Isomerization Of N-hexane Research Articles

Isomerization performance of n-hexane in hydrogen atmosphere over the multistage porous composite NixPy-MCM-41/MOR catalyst

With the increasingly strict environmental protection requirements and the continuous improvement for the performance of clean fuel, it is imperative to develop technology for producing high octane gasoline blending components. Alkane isomerization was one of the important ways due to it contain little olefin and aromatic components which are harmful to the environment. In this study, the multistage porous composite NixPy-MCM-41/MOR catalysts were synthesized in the hydrogen atmosphere, the conversion rate and selectivity of n-hexane hydrogen isomerization with different conditions was tested in a fixed bed reactor. The results shown that the loading volume of active components is 4.0 wt%, nickel-phosphorus ratio of 0.5, reaction temperature of 250 °C, reaction pressure 3.0 MPa and volume space velocity is 2.0 h−1 with the hydrogen condition showed good catalytic activity for the n-hexane isomerization. The conversion rate of n-hexane is 73.0 % and the selectivity of 84.0 %, respectively. The isomerization stability of the Ni2P-MCM-41/MOR catalyst was investigated. After the long period test, the catalytic activity of the catalyst could keep good. Based on the study of reaction effect with different test conditions in hydrogen atmosphere, the mechanism of alkane isomerization for Ni2P-MCM-41/MOR catalyst was proposed.

Pt-promoted mesoporous Beta zeolite catalysts for n-Hexane isomerization with enhanced selectivity to dibranched isomers

We report a facile yet effective strategy to prepare hierarchical Beta zeolite with high molecular transport effectivity in catalysis. Alkaline etching involves preferential desilication from Beta framework and collapse of microporosity. The preferential desilication from outer rim of Beta stacking faults enlarged intercrystallite mesopores, while the collapse of microporosity created cylindroid-like intracrystalline mesopore. Part of Altet with lower stability was removed during alkaline etching, leading to a decrease in acid sites density. Alkaline etching of Beta zeolite with 0.2 mol/L NaOH solution greatly improved n-hexane isomerization activity over Pt-based catalysts. The maximum yield of isohexane and dibranched isomers increased by 6.2 % and 38.6 %, respectively. The enlargement of intercrystallite mesopores and the generation of intracrystalline mesopores of Beta zeolite lowered apparent activation energy of reaction. The apparent diffusivities measurements further revealed that Pt/Beta-0.2 M showed much lower transport limitation than Pt/Beta-parent. Our findings provide a promising catalyst for industrial alkane isomerization.

Effect of Residence Time and Carrier Gas on the Dehydrogenation of n-Hexane over Alumina-supported Chromium Catalyst

CrOx/γ-Al2O3 catalyst was prepared by incipient wetness impregnation method, and the influence of residence time and carrier gas on the dehydrogenation of n-hexane were studied. It is found that n-hexane dehydrogenation over CrOx/γ-Al2O3 catalyst with H2 as carrier gas exhibits totally different catalytic behaviors with that of diluting n-hexane with N2. When diluting feed with N2, the selectivity to dehydrogenation product is promoted while the cracking reaction is exhibited with reducing residence time. However, the selectivity to dehydrogenation product is significantly decreased while the isomerization of n-hexane is promoted when using H2 as carrier gas. It is proposed that H2 undergoes dissociation on the dehydrogenation active site, and further facilitates the olefinic dehydrogenation products to form carbocation, which performing isomerization reaction on the acid site on the γ-Al2O3 surface. Therefore, the isomerization of n-hexane is promoted in cost of the selectivity to dehydrogenation product when using H2 as carrier gas.

CATALYSTS OF THE ISOMERIZATION PROCESS OF n-HEXANE

Information on the isomerization of n-hexane is systematized. It has been shown that the process of isomerization of n-alkanes is a priority issue in solving the problems of improving the quality of modern automobile gasolines and their compliance with environmental requirements. The use of low-octane fractions as raw materials determines the high efficiency of the process in addition to the production of high-value isomerizate. The obtained isomerizate meets all the requirements for motor fuels: high impact resistance, easy volatility, absence of benzene, olefins and sulfur. The article presents thermodynamic data, provides general information about modern catalytic systems used in the isomerization of n-alkanes, and shows their mechanisms of action. Comparative data on Friedel-Crafts catalyst, chlorinated alumina, zeolites, sulfated and tungsten-containing zirconium, and heteropolyacids are summarized. In the process of isomerization of the pentane-hexane fraction, platinum-containing catalysts based on chlorinated aluminum oxide, zeolites and sulfated zirconium dioxide are used in industry. SO4/ZrO2-based catalysts can be considered the most promising due to their high performance indicators. The current work is mainly focused on the systematic study of the physico-chemical regularities of the formation and isomerization activity of catalysts based on anion-modified oxides, depending on their composition and preparation conditions. Keywords: n-hexane, isomerization, thermodynamics, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, catalytic systems.

