N-decane Conversion Research Articles

A novel ray method for the coking of n-decane in circular tubes with flexible cross-section area

Coking of endothermic hydrocarbon fuels significantly deteriorates the efficiency of regenerative cooling for hypersonic airbreathing vehicles. A novel ray method based on dynamic mesh techniques is proposed to describe the coking behavior in a circular tube with a flexible cross-section area. This method can be used to identify metal and deposit coke efficiently, which promotes the applicability of the dynamic mesh method in flexible structures. The cooling performance of n-decane before and after coking is numerically simulated and compared. The deposition brings higher thermal risks by elevating the solid temperature. However, the deposition reduces the channel’s cross-sectional area and increases the flow speed, leading to decreased flow residence time. Because the suppressing effect from lower flow residence time outweighs the promotion effect from increased temperature, the n-decane conversion decreased after coking.

Numerical analysis of flow and heat transfer characteristics of supercritical endothermic hydrocarbon fuel in taper tube

To enhance the cooling performance of the scramjet regenerative cooling system, a novel taper tube is proposed. Under supercritical pressure, the flow characteristics and heat transfer characteristics of endothermic hydrocarbon fuel (EHF) in taper tube, narrow cylindrical tube, and wide cylindrical tube are numerical investigated and compared. The results of the investigation of flow and heat transfer processes in the above three tubes indicate that the taper tube effectively facilitates the pyrolysis of n-decane and the n-decane conversion is increased by 3.94%, compared with narrow cylindrical tube. Compared with wide cylindrical tube, the taper tube enhances cooling effect and the wall temperature near the outlet is reduced by 50.16 K. The taper tube contributes to the cooling structure optimization and promotion of regenerative cooling system performance.

A conjugate numerical model for the thermal analysis of the regenerative cooling of an X-51A-like aircraft

A conjugated computational fluid dynamics model using convective thermal boundaries is proposed for the thermal analysis of the regenerative cooling system of an X-51A-like hypersonic aircraft in conditions closer to realistic scenarios. By X-51A-like, we mean that the convective boundaries of the cooling system are determined according to the structure and flight conditions (Mach 6 and an altitude of 20 km) of the X-51A Waverider. The aerodynamic heating, supersonic combustion, and convective heat transfer with an interior (fuel tank) are simulated from an engineering perspective. The flow, heat transfer, and pyrolysis characteristics of endothermic hydrocarbon fuels (EHFs) flowing in B-channels (bottom), S-channels (side), and T-channels (top) considering buoyancy effect are simulated and compared. A distinct temperature distribution difference in the solid region is observed between the cases with different boundary conditions. However, the cooling performance of EHFs is insensitive to the type of thermal boundary. Five indices, the maximum temperature, outlet temperature, n-decane conversion, total heat sink, and pressure drop, are compared to comprehensively assess the cooling performance. The cooling demands in the B-channels and S-channels are about 1.3 times those in the T-channels because of the additional cooling effect from the adjacent fuel tank. This study should be of great significance in the practical and systematic design of regenerative cooling systems.

Improvement of regenerative cooling performance of hydrocarbon fuel via hybrid flow configuration

An innovative hybrid flow configuration is proposed to improve the cooling performance of regenerative cooling systems using endothermic hydrocarbon fuel (EHF) as the coolant. The flow and heat transfer characteristics of both hybrid and traditional flow configuration are investigated and compared numerically. Parametric simulation of cases with different flow ratios, heat fluxes, and gravity directions are conducted. Results indicate that compared with traditional flow configuration, hybrid flow configuration reduces the maximum solid temperature but elevates the n-decane conversion ratio (i.e., 3.49 % increment under heat flux of 1.5 MW m−2 and flow rate of 10 %) and optimizes the temperature distribution. Further increase the flow ratio leads to higher conversion ratio (i.e., 10.04 % increment with flow rate of 20 %) while the maximum solid temperature increases slightly. In addition, hybrid flow configuration enables dynamic fuel regulation under complex and volatile thermal environments via alterable flow ratio, which is of great potential for the design of regenerative cooling system in the future.

