Fulvic acid (FA) is composed of many molecular units with similar characteristic structures. The characterization and molecular model construction of coal-based FA is the key for the scientific basis and applied science of FA.

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Fulvic acid (FA) is a complex organic mixture composed of small molecules. The structure and composition of FA vary greatly because of the different raw materials used for preparing FA. In this work, FA was extracted from shallow lowrank lignite by hydrogen peroxide (H 2 O 2 ) in a microwave field, and the functional groups of FA were characterized. The optimal extraction process was determined, with the H 2 O 2 concentration being the key factor affecting the yield of FA. Thermogravimetric analysis showed that FA was mainly composed of low molecular weight and readily pyrolyzed compounds. As shown by Fourier transform infrared spectroscopy, in the process of FA extraction by H 2 O 2 oxidation of lignite, the content of −COOH increased, longchain aliphatic compounds decreased, stretching vibrations of aromatic ring skeletons disappeared, and aromatic ring substitution became mainly tri-or disubstitution. Fluorescence spectroscopy indicated that FA had a low degree of aromaticity. X-ray photoelectron spectroscopy qualitatively and quantitatively revealed that the main modes of carbon−oxygen bonding in FA were C−O−, COO−, and CO. Thus, this study not only lays a foundation for studying the composition and structure of coal-based FA but also opens a new avenue for a clean and efficient utilization of lignite.

l-Tryptophan (l-Trp) was separated from its aqueous solution by hyper-cross-linked resins. The adsorption and desorption performances of l-Trp on different resins were compared. The weakly polar resin XDA-200 was selected as an excellent adsorbent with high adsorption amount and easy elution. The resin has a high adsorption selectivity and strong salt resistance. The adsorption mechanism of l-Trp on resin XDA-200 was elucidated based on adsorption thermodynamics experiments, molecular dynamics simulations, and adsorption kinetics experiments. The dynamic separation process of l-Trp was finally studied. The adsorption of l-Trp on resin XDA-200 is a spontaneous process driven by adsorption enthalpy. l-Trp± is the most favorable form for l-Trp adsorption on resin XDA-200 because of the strongest affinity of l-Trp± to the resin and relatively low water solubility. The adsorption of l-Trp is mainly based on π–π and hydrophobic interactions. Surface diffusion is the sole rate-limiting step of l-Trp mass transfer on resin XDA-200. l-Trp was separated satisfactorily from l-glutamic acid (l-Glu) and NaCl with both the recovery rate and purity of l-Trp higher than 99% in the fixed bed packed with resin XDA-200.