**4. Conclusions**

(1) The molecular formula of the three structures was determined by elemental analysis. The average molecular formula of HLH raw coal configuration was C167N3O27H149, and the aromatic part consists of five benzene rings, six naphthalene rings, two pyrrole rings and one pyridine ring. The average molecular formula of Mm coal configuration was C148H129N3O20, the aromatic structure includes three benzene rings, four anthracene rings, four naphthalene rings, one anthracene ring, one pyridine ring and two pyrrole rings. And the average molecular formula of Um coal configuration was C155H131O23N23, the aromatic structure includes three benzene rings, five anthracene rings, four naphthalene rings, one anthracene ring, one pyridine ring, and two pyrrole rings.

(2) It was found that after microwave and ultrasonic treatment, the orderliness of aromatic ring layer arrangement increased. The content of fat chain and side chain decreased, and the existence form of oxygen atoms also changed, in which the proportion of C-O and COO- form shows a decreasing trend. It was found that the total energy of the three structures decreased significantly after optimization. The chemical bonds between the atoms are obviously bent and distorted, and the space configuration is more stereoscopic. Although the model constructed in this paper is not the most comprehensive and optimized configuration before and after HLH modification, some problems such as isomers are considered in the process of construction, which has a certain reference value for better understanding and application of lignite upgrading.

**Author Contributions:** J.L. provided methodology and original draft writing. Z.H. and Y.Y. conceived and designed the study. S.Q. performed the experiments. Y.Y. provided the samples. S.Q. wrote the paper. Z.H. reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was financially supported by National Natural Science Foundation of China (51874171) and and University of Science and Technology Liaoning Talent Project Grants (No. 601011507-05).

**Conflicts of Interest:** The authors declared that they have no conflict of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
