Five ASTM-certified SAF pathways currently lead to one shared specification: fuel that blends with conventional Jet-A and runs in commercial aircraft engines without modification. Their feedstocks, chemistry, costs, and scaling profiles differ sharply. Identifying where a new entrant belongs requires stating which of these dimensions matter to the near-term market.
This piece reviews the five pathways, places methanol-to-jet within the ecosystem, and defines Metafuels' role. We founded the company in 2023 around one narrow area: improving process efficiency between green methanol feedstock and certified e-SAF output. This focus reflects a specific market need.
Five Pathways, Different Economics
As of early 2025, the five ASTM-certified SAF pathways are hydroprocessed esters and fatty acids (HEFA), alcohol-to-jet (ATJ), Fischer-Tropsch synthetic paraffinic kerosene (FT-SPK), synthesized paraffinic kerosene from fermented sugars (DSHC), and methanol-to-jet (MtJ) under ASTM D7566 Annex A7. Each arose from different industrial assumptions about feedstock abundance and cost competitiveness in different production settings.
Commercial maturity is uneven. HEFA supplies the large majority of current SAF volume. ATJ facilities operate or are being built at early commercial scale. FT-SPK draws on decades of synthetic fuel experience from gas-to-liquids. DSHC remains at demonstration scale. Green methanol MtJ is at pilot and early commercial demonstration stage, where we operate.
HEFA: The Incumbent Pathway
Hydroprocessed esters and fatty acids converts waste fats, oils, and greases, or purpose-grown lipids, into jet-range hydrocarbons through hydroprocessing. Its advantages include compatibility with refinery infrastructure, relatively mature hydrogen supply chains, and feedstock channels shared with biodiesel production.
HEFA's limiting factor is feedstock availability at scale. Global supplies of waste cooking oil, tallow, and related lipids are finite. Industry consensus is that these feedstocks cannot satisfy long-term SAF mandates without purpose-grown energy crops, bringing land use and food system implications. HEFA leads current production but has a structural scaling ceiling unless its feedstock base changes.
HEFA is also the most mature pathway in process engineering. Compared with newer routes, it offers less optimization headroom because decades of commercial operation have captured much of the available efficiency gain. Process intelligence therefore has greater potential where the process has more room to improve.
ATJ: Scale Potential, Upstream Complexity
Alcohol-to-jet converts ethanol or isobutanol into jet-range hydrocarbons by dehydrating and oligomerizing the alcohol. Ethanol benefits from an established agricultural fermentation supply chain. However, agricultural ethanol can carry land use change and fertilizer burdens in its carbon accounting, limiting lifecycle CO2 reduction against fossil Jet-A under some regulatory frameworks.
Cellulosic ethanol and waste-derived ethanol offer better CI profiles but need more complex feedstock chains. ATJ using sugarcane ethanol in Brazil is a competitive near-term route, especially where sugarcane's carbon accounting is favorable. The pathway is scaling and is the most direct medium-term competitor to MtJ in SAF supply.
FT-SPK: The Established Synthetic Route
Fischer-Tropsch converts syngas, a CO and H2 mixture, into synthetic hydrocarbons. The process has industrial roots in the early 20th century and well-established scale-up engineering. SAF versions can use biomass syngas, waste gas, or electrolytic hydrogen with CO2 to make syngas. Its chemistry and large-scale engineering are well understood.
For FT-SPK, especially electrolysis-based versions, syngas production is complex and costly, while reactors require substantial scale. Fischer-Tropsch becomes competitive at high throughput and has traditionally belonged to major energy companies. Small and mid-scale FT SAF plants have struggled to achieve competitive unit economics.
PtL and the e-SAF Category
Green methanol e-SAF belongs to the PtL category. Renewable electricity powers electrolysis to make hydrogen, which combines with captured CO2 to produce methanol; methanol then becomes jet fuel. The carbon cycle uses captured and recycled CO2, while renewable electricity supplies the energy throughout.
This route offers the highest theoretical lifecycle CO2 reduction potential among current SAF pathways, approaching near-zero or, under some accounting frameworks and specific renewable electricity and carbon capture conditions, negative CI. It also has the highest current production cost because cheap renewable electricity and cost-effective CO2 capture are not yet available at the scale required by volume mandates.
EU and UK policy focus on PtL for the long term because it is the only route able to scale for large SAF mandates without biological feedstock constraints. ReFuelEU's electrofuel sub-mandate, rising from 0.7 percent in 2030 toward higher percentages in subsequent years, expresses that intent directly.
Why MtJ Within the PtL Space
PtL offers multiple ways to turn green hydrogen and CO2 into jet fuel. Direct Fischer-Tropsch from electrolytic syngas is one. Another uses methanol as an intermediate, followed by conversion to jet fuel through the MtJ pathway.
The methanol route offers practical near-term advantages. As a liquid at ambient temperature and pressure, methanol is easier to transport, store, and handle than hydrogen or synthesis gas. Europe's methanol infrastructure includes production facilities, storage terminals, and shipping logistics that an emerging supply chain can partly access. MtJ chemistry builds on industrial MTO and olefin oligomerization used commercially outside aviation, giving its scale-up a clearer basis than some newer direct PtL routes.
We are not saying MtJ is the only viable PtL pathway or will necessarily dominate long term. We are saying its chemistry, tradable intermediate product, and conversion step create a practical near-term basis for process optimization, where efficiency gains can have the greatest proportional economic effect.
The Process Efficiency Variable
For every SAF pathway, production economics depend heavily on how efficiently a facility turns costly renewable feedstock into saleable fuel that meets specifications. That applies across all five routes, although the available optimization potential differs substantially.
HEFA has modest remaining efficiency headroom after decades of commercial optimization. MtJ from green methanol has much more, with commercial operating history limited to a handful of demonstration-scale facilities. A new MtJ plant without a run-history database operates below its potential efficiency ceiling. Proper analysis of each campaign's data progressively closes that gap.
In MtJ, process intelligence software creates value by accelerating learning. Rather than requiring five to seven years of trial-and-error campaigns to approach optimum operating conditions, the optimization layer systematically extracts information from every run and compresses that timeline.
What Metafuels Builds
We develop process control software for methanol-to-jet facilities. It connects to plant DCS infrastructure through OPC-UA, records and analyzes campaign data, and recommends setpoints for later runs from the accumulated history. This run-to-run loop improves jet-cut yield and lowers energy use per kilogram of e-SAF.
We are a software company in industrial process control. We are not a fuel producer, do not operate commercial MtJ plants, and do not supply SAF to airlines. We build the process intelligence layer for fuel producers. That choice brings different capital needs, risks, and deployment routes from fuel infrastructure.
What We Are Not
We are not saying process optimization closes the e-SAF cost gap on its own; we are saying it improves conversion efficiency inside the plant. Software cannot solve the green methanol versus fossil methanol feedstock price difference, which is a commodity market issue. It can address the controllable conversion portion using existing equipment.
SAF economics depend on feedstock supply, electricity cost, conversion efficiency, capital cost, and regulatory compliance documentation. We work on conversion efficiency. Other organizations address feedstock availability, electrolysis cost reduction, and carbon policy. The ecosystem requires progress on each in parallel.
Our contribution is to reduce waste in the conversion step and shorten its optimization cycle. That is the specific problem we are equipped to address.