Heptane Isomers Research Articles

Porous Alumina-Supported Tungstated Zirconia Catalysts for Heptane Isomerization

Porous Alumina-Supported Tungstated Zirconia Catalysts for Heptane Isomerization

Tungstated zirconia catalysts with a porous support for heptane isomerization

Tungstated zirconia catalysts with a porous support for heptane isomerization

Preparation of Pd/Ce(F)-MCM-48 catalysts and their catalytic performance of n-heptane isomerization

Abstract Ce and F were added to MCM-48 molecular sieve by hydrothermal synthesis, and Pd/Ce(F)-MCM-48 metal acid bifunctional catalysts were prepared by impregnation method. The physical and chemical properties of Ce(F)-MCM-48 and Pd/Ce(F)-MCM-48 were characterized by X-ray diffraction, scanning electron microscope, NH3 temperature programmed desorption instrument, Fourier infrared spectrometer, and X-ray photoelectronic spectrometer characterization methods. The results showed that when the molar ratio of the raw materials was n(Ce):n(TEOS) = 0.02 and n(NaF):n(TEOS) = 0.10, Ce(F)-MCM-48-0.10 molecular sieve had a high degree of order and large specific surface area and pore volume, the total acid content increased, and the acid strength also increased. And it had an acidic center and generated certain oxygen vacancies. The catalyst prepared after Pd impregnation had good dispersibility. 0.4% Pd/Ce(F)-MCM-48-0.10 catalyst still maintained the crystalline phase of MCM-48 molecular sieve. A micro-reaction device was used to examine the catalytic performance of n-heptane isomerization of Pd/Ce(F)-MCM-48-0.10 catalysts. When the hydrogen flow rate was 30 mL·min−1, reduction temperature was 300°C, reduction time was 4 h, weight hourly space velocity was 7.6 h−1, and reaction temperature was 280°C, 0.4% Pd/Ce(F)-MCM-48-0.10 catalyst was used in the heptane isomerization reaction, where the conversion of n-heptane was 67.3% and the selectivity of isoheptane was 96.5%.

Simultaneous Isomerization of Hexane and Heptane in the Presence of Pt-Containing Tungstated Zirconia Catalysts

Isomerization of heptane and hexane and their mixtures in the presence of Pt/WO3-ZrO2 catalysts with the tungsten oxide content of 10–35 wt.% was studied. The best characteristics of isomerization of the С6–С7 alkanes mixture were observed on the catalysts with the WO3 content of 15–20 wt.%. According to ammonia thermodesorption data, the number of acid sites typically increases in this range of tungsten oxide content; according to IR spectroscopy of adsorbed CO, this occurs mostly with an increase in the number of Broensted acid sites.

Kinetics of zeolite-catalyzed heptane hydroisomerization and hydrocracking with CBMC-modeled adsorption terms: Zeolite Beta as a large pore base case

A reactor model that deconvolutes thermodynamics of adsorption of hydrocarbon in the pores of zeolite Beta, obtained by Configurational-bias Monte Carlo simulations, from intrinsic, intraporous kinetics of hydroisomerization and hydrocracking reactions, provides a good quantitative description of all significant reactions in the kinetic network for interconversion and cracking of different heptane isomers. Activation enthalpies obtained for intraporous reactions follow the expected order according to the carbenium ion formalism:methyl shift< ethyl shift < isom(B) ∼ crack(B2) < crack(B1) < crack(C) ∼ crack(D) < crack(E)and apparently within each isomerization class, in terms of carbenium ions formally involved:sec → tert < sec → sec ∼ tert → tert < tert → sec.except for the ethyl shift reaction forming 3-ethylpentane. Cracking happens primarily through 2,4-dimethylpentane (type B2), regardless of the initial reactant. The model can be subsequently used to separate the effect of pore structure on selective adsorption and on intraporous reaction kinetics. Zeolite Beta will serve as a base case for a comparison of different zeolite structures.

