Transformation mechanism of FCC flue gas pollutants

摘要

Fluid catalytic cracking processes generate various gas pollutants, which are the major concern for environmental protection in refineries. However, the transformation mechanism from deposits to gas pollutants is not well understood. In this work, spent catalysts from different typical FCC units were analyzed to evaluate the effect of pollutant precursors on pollutant emission. The main carbon, nitrogen and sulfur precursors of FCC pollutant emission were identified. Regeneration experiments were conducted to assess the relationship between regeneration temperature and pollutant emission under partial combustion conditions. Results showed that the same precursors from different catalysts result in close temperatures at which characteristic pollutants occurred. VOCs are firstly generated by the coke branches cracking under low temperature. Then, nitrogen-containing compounds convert to NH3 and HCN, and some of them are oxidized into NOx. After that, sulfur-containing compounds convert to C-S group and H-S group, which finally convert to SO2 at high temperature. At last, a full view of transformation mechanism of FCC pollutant emission is presented, which will give a further insight into the prediction and control of pollutants.