Effects of Relative Volatilities

All Other parameters are kept the same as the base case column configuration, pressure, tray holdup, and conversion. 

Two types of changes in relative volatilities are considered in this section. The first is a simple change from the value of 2 for the relative volatilities of adjacent components. As expected, energy requirements increase as the separation becomes more difficult. The second type of change is when the volatilities are temperature dependent. In this case. 

TABLE 23 Coefficienls and Vapor Boilup Required for Constant uca and Obd Cases 

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Figure 1.1 Hie relative volatility concert, (a) Concentration the more-volatile component (MVC) in the vapor. (6) Effect of relative volatility on the concentration of the MVC in the vapor.

Effect of Relative Volatility on Required Stages for a Typical Separation... 

Next the effects of relative volatilities on the optimal trajectory are examined. Fig. 2B shows that, for fixed reactor outlet temperature, changes in the relative volatility of intermediate key (B) from aB=1.5 to aB=3 do not produce significant difference. Because a larger ae results in a lesser separation cost and, therefore, the trajectory converges to center line at a lower conversion, but not by much. 

Figure 8.1.28. Effect of relative volatility and viscosity on plate efficiency of fractionating columns. Reprinted, with permission, from O Connell, Trans. AlChE, 42, 741 (1946). Copyriffit (1946] American Institute of Chemical Engineers (AIChE).

B. Kaymak, W. L. Luyben, and O. J. Smith IV, Effect of relative volatility on the quantitative comparison of reactive distillation and conventional multi-unit systems, Ind. Eng. Chem. Res. 43, 3151-3162 (2004). 

Although SPME was applied initially for the analysis of relatively volatile environmental pollutants in waters, rapid developments have enabled SPME to be successfully applied for the analysis of pesticides in water, wine and more complex food samples such as honey, fruit juice and pears, vegetables and strawberries. With food samples, most analysts recognize the need for some sample pretreatment in order to minimize matrix effects. The matrix can affect the SPME efficiency, resulting in a reduced recovery of pesticides. The most common method is simply to dilute the sample or sample extract with water. Simpltcio and Boas comminuted pears in water prior to the determination of pesticides. Volante et al. extracted over 100 pesticides... 

Pankow, J. F., J. M. E. Storey, and H. Yamasaki, Effects of Relative Humidity on Gas/Particle Partitioning of Semi-Volatile Organic Compounds to Urban Particulate Matter, Environ. Sci, Technol., 27, 2220-2226 (1993). 

This equation relates a so-called improvement factor, the logarithm of the ratio of relative volatility with and without salt present, to the salt concentration in the liquid phase under the condition of fixed mixed-solvent composition, by a salt effect parameter k. Usually, the added salt lowers the volatility of both components in the liquid phase. If the extent of this lowering is different for... 

Neglecting vapor-phase corrections and the Poynting effect, the relative volatility between the key components in the presence of the solvent is... 

In analytical distillation it should be the aim to achieve a maximum separating effect the relative volatility should therefore be as large as possible, and in an ideal mixture this is so at the pressure at which the ratio of the vapour pressures is a maxi-... 

If membrane permeability or selectivity is introduced in lieu of relative volatility, then the effect would seemingly enhance the separation, as follows ... 

Accidental exposures to concentrations higher than the TLV should be treated by prompt removal to fresh air. Severe exposures requiring medical attention should not be treated with stimulants or adrenaline, since high concentrations of these fluorocarbons may result in a sensitization of the heart to adrenaline (a relatively common effect of many volatile organic compounds). 

To study the effect of the temperature dependency of relative volatilities on the steady-state design of both flowsheets, the relative volatilities between adjacent components are assumed to be 2 at a temperature of 320 K but become smaller at higher temperatures. The 320 K temperamre is chosen because it corresponds to the normal reflux-dmm temperature that can be achieved in a distillation column while using cooling water in the condenser. The distillation columns of the conventional system can operate at this temperature and the same pressures as used in the base case conditions. 

Reactions with the heavy reactant decomposing into lighter products, HK LK + IK, is the more general case in ternary decomposition reactions. This type of relative volatility may have adverse effects on column design because the heavy reactant tends to stay in the lower part of the column. This makes it difficult to remove light products from the column base. 

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