Critical data

This database provides thermophysical property data (phase equilibrium data, critical data, transport properties, surface tensions, electrolyte data) for about 21 000 pure compounds and 101 000 mixtures. DETHERM, with its 4.2 million data sets, is produced by Dechema, FIZ Chcmic (Berlin, Germany) and DDBST GmhH (Oldenburg. Germany). Definitions of the more than SOO properties available in the database can be found in NUMERIGUIDE (sec Section 5.18). 

The other modern equation used for correlation is the modified and linearized Wagner "" equation (2-30), which has the advantage that it will match critical data exactly, although it cannot be extrapolated above the critical point. The equation is also included with coefncients to several hundred compounds in the Technical Data Book—Petroleum Refining. 

Modern day turbomachinery is built to last between 30-40 years. Thus, the keeping of basic maintenance records and critical data is imperative for a good maintenance program. Economic justification is always the controlling factor for any program, and maintenance practices are not different. 

Helpful surveys and reviews can now be found in the literature and readers are invited to consult them. Janz and Tomkins gave a critical data... 

Berthelot showed that the mean compressibility between 1 and 2 atm. does not differ appreciably from that between 0 and 1 atm. in the case of permanent gases, and either may be used within the limits of experimental error. But in the case of easily liquefiable gases the two coefficients are different. According to Berthelot and Guye the value of aJ can be determined from that of aj by means of a small additive correction derived from the critical data, and the linear extrapolation then applied Gray and Burt consider, however, that this method may lead to inaccuracies, and consider that the true form of the isothermal can only be satisfactorily ascertained by the experimental determination of a large number of points, followed by graphical extrapolation. 

Madame Ivirstine Meyer (1900) has shown that the discrepancies are not to be explained by errors in the critical data the law of corresponding states can be tested without making use of these constants, and differences between the observed and calculated magnitudes are still apparent. D. Berthelot (Journ. de Phys., 1903) has deduced some new equations. 

To obtain an analytic function / in Eq. (55), Chueh uses the Redlich-Kwong equation however, since the application is intended for liquids, the two constants in that equation were not evaluated (as is usually done) from critical data alone, but rather from a fit of the pure-component saturated-liquid volumes. The constants a and b in the equation of Redlich and Kwong are calculated from the relations... 

Critical data for some substances, which are frequently used as solvents under supercritical conditions in chemical reactions, are reported [76] in Table 6.13. 

In the context of drug discovery, computational methods do not add value unless they can achieve practical results. Results must be produced quickly enough so that they can influence decision making in chemical synthesis. Most importantly, computational methods must be accurate enough to maintain the trust of the medicinal chemist. Without this trust, computational predictions will rarely be tested in the laboratory, which will then prevent the generation of critical data useful for improving the original predictions. 

It is assumed that there are available NCP experimental binary critical point data. These data include values of the pressure, Pc, the temperature, Tc, and the mole fraction, xc, of one of the components at each of the critical points for the binary mixture. The vector k of interaction parameters is determined by fitting the EoS to the critical data. In explicit formulations the interaction parameters are obtained by the minimization of the following least squares objective function ... 

In principle, one may combine equilibrium and critical data in one database for the parameter estimation. From a numerical implementation point of view this can easily be done with the proposed estimation methods. However, it was not done because it puts a tremendous demand in the correlational ability of the EoS to describe all the data and it will be simply a computational exercise. 

W. L. Wiese, J. R. Fuhr and T. M. Dieters, Atomic Transition Probabilities for Carbon, Nitrogen and Oxygen A Critical Data Compilation, J. Phys. Chem. Ref. Data, Monograph 7, 1996. 

Critical data Second virial coefficient Viscosity Average value... 

This introduces two "interaction parameters" per binary pair. The pure component coefficients, a and b i, are evaluated from critical data and the acentricity, as proposed by Soave in his original paper (1). The pure component aii varies with reduced temperature so as to match vapor pressure. (Soave s recently revised expression for a (17) has not been used.)... 

The calculated critical points of the binary pairs, particularly the critical pressures, are quite sensitive to the values used for the interaction parameters in the mixing rules for a and b in the equation of state. One problem in undertaking this study is that no data are available on the critical lines of any of the binary pairs except for CO2 - H2O. Even for C02 - H2O, two sets of critical data available (18, 19) are in poor quantitative agreement, though they present the same qualitative picture of the critical phenomena. 

The equation-of-state method, on the other hand, uses typically three parameters p, T andft/for each pure component and one binary interactioncparameter k,, which can often be taken as constant over a relatively wide temperature range. It represents the pure-component vapour pressure curve over a wider temperature range, includes the critical data p and T, and besides predicting the phase equilibrium also describes volume, enthalpy and entropy, thus enabling the heat of mixing, Joule-Thompson effect, adiabatic compressibility in the two-phase region etc. to be calculated. 

The parameters were optimised to represent the critical data p and T, the vapour pressure from room temperature up to the critical point and the saturated vapour and liquid molar volumes. Account was also taken of the representation of the binary systems H20-CH. to C.H.q. Initially the method of Powell... 

The critical data and values used for inert components were those given by Ambrose (24). The interaction parameters between the water and the inert component were found by performing a dew-point calculation as described above but with the interaction parameter k.. rather than P taken as the iteration variable. 

Simmrock, K. H., R. Janowsky and A. Ohnsorge, CRITICAL DATA OF PURE SUBSTANCES. Vol. II, Parts 1 and 2, Dechema Chemistry Data Series, 6000 Frankfurt/Main, Germany (1986). 

Kistiakowsky-Fishtine equation puys chem An equation to calculate latent heats of vaporization of pure compounds useful when vapor pressure and critical data are not available., kis-te-a k6f-ske fa shtTn i,kwa-zhan kitol oRG CHEM C40H60O2 One of the provitamins of vitamin A derived from whale liver oil crystallizes from methanol solution. ke,tol ... 

Table 10.4 gives critical data for the most common solvents used in high-pressure extraction. Table 10.5 illustrates the favorable mass transport properties that can be achieved in the supercritical area owing to a low viscosity and a high diffusivity, compared with the liquid phase. 

Greim H (ed) Occupational Toxicants, Vol 13, critical data evaluation for MAK values and classification of carcinogens. Commission for the investigation of health hazards of chemical compounds in the work area, Bisphenol A, p 49. New York, VCH, 1999... 

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