Preventing mesophase growth in petroleum pitches by the addition of coal-tar pitch

摘要

In recent years a series of problems in relation with the use of traditional coal-tar pitches has come to light. First, coal-tar production has declined and coal-tar is not always located at the point of demand, which is especially worrying in the case of North America [I]. Second, the processing of coal-tar pitches in non-controlled environments (e.g., Soderberg carbon anode installations) gives rise to environmental and worker health problems due to the emission of polycyclic aromatic hydrocarbons (PAH). Some of these PAH are catalogued as toxic and/or carcinogenic [2-4]. Recently, a new type of binder based on the use of petroleum pitches, which are potentially less toxic and carcinogenic than coal-tar pitches 141, has come onto the market. Blends with optimum properties can be obtained by combining coal-tar pitch and petroleum pitch in different ratios [5]. The characteristics of such blends resemble those of coal-tar pitch or petroleum pitch (Table 1), depending on the composition of the blend. However, when blends are pyrolyzed they exhibit a behaviour that is dependent not only on the characteristics of the parent pitches but also on the mutual interactions between the two components 161. These interactions are particularly patent during the formation and growth of mesophase. In this work. the blends were prepared from a typical binder coal-tar pitch (CTP-A) and a petroleum pitch (PP-B) by mixing CTP-A:PP-B in different ratios 161: 85:15 (AB 15), 70:30 (AB30). 55:45 (AB45) and 40:60 (AB60). Single pitches and their blends were pyrolyzed to 450 deg C for a residence time of 30 min, using test tubes. The pyrolyzed products were then embedded in epoxy resin and ground and polished for polarized-light microscopy studies.