Characteristics of microwave⁃assisted Fe⁃catalyzed pyrolysis of Huaxia coal and char structure evolution

Microwave⁃thermal treatment offers a novel approach for the clean and high⁃efficient utilization of coal re⁃ sources based on pyrolysis conversion due to its unique merits of quick and even heat transfer and optional heat transfer. This study investigated the effect of the Fe⁃based catalyst with both catalytic activity and dielectric response on the tem⁃ perature⁃rising and thermal weight loss characteristics of coal samples， release law of gas components， dielectric properties and the evolution behavior of carbon microcrystalline structure of coal chars.Microwave⁃assisted Fe⁃catalyzed pyrolysis of Huaxia low⁃rank coal was carried out in a microwave tube furnace under different radiation time.Physico⁃ chemical properties of coal chars were characterized by vector network analyzer，N2⁃adsorption，FT⁃IR，XRD，Raman and synchronous thermal analyzer. Results manifested that the introduction of the Fe catalyst could effectively enhance the deep release of pyrolysis volatiles within 5 - 15 minutes， resulting in the coal samples exhibiting a conspicuous thermal weight loss peak. Microwave interacted preferentially with the Fe catalyst could generate a large number of active sites，which efficiently induces the occurrence of thermal cracking reactions of coal macromolecu⁃ lar chains and functional groups.Microwave⁃assisted Fe is conducive to the rapid generation of H2 and CO within 5 mi⁃ nutes of continuous radiation，leading to the syngas yield is considerably improved from 198 mL / g of pure coal sample to 370 mL / g of coal sample load with the Fe catalyst.Furthermore，the appearance of Fe effectively inhibits the planar ex⁃ tension and longitudinal stacking of aromatic carbon layer of coal chars，which can significantly augment the irregularity of carbon crystallites and enrich the defect structure in the carbon skeleton，resulting in the gasification reaction index of coal chars increasing by 4-5 times through sufficiently enhanced gasification reaction rate.The rapid release of vola⁃ tiles under the catalytic action of Fe and the generation of metal oxides have fully strengthened the ability of coal chars to dissipate the microwave energy with the form of heat energy，which enables the dielectric loss factor ε′′r to exhibit a dramatic increase within 10 - 20 minutes of microwave radiation. Additionally， the microwave⁃assisted Fe can corrode the surface of coal matrix to exert the influence of pore formation and expansion，which is conductive to the generation of high specific surface area and the construction of developed pore structure of coal chars.