Boiling point temperature, calculation

To extend the applicability of the characterization factor to the complex mixtures of hydrocarbons found in petroleum fractions, it was necessary to introduce the concept of a mean average boiling point temperature to a petroleum cut. This is calculated from the distillation curves, either ASTM or TBP. The volume average boiling point (VABP) is derived from the cut point temperatures for 10, 20, 50, 80 or 90% for the sample in question. In the above formula, VABP replaces the boiling point for the pure component. 

The highly interactive nature of the balance and equilibria equations for the distillation period are depicted in Fig. 3.66. An implicit, iterative algebraic loop is involved in the calculation of the boiling point temperature at each time interval. This involves guessing the temperature and calculating the sum of the partial pressures, or mole fractions. The condition required is that Zyi + yw = 1. The iterative loop for the bubble point calculation is represented by the five interconnected blocks in the lower right hand corner of Fig. 3.66. The model of Prenosil (1976) also included an efficiency term E for the steam heating, dependent on liquid depth L and bubble diameter D. 

The molar volumes are in some cases at the stated temperature and in other cases at the normal boiling point. Certain calculated molecular volumes are also used thus the reader is cautioned to ensure that when using a molar volume in any correlation, it is correctly selected. In the case of polynuclear aromatic hydrocarbons, the Le Bas molar volume is regarded as suspect because of the compact nature of the multi-ring compounds. It should thus be regarded as merely an indication of relative volume, not an absolute volume. 

If one completely vaporizes a measured amount of a volatile liquid, the molecular weight of the liquid can be determined by measuring the volume, temperature, and pressure of the resulting gas. When one uses this procedure, one uses the ideal gas equation and assumes that the gas behaves ideally. However, if the sample is slightly above the boiling point of the liquid, the gas deviates from ideal behavior. Explain the postulates of the ideal gas equation, and explain why, when measurements are taken just above the boiling point, the calculated molecular weight of a liquid deviates from the true value. 

A similar property of solutions is boiling point elevation. A solution boils at a slightly higher temperature than the pure solvent. The change in the boiling point is calculated from... 

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]. 

All of the methods calculate the critical temperature by di viding Ibc boiling point temperature by a constant. Vowtes. I.ydcrsen. and Riedel1 have proposed atomic contributions that can be summed to determine the constant. The error is... 

Cetane index an approximation of the cetane number (q.v.) calculated from the density (q.v.) and mid-boiling point temperature (q.v.) see also Diesel index. 

Values of isosteric sorption enthalpy, -AH, standard sorption entropy, AS°, and standard Gibbs free sorption energy, AG°, are calculated as dependences on n, cf., [4-8]. To calculate AG°, the boiling-point temperature of N2O is chosen as reference state. This choice provides a check for thermodynamic consistency of experimental data since dG°... 

The boiling point is calculated as the temperature at which the fugaclty is 1 atm for LlBOgCt) LlBOgCg). The enthalpy of vaporization Is the difference In a H" at the boiling point between liquid and gas. 

The vaporization studies are summarized on the ideal gas table. The boiling point is calculated as that temperature for which AG"... 

The two vaporization studies are summarized on the ideal gas table. The boiling point is calculated as that temperature for which aG° = 0 for Ti(t) = Tl(g). A pH is the corresponding enthalpy change. T p is the temperature at which fugacity is one bar. The normal boiling point (p=l bar) would be a slightly lower temperature. 

The normal boiling point has been selected by Stull 333) to be 331.4 K., although the recent measurements of Fischer and Bingle 113) give a somewhat higher value. The heat of vaporization at the normal boiling point is calculated to be 7170 cal./gram mole. Kobe and Lynn 193) list the critical temperature as 584 K. and the critical pressure as 102 atmospheres. 

The surface tension has been correlated with other physical parameters such as liquid compressibility, viscosity, molar fractions, and the refractive index. Rao et al. [8] developed a linear relationship between the surface tension at normal boiling point (log a ) and the reduced boiling point temperature (T ). Hadden [9] presented a nomograph for hydrocarbons that enables rapid calculation of a. For cryogenic liquids, Sprows and Prausnitz [10] introduced the equation... 

Data are presented in the form of constants for the Antoine equation for the temperature dependence of the vapor pressures of 806 substances in the normal and low pressure region. Almost all of the substances contain carbon. Experimental data from selected original sources are given, together with smoothed values obtained from the Antoine equations at the same temperature, and the absolute and percentage deviations. Standard deviations are calculated. A standard boiling point is calculated for each substance. 

For petroleum fractions or similar systems the treatment of phase equilibria will now be discussed briefly. The basic principles are the same as those outlined for polymer systems without recourse to segment-molar quantities. For petroleum fractions the phase-equilibrium problem of importance is the so-called flash calculation that is analogous to the calculation of coexistence curves for a polydisperse polymer solution and in the simplest case a single distribution function is required. For example, the system may contain many alkanes characterized by their normal boiling-point temperatures Tb that in this work will be denoted by x. At moderate pressures the equilibrium condition is given by the continuous thermodynamics form of Raoult s law ... 

