Cracking Of N-heptane Research Articles

Ni decorated three-dimension hierarchical pyramidal ZrO2–Al2O3 nanoporous sheets for methane production

ZrO2–Al2O3 nanocomposites were synthesized by a modified co-precipitation method and loaded with 5%Ni as catalysts for methane production via n-heptane cracking. The as-synthesized nanocomposites were characterized by several techniques such as XRD, N2 adsorption-desorption, XPS, TEM, SEM, AFM, TGA, DTG, NH3 -TPD and Raman analysis. The XRD results confirmed the synthesis of amorphous γ alumina and hexagonal phase of zirconium alumina oxide (Zr5Al3O0.5) solid solution. XRD and SEM analyses showed additional small size Related to monoclinic phase of ZrO2 particles loaded on the Al2O3 surface. BET analyses confirmed the ZrO2–Al2O3 formation in mesoporous sheets structure. TEM images of the neat alumina, 10 ZA and their corresponding Ni loaded samples (Ni@10 ZA) revealed well-defined 3D hierarchical pyramidal structures with a height about 200 nm. All catalysts under this study exhibited high tendency to favor methane production via n-heptane cracking. At higher reaction temperatures, Ni@10 ZA catalyst exhibited higher cracking activity compared to the other prepared catalysts under this investigation which confirmed by NH3 -TPD analysis. A promising yield of methane was achieved at about 88 % coupled with 94.71 % selectivity at reaction temperature of 400 °C. Herein, the data collected through this research work revealed that Ni@10 ZA is a promising candidate for methane production via n-heptane cracking.

The influence of pore-architecture over n-heptane cracking using MFI, *BEA and MSE zeolite catalysts: Multipore versus hierarchical porosity

The catalytic properties of zeolitic materials are governed by the intricate interplay between catalytic and transport processes, which, in turn, depend critically on the topology and morphology features. Here, the catalytic performance of typical three dimensional zeolites, including medium pore MFI, large pore *BEA and multi-pore MSE topologies with comparable Si/Al ratios are employed as n-heptane cracking catalysts to inspect the influence of topology on product slates for naphtha molecules. Furthermore, a bead-milling coupled with porogen assisted recrystallization method is used to fabricate hierarchically porous MSE zeolite for the first time. The catalytic n-heptane cracking properties of hierarchical MSE zeolite are compared with the hierarchical MFI and *BEA analogues, derived from the cracking mechanism ratio and the hydrogen transfer coefficient, respectively, to exam the influence of transport on product distributions. Multi-pore MSE zeolite outperforms MFI and *BEA zeolites in terms of light olefin selectivity and yield, owing to an exaggerated contribution from Haag-Dessau mechanism mediated cracking and a reduced probability for side-reactions, as a consequence of decreased residence time for the primary cracking product olefins. The developed methods to fabricated hierarchical zeolites and the revelation of structure-catalysis relationship may inspire future catalyst design for catalytic naphtha cracking.

Synthesis of self-pillared pentasil zeolites without organic templates and seeds.

Self-pillared pentasil (SPP) zeolites have received considerable interest due to their distinctive intergrowth structure, while the precise process and mechanism for the formation of SPP zeolites remain obscure. Herein, SPP zeolites (ZSM-5) have been successfully synthesized by pre-aging an Al-rich gel without employing any organic templates or seeds for the first time. The as-synthesized SPP zeolites possess a notably high external surface area while the micropores for Ar adsorption are partially blocked by excess Na+, which can be fully recovered by Mg2+ or H+ exchange. The crystallization process is monitored and the impacts of synthesis parameters are investigated. The results show that self-pillaring originates from the partial lattice distortion at the intersections of nanosheets, offering a new insight into the self-pillaring process. Typically, with decreasing SiO2/Al2O3 ratio, more crossovers could be observed in the crystals, hinting that self-pillaring predominately occurs at the (101) plane of twins in the ZSM-5 precursor due to Al-rich lattice distortion. Finally, in the catalytic cracking of n-heptane, H-SPP zeolites exhibit superior performance to commercial H-ZSM-5 zeolites due to their abundant Brønsted acid sites arising from a low framework SiO2/Al2O3 ratio of ∼21 and the short diffusion path originating from the house-of-cards structure.

