Characterization of coal- and petroleum-derived binder pitches and the interaction of pitch/coke mixtures in pre-baked carbon anodes.

摘要

Carbon anodes are manufactured from calcined petroleum coke (i.e. sponge coke) and recycled anode butts as fillers, and coal tar pitch (SCTP) as the binder. During the manufacturing of carbon anodes, coal tar pitch is mixed with calcined petroleum coke. The mix of binder, filler and some additives is heated to about 50°C above the softening point of the pitch, typically 160°C. This temperature is sufficient to enable the pitch to wet the coke particles. The mix is then either extruded, vibrated, or pressed to form a green anode. The binding between coke and pitch is very important to the anode properties.;There are different binder pitches used in this work, which were standard coal tar pitch (SCTP-2), petroleum pitch (PP-1), gasification pitch (GP-115), coal-extract pitch (WVU-5), and co-coking pitches (HTCCP and OXCCP). Petroleum pitch is a residue produced from heat-treatment and distillation of petroleum fractions. Production of coal-extract pitch involves a prehydrogenation of coal followed by extraction using a dipolar solvent. Gasification pitches are distilled by-product tars produced from the coal gasification process. Co-coking pitch was developed in this work and was obtained from the liquid distillate of co-coking process of coal and heavy petroleum residue. Understanding of composition and structures of pitches from different sources and processes would lead to greater understanding of the binding properties of pitch in carbon anodes and was one of the main focuses in this study. Characterization of pitches by using different techniques including gas chromatography/mass spectrometry (GC/MS), high performance liquid chromatography (HPLC), matrix-assisted laser desorption ionization/mass spectrometry (MALDI/MS), 1H and 13C solution-state nuclear magnetic resonance (NMR), and 13C solid-state NMR yield important chemistry and structural information.;The binding, or in other words the interactions in the pitch/coke mixture, is another interest in this study. Pitch itself is a very complex material. Studying the binding between pitch and the porous coke even adds another level of complexity to this subject. The high-temperature 1H NMR has been shown to be a promising technique to study the molecular interaction between different materials. The fraction of the mobile protons in the sample and their mobility as measured by the spin-spin relaxation time ( T*2 ), which is inversely proportional to the peak width at half maximum height (DeltaH1/2), seem to have a potential to probe the extent of the interaction between pitch and coke. Understanding of the interaction between coke and some simple compounds which are commonly found in pitch, i.e. model compounds, should help identify the binding efficiency between pitch and coke. The knowledge of (1) pitch chemistry and structure, (2) interaction between model compounds and filler cokes would lead to an understanding of the binding efficiency between pitch and coke.;The mass distribution by MALDI analysis showed that the majority of the compounds in these pitches is in the range of 200-700 Da. The hexane-soluble (HS) fractions of all of the pitch samples in this study mainly consist of four-ring polycyclic aromatic compounds (PACs) as observed by GC/MS and Pyrolysis-GC/MS techniques. Coal-derived pitches contained mainly cata- and peri-condensed PACs and a few alkyl- and heteroatomic-substituted PACs, whereas those peteroleum-derived pitches consisted of a number of alkyl-substituted PACs with high sulfur substitution.;Solid-state NMR results show that SCTP-2 and PP-1 contain six and five fused rings on average, respectively, whereas GP-115 and WVU-5 contain two and three fused rings on average, respectively. The latter two pitches contained mostly methyl substituents with a few ethyls. WVU-5 contains a higher degree of naphthenic substituents as compared to other pitches as confirmed by the GC/MS analysis. HTCCP and OXCCP contained three peri-condensed fused rings on average per molecule.;1H in-situ high temperature NMR and the solid echo pulse program were employed to study the change in mobility of model compounds, pitches and their mixtures with petroleum coke. Due to the limitation in number of model compounds used in this study, no correlation could be drawn between the extent of interaction of the model compound/coke mixtures and the size of the model compounds. Topology seemed to play an important role in enhancing the mobility of the model compound when mixed with petroleum coke. Peri-condensed and branched cata-condensed molecules tended to have higher mobility enhancement than the cata-condensed PACs. In the pitch/coke mixtures, pitch that contains a higher HS fraction tended to greater enhance the mobility between pitch and coke. Green density and the mobility enhancement were in agreement in comparing the ability of a pitch to wet the coke surface and form a good carbon anode. (Abstract shortened by UMI.)