Handbook of Thermal Analysis and Calorimetry

Recent Advances, Techniques and Applications

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• Publisher: Elsevier Science
• Year: 2018
• ISBN:
  9780444640635
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Handbook of Thermal Analysis and Calorimetry: Recent Advances, Techniques and Applications, Volume Six, Second Edition, presents the latest in a series that has been well received by the thermal analysis and calorimetry community. This volume covers recent advances in techniques and applications that complement the earlier volumes. There has been tremendous progress in the field in recent years, and this book puts together the most high-impact topics selected for their popularity by new editors Sergey Vyazovkin, Nobuyoshi Koga and Christoph Schick—all editors of Thermochimica Acta.

Among the important new techniques covered are biomass conversion; sustainable polymers; polymer nanocompsoties; nonmetallic glasses; phase change materials; propellants and explosives; applications to pharmaceuticals; processes in ceramics, metals, and alloys; ionic liquids; fast-scanning calorimetry, and more.

• Features 19 all-new chapters to bring readers up to date on the current status of the field
• Provides a broad overview of recent progress in the most popular techniques and applications
• Includes chapters authored by a recognized leader in each field and compiled by a new team of editors, each with at least 20 years of experience in the field of thermal analysis and calorimetry
• Enables applications across a wide range of modern materials, including polymers, metals, alloys, ceramics, energetics and pharmaceutics
• Overviews the current status of the field and summarizes recent progress in the most popular techniques and applications

Chapter 1

Development of Direct and Indirect Methods for the Determination of Vaporization Enthalpies of Extremely Low-Volatile Compounds

Sergey P. Verevkin*; Dzmitry H. Zaitsau*; Christoph Schick*; Florian Heym^{† *} University of Rostock, Rostock, Germany
^† University of Bayreuth, Bayreut, Germany

Abstract

Recent advances in experimental methods for the determination of vapor pressures and vaporization enthalpies of extremely low-volatile compounds related to ionic liquids and biodiesel components have been critically analyzed.

Keywords

Experimental methods; Vapor pressure; Vaporization enthalpy; Sublimation enthalpy; Ionic liquids

1.1 Introduction

Absolute vapor pressures are broadly used for practical applications ranging from technology to ecology. For example, transport, distribution, and the fate of pollutants in the atmosphere are governed by vapor pressure as the key property. Most separation technologies of industrially relevant mixtures are also based on the differences in vapor pressures of the individual compounds. The vapor pressure of a substance is not only a measure of its maximum possible concentration in the gas phase at a given temperature, but it also provides (over the vaporization enthalpy) an important quantitative information on the interaction forces among molecules in the condensed phase. The experimental vapor pressure data for about 10,000 chemicals have been tabulated in the open literature [1–5], however, most values are available at a limited temperature or pressure range. Moreover, the available data cover mostly easy or moderate volatile industrial solvents. A lack of reliable data in a broad temperature range and especially in the low-pressure region (below 1000 and 1 Pa) for technological and environmental applications is quite apparent. Experimental methods for the determination of vapor pressure can be divided into at least three main classes: the kinetic, the static, and the calorimetric methods. For volatile chemicals, the kinetic as well as the static methods are well established. Vaporization enthalpies of chemicals can be derived from the temperature dependence of vapor pressures and the available data are collected in extended compilations [6–9], and also with an emphasis on volatile compounds. However, two new research fields, biofuels and ionic liquids (ILs), highly investigated in the last decade, have clearly revealed the deficiency of the reliable vapor pressures for low-volatile compounds. Thermophysical properties of biofuel components such as oils, fats, fatty acids, fatty acids esters, and glycerides have gained scientific attention mostly because of the increase in biofuel production and processing. Measurements of thermophysical properties, as well as the thermodynamic modeling involving compounds related to biofuels, are becoming larger areas of research. Among other important thermophysical and thermodynamic properties, the knowledge of vapor pressure is relevant for understanding the behavior of these chemicals under processing conditions found in the physical refining of oils/fats in purification steps of biofuel and its application [10]. Unfortunately, most data available for compounds relevant to biofuels are measured at the beginning of the last century without purity attestation and at temperatures close to the normal boiling point where a possible decomposition could heavily affect the results. Thus, reliable vapor pressure data at possibly low or ambient temperatures are essentially required for further development of the biofuel research field.

