Key Takeaways & Executive Findings
- •• • HUSY-0.5M catalyst achieves 80.4% phenol conversion and 99.6% alkylation product selectivity, outperforming other zeolites and modified variants; this high selectivity minimizes byproduct formation, crucial for cost-effective fuel precursor production. • • Citric acid modification preserves HUSY crystallinity while optimizing acid site distribution; HUSY-0.5M exhibits the highest medium-strong acid to total acid ratio, directly correlating with enhanced catalytic activity and stability. • • Among tested zeolites (MCM-41, Hβ, HUSY, HZSM-5), HUSY shows superior performance due to balanced acidity and larger pore size, enabling efficient diffusion of bulky reactants and products, a key factor for industrial scalability. • • HUSY-0.5M demonstrates broad applicability across lignin-derived phenolics (p-cresol, anisole, guaiacol), indicating its potential as a versatile catalyst for upgrading diverse bio-oil fractions into high-density aviation fuel precursors.
Abstract
Lignin-derived oxygenated aromatics, particularly phenols and aromatic ethers, are promising feedstocks for synthesizing high-density, high-heat-sink aviation fuels via alkylation-hydrogenation processes. This study systematically evaluates the catalytic performance of various zeolites (Hβ, HZSM-5, MCM-41, and HUSY) in the alkylation of phenol with cyclohexanol. Characterization demonstrates that HUSY zeolite exhibits superior catalytic activity due to its favorable pore architecture and well-balanced acid site distribution, which synergistically facilitate molecular diffusion and catalytic transformations. To further enhance catalytic properties, HUSY was modified with citric acid at various concentrations and compared with NaOH and oxalic acid treatments. Results reveal that citric acid treatment preserves crystallinity while modulating acidity and pore structure. All modified zeolites enhance phenol alkylation activity. Notably, HUSY-0.5M, exhibiting the highest medium-strong acid to total acid ratio, achieves superior performance: 80.4% phenol conversion and 99.6% selectivity for alkylation products. The catalyst also shows high activity for various lignin-derived compounds (p-cresol, anisole, guaiacol), demonstrating broad applicability. This work provides a new strategy for valorizing lignin-derived phenols into high-value fuel precursors through alkylation.
1. Introduction
The aviation sector's reliance on fossil fuels and the difficulty of electrification necessitate sustainable aviation fuels (SAFs). Lignocellulosic biomass, particularly lignin-derived phenolic compounds, offers a renewable carbon source. However, direct hydrodeoxygenation of these monocyclic aromatics yields fuels with densities below 0.77 g/mL, failing to meet high-density fuel specifications. Alkylation of phenols with cyclic alcohols can increase molecular weight and density, but conventional catalysts suffer from poor selectivity or deactivation.
This study addresses the bottleneck by systematically screening zeolites and optimizing HUSY via citric acid modification. The resulting HUSY-0.5M catalyst achieves 80.4% phenol conversion and 99.6% selectivity, attributed to balanced acidity and pore architecture. This approach provides a feasible route to produce high-density fuel precursors from renewable lignin, offering a sustainable alternative to petroleum-derived aviation fuels.
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HUA Canhao, WU Jingfeng, ZHU Lingjun, XU Guangwen, WANG Shurong (2026). Citric Acid-Modified HUSY Zeolite Catalyzes Alkylation of Phenol with Cyclohexanol for High-Density Aviation Fuel Precursors. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(25)60581-0
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Frequently Asked Questions
What is the specific role of citric acid modification in enhancing HUSY catalytic performance?
Citric acid treatment at 0.5 M concentration optimally modulates the acid site distribution, increasing the ratio of medium-strong acid sites to total acid sites, which correlates with enhanced alkylation activity. It also preserves crystallinity while slightly altering pore structure, improving molecular diffusion and reducing secondary alkylation side reactions.
How does HUSY-0.5M compare to other zeolites in terms of phenol conversion and selectivity?
HUSY-0.5M achieves 80.4% phenol conversion and 99.6% selectivity for alkylation products, outperforming unmodified HUSY and other zeolites (Hβ, HZSM-5, MCM-41) due to its larger pore size and balanced acidity, which facilitate reactant diffusion and suppress side reactions.
What are the main byproducts or side reactions observed during phenol alkylation with cyclohexanol?
The primary side reaction is secondary alkylation, leading to polyalkylated products. The variation in performance across HUSY-x samples is mainly attributed to differences in secondary alkylation extent. HUSY-0.5M's optimized acidity minimizes this, achieving high selectivity.
Can HUSY-0.5M be applied to other lignin-derived phenolic compounds?
Yes, HUSY-0.5M exhibits excellent catalytic activity for p-cresol, anisole, and guaiacol, indicating broad applicability for upgrading various lignin-derived phenolics into high-density fuel precursors, which is essential for processing real bio-oil streams.
What is the industrial significance of achieving 99.6% selectivity in phenol alkylation?
High selectivity minimizes waste and simplifies downstream purification, reducing production costs. For aviation fuel production, this translates to higher yield of desired fuel precursors and lower environmental impact, making the process economically viable.
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