Skeletal isomerization of Fischer-Tropsch-derived pentenes: The effect of oxygenates

Skeletal isomerization of 1-pentene to 2-methyl-1-butene (2M1B) and 2-methyl-2-butene (2M2B) provides the precursors for etherification with methanol to produce tertiary amyl methyl ether ( TAME), an oxygenate fuel additive for octane improvement. Although the technology has been proven commercially, the use of a Fischer-Tropsch (FT)-derived pentene feed has not been examined previously. In this work, the effect of oxygenates present in an FT-derived pentene feed on conversion, selectivity, and the deactivation of a commercial catalyst is described. The results are compared with those obtained with a model feed containing no oxygenates and also with an FT feed from which the oxygenates have been removed. The presence of oxygenates in the feed required a start of run temperature above 320 degrees C to prevent competitive adsorption with the olefins, but these higher temperatures led to rapid catalyst deactivation. Oxygenates could successfully be removed from the FT feed by n-methylpyrolidone wash. This resulted in a longer catalyst cycle length (10-12 months) than in the presence of oxygenates (1-2 months).