At Elevated Pressure

Westerholt etal. [32] compared magnetic transition temperatures as a function of lattice constant in polycrystalline and single crystalline EuSe under hydrostatic pressure (p = 0 to 

Tc increases from 6.4 K at 14 kbar through 8.3 K at 20 kbar (range of suggested canted spin structure) to 13.2 K at 37 kbar. The increase of Tc has been correlated with a strong increase in the magnitude of the transferred hyperfine fields, Moser etal. [33]. 

The temperature T of the antiferromagnetic-ferrimagnetic transition in single crystals at 

It is not certain whether an additional magnetic phase induced by uniaxial stress exists, see p. 219. 

Vogt (Proc. Intern. Conf. Phys. Semicond., Exeter, Engl., 1962, pp. 727/31). 

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The theory and appHcation of SF BDV and COV have been studied in both uniform and nonuniform electric fields (37). The ionization potentials of SFg and electron attachment coefficients are the basis for one set of correlation equations. A critical field exists at 89 kV/ (cmkPa) above which coronas can appear. Relative field uniformity is characterized in terms of electrode radii of curvature. Peak voltages up to 100 kV can be sustained. A second BDV analysis (38) also uses electrode radii of curvature in rod-plane data at 60 Hz, and can be used to correlate results up to 150 kV. With d-c voltages (39), a similarity rule can be used to treat BDV in fields up to 500 kV/cm at pressures of 101—709 kPa (1—7 atm). It relates field strength, SF pressure, and electrode radii to coaxial electrodes having 2.5-cm gaps. At elevated pressures and large electrode areas, a faH-off from this rule appears. The BDV properties ofHquid SF are described in thehterature (40—41). 

The gasification is performed usiag oxygen and steam (qv), usually at elevated pressures. The steam—oxygen ratio along with reaction temperature and pressure determine the equiUbrium gas composition. The reaction rates for these reactions are relatively slow and heats of formation are negative. Catalysts maybe necessary for complete reaction (2,3,24,42,43). 

In a combined power cycle operation, clean (sulfur- and particulate-free) gas is burned with air in the combustor at elevated pressure. The gas is either low or medium heat-value, depending on the method of gasification. 

Carbon dioxide, the final oxidation product of carbon, is not very reactive at ordinary temperatures. However, in water solution it forms carbonic acid [463-79-6] H2CO2, which forms salts and esters through the typical reactions of a weak acid. The first ionization constant is 3.5 x 10 at 291 K the second is 4.4 x 10 at 298 K. The pH of saturated carbon dioxide solutions varies from 3.7 at 101 kPa (1 atm) to 3.2 at 2,370 kPa (23.4 atm). A soHd hydrate [27592-78-5] 8H20, separates from aqueous solutions of carbon dioxide that are chilled at elevated pressures. 

Overall comparison between amine and carbonate at elevated pressures shows that the amine usually removes carbon dioxide to a lower concentration at a lower capital cost but requires more maintenance and heat. The impact of the higher heat requirement depends on the individual situation. In many appHcations, heat used for regeneration is from low temperature process gas, suitable only for boiler feed water heating or low pressure steam generation, and it may not be usefiil in the overall plant heat balance. 

Because of the low boiling point of ethylene oxide, reactions are generally conducted in stirred autoclaves at elevated pressures. Economic Aspects. A breakdown of saUent 1987 world supply and demand figures for HEC is given in Table 5. 

The laboratory units that have been employed to date for these experiments were designed to operate at a total system pressure of about 100 kPa (1 atm) and at near-ambient temperatures. In practical situations, it may become necessaiy to design a laboratory absorption unit that can be operated either under vacuum or at elevated pressures and over a reasonable range of temperatures in order to apply the Danckwerts method. 

There are two types of FBC unit distinguished by their operating flow characteristics bubbling and circulating. These two types operate at atmospheric pressure, AFBC, or at elevated pressure, PFBC. Pressures for PFBC are in the range 0.6 to 1.6 MPa (90 to 240 psia). Typical superficial fluidizing velocities are tabulated as follows. 

At elevated pressure, the partial pressure of carbon dioxide inhibits calcination, and siilfur dioxide is captured by displacement of the carbonate radical. The overall effect is similar except, as no free hme is formed, the resulting sorbent ash is less alkahne, consisting solely of CaS04 and CaC03. 

The most common heterogeneous catalytic reaction is hydrogenation. Most laboratory hydrogenations are done on liquid or solid substrates and usually in solution with a slurried catalyst. Therefore the most common batch reactor is a stirred vessel, usually a stirred autoclave (see Figure 2.1.1 for a typical example). In this system a gaseous compound, like hydrogen, must react at elevated pressure to accelerate the process. 

The previous example was a rather unique application and not a typical case for fluidization. Although some fluidized bed reactions are executed at elevated pressure, like the naphtha reforming, most are used at atmospheric or at low pressures. The proceeding conceptual sketch. Figure 8.2.4, gives the most important features of a fluid-bed, cataljdic reactor. 

On the other hand, Mary, a research process development engineer, does not consider Joe s system to be inherently safer, because a truly inherently safer system would not require an interlock at all. The process uses flammable materials and operates at elevated pressure. Mary, looking at the entire process, would only consider it to be inherently safer if the flammable materials were eliminated or the process was operated at ambient pressure. Mary is considering the inherent safety characteristics of the entire process, rather than a single interlock system. 

Figure 21 DSC melting curves at atmospheric pressure for PE-ethyl cellulose mixture crystallized at elevated pressure. (a) 100 MPa (b) 150 MPa (c) 300 MPa (d) 400 MPa and (e) 750 MPa. (From Ref. 117.)...

Figure 9-79D. COg absorption from atmosphere effect of flow rates on Koa at elevated pressure. Reproduced by permission of the American Institute of Chemical Engineers, Spector, N. A., and Dodge, B. F., Trans. A.I.Ch.E., V. 42 (1946) p. 827 all rights resenred.

Obviously, the kinetics developed above apply to the specific catalyst used by those investigators. As the catalyst changes, the values of the factors (A, B, D, E, A, and B ) change. Furthermore, investigations at elevated pressures (12) indicated that these factors also vary with total pressure. 

B.H. Sage, Phase Behavior in Binary and Multi-component Systems at Elevated Pressures n-Pentane and Methane-m-Pentane , NSRDS-NBS 32 (1970) 20)A.S. Mal tseva et al,... 

M6. Matzner, B., Basic experimental studies of boiling fluid flow and heat transfer at elevated pressures, TID 12574, Columbia Univ. (1961). 

The main method of PA synthesis is by melt polymerization. The polymerization of PA-6,6 occurs in two stages, a prepolymerization of the PA salt at elevated pressures followed by a melt polymerization at atmospheric pressure. The prepolymerization stage requires an autoclave, preferably with a glass insert. The glass insert allows easy extraction of the polymer. PA-6 polymerization is simple it can be carried out at atmospheric pressure, and the evaporating water stirs the reaction medium. 

Figure 3.24 Influence of PA-6 polymerization process on relative viscosity as function of reaction time (i) atmospheric in VK column (ii) prepolymerization atmospheric followed by water removal (iii) prepolymerization at elevated pressure followed by water removal.31...

Many high-pressure reactions are done neat, but if a solvent is used, the influence of pressure on that solvent is important. The melting point generally increases at elevated pressures, which influences the viscosity of the medium (viscosity of liquids increases approximately two times per kilobar increase in pressure). Controlling the rate of diffusion of reactants in the medium is also important. In most reactions, pressure is applied (5-20kbar) at room temperature, and then the temperature is increased until reaction takes place. 

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