Effect of hydrogen reduction and palladium promotion of tungstate-modified zirconia on isomerization of heptane

The activity of Pd/WO3-ZrO2 catalysts in the reaction of heptane isomerization is determined by a complex of acid sites, primarily by the presence of LAS on the catalysts surface formed by the inclusion of W5+ atoms in their composition. This type of acid sites ensures high heptane conversion and acceptable selectivity in the formation of heptane isomers. The contribution of these acid sites to the activity of catalysts can be optimized at the stages of high-temperature activation in a hydrogen flow. The optimal temperature conditions for H2-activation should be chosen in the average temperature range of 200–300 °С, sufficient to achieve a fraction of W5+ atoms on the catalyst surface of ca. 35% (at. W5+/at. W6+). The second group includes Lewis acid sites, which are formed upon the introduction of palladium into the composition of the tungstated zirconia catalyst. The optimal loading of Pd is ca. 0.1 wt.%; above this amount, the acid sites are covered with dispersed palladium, which leads to a decrease in the total acidity of the catalyst. Stabilization of medium strength acid sites on the catalysts surface after the addition of Pd to the catalyst ensures the heptane isomerization reaction in hydrogen atmosphere at a moderate temperature of 200 °C with a high selectivity of 91.1–91.7%.

Statistical Mechanic and Phenomenological Approaches to Isomeric Effects in Thermodiffusion.

We present a model that explains variance in the thermodiffusion of hydrocarbon isomers in binary liquid mixtures. The model relies on material transport equations for binary nonisothermal liquid systems that were derived through a nonequilibrium thermodynamic approach in a previous work, coupled with one of two methods: (i) use of equilibrium chemical potentials for each component under conditions of constant pressure, derived using statistical mechanics or (ii) use of the temperature derivative of chemical potential expressed phenomenologically as molecular entropy. The model is evaluated using Soret coefficients (ST) measured in binary solutions of heptane isomers in benzene. The statistical mechanic approach yields moderately acceptable agreement with experimental data. The phenomenological approach, which relies on both measured and calculated values of molecular entropy from the literature, yields values of ST centered around the experimental data, with the scatter likely due to poor precision in the measured or calculated values of entropy. For the latter case, we identify several methods for calculating entropy that yield good agreement with experimental data.

Volatile organic compounds emission in the rubber products manufacturing processes

Volatile organic compounds (VOCs) emission from rubber products manufacture processes, mixing, shaping and vulcanization were investigated in four rubber products factories in China. The source emission air was passively sampled by pre-vacuumized stainless steel canister and analyzed by gas chromatography-mass spectrometry-flame ionization detection (GC/MS-FID). The species profile of 107 VOCs in the emission processes were obtained. We calculated the photochemical ozone formation potential (OFP) and carcinogenic risk (CR) of the VOCs for each manufacture process. The results showed that mixing process mainly released dichloromethane (14.53%), carbon disulfide (CS2) (6.88%), styrene (5.72%), 4-methyl-2-pentanone (5.22%) and naphthalene (3.69%) for solvents used and raw rubber degradation in the process. The C6–C8 alkanes, especially heptane and isomers of heptane (44.71%), were dominated in shaping process. The major species released from vulcanization process were carbon disulfide (29.72%), naphthalene (8.17%), acetone (7.73%) and dichloromethane (4.26%). VOCs emitted from vulcanization process had the highest OFP, which contributed by naphthalene, m/p-xylene, o-xylene and carbon disulfide. VOCs emission from mixing process had the highest CR, and 1,2-dibromoethane, 1,2-dichlorethane and 1,3-butadiene were the main contributors to CR. We also estimated the total VOCs emissions into the atmosphere from tires manufacturing in China, which were 7.58 × 105 t in 2018 and contributed about 9% of total industry processes VOCs emissions.

An Enhanced Non-Equilibrium Molecular Dynamics Algorithm to Simulate the Soret Coefficient in Heptane/Benzene Mixtures

In this work, the accuracy of the Soret effect was investigated at the situation of T = 303.15 K and P = 1.0 atm. The eHEX (enhanced heat exchange) algorithm and the TraPPE-UA force field were applied to simulate this thermal diffusion behavior. The equimolar mixtures of heptane isomers (n-heptane, 2-methylhexane, 3-methylhexane and 2, 3-dimethylpentane) and benzene were chosen to be the research fluids. The Soret coefficients were calculated to compare with the experimental data and other NEMD simulated results. The results showed great agreement with experimental data and a better accuracy compared to other NEMD simulated results. Moreover, the results shows that more branches may decrease the heat affinity of the component and increase the relaxation time of the thermal diffusion behavior.

Rank of a matrix of block graphs

AbstractThe block graphs are good models in many real‐world applications, such as molecular graph model for Polymers and windmill networks. A block graph is a graph in which every block is a complete graph. In this paper, we first prove that, the entries of distance matrix of block graph satisfy the famous () and we define an matrix and index inspired by the Wiener index . We find that, if the block graph is a tree or each of its blocks is a triangle, then and it is independent of the structure of block graphs . Finally, we obtain the index, Wiener index and Wiener polarity index of isomers of heptane, respectively.

