CoMo catalysts deactivation

Tests on several feedstocks were performed with the CoMo-C and CoMo-D catalysts. These tests were carried out for over 1000 hours, i.e. about one month and an half During testing, the reactor temperature (the main parameter that causes the catalyst ageing) was ramped from 325°C to 360°C with an average temperature higher than 340°C. At the end of the tests, the operating conditions were returned to the initial values in order to estimate catalyst deactivation. 

The deactivation is measured by the increase of temperature that is necessary to obtain the same HDS performance for the final point as for the initial point. It has been shown that the new high loading CoMo catalyst exhibits the same level of deactivation as the conventional CoMo. The maximum deactivation obtained with a conversion feedstock after high temperature operation for more than 1,000 hours is about 1°C. 

It was revealed that RhAJSY showed higher catalytic activity than commercial CoMo/ AI2O3 in the hydrodesulfurization of thiophene. The catalyst deactivation of RhAJSY with... 

The rate constants for deactivation of C0M0/AI2O3 and CoMo/AC catalysts were determined by Altajan et al using the VR derived from Athabasca bitumen. The study was conducted in a continuous fixed-bed reactor at 698 K and 13.9 MPa. For this purpose, the pseudo-turnover frequency (PTOF) was defined as the number of reactions per unit time and surface area. The following equations derived by these authors assumed the first-order kinetics for catalyst deactivation ... 

Pure silica-aluminas are strongly deactivated, losing about 80% of their activity before reaching the steady-state. The loss in pure CoMo/Si02 catalyst is much less pronounced (about 15%). Mechanical mixtures represent an intermediate case they lose between 35% and 50% of their activity. 

Natural materials such as manganese nodules and bauxite have been considered as catalysts for demetallation. These materials are attractive for applications where the catalyst is disposed after deactivation since conventional CoMo/A1203 desulfurization catalysts may be too expensive. The nodules also have their metallurgical value increased after accumulating Ni and V. 

Prevent deactivation. The increased hydrogenating ability of Co prevents accumulation of coke deposits. There is some merit in this proposal as Mo/Al catalysts appear to deactivate faster than CoMo/Al catalysts (100). However, initial activity of the sulfided catalyst was higher for the CoMo/Al catalyst (100). 

A series of CoMo/Alumina-Aluminum Phosphate catalysts with various pore diameters was prepared. These catalysts have a narrow pore size distribution and, therefore, are suitable for studying the effect of pore structure on the deactivation of reaction. Hydrodesulfurization of res id oils over these catalysts was carried out in a trickle bed reactor- The results show that the deactivation of reaction can be masked by pore diffusion in catalyst particle leading to erro neous measurements of deactivation rate constants from experimental data. A theoretical model is developed to calculate the intrinsic rate constant of major reaction. A method developed by Nojcik (1986) was then used to determine the intrinsic deactivation rate constant and deactivation effectiveness factor- The results indicate that the deactivation effectiveness factor is decreased with decreasing pore diameter of the catalyst, indicating that the pore diffusion plays a dominant role in deactivation of catalyst. 

Figure 2 shows that the desulfurization rate is a function of the Al/P ratio for CoMo/AAP catalysts. Under the reaction conditions, all catalysts showed a high initial activity followed by a deactivation. The decrease in activity during the initial period of time is very probably connected with coke formation (ref. 6). Although the poisoning effect is not entirely excluded for deactivation, its contribution is far smaller than coke in the initial period of time. 

In this equation, Cr is the concentration of reactant e.g., S, N, V, Ni and asphaltenes), ko and are first-order rate constants for deactivation and surface reactions, respectively, tpxoF is the time on stream, Pcat is the bulk density and A the surface area of catalysts. The kp and values are shown in Table 37. It is evident that the CoMo/AC catalyst was more prone to deactivation than the C0M0/AI2O3 catalyst. Thus, with the exception of HDNi, all other functionalities were deactivated at a greater rate over the former catalyst. The difference... 

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