Insight into performance over IM-5, ZSM-5 and ZSM-11 zeolites for n-heptane cracking to light olefins in the absence & presence of steam

The three dimension (3D) 10-membered ring channels zeolite has a unique advantage in increasing light olefins for catalytic cracking reaction. Herein, zeolites IM-5, ZSM-5 and ZSM-11 were synthesized hydrothermally to achieve comparable texture properties and SiO2/Al2O3 ratios. The acid content and acid strength of the three zeolites were as follows: IM-5 > ZSM-5 > ZSM-11. Meanwhile, 1H DQ MAS NMR confirmed that there was a synergistic effect between Brønsted and Lewis acids in IM-5 zeolite. However, IM-5 zeolite with lots of strong BAS had an unexpected low TOF in n-heptane cracking. Furthermore, the light olefins selectivity was as follows: IM-5 > ZSM-11 > ZSM-5 at 550–650 ℃ in the absence of steam. IM-5 zeolite had the particular advantage in ethylene, and its selectivity was up to 44.9 %. After steam was introduced, the monomolecular cracking reaction, the aromatization of propylene and the deep cracking of C3 and C4 hydrocarbons were inhibited over the three zeolites. Steam could prolong the activity of IM-5 zeolite, but accelerate the deactivation of ZSM-5 and ZSM-11 zeolites. The primary cause for the rapid deactivation of ZSM-5 and ZSM-11 zeolites was dealuminization in steam, whereas for the IM-5 zeolite, it was the rapid formation of coke on its surface, thereby blocking its micropore channels.

Exploration of new olefin production process: Effects of the addition of CO2 and H2O on n-heptane pyrolysis

In order to study the new cracking process characteristics of hydrocarbon feedstock to light olefins by direct flue gas heating, the pyrolysis experiments of n-heptane in CO2 and H2O atmosphere were performed in pretreated STS316L flow reactor (ϕ10 mm × 2.5 mm × 700 mm) at a temperature range of 1073–1373 K, pressure range of 0.1–1.0 MPa. By changing the n-heptane flow and system pressure to adjust the residence time, results show that the latter is not conducive to olefin formation, but the residence time range about high olefin formation of the latter is wider than that of the former. Due to the promotion of CO and the high-temperature solubility of CO2, the types and contents of PAHs in tar under H2O&CO2 atmosphere are higher. Based on the analysis of n-heptane cracking products stream, the reactivity of H2O and CO2 gradually appears at high temperature and the reactivity of H2O is significantly higher than that of CO2, resulting in higher yields of H2 and CO. The mainstream of the process is the cracking of n-heptane, in which H2O is the supply source of •OH and •H, and CO2 acts as a coking agent. High olefin yields can be achieved in either H2O-rich or CO2-rich atmosphere, and the ratio of the two needs to be properly regulated.

Insight into stepwise dealumination in acid-treatment of IM-5 for catalytic cracking of n-heptane and Fischer-Tropsch naphtha

10-membered ring IM-5 zeolite has shown excellent performance in many catalytic reactions. The efficient preparation of high silica IM-5 by situ synthesis remains huge challenge. Here, IM-5 with SiO2/Al2O3 ratio (SAR) of 49–116 was acquired by HNO3 treatment. An interesting stepwise dealumination behavior in IM-5 was discovered during the whole acid-treatment process (based on XRF characterization). Extra-framework Si (EF-Si) compensated for the defects in IM-5 framework, thereby postponed the removal of Al species at the initial period of acid treatment, as indicated by 27Al, 29Si, 1H NMR and density-functional theory (DFT) calculations. The dealuminated IM-5 were revealed to retain more than 83 % crystallinity with little loss in micropore volume. Bimolecular reaction was predominant in n-heptane cracking reaction resulted from decreased acid amount and strength in dealuminated IM-5. Meanwhile, high silica IM-5 improved overall yields to light olefins and liquid petroleum gas (LPG) and less coke production in Fischer-Tropsch naphtha (FT-naphtha) cracking reaction.

