The Methanol Institute Grade A standard specifies at least 99.85 percent purity by weight and no more than 0.10 percent water by weight. Those limits suit conventional industrial methanol, but for methanol-to-jet conversion with zeolite-based MTO catalysts they are only a starting point. Different green production routes can leave organic compounds that co-distill with methanol. In our process, that organic fraction has been more predictive of catalyst deactivation rate than water content alone.
This is a practical account of two years qualifying green methanol during pilot operation, using material from biomethane reforming and e-methanol synthesis. We wrote it for process engineers and procurement teams at SAF producers considering supply agreements, rather than as a full review of green methanol production chemistry.
Why the Catalyst Layer Limits Operation
In an MTJ process, the MTO catalyst is the operational cost constraint. Zeolites used for methanol dehydration and early olefin formation are highly sensitive to several contaminant classes. The main mechanisms are:
Permanent deactivation from strong bases. Sodium and potassium ions, even at parts-per-million levels, irreversibly neutralize zeolite acid sites. Standard regeneration cannot restore them. Feedstock with elevated alkali metals, especially from biomass routes using alkaline process steps, can permanently damage the catalyst, with losses accumulating run over run.
Sulfur species cause reversible but damaging deactivation. Low concentrations of dimethyl sulfide and methanethiol can occur in biomethane-derived methanol. They bind strongly to acid sites, reducing activity. Oxidative regeneration can recover part of that activity, but accelerates thermal aging of the zeolite framework. Our pilot-based internal benchmark keeps sulfur below 0.5 parts per million by weight in the methanol feed.
Higher alcohols and carbonyls cause gradual fouling. Biomethane-derived methanol commonly contains trace ethanol, acetaldehyde, and acetone. They may not rapidly deactivate the catalyst at low concentrations, but they change initial olefin distribution and move selectivity away from the MTO stage's target C4 to C6 range. That changes the downstream oligomerization catalyst feed and gradually reduces jet yield over a campaign.
The Water Content Question
Water matters, but not always in the expected way. The MTO reaction tolerates moderate feed water, and some water can moderate catalyst-surface temperature and slow coke formation. The concern is water together with organic contaminants, especially carbonyls, because it can promote hydrolysis reactions that generate further catalyst-poisoning species.
We have found Grade A methanol, with water below 0.10 percent by weight, from a clean e-methanol route to be fully satisfactory. Methanol with the same water content from a biomethane route but elevated carbonyl impurities produced noticeably different catalyst behavior within the first 200 hours of a campaign.
We are not saying biomethane-derived methanol is worse than e-methanol; we are saying its specification must cover organic impurities as well as purity and water. On a lifecycle emissions basis, biomethane-derived green methanol can reach carbon intensities suitable for SAF compliance, and its supply chain is more developed and geographically distributed than e-methanol's.
Qualifying a Green Methanol Supplier
Our qualification process has three stages. First, we review how the methanol is made: the synthesis route, upstream feedstock characteristics, and purification, including distillation column specifications and downstream treating. The route indicates which contaminant families to investigate before sampling.
Second, we analyze at least three representative batches from different production periods for purity and water content (standard), total sulfur (ASTM D5453 or equivalent), sodium and potassium (ICP-OES), higher alcohols (GC-FID), and carbonyl species (derivatization GC). Variation between batches matters as much as the average. A supplier on specification 70 percent of the time and off specification 30 percent of the time is harder to operate with than one consistently near the lower end of specification.
Third, suppliers considered for extended offtake complete a pilot-scale acceptance run: a short campaign using only the candidate feedstock, with catalyst activity indicators compared closely with our baseline. The run uses resources, but a deactivated catalyst bed during extended production costs substantially more than qualification.
E-Methanol and Biomethane-Derived Methanol: A Practical Quality Comparison
E-methanol made with direct air capture CO2 and green hydrogen generally carries fewer organic contaminants. DAC CO2 is dry and has few organic co-contaminants, while hydrogen from alkaline or PEM electrolysis is essentially pure. Synthesis, typically using copper-zinc oxide over alumina at 50 to 100 bar and 200 to 280 degrees C, is controlled, and the distillation train can be designed for the target purity from the outset.
Biomethane-derived methanol involves more upstream chemistry. Anaerobic digestion produces biomethane containing hydrogen sulfide, siloxanes, and halogenated compounds, all of which must be removed before reforming or synthesis. Cleanup quality varies considerably among biogas plant operators. Even well-cleaned biomethane may carry trace sulfur and nitrogen organic species into the product. Industrial methanol distillation was developed for fossil natural gas feedstock and may not fully remove contaminant families associated with biogas-derived synthesis gas.
The best biomethane-derived methanol we have handled has matched mid-grade e-methanol quality. The worst caused measurable catalyst activity loss within one pilot campaign, which we attributed to alkali contamination from inadequate biomethane cleanup upstream of the reformer.
Supply Chain Considerations for European SAF Producers
European green methanol output is increasing, but supply remains concentrated by geography and route. For European MTJ producers, the most accessible sources are large biomethane reformers in Scandinavia and the Netherlands, several producing to Grade A specification. E-methanol from renewable hydrogen is mainly at demonstration scale in northern Europe, with commercial volumes expected to grow significantly as electrolyzer capacity expands through 2027 and 2028.
For a small MTJ producer, the practical choice is not the theoretically cleaner route. It is the supplier able to provide reliable, characterized, consistent material at the required volume. Consistency matters more than average quality for catalyst management. Tight batch control with a slightly higher average impurity level is often preferable to excellent average quality with high variance.
Establishing supply relationships before commercial-scale production begins supports scale-up preparation. Pilot qualification data provides the analytical basis for feedstock specifications that commercial MTJ plant supply agreements will need.