Investigation of zeolite acid sites for 2,5-dimethylfuran conversion

Abstract

Finding new routes for chemical valorisation of biological feedstocks is an essential part for developing a biobased economy and reducing the use of fossil fuels. This project tailor’s new zeolite‐based catalytic materials over which green aromatics, i.e., benzene, toluene, and xylenes (BTX), can be produced from 2,5‐dimethylfuran (2,5‐dmf), which can be obtained from pre‐processed low‐cost hemicellulose. The acid sites present in different zeolite samples have been quantified and differentiated under several experimental conditions to better understand the role of the acid sites in zeolites. The samples studied are silica powder, alumina spheres and 3 HZSM‐5 zeolites ranging different SiO2/Al2O3 (SAR), 27, 55 and 330. The experiments have been performed in a continuous flow reactor whose final stream has been analysed by infrared and mass spectrometry in parallel. A, diffuse reflectance infrared Fourier transform spectroscopy, DRIFTS experiment has also been performed to analyse the in‐situ evolution of acid sites and products formed on the surface of the zeolite during a reaction. The experiments revealed a decrease on the total amount of acid sites before and after the reaction with 2,5‐dmf. Differences were found between the different types of acid sites, Brønsted acid sites (BAS) and Lewis acid sites (LAS). BAS are the most abundant types of acid sites on HZSM‐5‐SAR55 zeolite but are easily deactivated with time on stream, while LAS showed the opposite behaviour, allowing the production of compounds for longer periods of time and at higher temperatures. Different group compounds such as olefins, aromatics or isomers have different production trends over time. Aromatics production decreases faster with time on stream, compared to olefins and isomer production, which decreases at slower pace over time. Coke formation, as well as the production of compounds such as naphthalene, ethylene and toluene increase with temperature. Compounds such as p‐xylene, which has a high value and was not obtained during continuous reaction, was only produced when adsorbing 2,5‐dmf on the zeolite at low temperatures and then slowly increasing the temperature. This is an indicator of different reaction mechanism compared to continuous production.