Bio-based hydrocarbons and oxygenates from catalytic bio-ethanol dehydration: comparison between gallium and germanium oxides as promoters on HBeta zeolites with various silica to alumina ratios

Abstract

Hydrocarbons and oxygenates can be produced from methanol or ethanol via dehydration and other reactions as green alternative routes. One of the most important factors, which govern the activity and product distribution, is the silica/alumina ratio (related to acid strength and acid density) of a zeolite support used as a catalyst in ethanol dehydration. H-ZSM-5 zeolite was often used as a catalyst for methanol or ethanol dehydration because of its shape selectivity, but its pore size limits the production of large hydrocarbons. In this work, the effects of acid density and acid strength in the product distribution were investigated using various silica/alumina ratios of H-Beta zeolites with a larger pore size, aiming to produce larger hydrocarbons than gasoline range. Gallium and germanium oxides were also doped on the H-Beta zeolites, and their effects on the product distribution were examined and compared. As a result, it was found that increasing silica/alumina ratio resulted in the reduction of acid density and acid strength of H-Beta zeolites, and the highest oil yield was obtained from using a moderate silica/alumina ratio of H-Beta (silica/alumina ratio = 37), which highly consisted of large hydrocarbons (aromatics with carbon numbers higher than 9). The support with the lowest acid density and strength tended to produce oxygenates, non-aromatics, and benzene rather than large hydrocarbons. When loaded on the zeolites with the lowest and highest acidity, gallium and germanium oxides suppressed the oil yield, promoted the production of oxygenates and distillate-range hydrocarbons, and did not change the selectivity of p-xylene in mixed xylenes. However, the differences made by the two promoters were observed to be enhanced by the use of the support with moderate acidity, especially on the increases in non-aromatic formation and p-xylene selectivity.