Benzene evaporation rate

A test tube (0.0125-m diameter, 0.15 m deep) contains benzene at 26°C. What is the benzene evaporation rate to 26°C dry air Use the benzene properties of Problem 11-23. 

Figure 1.7.9 shows the distributions of mass and removal process rates for these four scenarios. Clearly, when benzene is discharged into a specific medium, most of the chemical is found in that medium. Only in the case of discharges to soil is an appreciable fraction found in another compartment, namely air. This is because benzene evaporates fairly rapidly from soil without being susceptible to reaction or advection. 

A tank has ruptured and a pool of benzene has formed. The pool is approximately rectangular with dimensions of 20 ft by 30 ft. Estimate the evaporation rate and the distance affected downwind. Define the plume boundary using the TLV-TWA of 10 ppm. It is an overcast day with a 9 mph wind. The temperature is 90°F. 

Evaporation. The primary weathering process involved in the natural removal of oil from the sea is evaporation. It is particularly dominant soon after oil is released. Evaporation involves the transfer of hydrocarbon components from the liquid oil phase to the vapor phase. Estimates from major spills as well as experimental data indicate that evaporation may be responsible for the loss of up to 50% of a surface oil slick s volume during its life. Evaporation rates of oil at sea are determined by wind velocity, water and air temperatures, sea roughness, and oil composition. Some of the light, low-boiling hydrocarbons, such as benzene, toluene, and xylenes, which are rapidly lost through evaporation, are the most toxic. Thus, their removal decreases toxicity to marine life of the oil remaining on the surface. 

A test tube 1.25 cm in diameter and 15 cm deep contains benzene at 26°C and is exposed to dry atmospheric air at 26°C. Using the properties given in Prob. 11-4, calculate the evaporation rate of benzene in grams per hour. 

PROBABLE FATE photolysis C-C bond photolysis can occur, not important in aquatic systems, photooxidation by U.V. light in aqueous medium 90-95°C, time for the formation of CO2 (% theoretical) 24% 3 hr, 50% 17.4 hr, 75% 45.8 hr, photooxidation in air 9.24 hrs-3.85 days oxidation probably not an important process hydrolysis very slow, not important, first-order hydrolytic half-life 207 days volatilization not an important process, calculated half-life in water 4590 hr 25°C and 1 m depth, based on an evaporation rate of 1.5x10 m/hr sorption important for transport to anaerobic sludges, 30-40% adsorbed on aquifer sand 5°C after 3-100 hr equilibrium time, 75-100% disappearance from soils 3-10 yrs biological processes biotransformation is the most important process other reac-tions/interactions electrochemical reduction with products of benzene and gamma-TCCH has been studied... 

To have some idea of the magnitude of the evaporation rate, let us take an example of benzene evaporation from a test tube having a diffusion length of 10 cm. Air is flowing across the tube at a rate such that the mole fraction of benzene at the top of the tube is very close to zero. The temperature and the pressure of the system are 25 and 760 Torr, respectively. The vapor pressure of benzene at this temperature is 100 Torr. The molecular diffusivity of benzene in air at 25 °C and 760 Torr is 0.0962 cmVsec. 

The flux expressed in mole/cm /hr is hard to give us a feel about the evaporation rate. It would be useful to have it expressed in terms of liquid volume per unit time. Knowing the molecular weight of benzene is 78 g/mole, and its liquid density is 0.879 g/cc, the evaporation rate of benzene is... 

Let us study the evaporation rate at another total pressure to investigate numerically the pressure dependence. We take a case of sub-ambient pressure with P = 300 Torr. The temperature is remained the same at 25 °C. With this new condition, the mole fraction of benzene right above the gas-liquid interface is ... 

Thus, the molar evaporation rate is higher when the total pressure is decreased. This is solely due to the increase in the mole fraction of benzene at the liquid interface (from 0.13 in the last example to 0.33 in this example). The increase in the molecular diffusivity as the total pressure increases is exactly compensated by the decrease in the total molar concentration. 

Figure 15.15 A liquid with weak intermolecular forces, such as benzene, is placed in an Erlenmeyer flask, which is then closed with a rubber stopper. At constant temperature and surface area, the liquid begins to evaporate at a constant rate. This rate is represented by the fixed length of the arrows pointing upward from the liquid in each view of the flask. It is also shown as the horizontal line in the graph of evaporation rate versus time. 

The benzene-toluene example gave low rates of transfer relative to the absolute evaporation rate, because (1) the interchange process introduces diffusional resistance and (2) the vapor approaches equilib-... 

Solvents (thinners) are volatile organic liquids which dissolve the binder or film former. They are used to liquefy the pigment/binder mixture suffieiently to allow the formation of a uniform film. The most commonly used thinners are organic solvents with the exception of benzene (e.g., hydrocarbons, alcohols, esters, and ketones) and water (in latex emulsions and water-soluble paints). The choice of solvent is not only based on solvency, but also on other important factors such as toxicity, odor, evaporation rate, flammability, and cost. ... 

Typical pure aromatic hydrocarbons include benzene, toluene, and xylene typical pure aliphatic hydrocarbons are hexane, heptane, and odorless mineral spirits. Ordinary mineral spirits are mostly aliphatic hydrocarbons. In the United States, aromatic and aliphatic hydrocarbons are usually derived fi"om petroleum by heat distillation. They are generally used as a mixture of aliphatic and aromatic components available in an extensive range of solvent strengths and evaporation rates. 

Example 3.3-1 Errors caused by neglecting convection Consider the experiments shown in Fig. 3.3-5. How much error is caused by calculating the rate of benzene evaporation if... 

Example 9.5-1 Fast benzene evaporation Benzene is evaporating from a flat porous plate into pure flowing air. Using the film theory, estimate how much a concentrated solution increases the mass transfer rate beyond that expected for a simple theory. Then calculate the resulting change in the mass transfer coefficient defined by Eq. 9.5-2. In other words, find (Vi/k ci, and k/k as a function of the vapor concentration of benzene at the surface of the plate. 

The reaction mixture is cooled to —15° 3° and 116 g. (1.16 moles) of concentrated sulfuric acid is added with vigorous stirring over approximately 1 hour at such a rate that the reaction temperature is maintained at —15°. The reaction mixture is allowed to warm to room temperature over a 4-hour period and to stir for another 4 hours at room temperature. The precipitate is removed by suction filtration and the filtrate is concentrated on a rotary evaporator under reduced pressure at 30-40°. The residual oil is dissolved in benzene and washed with water, The benzene layer is dried over anhydrous sodium sulfate and the benzene is removed by distillation. Further distillation under reduced pressure yields 30-32 g. (66-70%) of methyl nitroacetate, b.p. 80-82° (8 mm.). 111-113° (25 mm.) (Note 5). 

These facts suggest that variable recoveries of parathion from the evaporation procedure, as used routinely, should be expected. In general, however, the recovery data did not demonstrate a clear-cut distinction between acetone and benzene for the purpose at hand. A slow steady loss of parathion in proportion to the volume of either solvent evaporated (1) was not noted, which would indicate that the rate of evaporation is also important. The final decision as to solvent was determined by certain incidental properties of the parathion. 

Anderson and Kemball (35) examined the reaction between gaseous deuterium and benzene catalyzed by evaporated films of iron, nickel, palladium, silver, tungsten, and platinum. The order of reactivity (estimated from the temperature at which the addition reaction achieved an initial rate of 1% per minute for a 10 mg film at certain specified reactant... 

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