Three-dimensional coking simulation of endothermic hydrocarbon fuels in rectangular cooling channels

Coking deposition is a critical phenomenon for endothermal hydrocarbon fuel cooling that can significantly affect the performance of a regenerative cooling system. Because of the complicated interactions between fluid flow, heat transfer, fuel cracking, and precursor coking kinetics, previous numerical studies have been limited to simplified two-dimensional circular channels, which cannot reveal the actual spatial distribution with consideration of buoyancy effect in rectangular cooling channels. This work proposes a novel framework for shrinking motion with an O-type hybrid mesh, permitting the direct three-dimensional simulation of coke deposition in complex channels and the visualization of both the axial and circumferential deposition distributions. The concept is tested in a rectangular channel using n-decane as an example, combining a detailed pyrolysis kinetic model with the MC-II coking model, and predictive results have been obtained. Results indicate two locations with heavy deposition rates. The buoyancy effect is weakened due to the acceleration resulting from the reduced cross-sectional area of the channel by the coke layer. The coupling of the flow and pyrolysis is discussed in terms of the dimensionless Damköhler number. The maximum temperature after coking can be 138 K higher than the initial. However, the conversion of n-decane at outlet is decreased due to the reduced flow residence time. The decreased total heat sink per temperature increment and the higher pressure drop are also the penalties from coking. The new framework for the direct three-dimensional simulations of coking is significant for the comprehensive investigation of the efficiency of regenerative cooling.

Effects of Aluminum Source with Different Properties on the Properties of Pd/SAPO-41 and its Catalytic Hydroisomerization Reaction

Aluminium source is one of the main factors affecting the physicochemical properties of SAPO-41.Silicoaluminophosphate molecular sieves-SAPO-41 were prepared via hydrothermal synthesis using di-n-butylamine (DBA) as templating agent, pseudo-boehmites, phosphoric acid and silica sol as aluminum, phosphorus and silicon sources respectively. Using XRD, N2 physical adsorption, SEM and Py-IR analysis media, the effects of aluminum sources on the crystal and pore structure, morphology, B-acid center strength of the prepared SAPO-41 molecular sieves. The catalytic hydroisomerization performance over Pd/SAPO-41 bifunctional catalysts were investigated. Pseudo-boehmite type has little effect on the crystal structure and chemical composition of SAPO-41 molecular sieve, but has different effects on its morphology, pore structure, B-acid strength of SAPO-41, and Pd dispersion on Pd/SAPO-41. The hydroisomerization conversion of n-decane over 0.5Pd/S41-A1 can reach 88.56 %, and the selectivity of isoparaffin can reach 90.88%.This work provides a reference for selecting an ideal aluminum source for the synthesis of SAPO-41.

Dynamic coking simulation of supercritical n-decane in circular tubes

Carbon deposition is an inevitable phenomenon in regenerative cooling systems using endothermic hydrocarbon fuels (EHFs), which seriously affects heat transfer performance and even clogs cooling channels. In this study, a framework of 2D dynamic coking study is established by coupling simultaneously a detailed pyrolysis model with the MC-II coking model. Two types of coke, i.e., catalytic coke and pyrolytic coke, are considered, and the coking process is simulated via dynamic mesh techniques. The flow and heat transfer characteristics, and heat sink before and after the carbon deposition under typical working conditions are compared and discussed in detail. The results reveal that the secondary cracking reactions promote the concentration of the coking precursors, and the coking simulation results agree well with the experiment. The maximum fluid flow velocity and maximum solid temperature are increased after the coking formation due to the reduction of the cross section area and the poor thermal conductivity of the deposited coke. As the coke deposits, the total heat sink per temperature rise and pressure drop both deteriorate. However, the maximum conversion of n-decane is almost unchanged, which can be well explained by the local DamkÖhler (Da) number.

