Researchers from the Blechner Center for Industrial Catalysis and Process Development have demonstrated that a two-step catalytic process can effectively upgrade the light fraction of green syncrude into hydrocarbons suitable for synthetic aviation fuel. Published in Discover Chemical Engineering, the brief report details how the removal of oxygenates prior to oligomerization is critical for maintaining catalyst stability and maximizing the yield of jet-fuel-range hydrocarbons. The study focuses on the specific challenges posed by the complex composition of syncrude derived from lean-hydrogen syngas, which contains a significant proportion of alcohols, ketones, and esters that interfere with standard conversion pathways.
The aviation sector remains heavily dependent on fossil fuels, with carbon dioxide emissions reaching nearly 950 million tons in 2023, accounting for approximately three percent of global emissions. While sustainable aviation fuels are considered the most promising pathway for decarbonization, securing abundant and cost-effective feedstocks remains a central challenge. Current production methods, such as the hydroprocessing of esters and fatty acids, are limited by the supply of oil-based feedstocks like tallow and used cooking oil. An alternative route involves Fischer-Tropsch synthesis, where syngas is converted into synthetic crude over iron or cobalt-based catalysts.
In this study, the authors utilized an iron-based spinel catalyst developed for commercialization by NGV Earth, which operates using lean-hydrogen feedstocks. This process yields two liquid syncrude fractions: a heavier fraction rich in paraffins and olefins that can be easily upgraded via established hydrocracking technologies, and a lighter fraction comprising approximately 30 percent of the total syncrude. This light fraction is particularly challenging because it consists of 44 percent olefins, 23 percent paraffins, and 33 percent oxygenates, primarily alcohols, in the C2–C12 range. The presence of these oxygenates hinders efficient olefin oligomerization, a key step in converting lighter compounds into the jet-fuel range.
To systematically evaluate the impact of these oxygenates, the researchers prepared a synthetic mixture designed to mimic the distillation curve and composition of the light syncrude fraction. This approach allowed for controlled testing of catalytic performance while isolating the effects of specific components. The validity of this synthetic model was confirmed by comparing its distillation behavior after dehydration to that of actual dehydrated syncrude. The profiles aligned closely within the 10 to 90 percent recovery range, indicating that the synthetic mixture reliably represents the real feedstock for experimental purposes regarding olefin content and boiling point distribution.
The study compared a one-pot process, where dehydration and oligomerization occur simultaneously over a ZSM-5 catalyst, with a two-step process involving separate dehydration over gamma-alumina followed by oligomerization. In the one-pot configuration, alcohol dehydration was the dominant reaction, producing seven weight percent water, while the conversion of olefins to the jet-range fraction was limited. This inhibition was attributed to the competitive adsorption of alcohols on the Brønsted acid sites of the ZSM-5 zeolite, which blocked the sites necessary for oligomerization. The resulting distillate yield was significantly lower compared to the two-step method.
When the feed was switched from the alcohol-containing mixture to the dehydrated mixture, the distillate yield recovered from 41 percent to 73 percent within 24 hours. This reversible behavior indicated that the inhibition was caused by competitive adsorption or alteration of the reaction environment rather than permanent structural degradation of the catalyst. The two-step process, which included interim water separation, maintained a stable distillate yield of 73 percent over a 100-hour period. In contrast, integrating the dehydration and oligomerization reactors in series without water separation resulted in a sharp drop in olefin conversion from 80 percent to 17 percent due to the presence of water in the feed.
Water competes with olefins for Brønsted acid sites and can destabilize reactive carbocations, thereby reducing the number of active sites available for oligomerization. Prolonged exposure to water-rich feeds can also lead to the removal of aluminum atoms from the catalyst framework, lowering acid strength. To address this, the researchers emphasized the importance of water removal between process steps. The two-step process with water separation yielded the highest distillate fraction and enabled stable operation, highlighting the necessity of managing water content in the feed stream for efficient catalytic performance.
The performance of the ZSM-5 catalyst in oligomerizing dehydrated syncrude was evaluated at temperatures of 225 and 250 degrees Celsius. At 250 degrees Celsius, the conversion of C4-C8 olefins reached 76 percent, with a distillate yield of 65 percent. At the lower temperature of 225 degrees Celsius, the conversion was 69 percent and the yield was 53 percent. The higher temperature promoted more extensive chain growth, increasing the yield of the C9-C16 fraction, which corresponds to the jet fuel boiling range, by approximately four weight percent. This shift in product distribution demonstrates the sensitivity of the oligomerization process to thermal conditions.
Long-term stability tests revealed that the dehydrated syncrude feed caused a gradual decline in distillate yield, decreasing by approximately four percent every 24 hours. This decline was attributed to the presence of residual oxygenates, such as ketones and esters, which adsorb strongly onto the catalyst’s acid sites. Thermogravimetric analysis showed lower carbon deposition for syncrude compared to the synthetic mixture, suggesting that deactivation was primarily due to selective adsorption of these polar impurities rather than coke formation. The adsorption of ketones and esters suppresses oligomerization activity, leading to reduced formation of heavy hydrocarbons.
To mitigate the effects of residual oxygenates, the researchers investigated the impact of increasing the dehydration temperature. When the dehydration temperature was raised from 350 to 400 degrees Celsius, the concentration of ketones decreased significantly from 0.9 to 0.1 weight percent, and no esters were detected in the subsequent gas chromatography-mass spectrometry analysis. This higher temperature facilitated decarboxylation and decarbonylation reactions, effectively purifying the feed. As a result, the catalyst maintained high reactivity and stable activity for 184 hours on stream, with the distillate yield increasing from 50 percent at 350 degrees Celsius to 61 percent at 400 degrees Celsius.
The study concludes that the light syncrude fraction can be effectively upgraded via a dehydration-oligomerization process, increasing the distillate hydrocarbon fraction from 22 percent in the feed to 61 percent in the product. The two-step process, involving alcohol dehydration followed by oligomerization at 250 degrees Celsius with interim water separation, proved to be the most effective configuration. This approach not only maximizes the yield of jet-fuel-range hydrocarbons but also ensures long-term catalyst stability by minimizing the interference of oxygenates and water.
These findings underscore the importance of upstream pretreatment in the production of synthetic aviation fuels from Fischer-Tropsch syncrude. By optimizing the removal of reactive oxygenates and managing water content, the catalytic efficiency and stability of the oligomerization step can be significantly enhanced. The research provides a clear pathway for upgrading complex, oxygenate-rich feedstocks into sustainable aviation fuels, addressing key technical barriers in the transition away from fossil-based aviation fuels.
Subject of Research: Catalytic upgrading of light syncrude fraction for synthetic aviation fuel production
Article Title: Conversion of light fraction of green syncrude in production of synthetic aviation fuel
Article References: Cohen, O., Hos, T., Landau, M. V., & Herskowitz, M. (2026). Conversion of light fraction of green syncrude in production of synthetic aviation fuel. Discover Chemical Engineering, 6(1), Article 26. https://doi.org/10.1007/s43938-026-00129-9
Image Credits: AI Generated
DOI: 10.1007/s43938-026-00129-9
Keywords: synthetic aviation fuel, Fischer-Tropsch synthesis, syncrude, ZSM-5 catalyst, olefin oligomerization, alcohol dehydration, green hydrogen, catalyst stability, jet fuel range, oxygenate removal, Conversion, light
News Source: Bethany Barker. (November 7, 2026). Dehydration Key to Stable Jet Fuel from Syncrude. Scienmag.
