Eugene D. Nikitin

Vapour-liquid critical temperatures and pressures of normal alkanes with from 19 to 36 carbon atoms, naphthalene and m-terphenyl determined by the pulse-heating technique

Abstract The paper presents the results of measuring the critical temperatures and the critical pressures of normal alkanes: nonadecane, eicosane, docosane, tetracosane, hexacosane, octacosane, triacontane, hexatriacontane, and also naphthalene and m-terphenyl. The pulse-heating method of a wire probe immersed in the liquid under investigation applicable to thermally unstable substances has been used. Equations of state of a polymeric fluid of the van der Waals and Redlich-Kwong type have been written in a ‘self-consistent-field’ approximation. Dependences of the critical constants of chain molecules on the number of links have been obtained. Equations for calculating the critical temperatures and pressures of normal alkanes have been derived. The results of calculations are compared with experimental data.

Critical temperatures and pressures of 1-alkanols with 13 to 22 carbon atoms

Abstract The paper gives the results of measuring the critical temperatures and pressures of thermally unstable 1-alkanols CnH2n+1OH with a number of carbon atoms n=13–18,20,22. The method of pulse heating of a wire probe located in the liquid under investigation has been used. Equations that correlate the critical temperatures and pressures of 1-alkanols with the number of carbon atoms in a molecule have been obtained. The results of measurements are compared with the values predicted by various methods. The acentric factors of 1-alkanols have been calculated.

Acoustic method of measuring critical properties of thermally unstable substances

Abstract An acoustic method of measuring critical temperatures and pressures of thermally unstable substances is described. In the cell with the liquid under investigation there is a wire probe, 0.02 mm in diameter, which is heated by electric-current pulses with a duration of 0.025 to 0.25 ms. At the moment of liquid boiling-up in the layer that surrounds the probe, one can observe an acoustic wave, which is registered by a ceramic piezoelectric element on a base (PbZrO 3 +PbTiO 3 ). The probe temperature at the moment of boiling-up is determined from its resistance. With an increase of the pressure in the cell with the substance under investigation the amplitude of an acoustic signal decreases. The cessation of boiling-up and disappearance of the acoustic signal show that the critical state is reached. A more precise critical pressure is found by linear extrapolation of the amplitude of the acoustic signal to zero in an amplitude–log (pressure) plot. The paper reports the experimental critical temperatures T c and the critical pressures p c of reference substances: n -hexane, n -heptane, n -decane, benzene, and of thermally unstable n -alkanes: docosane and tetracosane, and also the critical curve of the system n -hexadecane–benzene. The critical constants of reference substances were measured by this acoustic method with an error that does not exceed 0.015 T c and 0.015 p c .

Estimation of the critical constants of long-chain normal alkanes

Correlations between the critical constants of normal alkanes and the number of carbon atoms in a molecule have been considered. In an approximation of a self-consistent field for a polymeric fluid, an equation of state of the van der Waals type has been written, and the dependences of the critical constants of chain molecules on the number of mers have been obtained. It has been found that for an infinitely long alkyl chain, the limiting values of the critical temperature, the critical pressure, and the critical density are equal to, respectively, 1135 K, 0 M Pa, and 0 kg · m−3. A method of pulse heating of a wire probe immersed in the substance under investigation has been used to measure the dependence of the temperature of the attainable superheatT* of low-density polyethylene on the pressure p and the duration of heating pulset*. Extrapolation has been used to obtain an estimation of the attainable-superheat temperature of polyethyleneT*(p=0,t*=0)= 1175 K, which can be treated as the “critical” temperature of polyethylene.

Critical temperatures and pressures of linear alk-1-enes with 13 to 20 carbon atoms using the pulse-heating technique

Abstract The paper presents experimental critical temperatures and critical pressures of thermally unstable alk-1-enes CnH2n with a number of carbon atoms n=13–20. The method of pulse heating of a wire probe placed in the liquid under investigation has been used. Equations for correlation of the critical temperatures and pressures of alk-1-enes with a number of carbon atoms in a molecule have been obtained. The acentric factors of alk-1-enes have been calculated.