The effect of the tungsten oxide concentration in Pt/WO3-ZrO2 catalysts on hydroisomerization of the heptane-benzene mixture

The effect of the tungsten oxide content in Pt/WO3-ZrO2 catalysts over the range of 10–35 wt.% on hydroisomerization of the heptanebenzene mixture (80/20, wt.%) was studied. The catalysts with the WO3 content of 15–25 wt.% were shown to have the highest fraction of the tetragonal zirconia phase (t-ZrO2, 87–96%), which allows achieving the highest yield of the sum of heptane isomers, particularly high-octane di- and trimethyl substituted isomers (DTMS), the yield of which reaches 69.4–76.7 and 24.5–27.9 wt.%, respectively. In the presence of such catalysts, the yield of methylcyclopentane is 52.1–61.3 wt.% at the 72.6–90.9 % selectivity of cyclohexane isomerization to methylcyclopentane.

Non-Equilibrium Molecular Dynamics Study of the Influence of Branching on the Soret Coefficient of Binary Mixtures of Heptane Isomers

Abstract Equimolar mixtures composed of isomers were firstly used to investigate the molecular branching effect on thermal diffusion behavior, which was not disturbed by factors of molecular mass and composition in this work. Eight heptane isomers, including n-heptane, 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane and 3-ethylpentane, were chosen as the researched mixtures. A non-equilibrium molecular dynamics (NEMD) simulation with enhanced heat exchange (eHEX) algorithm was applied to calculate the Soret coefficient at T = 303.15 T=303.15 K and P = 1.0 atm P=1.0\hspace{0.1667em}\text{atm} . An empirical correlation based on an acentric factor was proposed and its calculation coincides with the simulated results, which showed the validity of the NEMD simulation. It is demonstrated that the isomer with higher acentric factor has a stronger thermophilic property and tends to migrate to the hot region in the heptane isomer mixture, and the extent of thermal diffusion is proportional to the difference between the acentric factors of the isomers.

Systematic discrimination of heptane isomers with femtosecond laser linear time of flight mass spectrometry

The dissociative ionization processes of heptane molecule with nine isomers have been investigated and presented experimentally in detail by courtesy of femtosecond laser mass spectrometry technique with a fundamental wavelength of 800 nm and 90 fs pulse duration in this study. It has been aimed to show that the classification of heptane isomers using factor analysis as statistical method reducing the dimension of obtained data. The main mass ratio of heptane isomers is known as m/z 100 which is obtained. The dissociation process on the parent molecule was dominant at the laser intensity about 1.42 x 1014 W/cm2 used for all isomers. The ions obtained by the breakdown of the main ion peak were primarily determined as factors which were clearly distinguished from each other according to factor 1 and factor 2 axes by applying factor analysis.

Insights into Adsorption of Linear, Monobranched, and Dibranched Alkanes on Pure Silica STW Zeolite as a Promising Material for Their Separation

The adsorption of linear, monobranched and dibranched saturated hydrocarbons in the gasoline range has been studied on pure silica STW zeolite (Si-STW) by using pentane, hexane, and heptane isomers...

Isomerization of n-heptane on platinum-zeolite catalysts promoted by chlorine and fluorine

The isomerization of n-heptane on BEA supported platinum catalysts with the addition of chlorine and fluorine as promoters was studied. The use of the halides decreased the operating temperature of the n-heptane conversion. The samples prepared at the stage of peptization showed an increase in the total conversion accompanied by a decrease in the yield of heptane isomers of 6 for chlorine and 27 wt.% for fluorine. Promotion by the halides at the stage of platinum application led to an increase in the catalyst activity without decrease in the selectivity values.

Correction: Reliable prediction of n-heptane isomerization over Pt/(CrOx/ZrO2)-HMS via comparative assessment of regularization networks and surface response methodologies

Correction for ‘Reliable prediction of n-heptane isomerization over Pt/(CrOx/ZrO2)-HMS via comparative assessment of regularization networks and surface response methodologies’ by Nastaran Parsafard et al., RSC Adv., 2020, 10, 26034–26051, DOI: 10.1039/D0RA04313C.

