1. Table 1: Properties of zeolite and catalysts.
Production of gasoline-range hydrocarbons over dealuminated zeolite supported iron catalysts in Fischer Tropsch synthesis Murat Baranak1,2, Betül Gürünlü2, Alper Sarioglan1, Hüsnü Atakül2
1TUBITAK Marmara Research Center, Kocaeli/TR,
2Istanbul Technical University, Istanbul/TR
Introduction
The Fischer-Tropsch (FT) synthesis is carried out industrially at K and bar. A major limitation of the Fischer-Tropsch technology is the low selectivity of the conventional catalysts towards the desired compounds. The Anderson–Schulz–Flory (ASF) kinetics of the FT reaction imposes a limit of maximum 48% to the selectivity for gasoline-range products [1-2]. Selectivity can be enhanced by using bifunctional catalysts [3-5]. Zeolit Y is used to increase the ratio of gasoline through its favorable functions such as:
Shape selectivity
Acidic character  hydrocracking and isomerization reactions
Aim
The aim of this study is to produce gasoline with high octane number through FT reactions. In this study we synthesized and tested zeolite (Y) supported-iron type catalysts, to enhance the selectivity towards gasoline range hydrocarbons in FT synthesis.
Materials & Methods
Catalyst Preparation
The zeolite supported catalysts were prepared by the incipient wetness impregnation method from iron precursor and Zeolite Y with SAR ratios of 5 (Y5) and 80 (Y80). Base iron catalyst was prepared by precipitation method. Zeolite Y5 was also dealuminated and used. Catalysts are designated as follow: DY5 = Dealuminated Y5, respectively, BFe = Base iron, FeY5 & Fe80 = Y5 & Y80 supported iron catalyst, respectively, FeDY5 = DY5 supported iron catalyst, respectively.
FT Reaction Test System
Activity tests of the catalysts were carried out in a fixed bed reactor as shown in belowed Fig 3. and also flowchart of the system is shown in Figure 4.
Catalysts Characterization
H2 conversions of all catalysts are in same order with CO converions of them: FeDY5 > FeY5 > BFe > FeY80.
CO2 selectivity of base iron catalyst is 3-7 fold higher than that of zeolite Y including catalysts.
Hydrocarbon product selectivity of zeolite Y including catalysts are 13 – 25 fold higher than that of base iron catalysts.
Methane selectivity of Zeolite Y5 decreased sharply with increasing temperature to 553 K.
Olefin ratio (C2-C4) of base iron catalyst is slightly larger than zeolite containing catalysts.
The fresh zeolites and catalysts are characterized by XRD, BET and ICP analyses. Results are given in Table 1.:
Table 1: Properties of zeolite and catalysts.
The external surface area of zeolite significantly decreased after iron loading, likely due to the preferential deposition of iron species on the pore mouth.
FT Catalysts Test Results
CO conversions of all catalysts at 553 K/ 538 K/ 523 K are given in Fig. 5.
Figure 6: Hydrocarbon product selectivities of base iron and zeolite Y supported iron based catalysts.
Zeolite Y also improved the hydrocarbon productivity of catalyst through better dispersion and utilization of iron in catalysts.
Figure 5: CO conversions of BFe, FeY5, FeDY5 and FeY80
Conclusions
Presence of the zeolite Y in the catalysts considerably enhanced the catalytic activity. .
A mild dealumination of zeolite resulted in the elimination of the inactive and weak-acid sites. This enhanced activity of catalyst.
Gasoline range selectivity of Zeolite Y containing catalysts was times higher than that of conventional iron based catalyst. A maximum gasoline selectivity of 83% was obtained for the dealuminated Zeolite Y5 containing catalysts.
Presence of the zeolite Y in the catalysts decreased the CO2 selectivity and WGS activity of the catalysts.
References
M.E. Dry, Catal. Today 71 (2002) 227.
A.C. Vosloo, Fuel Process. Technol. 71 (2001) 149
3. T.Lin, L.H.Schwartz, J.B.Butt, J.Catal., 97 (1986) 177
4. A.N. Pour, Y.Zamani, A.Tavasoli, S.M.K.Shahri, S.A. Taheri, Fuel 87 (2008) 2004
5. C.D.Chang, W.H. Lang, A.J. Silvestri, J. Catal. 56 (1979) 274
Acknowledgements
This work was financially supported by The Scientific and Technological Research Council of Turkey (TÜBİTAK) through the project TÜBİTAK G043 “Liquid Fuel Production from Coal and Biomass Blends.”
All zeolite Y-supported catalysts displayed CO conversion ranging from %30,5 to 79% at 553 K. CO conversions of the catalysts were determined to be in the following order: FeDY5 > FeY5 > BFe > FeY80.
FT activity, selectivity and productivity of different catalysts are given in Table 2.
Table2: FT activity, selectivity and productivity of different catalysts (T= 553 K, P=19 bar, SV=2 Nl/h/g-cat)
Figure 1: Powder form of FeY5 catalyst
Figure 2: Gasoline range (C5-C11) hydrocarbon product
Catalyst
BFe
FeY5
FeDY5
FeY80
Conversion (%) CO
39,62
56,18
83,78
30,44 H2
33,38
47,44
71,00
29,94
Selectivity (%)
CO2
20,53
4,00
2,89
7,14
Productivity
Hydrocarbon (g/h/g-Fe)
0,03
0,45
0,75
0,39
Yield
Hydrocarbon (g/Nm3-syngas
converted)
186,97
225,51
227,63
197,72
Gasoline (g/Nm3-syngas converted)
409,59
166,37
189,48
100,21
Rate of syngas converted, mmol
(H2+CO)/g-cat/h
8,18
89,64
128,98
88,30
Product Composition
(wt.%) C1
15,58
6,42
3,19
14,67
C2-C4
35,94
14,54
7,27
31,54
C5-C11
40,96
73,77
83,24
50,68
C12-C18
6,83
4,93
5,89
2,91
C19+
0,69
0,34
0,40
0,20
Olefin ratio (mol%) (C2-C4)
37,21
7,09
15,24
28,03
6,44 cc of catalyst bed volume.(≈4.5 g of cat.)
P=19bar,
T=553°K/538°K/523°K
GHSV = 750 h-1
Feed gases:
3.0 nl/h of H2,
1.5 nl/h of CO
0.45 nl/h of N2.
Figure 3: Catalyst test system
Figure 4:Interface of PLC system