Cracking Of Heptane Research Articles

IM-5 zeolite with abundant narrow mesopores and modulated acidity as stable and selective cracking catalyst

High-performance IM-5 was prepared by tetrapropylammonium hydroxide (TPAOH) and NaOH alkaline treatment. The modification of combined alkaline treatment on the pore and acidity were systematically characterized. The 29 Si NMR results indicated that Si(4Si, 0Al) sites were protected by tetrapropylammonium cation (TPA + ) at low TPAOH/(NaOH + TPAOH) molar ratio, while the protection effect extended to some Si(3Si, 1Al) sites at TPAOH/(NaOH + TPAOH) ratio of 75%. And, the amount of strong Brønsted acid sites decreased significantly from 255 μmolg −1 to 119 μmolg −1 under the optimal TPAOH/NaOH alkaline treatment conditions. Compared to NaOH treatment alone, the mesopore volume and external surface area of IM-5 were further increased with TPAOH introduced, meanwhile, the mesopore size was shrunken into the range of 2–10 nm centered at 5 nm. Compared to NaOH treated IM-5 catalyst, the TPAOH/NaOH treated one exhibited higher initial light olefins yield (53.4% vs. 45.2% for n -heptane cracking) and better catalytic stability and regeneration properties. The abundant narrow mesopores contributed into high tolerance ability to coke deposition in IM-5 catalysts, as confirmed by TGA results. • TPAOH/NaOH treatment led to abundant well-spread mesopores in IM-5. • TPAOH/NaOH treatment lowered the amount of strong Brønsted acid sites. • TPA + extended protection effect to framework aluminum at high TPAOH concentration. • TPAOH/NaOH treated IM-5 reached high light olefins yield of 53.4%. • TPAOH/NaOH treated IM-5 kept stable in 5 regeneration cycles.

Synergistic B Al interaction in SBA-15 affording an enhanced activity for the hydro-isomerization of heptane over Pt B Al-SBA-15 catalysts

Abstract Mesoporous M-SBA-15 (M/Si = 1/10) (where M = Al, B or Al B in a ratio 0.5:0.5) were prepared via a known procedure using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as template. Further deposition of platinum on these supports has been achieved by impregnation with an aqueous solution of H2PtCl6. The prepared supports and catalysts were characterized by the adsorption-desorption isotherms of nitrogen at −196 °C, XRD and TEM measurements, and temperature-programmed desorption of ammonia (TPD-NH3). All these solids were investigated for the hydro-isomerization of heptane. In the investigated range of time (24 h) and temperatures (200–300 °C) the supports exhibited no isomerization activity but only a small cracking activity. The addition of platinum to these supports provided activity in this reaction even for a weak acid support as B-SBA-15. However, the presence of both aluminum and boron in a ratio of 0.5 to 0.5 led to a more efficient catalyst. Thus, the Pt Al B-SBA-15 catalyst showed a slightly higher conversion than the Pt Al-SBA-15 one. All the investigated Pt-SBA-15 provided high selectivity for the isomerization to methylhexanes. Dimethylpentanes were also produced but in a different extent, depending on the acidity of the support. Cracking of heptane to C1 C4 molecules accompanied the hydro-isomerization process but in a rather small extent (yields smaller than 5% after 24 h).

High Density Alkyl Diamondoid Fuels Synthesized by Catalytic Cracking of Alkanes in the Presence of Adamantane

Alkyl diamondoid fuel mixtures have been prepared under moderate conditions by AlBr3 catalyzed cracking of nonane and heptane in the presence of adamantane. The fuel mixture prepared with heptane as the alkyl source (HA) contains primarily 1-ethyl-3-methyl adamantane and 1-propyladamantane, while the mixture prepared from nonane (NA) contains primarily C13–C15 alkyl diamondoids. Both fuel mixtures exhibit densities greater than 0.9 g/mL and volumetric net heats of combustion approximately 10 and 6% higher than conventional jet and diesel fuels, respectively. The structural diversity of the fuel blends and presence of multiple branch sites lead to lower viscosities compared to pure alkyl diamondoid fuels. The lower molecular weight blend, HA, exhibits a 40 °C kinematic viscosity of 3.22 mm2 s–1, well within the specification for diesel fuel, and both blends have derived cetane numbers of >42, suggesting that they can be used directly in conventional diesel engines.