Cooling performance optimization of supercritical hydrocarbon fuel via bi-directional flow pattern

Regenerative cooling is a promising method to meet the increasing heat management requirement of hypersonic vehicles. In contrast to the traditional co-directional flow (CDF) pattern, here we propose an innovative bi-directional flow (BDF) pattern inside rectangular parallel channels to improve the active regenerative cooling performance. Based on a reliable CFD model, the flow and heat transfer performance of n-decane under two types of thermal boundaries are analyzed. Three types of channels at different locations considering buoyancy effect are also investigated. By observing the contour of specific heat, mass fraction of n-decane, temperature distribution, velocity field and calculating the heat sink and surface heat transfer coefficient, the cooling performance of BDF pattern is discussed and compared with that of CDF pattern. Results reveal that compared to the CDF pattern a more homogeneous temperature distribution and a higher conversion of n-decane (around 14% increment under thermal boundary: 1.9 MW/m2 and 1400 K) are obtained by BDF pattern. However, an increased pressure drop within a reasonable range and a higher surface temperature are observed for the BDF pattern. With overall consideration, a hybrid flow pattern is proposed which could maximize the cooling effect within the surface temperature constraint yet keeping its simple inner structure.

Mixture effects in alkane/cycloalkane hydroconversion over Pt/HUSY: Carbon number impact

Cycloalkanes are known to impact the metal–acid balance of the hydrocracking of n-alkanes with similar carbon number, however, how this impact varies with the carbon number of the components involved is still to be understood in more detail. For this purpose, the hydroconversion of n-octane and tert-butylcyclohexane, and n-decane and methylcyclohexane mixtures was investigated in this work over Pt/HUSY catalyst in both the ideal and the nonideal hydrocracking regime. Irrespective of the hydrocracking regime for pure n-octane, its conversion and isomer yields were significantly lowered upon admixture of tert-butylcyclohexane. On the other hand, n-octane admixture did not impact the tert-butylcyclohexane conversion nor its cyclic isomer yields. Upon methylcyclohexane admixture with n-decane, no impact was observed over the catalyst ensuring ideal hydrocracking of pure n-decane. Over the catalyst with significantly lower Pt loading, which does not ensure ideal hydrocracking of n-decane, methylcyclohexane lowered the n-decane conversion. A slightly negative impact of n-decane admixture on methylcyclohexane conversion was also observed. The observed effects are mainly attributed to the differences in adsorption strengths within the zeolite pores on top of differences in alkane and cycloalkane adsorption on the metal sites.

Advanced Study of Promoted Pt /SAPO-11 Catalyst for Hydroisomerization of the n-Decane Model and Lube Oil

SAPO-11 is synthesized from silicoaluminophosphate in the presence of di-n-propylamine as a template. The results show that the sample obtained has good crystallinity, 396m2/g BET surface area, and 0.35 cm3/g pore volume. The hydroisomerization activity of (0.25)Pt (1)Zr (0.5)W/SAPO-11 catalyst was determined using n-decane and base oil. All hydroisomerization experiments of n-decane were achieved at a fixed bed plug flow reactor at a temperature range of 200-275°C and LHSV 0.5-2h-1. The results show that the n-decane conversion increases with increasing temperature and decreasing LHSV, the maximum conversion of 66.7 % was achieved at temperature 275°C and LHSV of 0.5 h-1. Meanwhile, the same catalyst was used to improve base oil specification by increasing viscosity index and decreasing pour point. The isomerization reaction conditions, employed are temperature (200-300)ºC, the liquid hourly space velocity of 0.5-2h-1, and the pressure kept atmospheric. The present study shows that Pt Zr W/SAPO-11 minimizes the pour point of lubricating oil to -16°C at isomerization temperature of 300°C and LHSV of 0.5 h-1 and viscosity index 134.8.

