Hydroisomerization Of Heptane Research Articles

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.

Kinetics of Zeolite-Catalyzed Heptane Hydroisomerization and Hydrocracking with Cbmc-Modeled Adsorption Terms: Zeolite Beta as a Large Pore Base Case

Kinetics of Zeolite-Catalyzed Heptane Hydroisomerization and Hydrocracking with Cbmc-Modeled Adsorption Terms: Zeolite Beta as a Large Pore Base Case

Influence of Nanoscale Intimacy and Zeolite Micropore Size on the Performance of Bifunctional Catalysts for n-Heptane Hydroisomerization.

In this study, Pt nanoparticles on zeolite/γ-Al2O3 composites (50/50 wt) were located either in the zeolite or on the γ-Al2O3 binder, hereby varying the average distance (intimacy) between zeolite acid sites and metal sites from “closest” to “nanoscale”. The catalytic performance of these catalysts was compared to physical mixtures of zeolite and Pt/γ-Al2O3 powders, which provide a “microscale” distance between sites. Several beneficial effects on catalytic activity and selectivity for n-heptane hydroisomerization were observed when Pt nanoparticles are located on the γ-Al2O3 binder in nanoscale proximity with zeolite acid sites, as opposed to Pt nanoparticles located inside zeolite crystals. On ZSM-5-based catalysts, mostly monobranched isomers were produced, and the isomer selectivity of these catalysts was almost unaffected with an intimacy ranging from closest to microscale, which can be attributed to the high diffusional barriers of branched isomers within ZSM-5 micropores. For composite catalysts based on large-pore zeolites (zeolite Beta and zeolite Y), the activity and selectivity benefitted from the nanoscale intimacy with Pt, compared to both the closest and microscale intimacies. Intracrystalline gradients of heptenes as reaction intermediates are likely contributors to differences in activity and selectivity. This paper aims to provide insights into the influence of the metal–acid intimacy in bifunctional catalysts based on zeolites with different framework topologies.

The Influence of Size and Shape of Pd Nanoparticles on the Performances of Pd/Beta Catalysts for n‐Heptane Hydroisomerization

AbstractSeveral Pd/Beta catalysts with cubic (9 nm, 12 nm, 16 nm) and truncated‐octahedral (18 nm) Pd nanoparticles (NPs) were prepared to investigate the effect of size and shape of Pd NPs for n‐heptane hydroisomerization. Characterizations confirmed that the cubic Pd NPs solely exposed {100} crystal plane and truncated‐octahedral Pd NPs were enclosed by {100} and {111} crystal planes, and that the desorption temperature of subsurface hydrogen on Pd NPs showed size and shape dependence. Hydroisomerization results exhibits that the catalyst with 9 nm cubic Pd NPs displayed the higher isomers selectivity compared to the catalyst with 12 nm cubic NPs, 18 nm truncated octahedral NPs and 16 nm cubic NPs at similar conversion. This result suggested the size and shape dependence of (de)hydrogenation activity of Pd NPs, and further revealed the key role of subsurface hydrogen in determining the (de)hydrogenation activity.

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).

A study of Pt/WO4 2−/ZrO2 catalyst deactivation in the hydroisomerization of heptane and a heptane–benzene mixture

The dynamics of the catalytic properties of a Pt/WO4 2−/ZrO2 catalyst (17 mol % WO4 2−) in the hydroisomerization of heptane and a heptane–benzene mixture as a function of reaction time and temperature has been studied. It has been found that the heptane conversion decreases in the initial reaction period (within 2 h) and the isohexane selectivity symmetrically increases at 170–280°C, with the benzene hydrogenating activity decreasing at 250°C and higher temperatures. The observed changes in catalytic properties are attributed to the partial deactivation of both the acid and hydrogenation components of the catalyst. X-ray photoelectron spectroscopy has revealed the formation of carbon deposits on the catalyst surface; the structure of the deposits is determined by the reaction medium composition. The composition of the products formed on the catalyst after heptane hydroisomerization is mostly represented by aliphatic polymers of the “poly-СхНy” type, which are capable of blocking the active sites that catalyze the cracking reactions. The addition of benzene to heptane has led to the formation of graphite-like carbon deposits; this feature is apparently responsible for a decrease in both the acidity and hydrogenation activity of the catalyst. The phase state and textural characteristics of the catalysts are stable under the isomerization reaction conditions.

