Effect of Carbonaceous Precursors on the Structure of Mesophase Pitches and Their Derived Cokes

Abstract

Using six representative feedstocks as carbonaceous precursors, various mesophase pitches and their derived cokes were obtained by a heat-soaking method at a temperature range of 400−450 °C and a pyrolysis treatment at 900 °C, respectively. The optical texture and microstructure of the different mesophase pitches and their derived cokes were characterized by polarized-light microscope, scanning electron microscope, and X-ray diffraction. The results show that the formation and development abilities of liquid crystalline mesophase are obviously different for the various feedstocks. C 9 aromatic hydrocarbons and petroleum-derived paving pitch possess relatively high thermo-chemical reactivity due to the existence of low molecular substances and aliphatic groups, leading to form liquid crystalline mesophase easier and faster than those of naphthalene synthetic pitch and coal tar-based impregnating pitch under a similar condition, which however is undesirable to develop a bulk mesophase. Anthracene possesses a characteristic of forming a homogeneous bulk mesophase with a streamline texture under a suitable condition. The liquid crystalline transformation behavior of C 5 −C 9 aromatic hydrocarbons is unexpectedly similar to that of naphthalene synthetic pitch and markedly different from that of C 9 aromatic hydrocarbons. Carbonaceous precursors have a significant effect on the anisotropic content and the optical texture of the mesophase pitch products, which leads to the microstructure variety of the resultant cokes. Fine-grained and coarse-grained mosaic textures are, respectively, present in the cokes derived from C 9 aromatic hydrocarbons and petroleum-derived paving pitch. The cokes derived both from coal tar-based impregnating pitch and from C 5 −C 9 aromatic hydrocarbons possess a supra mosaic texture mingled with a local flow-induced orientation domain. A well-oriented lamellar texture is clearly found in the cokes derived from anthracene and naphthalene synthetic pitch.

Preparation, Characterization, and Applications of Carbonaceous Mesophase: A Review

“…Figure 3 shows the flow diagram of catalytic thermal polymerization of naphthalene molecule to prepare carbonaceous mesophase pitch as shown in Figure 2(b) by a two-step reaction process at a liquid-phase carbonization temperature of 350-450°C for a certain period of time. It could be concluded that some carbonaceous precursors (e.g., naphthalene) have undergone four stages of liquid-crystalline sphere development and transformation and finally formed a bulk liquid-crystalline mesophase from an isotropic matrix as illustrated in Figure 4 under a suitable reaction condition (i.e., reaction temperature and time) [2,15,16]. The general four-stage conversion of liquid crystals during the whole process is diagramed as follows: (I) generation of optically anisotropic spheres in isotropic matrix, (II) growth of anisotropic spheres in isotropic matrix, (III) coalescence of anisotropic spheres in isotropic matrix, and (IV) deformation and disintegration of anisotropic coalesced spheres to form bulk liquid-crystalline mesophase.…”

“…However, it has been demonstrated that the formation, development, and transformation of liquid-crystalline anisotropic spheres (i.e., nucleation, growth, coalescence and deformation and orientation) in an isotropic pitch matrix are unconcerted and inhomogeneous during the process of liquid-phase carbonization as shown in Figure 5 [16]. Furthermore, it is not easy to obtain a 100 vol.% anisotropic mesophase pitch (i.e., bulk mesophase) both with a fine flow optical texture and an acceptable softening point less than 300°C for subsequent fiber spinning.…”

“…This mainly depends on the carbonaceous precursors (e.g., molecular unit size, the flatness of molecules and the chemical reactivity, etc.) and the suitable thermal reaction conditions adopted [2,15,16].…”

“…It can be clearly seen that mesophase pitch-derived coke exhibits a well-oriented texture as shown in Figure 13(a, b), which is closely related to the formation and development of flow-type liquid crystalline in carbonaceous mesophase products during the process of delayed coking [5]. In contrast, coarse-grained mosaic texture is presented in the coke derived from commercial coal-tar pitch as shown in Figure 13(c, d) [16,20]. Thus it can be concluded that the carbonaceous feedstocks have a significant influence on the optical texture and microstructure of resulting coke, which depends on the development and evolution of carbonaceous mesophase during the liquid-phase carbonization process.…”

Preparation and characterization of pitch coke from oxidized polymerized pitch

“…As a type of polycyclic aromatic carbonaceous compounds with excellent physical and chemical properties, coal pitch has attracted more attention in varied fields such as: metallurgy, the chemical industry, machining, and construction 1–4 . In recent years, the efficient and high value‐added utilization of coal pitch has been a common research topic 5–8 . Coal pitch is usually divided into four categories in literature: high‐temperature coal tar pitch, 9 medium‐low‐temperature pitch, 10 coal liquefied pitch, 11 and synthesized pitch 12,13 …”