Procedure for the synthesis of AlSBA-15 with high aluminium content: Characterization and catalytic activity

Abstract In this study, AlSBA-15 materials with low nSi/nAl ratio were hydrothermally prepared by using three different acids, i.e. HCl, HNO3 and H2SO4, aiming to investigate the effect of the synthesis environment on their physicochemical properties. The resulting aluminium substituted molecular sieves were used as a supports for Pt catalysts. The AlSBA-15 materials and the Pt/AlSBA-15 catalysts were characterised by different techniques (N2 sorption, XRD, Py–FTIR, 27Al MAS NMR, CO chemisorption, TEM and SEM) and tested in n-heptane hydroconversion. It was found that the crystallisation of AlSBA-15 structure under the use of HNO3 led to the formation of AlSBA-15 with the highest amount of Al atoms in tetrahedral coordination. Depending on the AlSBA-15 preparation conditions, the Pt/AlSBA-15 catalysts displayed different physicochemical features, especially in term of acidity. As a consequence of the highest substitution of Al in tetrahedral positions in AlSBA-15 sample synthesised under the use of HNO3, the corresponding Pt catalyst exhibited the highest Bronsted acid sites concentration. The results of n-heptane hydroconversion showed that, this catalyst provided the highest yield of the most desired high-octane number products, i.e. multibranched heptane isomers. At the same time it was less selective towards hydrocarbons displaying the boiling temperatures higher than this of n-heptane (they are produced in cyclisation and aromatization) which are the precursors of carbonaceous deposits.

Proving hydrogen addition mechanism from manure to coal surface obtained by GC-MS and 1H-NMR analysis

In this study, to explain the possibility of hydrogen transfer paths from manure to coal, Elbistan lignite (EL) combined with manure liquefaction of oil + gas products were analysed with Gas Chromatography-Mass Spectroscopy (GC-MS) and Nuclear Magnetic Resonance Spectroscopy (1H-NMR) technique. In the same way, it is observed that oils which as they fragment to an alkane-alkene mixture, serve as a hydrogen “sponge” and put a serious hydrogen need on the parts of the free radicals and molecules that are currently hydrogen poor. Concerning Elbistan lignite and manure do not have any aromatic hydrogen. Moreover, when the aromatic compounds were hydrogenated, their aromatic hydrogen was transformed to naphthenic hydrogen. Hydrogen transfer was due to isomerization of heptane from 3-methylhexane obtained in test oil where only manure was present as hydrogen donor in the liquefaction environment despite hydrogenation of isomerization from naphthalene to azulene.

In situ fabrication of microporous organic network coated capillary column for high resolution gas chromatographic separation of hydrocarbons.

Microporous organic networks (MONs) are a new class of porous materials synthesized via Sonogashira coupling reactions between organic building blocks. Here we report an in situ synthesis approach to fabricate MONs coated capillary column for high resolution GC separation of hydrocarbons. The McReynolds constant evaluation reveals the MONs coated capillary is a non-polar column. The MONs coated capillary column shows good resolution for GC separation of diverse important industrial hydrocarbons such as linear and branched alkanes, alkylbenzenes, pinene isomers, ethylbenzene and styrene, cyclohexane and benzene. The MONs coated capillary column gave a high column efficiency of 1542 plates per meter for hexane and good precision for replicate separations of the selected hydrocarbons with the RSDs of 0.2-0.3, 1.5-3.1, and 1.9-3.3% for retention time, peak height and peak area, respectively. The MONs coated capillary also offered better resolution than commercial Inert Cap-1 and Inert Cap-5 capillary columns for hexane and heptane isomers. These results reveal the potential of MONs as novel stationary phases in GC.

Isomerization of n-Heptane in the Presence of Aromatic Hydrocarbons over Pt/MOR/Al2O3 and Pt/WO3/ZrO2 Catalysts

The effect of aromatic hydrocarbons (benzene, toluene) on the isomerization of n-heptane over Pt/MOR/Al2O3 and Pt/WO3/ZrO2 catalysts is studied. It is shown that the presence of aromatic hydrocarbons results in a need to raise the reaction temperature by 20–30°C to achieve n-heptane conversion at the same level as for individual n-heptane. It is established that the yield of heptane isomers falls in 1.5 times (from 60.1 to 39.9 wt %) during the isomerization of n-heptane mixed with aromatic hydrocarbons over Pt/MOR/Al2O3 catalyst and remains at the same level (60.4–68.0 wt %) over Pt/WO3/ZrO2 catalyst. The developed catalysts can be used in industry to isomerize the C7 fraction separated from straight-run and catalytic reforming gasolines. The presence of aromatic hydrocarbons in feedstocks is undesirable when Pt/MOR/Al2O3 catalyst is used, as it reduces the yield of isomers.