Gasification and Fischer-Tropsch SAF

The routes so far work with what the feedstock gives them. Gasification does the opposite: it reduces biomass — wood, straw, unrecyclable waste — to the simplest industrial gas mixture there is, CO and H2, and rebuilds from there. This is the thermochemical family of the cluster framework taken to its conclusion: total destruction of the molecule is the price of total feedstock flexibility. Nothing biological survives it, which is exactly why it can eat what digestion and fermentation cannot.

Gasification: controlled incomplete combustion

In a gasifier at 800–1200 °C, a small, deliberate shortage of oxygen splits the feed’s carbon three ways. Partial oxidation, C + ½O2 into CO, releases heat — it is the reaction that pays the process’s own thermal bill. That heat drives the endothermic steam reaction, C + H2O into CO + H2, and the Boudouard reaction, C + CO2 into 2CO. Together they convert most of the carbon into gas. A water-gas shift step then tunes the hydrogen-to-CO ratio, typically to about two to one, which is what downstream synthesis wants.

Cleanup: the part that actually decides feasibility

Raw syngas from biomass is filthy, and the filth is structural, not incidental. Tars — heavy aromatics born from the lignin fraction — stay gaseous only while hot and condense on the first cool surface: valves, lines, catalyst beds. Sulfur, mostly as H2S, is a quiet poison: a cobalt Fischer-Tropsch catalyst tolerates sulfur at the parts-per-billion level, far below what cheap cleanup delivers casually. The gap between “syngas we made” and “syngas the catalyst will forgive” is where most projects die, in capital cost and in downtime. It is the honest center of this technology: not the gasifier and not the synthesis loop, but the cleanup train between them.

Fischer-Tropsch: chain growth with one free parameter

Over an iron or cobalt catalyst, CO + 2H2 add carbon by carbon to a growing chain, releasing roughly 165 kJ per methylene unit — strongly exothermic, so reactor engineering is mostly heat-removal engineering; a hot spot shifts selectivity toward methane and kills the economics. The chemistry is a surface polymerization whose chain-growth probability, a single number usually written α, fixes the entire product slate through the Anderson-Schulz-Flory distribution. That mathematics is generous with wax and naphtha and stingy with anything in the middle: the theoretical maximum jet-range fraction is on the order of 40%, a ceiling no catalyst ingenuity moves. Real plants therefore plan on hydrocracking the wax back into range — the syncrude is a distribution to be reshaped, never a pure jet cut.

What the platform buys and what it costs

Against those burdens stands the payoff. The product is a pure paraffinic synthetic kerosene, precisely the drop-in molecule described under advanced biofuels, needing isomerization but no aromatics of its own. The same syngas, shifted differently, is hydrogen feedstock — the subject of its own page — and, offered instead to acetogenic bacteria, becomes the feed of gas fermentation, the biological rival for the same carbon. Syngas is the crossroads of this cluster; everything routes through it because everything can, once the molecule has been torn down and cleaned.