Atmospheric and high pressures pyrolysis study of n-decane in a flow reactor with online GC-MS/FID analysis: Experiments and modeling

The atmospheric and high-pressure pyrolysis of n-decane was studied in a flow tube reactor combined with online GC–MS/FID at 723−1123 K, 0.1–3.0 MPa (highly diluted in helium). Compared with 0.1 MPa, the conversion of n-decane and mole fraction of alkenes clearly increased at 3.0 MPa at the fixed temperature, and more aromatics were observed including toluene, styrene, ethylbenzene, indene and naphthalene, suggesting that the secondary reactions are more intense under high pressure. To account for these differences, a detailed kinetic model with 191 species and 1117 reactions was constructed by incorporating the aromatics subset to a n-decane model developed in previous low-pressure work, and further validated against literature data covering a wide pressure range (0.004–7.2 MPa) with reasonable reproducibility. The current model was compared against three literature kinetic models (LLNL, JetSurf 2.0 and Rev1stGen) and showed a better accordant with the conversion of n-decane and the selectivity of major products. Based on the rate of production and sensitivity analysis using the current model, the results show that although the total consumption of n-decane is weakly pressure-dependent at fixed temperature and residence time under the investigated conditions, the formation and consumption pathways of primary products change significantly attributed to the enhanced bimolecular abstraction and combination reactions at higher pressures. For the formation of benzene, the combination of 1,3-butadien-2-yl with ethylene is the main pathway at both 0.1 and 3.0 MPa, while the additional combination reactions: propargyl with allyl and cyclopentadienyl (c-C5H5) with CH3 become dominant at 0.1 MPa and 3.0 MPa, respectively. For the formation of larger aromatic naphthalene, the self-recombination of c-C5H5 is the most important channel at all investigated pressures.

Heterogeneous reaction and homogeneous flame coupled combustion behavior of n-decane in a partially packed catalytic bed combustor

The premixed combustion experiments of n-decane were conducted in micro-combustors. The characteristics and mechanism of three combustion modes were studied: homogeneous combustion (HMC), heterogeneous combustion (HTC), and coupled combustion (CC) with both HTC and HMC. The homogeneous flame in CC cases can be established downstream of catalytic bed. The stable combustion range of CC is near the stoichiometric ratio, and the lean/rich limits of equivalence ratio (Φ) are close to the lean limit of the HMC and the rich limit of the HTC respectively. The HTC cases show high CO2 selectivity, and CO2 is the major products even at Φ > 1. The different mechanisms of O2 and n-decane adsorption on the Pt active site have significant effects on the stable limits of HTC. Hot flame in the fire core is followed by warm flame in the HMC cases. When Φ > 0.9, n-decane can’t burn out in so small hot flame that the effect of warm flame becomes obvious, resulting in some combustible species being generated in products. CO becomes the main product instead of CO2 in the HMC cases, when Φ > 1.6. In the CC cases, high n-decane conversion owes to the coupling of homogeneous flame and heterogeneous reaction. The homogeneous flame presents warm flame properties at Φ = 1.3 ~ 1.4, and hot flame properties at Φ = 1. More importantly, compared with HMC and HTC, much longer combustion zone achieved in CC with more even distribution of wall temperature and without obvious hot spots, which is significative to actual applications like the thermo-photovoltaic system.

China to dominate Asian refinery fluid catalytic cracking units capacity growth by 2024

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.

Effects of CaO addition on Ni/CeO2–ZrO2–Al2O3 coated monolith catalysts for steam reforming of N-decane

A series of 10 wt%Ni/CeO2–ZrO2–Al2O3 (10%Ni/CZA) coated monolith catalysts modified by CaO with the addition amount of 1 wt%~7 wt% are prepared by incipient-wetness co-impregnation method. Effects of CaO promoter on the catalytic activity and anti-coking ability of 10%Ni/CZA for steam reforming of n-decane are investigated. The catalysts are characterized by N2 adsorption-desorption, XRD, SEM-EDS, TEM, NH3-TPD, XPS, H2-TPR and Raman. The results show that specific surface area and pore volume of as-prepared catalysts decrease to some extent with the increasing addition of CaO. However, the proper amounts of CaO (≤3 wt%) significantly enhance the catalytic activity in terms of n-decane conversion and H2 selectivity mainly due to the improved dispersion of NiO particles (precursor of Ni particles). As for anti-coking performance, reducibility of CeO2 in composite oxide support CZA is promoted by CaO resulting in providing more lattice oxygen, which favors suppressing coke formation. Moreover, the addition of CaO reduces the acidity of 10%Ni/CZA, especially the medium and strong acidity. But far more importantly, a better dispersion of NiO particles obtained by proper amounts of CaO addition is dominant for the lower carbon formation, as well as the higher catalytic activity. For the spent catalysts, amorphous carbon is the main type of coke over 10%Ni–3%CaO/CZA, while abundant filamentous carbon is found over the others.

