Ethanol to Aromatics on Modified H‐ZSM‐5 Part II: An Unexpected Low Coking

Abstract

In this study a commercial H-ZSM-5 zeolite (Si/Al = 11) was post-synthetically modified by a combined dealumination procedure to adjust its catalytic properties for the selective formation of aromatics from ethanol. The solid-state properties of original and modified zeolites are determined by structural, textural and acidity analysis. The formation of aromatics and durability of the zeolites were investigated depending on space velocity or contact time in the catalyst bed. In particular, the formation rate and desorption of aromatics from solid-state surface as well as their tendency to form coke precursors by consecutive build-up reactions determine the formation of coke. Therefore, the rate of buildup and finished aromatization by hydride transfer (predetermined by the kind, location and geometric arrangement of surface acid sites) and the statistical number of reaction events until final desorption at the specific contact time have to be harmonized to increase aromatics yield and to decrease catalyst decay by coke simultaneously.

Deactivation Kinetics of ZSM‐5 by Coke in Ethanol‐to‐Hydrocarbons Process

“…A summary of physico‐chemical data of commercial ZSM‐5 zeolite from recent reports 14, 15 describes a highly acidic (Si/Al = 11.2; 0.56 mmol(NH 3 ) g −1 ), high surface (BET: 390 m 2 g −1 )16 and mainly microporous material (BJH: ∼ 61 m 2 g −1 )17. During conversion tests for ethanol, a mass balance from GC gas and liquid phase as well as TG coke analysis helps to quantify conversion of the feed and yields of different product fractions at 350 °C for 10 h ToS .…”

“…Temperature program consists of a ramp between 35 °C and 850 °C with a rate of 10 K min −1 each run. 14, 15…”

“…Compound determination in gas phase was compared to results from gas chromatography and mass spectrometry (GC/MS) with a Clarus 680 GC and a Clarus SQ 8 S MS from PerkinElmer as well as a Rxi‐1ms column (100 m) with an extended DHA method as reported in previous work. 14, 15…”

“…8 A standardization of individual product streams to the current status of deactivation of the secondary conversion of C 2 (mainly ethylene) has been described for gas‐phase products C 2 , C 3 , C 4 and C 5+ in ethanol conversion process at almost complete ethanol conversion. 14, 15 An easy triangular plot is used to display changes in standardized C 3 *, C 4 * and C 5+ * with ToS and ongoing catalyst deactivation (see Fig. 1).…”

“…C 5+ is a measure for further build‐up and interconversion processes of hydrocarbon molecules. 14, 15…”