A series of Ag modified zeolites were prepared by incipient impregnation of nano-HZSM-5 with AgNO3 (0.5–2.0 wt %) aqueous solutions. It was found that the ion-exchange and impregnation effect both existed in this impregnation process, resulting in the formation of various silver species which altered the zeolite acid properties. The wall-coated nano-Ag/HZSM-5 zeolites were prepared on the inner surface of 304 stainless steel tubes though the washcoating method. Catalytic cracking of supercritical n-dodecane (4 MPa, 550 °C) was used to examine the catalytic activities of the prepared catalytic coatings. It is found that the modified samples with 1.0% Ag showed higher conversion (up to 1.50 times) than the parent one because of the dehydrogenation effect of silver species and that the overloaded (for example, 2.0 wt %) samples show lower performances ascribing to the blockage of diffusion pores by the silver species.

Dibenzothiophene (DBT, a typical sulfur compound) and dibenzothiophene sulfone (DBTO2, an oxidation product of DBT) were chosen as the model compounds, and their adsorption over a mesoporous silica (MCM-41) and a mesoporous carbon (CMK-3) were conducted under the exact same conditions. The adsorption amounts of DBTO2 over both adsorbents were enhanced compared to the DBT adsorption amounts, which clearly demonstrated that a combination of oxidation and adsorption is better than direct adsorption to achieve a better desulfurization performance. Besides, it was found that CMK-3 performed better for DBT removal compared to MCM-41, but the adsorption amount of DBTO2 over MCM-41 exceeded the corresponding value over CMK-3 (1.60 vs 0.88 mgS/g in p-xylene). Moreover, model fuels with varied hydrocarbon compositions were employed to investigate the impact of arene amounts. Finally, jet and diesel fuels were oxidized and treated with MCM-41, resulting in 85.6% and 81.4% sulfur removal, respectively. In contrast, when the fuels were directly treated with MCM-41, the corresponding sulfur removal amounts were only 19.8% and 40.9%. The results with real fuels further verified the necessity of the oxidation process. A simple washing method was found to be effective for regeneration of the adsorbent.

The ignition characteristics of endothermic hydrocarbon fuels (with different pyrolysis degrees) were investigated in a shock tube using n-decane as model compound. Six component surrogates (CH4/C2H4/C2H6/C3H6/C3H8/n-C10H22, marked as cracked n-decane) for thermally cracked n-decane were proposed based on the chemical compositions from the thermal stressing of n-decane on electrically heated tube under 5 MPa. Ignition delay times were measured behind reflected shock waves over a temperature range of 1296–1915 K, a pressure of 0.1–0.2 MPa, and equivalence ratios of 0.5–2.0. n-Decane showed a shorter ignition delay time than cracking gas at 0.1 MPa, demonstrating higher reactivity. For cracked n-decane, it was found that thermal cracking could improve the ignitability under certain conditions to a limited degree, i.e., at T > 1480 K for x = 37.97% and x = 17.61% and at T < 1480 K for x = 62.15% (x represents the conversion of thermal cracking of n-decane) in this work. Unimolecular decomposition reactions of n-decane producing active radicals and H atom would help chain initiation via H-abstraction reaction for unreacted fuels. This initial stage might accelerate ignition by activating cracking gas at these conditions. The empirical correlations for the ignition delay time of cracking gas and n-decane were also analyzed and compared with previous works. Two models were also used to simulate the experimental data of n-decane and cracking gas and showed good agreement with experimental results, and a combined model was utilized to predict results of cracked n-decane.

•Pressure effect on pyrolysis and coking of endothermic hydrocarbon fuel is studied.•Higher pressure promotes pyrolysis by increasing density and bimolecular reaction.•Reaction pathway under higher pressure approaches towards F-S-S mechanism.•Higher pressure promotes the formation of amorphous coke.Endothermic hydrocarbon fuel (EHF) is an ideal on-board coolant for the thermal management of the advanced aircrafts. To get more insights into controllable release of its heat sink in the regenerative cooling channels, the effect of pressure on the pyrolysis and coking of EHF in the temperature range of 500–750 °C was experimentally studied using electrically heated tube reactor under different pressures (0.7–6.0 MPa). At the constant feeding flow rate, the conversion for EHF pyrolysis under 6.0 MPa was 3.3-5.7 times that under 0.7 MPa in the temperature range of 650–720 °C, resulting from longer residence time and enhanced pyrolysis rate by the bimolecular reactions. The selectivity of hydrogen, methane and ethane increased as a function of conversion under elevated pressures, whereas the selectivity of ethylene and propylene decreased. The reaction pathway under elevated pressure approaches towards Fabuss-Smith-Satterfield mechanism where the bimolecular hydrogen abstraction reaction is dominant over the unimolecular β-scission under high substrate concentration. The elevated pressure promoted the coke deposition, mainly in amorphous coke with an increase by 4.4 times from 0.7 to 3.5 MPa due to high concentration of aromatics. The further formation of catalytic filamentous coke was inhibited by increasing amorphous coke indirectly under high pressure. When the pressure elevated to 6.0 MPa the coke rate was too high to complete the 30 min stability test.

