rapid tropospheric photooxidation by hydroxyl radicals yields many products, probable predominant fate hydrolysis too slow to be significant volatilization rapid volatilization is the major transport process, half-life from a model river 3 hr biological processes very low potential for bioaccumulation, and biodegradation is probably too slow to be significant evaporation from water 25°C of 1 ppm solution 50% after 24 min. and 90% after 83 min. evaporation half-life from 1 ppm aqueous solution 25 C, still air, and an average depth of 6.5 cm 24 min. adsorption to sediment probably not important considerable dispersal from source areas expected to occur... 

Hash devolatilization is a simple and effective method to remove the majority of solvent and unreacted monomers from the polymer solution. Product from the reactor is charged to a flash vessel and throttled to vacuum conditions whereby the volatile solvent and monomers are recovered and condensed. In the process, the polymer melt cools, sometimes considerably, due to the evaporation of volatiles. The polymer product is pumped from the bottom of the flash vessel with a gear pump or other suitable pump for viscous materials. Critical to operation of the flash devolatilization unit is prevention of air back into the unit that reduces stripping ability and potentially allows oxygen into the unit that can discolor products or pose a safety hazard if low autoignition temperature solvents are used. Often one flash devolatilization unit is insufficient to reduce the residual material to a sufficient level and thus additional units can be added in series [61]. In each vessel, the equilibrium concentration of volatile material in the polymer melt, is a function of the pressure and temperature the flash unit operates at, with consideration for the polymer solvent interaction effects described by the Hory-Huggins equation. Flash devolatilization units, while simple to operate, may be prone to foam development as the superheated volatiles rapidly escape from the polymer melt. Viscous polymers or polymers with mixed functionalities... 

Laboratory studies have demonstrated that tetrachloroethylene volatilizes rapidly from water (Chodola et al. 1989 Dilling 1977 Dilling et al. 1975 Okouchi 1986 Roberts and Dandliker 1983 Zytneretal. 1989b). One study found that only 2.7% of the initial mass of tetrachloroethylene remained in stagnant water with a surface-to-volume ratio of 81 m /m after 4.5 hours (Zytner et al. 1989b). Dilling et al. 

Contamination of drinking water supplies with tetrachloroethylene varies with location and with the drinking water source (surface water or groundwater). Generally higher levels are expected in groimdwater because tetrachloroethylene volatilizes rapidly from surface water. The EPA has estimated that approximately 5.3% of the U.S. population using public water supplies is exposed to tetrachloroethylene levels above 0.5 pg/L (0.5 ppb), and 0.4% are exposed to levels above 5 pg/L (5 ppb)... 

Vapour density is the concentration of a chemical in the air. When the concentration reaches a maximum, the vapour is saturated. The vapour density of a compound in the soil air determines the volatilization rate. Some chemicals require only a low total soil concentration to have a saturated vapour in moist soil. Thus, weakly absorbed compounds may volatilize rapidly, especially if applied only to soil surface. If the chemicals are incorporated into... 

In a vacuum reactor, heat transfer becomes more difficult because of the absence of a medium for convection, however. As a consequence, this type of reactor is characterized by slower heating rates. Still, it is possible for the vacuum pump to remove organic volatiles rapidly. Typically, bio-oU yields in vacuum reactors stay in the range 60-65 wt.%. Despite its use on the lab scale, the vacuum pump requirements make the vacuum reactors very difficult to scale up. 

Flux quantity may also be of concern in the wave-soldering process for yet another reason fire hazard. Flux-laden boards are preheated going into the wave. If the flux application is too heavy, the flux may drip onto preheater elements. This may cause the flux to volatilize rapidly, combine with oxygen in the atmosphere, and provide the right conditions for flame initiation. Even if there is not direct exposure of the liquid flux to preheaters, if the quantity of volatile, flammable components is high enough to be an ignition source, then an explosive condition may develop. With the advent of more eco-friendly, water-based fluxes, fire hazard is less of a concern. 

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