Influences of Reaction Temperature and Carrier Gas Flow‐Rate on n‐Heptane Cracking over ZSM‐5 Catalyst Without and With Activation of V2O5/Al2O3

The activation role of V2O5/Al2O3 during the cracking of heptane over ZSM‐5 catalysts has already been confirmed in our previous study. In order to get more details about the alternative reaction pathway contributed by the activation of V2O5/Al2O3, a comparative study of n‐heptane cracking over ZSM‐5 equilibrium catalyst without and with V2O5/Al2O3 introduction was performed at different temperatures and contact time. The results indicated that elevated reaction temperature weakened the role of V2O5/Al2O3 during the reaction process. While the impacts of contact time were not as strong as that of temperature, and the change of relative contribution of different reaction pathways, including thermal reaction, carbonium/carbenium ion cracking, and reaction of the intermediate species because of V2O5/Al2O3 activation, was concluded to be small at varied N2 flow rates.

Thermal Decomposition of Sulfur Compounds and their Role in Coke Formation during Steam Cracking of Heptane

AbstractSulfur‐containing compounds play a key role in many industrial processes. Particularly for the steam cracking process, they have been linked with increased olefin selectivity, CO formation, and coke inhibition. The influence of four different sulfur‐containing additives, methanedithione, (methyldisulfanyl)methane, (methylsulfanyl)methane, and dimethyl sulfoxide, on product selectivity, coke deposition, and CO production during steam cracking of a surrogate light naphtha feed is investigated. The use of online comprehensive 2D gas chromatography with sulfur chemiluminescence detection (GC×GC‐SCD) is the key enabling technology to characterize the sulfur compounds. Steam cracking in a pilot‐plant unit revealed that all studied sulfur compounds are efficient in reducing the CO yield. Simultaneously, they strongly promote coke.

Effect of steaming on acidity and catalytic performance of H-ZSM-5 and P/H-ZSM-5 as naphtha to olefin catalysts

The effect of steaming on the acidity and catalytic performance of H-ZSM-5 zeolites with various Si/Al atomic ratios and P/H-ZSM-5 as naphtha cracking catalysts to produce light olefin were investigated. The acid amount of H-ZSM-5(Si/Al atomic ratio=51) was monotonously decreased with the steaming time at 873K. However, the catalytic activity of H-ZSM-5(51) for heptane cracking was enhanced by the steaming for short times (∼0.5h). The activation energy for H-ZSM-5(51) steamed for 0.5h was lower than that for the parent H-ZSM-5(51). Moreover, the catalytic activity of H-ZSM-5(51) for cracking of cumene, from which the Brønsted acidity can be evaluated, was enhanced by the steaming for a short time of 0.5h. From these results, the stronger Brønsted acid sites might be generated by the steaming for short times, resulting in the enhancement in the catalytic activity for cracking of heptane. The catalytic activity of H-ZSM-5(51) for cracking of heptane considerably decreased after the steaming for long times. On the other hand, only a little decrease in the rate constant for cracking of heptane over H-ZSM-5(200) by the steaming for long times was observed. These findings suggest that the high silica H-ZSM-5 as H-ZSM-5(200) may have a high percentage of aluminum atoms which is highly resistant to the dealumination by the steaming. The catalytic activity for cracking of heptane over P/H-ZSM-5(51) was also enhanced by the steaming for a short time. The P/H-ZSM-5(51) steamed for 10h exhibited a much higher activity than the H-ZSM-5(51) steamed for 10h. These results indicate that the phosphorus impregnation greatly suppresses the dealumination of H-ZSM-5.

Kinetics and modelling of heptane steam-cracking

AbstractThe kinetics and product distribution during the cracking of heptane in the presence of steam were investigated. The experiments were performed in a flow reactor under atmospheric pressure in a temperature range of 680–760°C with a mass ratio of steam to heptane of 3: 1. The overall decomposition of heptane is represented by a first-order reaction with activation energy of 249.1 kJ mol−1 and a frequency factor of 3.13 × 1013 s−1. The reaction products were analysed using gas chromatography, the main product being ethylene. The molecular reaction scheme, which consists of a primary reaction and 24 secondary reactions between primary products, was used for modelling the experimental product yields. The yields of ethylene and hydrogen were in good agreement; however the experimental yields of propylene were higher than the predicted yields.

Ultra-high steaming stability of Cu-ZSM-5 zeolite as naphtha cracking catalyst to produce light olefin

Abstract H-ZSM-5 is an excellent catalyst to produce light olefin in naphtha cracking. But it is difficult to avoid the deactivation by coke formed, so the frequent regeneration of H-ZSM-5 by calcination is necessary. A little steam is generated during the calcination, resulting in the permanent deactivation by dealumination. We found that Cu-ZSM-5 exhibited an ultra-high steaming stability in the presence of oxygen and a comparable activity for heptane cracking in the reductive atmosphere, compared with H-ZSM-5. These results are attributed to a low Bronsted acidity in the presence of oxygen and a high Bronsted acidity in the reductive atmosphere.

