283267 Simple, Cheap Dry-Mix Method to Prepare Iron Fischer-Tropsch Catalysts

Monday, October 29, 2012: 1:10 PM
315 (Convention Center )
William C Hecker, Kyle M. Brunner, Kamyar Keyvanloo and William C. Schaffers, Chemical Engineering, Brigham Young University, Provo, UT

Simple, cheap dry-mix method to prepare iron Fischer-Tropsch catalysts


William C. Hecker, Kyle M. Brunner, Kamyar Keyvanloo, William C. Schaffers

Chemical Engineering, Brigham Young University, Provo, UT, USA



Highly active and selective Fe-Cu-K-SiO2 and Fe-Mn-K-SiO2 Fischer-Tropsch (FT) catalysts have been developed using a novel co-precipitation method. This is a simple, dry-mix method that produces the precursor catalyst (pre calcination and reduction) in about one-quarter the time that it takes to prepare standard precipitated catalysts.  The physical and chemical properties of these catalysts compare favorably with properties of representative precipitated iron catalysts described in the literature. Catalysts have surface areas between 50 and 150 m2/g and pore volumes of 0.15 to 0.30 mL/g. Hydrogen chemisorption measurements were 100 to 150 umol/g. Selectivity to methane was 0.040.06. Catalyst productivity to hydrocarbons was 0.550.72 gHC/gcat h.

Catalysts were prepared from nitrate salts of the Fe and Cu or Mn by a simple, proprietary co-precipitation method developed by Cosmas, Inc. After co-precipitation, the catalysts were either washed or not washed.  Next, in a second step, potassium (KHCO3) and silica (Cab-O-Sil) promotors were added to the wet precursor before the catalyst was dried. A one step method in which the potassium and silica were added at the same time as the nitrate salts was also tested. Nominal catalyst composition was 100 Fe/ 5Cu/ 4K/ 16SiO2 by mass. Catalysts were either dried slowly at 60C followed by 100-120C for 48 hours or dried quickly at 100-120C for 48 hours.  Catalysts prepared from ferrous sulfate salts instead of the nitrate salts were also tested and differences noted.  All catalysts were calcined at 300C for 10 hours in air with GHSV = 2000 h-1. After calcination, catalysts were reduced in H2 at 300C, GHSV of 2000 h-1. Following reduction, the catalysts were cooled to room temperature and then carefully passivated in air such that the bed temperature during passivation was 25-30C.

Activity studies were performed in a 3/8 inch ID fixed-bed reactor. Activation and reaction conditions were 300 psig, 31% H2, 31% CO, 4% Ar, 34% He, GHSV = 7,000-10,000 h-1. Activation was at 250C for 48-100 hours. Reaction temperatures were varied from 220 to 260C. Reactor effluent was analyzed online by an HP 6890 GC. Reaction rates at 260C for 6 catalysts prepared and tested as described showed that not washing the catalyst increases activity 100%.  The hydrogen uptakes for C01 and C02 were 143 and 157 µmol/g, respectively, indicating that washing did not have a great effect on the number of active sites in the respective catalysts, but that the activity per site was significantly higher.

These catalysts compare favorably with catalysts in the literature. Hydrogen uptakes are 100150 umol/g compared with 100150 umol/g in the literature. 1st-order activities (mmolCO/g h MPaH2) at 260C, 21 atm, and H2:CO=0.7-1 are 125-154 compared with 102-180 in literature. Selectivity to CO2 was 0.420.47 compared with 0.450.49 in the literature. Selectivity to methane was 0.040.06 compared to 0.02-0.04. Catalyst productivity to hydrocarbons was 0.550.72 gHC/gcath compared to 0.40.8 in the literature.

That the catalysts can be prepared using the Cosmas method with much less time and equipment will have a huge impact on the cost of production. Increased catalyst life and performance will increase the economics of running FT plants a current major obstacle to wide acceptance and implementation. Understanding the changes that occur during the washing step is fundamental to understanding activity on iron FT catalysts.



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