Fossil fuel-derived and synthesized pitches, consisting of a complex mixture of numerous aromatic hydrocarbons, are important resources of polycyclic aromatic hydrocarbons (PAH) that can be treated for the manufacturing of various carbon-based materials as graphite electrodes, carbon anodes, carbon fibers and composites fibers. The quality of the pitch-derived carbons is strictly dependent on the complex composition and properties of pitch precursors. Details on the PAH composition of parent pitches and the related soft interactions and assembly mechanism, are important for determining final pitch properties achieved after the heat treatment, typically involved in the production of carbon artefacts. Besides, pitches are readily available mixtures of large PAH which can be used in the place of purposely-synthesized individual PAH, as realistic models of the different nanosized sp2 domains featuring ordered and disordered carbon materials. The study of their chemical characteristics and spectroscopic features can hence be useful to infer the structural characteristics of sp2 nanostructures in disordered carbon materials. Large unsubstituted and substituted monomeric aromatic compounds, along with oligomeric systems where aromatic units can be connected by e.g. C-C single bonds (oligo-aryl type), -CH groups, ether bridges, are considered to be the basic constituents of both coal tar [1,2] and naphthalene-derived pitches [3]. As a consequence of their different source, coal tar pitch (CP) and naphthalene pitch (NP) have quite different properties as softening point, coke yield, etc., in spite of their similar H/C atomic ratio (around 0.5) and aromatic nature. In this work the comparative study of their properties was carried out by a multi-array analytical approach including heptane and toluene extractions. A detailed characterization of parent pitches and solvent separated fractions was performed. Composition and thermal behavior were analyzed by gas chromatography-mass spectrometry, size exclusion chromatography, thermogravimetry and laser desorption-mass spectrometry to compare the volatility and thermal stability in relation to their solubility and molecular weight distribution. Specific structural features were measured by infrared, UV-visible and fluorescence spectroscopy. The cross-check of the information obtained by different methodologies, picking up from each technique the most important information, was useful to deepen and validate the characterization of very structurally different large PAH systems featuring both pitches. The deep spectroscopic analysis used to get insights on structural features as aliphatic/aromatic hydrogen distribution and aromatic moieties allowed to differentiate between the class of ortho fused PAH, featuring CP, and the class of aromatic rylene moieties interspersed with aliphatic (mainly naphthenic) groups, which makes up NP.
Insights on structures of the large polycyclic aromatic hydrocarbons systems featuring coal tar pitch and naphthalene pitch
B Apicella;V Gargiulo;C Russo;F Stanzione;A Tregrossi;A Ciajolo
2015
Abstract
Fossil fuel-derived and synthesized pitches, consisting of a complex mixture of numerous aromatic hydrocarbons, are important resources of polycyclic aromatic hydrocarbons (PAH) that can be treated for the manufacturing of various carbon-based materials as graphite electrodes, carbon anodes, carbon fibers and composites fibers. The quality of the pitch-derived carbons is strictly dependent on the complex composition and properties of pitch precursors. Details on the PAH composition of parent pitches and the related soft interactions and assembly mechanism, are important for determining final pitch properties achieved after the heat treatment, typically involved in the production of carbon artefacts. Besides, pitches are readily available mixtures of large PAH which can be used in the place of purposely-synthesized individual PAH, as realistic models of the different nanosized sp2 domains featuring ordered and disordered carbon materials. The study of their chemical characteristics and spectroscopic features can hence be useful to infer the structural characteristics of sp2 nanostructures in disordered carbon materials. Large unsubstituted and substituted monomeric aromatic compounds, along with oligomeric systems where aromatic units can be connected by e.g. C-C single bonds (oligo-aryl type), -CH groups, ether bridges, are considered to be the basic constituents of both coal tar [1,2] and naphthalene-derived pitches [3]. As a consequence of their different source, coal tar pitch (CP) and naphthalene pitch (NP) have quite different properties as softening point, coke yield, etc., in spite of their similar H/C atomic ratio (around 0.5) and aromatic nature. In this work the comparative study of their properties was carried out by a multi-array analytical approach including heptane and toluene extractions. A detailed characterization of parent pitches and solvent separated fractions was performed. Composition and thermal behavior were analyzed by gas chromatography-mass spectrometry, size exclusion chromatography, thermogravimetry and laser desorption-mass spectrometry to compare the volatility and thermal stability in relation to their solubility and molecular weight distribution. Specific structural features were measured by infrared, UV-visible and fluorescence spectroscopy. The cross-check of the information obtained by different methodologies, picking up from each technique the most important information, was useful to deepen and validate the characterization of very structurally different large PAH systems featuring both pitches. The deep spectroscopic analysis used to get insights on structural features as aliphatic/aromatic hydrogen distribution and aromatic moieties allowed to differentiate between the class of ortho fused PAH, featuring CP, and the class of aromatic rylene moieties interspersed with aliphatic (mainly naphthenic) groups, which makes up NP.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