Study of the Relationship between Framework Cation Levels of Y Zeolites and Behavior during Calcination, Steaming, and n-Heptane Cracking Processes

The synthesis process and production of forms of the Y zeolite (i.e., NaY, NH4Y, HY, and USY) have been studied in depth, in order to investigate the thermal stability of the Y structure throughout calcination, steaming, and cracking processes. The results indicate that an increase in the cation content within the Y framework during calcination and/or steaming processes led to an increase in the catalyst stability and a reduction in the rate of any associated dehydroxylation reactions. It was also found that the presence of sodium ions hindered the extraction of Al atoms from the crystal lattice structure during the steaming treatment, which minimized partial and/or entire structural collapse at high temperatures. Finally, enhancements in the distribution of the acid sites, and an increase in the activity and selectivity of the produced USY catalysts during n-C7 cracking reactions, have also been observed.

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.

Kinetic Models for the Coke Combustion on Deactivated ZSM-5/MOR Derived from n-Heptane Cracking

The combustion behavior of coked H−ZSM-5/H−mordenite (ZSM-5/MOR) derived from catalytic cracking of n-heptane with and without water steam has been studied by thermogravimetric analysis (TGA). Catalytic cracking under vapor atmosphere with a water−oil ratio of 2 at 650 °C created only one type of coke deposit on the catalyst. On the other hand, two types of coke can be found on the coked catalyst deactivated by catalytic cracking without water steam. These results indicated different combustion kinetic models of different types of coke. A one-coke combustion model for the regeneration of coked catalyst obtained under water steam and a two-coke combustion model for the regeneration of coked catalyst derived without water steam were conducted by using TGA, respectively. Finally, the relationship between the C/H ratios and activation energies in the combustion kinetic models were investigated by ultimate analysis.

Effect of triethylamine on the cracking of heptane under a supercritical condition and the kinetic study on the cracking of heptane

The cracking of heptane (HEP) and the cracking of the binary system of triethylamine/heptane (TEA/HEP) in a continuous tubular reactor at 3.5 MPa are studied, to test the effect of triethylamine on the pyrolysis of heptane under a supercritical condition. It is found that triehtylamine can promote the cracking of heptane under the supercritical condition, and more effective in lower temperatures. The selectivity of ethane, ethylene, propylene, and C4 by pyrolysis of TEA/HEP is notably higher than that by HEP in a low temperature, while the difference of the selectivity is weak when in a high temperature. The kinetic character of the cracking of heptane under the supercritical condition is studied, through which the activation energy and the pre-exponential factor are obtained by pseudo-isothermal method with a quick convergence process.

Measurements of number and strength distribution of Brønsted and Lewis acid sites on sulfated zirconia by ammonia IRMS–TPD method

Abstract The ammonia IRMS–TPD (infrared-mass spectroscopy/temperature-programmed desorption) method was applied to sulfated zirconia in order to measure the acidic properties [number, strength and type (Bronsted or Lewis) of acid site]. Because the TPD profile was broad, the acid strength distribution was calculated by means of a simulation method on the basis of theoretical equations. The Bronsted acid strength distribution changed according to the calcination temperature of zirconia support. The presence of strong Bronsted acid site on samples prepared by an equilibrium adsorption of H2SO4 was in agreement with the high catalytic activity of these samples for reaction (mainly cracking) of heptane.

Tributylamine as an initiator for cracking of heptane

Tributylamine (TBA) was found to be effective in promoting the cracking of heptane. The conversion of heptane and the yield of gas product are both distinctly accelerated. The selectivity of propylene is remarkably promoted compared with that by cracking pure heptane at 550 °C, while at the higher temperature of 600 °C, the selectivity of all gas products changes very little. The cause to this effect could be that the butyl radical and its derivatives derived from TBA capture hydrogen from the heptane.

Theoretical study on the reaction route for the major liquid product from pyrolysis of triethylamine

Triethylamine can work as an initiator for promoting the cracking of heptane, and the mechanism study helps to understand the initiating effect. While, the components in liquid product can hardly be purely separated for further analysis. In this paper, two compounds are found of well matching a same mass spectrum, so the liquid product by the pyrolysis of triethylamine is further determined by Gaussian 98. It is found that N, N-diethyl radical is the most stable intermediate during the homologous pyrolysis process. The energies of two transition-states of two possible reaction routes from N, N-diethyl radical are compared, through which the reaction route is clarified and the liquid product is identified as N-ethylidene-ethanamine.

