Alkylation of isobutane with trans-2-butene on hydrothermally prepared BEA-type zeolitic materials with different crystallization time

Abstract

It is widely known that hydrofluoric and sulfuric acids are the conventional catalysts used in the alkylation reaction, an important petrochemical process in the production of automotive fuels. However, these inorganic acids are highly toxic and therefore, solid zeolitic catalysts have emerged as an environmentally friendly alternative. In this work, a series of BEA-type zeolitic materials were prepared in hydrothermal systems varying the crystallization time to test their catalytic performance in the alkylation of isobutane with trans-2-butene. The materials were characterized by Infrared Spectroscopy (FT-IR), X-ray Powder Diffraction (XRPD), Scanning Electron Microscopy (SEM), N2 physisorption, and total acidity measurements by ammonia method. The synthesis of BEA zeolite was successfully carried out at crystallization times between 8 and 20 h (ZB-8, ZB-12, and ZB-20 samples), whilst longer periods produce a combination of BEA and MFI zeolites (ZB-28 and ZB-96 samples). Based on the XRPD analysis, the possible presence of two polymorphs of the BEA zeolite is proposed. The synthesized materials in the acidic form were catalytically examined for 120 min at different contact times (0.078, 0.156, and 0.234 gcat × min × mol−1) and temperatures (40 and 60 °C). The reaction was fitted to second-order deactivation kinetics. High selectivity was observed for the group of C7-C9+ compounds in the steady-state condition, particularly towards the fraction of C8 compounds. The generation of the compounds that make up the alkylate group was favored in most catalytic tests. The highest yields for alkylate were achieved under conditions of 0.156 gcat × min × mol−1 and 40 °C with values of 9.5 and 12 % for the ZB-12 and ZB-96 catalysts, respectively. This study supported the importance of balancing the density of acidic sites and the porous topology of zeolitic materials in conjunction with the selection of reaction parameters such as temperature and contact time to favor the yield towards alkylate.