**Jihui Liu 1, Shuang Qiu 1, Zhijun He 1,\* and Yaowei Yu 2,\***


Received: 25 February 2020; Accepted: 23 March 2020; Published: 29 March 2020

**Abstract:** In this paper, Huolinhe lignite was selected as the lignite experimental sample, using microwave modification and ultrasonic modification separately as improvement methods. The three-dimensional molecular models of HLH before and after modification were established base on the parameters obtained by 13C NMR, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and Fourier transform infrared (FTIR). After the microwave treatment, the methylene carbon in the HLH coal sample structure mostly exists in the form of long straight chains, and after microwave and ultrasonic treatment, the -OH content of oxygen atoms in the coal sample increases, and form the CO- and the COO-. The proportion is decreasing. The models were adjusted and tested by the covalent bond concentration method and carbon chemical shift spectra calculation using Chemdraw software. A new method is proposed to study the structure and physicochemical properties of lignite modification from the molecular point of view through this study.

**Keywords:** Lignite; microwave and ultrasound modification; structural characterization; 3D molecular model; structural simulation