Synthesis of SAPO-41 Molecular Sieves with Different SiO2/Al2O3 Ratios and their Catalytic Performance of n-Decane Hydroisomerization

Using di-n-propylamine (DPA) as a template, SAPO-41 molecular sieves with SiO2/Al2O3 ratios (n) of 0.3, 0.5, and 0.7 were synthesized. Their structure, morphology and acidity were characterized by XRD, N2 physical adsorption, SEM, and Py-IR. All the synthesized samples have characteristic diffraction peaks corresponding to the AFO topological structure, which means that samples are pure phase SAPO-41 molecular sieve. The samples exhibited a highly ordered prismatic morphology with regular arrangement of individual grains, wrapped in flakes, and possessed complete channel structure. With the increase of n, the specific surface area and the amount of B acid showed a downward trend after increasing. Hydroisomerization reaction results of n-decane over SAPO-41 loaded with 0.5wt% Pd (Pd/SAPO-41(n)) showed that the higher the amount of B acid, the higher the conversion of n-decane,and high specific surface area and moderate B acid are favorable for yield of isomerization products. When the conversion of n-decane catalyzed by Pd/S41(0.3)-P was 88.9%, the yield of hydroisomerization products reached 83.3%.

Effect of the ZSM-23 Synthesis Method on the Properties of Pt/ZSM-23/Al2O3 Catalysts in n-Decane Conversion

Zeolites of the MTT framework type (Si/Al = 30) have been synthesized using dimethylformamide as a template and by a template-free method (Si/Al = 24). The morphology, textural, and acidic properties of the synthesized zeolites have been studied by scanning electron microscopy, high-resolution transmission electron microscopy, N2 adsorption, IR spectroscopy of adsorbed pyridine, and temperature-programmed desorption of ammonia and compared with the properties of a commercial ZSM-23 zeolite (Si/Al = 24). Zeolite powders have been used to prepare ZSM-23+Al2O3 supports and then Pt-modified bifunctional catalysts, the properties of which have been tested in n-decane hydroconversion. It has been shown that the isomerization activity of the Pt/ZSM-23/Al2O3 catalysts is largely determined by the texture and morphology of the original zeolites.

Study of Bifunctional Hydrocracking and Hydroisodeparaffinization Catalysts Based on Zeolites and Alumophosphates, Part 2: Effect of the Activity of Hydrogenating and Acidic Components on the Activity and Selectivity of Hydroisodeparaffinization Catalysts

Two different series of bifunctional hydroisodeparaffinization catalysts with deposited palladium and based on SAPO-11 and SAPO-31 are fabricated and studied, with (1) varied activity of the acidic component at a constant activity of the hydro–dehydrogenating component and (2) varied activity of the hydro–dehydrogenating component at a constant activity of the acidic component. It is shown that the temperature of 90% n-decane conversion on the catalysts with the same hydro–dehydrogenating activity depends linearly on the overall activity of the acidic catalyst component. The character of this dependence is identical for both structural types of SAPO-11 and SAPO-31 silicoalumophosphates. The bifunctional catalysts based on SAPO-31 are much more active than those based on SAPO-11. At the same overall activity of the acidic component, the temperature of 90% n-decane conversion on the Pd/SAPO-31 catalysts is 50°C lower than on the Pd/SAPO-11 catalysts. Ways of controlling the overall activity and selectivity of a hydroisodeparaffinization catalyst by varying the activity of the acidic and/or hydro–dehydrogenating component of a bifunctional catalyst are shown. An increase in the hydro–dehydrogenating activity of the catalyst enhances the hydroisomerizing activity of a bifunctional catalyst with virtually no changes in selectivity toward isomers. An increase in the overall activity of the acidic component also enhances the hydroisomerizing activity of a bifunctional catalyst, but appreciably alters its selectivity toward isomers.