Research on ILs and their industrial applications has expanded rapidly over the last 10 years. The ILs are regarded as organic salts which, conventionally, melt below 373 K and may be considered as either aprotic or protic in character. Protic ILs are formed by proton transfer from a Brönsted acid to a Brönsted base. One of the most attractive features of aprotic ILs is their negligible vapor pressure at ambient temperatures. At elevated temperatures (353–500 K) relevant for many applications of ILs, however, the vapor pressure is no longer negligible, even though it remains small (approximately at the level of a few Pa). Hence, for the application of ILs in chemical processing knowledge of the vapor pressure and vaporization enthalpies, Δ_l^gH_m^o, is indispensable. Moreover, vapor pressures and enthalpies of vaporization also play a crucial role in the development of liquid state theories, and so there is additional motivation to understand these properties for low-volatile substances. Experimental measurements of the vaporization enthalpies are extremely challenging because of two main problems: the vapor pressures of ILs at ambient temperature are so low as to be practically immeasurable, whereas at high temperatures where vapor pressures can be measured, possible thermal decomposition processes can distort the results [11]. In fact, with the exception of the Knudsen method, traditional experimental techniques for vapor pressure measurement have not been developed for the extremely low-volatile liquids such as ILs. This has stimulated the development of new direct experimental methods such as quartz crystal microbalance (QCM), thermogravimetry (TGA), fast scanning calorimetry (FSC), temperature programmed desorption and line-of-sight mass spectrometry (TPD-LOSMS), and high-temperature ultraviolet (UV) spectroscopic technique. The present chapter gives an overview of a recent development in the vapor pressure measurements with focus on low-volatile and extremely low-volatile compounds.

1.2 Kinetic Methods of Thermal Analysis (Vaporization) of Low-Volatile Compounds

Kinetic methods of tensimetry are based on the determination of the mass loss rate of the sample exposed to vacuum [12–14]. Knudsen proposed to use the rate of effusion of the gas sample into vacuum from a covered with a membrane cell equipped with a small orifice [15]. In contrast, Langmuir [16] proposed to consider the rate of evaporation from the open surface which is fully exposed to vacuum.

Knudsen effusion method (KEM). The vapor pressure is calculated by the Hertz-Knudsen equation as follows:

$p_{\mathrm{sat}}=\frac{\mathrm{d}m/\mathrm{d}\tau }{K}\sqrt{\frac{2\mathit{\pi RT}}{M}}$

(1.1)

where dm/dτ is a mass loss rate (kg s^{− 1}) at temperature T (K), M is the molar mass of the vapor phase (kg mol^{− 1}), the K-value in Eq. (1.1) is calculated as a product of the Clausing coefficient K_c [17] and the area of the orifice, S_orif, in the thin membrane. The mass loss rate is restricted to the effusion of the evaporating sample through the orifice with S_orif, taking into account the resistance of the membrane to effusion due to its definite thickness. The Clausing coefficient is usually calculated by the simplified equations 1/(1 + l/2r) or 1/(1 + 3l/8r), where l is the thickness of the membrane and r is the orifice diameter. Eq. (1.1) is generally valid for experimental conditions where the ratio of the mean free path λ to the orifice diameter (known as Knudsen number Kn = λ/2r) is equal to or > 10 [18]. In praxis, it is possible to maintain this condition for pressures at around 1 Pa and...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Foreword
• Chapter 1: Development of Direct and Indirect Methods for the Determination of Vaporization Enthalpies of Extremely Low-Volatile Compounds
• Chapter 2: Fast Scanning Chip Calorimetry
• Chapter 3: Dilatometry
• Chapter 4: Modern Isoconversional Kinetics: From Misconceptions to Advances
• Chapter 5: Kinetics and Mechanisms of Solid-Gas Reactions
• Chapter 6: Physico-Geometric Approach to the Kinetics of Overlapping Solid-State Reactions
• Chapter 7: Analysis of Polymer Crystallization by Calorimetry
• Chapter 8: Glass Transition and Physical Aging of Confined Polymers Investigated by Calorimetric Techniques
• Chapter 9: Decomposition of Organic Wastes: Thermal Analysis and Evolution of Volatiles
• Chapter 10: Thermal Analysis of Biobased Polymers and Composites
• Chapter 11: Polymer Nanocomposites
• Chapter 12: Thermal Behavior of Chalcogenide Glasses
• Chapter 13: Applications of Thermal Analysis to the Study of Phase-Change Materials
• Chapter 14: Characteristics of Thermal Decomposition of Energetic Materials in a Study of Their Initiation Reactivity
• Chapter 15: Pharmaceutical Applications of Thermal Analysis
• Chapter 16: Thermoanalytical Characterization Techniques for Multiferroic Materials
• Chapter 17: Chalcogenides for Phase-Change Memory
• Chapter 18: Recent Advances in Thermal Analysis and Calorimetry of Aluminum Alloys
• Chapter 19: Metals and Alloys
• Index