Abstract

The growing concern about environmental pollution necessitates the development of renewable and eco-friendly energy sources. Dimethyl ether (DME) has emerged as a promising alternative to diesel and LPG fuels and as a hydrogen carrier due to its favorable characteristics, such as high cetane number, oxygen content, absence of C-C bonds, and low CO and NOx emissions during combustion. Industrial DME production involves methanol dehydration, which requires a solid acid catalyst.
Common catalysts used in this process include γ-Al2O3 and ZSM-5 zeolite. However, γ-Al2O3 exhibits limited activity at lower temperatures, while ZSM-5 suffers from rapid deactivation and coke formation. Heteropoly acids have also been investigated as solid acid catalysts, but their low surface area limits their activity. Therefore, catalysts with increased acidity and improved selectivity towards DME are sought to enhance conversion efficiency and stability.
In this study, the use of alternative zeolites including KFI and RHO with varying crystallization times and template amounts was explored for methanol dehydration compared against commercial ZSM-5 and alumina catalysts. Steady-state methanol conversion experiments were carried out at 130 - 220°C using 30% methanol in an Ar balance. Long-term stability tests lasting 100 h were performed, and the catalysts were analyzed using SEM, EDS, XRD, BET, NH3-TPD, and TGA techniques.
The KFI and RHO zeolites exhibited equilibrium conversion (>90%) at lower temperatures (180-200°C) and demonstrated stability for more than 100 and 60 h, respectively. These outcomes can be attributed to high crystallinity, optimized crystal size, and large surface area resulting from the optimized synthesis process.