Triethylamine as an initiator for cracking of heptane

Triethylamine was found to be effective in promoting the cracking of heptane at the temperature of 550–650 °C. The experimental yields of ethylene and propylene are more than twice as high as the calculated values on hypothesis of no interaction between triethylamine and heptane, when the mass fraction reaches 6% at the most notable temperature of 550 °C. The accelerating mechanism is studied by gas chromatography–mass spectrometry (GC–MS) and it shows that the accelerating effect is mainly attributed to the initiative release of CH 3CH 2 from triethylamine by the scission of the C–N bond.

Craqueamento térmico de alcanos: uma aula prática de química orgânica para a graduação

In this work we describe an experiment for the thermal cracking of octane and heptane and the qualitative analyses of the products using the Baeyer test for unsaturated compounds and gas chromatographic analyses. The experiment is very simple and requires one period of two hours and is suitable for undergraduate organic chemistry experimental courses.

Predict Yields from a Kinetic Model of Catalytic Cracking Process at Any Temperature

It has been observed that yields of gasoline and other petroleum fraction in a catalytic cracking process depends significantly upon the reaction temperature besides on other operating conditions. In this work, first the model was developed with the help of literature data with out considering the temperature effect. The important optimum parameters like relative rate constant (K 1), rate of coke deactivation or decay constants (Kd ), order of reaction (m) etc. over suitable catalysts of cracking process were obtained using suitable numerical analysis techniques. On comparing the error based on the least square criteria, it has been noticed that the results from the first model show about 4% improvement in predicted error against literature results on cracking of normal Heptane [Corma, A., Wojciechowsky, B. W. ([1983]). Recent work on the fundamentals of catalytic cracking. American Chemical Society Reprints, Div. Chem. 28(3):861–874.] for fifteen data points. In the second step the software was modified to simulate the effect of reaction temperature by using two sets of laboratory data for the reaction of normal Hexadecane over ReY-Zeolite, a commercial cracking catalysts at two different reaction temperatures of 400 and 450°C respectively. Validation of modified software has been checked with the above system at 500°C and found that the predictions are quite close to experimental values. Such analytical model will be useful for finding optimum operating conditions to achieve maximum yields of potential products on cracking of a given feed without resource to conducting large number of experiments.

An attempt to predict the optimum zeolite-based catalyst for selective cracking of naphtha-range hydrocarbons to light olefins

Theoretical calculations were performed in order to determine, a priori, which in a range of small-to-medium pore zeolites would be the most effective at suppressing hydride transfer reactions by estimating the magnitude of steric hindrance. Steric hindrance was estimated as the difference between the enthalpies of adsorption of the transition-state complex and those of the two reacting hydrocarbons, calculated using the configurational-bias Monte Carlo (CBMC) method. As the concentration of adsorbed heptane also affects reaction rates adsorption equilibria were also calculated using this same theory. Heptane cracking experiments were then performed using acidic catalysts of this same series of zeolites to test the validity of these predictions. Reaction products were sampled during the first seconds on stream and extrapolation was made to zero time on stream in order to determine the initial catalytic activities and product selectivities in the absence of deactivation. Turnover frequency (TOF) decreased with decreasing pore diameter in agreement with predicted heptane adsorption equilibria. Hydride transfer was predicted to be most restricted in FER and TON, however, lower heptane adsorption capacities suggested that MFI would be the best compromise in terms of both high activity and selectivity. Although differences in paraffin product differences were observed that were consistent with an increasing degree of protolytic cracking with decreasing pore size, no discernible pattern was observed in olefin product distributions (ethylene–butenes).

Reaction Mechanisms of Isomerization and Cracking of Heptane on Pd/H-Beta Zeolite

The vapor-phase isomerization and cracking of heptane on H-Beta zeolites loaded with various amounts of Pd metal has been studied at a temperature of 505 K and at a total pressure of 0.3 MPa. The cracking of heptane is interpreted as a combination of classic bifunctional hydrocracking and dimerization cracking. The isomerization of heptane proceeds through the classic bifunctional mechanism and a second mechanism involving dimerization cracking. The contribution of the different mechanisms to the isomerization and cracking is derived from the formation of specific reaction products. The contribution of the different mechanisms is dependent on the Pd content of the zeolite.