The Studies On Color Stability Of Catalytically Cracked Diesel Oil

The technology of catalytic cracking has been rapidly developed recently. The crude oil which processed by catalytic cracking is increasing every year, so the proportion of catalytically cracked diesel oil in the finished stocks is expanded recently year. The problem of instability in catalytically cracked diesel oil is becoming more serious and of increasing concern. The degradation in diesel oil manifests itself in a variety of ways including color change, development of deposit. The degradation affects the engine performance in great extends. The deposit can be removed easily, but the color of the catalytically cracked diesel oil goes beyond the standard of diesel oil. For this, the emphasis in this paper is to investigate the color stability of catalytically cracked diesel oil. Firstly the method of spectral photometer to determine the color of diesel oil is set up by the Matlab software. Secondly, with respect to the color compounds in catalytically cracked diesel oil, efforts has been devoted to enrich and separate them in appropriate ways. Liquid chromatography and mass spectrum(LC/MS), gas phase chromatography and mass spectrum(GC/MS) have been used to identify the structure of the color compounds. Model compounds have been joined into the distillate diesel oil to investigate the impact of the enriched and separated compounds. At last, various means of treatment have been proposed for improving the color stability of catalytically cracked diesel oil, and generally compared them with each other. The results show that the main compounds which impact the color stability of the catalytically cracked diesel oil produced from SINOPEC Changling Company. are various. They are olefins, diolefins, aromatics, naphthenes, basic and nonbasic nitrogen compounds, and acidic compositions etc. The nonbasic nitrogen compounds are most important to affect the color of cracked oil, especially indole,carbazole and their derivates. The impact of the phenolic compounds, thiols and phenthiols can not be neglected. The more complex phenolic compounds effect not only the color but also the deposits of the cracked diesel oil. When the compounds exits all together, the color of the diesel oil is darker. Many control methods are proposed to improve the catalytically cracked diesel oil, such as caustic treatment, acetic treatment, extraction method, clay absorption and additive treatment. Caustic treatment and acetic treatment are more efficient than other methods, because the unstable compositions are almost eliminated.