Role of Coke Deposites in Isomerization Reaction of Ethylene Oxide Accompanied with Coke Deposition

Abstract

The isomerization reaction of ethylene oxide was carried out on a catalyst obtained by pretreatment of Japanese colloidal earth with hydrochloric acid. It was examined how the main reaction would be influenced by the coke deposit (Fig. 1). Further, the reaction mechanism including the deposition of coke was assumed from the study.
In spite of raising the reaction temperature, the reaction rates began to decrease, when a uniform coating of the pores resulted from coke deposition for lower feed concentration of ethylene oxide, or when the direct clogging of the open ends of pores resulted with higher concentrations (Fig. 3). The selectivity was not affected by the weight of coke and the conversion, because the main reaction and the coking were similarly impeded by the coke deposited with the elapse of time (Fig. 2). The selectivity, however, decreased by raising the reaction temperature or increasing the feed concentration of ethylene oxide, because the coking reaction was more predominant than the main reaction (Fig. 4). The yield increased with rise in conversion rate, and corresponding to the selectivity at the same conversion rate (Fig. 5), but decreased with accumulation of weight of coke (Fig. 6).
Acid strength at active sites was closely related to the formation of coke from acetoaldehyde, but were unrelated to the coke from ethylene oxide (Fig. 7). Furthermore, the main reaction was less predominant than the coking reaction and required active sites having high acid strength (Fig. 8, Table 1). From the above reason, the mechanism of this reaction system was presumed as follows (Fig. 9): In the main reaction adsorbed ethylene oxide produces adsorbed acetoaldehyde. The coke deposits on these adsorbed molecules are due to the polymerization of ethylene oxide or acetoaldehyde in the gas phase. Further, its rate determining step was regarded to be the formation reaction of precursor.