Experimental and Computational Investigations of the Deactivation of H‐ZSM‐5 Zeolite by Coking in the Conversion of Ethanol into Hydrocarbons

Abstract

The catalytic conversion of ethanol into hydrocarbons on a H-ZSM-5 zeolite with a molar Si/Al ratio of 12 was investigated under different reaction conditions (WHSV, carrier flow). During catalyst-deactivation, the selectivity changed towards C 2 products. These results indicated that the deactivation neither correlated with the total amount of deposits nor with the structural damage of the zeolite. Under the assumption that a poreblockage caused the change in selectivity, characterization of the catalyst sample (TPAD, IR spectroscopy), the formed deposits (TGA, DSC), and also the regeneration process were performed. The experimental results were discussed in terms of the nature of the deposits (i.e., aromatic compounds, substituted aromatic compounds, or olefins) and correlated with quantum chemical calculations at the ONIOM(B3LYP/6-31G(d):PM6) level of theory with a purely siliceous model to consider the effect of pore-blockage in an inert SiO 2 MFI network.

Durability improvements of H-ZSM-5 zeolite for ethanol conversion after treatment with chelating agents

“…[1,2] An accurate discussion of its reactivity and catalytic behaviour has to account for its geometric and its chemical properties. [3][4][5] With respect to the zeolite framework both diffusional and shape selective effects are important and with respect to its chemical properties different possible acid sites have to be considered. This includes framework Brønsted acid sites, but also extra-framework species (EFSPE) such as extra-framework silicon species (EFSI), extra-framework aluminium species (EFAL) and extra-framework aluminium silicon species (EFALSI).…”

“…The formed ethene may be consumed in different consecutive reactions in the hydrocarbonpool (HCP) at organic-inorganic hybrid catalytic sites, namely by polymerisation, cracking, hydride transfer or cyclisation reactions. [3,14,15] These catalytic sites are often discussed as cyclic or olefinic carbenium or radical organic species in vicinity to deprotonated zeolitic Brønsted acid sites. [15] Therefore ethene could be treated as feed for HCP-reactions in a proper sense, because dehydration of ethanol is an essential first step or it occurs simultaneously to the initial build-up reactions.…”

“…However, the formation of organic species which are catalytically inactive and too large to leave the catalyst pore system -generally denoted as coke -seems to be the fastest deactivation source in ETH process over H-ZSM-5 and is therefore the main subject on the debate. [3,17] Coke deposits block the access to active sites inside the pore system and therefore promote the formation of ethene, which may also form independently of a surrounding pore system or by thermal dehydration at temperatures over 350 ℃. Therefore ethene formation may be considered a measure of deactivation.…”

“…The pore blocking character during the reaction is possibly correlated to the chemical nature of the deposits in the following order: olefins < aromatics with side chains < high-molecular-weight aromatic compounds. [3] Coke formation occurs by growth and demobilisation of aromatic and olefinic precursor molecules, e.g. organic compounds of hybrid sites, until their center of reaction is no longer accessible for feed molecules and other HCP species.…”

Effect of steam during catalytic cracking of n-hexane using P-ZSM-5 catalyst

“…Most of deposited coke could be burned by the catalyst calcination at 893 K, which was higher than the reported temperature (ca. 773-823 K) of the calcination for the regeneration of the coke-deposited ZSM-5 catalysts [22][23][24]. The initial conversion of the 2nd run with 1.0 of S/nC6 ratio was 84%, which was higher than the conversion measured at the last of the 1st run (60%) and was lower than the initial conversion of the 1st run (90%), indicating that the P-ZSM-5 catalyst deactivated because of both the coke deposition and the dealumination of ZSM-5.…”