Ethanol transformation over HFAU, HBEA and HMFI zeolites presenting similar Brønsted acidity Original Research Article

Ethanol transformation into higher hydrocarbons in one step by heterogeneous acid catalysis was studied, under 350 °C and 30 bar of total pressure. A comparison was established among three zeolites (HFAU, HBEA and HZSM-5) having the same quantity of Brønsted acid sites but possessing different pore architectures. Large pore HFAU and HBEA zeolites gave mainly increasing yield of ethylene and diethyl ether with time-on-stream, due to the deactivation of the strongest acid sites and only a low quantity of C3+ hydrocarbons. This was explained by a faster deactivation of large pore zeolites due to fast coke formation which rapidly eliminates strong Brønsted acid sites, required for the transformation of ethylene into higher hydrocarbons. These coke molecules were identified as being polyaromatic compounds. Medium pore zeolite HZSM-5 showed an important formation of C3+ hydrocarbons (mostly C5–C11 compounds) and very small amounts of ethylene and diethyl ether. For this zeolite, after 16 h reaction, there was still complete ethanol transformation into C3+ hydrocarbons, even though a 55% loss of microporosity and 94% loss of Brønsted acidity were observed. On HZSM-5 the deactivation is slower and the formation of C3+ hydrocarbons was observed even when the catalyst was saturated with coke molecules (high activity for the hydrogen transfer reactions). It could be possible, that for this zeolite, reaction occurs at the pore mouth of the channel.