1. Betül GÜRÜNLÜ Istanbul Technical University
Fischer Tropsch Synthesis of Gasoline-Range Hydrocarbons over Fe/ZSM5 Catalysts
Murat Baranak*, Alper Sarıoglan*, Hüsnü Atakül°, Betül Gürünlü°
*TÜBİTAK Marmara Research Center, Kocaeli, Turkey, °Istanbul Technical University, Maslak, Turkey
Betül GÜRÜNLÜ
Istanbul Technical University

2. Presentation overview
Overview of Fischer Tropsch Process Development of Fischer Tropsch Catalysts Catalysts Preparation Characterization of Catalysts Performance Tests of Catalysts Experimental Results & Conclusions

3. Fischer Tropsch Process
FT synthesis is an excellent method for upgrading low-value coal and biomass to high-value, environmentally friendly liquid fuels with no sulfur contamination

4. Fischer Tropsch Synhesis

5. Why FT (Fischer Tropsch) Fuel?
Alternative for the countries which have large coal reserve but not having petroleum
Many raw materials (biomass blends ) can be used
The resultant fuel is colorless, odorless, and low in toxicity.
Interchangeable with conventional diesel fuels and can be blended with diesel at any ratio with little to no modification

6. FISCHER TROPSCH CATALYSTS

7. Development of Fischer Tropsch Catalysts
Development of Fe catalysts with high FTS activity, low methane selectivity, and long+term stability is of great importance.

8. Zeolite Supported FT Catalysts
ZSM5, Zeolit Y, Beta, Mordenite, Ferrierite
Remarkable points of zeolites are their framework structure and acidity.
Shape selectivity
Pore structure of ZSM5 does not allow to produce high hydrocarbons.
10 membered ring framework structure of ZSM5
Size of the catalyst particle settled in zeolite could not be larger than A°

9. Catalysts Preparation
Ammonium form ZSM5 (SiO2/AlO2=280) zeolite is used as support for impregnation (incipient wetness impregnation) of iron nitrate solution.
Catalysts which include 5%, 10% ve 20% (wt) of iron are obtained.

10. Characterization of Catalysts
XRD Results
The relative crystallinity of ZSM-5 was calculated based on the intensity of the peaks of angle 2θ=22–25
It can be observed a decrease in the peak intensities with the increase in the Fe content in the samples.
Fe-hematite (α-Fe2O3) phase was observed on the peaks of angle 2θ=
Fe-hematite phase peaks increase acoording to the percentage of iron

11. Characterization of Catalysts
BET Surface areas of catalysts and ZSM5
BET Surface Area
ZSM5
m²/g
5%Fe+ZSM5
m²/g
10%Fe+ZSM5
m²/g
20%Fe+ZSM5
m²/g
100% iron based cat.
m²/g
As the iron content increases, BET surface areas of the samples are lowered.

12. PERFORMANCE TESTS OF FT CATALYSTS

13. P:atm T: 475°C by the dry air - 14 hours
Test System
Reactor type
Fixed bed reactor
Catalyst bed volume
6,44 cc
Calcination procedure
P:atm T: 475°C by the dry air - 14 hours
Reduction procedure
P: atm T: 425°C by H hours
GHSV
750 1/h
Feed gases
H2: 3 nL/h, CO:1.5 nL/h, N2: 0.45 nL/h
Reaction operation cond.
P: 19 bar T: 265°C/250°C

14. GC Analysis of Hydrocarbons Products
Analysis time: 187 min.
7/24 Auto analysis
Including FID dedector and HP-pona column
Analysis up to C28 hydrocarbons
Reference material for calibration is paraffin, iso-paraffin and α-olefin mix

15. RESULTS of PERFORMANCE TESTS

16. Calculations
Conversion:
Selectivity:
Hydrocarbon Distribution:

17. Test Results CO Conversion Trends
CO conversion values are getting higher as the percentage of iron in catalyst increases.
For the zeolite based FT catalysts, CO conversion is %16 for %5 iron contained catalysts at 250°C. When iron content of catalyst increases, CO conversion reaches to %50 value.
Iron is the active phase of catalyst and FT reaction occurs on it. So; as percentage of iron is getting higher, increase of FT activity is expected.
In order to the higher reaction rate, when the temperature goes up, more bigger conversion values are obtained.
For both of the temperature magnitudes, %100 iron contained precipitated catalyst gives %90 conversion values.
CO conversion trend depends on the percentage of iron content (a:250°C, b:265°C)

