HZSM-5 zeolites undergoing the high-temperature process for boosting the bimolecular reaction in n-heptane catalytic cracking

High-temperature treatment is key to the preparation of zeolite catalysts.Herein,the effects of hightemperature treatment on the property and performance of HZSM-5 zeolites were studied in this work.X-Ray diffraction,N2physisorption,27Al magic angle spinning nuclear magnetic resonance(MAS NMR),and temperature-programmed desorption of ammonia results indicated that the hightemperature treatment at 650℃ hardly affected the inherent crystal and texture of HZSM-5zeolites but facilitated the conversion of framework Al to extra-framework Al,reducing the acid site and enhancing the acid strength.Moreover,the high-temperature treatment improved the performance of HZSM-5 zeolites in n-heptane catalytic cracking,promoting the conversion and light olefins yield while inhibiting coke formation.Based on the kinetic and mechanism analysis,the improvement of HZSM-5 performance caused by high-temperature treatment has been attributed to the formation of extra-framework Al,which enhanced the acid strength,facilitated the bimolecular reaction,and promoted the entropy change to overcome a higher energy barrier in n-heptane catalytic cracking.

Experiment and modeling of coke formation and catalyst deactivation in n-heptane catalytic cracking over HZSM-5 zeolites

Since paraffins catalytic cracking was of significant importance to light olefins and aromatics production,this work was intended to gain insights into the feature and model of coke formation and catalyst deactivation in n-heptane catalytic cracking over HZSM-5 zeolites. 18 tests of n-heptane catalytic cracking were designed and carried out over HZSM-5 zeolites in a wide range of operating conditions. A particular attention was paid to the measurement of the conversion, product distribution, coke content, and the porosity and acidity of the fresh and spent HZSM-5 zeolites. It was found that alkene and aromatic promoted coke formation, and it reduced the pore volume and acid site of HZSM-5 zeolites, tailoring its performance in n-heptane catalytic cracking. The specific relationship between HZSM-5 zeolites, n-heptane conversion, product distribution and coke formation was quantitively characterized by the exponential and linear function. Based on the reaction network, the coupled scheme of coke formation and catalyst deactivation were specified for n-heptane catalytic cracking. The dual-model was proposed for the process simulation of n-heptane catalytic cracking over HZSM-5 zeolites. It predicted not only the conversion and product distribution but also coke content with the acceptable errors.

Effect of particle size of single-crystalline hierarchical ZSM-5 on its surface mass transfer in n-heptane catalytic cracking

Single-crystalline hierarchical ZSM-5 zeolites with different particle sizes(namely 100,140,and 200 nm)were successfully prepared by adjusting the amount of tetrapropylammonium hydroxide(TPAOH),and investigated in n-heptane catalytic cracking reaction.Diffusional measurements by zero-length column(ZLC)method showed that the apparent diffusivities of n-heptane decreased with the reduction of particle size,indicating the existence of surface barriers.Moreover,with the decrease of particle size,the additional diffusion path length increased,which meant the influence of surface barriers became more apparent.Despite the change of surface barriers,the intracrystalline diffusion still dominated the overall diffusion.Catalytic performance showed that the zeolite with smaller particle size had better stability.

利用n-heptane详细模型对水乳化柴油燃烧的化学动力学研究

以4100QBZL-2型直喷柴油机为模拟对象,采用化学动力学计算软件CHEMKIN与LLNL的n-heptane详细氧化模型为基础,对柴油机燃用纯柴油,10%、20%、30%的水乳化柴油进行化学动力学模拟。数值模拟结果表明:水乳化柴油带来的滞燃期延长、着火滞后等现象,是乳化燃料中的水分在缸内的物理现象引起的。从纯化学动力学方面来看,掺入一定的水分可以促进H、O、OH、HO2等自由基在低温燃烧(LTC)阶段的生成,使得着火提前。通过敏感性分析可知,掺入的水分会对n-heptane氧LTC时期过氧烷基的异构化过程及过氧化氢酮的分解都会产生促进作用,从而导致n-heptane的快速分解及氧化。

A Promising MoO_x-based Catalyst for n-Heptane Isomerization

The SiO2 and g-Al2O3 supported MoOx catalyst and a MoOx-SiO2 catalyst have been studied in a conventional fixed-bed flow reactor for n-alkanes isomerization. It is shown that the MoOx-SiO2 catalyst with SiO2 framework, in which the bulk MoOx phase is large enough to form typical mesoporous structure, is promising in terms of its advantages of both improved mechanical strength and high catalytic properties over the supported MoOx and bulk MoOx catalyst.