Reducing the diffusion barriers of Pt/Beta catalyzed n-hexane isomerization by SBA-15 addition and high-energy milling

Aiming at improving reaction selectivity of zeolite Beta-catalyzed isomerization of normal alkane, we reported a facile but efficient route to prepare the Beta@SBA-15 composite supports with low surface diffusion barriers in isomers formation from normal alkane. Microporous Beta zeolite and mesoporous SBA-15 zeolite were physically mixed and milled by high-energy planetary ball-mill. The addition of SBA-15 and milling, which have little effect on the acid properties of Beta zeolites, disaggregate the Beta particles and anchor the Beta nanocrystals on the surface of SBA-15 mesostructure. The apparent diffusivities of 2-methyl pentane measured by zero-length column method increased by 50%. n-Hexane isomerization tests show that the Pt/Beta@SBA-15 catalysts exhibit much higher selectivity to isomers, especially the dibranched isomers and lower selectivity to cracking reaction, owning to the reduced transport limitation of composite supports.

Catalytic performance and kinetic modeling of n-hexane isomerization over phosphomolybdic acid (HPMo) combining palladium and platinum supported on metal-organic framework MIL-101(HPW)

A metal-organic framework MIL-101(HPW) was synthesized by hydrothermal reaction, and phosphomolybdic acid (HPMo) was synthesized by its precursor solution. Then (Pd + Pt)/HPMo/MIL-101(HPW) with different wt% were prepared by the impregnation method. The synthesized samples were characterized by XRD, FT-IR, NH3-TPD, N2 adsorption, FESEM, and TGA, and their performances were investigated in n-hexane isomerization. Under the optimized operating conditions (temperature of 180 °C, H2/nC6 molar ratio of 2, and WHSV of 3 h−1), the appropriate yield for the nC6 isomerization was provided. The (0.2%Pd + 0.3%Pt)/50%HPMo/MIL-101(HPW) sample showed a lifetime of 720 min with 92.5% iC6 selectivity and 75.3% nC6 conversion. Kinetic modeling of the n-hexane isomerization reaction was also performed, in which the classical bifunctional mechanism was used to calculate the kinetic parameters. The validity of the bifunctional behavior was proved by the high value of the statistical correlation coefficient of this model. The apparent activation energy of this mechanism was calculated at 42.5 kJ mol−1.

Study on the Role of Hydrogen in n-Hexane Isomerization Over Pt Promoted Sulfated Zirconia Catalyst

Study on the Role of Hydrogen in n-Hexane Isomerization Over Pt Promoted Sulfated Zirconia Catalyst

Tuning the acidity and pore structures of NiP based bifunctional catalyst for efficient n-hexane isomerization

Isomerization of alkane is one of the most important catalytic processes for producing environmentally friendly gasoline fraction with high octane number. However, the development of non-noble metal based catalysts with high conversion and selectivity towards multi-branched isomerized products is still challenging. Herein, we report that a NiP-Hβ/modified Kaolin catalyst was successfully prepared by ball-milling of amorphous NiP nanoparticles with Hβ/modified Kaolin composites and applied for n-hexane isomerization. The introduction of chemically modified Kaolin with abundant weak-medium acid sites and mesopores not only alleviates the cracking of isomerized products on the strong acid sites on Hβ, but also provides more active sites for the formation of di-branched isomerized products with high octane number. As a result, the NiP-Hβ/modified Kaolin catalyst shows an excellent catalytic performance for n-hexane isomerization in terms of good conversion (78.1%), high selectivity towards mono-branched (75.4%) and di-branched (21.4%) i-C6 products, and high liquid yield (99.9%). This work paves the way to the development of high performance non-noble metal based catalysts for large scale production of clean gasoline.

