Cracking Of N-heptane Research Articles

Dealumination kinetics of composite ZSM-5/mordenite zeolite during steam treatment: An in-situ DRIFTS study

Abstract To get a better understanding of structural deactivation of ZSM-5/MOR during the catalytic cracking of n-heptane in the steam atmosphere, a comprehensive mechanism of hydrothermal dealumination was proposed through in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) in this work. The mechanism can be divided into two steps: firstly, the hydrolysis of four Al O bonds, and secondly, the self-healing of Si OH bonds accompanied with partial condensation of the extra-framework Al species. Accordingly, the kinetics of dealumination process has also been fully discussed. In the IR spectra, the range of 3450–3850 cm− 1 could be deconvolved to distinguish the hydroxyl groups on the different position and calculate the consumption of each hydroxyl group during the reaction. Based on results from the in-situ DRIFTS, the kinetics of dealumination was hence developed and also in well agreement with the kinetics of deactivation of ZSM/MOR catalysts during the reaction in the presence of little coke deposits.

N-Heptane catalytic cracking on hierarchical ZSM-5 zeolite: The effect of mesopores

To investigate the effect of pore structure on catalytic cracking of n-heptane, hierarchical ZSM-5 zeolites with unchanged acidity were prepared by hydrothermal synthesis with organosilane ((3-aminopropyl) triethoxysilane, APTES) and tetrapropylammonium hydroxide (TPAOH) as double templates. Chemical and textural properties of samples were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-OES) and NH3 temperature programmed desorption (NH3-TPD). The results revealed that the dual functions of APTES and increasing amount of TPAOH favored for forming higher intercrystalline mesopore volume in the hierarchical ZSM-5 zeolites while maintained the micropores. Additionally, the crystal size distribution of the hierarchical samples ranging from 250 to 330nm did not influence the diffusion rate of light olefins. The improved selectivity of both ethylene and propylene was then ascribed to the decreased diffusion resistance caused by the presence of secondary porosity, comparing with traditional ZSM-5. We also proposed a related model accordingly.

Composite TiO2/fiberglass catalyst: Synthesis and characterization

The paper presents the synthesis and characterization of highly dispersed titania on the surface of fiberglass material. Scanning electron microscopy and X-ray digital 3D-microtomography showed that each support fiber was uniformly coated by modifying component. The layer of titania consisted of anatase particles of 18nm, an average pore size was 3.1nm. The prepared material revealed a catalytic activity in n-heptane cracking, deep and partial oxidation. The major products of n-heptane conversion at 300–400°C in the presence of oxygen were ketones with a carbon number of 3–4. Above 500°C, the deep oxidation increased dramatically with a simultaneous appearance of α-olefins.

Generation of Catalytic Films of Alumina and Zeolites on FeCralloy Rods

FeCralloy rods (0.5 mm thickness) were subjected to high temperature thermal oxidation to produce a metastable alumina phase. This structured layer acts as an anchor to bind additional coatings of alumina via washcoat techniques, thereby improving the layer thickness and increasing adhesion of the catalytic surface. In addition, thin films of structured zeolite catalysts (ZSM-5 and Zeolite Y) were grown onto the surface of a metal substrate using in-situ hydrothermal synthesis. All catalysts were fully characterised by SEM, EDX and XRD. The cracking of n-heptane over structured catalysts for both ZSM-5 and Zeolite Y showed very similar product selectivity compared with similar traditional pelleted catalyst forms. The alumina coated FeCralloy rods were impregnated with 1 wt. % platinum and tested in a fixed bed reactor to assess the impact on yield for the dehydrogenation of methylcyclohexane and compared with conventional 1 wt. % Pt/Al2O3 pellets. This paper demonstrates that structured catalysts can be manufactured with excellent alumina and zeolite adherence and when suitably activated/modified gives comparable catalytic results to the pelleted powder forms. These coated structured catalysts enhance temperature distribution in highly exothermic and endothermic catalysed processes in addition to improving the mass transfer properties of the reactor system.