•Reaction pathways of n-pentane cracking over zeolites have been systematically investigated.•First scission of n-pentane cracking over zeolites mainly took place at CH or C2C3 bond.•HZSM-5 zeolite exhibited the highest selectivity to light olefins compared to HZSM-35 and H-Beta.•Ag-incorporated HZSM-5 can enhance the cleavage of CH bond promoting the selectivity to light olefins.Reaction pathways including monomolecular protolytic cracking, hydride transfer, β-scission, and certain side reactions of n-pentane cracking over zeolites have been systematically investigated. Monomolecular protolytic cracking routes were mainly initiated by attack of acid sites on CH or C2C3 bonds. Operating conditions or zeolite pore caliber can tailor not only the first scission, but also the balance among carbenium ions related routes, e.g. hydride transfer, deprotonation, side reactions, etc. Increasing reaction temperature or zeolite pore caliber promoted the cleavage of CH bond, and large pore caliber and high conversion were beneficial to the hydride transfer and side reactions. Compared to HZSM-35 and H-Beta, HZSM-5 zeolite with middle pore caliber exhibited the highest selectivity to light olefins, and Ag-incorporation can further promoted selectivity to light olefins at a little cost of P/E (propylene to ethylene) ratio. Promotion of Ag-incorporation on light olefins formation was probably due to the active sites generated by silver species acting as dehydrogenation sites, and enhancing the cleavage of CH bond.Controllable reaction pathways for n-pentane cracking over zeolites were proposed.Download high-res image (111KB)Download full-size image

•High surface area Ce0.75Zr0.25O2 (HSA-CZ) is hydrothermally synthesized with CTAB.•Steam reforming of n-dodecane over Ru/HSA-CZ catalyst at 550–750 °C.•Ru/HSA-CZ has high Ru dispersion and favorable interaction with the support.•Ru/HSA-CZ shows 100% conversion of n-dodecane without deactivation in 7 h.A high surface area (HSA) Ce0.75Zr0.25O2 (CZ) support was synthesized by hydrothermal synthesis method with assistance of surfactant (cetyltrimethyl ammonium bromide, CTAB), and then 2.0 wt% Ru was impregnated on it to obtain a steam reforming catalyst for n-dodecane. The surface area of Ru/HSA-CZ catalyst is 107.6 m2 g−1, which is ca. three times higher than that prepared through the sol-gel (sg) method (34.3 m2 g−1, Ru/CZ-sg) and ca. 40% higher than that without CTAB (76.7 m2 g−1, Ru/CZ-wo). Catalytic steam reforming of n-dodecane, shows the completely conversion of n-dodecane over Ru/HSA-CZ and slightly drops about 6% (650 °C, LHSV = 12 mL/g h, S/C = 4, time on stream = 7 h) while 81% and 70% were observed for the Ru/CZ-wo and Ru/CZ-sg but with twice (or triple) deactivation rates. The possible reason for observed better performance of Ru/HSA-CZ should be attributed to the high metal dispersion of Ru over HSA-CZ, and the favorable Ru-support interaction as evidenced by H2-Temperature programmed reduction (H2-TPR), and high redox ability of high surface area Ce0.75Zr0.25O2 support thanks to high Ce3+ content. Further steam reforming of n-dodecane over Ru/HSA-CZ at higher LHSV (750 °C, LHSV = 36 mL/g h, S/C = 4) exhibits completed conversion and without significant deactivation.High surface area (HSA) Ce0.75Zr0.25O2 (CZ) supported Ru catalyst was synthesized by hydrothermal synthesis method with assistance of surfactant. Steam reforming of n-dodecane over Ru/HSA-CZ at higher LHSV (750 °C, LHSV = 36 mL/g h, S/C = 4) exhibits completed conversion and without significant deactivation.Download high-res image (327KB)Download full-size image

•Aviation hydrocarbon fuel samples were analyzed by GC×GC–MS/FID.•A series of composition matrixes together with property matrices were build.•A modified weighted average method was developed to establish fuel properties.Quantitative composition-property relationship of aviation hydrocarbon fuel consisting of hundreds of various hydrocarbons is one of the most important and challenging concerns for the rapid prediction of various specifications or other properties, and screening the suitable hydrocarbon fractions or classes for the specific application proposed. In this work, the detailed chemical compositions of seventeen kerosene-based hydrocarbon fuels were analyzed using the comprehensive two-dimensional gas chromatography coupled with quadruple mass spectrometry and flame ion detector (GC×GC–MS/FID), and hydrocarbons are classified by hydrocarbon classes (such as normal-paraffins, isoparaffins, cycloparaffins and substituted cycloparaffins) and carbon numbers (C7-C19) forming a series of composition matrices of their mass percentages. For each element of the matrix, a series of lumped compounds and the corresponding properties (density, freezing point, flash point and net heat of combustion) were defined according to the measured or theoretical properties of those similar hydrocarbons. The relationships between the detailed composition and the measured density, freezing point, flash point, and net heat of combustion of those kerosene-based hydrocarbon fuels were then established using the property matrices and several correlation algorithms. Compared with our previous work, it is found that the proposed quantitative composition-property relationship based on modified weighted average (MWA) method has achieved better performance in the predictions of density and the other specification properties with a higher determination coefficients and lower mean of absolute errors (MAE) of 0.82 °C in prediction of freezing point, 0.0102 MJ/kg in prediction of net heat of combustion and lower mean of absolute relative errors (MARE) of 0.2085% in prediction of density, 1.24% in prediction of flash point.Download high-res image (108KB)Download full-size image

The catalyst [(CH3)3NC16H33]4Mo8O26 has been synthesized by a direct precipitation method under room conditions from commercially available (NH4)6Mo7O24·4H2O and (CH3)3NC16H33Cl, avoiding the use of any toxic organic solvents. The catalyst was employed in oxidative desulfurization using H2O2 as an oxidant under mild conditions. High dibenzothiophene (DBT) removal (99.4%) was achieved after an adsorption process to remove the residual DBT sulfone (DBTO2), and the catalyst could be used for at least nine cycles without a noticeable decrease in activity. Leaching of Mo species was found to be negligible during the reaction. Moreover, it was found that the sulfur removal remained unchanged, decreased slightly or dramatically in the presence of 10 wt% n-octene, para-xylene or naphthalene, respectively, which was attributed to the different solubilities of DBTO2 in these solvents. The reaction system was further applied for the desulfurization of a kerosene-range jet fuel and a diesel fuel. After oxidation and extraction, 86.4% and 93.2% sulfur removals were derived for the diesel fuel and jet fuel, respectively.

