FT Synthesis

Module from the Process Technology Training Series curriculum.

Fischer-Tropsch Synthesis · Process Fundamentals · Fischer-Tropsch converts synthesis gas (CO + H2) into liquid hydrocarbons via catalytic polymerization. Catalyst selection (iron vs. cobalt) and reactor configuration (fixed-bed, slurry, microchannel) determine product slate, conversion, and scalability. · Catalyst Comparison

Parameter	Iron Catalyst	Cobalt Catalyst	Units	Notes
Activity (per site)	0.4–0.8	1.0–2.0	g HC/(g cat·h)	Co ~2–4x higher activity
Selectivity (C5+)	65–75%	75–85%	% product	Co favors long-chain
H2/CO Ratio	1.8–2.0	2.0–2.1	mol/mol	Critical for stoichiometry
Operating Temp	300–350	200–250	°F	Co lower, less coke
Operating Pressure	200–350	250–400	psig	Higher P favors longer chains
Cost	Low ($2–5/g)	High ($10–20/g)	$/gram	Fe economically preferred at scale
Attrition/Fines	High (2–5%)	Low (0.5%)	% per cycle	Slurry reactors manage better
Water Sensitivity	Moderate	Very High	—	Co requires dry synthesis gas
Sulfur Tolerance	<0.1 ppm	<0.01 ppm	S (ppm)	Fe more robust
ASF Alpha (chain growth)	0.80–0.88	0.87–0.92	—	Higher = longer products
Reactor Technologies
Reactor Type	Advantages	Disadvantages	Commercial Examples	Typical Scale
Fixed-Bed (Tubular)	Easy scale-up, simple ops, low investment	Heat removal limits (runaway risk), coking	Sasol (Secunda), Shell	5–20 KBPD
Slurry (Bubble Column)	Excellent heat control, high conversion, long catalyst life	Complex product recovery, attrition	ExxonMobil, Velocys	1–10 KBPD
Microchannel	Superior heat transfer, safety, modular	Very high CapEx, small scale, catalyst loading	Academic, pre-demo	100–500 BPD
Moving Bed	Good heat control, active catalyst recycling	Catalyst circulation complexity	Lurgi, historical	Demo-scale
Three-Phase Reactor (Gas/Liquid/Solid)	High productivity, long catalyst use	Catalyst separation required	Emerging technologies	Pilot-scale
Anderson-Schulz-Flory Distribution
Hydrocarbon product distribution follows ASF kinetics: wn = (1–α)²·α^(n-1), where α (chain growth probability, 0.80–0.92) determines C1 to C30+ yield. Higher α shifts product toward longer chains; lower α yields more C1–C4 (syngas fuel).

Source: Process_Technology_Training_Series_v1.xlsx · Sheet: FT Synthesis

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