Effect of iridium loading on HZSM-5 for isomerization of n-heptane

The effect of iridium loading on the properties and catalytic isomerization of n-heptane over Ir-HZSM-5 is studied. Ir-HZSM-5 was prepared by impregnation method and subjected to isomerization process in the presence of flowing hydrogen gas. XRD and BET studies show that the presence of iridium stabilizes the crystalline structure of HZSM-5, leading to more ordered framework structure and larger surface area. TGA and FTIR results substantiate that iridium species interacts with OH group on the surface of HZSM-5. Pyridine FT-IR study verifies the interaction between iridium and surface OH group slightly increased the Bro¨nsted and Lewis acid sites without changing the lattice structure of HZSM-5. The presence of iridium and the increase of strong Lewis acid sites on HZSM-5 were found to bring an increase about 4.1%, 33.2% and 11.8% in conversion, selectivity and yield of n-heptane isomerization, respectively.

An asymmetric membrane of polyimide 6FDA-BDAF and its pervaporation desulfurization for n-heptane/thiophene mixtures

Polyimide（PI） is a type of important membrane material. A soluble polymer was synthesized from 4,4′-（hexafluoroisopropylidene） diphthalic anhydride（6FDA） and 2,2-bis[4-（4-aminophenoxy） phenyl] hexafluoropropane（BDAF） by the two-step polymerization method. The polymer was proved to be polyimide 6FDA-BDAF by the Fourier transform infrared（FT-IR）, the 1H-NMR and ^（19）F-NMR spectra. An asymmetric membrane was prepared with the synthesized polyimide 6FDA-BDAF, it was porous in the 50 μm height bulk and dense in a 3–5 μm height surface. The membrane was used to separate n-heptane/thiophene mixtures by pervaporation with sulfur（S） contents from 50 to 900 μg g^（–1）. The total flux was enlarged from 7.96 to 37.61 kg m^（–2） h^（–1） with temperature increasing from 50 to 90°C. The membrane＇s enrichments factor for thiophene were about 3.13 and dependent on the experimental conditions. The experimental results demonstrated that polyimide 6FDA-BDAF would be a potential membrane material for desulfurization and controlled release of the S-containing fertilizer.

SOLUBILITIES OF CARBON DIOXIDE IN MIXTURES OF n-DECANE-n-HEXADECANE AND n-HEPTANE-TOLUENE

Solubilities of CO2 in binary mixtures of n-decane-n-hexadecane and n-heptane-toluenewere measured in a glass apparatus by a synthetic method.Henry’s constants at several temperaturesand solvent compositions were reported.While the Henry’s constants of CO2 in mixtures of decaneand hexadecane can be satisfactorily predicted by a simple linear interpolation,prediction of Henry’sconstants for CO2 in mixtures of heptane and toluene requires excess Gibbs energy of the solvent mix-tures.The standard thermodynamic functions of solution（ΔH0,ΔG0,and ΔS0）were reported.

Numerical study of n-heptane/benzene separation by thermal diffusion column

In this article,numerical simulations are performed to investigate the performance of the thermal diffusion column for the separation of n-heptane/benzene mixture.The present work tried to optimize column by analyzing significant parameters such as feed flow rate,temperature and cut.In order to obtain the hydrodynamic and temperature and mass distribution inside thermal diffusion column,computational fluid dynamic(CFD) method is applied to solve the Navier-Stocks equations.Numerical simulations are conducted to study the main parameters in both stationary and time-dependent conditions.By using the separation work unit as a function of cut,the optimal cut for maximum SWU occurs within a limited range of 0.47-0.5 for feed rate between 0.5 and 4 g min^-1.Our findings reveal that the optimum feed rate in the range of optimum cut is about 1 g min^-1.In transient study,results show that the best cut for reaching to steady-state condition is θ=0.5.

n-Heptane Isomerization over the Shaped Catalyst Pt/WO_(3)- ZrO_(2) and the Role of the Pseudo-Boehmite Binder