Fe–Al isomorphous and self-pillared ZSM-5 nanosheet catalyst for cracking of n-heptane with enhanced selectivity of light olefins

Series Fe–Al isomorphous and self–pillared ZSM–5 nanosheets zeolite (Al–Fe–SPZ) with different Fe/Al molar ratios were synthesized by one–pot strategy for catalytic cracking of n–heptane to produce light olefins. All the Al–Fe–SPZ catalysts gave high surface areas and pore volumes, ascribing to the intersection of nanosheet layers. The addition of Fe in zeolite framework resulted in the decrease of surface acid concentrations (especially the strong acid concentrations). The effect of Fe modification on olefins selectivity in catalytic cracking reaction had two sides. On one hand, reducing the amount of acid, helped to inhibit the hydride transfer, cyclization and aromatic cyclization of olefins in the product at adjacent Brønsted acid sites. However, the reduced acid concentrations led to the decrease of the cracking depth, and the cracking of intermediate products (C4 and C5) was inhibited, thus giving a decreased olefin selectivity. With Si/(Al+Fe) molar ratio of 100 and Al/Fe ratio of 84/16, Al–Fe–SPZ catalyst gave the highest yield of light olefins (44.8 wt% of ethylene and propylene) in cracking of n–heptane. In addition, Fe modified zeolite catalyst show excellent cracking stability with low coke deposition.

Different approaches to the synthesis of ZSM-22 zeolite with application in n-heptane cracking

The synthesis of ZSM-22 zeolite has been extensively studied due to its properties of form selectivity, acidity and hydrothermal stability, which is applied in important reactions in the areas of petroleum refining and petrochemicals. In view of this, the present work studied different approaches of synthesis of ZSM-22 using: 1-diaminohexane as a structure directing agent, (ii) methanol and seed crystals, (iii) aging of the synthesis gel with addition of polymer, surfactant and silane and (iv) starch, calcium carbonate and silanized silica with subsequent desilication. Thus, the effects of these methodologies on the textural properties, acidity and catalytic activity of the zeolites obtained were evaluated. The samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscopy (SEM), ammonia desorption at programmed temperature (NH3-TPD) and thermal analysis (TG/DTG). The catalytic activity and selectivity of the catalysts were evaluated in the model catalytic cracking reaction of n-heptane at 650 °C for 180 min. The synthesis route using methanol and seed crystals allowed obtaining ZSM-22 in 3 h of crystallization, drastically reducing the synthesis time compared to other methodologies. Despite this, the use of 1-diaminohexane led to the obtaining of zeolite with textural properties, acidity and catalytic activity superior to the other samples. The generation of mesoporosity was obtained through the use of silanized silica and subsequent desilication, leading to greater catalytic stability and less deactivation by coke. All catalysts showed similar selectivity to the formation of compounds in the range C2 to C4.

Effect of ZSM-5 zeolite porosity on catalytic cracking of n-heptane

The selectivity of ethylene and propylene in cracking of n-heptane is connected to the micropore to mesopore ratioof ZSM-5 structure.

Catalytic cracking of n-heptane over Fe modified HZSM-5 nanosheet to produce light olefins

Aiming at the acid modification and stabilization of ordered mesopores in HZSM-5 nanosheet (NS) zeolite for catalytic cracking, two kinds of Fe-modified NS zeolite catalysts were prepared by incipient wetness impregnation (Fe/NS) and an in-situ hydrothermal synthesis method (Fe@NS, N-[3-(trimethoxysilyl)propyl]ethylenediamine complexed Fe as precursors). Fe modification conveyed a lower n-heptane cracking conversion by the Fe/NS catalyst because of the decreased total acid content compared with the parent NS catalyst. However, the decreased Brønsted to Lewis acid ratios by Fe modification restricted the deep hydrogen transfer of olefins, leading to an enhanced ethylene and propylene yields in the product. Furthermore, for Fe@NS catalyst, the highly dispersed FeOx between the nanosheet layers stabilized the mesopore arrangement, and the facilitated diffusion by highly connected channels further alleviated olefin consuming. At reaction temperature of 550 °C with a weight hourly space velocity of 8.64 h−1, a 41.8 wt% yield of light olefins (ethylene of 12.2 wt% and propylene of 29.6 wt%) by the Fe@NS catalyst was realized, which was 10.4% and 21.7% higher than that of the Fe/NS and parent NS catalysts, respectively. Moreover, Fe@NS also showed a good catalytic stability with a deactivation rate of only 4.37% after 18 h reaction.

