Introduction to Fischer Tropsch Synthesis

1. Introduction to Fischer Tropsch Synthesis RuiXu Department of Chemical Engineering Auburn University Jan 29th, 2013 CHEN 4470 Process Design Practice

2. Syngas Processing Gasification XTL Technology L G X Coal Biomass Natural Gas Fischer- Tropsch Synthesis Syncrude Refining & Upgrading Fuel & Chemicals

3. Natural Gas Gasification • Steam Reforming • CH4+ H2O → CO + 3H2 (Ni Catalyst) • H2/CO = 3 • Endothermic • Favored for small scale operations • Partial Oxidation • CH4 + ½O2→ CO + 2H2 • H2/CO ≈ 1.70 • Exothermic • Favored for large scale applications • AutothermalReforming • A combination of Steam Reforming and Partial Oxidation

4. Coal Gasification 2(-CH-) + O2→ 2CO + H2 • H/C Ratio • Produces Leaner Syngas (Lower H2:CO Ratio) • Ash • Non-flammable material in coal complicates Gasifier design • Impurities (Sulfur) • Necessitates greater syngas cleanup

5. Biomass Gasification 2(-CH-) + O2→ 2CO + H2 • H/C Ratio • Similar issues to coal • Ash • Biomass aggressively forms ash • Impurities (Sulfur, Nitrogen) • Necessitates greater syngas cleanup • Moisture • High moisture levels lower energy efficiency • Size Reduction • The fibrous nature of biomass makes size reduction difficult

6. Syngas Processing • Water Gas Shift Reaction • CO + H2O ↔ CO2 + H2 • Purification • Particulates • Sulfur (<1 ppm) - ZnO Sorbent • Nitrogenates(comparable to Sulfur compounds) • BTX (Below dew point)

7. GTL Technology and Syngas Processing

8. Fischer Tropsch Synthesis Introduction and History Reactions and Products Catalysts and Reactors Mechanism and ASF plot Economy

9. Fischer Tropsch Synthesis • Kaiser Wilhelm Institute, Mülheim, Ruhr • 1920s • Coal derived gases • Aim to product hydrocarbons • Commercialized in 1930s Franz Fischer Hans Tropsch

10. FTS Industrial History Germany • 1923, Franz Fischer and Hans Tropsch • 1934,first commercial FT plant • 1938, 8,000 barrels per day (BPD) U.S.A • 1950, Brownsville, 5,000 BPD South Africa • 1955, Sasol One, 3,000 BPD • 1980, 1982, Sasol Two and Sasol Three, 25,000 BPD Malaysia and Qatar • 1993, Shell, Bintulu, 12,500 BPD • 2007, Sasol, Oryx GTL, 35,000 BPD China, Nigeria etc.

11. Fischer Tropsch SynthesisCO + 2H2→ (CH2) + H2O

12. Fischer Tropsch Synthesis Introduction and History Reactions and Products Catalysts and Reactors Mechanism and ASF plot Economy

13. Reactions in FTS

14. Standard LTFT product distribution

15. Fischer-Tropsch Products Hydrocarbons Types • Olefins • High chemical value • Can be oligomerized to heavier fuels • Paraffins • High cetane index • Crack cleanly • Oxgenates • Branched compound (primarily mono-methyl branching) • Aromatics (HTFT)

16. Fischer Tropsch Synthesis • Introduction and History • Reactions and Products • Catalysts and Reactors • Mechanism and ASF plot • Economy

17. Fischer-TropschCatalysts Iron oxide 1500 °C Molten Magnetite (Fe3O4) Cooled rapidly Fused Iron K2O Crushed in a ball mill Air MgO or Al2O3 • Fused Iron Catalysts – HTFT • Alkali promotion needed • Products are high olefinic • Cheapest • Reactor: Fluidized bed

18. Fischer-TropschCatalysts Fe(NO3)3 Na2CO3 K2CO3 pH = 7 Washing Drying Calcination Precipitate Iron Cat. • Precipitated iron catalysts - LTFT • Co-precipitation method • Alkali promotion is also important • Cost more than fused iron catalyst • Reactor: slurry phaseor fixed bed

19. Fischer-TropschCatalysts Co(NO3)2 Support Drying Calcination Supported Co Cat. • Supported cobalt catalysts - LTFT • Incipient wetness impregnation method • Oxide support: silica, alumina, titania or zinc oxide • Products: predominantly paraffins • Low resistance towards contaminants

20. Comparison of Co and Fe LTFTS Catalyst

21. FTS Reactors

22. FTS Reactors

23. LTFT ReactorsCO + H2→ (CH2) + H2O + 145kJ/mol1800 oCAdiabatic Temperature Rise • Fixed Bed (Gas Phase Reaction Media) – Shell SMDS • Excellent reactant transport • Simple design • Poor product extraction, heat dissipation • Limited scale-up • Potential for thermal runaway • Slurry Bed (Liquid Phase Reaction Media) – Sasol SPR • Thermal uniformity • Excellent product extraction • Excellent economies of scale • Requires separation of wax (media) from catalyst • High development cost

24. Fischer Tropsch Synthesis • Introduction and History • Reactions and Products • Catalysts and Reactors • Mechanism and ASF plot • Economy

25. FTS Polymerization Process Steps • Reactant adsorption • Chain initiation • Chain growth • Chain termination • Product desorption • Readsorption and further reaction

26. FTS Polymerization process steps • Reactant adsorption • Chain initiation • Chain growth • Chain termination • Product desorption • Readsorption and further reaction

27. FTS Polymerization Process Steps • FTS Mechanisms • Alkyl mechanism • Alkenyl mechanism • CO insertion • Enol mechanism