The present paper reports new results regarding the addition of pseudo-boehmite as a binder during the synthesis of shaped Pt/WO_(3)-ZrO_(2)-Al_(2)O_(3) (PtWZA) catalysts. Binder shaping can noticeably influence not only the structure and acidity of catalyst and improve its catalytic performance with regard to n-heptane isomerization, but the mechanical strength of the catalyst. A suitable binder content can improve the isomerization activity or selectivity by changing the acidity of PtWZA. The influence of the binder content depends on the WO_(3) content of the catalyst. PtWZA catalysts that contain 5%-15% binder on a dry basis exhibit favorable isomerization performance that depends on WO_(3) content. Suitable catalysts include Pt20WZ5A and Pt30WZ15A, which provide conversions of approximately 80%-90% and a selectivity of 90%. These new findings enrich researcher knowledge of the effect of the binder on the catalyst shaping process and are useful in the production of industrial catalysts.

A Novel MIL-101(Cr)Acidified by Silicotungstic Acid and Its Catalytic Performance for Isomerization of n-Heptane

The 0.4%Pt/xSTA-MIL-101(Cr)metal-acid bifunctional catalysts were prepared by impregnation using STA-MIL-101(Cr)as the support.The synthesized samples were verified to exhibit a typical octahedral structure of MIL-101(Cr)and the pore structure was arranged orderly.The specific surface area of the samples was extremely high and the samples were made of micro-mesoporous composite materials.Silicotungstic acid could retain its Keggin structure in the 0.4%Pt/xSTA-MIL-101(Cr)samples and the catalyst possessed moderately strong Brønsted acid sites.Besides,the dispersion of Pt particles in MIL-101(Cr)was relatively high.n-Heptane isomerization was first used as a probe to test the novel 0.4%Pt/xSTA-MIL-10(Cr)catalyst.Compared with the conventional silicate catalysts,the catalytic performance of 0.4%Pt/30%STA-MIL-101(Cr)was significantly improved with a n-heptane conversion of 58.93%and an iso-heptane selectivity of 95.68%,respectively,under conditions covering a reaction time of 2 h and a reaction temperature of 260°C.The catalyst could still maintain a relatively high catalytic performance after a reaction time of 5 h.Compared with the non-noble metal catalyst,the catalytic efficiency of 0.4%Pt/30%STA-MIL-101(Cr)is relatively high.The mechanism model of n-heptane isomerization over 0.4%Pt/xSTA-MIL-101(Cr)catalyst was established.

Preparation and Property of Ni/TiO₂-SAPO-11 Catalyst for N-Heptane Isomerization

For enhancing the activity of Ni/TiO2-SAPO-11 catalyst, SAPO-11, the precursor was prepared by hydrothermal crystallization, and TiO2-SAPO-11 complex carrier was prepared by sol-gel method, then Ni/TiO2-SAPO-11 was produced by the final product. The catalytic performance of Ni/TiO2-SAPO-11 was studied in n-heptane isomerization, and the impact of catalyst preparation conditions on n-heptane isomerization was discussed in detail. The results showed that, with 20% of TiO2 composition, 2% of Ni capacity percentage and calcined temperature at 500°C, conversion of n-heptane and isomerization selectivity was up to 40.94% and 88.97% respectively.

δ-MnO_(2) decorated layered double oxides in-situ grown on nickel foam towards electrothermal catalysis of n-heptane

Energy-saving and efficient monolithic catalysts are hotspots of catalytic purification of industrial gaseous pollutants.Here,we have developed an electrothermal catalytic mode,in which the ignition temperature required for the reaction is provided by Joule heat generated when the current flows through the catalyst.In this paper,Mn/NiAl/NF,Mn/NiFe/NF and Mn/NF metal-based monolithic catalysts were prepared using nickel foam (NF) as the carrier for thermal and electrothermal catalysis of n-heptane.The results indicated that Mn-based monolithic catalysts exhibit high activity in thermal and electrothermal catalysis.Mn/NiFe/NF achieve conversion of n-heptane more than 99%in electrothermal catalysis under a direct-current (DC) power of 6 W,and energy-saving is 54% compared with thermal catalysis.In addition,the results indicated that the introduction of NiAl (or NiFe) greatly enhanced the catalytic activity of Mn/NF,which attributed to the higher specific surface area,Mn3+/Mn4+,Ni3+/Ni^(2+),adsorbed oxygen species (Oads)/lattice oxygen species (Olatt),redox performance of the catalyst.Electrothermal catalytic activity was significantly higher than thermal catalytic activity before complete conversion,which may be related to electronic effects.Besides,Mn/NiFe/NF has good cyclic and long-term stability in electrothermal catalysis.This paper provided a theoretical basis for applying electrothermal catalysis in the field of VOCs elimination.