Effect of coke deposition over microporous and hierarchical ZSM-23 zeolite

The effects of deactivation by coke deposition after the n-heptane cracking reaction were evaluated on crystallinity, acidity and activation energies for the coke thermal oxidation process in microporous and hierarchical ZSM-23 zeolites. The fresh and coked catalysts were characterized by X-ray diffraction, temperature-programmed desorption of ammonia and thermogravimetric analysis. The Flynn–Wall–Ozawa and Vyazovkin kinetic models were used to determine the activation energy of the catalyst regeneration process, using integral dynamic curves from thermogravimetric analysis data obtained with different heating rates. The generation of micro-/mesoporous structures provided a beneficial effect by inhibiting the loss of crystallinity and preserving a certain degree of acidity after catalyst deactivation. The hierarchical ZSM-23 zeolites showed lower deposited coke amounts and activation energy values for the coke thermal oxidation process, providing greater stability, activity and lower energy level required for regeneration in comparison with the microporous zeolites.

N-Heptane catalytic cracking on ZSM-5 zeolite nanosheets: Effect of nanosheet thickness

To explore the effect of channel properties on catalytic activity, ZSM-5 zeolite nanosheets were synthesized with di-quaternary ammonium-type surfactant and used in n-heptane cracking reaction. Nanosheet thickness was changed from around 4 nm–20 nm by adjusting the ratio of surfactant to tetraethyl orthosilicate (TEOS). The synthesized zeolite nanosheets were characterized by physical and chemical adsorption, electron microscopy, X-ray diffraction (XRD), pyridine infrared (Py-IR), Thermogravimetric analysis (TGA) and Raman spectra. The results showed that zeolite with thicker nanosheets had more microporosity and was more conducive to remarkably improving the selectivity of light olefins. High mesoporosity of zeolite nanosheets greatly reduces the diffusion resistance and accelerates mass transfer which even increases the direct diffusion of insufficiently cracked intermediates. Thicker zeolite nanosheets with more micropores prolong the reaction time and thus improve the selectivity of target products. • Ordered mesoporous nanosheet zeolites were synthesized and used in catalytic cracking reaction. • Nanosheet thickness was regulated from around 4 nm–20 nm through the change of template concentration in synthetic gel. • Thicker nanosheet zeolite with more micropores was conducive to the production of ethylene and propylene. • A well linear dependence was found between total selectivity and HFʺ.

Synthesis and catalytic performance of zeolite-Y supported on silicon carbide in n-heptane cracking

In this work, we demonstrate a facile approach for the synthesis of zeolite-Y crystals (size, ca. ∼400 nm) supported on silicon carbide (SiC) with the assistance of the cationic template (polydiallyldimethylammonium chloride, PDDA). The polymeric cationic template used to treat SiC particles induces a positive charge on SiC surface which electrostatically attracts negatively charged aluminosilicate seeds and promotes the growth of zeolite (ZY) particles over SiC, thus leading to the formation of stable ZY@SiC supported catalysts. The supported ZY catalysts with different weight ratio of ZY and SiC were synthesized and characterized by various techniques such as XRD, SEM, SEM-EDX, SEM-mapping, TEM, STEM, FT-IR, 27Al MAS NMR and N2 sorption. The characterization of the supported ZY catalysts suggests the uniform growth of ZY particles over SiC together with the creation of hierarchical micro-mesopores assembly. In the catalytic cracking of n-heptane, the catalyst ZY@SiC-50 displayed a remarkable improvement in reaction rate when compared to commercial zeolite-Y (CBV-600) amounting to 3.5 folds enhancement. Interestingly, the light olefins yield is also substantially improved. At WHSV of 8 h−1 and 475 °C, the highest light olefin yield (24–36 %) was achieved over ZY@SiC-50 whereas the reference catalyst, CBV-600 produced lower light olefins yield (7–17 %). Moreover, the supported ZY catalyst exhibited less deactivation rates. This improved performance is attributed to the hierarchical micro-mesopores assembly created by the homogeneous dispersion of zeolite crystals on SiC which offers fast diffusion pathways for the reactants and enhanced accessibility to active sites thus leading to higher observed reaction rates and fast diffusion of products thus minimizing the occurrence of side reactions.

