Study on compositions of FCC flue gas and pollutant precursors from FCC catalysts.

Abstract

Fluid catalytic cracking (FCC) unit emits a large amount of flue gas, which is a major issue of environmental protection supervision. A spent FCC catalyst from a typical FCC unit was characterized by NMR, XPS, EA TGA and TPD-MS methods. XPS results presented that the nitrogen compounds in coke were pyridine nitrogen, pyrrole and quaternary nitrogen. Sulfur compounds in coke are in the form of thiophene and thiols. TGA and TPD-MS results indicated that the soft coke in the spent catalyst may decompose to small molecular such as NOx, SO2 and HCN. NH3 and HCN are mainly emitted due to the incomplete combustion. The flue gas from the FCC unit is monitored by different on-line monitoring instruments. Results showed that the existence of ammonia greatly affected the value of SO2 during the venting process or instruments' inlet piping system, where saturated vapor in flue gas is partially condensed. The concentration of NH3 and HCN is more than 100ppm, which should be paid more attention to. Taken together, fourier transform infrared method was more applicable for monitoring FCC flue gas than non-dispersed infrared method and ultraviolet fluorescence method.