Characteristics of catalytic pyrolysis of low-rank coal via microwave-assisted Fe

Microwave heating technology offers a new way for an efficient coal-staged conversion due to its advantages of rapid and uniform heating,selective heating and high efficiency and safety. This study was undertaken to investigate the effect of metal species Fe with both catalytic action and dielectric response on the product distribution,gas compo- sition,and the char carbon crystallite structure of microwave-assisted pyrolysis of low-rank coal,and the catalytic pyrol- ysis experiments of demineralized Huaxia low-rank coal loaded with different amounts of Fe has been conducted in a microwave tube furnace. Physicochemical properties of chars produced from the microwave-assisted pyrolysis of coal samples loaded with different amounts of Fe were characterized by a vector network analyzer,XRD,FT-IR,Raman and SEM. Results show that the introduction of Fe can effectively strengthen the dielectric loss of coal samples and can pro- mote coal samples achieve the final pyrolysis temperature within a short time by improving heating rate. Microwave interacted preferentially with Fe catalyst can efficiently induce the occurrence of catalytic cracking reaction of coal mac- romolecular organic matter,resulting the syngas yield is significantly increased from 221 mL / g of demineralized coal to 273,394 and 457 mL / g of coal samples load with 1% ,3% and 5% Fe. Furthermore,the addition of Fe considerably improves the ability of coal chars of dissipate microwave energy with the form of heat by increasing the value of dielec- tric loss factor εr″ and loss tangent tan δ. Microwave assisted Fe inhibits the internal growth of char basic structural unit while remarkably increasing the irregular value of the aromatic carbon network. In the meantime,the amount of small aromatic rings and amorphous carbon in carbon skeleton structure are dramatically improved which is favorable for en- hancing the char gasification reactivity. Additionally,the introduction of Fe catalyst is conducive to the construction of pore structure of coal chars and can promote the development of surface morphology of coal chars from smooth and dense to porous under microwave radiation.