18. Test Results H2 Conversion Trends
H2 conversion increases according to raising the percentage of iron content and temperature.
%100 iron contained precipitated catalyst gives H2 conversion is %48 at 250°C and raises to %54 at 265°C.
Although H2 and CO are fed as stoichiometric ratio, because of water-gas shift (WGS) reaction, H2 conversion is lower than CO conversion.
H2 conversion trend depends on the percentage of iron content (a:250°C, b:265°C)

19. Test Results CH4 Selectivity Trends
Zeolite based iron catalysts have lower methane selectivity than the only-iron based catalysts.
Methane selectivity value is %10-20 for zeolite based catalysts and %30 for only-iron based catalysts.
As a result, methanation has lower reaction rate for zeolite based catalysts.
Methane is unwanted product in FT processes, so having lower methane selectivity value is an advantage for zeolite based catalysts.
CH4 selectivity trend depends on the percentage of iron content (a:250°C, b:265°C)

20. Test Results C2-C4 Selectivity Trend
C2-C4 selectivities are lower for the zeolite based catalysts.
C2-C4 selectivity value is %25-35 at 250°C and %35-45 at 265°C for zeolite based catalysts. When we examine only-iron based catalysts, C2-C4 selectivity value is %49 at 250°C and %40 at 265°C.
Lower olefin/paraffin ratio in C2-C4 range hydrocarbons are obtained for zeolite based catalysts. Olefin/parafin ratio in C2-C4 range hydrocarbons is %5 to %10 for zeolite based catalysts. For only iron based catalysts this ratio rises to %25 at 250°C and decreases to %10 at 265°C.
It is predicted that the reason of lower olefin/parafin ratio and C2-C4 selectivity is chain growth caused by readsorbing alpha - olefin molecules in nanopores by oligomerization.
C2-C4 selectivity trend depends on the percentage of iron content (a:250°C, b:265°C)

21. Test Results C5+ Selectivity Trend
C5+ selectivities are higher for the zeolite based catalysts than %100 of iron based catalyst.
C5+ selectivity value is %50-60 at 250°C and %40-50 at 265°C for zeolite based catalysts.
As the temperature goes higher, chain growth is decreased because of the increasing hydrogenation (chain termination).
C5+ selectivity value is %19 at 250°C and %31 at 265°C for %100 iron based catalysts.
C5+ selectivity trend depends on the percentage of iron content (a:250°C, b:265°C)

22. Test Results CO2 Selectivity Trend
CO2 selectivity shows that the activity of WGS reaction.
C5+ selectivity value varies from %5 to %20 at 250°C and from %9 to %25 at 265°C for zeolite supported catalysts.
CO2 selectivity value is %44 at 250°C and %37 at 265°C for %100 iron based catalysts.
Because of the suppressing effect of zeolite supported catalysts on the WGS, lower CO2 selectivity is obtained.
CO2 selectivity trend depends on the percentage of iron content (a:250°C, b:265°C)

23. Sum of Test Results
Table 1 Conversion and selectivity values of FT reaction (250°C)
Table 2 Conversion and selectivity values of FT reaction (265°C)

24. GC analysis of liquid HCs

25. GC analysis of liquid HCs

26. Liquid product
%95 of liquid produced by using zeolite supported catalysts is C5-C12 range hydrocarbons. This range of hydrocarbons represents gasoline.
No additional process such as distillation, treatment by hydrogen or alkylation etc. is required to obtain gasoline product by using zeolite supported catalysts.
Consequently, one stage gasoline production is achieved.

27. Conclusions
According to the test results, almost 40-60% of produced HCs by FT process are in the range of gasoline.
CO2 selectivity is varied from 10% to 20% by using the zeolite supported catalysts and so they have higher WGS activity.
CH4 selectivity is in the range of 15-20% and C2-C4 selectivity is in the range of 25-45%. In order to decrease the selectivity of C1 and c2-c4, promoters could be added to the catalysts also, process could be optimized.
Comparing with 100% iron based catalyst, zeolite supported catalysts have lower C1-C4 selectivity and higher C5+ selectivity.