28. FTS Mechanisms The Alkyl mechanism • 1i). CO chemisorbs dissociatively • 1ii). C hydrogenates to CH, CH2, and CH3 • 2). The chain initiator is CH3 and the chain propagatoris CH2 • 3i). Chain termination to alkane is by α-hydrogenation • 3ii). Chain termination to alkene is by β-dehydrogenation

29. FTS Mechanisms • The Alkenyl Mechanism • 1i). CO chemisorbs dissociatively • 1ii). C hydrogenates to CH, CH2 • 1iii). CH and CH2 react to form CHCH2 • 2i). Chaininitiator is CHCH2and chain propagator is CH2 • 2ii). The olefin in the intermediate shifts from the 2 position to the 1 position • 3). Chain terminates to alkene is by α-hydrogenation

30. FTS Mechanisms • The CO Insertion Mechanism • 1i). CO chemisorbs non-dissociatively • 1ii). CO hydrogenates to CH2(OH) • 1iii). CH2(OH) hydrogenates and eliminates water, forming CH3 • 2i). Chain initiator is CH3, and propagator is CO • 2ii). Chain propagation produces RC=O • 2iii). RC=O hydrogenates to CHR(OH) • 2iv). CHR(OH) hydrogenates and eliminates water, forming CH2R • 3i). CH2CH3R terminates to alkane by α-hydrogenation • 3ii). CH2CH3R terminates to alkene by β-dehydrogenation • 3iii). CHR(OH) terminates to aldehyde by dehydrogenation • 3iv). CHR(OH) terminates to alcohol by hydrogenation

31. FTS Mechanisms • The Enol Mechanism • 1i). CO chemisorbs non-dissociatively • 1ii). CO hydrogenates to CH(OH) and CH2(OH) • 2i). Chain initiator isCH(OH) and chain propagator is CH(OH) and CH2(OH) • 2ii). Chain propagation is by dehydration and hydrogenation to CR(OH) • 3i). chain termination to aldehyde is by desorption • 3ii). Chain termination to alkane, alkene, and alcohol, is by hydrogenation

32. FTS Mechanisms - ASF Plot • Propagation is exclusively by the addition of one monomer • αi + bi = 1 (by definition) • Propagation probability is independent of carbon number

33. FTS Mechanisms - ASF Plot α = Rp/ (Rp+ Rt) The weight fraction of a chain of length n, Wn, can be measured as a function of the chain growth probability. Wn= nαn-1(1- α) The logarithmic relation is as follows: ln (Wn/ n) = nlnα + ln((1- α)/ α)

34. Standard FTS Product Distribution

35. FTS Kinetics • Iron - based FT catalyst • Cobalt - based FT catalyst • Iron catalyst: at low conversion (P H2O ≈0 ), the reaction rate is only a function of hydrogen partial pressure. • The kinetic equations imply that water inhibits iron but not cobalt. • For cobalt catalyst, when the CO partial pressure is very high, (1+bPCO) 2→ (bPCO) 2, the reaction rate is proportional to the ratio of P H2 ⁄PCO. • Both denominators involve partial pressure of CO, indicating CO’s general status being a (reversible) catalyst poison. • Both kinetic equations indicate hydrogenation as the rate-limiting step.

36. Fischer Tropsch Synthesis • Introduction and History • Reactions and Products • Catalysts and Reactors • Mechanism and ASF plot • Economy

37. FTS Economics Overall Cost • Capital Cost • 50% to 65% of total production cost is due to capital cost • $10 per BBL for Natural Gas feedstock, $20 per BBL for Coal or Biomass feedstock • Operating Cost • 20% to 25% of total production cost is due to operating costs • $5 per BBL for Natural Gas, $10 per BBL for Coal or Biomass • Raw Material Cost • Waste or stranded resources are preferred • At market value ($4.50 / MMBTU), natural gas costs $45 / BBL • At market value ($70 / ton), coal costs $35 / BBL • At market value ($30 / ton), biomass costs $30 / BBL

38. XTL technology Economy • Cost Distribution • NTL case 1: 25% for the gas, 25% for the operations and 50% for the capital • NTL case 2: 15% for the gas, 21% for the operations and 64% for the capital (28% reforming, 24% FTS system, 23% oxygen plant, 13% product enhancement and 12% power recovery) • BTL capital (21% for biomass treatment, 18% for gasifier, 18% for syngas cleaning, 15% for oxygen plant, 1% for water-gas-shift (WGS, CO + H2O → CO2 + H2) reaction, 6% for FTS system, 7% for gas turbine, 11% for heat recovery / steam generation, 4% for other) • Recycle, power and heat integration • CO2 transport and storage

39. Syncrude Upgrading • Extraction and Purification • Terminal Olefins, Oxygenates, and FT Wax have high value • Hydrocracking • Converts wax into liquid fuels • Oligomerization • Converts light olefins to liquid fuels • Other Reactions • Alkylation, Isomerization, Aromatization, etc. • Polymerization • HTFT ethylene and propylene can be made into polymers • Hydrogenation • Promoted fuel stability

40. Reference • www.fischer-tropsch.org • Book: Fischer Tropsch Technology • Review Articles: • The Fischer-Tropsch process 1950-2000 (Dry, 2002) • High quality diesel via the Fischer–Tropsch process – a review (Dry, 2001) • Kinetics and Selectivity of the Fischer–Tropsch Synthesis: A Literature Review (Gerard, 1999) • Design, synthesis, and use of cobalt-based Fischer-Tropsch synthesis catalysts (Iglesia, 1997)