Zhenjing Jiang,Wuyu Wang,Xuelai Zhao,Xinghua Zhang,Qi Zhang,Longlong Ma
Production of jet fuel is not only promising but challenging in the field of biomass utilization. Here we proposed a novel route to produce highly branched alkanes with ultra-low freezing point using n-butyraldehyde as feedstock by self-aldol condensation and subsequent hydrodeoxygenation (HDO). The catalyst characterization revealed that the MgO-SiO 2 catalyst played an acid-base synergetic effect role in the self-aldol condensation of n-butyraldehyde using n-butanol as solvent, which obtained C8 oxygenate and C12 oxygenate with yield of 69.3 % and 26.8 % respectively. The medium Brønsted base site of the catalyst captured α-H to promote the formation of enolate from n-butyraldehyde, and the Lewis acid sites promoted the dehydration of intermediate products. DFT simulation showed that n-butanol activated α-C in enolate in aldol condensation, and deactivated the oxygen atoms in enolate by hydrogen bonds to inhibit side reactions. Finally, the obtained condensation products were subjected to HDO reaction over the 5 wt% Pd/C and HZSM-5 catalysts, obtaining the highly branched alkanes with an ultra-low freezing point of -120.7 °C for C8 alkane and -78.7 °C for C12 alkane suitable for bio-jet fuels.
The oxidation of pure n-butanal and the n-butanal/NO mixture was investigated in an atmospheric jet-stirred reactor at stoichiometric conditions and over the temperature range of 425–925 K. Mole fraction profiles of characteristic intermediates, like nitrogenous, carbonyl, and hydrocarbon intermediates were obtained using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV–PIMS) via molecular beam sampling. A previous reported kinetic model of n-butanal oxidation was improved and a submechanism interpreting n-butanal/NOx interaction kinetics was developed and validated against experimental measurements. Results show that NO addition results in a featured temperature dependence of n-butanal reactivity similar to that of hydrocarbon fuels, i.e., inhibiting reactivity at low temperatures while promoting at intermediate temperatures. However, the presence of the n-butanal carbonyl group introduces distinct kinetic effects on this system compared to previously reported hydrocarbon/NO systems. Model analysis suggests a pronounced interaction between NO and the n-butanal carbonyl group, particularly at low temperatures where NO notably accelerates the removal of the carbonyl group, yielding large amounts of propyl radicals. This interaction results in the suppression of peroxy radical chemistry on the alkyl chain and chain-branching reactions of the propyl radical, thus decreasing the low-temperature reactivity of n-butanal. At intermediate temperatures, the influence of the carbonyl group on reactivity is not as pronounced and the increased reactivity primarily depends upon the impact of NOx on the active radical pool. For example, NOx-related chemistry accelerated the formation of OH radicals, thus facilitating fuel decomposition and the further conversion of CO to CO2. Besides, NO addition significantly affects the speciation of several products, such as methane, ethane, and formaldehyde, which was correlated to the additional competitive pathways introduced by NOx.
Meng Li,Diangen Zhou,Hualiang An,Shanshan Dong,Xinqiang Zhao,Yanji Wang
2-Ethylhexanal (2EH) is an important intermediate for the production of 2-ethyhexanoic acid (2-ETA), and studying the direct synthesis of 2EH through heterogeneous catalysis of n-butanal aldol condensation-selective hydrogenation reaction integration is of great significance for the industrial production of 2-ETA. Herein, a series of Pd/TiO2 catalysts were prepared and characterized by XRD, CO pulse adsorption, TEM, CO2/NH3-TPD and H2-TPR. Their catalytic performance for direct synthesis of 2EH from n-butanal was investigated in stainless steel autoclave first. The results showed that the Pd/TiO2 prepared by the excessive impregnation method, loaded with 0.5 wt.% of Pd, and reduced at 400 ℃ showed excellent catalytic performance: 95.4% conversion of n-butanal and up to 99.9% selectivity of 2EH. The particle size of Pd, the base strength and the amount of acid/base of the catalyst are the main factors affecting its catalytic performance. The smaller the particle size of Pd, the greater the base strength and the larger the amount of acid/base of the catalyst, the better its catalytic performance. Then the integrated reaction mechanism was established based on the results of characterization and FT-IR of online sampling. Furtherly, the continuity of the reaction process was achieved on fixed-bed reactor. Under the reaction conditions of a liquid hourly space velocity (LHSV) of 7.2 h-1, a reaction temperature of 190 °C and a H2 pressure of 3.2 MPa, the conversion of n-butanal and the selectivity of 2EH were 91.2% and 89.8%, respectively. During the continuous operation for 300 h under optimal conditions, the conversion of n-butanal decreased slightly first and then stabilized, while the selectivity of the target product 2EH remained basically unchanged.
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