CFD Simulation of Catalytic Cracking of n-Heptane in a Fixed Bed Reactor

This work aims to three-dimension computational fluid dynamics (CFD) simulation of n-heptane catalytic cracking in fixed bed reactor (L=0.80 m) and to promote the cracking model of n-heptane using CFD. The catalyst granules were located in middle section of the reactor. The reaction scheme of n-heptane catalytic cracking was involved one primary reaction and 24 secondary reactions. Catalytic cracking process with a model of 25 molecular reactions was simulated by Fluent 6.0 software. The ratio of tube-to-particle diameter was considered N=2. The contours of coke deposition rate, vorticity, velocity and coke precursors and their relations along the reactor were predicted and discussed.

Reactive molecular dynamics simulation on thermal decomposition of n-heptane and methylcyclohexane initiated by nitroethane

Normal alkanes and cycloalkanes are important components of endothermic hydrocarbon fuels. The present work conducts the reactive molecular dynamics (RMD) simulations based on reactive force field to compare the thermal cracking of n-heptane and methylcyclohexane (MCH) with the same carbon atom number initiated by nitroethane, focusing on initial decomposition temperature, intermediates and product distribution, and the related kinetics. From the RMD simulations, we find nitroethane can accelerate both n-heptane and MCH decompositions, since the C–NO2 bond rupture of nitroethane can proceed at relatively lower temperatures to produce the reactive radicals compared to the C–C bond cleavage of n-heptane and MCH to start the free radical chain reactions, but the promoting effect becomes weaker after it reaches a certain level with temperature. Reasonable Arrhenius parameters estimated from RMD simulations based on first-order kinetic analysis compare well with experimental results. The observed difference of pyrolysis behaviors and kinetic parameters between n-heptane and MCH can be ascribed to their molecular structure, coinciding with experimental observations. In the presence of nitroethane, reductions of initial temperature and activation energy for n-heptane decomposition are larger than those for MCH decomposition. More alkenes are observed in n-heptane decomposition compared to MCH decomposition. Due to the endothermic capacities of fuel being sensitive to the yields of alkenes, more heat could be absorbed by the n-heptane decomposition. These results indicate that RMD simulations can provide important insights at the atomistic level on the difference of decomposition behaviors between normal alkanes and cycloalkanes initiated by nitroethane under supercritical conditions.

Cracking of n-heptane with activation of vanadium oxide based catalyst: effect of support and modification by K or P

In the present study, n-heptane cracking was comparatively investigated over ZSM-5 equilibrium catalyst with introduction of VOX/Al2O3, VOX/SiO2 and VOX/MgO, as well as the potassium or phosphorous incorporated VOX/Al2O3. The results showed that the conversion varied significantly with introduction of different VOX/support catalysts. The conversion decreased in the order of Base (without introduction) < + VOX/SiO2 < + VOX/MgO < + VOX/Al2O3. The different extent of improvement in conversion could be closely associated with the reducibility of them. The incorporation of potassium or phosphorous modified the acid properties of VOX/Al2O3. But the conversions were barely influenced. There was an increasing trend of selectivity to hydrogen and aromatic products with increasing acidity of the vanadia based catalysts. It was suggested that the improved basicity favored desorption of the active intermediate species from VOX unit, leading to a lower selectivity to hydrogen and aromatics produced.