Critical temperatures and pressures of some alkanoic acids (C2 to C22) using the pulse-heating method

Abstract This paper presents experimental critical temperatures and pressures of 12 alkanoic acids C n H 2 n O 2 with carbon numbers from 2 to 22. The method of pulse heating of a wire probe placed in the liquid under study has been used. Equations for the correlation of the critical temperatures and pressures of alkanoic acids with the number of carbon atoms and molar mass have been obtained.

Validation of a recent generalized expression of Tc/Pc vs. the van der Waals surface area according to recent measurements

Abstract Recently, Kontogeorgis et al. [G.M. Kontogeorsis, I.V. Yakoumis, P. Coustikos, D.P. Tassios, Fluid Phase Equilibria, 140 (1–2) (1997) 145–146] developed a generalized expression for the ratio of the critical temperature to the critical pressure (Tc/Pc) with the van der Waals surface area (Qw). Despite the extensive database involved in the development of this equation, the heaviest compounds involved were n-tetracosane in terms of Tc/Pc ratio and PEG-400 in terms of highest Tc. The maximum Tc/Pc value was below 100. The correlation is further validated in light of recent critical data appearing in the literature for heavy compounds with Tc/Pc ratio up to 185. The satisfactory agreement between experimental and predicted Tc/Pc ratios justifies its application to high molecular weight compounds other than those employed for its development.

Heat capacities and thermal diffusivities of n-alkane acid ethyl esters—biodiesel fuel components

The heat capacities and thermal diffusivities of ethyl esters of liquid n-alkane acids CnH2n–1O2C2H5 with the number of carbon atoms in the parent acid n = 10, 11, 12, 14, and 16 are measured. The heat capacities are measured using a DSC 204 F1 Phoenix heat flux differential scanning calorimeter (Netzsch, Germany) in the temperature range of 305–375 K. Thermal diffusivities are measured by means of laser flash method on an LFA-457 instrument (Netzsch, Germany) at temperatures of 305–400 K. An equation is derived for the dependence of the molar heat capacities of the investigated esters on temperature. It is shown that the dependence of molar heat capacity Cp,m(298.15 K) on n (n = 1–6) is close to linear. The dependence of thermal diffusivity on temperature in the investigated temperature range is described by a first-degree polynomial, but thermal diffusivity a (298.15 K) as a function of n has a minimum at n = 5.

Temperatures of the attainable superheat of some thermally unstable liquids

The paper gives the results of measuring the temperatures of the attainable superheat of some liquids that are thermally unstable at these temperatures. The technique of heating a thin wire probe placed into a liquid under study with electric-current pulses has been used. The length of pulses is from 10−5 to 10−3 s, which corresponds to a heating rate of 105 to 108 K·s−1. The influence of a chemical reaction in the liquid phase on the temperature of the attainable superheat has been considered. In particular, it has been shown that boiling initiated by an elementary act of an exothermic chemical reaction is of a low probability. A method of calculating the temperature of the attainable superheat of thermally unstable liquids under conditions of quick heating has been developed. A method for the determination of the kinetic parameters of thermal decomposition from the measurements of the temperature of the attainable superheat is discussed.

Temperature of Attainable Superheating of Some Commercial Petroleum Products

Measurements of the temperature of attainable superheating of A-76L and AI-93 motor gasolines; L-0.5–40, L-0.2–40, and Z-0.5–35 diesel oils; TS-1 and RT jet propellants; and T-1500 transformer oil are performed by the method of pulsed heating of a wire probe placed into the liquid under study. The rate of increase of the probe temperature is 105–107 K/s. The pressure varies from atmospheric to near-critical. The temperature of attainable superheating of rocket propellants is also calculated by the theory of homogeneous nucleation. A conclusion is made that, if the thermal properties of a concrete batch of petroleum products are known, the theory of homogeneous nucleation provides a fairly accurate estimate of the temperature of attainable superheating of substances with so complex a composition.