Analysis of the carbonization and formation of coal tar pitch mesophase under dynamic conditions

doi:10.1016/S0008-6223(03)00301-4

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Volume 41, Issue 12, 2003, Pages 2413-2424

https://doi.org/10.1016/S0008-6223(03)00301-4 Get rights and content

Abstract

Thermokinetic analysis of three pitch samples was carried out: coal tar pitch obtained from light coke oven tar (P), mesophase pitch after 10.5 h (MP1), and mesophase pitch after 12 h (MP2) thermopreparation at 410 °C. The process was realized in a continuous system with a 10 kg mass being charged to the reactor. It was demonstrated using Kissinger’s law that the temperature criterion, the first-order thermokinetics and the calculated Arrhenius law parameters fulfill the isokinetic effect when the classical routes of thermokinetic analysis of the samples prepared under dynamic conditions (at three heating rates) are used, which makes the qualitative interpretation of differences between these samples difficult. An alternative solution was proposed using the relative rate of thermal decomposition. The temperature ranges of the chemical reactions leading to the formation of mesophase structures, as well as the temperature ranges of the coking processes of the Fixed Carbon phase, were determined.

Introduction

The advantage of using coal tar pitch in various applications results from its ability to form pure carbon residue from the liquid phase in high yield. It also has good adhesive properties as a binder. Coal tar pitch is used both in traditional industry as well as in modern material engineering [1], [2], and its properties can be tailored within a broad range according to the designed application [3].

Adaptation of the properties of coal tar pitch for use as a substrate for different materials depends mainly on the heat treatment process (thermopreparation). Thermopreparation is a preliminary stage of low-temperature pitch pyrolysis, which is usually followed by further stages, up to carbonization and graphitization temperatures. Coal tar pitch is a mixture of organic compounds forming complex polyazeotropic and polyeutectic systems. Hence, during pyrolysis, several exo- and endothermic reactions take place, which influence the overall kinetics and the resulting energetic effect. Pitch thermolysis is usually associated with phenomena similar to the carbonization of individual high-molecular-weight organic compounds. Reactive radical centers, which are formed during pyrolysis, initiate condensation reactions, i.e. dimerization and oligomerization of aromatic compounds [4], [5]. According to earlier investigations, bond breaking, polymerization, condensation and intermolecular reorganization reactions play a major role during this process [6], [7]. The formation of a mesophase is the fundamental process during preliminary pyrolysis, and the mesophase can be considered as a liquid crystal or intermediate plastic stage of anisotropic character [8]. It is known that the transition through a well-formed mesophase is the precondition for obtaining the desired graphite structure in the final product [2].

The aim of this work was to assess the thermopreparation of coal tar pitch in a continuous experimental system, and this was achieved by means of the thermokinetic analysis of the initial pitch (P). In addition, two mesophase pitches (MP1, MP2), different in their degree of transformation into the mesophase, were also analyzed. It was assumed that the thermal analysis of pitches can be carried out independently by different methods: an analysis by the mathematical transformation of the degree of conversion by conventional methods (Kissinger’s law), by a temperature criterion, and by first-order thermokinetics. Moreover, the related rate of thermal decomposition was also analyzed.

Section snippets

Experimental

The initial pitch was obtained by distillation of light tar with a small amount of primary phases insoluble in quinoline. After removal of water from the water–tar condensates, the light tar was distilled in the installation, maintaining the distender temperature within the range 340–350 °C, obtaining the initial pitch for thermopreparation.

The properties of the light tar and those of the pitch obtained from distillation of the tar are given in Table 1.

