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Three coal macerals with high purities were separated from Pingshuo gas coal. The formation rules of HCN and NH3 during macerals pyrolysis and gasification were investigated. Experiments were carried out in a tubular quartz reactor at atmospheric pressure. The reactor allowed coal particles to be heated up rapidly and held for a prespecified period of time at a peak temperature. The amount of HCN and NH3 were quantified by ion chromatography. The influence of temperature and macerals type on the formation rules of HCN and NH3 was discussed. Results showed that the formation of HCN was mainly due to the thermal cracking of volatile, and NH3 formed both from the thermal cracking of volatile and the cracking of nascent char. The HCN yield increased with an increase in pyrolysis temperature. For three coal macerals (liptinite, vitrinite and inertinite), the yield of HCN depended not only on their volatile contents but also nitrogen-containing functional groups, in which more pyrrole-type nitrogens would form more amount of HCN at lower temperature. The yield of NH3 depended on the ability of forming ‘H’ radical. Under the experiment condition in this study, inertinite could convert more nitrogen into NH3 than vitrinite and liptinite. The yield of HCN during gasification was almost the same as that during pyrolysis, the yield of NH3 during gasification was little higher than that during pyrolysis. [Copyright &y& Elsevier]

Our results indicate that the gas atmosphere surrounding coal/char particles can greatly affect the formation of NH3 and HCN through its influence on the availability of H radicals. Based on our results, it is believed that the chemisorption of CO2 on the nascent char surface can consume H radicals or block the access of N-sites by H radicals for the formation of NH3 and HCN. For the chars whose thermal cracking generates little H radicals, the gasification of char by CO2 can also generate additional H radicals, enhancing the formation of NH3. However, even gasification of char in CO2 at 950 °C does not lead to the formation of HCN. The oxidation of coal with 4% O2 at low temperatures (400–600 °C) leads to the formation of HCN as well as NH3 due to the enhanced formation of (H) radicals. The gasification of coal with 15% H2O drastically enhances the formation of NH3 due to the greatly enhanced availability of H as an intermediate between the reactions of H2O and char. These results support our reaction mechanisms proposed previously, emphasising the importance of H on the formation of NH3 and HCN during pyrolysis, which can also be extended to the conversion of coal-N during gasification. [Copyright &y& Elsevier]