## 4 Conclusions  
In this paper, tar-rich coal was used as the carbon source, which has low cost and wide availability. By co-pyrolysis with different nitrogen-containing compounds, nitrogen-rich  
Figure 8: FTIR spectra of the co-pyrolysis of tar-rich coal and NH\({}_{4}\)Cl. Figure 7: Colors of the three solids. tar was successfully prepared. In the experimental setup of this paper, the best effect was achieved when the temperature was 600 \({}^{\circ}\)C, the pyrolysis time was 4 min, and the ratio was tar-rich coal: nitrogen-containing compounds = 1:3. When no nitrogen-containing compounds were introduced into the coal pyrolysis, there was almost no effect on the original N elemental morphology distribution in the coal, and when nitrogen-containing compounds were added, the N elemental content in all six products was significantly increased, among which the N elemental content in the melamine coke and tar was increased by 14.69 times and 2.85 times. After that, the main components in the high-nitrogen tar were analyzed, which provided some help for the high-value utilization of coal tar. From the experimental results, only under the condition of sufficient pyrolysis time, the nitrogen-containing compounds were the most abundant and had the highest content. The GC/MS analysis of the tars co-pyrolyzed with six kinds of nitrogen-containing compounds and tar-rich coal revealed that the contents of nitrogen-containing compounds in the tars of NH4 Cl and melamine were all over 60%, and the rest of the several kinds of tars were also significantly increased. The nitrogen-containing compounds in the tar were also labeled using \({}^{15}\)NH4 Cl to further determine the types and contents in the co-pyrolysis tar of NH4 Cl and tar-rich coal, and 26 nitrogen-containing compounds were screened out accounting for 66.28% of the total, among which the content of the five-membered nitrogen heterocyclic ring was the highest, which could be up to 34.88%. Furthermore, by using XPS analysis, it was found that the content of pyrro-N in the tar was the highest. Finally, FTIR analysis was used to discover the absorption peaks of aromatic amines, fatty amines, nitrogen heterocycles, etc. These results are all consistent with the GC/MS analysis, further mutually verifying the accuracy of the experiment. In the subsequent studies, more methods will be used to further analyze the structure of different nitrogenous compounds in high-nitrogen tar. At the same time, the conclusions of this paper will be applied to the co-pyrolysis of coal and nitrogenous wastes to observe the changes in the content and structure of nitrogenous compounds therein. In addition, the semi-coke produced from the co-pyrolysis of coal and nitrogenous compounds will also be further analyzed, which will provide a certain reference value for the high-value utilization of coal tar and the application of char in other industries. Conceptualization, F.C., G.L. and A.Z. ; methodology, P.C. and J.S. ; validation, G.L. and P.C. ; investigation, J.S. and Q.W. ; resources, B.B. and A.Z. ; data curation, X.H. and J.H. ; writing--original draft preparation, P.C. and J.H. ; writing--review and editing, F.C., B.B. and G.L. ; supervision, Q.W. ; project administration, F.C. ; funding acquisition, X.H., Q.W. and A.Z. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Fundamental Project (No. 32202164, 52174208, U24A20552), Shaanxi Natural Science Foundation (2021)Q556), China Postdoctoral Science Foundation (No. 2020M673610 XB), Scientific Research Program Funded by Shaanxi Provincial Education Department (No. 21 JK0772), Xi'an Science and Technology Plan Project (No. 23 NYGG-0068) for the financial support. Not applicable. The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author. Authors [PERSON], [PERSON] and [PERSON] were employed by the company Changqing Industrial Group Co., Ltd.