Sulfuric acid vapor pressure

Acid Dew Point For fossil fuels, the acid dew point temperature is that temperature at which the actual mixed acid vapor pressure equals the mixed acid vapor saturation pressure. The mixed acid dew point can be approximated by the sulfuric acid dew point (Fig. 24-56). It can be described as a function of the SO3 and water content of the flue gas (Huijbregts). These concentrations result from the sulfur, hydrogen, and free water content of the fuel the relative humidity of the air and the amount of excess air used. Using the equation of Ver-hoff, where T is degrees K and P is mm Hg (see OUces, A.G.) ... 

When two or more condensable species present simultaneously in the gas are strongly interacting, nucieation can take place at partial pressures much lower than those required for the nucieation of the pure vapors. A well-known example is the water vapor-sulfuric acid vapor system. The details of this process, known as helewmolerular nucieation, are beyond the scope of this text (Reiss, 1950). 

A tabulation of the partial pressures of sulfuric acid, water, and sulfur trioxide for sulfuric acid solutions can be found in Reference 80 from data reported in Reference 81. Figure 13 is a plot of total vapor pressure for 0—100% H2SO4 vs temperature. References 81 and 82 present thermodynamic modeling studies for vapor-phase chemical equilibrium and liquid-phase enthalpy concentration behavior for the sulfuric acid—water system. Vapor pressure, enthalpy, and dew poiat data are iacluded. An excellent study of vapor—liquid equilibrium data are available (79). 

Fig. 13. Vapor pressure of sulfuric acid (81). To convert Pa to mm Hg, multiply by 0.0075.

The sulfur trioxide produced by catalytic oxidation is absorbed in a circulating stream of 98—99% H2SO4 that is cooled to approximately 70—80°C. Water or weaker acid is added as needed to maintain acid concentration. Generally, sulfuric acid of approximately 98.5% concentration is used, because it is near the concentration of minimum total vapor pressure, ie, the sum of SO, H2O, and H2SO4 partial pressures. At acid concentrations much below 98.5% H2SO4, relatively intractable aerosols of sulfuric acid mist particles are formed by vapor-phase reaction of SO and H2O. At much higher acid concentrations, the partial pressure of SO becomes significant. 

Oleum Ma.nufa.cture, To produce fuming sulfuric acid (oleum), SO is absorbed in one or more special absorption towers irrigated by recirculated oleum. Because of oleum vapor pressure limitations the amount of SO absorbed from the process gas is typically limited to less than 70%. Because absorption of SO is incomplete, gas leaving the oleum tower must be processed in a nonfuming absorption tower. 

Reaction of myrcene and sulfur dioxide under pressure produces myrcene sulfone. This adduct is stable under ordinary temperatures and provides a way to stabilize the conjugated diene system in order to hydrate it with sulfuric acid. The myrcene sulfone hydrate produced is pyrolyzed in the vapor phase in order to regenerate the diene system to produce myrcenol [543-39-5] (50). 

The activity coefficients of sulfuric acid have been deterrnined independentiy by measuring three types of physical phenomena cell potentials, vapor pressure, and freeting point. A consistent set of activity coefficients has been reported from 0.1 to 8 at 25°C (14), from 0.1 to 4 and 5 to 55°C (18), and from 0.001 to 0.02 m at 25°C (19). These values are all based on cell potential measurements. The activity coefficients based on vapor pressure measurements (20) agree with those from potential measurements when they are corrected to the same reference activity coefficient. 

Table 1 gives the calculated open circuit voltages of the lead—acid cell at 25°C at the sulfuric acid molalities shown. The corrected activities of sulfuric acid from vapor pressure data (20) are also given. 

Beryllium Sulfate. BeiyUium sulfate tetiahydiate [7787-56-6], BeSO TH O, is produced commeicially in a highly purified state by fiactional crystallization from a berylhum sulfate solution obtained by the reaction of berylhum hydroxide and sulfuric acid. The salt is used primarily for the production of berylhum oxide powder for ceramics. Berylhum sulfate chhydrate [14215-00-0], is obtained by heating the tetrahydrate at 92°C. Anhydrous berylhum sulfate [13510-49-1] results on heating the chbydrate in air to 400°C. Decomposition to BeO starts at about 650°C, the rate is accelerated by heating up to 1450°C. At 750°C the vapor pressure of SO over BeSO is 48.7 kPa (365 mm Hg). 

It has good capacity and drying capabiHty as illustrated by the vapor pressure curves in Figure 5. At 25°C, the dew point attainable in gases dried with 95% sulfuric acid is less than —75°C. 

Fig. 5. Vapor pressure of water over sulfuric acid solutions. Percentage of H2SO4 noted on each curve.

Vapor Pressures of the System Water-Sulfuric Acid-Nitric... 

FIG. 2-30 Entbalpy-concentration diagram for aqueous sulfuric acid at 1 atm. Reference states enthalpies of pure-bquid components at 32 F and vapor pressures are zero. NOTE It should be observed that the weight basis includes the vapor, which is particularly important in the two-phase region. The upper ends of the tie bnes in this region are assumed to be pure water. (Hougen and Watson, Chemical Process Principles, I, Wiley, New York, 1943. )... 

Volatile organic compounds (VOCs) include organic compounds with appreciable vapor pressure. They make up a major class of air pollutants.I his class includes not only pure hydrocarbons but also partially oxidized hydrocarbons (organic acids, aldehydes, ketones), as well as organics containing chlorine, sulfur, nitrogen, or other atoms in the molecule. 

Determining the potential for dangerous interactions is not always easy. Take concentrated sulfuric acid as an example. By itself, it is very stable unless heated to high temperatures. It is nonflammable, and has a fairly low vapor pressure. However, mix it with water, or worse, a caustic solution, and it can rupture a tank in seconds. The key to evaluating the reactive hazard in this example is to first identify that both concentrated sulfuric acid and caustic are present. Then, safeguards can be put in place to ensure the two materials do not come into uncontrolled contact. 

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