Effect of hierarchical ZSM-5 zeolite crystal size on diffusion and catalytic performance of n-heptane cracking

Hierarchical ZSM-5 zeolite aggregates with different sizes of nanocrystals were synthesized using different amounts of the mesoporogen 3-aminopropyltriethoxysilane. The effect of the crystal size on the catalytic cracking of n-heptane was investigated and the Thiele modulus and effectiveness factor were used to determine the reaction rate-limiting step. The crystal size affected the textual properties of the catalysts but not the acidic properties of the catalysts. The reaction rate was first order with respect to the n-heptane concentration. Cracking over hierarchical zeolites with nanocrystal sizes larger than about 50 nm took place under transition-limiting conditions, whereas the reaction over hierarchical zeolites with nanocrystal sizes of 15 or 30 nm proceeded under reaction control conditions. Hierarchical ZSM-5 zeolite aggregates with smaller nanocrystals had better selectivity for light olefins which can be ascribed to the shorter diffusion path lengths and lower diffusion resistance in these catalysts. Furthermore, these catalysts had lower coking levels which can be attributed to the substantial number of mesopores which prevent the formation of coke precursors. Open image in new window

Catalytic Cracking of n-Hexane and n-Heptane over ZSM-5 Zeolite: Influence of SiO2/Al2O3 Ratio

The performance of two types of ZSM-5 zeolite catalysts (MFI-type zeolite, SiO2/Al2O3 = 50 and 300) was studied in the catalytic cracking of n-hexane and n-heptane as a model compound of light naphtha for production of light olefins at 500, 550, and 600°C. The physicochemical properties of ZSM-5 catalysts were characterized by means of XRD, BET, SEM and NH3-TPD. The influence of SiO2/Al2O3 molar ratio was investigated on conversion and product selectivity. ZSM-5 zeolite yielded higher conversion in the cracking of n-hexane compared to n-heptane and maximum conversion was achieved over ZSM-5(50) at 600°C. ZSM-5(50) showed higher alkane selectivity rather than olefins. It was found that ZSM-5(300) was more desirable in terms of having significant selectivity to light olefins as well as producing high propylene to ethylene ratio. The maximum propylene to ethylene ratio of 2.7 and 2.48 was observed over ZSM-5(300) at 500°C for n-hexane and n-heptane cracking, respectively.

Kinetic Study of Catalytic Cracking of n-Heptane on a ZSM-5 Based Mesoporous Catalyst with Small Crystal Size

The aim of the work was to investigate the mechanism of cracking of n-heptane in the presence of a medium-pore finely crystalline catalyst based on zeolite ZSM-5 and the development of a kinetic model of the mechanism of the thermic and catalytic reaction. The catalyst based on zeolite ZSM-5 has high catalytic activity for the catalytic cracking of n-heptane, high stability, and long life time. The kinetic model includes 12 chemical substances and 11 reactions. The values predicted by the model were in good agreement with the experimental data, and the average relative error in the main products was not greater that 10%. The model showed good agreement between the calculated yields of the final product and the experimental data for the catalytic cracking of n-heptane.

Hierarchical ZSM-5 zeolite designed by combining desilication and dealumination with related study of n-heptane cracking performance

The effect of the basic (NaOH) and/or acid (citric acid and EDTA-2Na) treatment of ZSM-5 zeolite has been studied comparing the structural and acidic features and their catalytic performance in n-heptane cracking. The properties of the catalysts have been elucidated using XRD, N2 low-temperature sorption, 27Al and 29Si NMR, pyridine adsorbed FTIR, NH3–TPD, SEM and TEM analysis. The results showed that the degree of desilication and dealumination of ZSM-5 zeolites was greatly dependent on the agents. NaOH obviously created new mesopores on parent ZSM-5 zeolites by desilication. Citric acid contributed to the removal of nonframework Al species, causing the increase of micropore surface area. EDTA-2Na promoted desilication and simultaneously converted part of removed framework Al species into nonframework Al species. The treatment of ZSM-5 combined with those three agents was very effective to obtain a hierarchical structure with partial breakdown of the crystallites and high acid amounts of both Bronsted and Lewis acid sites. Catalytic tests showed that the post-treated ZSM-5 catalysts had higher activity and stability than parent ZSM-5 catalyst at the same reaction temperature. The synergetic effect of Bronsted acid and Lewis acid of ZSM-5 catalyst (Z5-ACE) probably facilitated n-heptane conversion, while more clean micropore and newly created mesopores facilitated the slight increase of olefin selectivity and suppressing the formation of coke deposition in its inherent micropores to some extent.