Multifunctional Two-Stage Riser Catalytic Cracking of Heavy Oil

The continuous deterioration of feedstocks, the increasing demand of diesel, and the increasingly strict environmental regulations on gasoline call for the development of fluid catalytic cracking (FCC) technology. To increase the feed conversion and the diesel yield as well as produce low-olefin gasoline, the multifunctional two-stage riser (MFT) FCC process was proposed. Experiments were carried out in a pilot-scale riser FCC apparatus. Results show that a higher reaction temperature is appropriate for heavy cycle oil (HCO) conversion, and the semispent catalyst can also be used to upgrade light FCC gasoline (LCG). The synergistic process of cracking HCO and upgrading LCG in the second-stage riser can significantly enhance the conversion of HCO while reducing the olefin content of gasoline at less expense of gasoline yield. Furthermore, the novel structure riser reactor can increase the conversion of olefins in gasoline. Because of the significant increase of HCO conversion, the fresh feedstock can be cracked under mild conditions for producing more diesel without negative effects on the feed conversion. Compared with the TSR FCC process, in the MFT FCC process, the increased feed conversion, diesel and light oil yields can be achieved, at the same time, the olefin content of gasoline decreased by approximately 17 wt %

In Situ Upgrading of Light Fluid Catalytic Cracking Naphtha for Minimum Loss

The key to reducing the olefin content in fluid catalytic cracking (FCC) gasoline is to upgrade the olefin-rich light FCC naphtha (LCN). To minimize the naphtha loss, several parameters were investigated in a pilot-scale riser FCC apparatus. The results indicate that, besides the reaction temperature, the catalyst-to-oil ratio, and the catalyst type, the boiling range and the olefin content of LCNs also have significant influence on the upgrading effect. Moreover, a relatively short residence time is beneficial for efficiently upgrading LCNs. In addition, the influence of the reactor structure should be brought to our attention. When a novel structurally changed reactor with a multinozzle feed system was used, significantly increased olefin conversion and decreased naphtha loss can be achieved. The calculation of hydrogen balance indicates that, because of the decrease of dry gas and coke yields, more hydrogen in the feed can be distributed into the desired products

Fluid Catalytic Cracking Study of Coker Gas Oil: Effects of Processing Parameters on Sulfur and Nitrogen Distributions

To investigate the effects of operating conditions and the catalyst activity on the transfer regularity of sulfur and nitrogen during the cracking process of coker gas oil (CGO), the CGO was catalytically cracked in a pilot-scale riser fluid catalytic cracking (FCC) apparatus at different test environments. Then the cracked liquid products were analyzed for sulfur and nitrogen distributions with boiling point, from which the sulfur and nitrogen concentrations of gasoline, light cycle oil (LCO), and heavy cycle oil (HCO) fractions were determined. The sulfur and nitrogen compounds in each product cut, and their possible reaction pathways were reviewed and discussed. The results show that sulfur-containing species are easier to crack but more difficult to be removed from the liquid product, while nitrogen compounds are easier to form coke, then be removed from the liquid product. The sulfur distribution of CGO is different from that of conventional feedstocks. Different processing parameters can significantly affect the sulfur and nitrogen distribution yields and concentrations in liquid products. Increasing the reaction temperature and the catalyst-to-oil ratio as well as shortening the residence time cannot only increase the light oil yield but also improve the product quality and reduce the SO_<i>x</i> and NO_<i>x</i> emissions in the regenerator

Vacuum Residue Thermal Cracking: Product Yield Determination and Characterization Using Thermogravimetry–Fourier Transform Infrared Spectrometry and a Fluidized Bed Reactor

To make full use of heavy oil by thermochemical conversion, the thermal behaviors of vacuum residue (VR) were investigated first by thermogravimetry–Fourier transform infrared spectrometry (TG–FTIR) and then via a laboratory-scale fluidized bed reactor (FBR). The TG–FTIR results showed that the changes in the absorbance of volatiles during thermal cracking were consistent with the weight loss in the derivative thermogravimetric curve. The dynamic information about the release profiles of the typical gaseous products such as CO, CO₂, CH₄, C₂H₄, light aromatics, and aliphatic olefins revealed the cleavage of varied structures and functional groups of VR at different temperatures. Moreover, the peaks for the maximum releasing rate on the evolving profiles of gaseous products became narrower and sharper, and the yield at maximum releasing rate for the gaseous species increased with increasing the heating rate. The pyrolysis experiments in a FBR with silica sand as a heat carrier showed that alkenes were the dominant gaseous products, with light olefin selectivity higher than 53%. The coke/Conradson carbon residue ratio was lower than that in the delay coking process. Furthermore, analysis of liquid oil using gas chromatography/time-of-flight mass spectrometry showed that 1-alkenes was the most abundant decomposition product and the selectivity of total olefins from C₆ to C₂₂ was 62.74%

Synergistic Process for Coker Gas Oil Catalytic Cracking and Gasoline Reformation

The most critical problem of processing coker gas oil (CGO) is its high nitrogen content, especially the basic nitrogen compounds, which limits its cracking performance in the fluid catalytic cracking (FCC) process. For enhancing the conversion of CGO, three processing schemes were evaluated in a pilot-scale riser FCC unit. Four indexes (thermal cracking index, dehydrogenation index, hydrogen transfer coefficient, and isomerization reaction index) were used to investigate the effects of operating conditions on the reactions of CGO cracking. Results show that the optimal operating conditions for CGO cracking are high reaction temperature and large catalyst-to-oil ratio with a short residence time. Therefore, we proposed a synergistic process by selectively recycling light FCC gasoline (LCG) from the upper position of the riser reactor, which can provide a high-severity reaction zone for CGO cracking and a low-severity reaction zone for gasoline upgrading. To further investigate the mutual effect of the two feeds, different recycle ratios of LCG were tested. Results indicate that the conversion of CGO significantly increased with the LCG recycle ratio. When the recycle ratio reached 50 wt %, the gasoline could be upgraded at a higher efficiency. To ensure the optimal recycle ratio and improve the gasoline quality, a two-stage synergistic (TSS) process was proposed. The simulated experiments of the TSS process show that the higher conversion and more desired products can be achieved, even though under a high processing ratio of CGO to conventional feeds