Influences of cerium on structure and catalytic performance of n-heptane hydroisomerization of Ni-HPW/MCM-48

By means of X-ray diffraction（XRD）, N2 adsorption-desorption, Fourier transform infrared spectroscopy（FT-IR）, scanning electron microscopy（SEM）, NH3-temperature（NH3-TPD）, Py-infrared（Py-IR） and thermogravimetry-differential scanning calorimetry（TG/DTA） techniques, the influences of Ce on the structure, acidity, stability and hydroisomerization performance of Ni-HPW/MCM-48 and Ni-HPW/Ce-MCM-48 catalysts were studied. The results showed that introduction of appropriate content of Ce into MCM-48 could improve the crystallinity, acidity and stability of mesoporous silica. The acidity and stability of the Ni-HPW/Ce-MCM-48 catalyst was also increased. Besides, the catalytic performance of the Ni-HPW/Ce-MCM-48 catalyst for n-heptane hydroisomerization was promoted. The conversion and selectivity of the Ni-HPW/Ce-MCM-48 catalyst reached 41% and 91% respectively at the preparation conditions of 4 wt.% Ni, 20 wt.% HPW, 0.03 Ce/Si molar ratio.

Hydroisomerization of n-heptane over bimetal-bearing H_3PW_(12)O_(40) catalysts supported on dealuminated USY zeolite

The bimetal-bearing (CePt or LaPt) 12-tungstophosphoric acid (H3PW12O40 (PW)) catalysts supported on dealuminated USY zeolite (DUSY) were prepared by impregnation and characterized by XRD, BET, IR, and H2-chemisorption. Their catalytic activities were tested in the hydroisomerization of n-heptane with a continuous atmospheric fixed-bed reactor. After the steam treatment combined with the acid leaching, as well as the supporting with PW and the bimetals, the DUSY support retains the Y zeolite porosity and the PW well keeps its Keggin structure in catalysts. The doping of Ce into the catalysts enhances the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Ce or La, especially Ce, exhibit much higher catalytic activity and selectivity than the catalysts without dopants at lowered reaction temperatures. At the optimal reaction conditions, i.e., the reaction temperature of 250℃ and WHSV of 1.4 h1, the catalyst with a Pt loading of 0.4%, PW loading of 10% and a molar ratio of Ce to Pt of 15:1 shows a conversion of n-heptane of 70.3% with a high selectivity for isomerization products of 94.1%.

Effect of 2,5-dimethylfuran addition on ignition delay times of n-heptane at high temperatures

The shock tube autoignition of 2,5-dimethylfuran (DMF)/n-heptane blends (DMF)/n-100%, by mole fraction) with equivalence ratios of 0.5, 1.0, and 2.0 over the temperature range of 1200-1800 K and pressures of 2.0 atm and 10.0 atm were investigated. A detailed blend chemical kinetic model resulting from the merging of validated kinetic models for the components of the fuel blends was developed. The experimental observations indicate that the ignition delay times nonlinearly increase with an increase in the DMF addition level. Chemical kinetic analysis including radical pool analysis and flux analysis were conducted to explain the DMF addition effects. The kinetic analysis shows that at lower DMF blending levels, the two fuels have negligible impacts on the consumption pathways of each other.As the DMF addition increases to relatively higher levels, the consumption path of n-heptane is significantly changed due to the competition of small radicals, which primarily leads to the nonlinear increase in the ignition delay times of DMF/n-heptane blends.

