(173c) A Kinetic Study of the Ethylene Oligomerization over a Nibea Catalyst

Ethylene oligomerization is a chemical process of foremost importance in the production of olefins which are the primary feedstock to produce fuels and chemicals. Currently, this process is available commercially and uses homogenous catalysts, which are not environmentally friendly. The replacement of homogenous for heterogeneous catalysts makes this process promising from the perspective of environmental protection since it does not require disposal of solvents which are harmful to the environment. Different studies reported the use of heterogeneous catalysts for ethylene oligomerization. Most of them focused on the introduction of metals, such as nickel, on acidic inorganic structure to reduce the requirements for ethylene oligomerization reaction conditions. The introduction of nickel on solid inorganic structures with BEA topology has been shown as a promising alternative for the production of liquid fuels in the range of C₄ to C₁₂. However, a better understanding of the kinetics involved in the ethylene oligomerization over solid inorganic catalysts is required to make this process competitive relative to the existing homogeneous ethylene oligomerization process. Currently, only a few publications performed a kinetic study of the ethylene oligomerization over heterogeneous catalysts. Additionally, to the best of our knowledge, only one publication reported the kinetic study of ethylene oligomerization over NiBEA catalysts. Therefore, we propose in this work a kinetic study of the ethylene oligomerization over a NiBEA catalyst.

We suggest the Langmuir-Hinshelwood Hougen-Watson kinetic mechanism to study the ethylene oligomerization over the NiBEA catalyst. Additionally, we propose two distinct mechanisms. The first mechanism involves the reaction between two adsorbed ethylene species. On the other hand, the second mechanism considers that one of the ethylene species is adsorbed on the catalyst surface and the other one is in the gas phase. The latter mechanism is denominated Eley-Rideal. We performed the experiments on a packed bed reactor with a catalyst loading of 0.25 grams and a WHSV of 30.24 h^-1. Prior to the kinetic data acquisition, we performed experiments to determine if the system was limited by diffusion mechanisms. Therefore, we performed oligomerization experiments at different temperatures ranging from 30 to 200 ^oC at fixed conditions. We used this data to calculate the activation energy and the pre-exponential factor of the Arrhenius equation. We found the activation energy and the pre-exponential to be equal to 11 kJ/mol and 182 g ethylene g catalyst^-1 h^-1, respectively. We approached the development of the kinetic model from two different perspectives. First, we developed a kinetic model based on the consumption of ethylene in the reaction system. Second, we used the rate of production of products ranging from C₄ to C₈ to develop the kinetic model. This model is able to predict not only the total ethylene consumed in the system but also the major products produced during the reaction. It is important to highlight that the product range listed is suitable to be used as gasoline additives.