Presentation on theme: "Introduction to Fischer Tropsch Synthesis"— Presentation transcript:
1 Introduction to Fischer Tropsch Synthesis Rui XuDepartment of Chemical EngineeringAuburn UniversityJan 29th, 2013CHEN 4470Process Design Practice
2 XTL Technology X G L Coal Biomass Natural Gas Gasification Syngas ProcessingFischer-TropschSynthesisSyncrudeRefining &UpgradingFuel&Chemicals
3 Natural Gas Gasification Steam ReformingCH4 + H2O → CO + 3H2 (Ni Catalyst)H2/CO = 3EndothermicFavored for small scale operationsPartial OxidationCH4 + ½O2 → CO + 2H2H2/CO ≈ 1.70ExothermicFavored for large scale applicationsAutothermal ReformingA combination of Steam Reforming and Partial Oxidation
8 Fischer Tropsch Synthesis Introduction and HistoryReactions and ProductsCatalysts and ReactorsMechanism and ASF plotEconomy
9 Fischer Tropsch Synthesis Kaiser Wilhelm Institute, Mülheim, Ruhr1920sCoal derived gasesAim to product hydrocarbonsCommercialized in 1930sFranz Fischer Hans Tropsch
10 FTS Industrial History Germany1923, Franz Fischer and Hans Tropsch1934, first commercial FT plant1938, 8,000 barrels per day (BPD)U.S.A1950, Brownsville, 5,000 BPDSouth Africa1955, Sasol One, 3,000 BPD1980, 1982, Sasol Two and Sasol Three, 25,000 BPDMalaysia and Qatar1993, Shell, Bintulu, 12,500 BPD2007, Sasol, Oryx GTL, 35,000 BPDChina, Nigeria etc.
15 Fischer-Tropsch Products Hydrocarbons Types OlefinsHigh chemical valueCan be oligomerized to heavier fuelsParaffinsHigh cetane indexCrack cleanlyOxgenatesBranched compound (primarily mono-methyl branching)Aromatics (HTFT)
16 Fischer Tropsch Synthesis Introduction and HistoryReactions and ProductsCatalysts and ReactorsMechanism and ASF plotEconomy
17 Fischer-Tropsch Catalysts Fused Iron Catalysts – HTFTAlkali promotion neededProducts are high olefinicCheapestReactor: Fluidized bedIron oxide1500 °CMolten Magnetite (Fe3O4)Cooled rapidlyFused IronK2OCrushed in a ball millAirMgO or Al2O3
18 Fischer-Tropsch Catalysts Precipitated iron catalysts - LTFTCo-precipitation methodAlkali promotion is also importantCost more than fused iron catalystReactor: slurry phase or fixed bedFe(NO3)3Na2CO3K2CO3pH = 7WashingDryingCalcinationPrecipitate Iron Cat.
19 Fischer-Tropsch Catalysts Supported cobalt catalysts - LTFTIncipient wetness impregnation methodOxide support: silica, alumina, titania or zinc oxideProducts: predominantly paraffinsLow resistance towards contaminantsCo(NO3)2SupportDryingCalcinationSupported Co Cat.
28 FTS Mechanisms The Alkyl mechanism 1i). CO chemisorbs dissociatively 1ii). C hydrogenates to CH, CH2, and CH32). The chain initiator is CH3 and the chain propagator is CH23i). Chain termination to alkane is by α-hydrogenation3ii). Chain termination to alkene is by β-dehydrogenation
29 FTS Mechanisms The Alkenyl Mechanism 1i). CO chemisorbs dissociatively 1ii). C hydrogenates to CH, CH21iii). CH and CH2 react to form CHCH22i). Chain initiator is CHCH2 and chain propagator is CH22ii). The olefin in the intermediate shifts from the 2 position to the 1 position3). Chain terminates to alkene is by α-hydrogenation
30 FTS Mechanisms The CO Insertion Mechanism 1i). CO chemisorbs non-dissociatively1ii). CO hydrogenates to CH2(OH)1iii). CH2(OH) hydrogenates and eliminates water, forming CH32i). Chain initiator is CH3, and propagator is CO2ii). Chain propagation produces RC=O2iii). RC=O hydrogenates to CHR(OH)2iv). CHR(OH) hydrogenates and eliminates water, forming CH2R3i). CH2CH3R terminates to alkane by α-hydrogenation3ii). CH2CH3R terminates to alkene by β-dehydrogenation3iii). CHR(OH) terminates to aldehyde by dehydrogenation3iv). CHR(OH) terminates to alcohol by hydrogenation
31 FTS Mechanisms The Enol Mechanism 1i). CO chemisorbs non-dissociatively1ii). CO hydrogenates to CH(OH) and CH2(OH)2i). Chain initiator is CH(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 desorption3ii). Chain termination to alkane, alkene, and alcohol, is by hydrogenation
32 FTS Mechanisms - ASF Plot Propagation is exclusively by the addition of one monomerαi + bi = 1 (by definition)Propagation probability is independent of carbon number
33 FTS Mechanisms - ASF Plot α = Rp / (Rp + Rt)𝑀 𝑛 = 1−α α (𝑛−1)𝑊 𝑛 = 𝑀 𝑛 ∗𝑛/( 1 1−α )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) = nln α + ln((1- α)/ α)
35 FTS KineticsIron - based FT catalyst 𝑟= 𝑚 𝑃 𝐻 2 𝑃 𝐶𝑂 𝑃 𝐶𝑂 +𝑎 𝑃 𝐻 2 𝑂Cobalt - based FT catalyst 𝑟= 𝑚 𝑃 𝐻 2 𝑃 𝐶𝑂 (1+𝑏𝑃 𝐶𝑂 ) 2Iron 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 HistoryReactions and ProductsCatalysts and ReactorsMechanism and ASF plotEconomy
37 FTS Economics Overall Cost Capital Cost Operating 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 feedstockOperating Cost20% to 25% of total production cost is due to operating costs$5 per BBL for Natural Gas, $10 per BBL for Coal or BiomassRaw Material CostWaste or stranded resources are preferredAt market value ($4.50 / MMBTU), natural gas costs $45 / BBLAt market value ($70 / ton), coal costs $35 / BBLAt market value ($30 / ton), biomass costs $30 / BBL
38 XTL technology Economy Cost DistributionNTL case 1: 25% for the gas, 25% for the operations and 50% for the capitalNTL 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 integrationCO2 transport and storage
39 Syncrude Upgrading Hydrogenation Extraction and Purification Terminal Olefins, Oxygenates, and FT Wax have high valueHydrocrackingConverts wax into liquid fuelsOligomerizationConverts light olefins to liquid fuelsOther ReactionsAlkylation, Isomerization, Aromatization, etc.PolymerizationHTFT ethylene and propylene can be made into polymersHydrogenationPromoted fuel stability
40 Reference www.fischer-tropsch.org Book: Fischer Tropsch Technology Review Articles:The Fischer-Tropsch process (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)