Modeling the Coal Tar Pitch Primary Carbonization Process

ABSTRACT: The properties of the carbon materials obtained as the final product of coal tar pitch carbonization process are a consequence of the type of chemical and physical phenomena occurring through the process. A new simplified approach for modeling of the primary carbonization is presented to provide the semi-quantitative knowledge about the process useful for improving the efficiency of the industries that deal with this process. The proposed approach is based on defining thermodynamic and kinetic equations simply representing numerous phenomena happening during primary carbonization. Partial pressures of emitted volatiles in a simple pitch system are studied. The model enables estimating the mass and enthalpy changes of pitch through thermal treatment consistent with experimental data for mass losses of pitch heat treated up to 550 ◦C. Application of the model to describe molecular weight distribution changes of pitch during primary carbonization is demonstrated, showing a good agreement between the presented results and the investigations reported by Greinke. For the first time, the effect of important parameters in pitch carbonization, such as the heating rate of the pitch and the carrier gas flow rate, on the emission rate of volatiles is successfully modeled. The present model is well able to estimate the energy requirement for thermal treatment of pitch up to 350 ◦C

Thermodynamic Model for Coal Tar Pitch and Carbonaceous Mesophase Present during Primary Carbonization: Thermal Treatment of Carbon Pastes in the Aluminum Industry

RÉSUMÉ: Il est bien établi que le procédé de carbonisation des matériaux joue un rôle critique dans la production de matériaux à base de carbone. La carbonisation est définie par la transformation thermique d’une substance carbonée en charbon (« carbon material », CM). Les CMs ont plusieurs usages, par exemple : les électrodes en graphite pour les fours à arc électriques, les brosses de charbon pour moteurs électriques, les scellants, les roulements à bille en acier et carbone, les accumulateurs électriques, les anodes et cathodes des alumineries. Le brai provenant du goudron (« coal tar pitch », CTP) est par ailleurs très utilisé comme liant dans les procédés industriels mentionnés ci-dessus. Par exemple, le CTP est le principal matériau utilisé dans la fabrication du liant de la pâte de Söderberg, utilisée dans les anodes précuites du procédé Hall-Héroult des alumineries. Le CTP constitue entre 14 et 17% du poids total des blocs anodiques de coke vert. Les CTPs industriels ont une composition chimique extrêmement complexe, contenant des centaines, voire des milliers de composés, y compris des monomères, des oligomères et des polymères d’hydrocarbures aromatiques polycycliques (PAH) avec une large gamme de poids moléculaires. Une meilleure compréhension des propriétés thermodynamiques et du comportement des phases des constituants des CTPs lors de la carbonisation, et ce à plusieurs températures, améliore les procédés de production de CMs et, par conséquent, les propriétés des CMs résultants. L'acquisition de connaissances sur la description thermodynamique et la configuration d'équilibre de la mésophase, qui apparait lors de la cuisson des blocs anodiques verts et des pâtes à enfoncer entre les blocs cathodiques, se traduira par une amélioration de l’efficacité du processus de production d'aluminium Hall-Héroult. ----------ABSTRACT: The critical technological role played by the carbonization process in the production of carbon-based materials is well established. Carbonization is formally defined as the thermal transformation of carbonaceous materials into carbon materials (CM). CMs are widely used to produce various materials ranging from needle coke for graphite electrodes used in electric-arc furnaces, electrical and mechanical carbon materials widely applied to electric motors brushes, sealing materials, carbon bearings, current collectors, pitch-based fibers to aluminum-smelting prebaked electrodes. Coal tar pitches (CTP) are of great interest as precursors (binders) in the above-mentioned industrial production processes. As a specific example, the major constituent of the binder of Soderberg paste used in carbon prebaked anodes in the Hall-Héroult process used for commercial plants of aluminum production is coal tar pitch, constituting between 14% and 17% (by mass) of the green anode blocks. Commercial CTPs are exceedingly complex materials containing hundreds to thousands of different constituents, including monomers, oligomers and polymers of polycyclic aromatic hydrocarbon (PAH) and heterocyclic compounds with a wide range of molecular weights. A better understanding of the thermodynamic properties and phase behavior of the constituents of CTPs during carbonization over a wide range of temperatures will improve CM production processes and, consequently, the properties of the resultant CMs. Obtaining the knowledge about thermodynamic description and equilibrium configuration of mesophase-containing pitches, which appear during baking of green anode blocks and ramming paste between cathode blocks, will result in efficient Hall-Héroult aluminum production process

Modeling the Coal Tar Pitch Primary Carbonization Process

The properties of the carbon materials obtained as the final product of coal tar pitch carbonization process are a consequence of the type of chemical and physical phenomena occurring through the process. A new simplified approach for modeling of the primary carbonization is presented to provide the semi-quantitative knowledge about the process useful for improving the efficiency of the industries that deal with this process. The proposed approach is based on defining thermodynamic and kinetic equations simply representing numerous phenomena happening during primary carbonization. Partial pressures of emitted volatiles in a simple pitch system are studied. The model enables estimating the mass and enthalpy changes of pitch through thermal treatment consistent with experimental data for mass losses of pitch heat treated up to 550 °C. Application of the model to describe molecular weight distribution changes of pitch during primary carbonization is demonstrated, showing a good agreement between the presented results and the investigations reported by Greinke. For the first time, the effect of important parameters in pitch carbonization, such as the heating rate of the pitch and the carrier gas flow rate, on the emission rate of volatiles is successfully modeled. The present model is well able to estimate the energy requirement for thermal treatment of pitch up to 350 °C