Fabrication of desilicated MTW zeolite and its application in catalytic cracking of n-heptane

Desilicated MTW zeolite was developed for long chain hydrocarbon cracking such as n-heptane cracking. The catalytic performance of desilicated ZSM-12 (MTW) zeolite was investigated for n-heptane cracking in a fixed bed reactor at 650°C and atmospheric pressure. Average conversion of 75.3% was achieved with a stability of 240min. Higher selectivity to olefins (63.51%) was observed over a mesoporous MTW catalyst (treated with 0.2M sodium hydroxide for 10min) with average propylene to ethylene ratio (P/E) of 0.73. Desilicated MTW zeolite was prepared by using alkaline treatment under microwave irradiation to obtain ZSM-12 with larger pore volume (mesopores), larger surface area and different strength of acid sites. Maximum mesopore volume was 0.53cm3g−1 with external surface area of 437m2g−1. This is a remarkable result for mesoporous MTW prepared by post-alkaline treatment.

Simultaneous realization of high catalytic activity and stability for catalytic cracking of n-heptane on highly exposed (010) crystal planes of nanosheet ZSM-5 zeolite.

Nanosheet ZSM-5 zeolite with highly exposed (010) crystal planes demonstrates high reactivity and good anti-coking stability for the catalytic cracking of n-heptane, which is attributed to the synergy of high external surface area and acid sites, fully accessible channel intersection acid sites, and hierarchical porosity caused by the unique morphology.

Catalytic cracking of n-alkane naphtha: The impact of olefin addition and active sites differentiation

An extended dual kinetic model allows to fit the n-heptane cracking results working in a wide range of reaction conditions. The duality of the model is provided by the contribution of monomolecular and bimolecular cracking mechanisms. It takes into account the role played by the olefins formed on the global cracking or added within the feed. Furthermore by means of this model and the kinetic parameters obtained when cracking n-heptane on ZSM-5, it has been observed that, while some characterization techniques show a homogeneous zeolite surface from the point of view of the active sites, rigorous kinetic experiments point to the possibility that the reactant sees a heterogeneous surface with, at least, two groups of cracking active sites. Those differentiated active sites give different cracking rates and different activation energies for the process and, in the case of ZSM-5, could be assimilated to sites pointing to the 10R channels and sites pointing into the crossing of the 10R channels, mainly due to differences in acid site location and confinement effects.

Mesoporous ZSM5 having both intrinsic acidic and basic sites for cracking and methanation

Mesoporous ZSM5 (mZSM5) was prepared by the dual templating method for n-heptane cracking and CO methanation. The properties of mZSM5 were tailored by varying the aging time in the 0.5–3-day range. The physical properties of the catalysts were characterized with XRD, FESEM, nitrogen physisorption and IR. XRD and FESEM analyses indicated that mZSM5s possessed a high crystalline structure with coffin-type morphology. Nitrogen physisorption analysis revealed the presence of both micropores and mesopores in high surface area mZSM5s with inter- and intra-particle porosity. The pyridine and pyrrole adsorbed IR spectroscopy results demonstrated that mZSM5s have both intrinsic acidic and basic sites, which are suitable for acid and/or base catalyzed reactions. The bare mZSM5-0.5D exhibited the highest rate of conversion of n-heptane (0.0230μmol/m2s) and CO (0.0226μmol/m2s) at 573K and 723K, respectively. The mZSM5s performed with good stability and no deactivation up to 30h for n-heptane cracking and CO methanation. Co-existence of micro-mesopores and intrinsic acidic–basic sites is vital for acid-catalyzed and base-catalyzed reactions.

