Study On Catalytic Steam Cracking Of Vacuum Residue

Residual oil, which has the complicated composition, is the heaviest part of crude oil after atmospheric and vacuum distillation. Compared to distillate oil, residual oil shows the characteristics of high density and boiling points, low H/C ratio, high content of metal and mixed elements, which make it hard to process and utilize. The effective approach to utilize residual oil is to convert the heavy oil into lighter fuel oil and chemical materials. So far, hydrocracking is the most ideal method for heavy oil upgrading, however, it must be conducted under high pressure with hydrogen atmosphere, which causes the problems of harsh requirement of equipment, high construction expense and production cost. So, developing new process like catalytic steam cracking shows great practical significance.The core task of developing catalytic steam cracking process is to find the appropriate catalyst. In this paper, an iron based catalyst composed of three metal oxide was prepared through co-precipitation method. The catalyst shows dual function:decompose the steam to produce active hydrogen and oxygen; catalytic crack of large molecules into lighter oil. The structure of the catalyst was characterized through BET, pore size distribution, particle size distribution and x-ray diffraction (XRD).Heavy oil conversion and light oil yield are the most important parameters to determine the performance of the catalyst. This paper proposed a simulated distillation method to obtain the boiling range of vacuum residue and the liquid product by using thermogravimetric analyzer (TGA). Some compounds in the liquid product, such as naphthalene,2-methylnaphthalene, biphenyl, fluorine, phenanthrene, Fluoranthen and pyrene were used as samples and dissolved in toluene. The TGA experiments were carried out and the temperature corresponding to the maximum weight loss rate of sample/toluene solution was defined as TG apparent boiling point of the sample. The relationship of boiling point and TG apparent boiling point was correlated and found to be a linear equation. The effect of TG heating rate and sample concentration in toluene on the linear equation was clarified. Sample concentration offered no influence the linear equation. Lower heating rate was beneficial to good linear relation.The paper used three catalysts for catalytic steam cracking in a fixed bed reactor, the comparison result indicated that iron based catalyst(denoted as Zr/Al/FeOx)showed the highest catalytic effect, the conversion and yield were determined by the content of the supporting ZrO2 and could be maximized as 77.5% and 65.0% respectively under appropriate content of ZrO2.The effect of operation factors like reaction temperature and W/F was studied and the result showed that at 500℃with W/F ratio at 0.8, a relatively high conversion and yield could be got. The reuse property of the catalyst was also studied and the result demonstrated that although the catalytic activity decreased remarkably when the catalyst was used repeat after reaction without regeneration, the activity remained at high level when the catalyst was regenerated after reaction.