Ordered meso-HZSM-5 zeolites with Al-MCM-41 shells were synthesized by a surfacant-directed encapsulating process. It was found that ordered meso-HZSM-5, which was used as a core, could be synthesized using a designed amphiphilic organosilane as a surfactant and that the mesopore size of the MCM-41 shell can be adjusted from 2.5–3 to 4.5–10 nm by changing the structures of alkyltrimethylammonium bromide and the trimethylbenzene amount. Catalytic cracking performances of supercritical n-dodecane (500 °C and 4 MPa) show that ordered meso-HZSM-5 zeolites with Al-MCM-41 shells of 4.5–10 nm exhibit a 28% higher catalytic activity and a 25% lower deactivation rate compared to the conventional HZSM-5 zeolites. With an increasing mesopore size of the MCM-41 shell, the acid sites accessibility increased gradually and, thus, led to enhanced catalytic activity and decreased secondary reaction ability. In addition, ordered hierarchical zeolites show a well connection of ordered mesopores between the core and shell, which could also lead to the enhanced acid site accessibility.

Thermal decomposition of tetrahydrotricyclopentadiene (THTCPD, C15H22), a high-energy-density hydrocarbon fuel, was conducted in a batch reactor at 385–425 °C to investigate its kinetics and decomposition products. The reaction activation energy and pre-exponential coefficient were established as 248.5 kJ mol–1 and 1.5 × 1015 s–1, respectively. The detailed analysis of the decomposition products indicated that THTCPD was first cracked into ethylene, C5 (1,3-cyclopentadiene, cyclopentene, and cyclopentane), benzene, and C10 (JP-10 and its isomers) and then to form secondary products. The possible primary mechanism was that the cleavage of the C–C bond of THTCPD produced diradicals, which were further converted into monoradicals through intermolecular hydrogen abstraction, and then the monoradicals generated primary products through β-scission, isomerization, and intermolecular hydrogen abstraction reactions. Possible secondary decomposition of primary products (C10 and C5 species) may form small molecules (C1–C4 species, methyl- and ethyl-cyclopentane, etc.), while some bimolecular reactions of C5 species may form naphthalene and 2,3-dihydro-4-methyl-1H-indene. This study may provide possible fundamental experimental information and kinetics for the potential application of THTCPD fuel.

Activated carbons derived from hydrothermal carbonization of sucrose and subsequent KOH activation have been prepared and tested for the adsorptive removal of refractory thiophenic compounds. Textural and chemical properties of the carbons and their corresponding impacts on adsorption rates and capacities were discussed in detail. The optimum carbon possessed high adsorption capacity (41.5 mgS/g for 300 ppmwS model oil), fast adsorption rate (97% saturated within 5 min) as well as relatively good selectivity for the adsorption of thiophenic compounds due to the abundant small micropores, suitable mesopore fraction and various oxygen functionalities present in the carbon. Combined with the economic and environmental merits of the preparation procedure, the sucrose-derived activated carbons are promising candidates for potential practical applications.Keywords: Activated carbon; Adsorption; Desulfurization; Dibenzothiophene; Sucrose;

•Nano-beta zeolites were controllably synthesized by silanizing protozeolitic units.•There exist relationships between size of protozeolitic units and silanized crystals.•A possible mechanism of controllable synthesis of nano-beta was proposed.Hierarchical beta nanozeolites were controllably synthesized by tailoring seeds (or protozeolitic units, nanocrystals) grafted with phenylaminopropyltrimethoxysilane (PHAPTMS). The investigation of beta zeolite crystallization reveals that it proceeds through condensed-step mechanism, gradually growing in size along two populations of particles and evolving in internal structure. Based on the zeolitic seeds formation process, there were two roles of organosilane: the more-like mesoporogen agent in short precrystallization time and the growth inhibitor after the formation of secondary particles with significant amounts of terminal silanol groups. It was also found that both the mesopore properties and the crystal size of the prepared hierarchical beta nanozeolites were also strongly dependent on the properties of seeds. Moreover, the mechanisms for the formation of hierarchical beta nanozeolites, including size of the nanoseeds as well as its nature on the final crystal size, pore characteristics, crystallinity, and morphology were proposed and discussed in detail.

Hierarchical HZSM-5 zeolites with uniform mesopore distribution were synthesized by hydrothermal synthesis (HTS) and steam-assisted crystallization (SAC) methods using multi-walled carbon nanotubes (CNTs) as hard templates. Compared with the HTS method, the SAC method favored the utilization of CNTs because of lower phase separation degree. It was also found that the crystallization process of HZSM-5 was slowed down after the addition of CNTs in the HTS method, while was accelerated in the SAC method. Furthermore, after the addition of CNTs, the hierarchical samples prepared by the HTS method showed lower Si/Al ratios and higher acid amounts while slight changes in the acid properties were observed for those prepared by SAC method. The synthesized hierarchical HZSM-5 zeolites using the SAC method exhibit similar catalytic activities but better stabilities in the catalytic cracking of n-decane than the HTS samples as a result of the presence of more mesopores.

