High pressure thermodynamic principles

In the light of all the facts now available from many independent sources, new furfural processes, as the SUPRATHERM and STAKE processes, aim at the increased yields obtainable at high temperatures, even without removal of the furfural from the scene of the reaction. Although this leads to somewhat uncomfortable high pressures, it is certainly a correct route towards higher yields, based on a fundamental principle of thermodynamics, and in hindsight the circumstances at the birth of the furfural industry must be deplored. 

McHale JM, Auroux A, Perrotta AJ, Navrotsky A (1997) Surface energies and thermodynamic phase stability in nanocrystalline aluminas. Science 277 788-791 Molteni C, Martonak R, Parrinello M (2001) First principles molecular dynamics simulations of pressure-induced stiuctural transformations in silicon clusters. J Chem Phys 114 5358-5365 Murray CB, Norris DJ, Bawendi MG (1993) Synthesis and characterization of nearly monodisperse CdE (E = S, Se, Te) semiconductor nanocrystallites. J Am Chem Soc 115 8706-8715 Onodera A (1972) Kinetics of polymorphic transitions of cadmium chalcogenides under high pressure. Rev Phys Chem Japan 41 1... 

Much of the increasing interest in exploiting the effects of high pressures is based on research carried out on the thermodynamic and chemical principles that support HP. In order to understand about actual and potential applications of HP on foods, a short review of those principles are presented in this contribution. 

We begin with a description of the high-pressure polymerization process since it is an authentic example of how the principles of thermodynamics and kinetics can be combined with creative engineering to develop an economically viable high-pressure process. These principles can be generalized and extended to other high-pressure processes. After describing the polyethylene process, we move on to more recent work on polyethylene and ethylene copolymers, followed by a discussion of other recent SCF studies with a variety of other polymers and monomers. 

Many or even most liquid mixtures encountered in industrial practice exhibit a nonideal equihbrium behavior. In high-pressure systems both the vapor phase and the liquid phase can deviate fiom Dalton s and Raoult s laws (e.g., Prausnitz et al. 1998). In low-pressure systems deviations from Raoult s law prevail. The fundamental principles for formulating the thermodynamics of nonideal systems are presented in Chap. 2. 

The above-mentioned phase transitions conform to the Le Chatelier principle, the sample volume decreasing under high pressure. They are not basically different Irom those observed in the static method, under conditions of thermodynamic equilibrium. There is, however, a class of anomalous phase transitions, which occur only in dynamic experiments and in which the shock compression gives rise to lower densities. The first of such phases was obtained in 1965 by shock treatment of the turbostratic BN [224] the new phase differed from both the graphite-Uke (/i-BN) like (c-BN) polymorphs of boron nitride and was named E-BN (E standing for the explosion phase ). Later, it appeared that the lattice parameters of E-BN are nearly identical to one of the phases of fullerene Ceo [225, 226], viz. a = 11.14, ft = 8.06, c = 7.40 A for E-BN, cf. a= 11.16, = 8.17, c = 7.58 A for Qo, with similar densities of 2.50 g/cm. Thus, the BN-fullerene was obtained by explosion (though not recognized as such) some 25 years before the carbon fuUerene was identified. Later on. 

Table 2.2 Correspondence principle parameters for the standard ionic partial molar volume (Reproduced from Geochimica et Cosmochimica Acta, Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures with permission from Elsevier)...

The term high pressure depends strongly on the problem. It seems to us that its use is justified only if the applied pressure changes significantly the property under study. In the case of molecular crystals or liquid systems there are only relatively weak intermolecular interactions, therefore pressures from a few tenths MPa up to 300 MPa are usually sufficient in order to induce considerable changes in the physical properties of the system. Although pressure and temperature are in principle equivalent thermodynamic parameters, they affect the molecular system differently Temperature causes mainly an excitation of rotational and... 

We now apply the basic thermodynamic principles to study physical properties of selected materials, the first of which is an ideal gas that obeys the equation of state PV = RT. For a mixture of ideal gases the individual chemical constituents i obey the relation P,V = ntRT, or P,-V = RT. As stated in Section 1.13, no material with such properties actually exists, but the ideal gas concept serves as a good model for many gases at a sufficiently high temperature and low pressure. On account of the simple equation of state it is worthwhile to examine the thermodynamic characteristics of this postulated species. 

At this point, we would like to proceed to apply the KMTG to experimentally measurable quantities, but we need a firmer foundation for the velocities and speeds of atoms/molecules in the gas phase. The velocity based on the phenomenological ideal gas law is suspect because we know it may not apply to high pressure and/or low temperature, so we need a more rigorous method. The concept/principle of weighted averaging occurs in kinetics, statistical thermodynamics, and in quantum mechanics, so we think this is more than just a math interlude it is a unifying principle. 

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