The theoretical boiling point is calculated as follows — The increase of pressure for 1° rise of temperature from 90° to 91° is 761-6—733-8 = 27 8 mm. It may be assumed without sensible error that the value of dpfdt is constant over this small range of temperature and the boiling point should therefore... 

Nevertheless, all predictions indicate normal boiling point temperatures well above the decomposition temperatures of the ILs, which means that the results may never be corroborated experimentally by direct measurements. Moreover, the different sets of data show that there is a tendency for a decrease in the normal boiling point temperature as the length of the alkyl side chain is increased, thus qualitatively corroborating preliminary estimates (Rebelo et al. [29]). Nonetheless, the observed tendency is not so strong if one uses these new y and V data in an extended temperature range instead of the old data taken from a much narrower temperature interval. This subdued tendency is also in better agreement with the data calculated from the vapor pressure measurements. 

Flash models require heat capacity, latent heat of vaporization data for the pure materials, normal boiling point temperatures, as well as the initial conditions of temperature and presstire. The AIChE/DIPPR physical properties compilation (Danner and Daubert, 1985) is a useful source of temperature dependent properties. For flashing mixtures a commercial process simulator would normally be used. If droplet size is to be determined to allow estimation of settling velocity, the velocity of discharge must be calculated, along with density and surface tension of the liquid and the density of gas. 

The triple-point temperature of air is the solidification temperature of the liquid (see Reference 2 for details). The boiling-point temperature for air is the bubble-point temperature (i.e., the temperature at which boiling begins as the pressure of the liquid is lowered). The dew-point (vapor) properties of air at 101.325 kPa are calculated at a temperature of 81.72 K the liquid and vapor properties of these two state points are not in equilibrium. The triple-point properties of helium are given at the temperature of the lambda line (change from normal-to-superfluid helium) for the saturated-liquid state. 

The adsorption of molecules in multilayers occurs typically when the temperature is near the boiling point. However, when adsorbed as monolayer, there is a direct link between adsorbed and adsorbent, occurring at a higher than the boiling point temperature. For example, CO molecules can adsorb on a platinum surface at 10 torr and 400 K. In general, the adsorbed density of a monolayer looks like a liquid film, which means, the adsorbed molecules on a monolayer are very close together. Calculations show that water vapor can be adsorbed forming a layer of 3 A° and the number of adsorbed molecules is... 

In a new case in Hysys, add all components involved in the mixture, select Anto/ne as the fluid package, and then enter the simulation environment. Click on stream in the object pallet, then click on any place in the PFD, double click on the stream and enter molar compositions of each component. In the conditions page set the vapor/phase fraction = 0 the calculated temperature (which is the boiling point temperature at the given pressure 1.5 atm) is 105.5°C as shown in Figure 1.1. 

In practice vapor-liquid equilibrium calculations using an equation of state, that is applicable to both phases, can be carried out with sufficient accuracy only for systems that are up to moderately nonideal, typically hydrocarbon mixtures alone or with such gases as H2S, CO, CO2, etc. Furthermore, since separation of such systems by distillation - because of their typically low boiling point temperatures at atmospheric pressure - is carried out at high pressures, this methodology represents what is traditionally referred to as the High Pressure or Equation of State approach to... 

The composition of the vapour can easily be calculated as follows — Assuming that the gas laws are applicable, it follows that the number of molecules of each component in the vapour wdll be proportional to its partial pressure, i.e., to the vapour pressure of the pure liquid at that temperature. If and p are the vapour pressures of the two liquids A and B at the boiling point of the mixture, then the total pressure P is given by ... 

The comparatively inexpensive long-scale thermometer, widely used by students, is usually calibrated for complete immersion of the mercury column in the vapour or liquid. As generally employed for boiling point or melting point determinations, the entire column is neither surrounded by the vapour nor completely immersed in the liquid. The part of the mercury column exposed to the cooler air of the laboratory is obviously not expanded as much as the bulk of the mercury and hence the reading will be lower than the true temperature. The error thus introduced is not appreciable up to about 100°, but it may amount to 3-5° at 200° and 6-10° at 250°. The error due to the column of mercury exposed above the heating bath can be corrected by adding a stem correction, calculated by the formula ... 

Di-n-amyl ether. Use 50 g. (61 5 ml.) of n-amyl alcohol (b.p. 136-137°) and 7 g. (4 ml.) of concentrated sulphuric acid. The calculated volume of water (5 ml.) is collected when the temperature inside the flask rises to 157° (after 90 minutes). Steam distil the reaction mixture, separate the upper layer of the distillate and dry it with anhydrous potassium carbonate. Distil from a 50 ml. Claisen flask and collect the fractions of boiling point (i) 145-175° (13 g.), (ii) 175-185° (8 g.) and (iii) 185-190° (largely 185-185-5°) (13 g.). Combine fractions (i) and (u), reflux for 1 hour in a small flask with 3 g. of sodium, and distil from the sodium amyloxide and excess of sodium this yields 9 5 g. of fairly pure n-amyl ether (iv). The total yield is therefore 22 - 5 g. A perfectly pure product, b.p. 184 185°, is obtained by further distillation from a Little sodium. 

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