Different influences of V2O5/Al2O3 introduction on initial conversion of n-heptane over fresh and equilibrium ZSM-5 catalyst

Previous studies showed that the introduction of V2O5/Al2O3 could improve catalytic performances of ZSM-5 catalyst for n-heptane cracking. In order to clarify influences of V2O5/Al2O3 introduction on the initial reaction of n-heptane, performances of n-heptane cracking over fresh and equilibrium ZSM-5 catalyst without and with V2O5/Al2O3 introduction were comparatively studied in this paper. The results showed that the introduction of V2O5/Al2O3 brought significant influences to initial reactions of n-heptane over the equilibrium ZSM-5 catalyst. The initial reaction rate was significantly improved, and the product selectivity was greatly changed by V2O5/Al2O3 introduction. But no such effect was observed for the fresh ZSM-5 catalyst. It was supposed that the presence of V2O5/Al2O3 offered another pathway for initial conversion of n-heptane, and this reaction path played a more important role in the reaction over the mixed V2O5/Al2O3 and equilibrium ZSM-5 catalyst.

Comparison of steaming stability of Cu-ZSM-5 with those of Ag-ZSM-5, P/H-ZSM-5, and H-ZSM-5 zeolites as naphtha cracking catalysts to produce light olefin at high temperatures

We performed n-heptane cracking over Cu-ZSM-5, Ag-ZSM-5, and P/H-ZSM-5 before and after steaming under various conditions. The reduced Cu-ZSM-5 and Ag-ZSM-5 exhibited similar n-heptane cracking activities to H-ZSM-5 due to generation of Brønsted acid sites by reduction of metal cations. The order of steaming stabilities in the presence of O2 was Cu-ZSM-5>Ag-ZSM-5 ≫ P/H-ZSM-5, which was the reverse order of cumene cracking activities in the presence of O2. Cumene cracking activity is a function of Brønsted acidity. Therefore, these findings indicate that the steaming stability of a catalyst is strongly related to its Brønsted acidity. Cu2+ and Cu+ cations in the 194%Cu-ZSM-5 were not reduced to Cu0 at a high temperature of 1023K in the presence of O2 and, therefore, 194%Cu-ZSM-5 exhibited an ultra-high steaming stability in the presence of O2. The Brønsted acidity of 95%Ag-ZSM-5 was extremely low, almost equal to 194%Cu-ZSM-5. However, the thermal reduction of Ag+ took place during steaming even in the presence of O2 at a high temperature of 1023K and, therefore, the steaming stability of 95%Ag-ZSM-5 in the presence of O2 was much lower than that of 194%Cu-ZSM-5.

Influence of rare earth elements on the acid and metal sites of Pt/HBEA catalyst for short chain n-alkane hydroisomerization

The doping effect of rare earth (RE) elements La, Nd and Yb on the acidity and metal function of Pt/HBEA catalysts was investigated, as well as its influence in the hydroisomerization of n-hexane. HBEA zeolite was submitted to ion exchange with increasing amounts of RE using nitrate solutions, followed by Pt introduction. The samples were characterized by powder X-ray diffraction, chemical analysis and low temperature N2 adsorption. The acidity of the samples was study through pyridine adsorption followed by FTIR spectroscopy and the model reaction of n-heptane cracking. The influence of RE elements on the metal function was studied by magnetic susceptibility measurements, model reaction of toluene hydrogenation and H2 chemisorption analysis. The characterization methods showed that the presence of very small amounts of RE elements increases the strength and density of the acid sites due to the appearance of new Lewis acid sites that are detected upon RE loading. The electronic properties and metal dispersion of Pt were also improved. In n-hexane hydroisomerization reaction an increased catalytic activity and selectivity into dibranched isomers is detected in the presence of very low contents of La and Nd (less than 0.4wt.%). For higher amounts and also in the case of Yb doped samples, where the amounts introduced were higher, a decrease in catalytic activity as well as a higher selectivity in cracking products is noticed as a result of stereochemical limitations inside the zeolite pore structure.

