Effect of Oxygenates on the Oligomerization of Fischer−Tropsch Olefins over Amorphous Silica−Alumina

The oligomerization of Fischer−Tropsch derived olefins over amorphous silica−alumina (ASA) has been investigated with feed materials containing 1−4% oxygenates to determine the effect of the oxygenates on catalyst performance and transportation fuel quality. The main differences between the oligomerization of oxygenate-containing and oxygenate-free olefinic feeds were: (a) higher deposition rate of carbonaceous material on the catalyst due to the carbonyls in the feed being converted to aromatic coke precursors; (b) shorter cycle length, although cycle lengths up to 8 months could be achieved with careful operation; and (c) formation of carboxylic acids from the carbonyls in the feed. Reaction over alumina and water washing were evaluated as feed pretreatment steps to reduce the oxygenate content in the feed, but neither were able to completely remove the carbonyls. All tests were done at pilot plant scale in the operating range 110−300 °C and 6 MPa.