Bilayered HZSM-5 zeolite coatings with additional nonzeolite pores were synthesized on the inner surface of stainless steel tubes by a secondary growth method with the addition of ethanol into the synthesis batch. The as-synthesized coatings were characterized by scanning electron microscopy and gas permeation, indicating that additional nonzeolitic pores were formed in the presence of ethanol. A remarkable greater than 1000-fold improvement in N2 permeation was observed. Catalytic cracking of supercritical n-dodecane (500 °C, 4 MPa) over a series of bilayered HZSM-5 coatings showed that the HZSM-5 coatings with additional nonzeolite pores also exhibit a remarkable catalytic activity improvement by ca. 150% and that the amount of nonzeolite porosity may play a determining role in the enhancement of the catalytic performance. According to cracking products and the permeation test, the performance enhancement may be attributed to the effective access of reactant to the acid sites in the zeolite pores due to the enhanced diffusion of supercritical n-dodecane in the zeolite coatings with the nonzeolite pores.

•Hydrocarbon dispersible zeolite (HDZ-O) was prepared by silanizing in organic phase.•Organic solvent is more efficient than aqueous in improving zeolites hydrophobility.•Quasi-homogeneous catalytic reaction of JP-10 was realized by HDZ-O.•HDZ-O can effectively promote the cracking conversion and heat sink of the fuel.Quasi-homogeneous catalytic cracking of hydrocarbon fuels using high dispersible zeolite is an effective way to improve their cooling capacity for the future aircrafts. High hydrocarbon dispersible beta nanozeolites (HD-NZs) were hydrothermally synthesized using silanizing seeds with phenylaminopropyltrimethoxysilane in the organic medium (HDZ-O) and aqueous medium (HDZ-W). IR and TG characterizations indicated that the HDZ-O has more organic groups anchored on its surface than HDZ-W, leading to a higher external surface area and better dispersibility in the jet propellant JP-10 (exo-tricycle[5.2.1.02.6]decane). The quasi-homogeneous catalytic cracking of JP-10 was conducted in an electrically heated tube under 4 MPa. The heat sink of JP-10 reaches 2800 kJ/g at 700 °C using 100 ppm HDZ-O as a result of high catalytic cracking conversion of 63.3% and alkenes selectivity (57.5% in the gaseous products), compared with both thermal cracking and catalytic cracking of JP-10 with HDZ-W. The excellent catalytic performance may be contributed to its high external surface area and good dispersibility in the jet propellant JP-10 to form a quasi-homogeneous system.

•Phase pure AlPO4-5 molecular sieves were ionothermally synthesized.•A series of tri-substituted imidazolium bromide ionic liquids (ILs) were used.•The obtained AlPO4-5 possessed different morphologies depending on the IL used.The ionothermal synthesis of phase pure AlPO4-5 was achieved using a series of tri-substituted imidazolium bromides (1-ethyl-, 1-butyl- and 1-hexyl-2,3-dimethylimidazolium bromides [EMMIMBr, BMMIMBr and HMMIMBr]). 13C nuclear magnetic resonance (NMR) measurements revealed that the cations of the ionic liquids were incorporated into the final structures. It was also found that the morphologies of the samples varied with the types of IL used. The possible reason for the different morphologies was that the decreasing charge density gradually weakened the interaction between the AlPO4–AFI framework and the IL cation, with an increase in the alkyl chain length.

•NKX-2 was successfully synthesized in the ionothermal approach.•This is the first aluminophosphite synthesized in the ionothermal way.•The synthesis process was fast and convenient.•The product possessed a novel stick-like morphology with a high aspect ratio.Aluminophosphite NKX-2 was ionothermally synthesized using 1-ethyl-2, 3-dimethylimidazolium bromide (EMMIMBr) ionic liquid (IL). The synthesis could be achieved in an open vessel for about 3 h, which was fast and convenient. NKX-2 could also be obtained using the same batch composition in a closed vessel under modified conditions. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra of the products were in well accordance with previous reports. Energy-dispersive spectroscopy (EDS) measurements gave P/Al ratios quite close to 1.5, in agreement with the value calculated by the empirical formula (P6Al4O18H6) of NKX-2. The obtained products possessed a novel stick-like morphology with a high aspect ratio of ~10.

•Pyrolytic depositions of hydrocarbon fuel in regenerative cooling channel were studied.•Pyrolytic deposition is a typical CVD-like process in primary stage.•The initial coking rate rapidly decreases with extension of time-on-stream.•A kinetic model of pyrolytic deposition of hydrocarbon fuel was developed.Coke deposition is one of crucial issues to be carefully taken into considerations in developing regenerative cooling technology for next-generation aircrafts. Pyrolytic depositions experiments of n-decane and Chinese No. 3 jet fuel were experimentally performed using electrically heated tubes (Φ2 × 0.5 mm, Φ3 × 0.5 mm) made of nickel-based alloy at different time-on-stream (TOS = 0–20 min), heat flux density (0.33–0.63 MW/m2), and mass flow rate of hydrocarbon fuel (0.60–1.25 g/s). The local concentrations of coke precursors were also determined by changing the length of electrically heated tubes. The initial coking rates increases with the increasing thermal cracking conversions and wall temperatures, but gradually decreases with extension of TOS. Characterization on reactivities and morphologies of cokes indicates that pyrolytic depositions are produced through surface catalysis and lateral growth mechanisms, and that the decreased coking rate is ascribed to gradual surface coverage with cokes. An empirical coking kinetic model has been developed to calculate the rate of coke formation considering the effect of surface coverage, local precursor concentrations, and wall temperature. The developed kinetic model satisfactorily predicted the pyrolytic depositions with an averaged absolute deviation of 10.5% and a maximal deviation less than 20%.