Cracking and isomerization functionalities of bi-metallic zeolites for naphtha value upgradation

Effect of acid and metal functionalities of several mono- and bi-metallic wide pore zeolites such as BEA and Y on the cracking and isomerization properties of n-heptane as well as two industrial naphtha feedstocks have been studied. Among these, the bi-metallic Pt–Cr–HBEA catalyst exhibited appropriate catalytic properties responsible for high isomerization and octane boosting. Detailed studies envision that the role of Cr is bi-functional, namely, to change the acidity of the zeolite support towards the moderate strength responsible for controlled cracking and to promote the reducibility and dispersion properties of the Pt for the effective isomerization reaction. This has resulted in enhancement in research octane number (ΔRON) of two industrial naphtha feedstocks with 22 and 43 units increase in RON along with negligible amount of aromatics, especially benzene that makes the product suitable for gasoline applications. The catalyst exhibited constant performance in the studied period of 70h.

Effect of morphology and particle size of ZSM-5 on catalytic performance for ethylene conversion and heptane cracking

To determine the effect of morphology and particle size of ZSM-5 (particle type ZSM-5) on catalytic performance (catalytic activity, product distribution, and catalyst lifetime), ZSM-5 with varying particle size and a ZSM-5 nanosheet were prepared to study the conversion of ethylene and cracking of n-heptane. The physicochemical properties were also investigated by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, 29Si MAS, and 27Al 3Q MAS nuclear magnetic resonance.The rate of ethylene conversion was found to increase with decreasing ZSM-5 zeolite particle size, while the product distribution was independent of the particle size and morphology of the catalyst. In n-heptane cracking, the ZSM-5 nanosheet showed lower catalytic activity than particulate ZSM-5, and the distribution of hydrocarbon products was independent of the morphology of ZSM-5. In both reactions, the effects of morphology and particle size on catalytic performance will be discussed.

ZSM-5 crystals grown on the wall of a long tubular reactor as a structured catalyst for cracking of endothermic fuels

In situ growth of ZSM-5 crystals on the surface of Ni-based alloy supports by hydrothermal synthesis and their mechanical, structural stability were investigated. ZSM-5 crystals grown on the wall of a long (750mm) tubular reactor with a small inner diameter (1mm) was evaluated as a structured catalyst for cracking of n-heptane as a model endothermic fuel. The results have shown that the adhesion strength between ZSM-5 crystals and the support was strong enough to resist a heating/fast-cooling cycle (the sample was immersed into water immediately after being heated to be 750°C). The crystalline structure of ZSM-5 crystals was also stable against the heating/fast-cooling cycle. The structured catalyst was shown to be catalytically active for cracking of n-heptane (LHSV=200h−1) at 700°C. The formation rates of gaseous cracking products were 9.8mlmin−1 and 29.3mlmin−1 for the bare tubular reactor and the tubular reactor with ZSM-5 crystals grown on the wall, respectively. These structured catalysts show high promise for cracking of endothermic fuels at high temperatures.

Catalytic coupling and cracking reactions of alkanes in Lewis acidic chloroaluminate ionic liquids enhanced by molecular oxygen

In the presence of molecular oxygen, [BMIM]+[Al2Cl7]− (BMIM = 1-butyl-3-methylimidazolium) ionic liquids catalyzed coupling reactions of cyclohexane and methylcyclohexane to give dimers and trimers. Further, conversions and reaction rates of n-heptane cracking and disproportionation reactions were strongly enhanced if an atmosphere of dry air was applied instead of an inert gas.

Synthesis of hierarchical porous zeolite and its performance in n-heptane cracking

A series of hierarchical porous zeolites (ZSM-5–ZRP-1) was synthesized by adding different contents of ZRP-1 to the procedure of hydrothermal synthesis of ZSM-5. The prepared samples were characterized by using N2 adsorption–desorption, XRD, SEM, TEM, NH3-TPD, Py-FTIR and investigated in cracking of n-heptane. The results indicate that physicochemical properties and catalytic performances of ZSM-5–ZRP-1 samples are quite different from those of HZSM-5 or ZRP-1. ZSM-5–ZRP-1 samples have a lot of mesopores and suitable amount of B + L acid sites as well as higher L/B ratio compared with HZSM-5 or ZRP-1, and also show medium acid amount and strength. These lead to a higher selectivity of olefins (ethylene plus propylene) obtained on it.

