Oligomerização de 1-buteno catalisada por zeólitas ZSM-5

Abstract

The search for renewable raw materials to reduce dependence on oil and address environmental preservation concerns has been encouraged. This process enables the efficient utilization of petrochemical by-products and may contribute to the development of sustainable fuels aligned with the global energy transition. In this context, the oligomerization of light olefins emerges as a promising alternative for producing fuels free of aromatic and sulfur compounds. Among the most studied catalysts for olefin oligomerization, zeolites with MFI topology stand out due to their acid and textural properties, which can be adapted through post-synthesis modifications. In this work, the effect of ZSM-5 zeolite modification on catalytic performance in the oligomerization of 1-butene under atmospheric pressure was investigated. Two modification strategies were explored: metal impregnation (La, W, and Fe), and mesopore generation through alkaline desilication, followed by post-treatment with oxalic acid and ion exchange. The resulting samples were characterized by different techniques, including X-ray fluorescence (XRF), X-ray diffraction (XRD), nitrogen adsorption-desorption, ammonia temperature-programmed desorption (NH₃-TPD), diffuse reflectance infrared Fourier-transform spectroscopy with pyridine adsorption (DRIFTS), and ²⁷Al magic-angle spinning nuclear magnetic resonance (MAS-NMR). Metal impregnation significantly affected the acid and textural properties of ZSM-5. Samples modified with W and Fe exhibited Lewis acid sites and an increased proportion of strong acid sites, which promoted cracking and isomerization reactions. In contrast, La-ZSM-5, with a predominance of intermediate-strength Brønsted acid sites, showed improved performance in the formation of C8 and C9+ oligomers but experienced selective deactivation over time. The desilicated zeolites, particularly the D-ZSM-5-OX sample treated with oxalic acid, exhibited larger mesopore volumes and a reduced amount of extra-framework aluminum species (EFAL), enhancing accessibility to active sites and selectivity toward heavier oligomers. This sample demonstrated excellent catalytic performance and stability over 23 hours of reaction. An increase in reaction temperature up to 400 °C favored the formation of higher molecular weight oligomers, overcoming limitations associated with atmospheric pressure operation. The results highlight the potential of modified ZSM-5 zeolites, especially those subjected to selective desilication and oxalic acid treatment, as efficient and selective catalysts for the production of synthetic fuels from 1-butene.