Combined in situ XAS and DFT studies on the role of Pt in zeolite-supported metal catalysts for selective n-hexane isomerization

In this study, we used several in situ, and spectroscopy analyses to investigate the roles of platinum (Pt) in zeolite-supported Pt catalysts for selective n-alkane isomerization. HY zeolites were synthesized using the rice husk silica and impregnated with Pt precursor by incipient wetness impregnation. Typically, HY zeolites have proved to be active hydrocarbon cracking catalysts. The particular challenge is to find an effective catalyst, which favors the isomerization of n-alkanes without too much cracking. In this work, adding Pt atoms to HY zeolite provides an enhanced multifunctional catalyst for converting n-alkanes to branched hydrocarbons. To understand the effect of Pt, we further investigated the reaction mechanism of n-hexane isomerization to 2–methylpentane (2MP) and 3-methylpentane (3MP) by DFT simulations, using a cluster of 30T HY zeolite modeled through B3LYP + 3D calculations. We found that, at 450 °C, the isomerization on Pt-HY gives higher cracking products. Decreasing temperature to 300 °C yielded greater selectivity of branched hydrocarbons. In addition, DFT calculations demonstrate that the 2MP production via route A1 (C3-C4 bond activation) and a rate-determining step of 0.97 eV proved more thermodynamically and kinetically favorable than the 3MP product. This agrees well with our experimental observations. Consequently, the presence of Pt on the HY zeolite plays an essential role in both CC forming and breaking. Finally, the Pt–HY zeolite is an efficient catalyst for petroleum production, improving the octane number for catalytic performance and product selectivity by isomerizing straight-chain alkanes to their branched chain isomers.

Reuse of ionic liquid in n-hexane isomerization reaction

The article presents the study results of the reuse of the ionic liquid triethylamine hydrochloride-aluminum chloride in the isomerization of n-hexane. Regularities in the behavior of an ionic liquid during its repeated use are established. It was revealed how the yield of the main products changes after four successive isomerization reactions.

Synthesis and Characterization of Ni-WO3/Sulfated Zirconia Nano catalyst for Isomerization of N-Hexane and Iraqi Light Naphtha

This work deals with preparation of Sulfated Zirconia catalyst (SZ) for isomerization of n-hexane model and refinery light naphtha, as well as enhanced the role of promoters to get the target with the mild condition, stability, and to prevent formation of coke precursors on strong acidic sites of the catalyst. The prepared SZ catalysts were characterization by fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer –Emmett-Teller (BET) surface area analysis, Thermogravimetric Analysis (TGA), Scanning Electron Microscope (SEM) and atomic force microscopy (AFM) Analyzer. The results illustrate that the maximum conversion and selectivity for n-hexane isomerization with Ni-WSZ and operating temperature of 150 °C was 80.1% and 96 % respectively .Other set of experimental with light naphtha , the results show that the maximum conversion and selectivity with Ni-WSZ and operating temperature of 150 °C was 73.6% and 74% respectively.

Kinetics of n-hexane hydroisomerization over HZSM-5 supported platinum catalysts. Features of the process mechanism and the Ni-promoting effect

• Bimetallic platinum-containing zeolites are effective catalysts for the paraffins isomerization • The presence of Ni in Pt/HZSM-5 reduces the particle size of the active phase and its stability • The introduction of Ni into Pt/HZSM-5 significantly increased the rate of hydroisomerization • The mechanism of hydroisomerization of n-hexane assumes the direct participation of hydrogen in the skeletal rearrangement • The increase in the rate of isomerization of n-hexane from the hydrogen content is close to linear Kinetic studies of the hydroisomerization of n-hexane under stationary and non-stationary conditions for Pt/HZSM-5 catalysts promoted and non-promoted with nickel have been carried out. The catalysts were studied by the low-temperature N 2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, TPR-H 2 , and TPD-NH 3 methods. It is found that the kinetic equation of n-hexane isomerization on both catalysts is written by a common fractional-rational equation, in which the hydrogen exhibits a positive effect on the reaction rate. However, the values of the kinetic constants of the reaction on the two catalysts differ, showing the influence of the Ni additive on the catalyst properties and the reaction kinetics. The introduction of Ni into Pt/HZSM was accompanied by a decrease in the particle size of the active phase, an increase in the concentration of adsorbed hydrogen, which significantly increased the rate of hydroisomerization. In addition, the distinctive characteristics of the kinetic model of the reaction on the Pt-based and the Pd-based catalyst were elucidated.

