Deep eutectic solvent assisted swell and highly efficient catalytic pyrolysis of raw coal

The development of catalytic pyrolysis strategy is the key to the efficient utilization of raw coal. Herein, a novel microwave-assisted deep eutectic solvent (DES) swelling strategy was used to catalyze the pyrolysis of Naomaohu coal. The multifunctional FeCl3-Levulinic acid DES was synthesized, it could not only act as the solvent to swell coal, but to highly efficient catalyzed the pyrolysis of the swelled coal. During the process of microwave swelling, DES enhanced the induced polarization of unsaturated bonds, destroyed the weak intermolecular chemical bonds, increased the spacing of aromatic layers and reduced the particle size of raw coal, thus exhibiting a superior swelling effect. Notably, with the catalytic action of DES, it effectively promoted the conversion of coal as well as the escape of light components in the pyrolysis process. Based on the advantages of DES, the pyrolysis tar yield increased significantly (from 11.85% to 17.63%) and the yield of Benzene-Toluene-Xylene was as high as 11.31% in the tar and its content was 14.48 mg g−1. The light component (BP ≤ 360 °C, 67.50%) and light oil (BP ≤ 170 °C, 42.00%) of the tar reached high levels. What's more, the pyrolysis behavior and kinetics results indicated that the pre-exponential factor was 2.61 × 1016 min−1 and the average apparent activation energy was 267.39 kJ mol−1. The proposed efficient method is expected to provide novel strategy for the swell and catalytic pyrolysis of raw coal using diverse multifunctional DES.