(78b) Simple, Cheap Dry-Mix Method to Prepare Iron Fischer-Tropsch Catalysts

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 0.04?0.06.
Catalyst productivity to hydrocarbons was 0.55?0.72 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 60°C followed by 100-120°C for
48 hours or dried quickly at 100-120°C 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 300°C for 10 hours in air with GHSV = 2000 h^-1. After
calcination, catalysts were reduced in H₂ at 300°C, 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 25-30°C.

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 250°C for 48-100
hours. Reaction temperatures were varied from 220° to 260°C. Reactor effluent
was analyzed online by an HP 6890 GC. Reaction rates at 260°C 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 100?150 umol/g compared with 100?150 umol/g
in the literature. 1^st-order activities (mmol_CO/g
h MPa_H2) at 260°C, 21 atm, and H₂:CO=0.7-1 are 125-154 compared with 102-180 in literature.
Selectivity to CO₂ was 0.42?0.47 compared with 0.45?0.49 in the
literature. Selectivity to methane was 0.04?0.06 compared to 0.02-0.04.
Catalyst productivity to hydrocarbons was 0.55?0.72 g_HC/g_cath compared to 0.4?0.8 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.