Study on the Mechanism of Water Poisoning Pt-Promoted Sulfated Zirconia Alumina in n-Hexane Isomerization

Study on the Mechanism of Water Poisoning Pt-Promoted Sulfated Zirconia Alumina in <i>n</i>-Hexane Isomerization

A Novel B-Doped NiP/Hβ Catalyst for n-hexane Isomerization with Synergistic Catalytic Mechanism of Metal Sites–Acid Sites

A Novel B-Doped NiP/Hβ Catalyst for n-hexane Isomerization with Synergistic Catalytic Mechanism of Metal Sites–Acid Sites

Linear Hexane Isomerization Over Bimetallic Zeolite Catalysts

The aim of this study was to evaluate the activity and selectivity in isomerization of n-hexane of bimetallic zeolite catalysts containing a nickel transition metal in addition to palladium. Bimetallic bifunctional linear alkane isomerization catalysts based on the hydrogen form of MFI zeolite have been synthesized. The porous properties of the samples were investigated by means of low-temperature nitrogen adsorption/desorption, the size of the metal component – by TEM, and the catalytic properties – in the micro-pulse isomerization of n-hexane. Antisymbatic correlation between the temperature of the maximum yield of hexane isomers and the amount of nickel in the sample was found for a stable palladium content. The introduction of nickel allows to reduce the optimum process temperature from 598 to 523 K.

Synthesis of Zeolite supported bimetallic catalyst and application in n-hexane hydro-isomerization using supercritical CO2

The loading of novel bi-and tri-metallic bifunctional catalysts such as Pt–Ru, Pt–Zr, and Pt–Ru–Zr over original zeolites (H-MOR and H-ZSM-5) and new cations modified zeolites (Sr-MOR, Ba-MOR, Sr-ZSM-5, and Ba-ZSM-5) by supercritical CO2 method are investigated for n-hexane isomerization. A fixed bed micro-reactor unit was used for catalytical hydro-isomerization of n-hexane at different temperature ranges (250–325 °C), H2/HC ratios of 3, 6, and 9 mol and pressure of 5 bar. The chemical and physical properties of prepared zeolite nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and thermogravimetric analysis (TGA). It is reported that the metal loaded in scCO2, results in more uniform and tiny metal nanoparticle (1.37 nm) dispersion with high stability and revealed that high loading pressure in scCO2 (280–300 bar) results in higher catalytic activity and surface area. H-MOR and H-ZSM-5 possess the maximum BET surface area of 539.21 and 403 m2/g and pore size of 90.73 and 105.06 Å respectively. The finding also revealed the maximum n-hexane conversion and selectively of about 99.10% and 32.23% for Pt–Ru/H-ZSM-5%, 93.55%, and 99.72% for Pt-Zr/H-ZSM-5, and 97% and 29.74% for Pt–Ru–Zr/H-MOR catalysts respectively at H2/HC ratio of 9 and 250–325 °C. Moreover, Pt–Ru/H-ZSM-5, Pt–Zr/Ba-ZSM-5, and Pt–Ru–Zr/Ba-ZSM-5 showed the maximum yield of 11.5% and 17.7%, 40.58% and 33.19%, and 11.5% and 9.1% of 2-methyl-pentane (2-MP) and 3-methyl-pentane (3-MP) respectively at H2/HC ratio 9 and 250–325 °C. Based on results, it is concluded that Pt–Zr catalyst over ZSM-5 showed better catalytical activity among all for n-hexane isomerization, while Pt–Ru and Pt–Ru–Zr demonstrated better hydrocracking reactions.

Isomerization of linear hexane over acid-modified nanosized nickel-containing natural Ukrainian zeolites

Bifunctional catalysts on the basis of Ukrainian natural mordenite-clinoptilolite rocks modified by hydrochloric acid and by witness impregnation with nickel have been synthesized. Samples have been characterized by means of XRD, XRF, FTIR-spectroscopy, low temperature nitrogen adsorption/desorption, DTA/TG, TEM. Catalysts have been tested in micro pulse linear hexane isomerization. Hydrochloric acid treatment of natural zeolite rock leads to silica-to-alumina ratio increasing and raising the BET surface as well as the volumes of mesopores and micropores. The nickel nanoparticles deposited over zeolite crystals have a predominant size of 10 nm, but for some samples smaller ones of 5 nm and bigger ones of 20–50 nm have been found using TEM investigations. Pyridine sorption shows Bronsted and Lewis acidity of the catalysts, moreover the lower hydrochloric acid concentration using leads to practically equal Bronsted and Lewis acidity, the higher acid concentrations causes the Lewis acidity predominance. DTA/TG investigations show that water physically sorbed in the pores of the samples has been removed up to 200 °C from lager cavities of acid-treated catalysts and up to 500 °C from narrower cavities for untreated initial rock. Removing zeolite structure water up to 800 °C causes the dehydroxylation and Bronsted acidity transformation into Lewis acidity. The sample dealuminated by 1 mol dm−3 acid with nickel nanoparticles of 5–8 nm demonstrates the best performance in the isomerization of n-hexane. It is characterized by a 20% yield of hexane isomers at 250 °C and 70% selectivity.

