Properties, estimation boiling point

Li, Q., Chen, X. and Hu, Z. (2004) Quantitative structure-property relationship studies for estimating boiling points of alcohols using calculated molecular descriptors with radial basis function neural networks. Chemom. Intell. Lab. Syst., 72, 93-100. 

Critical properties, if not available, can be estimated from tbe methods of tbe previous section. T,. is tbe reduced temperature at tbe temperature of interest, while Tr is tbe reduced temperature at tbe normal boiling point. 

The heat requirements in batch evaporation are the same as those in continuous evaporation except that the temperature (and sometimes pressure) of the vapor changes during the course of the cycle. Since the enthalpy of water vapor changes but little relative to temperature, the difference between continuous and batch heat requirements is almost always negligible. More important usually is the effect of variation of fluid properties, such as viscosity and boiling-point rise, on heat transfer. These can only be estimated by a step-by-step calculation. 

These results thus show that whereas the flashpoint was only moderately influenced by the compound structure (their chemical functionality but especially their atomic composition and vapour), autoignition temperatures seem to be closely linked to the structural factors that affect the chain. So additivity rules for estimation of AIT should be sought. Every time a chemical or physical property is highly influenced by the structure, chemists tried to establish rules that enable one to reduce a molecule to characteristic groups for which the contribution to the value of this property is known. This was done for instance by Kinney for boiling points and Benson2 for thermochemical properties. 

Successful isolation of a new compound obtained in a synthesis depends on making reasonably accurate estimates of the physical properties of its melting point, boiling point, and solubilities. 

From the viewpoint of developing quantitative correlations it is desirable to seek a linear relationship between descriptor and property, but a nonlinear or curvilinear relationship is adequate for illustrating relationships and interpolating purposes. In this handbook we have elected to use the simple descriptor of molar volume at the normal boiling point as estimated by the Le Bas method (Reid et al. 1987). This parameter is very easily calculated and proves to be adequate for the present purposes of plotting property versus relationship without seeking linearity. 

Most data on VPIE s for heavier pairs are at or below the normal boiling point, Tr-0.7. Of the critical property IE s, ln(Tc /Tc) is the easiest to measure and the most reliably known. Often lnlPc /Pd, and very often ln(pc /pc), are unknown or imprecisely known, and IrHp /p) has been measured only at or near room temperature or must be estimated. 

To model the solubility of a solute in an SCF using an EOS, it is necessary to have critical properties and acentric factors of all components as well as molar volumes and sublimation pressures in the case of solid components. When some of these values are not available, as is often the case, estimation techniques must be employed. When neither critical properties nor acentric factors are available, it is desirable to have the normal boiling point of the compound, since some estimation techniques only require the boiling point together with the molecular structure. A customary approach to describing high-pressure phenomena like the solubility in SCFs is based on the Peng-Robinson EOS [48,49], but there are also several other EOS s [50]. 

T(°K)]. Several thermodynamic properties of FCIO2 have been estimated by Rips et al. 235) by means of correlation increments using only the boiling point of the substance. Whereas the correct boiling point of FCIO2 was used, its structure was erroneously assumed to be that of the hypofluorite F—0—01=0. 

I. Estimate the densities, melting points, and boiling points of a number of compounds by association and trend. You may use the properties of any compound from handbooks and electronic sources, except the assigned compound of course. 

The cetane index is an estimation of the cetane number from fuel physical properties such as the 10%, 50%, and 90% boiling points and the °API. 

To design a supercritical fluid extraction process for the separation of bioactive substances from natural products, a quantitative knowledge of phase equilibria between target biosolutes and solvent is necessary. The solubility of bioactive coumarin and its various derivatives (i.e., hydroxy-, methyl-, and methoxy-derivatives) in SCCO2 were measured at 308.15-328.15 K and 10-30 MPa. Also, the pure physical properties such as normal boiling point, critical constants, acentric factor, molar volume, and standard vapor pressure for coumarin and its derivatives were estimated. By this estimated information, the measured solubilities were quantitatively correlated by an approximate lattice equation of state (Yoo et al., 1997). 

If the potential parameters for the pure components are not found in the tables given in (Hll) and (Bll), and if viscosity and second virial data are not available for their determination, then for the Lennard-Jones (6-12) potential it is possible as a last resort to estimate these parameters from the properties of the substance at its critical point c, its melting point m, or its boiling point b these relations give /k in °K. and a in Angstrom units (1 A. = 10-3 cm.) ... 

The method of Lydersen [28] is a GCM of this type to estimate the critical temperature, Tc. Other approaches to non-linear GCMs include the model of Lai et al. [29] for the boiling point, Tby and the ABC approach [30] to estimate a variety of thermodynamic properties. Further, artificial neural networks have been used to construct nonlinear models for the estimation of the normal boiling point of haloalkanes [31] and the boiling point, critical point, and acentric factor of diverse fluids [32]. 

Modified QCMs GCM schemes often consider extra contributions. These contributions can be physicochemical properties, molecular descriptors, and various correction factors. For example, to estimate the critical temperature, Tc, the input of the normal boiling point, Tb, is required by certain GCMs [33]. In this case a typical approach is based on the modification of eq. 1.6.3 as follows ... 

Rechsteiner, C. E., Boiling Point, in Handbook of Chemical Property Estimation, W. J. Lyman, W. F. Reehl, and D. H. Rosenblatt, Editors, 1990. Washington, DC American Chemical Society. 

Methods to Estimate pv from Tb Only The modified Watson correlation [2] applies for liquids and solids in the pv range from 10-7 to 760mmHg. This method is based on the Watson equation (8.5.1) and requires the input of the normal boiling point temperature, Tb, and of AHvb. However, the latter property is itself calculated from Tb and from structural parameters. For compounds with pv between 10 and 760mmHg, a method error of 2.5% has been reported, whereas a considerably higher error has been found for compounds with pv below lOmmHg. The method has been illustrated for benzene and DDT [2]. A large number of other Tb/pv correlations have been discussed by Horvath [17]. 

Kobe and co-workers have measured the critical properties and sapor pressures of all four compounds 0 Additional data are available from several other sources.The cntical density of MIBK was estimated by the method of Vowlcs. with a probable error ol less than 1%. Figure 26-2 presents the boiling point of aqueous acetone solutions (sec also Table 26-11. 

The critical properties have been experimentally measured for bromobenzcnc, chlorobenzene, and fluorobcn-Mnc s.s.iuj.w Lydcrsen s method wus used U calculate the critical properties of benzyl chloride 1 Literature data arc reported for the vnpnr pressure ot bru-mobenzene, chlorobenzene, and fluorobcn/ertc up to the critical point, -1" 271 Stull has compiled the vapor pressure data on benzyl chloride up to its boiling point J Ashcroft pce cms data from 48T to I I C. 275 The vapor pressure above the boiling point was estimated ... 

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