Alkylation of 1-butene with isobutane using EMT and Y zeolites.

摘要

Alkylate is the preferred blending stock of reformulated gasoline as it is clean burning, producing less emissions, and possesses high energy and octane. Commercial liquid catalysts employed for the alkylation of butene with isobutane pose significant environmental hazards. Many solid acids have been investigated towards this reaction, but none have reached commercial success. Although high initial activity is demonstrated, rapid deactivation ensues, primarily due to a loss in hydride transfer functioning.; The preferential adsorption of the olefin relative to the isoparaffin makes deactivation an inevitable outcome. The catalyst surface selectively adsorbs butene from the feed, regardless of the feed composition. Eventually the surface acid sites become saturated with oligomers of butene. Pulse feed delivery, with interim isobutane flush periods, can restore deactivated catalysts to fresh state levels. It is possible that catalytic distillation may hold some promise for this challenging reaction, if a suitable solid acid catalyst can be found.; The zeolite, EMT, is a hexagonal phase faujasite synthesized in the presence of a crown-ether template. Literature measurements for pyridine desorption conclude that this zeolite possesses primarily Bronsted acidity, with significant amounts of strong acid sites. These properties are ideally suited to promote efficient hydride transfer in the alkylation of butene with isobutane.; The catalyst, EMT, demonstrated superior performance relative to Y zeolite, improving the Useful Catalyst Lifetime period (butene conversion maintained above 80%) by 41%. Approximately half of the alkyate produced was composed of Ca compounds, of which roughly 60 to 80% were trimethylpentanes (TMPs). The most valuable octane isomer, 2,2,4-TMP, was present in the largest quantities in the alkylate, accounting for 30 to 60% of the TMP fraction. It is believed that the uneven distribution of acid sites on EMT discourages deactivation processes. Alternatively, it is also possible that isobutane adsorption capacity on EMT is improved relative to Y.; The impregnation of 0.5% Pt onto EMT (0.5%Pt/EMT) produced a minor improvement in the Useful Catalyst Lifetime period and alkylate quality (as measured by TMP content). The levels of TMP were notably higher on 0.5%Pt/EMT, accounting for 80% of the C8 fraction. These improvements are attributed to an increase in the concentration of reactive hydrogen. (Abstract shortened by UMI.)