Pressure example

The vapor pressure of a compound is important in determining the upper limit of its concentration in the atmosphere. High vapor pressures will permit higher concentrations than low vapor pressures. Examples of organic compounds are methane and benzo[fl]pyrene. Methane, with a relatively high vapor pressure, is always present as a gas in the atmosphere in contrast, benzo[fl]pyrene, with a relatively low vapor pres.surc, is. id-... 

Figure 8-19. X-y diagram for benzene in benzene-toluene mixture at 760 mm Hg total pressure, Example 8-5.

The AA-BB polyamides are nearly always prepared using bulk polymerization with a prepolymerization step at higher pressure, although not every laboratory has die facility to carry out a polymerization in an autoclave. Nielinger50 has reported bulk polymerization of PA-6,1 from its salt solution at atmospheric pressure (Example 11). This mediod may also be usable for other laboratory polymerizations like PA-6,6. 

The partial pressure of a component in a gas mixture is its mole fraction times the total pressure. Example illustrates calculations with gas mixtures. 

If chemical-specific information is not available, the consequences may be able to be predicted by methods using compatibility groups, or chemicals with similar chemical structures that are expected to have similar chemical reactivity characteristics. One computerized tool that uses this approach is the Chemical Reactivity Worksheet made available by the U.S. National Oceanic and Atmospheric Administration (NOAA 2002). This program has over 6000 chemicals, mixtures, and solutions included in its database. It also predicts chemical reaction consequences of combining two materials at a time (e.g., "Heat generation by chemical reaction, may cause pressurization"). Examples from the Chemical Reactivity Worksheet are shown in Section 4.2. It is critical that all chemicals be positively identified to have a complete evaluation of all potential incompatibilities. 

Figure 11.29. Enthalpy-composition diagram for ammonia-water at 1.0 MN/m2 pressure (Example 11.10)...

The tabulated values maybe used for prediction and calculation of vapor pressure. Examples are shown in Table 2-2. 

If the pump is protected using a diaphragm-type pressure switch, then the pump will be switched on automatically. If a combination of roots pump and roughing pump is to convey highly volatile substances such as liquids with a low boiling point, then it is advisable to use a roots pump which is equipped with an integral bypass line and a valve which will respond to a pre-set pressure. Example Roots vacuum pumps RUVAC WAU / WSU. 

Predict the relative value of the vapor pressure, Example 8.1... 

The formylation reaction of vinylic, aryl, and heterocyclic halides proceeds in good yields, generally at 115 to 150° under several hundred pounds pressure. The hydrogenation does not take place at atmospheric pressure. Examples of the formylation reaction appear in Table IV. 

In several other instances, a direct relationship between the reaction outcome and pressure was not observed. In two cases, an optimum was found for the reaction rate (Ikushima et al., 1996 Yoon et al., 1996). As was the case for the effects of temperature, while many of the products became more soluble as pressure increases, sometimes the enzyme activity and stability are adversely affected by the increased pressure. Examples of enzymatic stabilities at various reaction conditions may be seen in Table 6.2. 

The negative derivative with respect to distance of the Gibbs energy of interaction per unit area yields a force per unit area between colloidal species, termed the disjoining pressure . Example In a thin liquid film, the disjoining pressure equals the pressure, beyond the external pressure, that has to be applied to the liquid in the film to maintain a given film thickness. 

Iron catalysts have found only limited use in usual hydrogenations, although they play industrially important roles in the ammonia synthesis and Fischer-Tropsch process. Iron catalysts have been reported to be selective for the hydrogenation of alkynes to alkenes at elevated temperatures and pressures. Examples of the use of Raney Fe, Fe from Fe(CO)5, and Urushibara Fe are seen in eqs. 4.27,4.28, and 4.29, respectively. 

Over nickel catalysts, aromatic carboxylic acids can be hydrogenated without difficulty as their sodium salts. Thus, e>-179 and m-toluic acids,180 m-hydroxybenzoic acid,181 and tetrephthalic acid182 were hydrogenated to the corresponding saturated acids in high yields over Raney Ni at elevated temperatures and pressures. Examples are shown in eqs. 11.47 and 11.48. o-Toluic acid and terephthalic acid afforded the trans acids predominantly under these conditions. 

Related Calculations. This illustration outlines the procedure for obtaining coefficients of a liquid-phase activity-coefficient model from mutual solubility data of partially miscible systems. Use of such models to calculate activity coefficients and to make phase-equilibrium calculations is discussed in Section 3. This leads to estimates of phase compositions in liquid-liquid systems from limited experimental data. At ordinary temperature and pressure, it is simple to obtain experimentally the composition of two coexisting phases, and the technical literature is rich in experimental results for a large variety of binary and ternary systems near 25°C (77°F) and atmospheric pressure. Example 1.21 shows how to apply the same procedure with vapor-liquid equilibrium data. 

Pressure may be used in two quite different ways to influence solid state reactions or chemical reactions in general. One way is to apply mechanical pressure directly, either uniaxial or hydrostatically. To some extent, but with different intention, this is already done when a reaction mixture is pressed into pellets. A second way of using pressure as parameter in a reaction is the application of a gaseous reactant under increased pressure. Examples will be given in subsequent sections of this chapter. 

The simplest case of a genuine nonequilibrium system is one with uniform and time constant temperature and pressure. Examples include open or closed systems that consist of low intensive ( sluggish ) chemical processes where molecules of the initial reactants, final products, and intermediates may all be considered thermalized. 

T. Kimura et al. tested a large number of candidate materials as adducts. They can drastically reduce the melting point of the Sr(thd)2 and increase the vapor pressure examples are triethylenetetramine (trien) or tetraethylenepentamine (tetraen). The decrease in melting point of the precursor indicates that... 

Heating of white phosphorus in the absence of air gives red phosphorus, an amorphous material that exists in a variety of polymeric modifications. Still another al-lotrope, black phosphoms, is the most thermodynamically stable form it can be obtained from white phosphorus by heating at very high pressures. Black phosphorus converts to other forms at still higher pressures. Examples of these structures are shown in Figure 8-23. The interested reader can find more detailed information on allotropes of phosphorus in other sources." ... 

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