In Situ Observation of Fouling Behavior under Thermal Cracking Conditions: Hue, Saturation, and Intensity Image Analyses

摘要

Thermal cracking reactions of a variety of heavy petroleum feeds were analyzed by in situ cross-polarized microscopy using a reactor equipped with a sapphire window. Cross-polarized microscopy is a powerful technique for detecting the formation of anisotropic domains of carbonaceous material (mesophase coke). The present study, however, focused on the characterization of the chemical and physical events prior to the formation of new phases by evaluating the changes in image properties with reaction time. Results showed that changes in image brightness were strongly correlated to the conversion of 524+ degrees C material but could not provide much insight regarding the stability of reacting oils. Color analyses of the cross-polarized micrographs, however, revealed a consistent red-to-blue color shift around the point of instability. This color shift corresponded to either the formation of a fouling layer of isotropic material or a homogeneous color change of the reacting medium, indicating the formation of CS2-insoluble material. In both cases, the beginning of the color shift preceded the formation of mesophase, whose appearance had the effect of enhancing the blue color of the samples. The detection of the red-to-blue color shift in reacting samples under thermal cracking conditions provides an improved framework for testing the fouling propensity of feeds or for developing online sensors operating on industrial units.