Applicability of high dimensional model representation correlations for ignition delay times of n-heptane/air mixtures

It is difficult to predict the ignition delay times for fuels with the two-stage ignition tendency because of the existence of the nonlinear negative temperature coefficient (NTC) phenomenon at low temperature regimes. In this paper, the random sampling-high dimen-sional model representation (RS-HDMR) methods were employed to predict the ignition delay times of n-heptane/ air mixtures, which exhibits the NTC phenomenon, over a range of initial conditions. A detailed n-heptane chemical mechanism was used to calculate the fuel ignition delay times in the adiabatic constant-pressure system, and two HDMR correlations, the global correlation and the stepwise correlations, were then constructed. Besides, the ignition delay times predicted by both types of correlations were validated against those calculated using the detailed chemical mechanism. The results showed that both correlations had a satisfactory prediction accuracy in general for the ignition delay times of the n-heptane/air mixtures and the stepwise correlations exhibited a better performance than the global correlation in each subdo-main. Therefore, it is concluded that HDMR correlations are capable of predicting the ignition delay times for fuels with two-stage ignition behaviors at low-to-intermediate temperature conditions.

Mechanism of Methane Addition Affects the Ignition Process of n-heptane under Dual Fuel Engine-Like Conditions

For saving energy and protecting the environment,natural gas has been widely used in internal combustion engines,which makes the study on the ignition characteristics of natural gas/diesel mixtures important.In this work,the effects of trace methane addition on the ignition delay of n-heptane/air mixtures are numerically studied using a detailed n-heptane mechanism under marine engine-like conditions.The simulations are carried out based on the software CHEMKIN-PRO 18.0 with a closed homogeneous reactor.Results show that the prolonged ignition delay times(IDs)of n-heptane/air mixtures are observed over the whole initial temperature range after methane is added,and the increment of IDs in the negative temperature coefficient(NTC)region is significantly higher than that in high temperature region.The sensitivity analysis indicates that both inhibition and promotion effects of important elementary reactions on n-heptane oxidation are weakened because of methane addition.However,the weakening influence on the promoting effect is more prominent.In addition,the inhibition effect of some elementary reactions that are related to the methane oxidation is enhanced.Thus,the IDs of n-heptane/air mixture are prolonged.The analyses of reaction rate of production(ROP)show that the both the production and consumption rates of key radicals decrease significantly in NTC region after methane is added,but it is negligible in the high temperature region.The study can extend the theoretical basis of ignition characteristics of methane/n-heptane blends under elevated temperatures and pressures.

Numerical simulation of diesel combustion based on n-heptane and toluene

Considering the self-ignition characteristic and C/H ratio,n-heptane and toluene(6:4 by mass)are chosen to constitute diesel surrogate fuel,and a reduced oxidation mechanism was developed.This mechanism was firstly validated by the combustion of diesel fuel in different oxygen concentrations within a constant volume vessel by high-speed photography.The simulated flame temperature distribution reproduces the diesel combustion process quite well.For further validation,combustion in real diesel engine was also investigated numerically and experimentally using a light duty diesel and a marine diesel.The calculated pressure curves in different operation conditions fit the measured data reasonably well.The oxidation mechanism could reproduce the main characteristics including combustion phase and NOx emission of diesel combustion in different cases.

Effects of Magnetic Fields on Morphology and Nanostructure Evolution of Incipient Soot Particles from n-heptane/2,5-dimethylfuran Inverse Diffusion Flames

Differences of the morphology and nanostructure evolution of incipient soot particles generated in n-heptane/2,5-dimethylfuran(DMF)inverse diffusion flames(IDFs)with/without magnetic fields were investigated.Utilizing a high resolution transmission electron spectroscopy,the morphology and nanostructures of soot sampled from spatial locations at different heights in IDFs were analyzed.The graphitization and the oxidation reactivity of soot were tested by an X-ray diffraction and a thermogravimetric analyzer,respectively.Results demonstrated that the magnetic force on paramagnetic species,such as oxygen molecules,can modify the soot formation and oxidation.More incipient soot particles with larger diameters appeared in chains or branches or tufted forms on the flame wing region and the higher position than that on the flame centerline region and the lower position.With magnetic fields,greater amounts of clustered soot particles displayed more crowded distribution and larger diameters.Soot particles with typical structures of the core-shell were promoted to own more orderly bordered lamellae with longer fringe length and smaller fringe tortuosity by the magnetic force acting on oxygen at the same sample position.These modifications resulted in relatively larger diffraction angle of the peak,higher graphitization degree and slightly lower oxidation reactivity of soot.