## 3 Results and Discussions  
### Properties of the MLCTs and Their Narrow Distillate Fractions  
Table 1 shows the main properties of the MLCTs. The density of MLCT-Z and MLCT-S are 1.032 g/cm\({}^{3}\) and 1.038 g/cm\({}^{3}\) (after dehydration at 20 \({}^{\circ}\)C), the H/C ratios are 1.339 and 1.314, and the molecular weights are 203 and 187, respectively. It can be seen that they have a relatively high H/C ratio, low contents of the insoluble fraction, and a high content of oxygen and nitrogen. Meanwhile, theelements with higher content are Fe, Ca, and Al, mainly exist in the form of different salts. Compounds containing oxygen are key characteristic components of MLCT, accounting for 4.11% and 4.96% of the MLCTs, and mainly exist in phenolic compounds. The chemical instability of the MLCTs is caused by heteroatomic compounds containing oxygen, nitrogen, and metal. Fortunately, the low sulfur is very favorable for the deep processing of coal tar. The initial boiling point and temperature of the 80% distillate of MLCT were relatively high, implying that heavy components still occupied a large proportion of the fraction. MLCT-Z and MLCT-S show obvious characteristics of medium- and low-temperature coal tars, such as a high H/C ratio, low contents of sulfur and insoluble fractions, a low density, and a low viscosity, while the contents of ash and carbon residue are high. Figures 1 and 2 show the yields and molecular weights of the narrow distillate fractions, respectively. Different compounds in MLCT have different boiling points, so that the distillate fractions can be separated according to their boiling points. Moreover, true boiling point distillation can effectively control the carbon number of compounds in each narrow distillate fraction. The total fraction of MLCT was fractionated into 11 distillate fractions. As the boiling point increases, the yield of each distillate fraction increases gradually, except for the 270-300 \({}^{\circ}\)C distillate fractions. With the boiling point temperature increasing from IBP-170 \({}^{\circ}\)C to \(>\)360 \({}^{\circ}\)C, the molecular weight of each distillate fraction increases continuously. In the same boiling range, the relative molecular mass of different MLCT fractions is different. According to the boiling point temperatures of MLCT-Z and MLCT-S, the yields are as follows: Naphtha fraction (IBP-170 \({}^{\circ}\)C) 1.15 and 0.93 wt %, phenol oil fractions (170-230 \({}^{\circ}\)C) 8.36 and 11.45 wt %, and diesel fraction (230-360 \({}^{\circ}\)C) 36.52 and 35.86 wt %. The yield of the \(>\)360 \({}^{\circ}\)C distillate fraction of MLCT-Z is 2.21% higher than that of MLCT-S, but the yield of the 170-230 \({}^{\circ}\)C distillate fraction of the MLCT-Z is 3.09%, which is relatively low. The \(>\)360 \({}^{\circ}\)C heavy distillate fraction (distillation residue) accounted for about half mass of the total MLCT, which belongs to coal tar pitch (mainly composed of polycyclic aromatic hydrocarbons), and was the main component of the MLCTL Researches [7; 8; 36; 37] have shown that the \(>\)360 \({}^{\circ}\)C heavy distillate fraction is exceedingly difficult to hydrogenate and has a low economic value. Figure 3 shows the elemental composition analysis of the narrow distillate fractions. The elemental composition is the basic data reflecting the chemical essence of coal tar. The comparison between MLCT-Z and MLCT-S shows that there is no difference in the type of elements in the narrow fractions, and the variation trend of the elemental content is basically the same. Each narrow distillate fraction has a certain amount of nitrogen and sulfur. Hence, the full enrichment of nitrogen and sulfur in certain distillates was not reached through distillation. By contrast, the total heteroatom content of MLCT-Z is higher than that of MLCT-S. In particular, the difference in the nitrogen and oxygen contents is mainly due to the difference in coal properties and pyrolysis conditions. Figure 1: Yields of the distillates.