On the involvement of radical "coke" in ethanol conversion to hydrocarbons over HZSM-5 zeolite
Résumé
During ethanol-to-hydrocarbons (ETH) process at 623 K and 30 bar on HZSM-5(40), side reactions occur leading to the formation of carbonaceous materials, defined as "coke" which is composed mainly of alkylbenzenes and alkylnaphthalenes. The "coke" molecules, trapped inside the channels have first a direct effect on the Brønsted acid sites by poisoning them; however, they can also have an indirect effect. Indeed, some "coke" molecules lead to radicals formation by spontaneous ionization which could potentially act as active species in ethene oligomerization. Nevertheless, the radicals could also condensate into bulkier molecules leading to inactive species and consequently undergoing to catalyst deactivation. The participation of radical "coke" in EtOH transformation into higher hydrocarbons was demonstrated by adding in the feed gas a radical inhibitor such as hydroquinone (HQ). Indeed, the consumption of radical species by HQ, enhanced the catalyst deactivation.