Separation and analysis of thiols in FCC and RFCC gasoline

Based on the theoretical analysis, an effective composite extractant which has high efficiencies of extraction and recovery of thiols from petroleum ether as well as gasoline was selected. The gas chromatograph equipped with a flame photometric detector (FPD) and the normalizaion method were used to analyze the enriched thiol sample for the composition and structure of thiols. The analysis has a good accuracy and precision, and the analysis sensitivity of single mercaptan. sulfur can reach mug/g level. FCC gasoline samples of caustic washing before, caustic washing after, and sweetening after were analyzed respectively and the results showed that there were more than 20 kinds of C-1 similar to C-9 thiols in the FCC gasoline of cautic washing before, with the majority of thiols below C-4 and there were mainly isomeric greater than or equal toC(5) thiols in the FCC gasoline of caustic washing after and sweetening after. The article points out that the key of improving the sweetening of gasoline is to increase the removing efficiency of isomeric greater than or equal toC(5) thiols and high molecular weight (>C-7) normal thiols. It is also elucidated why RFCC (residual fluid catalytic cracking) gasoline is more difficult to be sweetened than FCC gasoline.