Selective formation of light olefin by n-heptane cracking over HZSM-5 at high temperatures

The catalytic cracking of n-heptane has been performed over HZSM-5 catalysts with various Si/Al ratios at 723–923 K to form light olefins selectively. The HZSM-5 zeolites with various acid site densities exhibited almost the same selectivity at the same conversion. The ethylene + propylene selectivity increased, while the propylene/ethylene ratio decreased with an increase in reaction temperatures. It is found that a high temperature is required to obtain a high ethylene + propylene yield. The highest ethylene + propylene yield obtained in this study was 59.7 C-% with a propylene/ethylene ratio of ca. 0.72 at 99.6% conversion over HZSM-5 (Si/Al = 31) at 923 K. Moreover, it is concluded from the selectivities and activation energies that the monomolecular cracking is predominant at a high temperature as 923 K.

Kinetic Modeling of the Free-Radical Process during the Initiated Thermal Cracking of Normal Alkanes with 1-Nitropropane as an Initiator

To elucidate the accelerating effect of 1-nitropropane on the thermal cracking of normal alkanes, ab initio and density functional theory calculations were performed to investigate the elementary reactions involved in the initiated thermal cracking of a 1-nitropropane/n-heptane mixture. The kinetic parameters were evaluated on the basis of standard transition state theory (TST) or variational transition state theory (VTST) with Wigner tunneling correction. The activation energy for the C–N bond rupture of 1-nitropropane to produce primary n-propyl and nitro radicals is calculated to be 234–269 kJ/mol, while the bond dissociation energy of the C–C bond within the n-heptane molecule is predicted to be at least 335 kJ/mol. These calculated results demonstrate that the presence of 1-nitropropane makes the free radical formation become relatively easier compared with single n-heptane cracking. Furthermore, compared with the C–H bond cleavage and 1,3-H intramolecular transfer, the unstable n-propyl radical main...

Catalytic cracking of n-heptane under activation of lattice oxygen in a circulating fluidized bed unit

A circulating fluidized bed unit was used to evaluate influences of lattice oxygen introduction over catalytic cracking of n-heptane over HZSM-5 catalyst in a continuous reaction fashion. The results demonstrated that V 2O 5/Al 2O 3, which functioned as lattice oxygen supplier, promoted conversion of n-heptane in a much larger extent, compared with fixed-bed reactor. It also improved yields of propylene and butylenes, and intensified formation of aromatics and coke. Besides lattice oxygen species, some adsorbed oxygen species also participated into the reaction. CO and H 2O were formed as main oxygenated products. Steam introduction improved selectivity of propylene and butylenes, promoted desorption of strong adsorbed species in V 2O 5/Al 2O 3, and thus formation of coke was depressed; however, the damage to HZSM-5 framework was aggravated simultaneously.

Catalytic cracking of n-heptane over HZSM-5 catalysts with the activation of lattice oxygen

Paraffin, one of the major components of straight-run naphtha, is relatively inert compared with olefin, which poses a difficulty for catalytic cracking of naphtha. The present study proposed introducing lattice oxygen into previous HZSM-5 catalyst system to improve conversion and light olefin selectivity. Vanadium oxide based catalyst was prepared separately as the lattice oxygen provider and then mixed with HZSM-5 catalyst for evaluation in a fixed-bed reactor using n-heptane as model compound. The results demonstrated that conversion of reactant increased from ∼51% to ∼59% by replacing 20% of HZSM-5 catalyst with V 2O 5/Al 2O 3; depending on different location of V 2O 5/Al 2O 3 relative to HZSM-5 catalyst in the reactor, conversion and product distribution varied significantly, while the addition of pure alumina did not have such an effect. Besides, water was formed in liquid products accompanied by reduction of V 5+ during the reaction, as revealed by FT-IR and XRD results, respectively; the oxidized V 5+ seemed to have greater capability in promoting conversion of n-heptane. Therefore, it was concluded that n-heptane could be activated by lattice oxygen provided by oxidized vanadia before further cracking over acidic sites in HZSM-5 catalyst.