COKE FORMATION IN THE FLUID CATALYTIC CRACKING PROCESS BY COMBINED ANALYTICAL TECHNIQUES

A combination of analytical techniques, including X-ray photoelectron spectroscopy (XPS), solid state C-13 nuclear magnetic resonance (NMR) spectroscopy, and supercritical fluid extraction/mass spectrometry (SF E/MS), were used to characterize the detailed composition and structur e of coke formed on catalyst in the fluid catalytic cracking (FCC) pro cess. By characterizing coke samples from a series of designed FCC exp eriments, the effects of conversion on coke composition were systemati cally studied. SFE is shown to be an effective technique for removing low molecular weight coke molecules from the catalyst. When combined w ith mass spectrometry, the technique provided molecular level informat ion of the extracted coke species. The coked catalysts were directly a nalyzed by XPS and NMR to obtain information relevant to surface and b ulk coke structures, respectively. The study revealed the presence of two types of nitrogen-based coke and showed that N distributions were strongly affected by FCC conversion level. The study also suggests tha t most nitrogen-containing coke is formed in the earlier stages of cra cking while hydrocarbons are the primary contributors to coke yield in the later stages of cracking. The aromaticity of coke remains fairly constant at high conversions.