EFFECT OF INITIAL WAX MEDIUM ON THE FISCHER-TROPSCH SLURRY REACTION

This investigation measured the impact of the liquid starting medium o n syngas (H-2+CO) conversion via the Fischer-Tropsch (F-T) synthesis i n a 11 continuous stirred tank reactor (CSTR). The experiments were co nducted with a low-wax producing iron catalyst, so that the liquid med ium composition was unaltered by accumulation of product wax throughou t the experiment. Our results show a greater deactivation rate for the F-T reaction in heavier starting media (Polywax-655, Allied AC-1702, and Mobil F-T product wax) versus the lighter medium (n-octacosane). T he syngas (H-2+CO) conversions were approximately equal and steady for the first five days in both light and heavy, commercially available w ax media. However, the conversions dropped more rapidly in the heavier wax media (from 85% to 60% in 12-13 days), but only modestly in the l ight wax media (from 90% to 85% in 15 days). An even sharper deactivat ion rate occurred with the heavy Mobil F-T wax (from 85% to 60% in six days). For all experiments, the water gas shift (WGS) ratio in the ou tlet gases dropped concurrently. One proposed explanation for this inc reased deactivation in the heavier waxes is that heavier products are being formed by secondary reactions. These products could build up ove r time and restrict the diffusion of hydrocarbon products and water va por out of the pores. The presence of higher partial pressures of wate r vapor could irreversibly oxidize the catalyst. (C) 1997 Elsevier Sci ence B.V.