## 1 Introduction  
Carbon/graphite materials exhibit excellent physical and chemical properties such as high electrical/thermal conductivity, mechanical strength, and thermal/chemical resistance due to their unique molecular and orbital structures. With these beneficial engineering properties, works on various applications have been reported [1; 2; 3]. Coal tar pitch has a high degree of aromaticity of constituent atoms and is able to develop layered graphene structures through intermolecular stacking upon heat treatment. Due to its unique molecular structure and composition, superior properties (e.g., high carbonization yield, high degree of graphitization) in the final carbonaceous/graphitic products thereof can be obtained. Like petroleum-based raw materials (i.e., residues, heavy oils from oil refineries), coal tar pitch is also regarded as an important resource for the production of needle coke and artificial graphite and is widely used in the carbon/graphite materials industry. It is generally known that quinoline insolubles (QI) and aromatic properties existing in raw coal tar pitch are critical components determining micro-texture development in the delayed cooking process. [4; 5; 6]. QI can be defined as a variety of solid carbonaceous particles and highly aromatic hydrocarbons with a high molecular weight that are the by-products of the metallurgical coke production process. The solid carbonaceous particles in QI are generally ashes, cenospheres, char, and pyrolytic carbon [7]. The concentration of QI should be minimized to promote the coalescence of burgeoning mesophase spheres upon heat treatment of coal tar pitch, yielding the needle-shaped (uniaxially oriented) coke texture [8; 9; 10; 11; 12]. However, the QI removal (or extraction) process is known to be strenuous and complicated due to the complexity of the coal tar pitch composition and the requirement of delicate process controls [13]. In this work, aliphatic-rich solvents fractionally distilled at different boiling point ranges were used as additives in the extraction process to separate the QI component present in coal tar pitch. For an efficient extraction process, mixing between coal tar and the added solvent was conducted under pressurized and heated conditions. The aliphatic components in the extraction solvent are believed to facilitate the precipitation of QI in coal tar pitch by undermining the stabilized dissolution state of QI [14]. The paraffinicity of the aliphatic solvent can be estimated with a \(K\)-factor, as defined in the following formula [15]:  
\[K\ =\ \frac{\sqrt[3]{1.8\ T_{b}}}{S.G.} \tag{1}\]  
where \(T_{b}\) is the molar average boiling point (Kelvin) and \(S.G.\) is the specific gravity. As shown in Equation (1), paraffinicity is relevant to the boiling point and specific gravity of the solvent. The stronger paraffinicity of a solvent is expected to reduce its dissolution performance toward larger molecules with high aromaticity (i.e., QI components in coal tar pitch), yielding easier precipitation of QI. To alter solvent paraffinicity, fractional vacuum distillation with a multi-columned apparatus was conducted on a petroleum-derived aliphatic-rich solvent. Each recovered distillate fraction possessing a different \(K\)-factor (calculated from Equation (1)) was used as an additive in the consecutive QI extraction process. For efficient mixing between coal tar and the added solvent, a pressurized heating reactor was used, as shown in Figure 1. Through the extraction process, QI-rich fractions in coal tar are precipitated and concentrated at the bottom of the reactor; thus, QI-removed fractions can be separated easily. For the evaluation of rheological properties, dynamic viscosity measurement over coal tar pitch was performed at various shear rates and temperatures. The coke-forming behavior was evaluated with a lab-scale cooking apparatus. Polarized microscopy was used to obtain micro-texture images from the produced coke specimens.