Influence of alumina addition on structural and catalytic properties of sulphated zirconia in isomerization of n-hexane

New binary catalytic systems based on sulphated zirconia-alumina were synthesized by controlled hydrolysis of alkoxides using relative molar ratios of constituents 1:1, 1:2 and 1:3 in favour of zirconia. The obtained differences in the final catalytic material?s properties may be related to organic precursor memory effect, the applied calcinations temperatures and used alumina contents. The addition of alumina to zirconia affected the structural and surface properties stabilizing bare zirconia by means of slower phase transformation of tetragonal zirconia crystal phase into monoclinic one, further resulting in smaller crystallites sizes and higher surface density of acidic function (sulphates). The best alumina impact on physico-chemical properties was achieved when the highest amount of alumina (e.g. 50%) and lower calcination temperature (500?C) were used, causing relatively high steady-state activity in isomerization of n-hexane at reaction temperature 250 ?C. On the other hand, higher calcination temperature (600 ?C) played a role in the genesis of greater sulphate density. Catalytic activity and selectivity are expressed as a complex synergistic function of relative density of acid sites together with positive status of other optimized physico-chemical properties of the catalytic material (by activation and calcination temperatures).

N-Hexane hydroisomerization over Zr-modified bicontinuous lamellar silica mordenite supported Pt as highly selective catalyst: Molecular hydrogen generated protonic acid sites and optimization

Zr-modified bicontinuous lamellar silica mordenite supported Pt catalysts were synthesized using the zirconyl chloride oxahydrate as the precursor for Zr species by the incipient wetness impregnation method. The influence of zirconium loading on the properties of Zr-modified HM@KCC-1 catalysts for n-hexane isomerization were studied. The results of XRD and lattice structure from IR study indicated that increasing zirconium loading did not change the properties of catalysts. The IR study with pre-adsorbed 2,6-dimethylpyridine as a probe molecule affirmed that increasing zirconium loading could increase the Lewis acid sites. The generation of protonic acid sites which were active in n-hexane hydroisomerization was mainly from molecular hydrogen through a hydrogen spill-over mechanism as established by in situ-IR study. The results for the catalytic testing indicated that PtZr/HM@KCC-1 catalyst was highly selective in n-hexane hydroisomerization due to abundant permanent Lewis acid sites for its promotive effect in the generation of protonic acid sites. However, the incorporation of excessive zirconium amount up to 10 wt percent loading led to a decline in the amount of protonic acid sites generated, thus reduced the hydroisomerization performance in the process. The optimum conditions for hydroisomerization of n-hexane over Pt5Zr/HM@KCC-1 were reaction temperature of 293 °C, treatment temperature of 474 °C and F/W of 502 mL/g.min with the predicted value for isomer yield of 83.9%.

Isomerization of Alkanes over Ionic Liquids Supported on SBA-15

Exploring the catalytic efficiency of ionic liquid supported on mesoporous material as heterogeneous organ catalysts for example, 1-Ethyl-3-methylimidazolium triflate and 1-ethyl-3-methylimidazolium chloride + AlCl3 (different ratio) immobilized on SBA-15 that contains 0.5% platinum, with regard to isomerization of n-pentane and n-hexane, along with commercial light naphtha feed conversion reactions. The prepared materials were characterized by several instrumental methods, which include temperature-programmed desorption to evaluate acid strength. The reactions were performed in a fixed-bed stainless steel reactor having high pressure by the down-flow method. This valuable novel isomerization reaction was strongly influenced by many key parameters, for instance, temperature, pressure, weight hourly space velocity, and flow rate of H2, which are discussed in detail. The Pt/EMIM-AlCl4(1:1)20/SBA-15 ionic liquid catalyst showed superior catalytic performance out of the four-catalyst system examined toward the above reactions, which is undoubtedly due to its significant turnover frequencies values of 8.6 s–1 and 8.5 s–1 and specific reaction rates values of 8.01 × 10–4 mol g–1 s–1 and 8.00 × 10–4 mol g–1 s–1 for n-pentane and n-hexane correspondingly. The order of catalytic activity is Pt/EMIM-AlCl4(1:1)20/SBA-15 > Pt-EMIM-Tf/SBA-15 > Pt/EMIM-Al2Cl7(1:2)20/SBA-15 > Pt-EMIM-Al2Cl7(1:2)30/SBA-15.