The thermopreparation process for obtaining

Thermokinetic equations

Thermogravimetric techniques (TG, DTG) are commonly used for monitoring the variation of the properties of pitches and other substances (such as bitumens) during heat treatment, and eventually they are also used for consideration of particular thermal effects [9], [10], [11], [12], [13], [14], [15]. However, only a few studies have considered the transformation of mass change rates during thermal treatment under dynamic conditions (linear temperature increase) into new temperature-dependent

The Kissinger law

The Kissinger law (5) is very useful to determine the Arrhenius law parameters (E and A), as the parameters represented by the functions f(α) or g(α) are not needed, provided that thermal decomposition takes place according to nth-order kinetics (n>0). Fig. 1 shows that, for pitch P (Fig. 1a) and for mesophase pitch MP2 (Fig. 1c), the relations between the heating rate q and the temperature of the maximum rate of the degassing reaction T_m are very similar in terms of linear equation parameters,

Discussion

The results of this study and those of Ref. [1] indicate that the thermopreparation of coal tar pitch occurs in multidirectional reaction routes as a result of chemical reactions interfering with the volatilization of various compounds and the formation of an anisotropic phase from the liquid isotropic phase.

The route of subsequent reactions may be formulated in two stages [25], [26]: $coal tar pitch (P) → >200–550 °C mesophase pitch (MP) → 360–600 °C char (Ch) → 550–600 °C Fixed Carbon (FC)$ $(FC)_{i} → ≥600 °C (FC)_{f}$

Conclusions

1.
The analysis of both coal tar pitch and mesophase pitch obtained from coal tar pitch according to the technology described in Ref. [2] and performed with the use of classical methods (Kissinger’s law, temperature criterion and first-order thermokinetics) shows that there is an isokinetic effect, which makes identification of the observed qualitative pitch changes difficult. Only the Kissinger law offers the suggestion of a very similar thermo-chemical reactivity of all samples. It was possible

Acknowledgements

This work was supported by the Polish State Committee for Scientific Research, grant No. 7T08D03119.

References (26)

I. Mochida et al.
Chemistry of synthesis, structure, preparation and application of aromatic-derived mesophase pitch
Carbon
(2000)
I.C. Lewis
Chemistry of carbonization
Carbon
(1982)
J.D. Brooks et al.
The formation of graphitizing carbons from the liquid phase
Carbon
(1965)
G.W. Collett et al.
Thermogravimetric investigation of the pyrolysis of pitch materials. A compensation effect and variation in kinetic parameters with heating rate
Thermochim Acta
(1980)
I. Charit et al.
Thermogravimetric characterization of the suitability of various pitches as a matrices for carbon–carbon composites
Thermochim Acta
(1983)
M. Alula et al.
Contribution to the characterization of pyrolysis coal products by means of thermal analysis
Fuel
(1990)
A. Martinez-Alonso et al.
Suitability of thermogravimetry and differential thermal analysis techniques for characterization of pitches
Fuel
(1992)
J.M. Jiménez-Mateos et al.
Characterisation of petroleum bitumins and their fractions by thermogravimetric analysis and differential scanning calorimetry
Fuel
(1996)
C. Yue et al.
Pyrolysis of pitch
Fuel
(1998)
A. Mianowski et al.
The possibility of identification of activation energy by means of the temperature criterion
Thermochim Acta
(1994)

K.J. Hüttinger et al.

Kinetics of mesophase formation in a stirred tank reactor and properties of the product—II. Discontinuous reactor

Carbon

(1992)

K.J. Hüttinger et al.

Kinetics of mesophase formation in a stirred tank reactor and properties of the product—III. Continuous reactor

Carbon

(1992)

Z. Robak et al.

Preparation of the mesophase coal tar pitch and its application study

Pol. J. Chem. Technol.

(2000)

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Analysis of the carbonization and formation of coal tar pitch mesophase under dynamic conditions

Abstract

Introduction

Section snippets

Experimental

Thermokinetic equations

The Kissinger law

Discussion

Conclusions

Acknowledgements

Carbon

Carbon

Carbon

Thermochim Acta

Thermochim Acta

Fuel

Fuel

Fuel

Fuel

Thermochim Acta

Carbon

Carbon

Preparation of the mesophase coal tar pitch and its application study

Pol. J. Chem. Technol.