Hydrocracking of Vacuum Residue

Figure 6.9 shows the yields of the different products obtained during the thermal hydrocracking of vacuum residue. The data shown in Figure 6.9 correspond to the results obtained at Ftrij-IVsic ratio of 0.23 and 0.65 gx Icmac 1h . 

The catalytic hydrocracking of heavy oil has been well represented by the five-lump kinetic model shown in Figure 6.15 (Sdnchez et al., 2005). Although catalytic and thermal reactions follow different mechanisms, the same kinetic model was used to represent the NHDC. Hydrocracking of vacuum residue was assumed to follow second order as demonstrated earlier, while first order was considered for the other reactions. The reaction rate (r for each lump as a function of the product composition (y and the corresponding kinetic constant k is as follows ... 

Reaction order for the thermal hydrocracking of vacuum residue, NHDN or NHDM... 

For each reaction, a kinetic expression (r was formulated as a function of the product composition (y, kinetic constant, and effectiveness factor. Product compositions were determined from bench-scale mass balances and simulated distillation curves. The hydrocracking of vacuum residue was considered to follow second-order reaction, while the remaining reactions were assumed to be first-order as reported in the literature (Sanchez and Ancheyta, 2007). On the basis of these considerations, the reaction rates of the proposed model are as follows ... 

Kinetic parameters of a live-lump kinetic model for hydrocracking of a heavy oil taking into account catalyst deactivation were obtained in a CSTBR in the range of reaction temperature of 380°C-420°C and LHSV of 0.5-1.25m, y(mL, h). The hydrocracking of vacuum residue, VGO, and middle distillates indicates a high selectivity toward the heavier lumps at the studied temperatures. 

Ratio of solid-free wake size to bubble size, dimensionless Global rate constant for hydrocracking of vacuum residue, gj -igco,... 

Second-order rate constant for hydrocracking of vacuum residue to gas,... 

Richardson-Zaki index, dimensionless Reaction order of the hydrocracking of vacuum residue Pressure, Pa... 

Ternan, M. Can. J. Chem. Eng., 65, 244 (1987) In Pore Diffusion of Vacuum Residue Moledules and Hydrogen Dissociation on Reaction Sites Essential Steps in Hydrocracking Catalysis, 14th Canadian Symposium on Catalysis, Whistler, B.C., 1996. 

Eleven different distillation residues from five oil regions were used for investigations on the hydrocracking reaction. Vacuum residues (VR) and a visbreaker residue (VVR) produced from each were available from a Mexican and a Libyan erode. The residues and their origins are listed in Table 4-127 their analytical data is given in Table 4-128. It is evident that the content of heteroatoms varies considerably depending on the origin of the samples, whereas the atomic H/C ratio exhibits only small differences (mean value x = 1.415, standard deviation x = 0.022 equals a coefficient of variation V = 1.56 % relative). 

During the thermal cracking of vacuum residues, maltenes play an important role in the conversion of asphaltenes. Wiehe has shown that in the hydrocracking of CL VB (Cold Lake Vacuum Bottoms), the presence of maltenes in the resid increases (prolongs) the coke induction period significantly. The results were interpreted based on the efiectiveness of maltenes as hydrogen donors to cap free radicals produced by the thermal cracking of asphaltenes. 

Catalytic and thermal reactions follow different reaction mechanisms therefore, different reaction orders would be expected. The vacuum residue conversion obtained with catalytic hydrocracking has been properly represented by second-order reaction kinetics (Sanchez and Ancheyta, 2007). Regarding the NHDC reaction, the following expressions can be derived as functions of vacuum residue conversion, kinetic parameters (n reaction order, k kinetic constant), the total mass flow, and the inert material volume ... 

Chang, J., Tsubaki, N., Fujimoto, K., Elemental Sulfur as an Effective Promoter for the Catalytic Hydrocracking of Arabian Vacuum Residue. Fuel, 2001. 80(11) pp. 1639-43. 

Stanislaus, A., Absi-Halabi, M., Khan, Z., Influence of Catalyst Pore Size on Asphaltenes Conversion and Coke-Like Sediments Formation During Catalytic Hydrocracking of Kuwait Vacuum Residues, In Catalysts in Petroleum Refining and Petrochemical Industries. Studies in Surface Science and Catalysis. 1996, Elsevier New York, USA. pp. 189-197. 

Combined with hydrodesulfurization, the process is fully applicable to the feed preparation for fluid catalytic cracking and hydrocracking. The process is capable of using a variety of feedstocks including atmospheric and vacuum residues derived from various crude oils, oil sand, visbroken tar and so on. 

Several of the commercial simulation programs offer preconfigured complex column rigorous models for petroleum fractionation. These models include charge heaters, several side strippers, and one or two pump-around loops. These fractionation column models can be used to model refinery distillation operations such as crude oil distillation, vacuum distillation of atmospheric residue oil, fluidized catalytic cracking (FCC) process main columns, and hydrocracker or coker main columns. Aspen Plus also has a shortcut fractionation model, SCFrac, which can be used to configure fractionation columns in the same way that shortcut distillation models are used to initialize multicomponent rigorous distillation models. 

INFLUENCE OF CATALYST PORE SIZE ON ASPHALTENES CONVERSION AND COKE-LIKE SEDIMENTS FORMATION DURING CATALYTIC HYDROCRACKING OF KUWAIT VACUUM RESIDUES... 

Broader commercial application of residue hydrocracking technologies to vacuum residues, especially with ebullating bed processes. 

Comparison of f 600 and / 800 shows that, with one exception, there is only a difference of 1 or 2 %, which implies that, above 600 °C, hardly any degradable material is left. The coke residue decreases slightly with increasing residence time, but the amount of coke is small compared to that of the vacuum residue. This indicates that the high-molecular-weight material does not undergo conversion under the reaction conditions of the hydrocracking process. 

---