(30c) Evaluation of a Long-Term Fischer-Tropsch Test and the Resulting Spent Iron Catalyst

A precipitated iron Fischer-Tropsch catalyst (100 Fe: 5Cu: 4.2 K: 17 SiO2) was run continuously for 500 hours in a 1.0 liter CSTR under highly carburizing conditions. The slurry initially consisted of 10 g of the catalyst dispersed in Oronite synfluid. The simulated syngas feed for the test consisted of H2 and CO with a small amount of argon as an internal standard. The H2 to CO mole ratio of the syngas feed was maintained at 0.7 to simulate a syngas obtained from a biomass or coal gasifier. Following catalyst activation in syngas, steady state conditions were established at 375 psig and 240oC at a space velocity of 2,200 per hour. Under these conditions, the reactor outlet H2 to CO mole ratio was approximately 0.6. The CO conversion and C5+ hydrocarbon yield over the run were constant at about 40 % and 2 g/h, respectively, for about 425 hours when the activity began to decline rapidly. Over-carburizing of the catalyst is thought to be the primary reason for this decline, as such a decline has not been observed in previous long-term tests of 500 hours under less carburizing conditions. The catalyst sample was recovered from the product wax and analyzed by XRD, XPS, and Mossbauer spectroscopy to understand the phase changes associated with the activity decline.