Regenerative cooling with hydrocarbon aviation fuels on board is taken as a promising technology for the thermal management system of next-generation aircraft. An improved methodology of an electrically heated tube (1 mm i.d.), i.e., applying the variable reactor tube length to carry on thermal cracking of supercritical hydrocarbon aviation fuels as the electric current heating maintains constant, was proposed to experimentally obtain detailed information on the local concentration and temperature along the microchannels of a heat exchanger. For the first time a series of experimental data on detailed local chemical compositions of cracked hydrocarbon fuel along the cooling microchannels were reported under supercritical conditions (5 MPa, 680–700 °C), and the calculated thermodynamic properties, velocity, and residence times along the tube were also reported. A modified molecular reaction model consisting of 18 species and 24 reactions was developed to predict thermal cracking of hydrocarbon aviation fuels in a wide range of cracking conversion (up to 86%). The work is significant for the design of regenerative cooling structures in predicting the local chemical compositions, estimating thermophysical properties, and coking of the cracked hydrocarbon fuels for heat transfer analysis.

For advanced thermal management technology of next-generation aircraft, hydrocarbon fuel cooling technology using endothermic cracking reactions is taken as a promising approach to removing heat loading but with a fatal drawback of forming carbonaceous deposits. To develop an effective anticoking technique to resolve this problem, a series of alumina coatings with various thicknesses (318–1280 nm) were prepared in stainless steel 321 tubes (2-mm i.d.) by metal–organic chemical vapor deposition (MOCVD) using aluminum tri-sec-butoxide. X-ray diffraction characterization showed that the prepared MOCVD alumina coatings were essentially amorphous. The anticoking performances of the MOCVD alumina coatings were evaluated using thermal cracking of Chinese RP-3 jet fuel under supercritical conditions (inlet temperature, 575 °C; outlet temperature, 650 °C; pressure, 5 MPa). The results showed that the anticoking performance increased from 37% to 69% as the thickness of the alumina coatings increased from 318 to 1280 nm. Further characterizations of the cokes with temperature-programmed oxidation and scanning electron microscopy indicated that the MOCVD alumina coatings were favorable for depressing metal catalysis cokes over the tube surface, as well as aromatic condensation cokes from bulk cracked fuel.

Wall-coated HZSM-5 with micro- and nanoscale crystal sizes were prepared and coated to the inner surface of SS304 stainless-steel tubes using washcoating methods. It was found that nanoscale HZSM-5 zeolite slurry has different rheological properties, washcoat loadings, and adhesions with microscale HZSM-5. Catalytic activities of the prepared micro- and nanoscale HZSM-5 zeolite coatings were studied using catalytic cracking of supercritical-phase n-dodecane (550 °C and 4 MPa), indicating that catalytic cracking activity and stability were remarkably improved more than 1 time by nanoscale HZSM-5 coatings compared to microscale HZSM-5 coatings. Acid and pore structure characterization showed that the better performance of nanoscale HZSM-5 coating may be attributed to the shorter diffusion length of the micropore, the higher diffusion rate of supercritical n-dodecane in the intracrystal mesopore, and the special acid nature of nanoscale HZSM-5 coatings.

Thermal decompositions of a serials of normal- and iso-dodecane mixtures with different iso/normal ratios were performed in a tubular reactor under supercritical conditions (550–680 °C, 4.0 MPa). It was found that iso-dodecane has an accelerating effect on the pyrolysis of n-dodecane depending upon iso/normal ratio of the mixture, and that accelerating factor reaches up to almost 4 at iso/normal ratio of 3/1. Decomposition conversions of the mixtures show a strong dependence on the iso/normal ratio and the temperature owing to their possible effect on the radical generation mechanism and the decomposition kinetics. In addition, iso/normal ratio of the mixture also affects the formation rates and morphologies of cokes due to the variation of decomposition conversion.

A quasi-homogeneous catalytic cracking using hydrocarbon dispersible zeolite is proposed for the potential applications in some special fields, such as advanced cooling technology of future aircrafts using hydrocarbon fuel as heat sink. Hydrocarbon dispersible HZSM-5 nanocrystals were prepared by grafting HZSM-5 nanocrystals (ca. 50 nm) with trimethylsilylane for this propose. The structure and surface properties of the trimethylsilylated HZSM-5 nanocrystals were characterized by solid-state nuclear magnetic resonance (NMR), N2 adsorption–desorption isotherms, and transmission electron microscopy (TEM), and the quasi-homogeneous catalytic cracking activities of n-dodecane. It is revealed that the prepared hydrocarbon dispersible HZSM-5 nanocrystals show about two times improvement of cracking rate of n-dodecane compared with the thermal cracking under supercritical condition (3.5 MPa and 425 °C), and that quasi-homogenous catalytic activities of hydrocarbon dispersible HZSM-5 nanocrystals are slightly lower (about 5–10%) than that of parent HZSM-5 nanocrystals due to the pores blockage and reduced surface acidities.Graphical abstractQuasi-homogenous catalytic cracking of n-dodecane using hydrocarbon dispersible HZSM-5 nanocrystals improves cracking rate by 1 times compared to thermal cracking.Highlights► Hydrocarbon dispersible HZSM-5 nanocrystals are prepared by grafting with trimethylchlorosilane. ► Trimethylsilylated HZSM-5 nanocrystals can stably dispersed in hydrocarbons. ► Hydrocarbon dispersible HZSM-5 nanocrystals improves cracking rate by about 1 times compared to thermal cracking.

