Elsevier

Chemical Physics Letters

Volume 715, January 2019, Pages 186-189
Chemical Physics Letters

Prediction of enthalpy for the gases CO, HCl, and BF

https://doi.org/10.1016/j.cplett.2018.11.044Get rights and content

Highlights

  • We present an efficient closed-form representation of molar enthalpy for gaseous substances.

  • Present molar enthalpy calculation model only involves four molecular constants.

  • We excellently predict molar enthalpy values for the CO, HCl, and BF gases.

Abstract

We present a universal efficient closed-form representation for the molar enthalpy of gaseous substances. The predicted molar enthalpy values show excellent agreements compared to the experimental data in a wide temperature range for the gases CO, HCl, and BF. The proposed model is away from the need of plenty of experimental spectroscopy data, and depends on only four molecular constants, for which the experimental values can be easily found in the literature.

Introduction

An explicit representation of the molar enthalpy of the system can provide a simple and efficient way to perform calculations of the enthalpy change during the process under consideration. However, obtaining a universal closed-form expression of the molar enthalpy for gaseous substances remains a formidable goal in chemical engineering. As far as we know, one has not reported an available closed-form representation governing the molar enthalpy values for the gases carbon monoxide (CO), hydrogen chloride (HCl), and boron fluoride (BF). The enthalpy change of the system is important to address many issues, including the chemical reaction [1], [2], [3], [4], [5], phase transition [6], [7], [8], [9], [10], and adsorption [11], [12], [13], [14], [15]. With the help of gasification technology, any carbonaceous fuel (coal, biomass, waste stream) can be converted into syngas (CO and H2) [5]. The gasification process involves a long list of gas species, including H2, CO, CO2, N2, CH4, H2O, O2, NO2, NO, S, SO2, SO3, H2S, COS, C2H2, and solid carbon [5]. Oxy-fuel combustion has the higher concentration of pollutant components in the flue gas, including sulfur oxides, carbon monoxide, nitrogen oxides, and hydrogen chloride. HCl can affect the oxidation of CO and the formation of nitrogen monoxide (NO) in combustion [16]. The adsorption and sorption processes of CO and CO2 in various adsorbent materials have attracted extensive interest. In general, the negative or positive value of the enthalpy change can tell us whether an adsorption process is to release energy or adsorb energy in the form of heat to its surroundings, respectively. From the well-known van’t Hoff equation, we know that the Langmuir adsorption constant is directly related to the enthalpy change and entropy change. Investigation on the change in enthalpy of the system under consideration is a conventional manipulation in dealing with the gasification, combustion and adsorption problems.

On the basis of the dissociation energy and equilibrium bond length for explicit parameters, the improved versions have been suggested for the well-known Rosen-Morse, Tietz, and Frost-Musulin oscillators [17]. The improved oscillators could be regarded as useful models to calculations of molecular vibrational partition functions and thermochemical properties, including the enthalpy, entropy and Gibbs free energy [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29]. In this work, through describing the molecular internal vibration with the improved Tietz oscillator, we establish a universal four-parameter molar enthalpy calculation model for gaseous substances. To examine the availability of the proposed enthalpy calculation scheme, we model the variations of molar enthalpy values with respect to temperature for the CO, HCl, and BF gases. Large quantity of CO is produced as a byproduct in tail gases, including coke oven gas, carbon black manufacturing tail gas and blast furnace gas. Adsorptive separations of gas mixtures containing CO have become quite important nowadays. Sorption of CO on different materials and electroreduction of CO to liquid fuel and have attracted much interest [11], [30], [31]. The BF molecule is one of the most intriguing diatomic molecules formed from first-row elements, being isoelectronic to CO [32], [33]. An acidic solution is injected into the rock for dissolving the rock and increasing the permeability. Hydrochloric acid (HCl) has been widely used as the main stimulation treatment to improve formation permeability and increase hydrocarbon production [34], [35], [36]. The proposed enthalpy calculation method appears to offer the reliable completely predictive values compared to the experimental data.

Section snippets

Analytical representation of enthalpy

Here, we describe the internal vibration of a molecule by the aid of the improved Tietz oscillator, which possesses the simplicity, accuracy and flexibility. The vibrational partition function of the improved Tietz oscillator is written in the form [18]Q=12e-DekTeλa2kT-eλb2kT+πkTλerfiλkTa-erfiλkTb-e-2λδ1kTerfiλkT2δ1+a+e-2λδ1kTerfiλkT2δ1+b,in which De represents the dissociation energy of the diatomic molecule, k denotes the Boltzmann’s constant, and T is the absolute temperature. In expression

Applications

To determine whether our proposed molar enthalpy calculation scheme is available, we attempt to reproduce the total molar enthalpy values at different temperatures for the CO, HCl, and BF gases. The experimental data of molecular constants De, re, ωe and αe are collected from the literature: CO [38], HCl [38], and BF [32]. We give the molecular constant values in Table 1. In terms of expression (10), we calculate the molar enthalpy values for the gases under consideration. The results with

Conclusions

On the basis of the improved Tietz oscillator in the description of molecular internal vibration, we construct a universal efficient closed-form expression of the molar enthalpy for gaseous substances. The proposed molar enthalpy calculation model can accurately predict the molar enthalpy values for the CO, HCl, and BF gases. The proposed model only contains four molecular constants, including the dissociation energy, equilibrium bond length, harmonic vibration frequency and vibrational

Acknowledgments

We would like to thank the kind referee for positive and invaluable suggestions which have greatly improved the manuscript. This work was supported by the Key Program of National Natural Science Foundation of China under Grant No. 51534006 and the Sichuan Province Foundation of China for Fundamental Research Projects under Grant No. 2018JY0468.

References (39)

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