Catalytic effects of metal chlorides on the pyrolysis of lignite

The catalytic effects of five metal chlorides, including CaCl2, KCl, NiCl2, CoCl2, and ZnCl2, on the pyrolysis of lignite were investigated by thermogravimetry Fourier transform infrared (TG-FTIR) analysis. The results showed that CaCl2 and ZnCl2 inhibited the conversion of organic matters into light species during pyrolysis of lignite samples, while KCl, NiCl2, and CoCl2 promoted the conversion. The catalytic effectiveness of these metal chlorides on the conversion of organic matters in lignite samples decreased in the following order: CoCl2 > KCl > NiCl2 > CaCl2 > ZnCl2. The yields of light species from lignite pyrolysis can be decreased by CaCl2. The effect of NiCl2 was similar to that of CaCl2 except it increased the yield of CO2. When CoCl2 or ZnCl2 was impregnated into lignite samples, the yields of monocyclic aromatic hydrocarbon, phenol, and carboxylate increased but the yield of aliphatic hydrocarbon decreased. The effect of KCl was opposite to that of CoCl2 and ZnCl2. These chlorides were analyzed by X-ray diffraction (XRD) before and after pyrolysis. The XRD results indicated that the catalytic active sites of alkali or alkaline earth metal (AAEM) chlorides catalysts were the interactions between the AAEM species and oxygen-bearing anions. However, the catalytic activities of transition metal chlorides might be in their metallic state. In addition, the effects of CoCl2 on the pyrolysis of raw lignite have also been investigated with a spout-entrained reactor. The results suggest that impregnating 15% CoCl2 to lignite can increase the yields of total volatile matters more than 2-fold. The catalytic effect of CoCl2 impregnated to zeolite is lower than that directly impregnated to lignite. However, catalytic pyrolysis of lignite with Co-zeolite should be feasible in an industrial setting because it is easy to separate and recycle.