A series of wall-coated catalysts were prepared in stainless-steel microchannels with HZSM-5 zeolites with a Si/Al molar ratio of 25–140 by washcoating methods. Catalytic cracking of supercritical n-dodecane (4 MPa and 550 °C) was used to examine the catalytic activity and stability of HZSM-5 coatings (ZC). It is found that catalytic cracking activities and stabilities of the coatings increase by the following order: ZC25 < ZC50 < ZC100 < ZC140 (with the numbers representing the Si/Al ratio), which is in well accordance with the increasing Lewis acid and decreasing Brönsted acid amount of parent HZSM-5. Temperature-programmed oxidation (TPO) characterization of cokes deposited on the HZSM-5 coatings indicates that the coke amount deposited over coatings also increases with Si/Al ratios of parent zeolites, owing to the interaction of the coke formation and its supercritical extraction. Rapid deactivation of ZC25 was possibly caused by pore-mouth plugging by a little amount of coke, while a large amount of cokes of ZC140 may be a result of the gradual and uniform buildup of cokes in the pore under kinetic control.

Thermal cracking of a series of model compounds (n-octane, n-decane, n-dodecane, cyclohexane, methylcyclohexane), as well as a commercial Chinese jet fuel RP-3, was performed in a flowing reactor consisting of an electrically heated tube under a pressure of 5 MPa to obtain the chemical compositions of the cracked hydrocarbon fuels at different levels of cracking conversion. The phase envelopes and critical points of the cracked hydrocarbon fuels were calculated using the Peng–Robinson and Soave–Redlich–Kwong equations. The calculation results showed that the critical points for cracked hydrocarbon fuels are strongly dependent on the hydrocarbon type and cracking conversion and that the critical temperature of cracked fuel decreases but the critical pressure increases sharply from 2–4 to above 10 MPa because of the appearance of many small-molecule products. Therefore, phase changes of the hydrocarbon fuel from compressed liquid phase to supercritical phase and then to gas phase possibly occurred in the electrically heated tube reactor when the cracking conversions exceeded 30%. Based on the calculation results, the supercritical cracking of hydrocarbon fuels should be carefully used at higher cracking conversions of hydrocarbon fuels under high pressure.

A pseudohomogeneous method of catalytic cracking of hydrocarbon fuels using a highly dispersed nano-HZSM-5 catalyst is developed. Hydrophilic nano-HZSM-5 is transformed into a hydrophobic form via organic silanization of the zeolite surface, which makes it dispersible in a model endothermic fuel such as n-dodecane. Compared with thermal cracking, catalytic cracking of n-dodecane with highly dispersed nano-HZSM-5 catalyst exhibits remarkably enhanced conversion.

To improve the cracking rate of supercritical hydrocarbon fuels, HZSM-5 coating was prepared over the inner surface of microchannels reactors by the washcoating method. Thermal or catalytic cracking of n-dodecane, a model compound of hydrocarbon fuels, was experimentally investigated in the stainless steel microchannel coated with HZSM-5 coatings under supercritical conditions (p > 4 MPa, T > 450 °C). It is found that cracking of n-dodecane was enhanced more than 100% by HZSM-5 coatings in 30 min reaction durations at 525 and 550 °C despite gradual deactivations of catalytic activities due to conversion coke from pyrolysis and acid-catalyzed reaction. Cokes deposited on the microchannels with and without HZSM-5 coating were characterized by scanning electron microscopy (SEM) and temperature-programmed oxidation (TPO), indicating that HZSM-5 coating effectively reduces formation of filamentous cokes and its damage on the micro channel surface by shielding surface metals when the temperature is higher than 600 °C.

Supercritical catalytic cracking of hydrocarbon fuels over zeolite coatings is an important technique to improve cooling capacity of hydrocarbon fuels for the advanced aircraft. A series of HZSM-5 zeolite coatings with different thickness (6.13−18.27 μm) was prepared in the stainless steel tubes by washcoating methods to study the effect of the coating thickness on the catalytic activity, deactivation of catalyst, and adhesion strength. Scanning electron microscopy (SEM) characterization of prepared coatings indicated that the uniformity of the coating surface as well as the thickness was enhanced by repeated washcoating. The catalytic activity and deactivation of the coatings was investigated using catalytic cracking of n-dodecane under supercritical phase (550 °C, 4.0 MPa). It was found that the catalytic activity during 30 min raises from 12.5 to 19.2% (about 53.2% improvements) when the thickness of the HZSM-5 coating increases from 6.13 to 18.27 μm, but the significant deactivation was also observed due to more coke being generated (from 2.4 mg/cm2 to 10.7 mg/cm2). According to the temperature-programmed oxidation and SEM characterizations on deactivated HZSM-5 coatings, a hypothesis of thickness effect on coke distribution and formation in HZSM-5 coating was proposed and further confirmed by EDS anaylsis on cross-sections of deactivated HZSM-5 coatings.