Role of acidity in catalytic cracking of n-decane over supported Pt-based catalysts

Different acidic-basic oxides, Al2O3, SiO2, MgO, MgO-SiO2, MgO-Al2O3 and SiO2-Al2O3, were employed as supports of Pt-based catalysts for n-decane cracking, aiming to investigate the effect of acidity on cracking activity and coking behaviors. The as-prepared catalysts were characterized by the techniques of N2 absorption-desorption, X-ray diffraction (XRD), CO chemisorption, temperature programmed desorption of ammonia (NH3-TPD) and Fourier transform infrared spectroscopy (FTIR) of adsorbed pyridine. The results showed that acidic support catalysts are more suitable for catalytic cracking reaction of n-decane than alkaline support catalyst. Particularly, Pt/SiO2-Al2O3 catalyst exhibited the optimal catalytic activity, leading to heat sink of 3.920 MJ/kg and n-decane conversion of 85.5% at 750 °C. Meanwhile, excellent cracking activity over Pt/SiO2-Al2O3 catalyst is due to large ratio of strong to total acid sites and large amount of Lewis acid sites. Additionally, stability and regeneration experiments of Pt/SiO2-Al2O3 showed that coverage of active sites due to coke deposition is main factor to catalyst deactivation, and carburization of Pt metals will lead to the reduction of catalytic activity.

Designing a Mesoporous Zeolite Catalyst for Products Optimizing in n-Decane Hydrocraking

Mesoporous ZSM-5 zeolite is developed to enhance the catalytic performance in a hydrocracking reaction. The generated mesopores and mesoporous channels in the new catalyst supply more opportunities for reactant accessing the active sites according to the better mass transfer and diffusion. Meanwhile, the acidity of the mesoporous catalyst is also weakened because of the removal of Si and Al species from its MFI structure, which makes the products distribution drift to more valued chemicals such as olefins. In the modified mesoporous ZSM-5 zeolites via different metallic promoters, the olefins’ selectivity increases as the alkalinity of the catalyst increases. The reason for this is that the formed olefins will be further hydrogenated into corresponding alkanes immediately over the extremely acidic zeolite catalyst. Hence, the moderate alkalinity will limit this process, while at the same time the remaining olefins products will too. Furthermore, the Pd-based mesoporous ZSM-5 zeolite shows an excellent n-decane conversion and high propane selectivity due to the occurrence of hydrogen spillover via the Pd promoter. The phenomenon of hydrogen spillover supplies more chemisorbed sites of hydrogen atoms for hydrocracking and hydrogenating in this reaction. In short, this study explores the important effect factors in n-decane hydrocracking reaction activity and products distribution. It also shows a potential for the further industrial application of petroleum-derived fuel hydrocracking according to the optimized products distribution under metallic promoted mesoporous zeolite.

Fluoride-modified ZSM-5 for endothermic catalytic cracking of n-decane

Endothermic catalytic cracking of hydrocarbon fuel is a promising technique for active thermal protection of advanced aircrafts. Catalyst with high activity and stability is crucial for obtaining high heat-absorbing capability. Here, a series of fluoride-modified ZSM-5 catalysts (FZ) were prepared and characterized with XRD, SEM, 27Al and 29Si NMR, Ar physisorption, NH3-TPD, XRF and Py-IR. Significant changes in porosity and acidity were revealed on the fluoride-modified samples owing to framework dealumination and fluoride residue. Catalytic and endothermic performances were also investigated in supercritical cracking of n-decane. Good performances with obviously enhanced n-decane conversion and heat sink, and decreased coke deposition were obtained via appropriate fluoride modification.