the effect of binder pitch quinoline insolubles content - Coke Oven ...

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BINDER PITCH QI CONTENT – ALUMINIUM ANODE 450 – 600 600 - 900 900 - 1200 132 Coking – Formation and growth of mesophase leading to the transition from a plastic to a solid binder matrix. The binder coke forms “bridges” between the filler particles. Release of the major amount of non-coking volatiles. Post coking – Release of heavy cracked volatiles, methane, and hydrogen. Annealing of tensions in the coked structure Crystalline re-orientation and growth of the binder carbon and possibly the lowest calcined filler coke. The formation and growth of mesophase in the binder pitch has a strong influence on anode properties [2]. If mesophase can grow and coalesce unhindered, the resulting binder coke will be well ordered with an anisotropic “flow” optical texture when examined under a microscope using cross-polarised light. Anisotropic binder cokes tend to reduce the electrical resistivity and reactivity of the anode; however the anode strength can also be reduced due to cleavage between the layers in the structure [2]. Disruption of mesophase development results in a more disordered or isotropic coke structure that imparts greater strength to the anode. The influence of normal QI on this carbonization process, and hence anode properties, has been studied extensively. A feature of these studies, however is wide disagreement on what the effect is of varying amounts of normal QI on binder pitch performance. A review of the literature shows that the following have been attributed to the presence of normal QI in pitch: Wetting of the filler particles: There is disagreement as to whether normal QI improves the coating of petroleum coke particles by pitch [3,4], makes it worse [5,6] or has no influence [7].
COKE OVEN MANAGERS’ YEAR BOOK Controls the penetration of pitch into coke porosity by forming a filter cake at the pore entrance. [2,3,8,9]. This filter cake of normal QI carbonizes to a tough, strong carbon imparting strength to the coke/pitch interface. Provides a pathway for the release of volatiles from the binder during baking [3,4]. Increases the coking value of pitch due to its own high coking value [3] There is general agreement that the presence of normal QI increases the amount of disorder (isotropy) in the binder coke [2,3,5,8,10,11,12,13]; however how this isotropy is achieved is not agreed: One view is that normal QI influences the chemistry of the carbonization process by acting as a site for mesophase nucleation [3,14], thereby increasing the coking value of pitch beyond the contribution of its own coking value; or by acting as a cross linking agent to reduce the size of the binder coke optical texture [11,13]. It has also been reported that normal QI slows the carbonization process up to temperatures of 850 – 900 o C [15]. The alternative viewpoint suggests that the influence of normal QI on the carbonization process is only physical, i.e. the normal QI acts as additional aggregate particles [2,5,12,16,17,18] that are physically absorbed onto the surface of the growing mesophase, inhibiting their ability to grow by coalescence [2,3,10,12]. This results in pockets of high normal QI and isotropic carbon in a more anisotropic binder matrix. Greater levels of normal QI, increase the anode optimum pitch requirement [5,14,19,20,21]. This is due to the normal QI particles being wet by, and hence effectively consuming, liquid pitch and by these particles taking up volume in the binder that could otherwise be occupied by liquid pitch. The reported increase in optimum pitch requirements is about 0.1% for each additional 1% of normal QI in the binder [5]. 133
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