Solid depositions from thermal stressing of a jet fuel model compound, n-dodecane (Dod), is studied in the presence of three initiator additives, 1-nitropropane (NP), triethylamine (TEA), and 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane (TEMPO), to show the role of initiators in the carbon deposition because of thermal cracking of jet fuels. It is found that the thermal cracking rate of Dod is enhanced by the initiators in the following order: TEMPO > NP > TEA and that TEMPO and TEA remarkably inhibit the formation of pyrolytic deposit by 30−50% at a similar conversion level. Temperature-programmed oxidation (TPO) of deposits indicates that reactive deposition is improved slightly by TEMPO and TEA but the less reactive deposits are reduced because of possible radical scavenging or the hydrogen donation effect, resulting from the decomposition of TEMPO and TEA. Scanning electron microscopy (SEM) shows that TEA and NP also have a significant effect on the deposit morphologies. Those results are also observed in the thermal stressing of Chinese RP-3 jet fuel with initiators.

Use of hydrocarbon fuels as coolants for future high-Mach aircraft is challenged by the formation of carbonaceous deposits during thermal stressing at high temperatures (>500 °C). Three hydrogen donors, tetralin (THN), α-tetralone (THNone), and benzyl alcohol (BzOH), and two organic selenides, diphenyl selenide (Ph2Se) and diphenyl diselenide (Ph2Se2), as well as their mixtures, are selected as thermally stable additives to inhibit the deposition from the thermal stressing of n-dodecane and Chinese RP-3 (No. 3 jet fuel). It is found that the amount of solid deposits from thermal stressing of RP-3 is reduced by 77.0% with the additive of Ph2Se2/THN/THNone. The carbonaceous solid is further characterized using temperature-programmed oxidation (TPO), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). It is revealed that hydrogen donor THN/THNone and organic selenides possibly reduce the carbon deposits through retarding the thermal cracking rate, blocking surface catalysis, and depressing reactivity of sulfur with the surface metals, as well as their synergistic effect. The morphologies of deposits also dramatically change after adding organic selenides or hydrogen donors.

Supercritical initiative-thermal cracking of a jet fuel model compound, n-dodecane, was studied in presence of several initiative additives, such as1-nitropropane (NP), triethylamine (TEA), and 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane (TEMPO) in view of improving heat sink of jet fuel. It was found that remarkable promoting effect of the initiative additives on the cracking rates, compared with the thermal cracking of pure n-dodecane, were observed up to 20−150% in the following order: NP > TEMPO > TEA. Comparisons of products distributions from the thermal cracking of n-dodecane with and without initiators indicated that initiators type had a slight effect on the gas products selectivity, but a non-negligible effect on liquid products distributions. Apparent first-order kinetics was used to describe the supercritical initiative-thermal cracking of n-dodecane, and the apparent cracking activation energy of pure n-dodecane were 256.56 kJ/mol, which decreased to 185.80 kJ/mol by NP, 196.05 kJ/mol by TEMPO, and 242.83 kJ/mol by TEA. Attempts were also made to explain the observed experimental results with proposed reaction mechanisms for the thermal cracking of pure initiators.

Liquid–liquid equilibrium (LLE) data for a ternary system water + methyl isobutyl ketone (MIBK) + tert-butyl alcohol (TBA) were experimentally measured at atmospheric pressure over a temperature range of (287.65 to 333.35) K. The consistency of experimental tie-line data has been tested with Othmer−Tobias and Bachman correlations. Binary interaction parameters of NRTL and UNIQUAC models were regressed to correlate the experimental data. It is concluded that UNIQUAC and NRTL equations are reliable to fit the experimental data with the average root-mean-square deviations of 0.87 % and 0.70 %, respectively.

The relationships of composition–properties of 80 jet fuels concerning chemical compositions and several specification properties including density, flashpoint, freezing point, aniline point and net heat of combustion were studied. The chemical compositions of the jet fuels were determined by GC–MS, and grouped into eight classes of hydrocarbon compounds, including n-paraffins, isoparaffins, monocyclopraffins, dicyclopraffins, alkylbenzens, naphthalenes, tetralins, hydroaromatics. Several quantitative composition–property relationships were developed with three artificial neural network (ANN) approaches, including single-layer feedforward neural network (SLFNN), multiple layer feedforward neural network (MLFNN) and general regressed neural network (GRNN). It was found that SLFNNs are adequate to predict density, freezing point and net heat of combustion, while MLFNNs produce better results as far as the flash point and aniline point prediction are concerned. Comparisons with the multiple linear regression (MLR) correlations reported and the standard ASTM methods showed that ANN approaches of composition–property relationships are significant improvement on MLR correlations, and are comparable to the standard ASTM methods.

Unsteady-state operation of a trickle-bed reactor (TBR) was investigated using a multi-step exothermic reaction, hydrogenation of dicylcopentadiene (DCPD) in the presence of Pd/Al2O3 catalyst. The influences of five operation strategies on the reactor performance were symmetrically studied and compared with the steady-state operation, including ON–OFF and PEAK–BASE modulations of the liquid flow rate or concentrations, and a novel hybrid modulation of liquid flow rate and concentration. Attempts were also made to develop an unsteady-state operated TBR model based on a plug-flow model incorporating fluid flowing behaviors, three-zone partial wetting catalyst, vapor–liquid phase equilibrium and enthalpy balance, to predict the overall performance under unsteady-state operations. Compared with the experimental observations, it is indicated that the developed model is generally reliable to predict performance enhancement for different modulation strategies.

HZSM-5 nanocrystals grafted with different alkyl groups (ethyl, butyl, hexyl, dodecyl, and hexadecyl groups) were prepared to study their stable dispersion in the hydrocarbons as well as the quasi-homogeneous catalytic activities. The physical properties of the prepared zeolites were characterized by solid-state nuclear magnetic resonance, X-ray diffraction, N2 adsorption–desorption, fourier transform infrared spectra of pyridine adsorbed, and dynamic light scattering. The results showed that the ZSM-5 crystal structure were kept without obvious change after grafting alkyl groups, but that their stable dispersions in the hydrocarbon significantly improved with increasing chain length of grafted alkyl groups by reducing aggregate size of HZSM-5 nanocrystals. Quasi-homogeneous catalytic cracking of n-dodecane at 427 °C showed that the cracking rates with hydrocarbon dispersible HZSM-5 nanocrystals improved by more than 2 times compared with thermal cracking, wherein the zeolites grafted hexyl group had the best catalytic activity in good agreement with its larger acid amount.Graphical abstract.Download high-res image (168KB)Download full-size imageHighlights► Improving hydrocarbon dispersion of HZSM-5 nanocrystals by regulating grafted alkyl groups. ► Grafting alkyl groups influences the acidity of zeolite. ► Quasi-homogeneous catalytic activity is higher with C6-alkyl groups.

The catalytic cracking of n-dodecane over HZSM-5 zeolite catalyst was investigated at 400–450 °C under supercritical and subcritical pressures (0.1–4.0 MPa). The results show that both the activity of the catalyst and its stabilization towards deactivation decrease with increasing pressure, and the catalyst maintains substantially higher activity when feed rate exceeds 4.00 ml/min under supercritical conditions. A first-order Langmuir kinetic model with a novel decay function is developed for the supercritical catalytic cracking of hydrocarbon incorporating supercritical extraction effect on catalyst stability, which is satisfactory to describe the kinetic behaviors of catalytic cracking of supercritical n-dodecane. According to the estimated reaction rate and adsorption constant of n-dodecane on HZSM-5 at different temperature, the activation energy of 125.4 kJ/mol and adsorption heat 109.5 kJ/mol were calculated. An index of CRSE is proposed to define contribution ratio of supercritical extraction to the activity of the HZSM-5 catalyst in the developed kinetics model, and it is found that the CRSE increases with increasing hydrocarbon feed rates and decreasing catalytic activities, and reaches maximum value when the coke formation rate equals to the coke removal rate by supercritical hydrocarbon.

Transient behavior of local liquid-holdup of air–kerosene fluids in periodically operated trickle-bed reactor (TBR) is investigated in an acrylic column (140 mm ID and a height of 980 mm) packed with 3.6 mm glass spheres using a nonintrusive technique of electrical capacitance tomography (ECT). Local liquid-holdups determined from ECT images of normalized permittivity are experimentally calibrated under the steady-state operation with that from the classic drainage method. The instantaneous ECT images are captured at several axial positions along the column for the periodically operated TBR with slow-mode. The effect of periodic operation parameters (split, period, and time-average flow rate) on the instantaneous profiles of local liquid-holdup is firstly examined compared with the previous results. Transient variations of radial distributions of liquid and their maldistribution factor are calculated and further analyzed to provide more liquid distribution information under periodic operations.

•The catalytic cracking activity of HZSM-5 was influenced by the calcination temperature.•Influence of calcination temperate on the structure and acid property of ZSM-5 was investigated.•NH4Cl and H2O2 treatments are effective for the recovery of Brønsted acid sites.•The Brønsted acid sites in HZSM-5 are recoverable when calcinated below 700 °C.HZSM-5 was prepared by the hydrothermal method using TPAOH as a structure directing agent without Na+ addition. The calcination process for removing the organic templates was studied and particularly the influence of calcination temperature on zeolite structure and acid property was investigated. It was found that dehydrogenation of Brønsted acid sites in zeolite framework occurred with the elevation of calcination temperature, leading to a decrease of catalytic activity for n-decane cracking. To recover the Brønsted acid sites in zeolite lost during calcination, the calcinated zeolite was treated with various reagents, including H2O, H2O2, NH3 and NH4Cl, to turn Lewis acid sites back to Brønsted acid sites. Among them, the NH4Cl treatment was found to be the most effective way, which increased conversion of n-decane from 6% to 77% and increased the B/L acid sites ratio from 0.503 to 3.95. This enhancement of catalytic cracking ability is probably related to the formation of an intermediate active component ([AlO4]0) during high temperature calcination, and these intermediate sites promoted the protonation of Lewis acid sites in the NH4Cl treatment process.

The catalyst [(CH3)3NC16H33]4Mo8O26 has been synthesized by a direct precipitation method under room conditions from commercially available (NH4)6Mo7O24·4H2O and (CH3)3NC16H33Cl, avoiding the use of any toxic organic solvents. The catalyst was employed in oxidative desulfurization using H2O2 as an oxidant under mild conditions. High dibenzothiophene (DBT) removal (99.4%) was achieved after an adsorption process to remove the residual DBT sulfone (DBTO2), and the catalyst could be used for at least nine cycles without a noticeable decrease in activity. Leaching of Mo species was found to be negligible during the reaction. Moreover, it was found that the sulfur removal remained unchanged, decreased slightly or dramatically in the presence of 10 wt% n-octene, para-xylene or naphthalene, respectively, which was attributed to the different solubilities of DBTO2 in these solvents. The reaction system was further applied for the desulfurization of a kerosene-range jet fuel and a diesel fuel. After oxidation and extraction, 86.4% and 93.2% sulfur removals were derived for the diesel fuel and jet fuel, respectively.