Dynamics of the Activity and Physicochemical Characteristics of Pt/WO4 2−–ZrO2 Catalysts in the Hydroisomerization of Heptane and Heptane–Benzene Mixtures

The dynamics of the activity and selectivity of bifunctional platinum tungstated zirconia PtWZ catalyst in the hydroisomerization of n-heptane and heptane–benzene mixture is discussed in the paper. The change in the properties of the catalyst before and after reaction were characterized using different techniques. The catalyst showed high efficiency for the hydroisomerization of heptane and heptane–benzene mixture, however, deactivation occurred with time on stream, more significantly when benzene was present in the reaction mixture. The carbonaceous matter was deposited on the catalyst (up to 0.8%) during the hydroisomerization reaction. Predominantly aliphatic carbonaceous «poly-CxHy» species, much less oxidized and little aromatic «graphite-like» species were identified by XPS spectra on the catalyst after the heptane isomerization. In the presence of benzene, the formation of «graphite-like» matter increased progressively as temperature increased. However, no appreciable changes in the bulk properties of the t-ZrO2 matrix (phase composition, specific surface area, pore volume, pore size distribution) and in the state of platinum component were revealed, though an increased extent of W6+ to W5+ reduction was detected by XPS spectra irrespectively of the reaction conditions. The deactivation of the PtWZ catalyst was suggested to result from the blocking the active centers by carbonaceous deposits, the deactivation of the acidic centers being more pronounced as compared to metallic ones. All the carbonaceous deposits were burned-off completely below 450–500 °C.

Evaluation of the acidic properties of the B2O3–Al2O3 and Pt/B2O3–Al2O3 systems by spin probe EPR spectroscopy and their correlation with the occurrence of the joint hydroisomerization of heptane and benzene

The acidity of a series of borate-containing aluminum oxide samples with the concentrations of B2O3 from 0.9 to 27.5 wt % and Pt-containing catalysts obtained on their basis was studied by spin probe EPR spectroscopy. With the use of anthracene and the TEMPO nitroxide radical as probe molecules, it was established that an increase in the B2O3 content of the B2O3–Al2O3 and Pt/B2O3–Al2O3 systems leads to a symbatic increase in the number of medium-strength Bronsted acid sites (BASs). In this case, the yields of target hydroisomerization products (isoheptanes and methylcyclopentane) correlate with the number of BASs.

Porous clay heterostructures (PCHs) from Al13-intercalated and Al13-pillared montmorillonites: Properties and heptane hydro-isomerization catalytic activity

The conventional method of synthesizing porous clay heterostructures (PCHs) is based on the use of cetyltrimethylammonium cations, amines (as a co-surfactant) and a silica source. In the present study, we report the preparation of PCH materials from Al13-intercalated montmorillonite and its pillared derivatives using one directing template (dodecylamine) and a silica source. This method allowed us to reduce the use of the organic template and to incorporate the aluminum species directly into the silica framework intercalated between the clay sheets in one step. The dodecylamine template was removed by calcination at 550°C in air. The PCH material prepared from the Al13-intercalated clay exhibited a higher surface area, mesopore volume and acidity, as well as strong Brønsted and Lewis acid sites. However, the use of pillared clays did not lead to the formation of PCH material due to the strong interaction between the alumina species and the clay sheets, which hindered their exchange with dodecylamine, as indicated by XRD and 29Si and 27Al solid-state NMR techniques. The hydro-isomerization reaction of heptane was tested on the differently prepared PCHs with a conversion of 60% and isomer yield of 50% at 350°C.

Influence of preparative method on Al2O3-doped Pt/WO3-ZrO2 catalyst for n-heptane isomerization

Alumina-doped Pt/WO 3 /ZrO 2 catalysts were prepared using either a constant or variable pH method. The obtained catalyst samples were characterized using N 2 adsorption, X-ray diffraction, ultraviolet-visible diffuse reflectance, CO chemisorption, X-ray photoelectron spectroscopy, 27 Al magic-angle spinning nuclear magnetic resonance, and infrared spectroscopy of adsorbed pyridine. Compared to the catalyst prepared using the variable pH method, the catalyst prepared using the constant pH method had a higher surface area and Pt dispersion. More Brönsted acid sites were generated in the presence of H 2 on the latter catalyst, and this was responsible for its higher catalytic activity in n -heptane hydroisomerization. When the reaction temperature was 200 °C and the weight hourly space velocity of n -heptane was 0.9 h −1 , the Pt/WO 3 /Al 2 O 3 -ZrO 2 catalyst prepared using the constant pH method gave 70.0% conversion of n -heptane, which was significantly greater than the conversion obtained using the corresponding catalyst prepared using the variable pH method (43.5%). 采用恒pH法和非恒pH法制备了Al 2 O 3 掺杂的Pt/WO 3 /ZrO 2 催化剂, 并用N 2 吸附-脱附、X射线衍射、紫外-可见漫反射、CO化学吸附、X射线光电子能谱、 27 Al魔角旋转核磁共振和吡啶吸附红外等技术对催化剂进行了表征. 结果表明, 相比于非恒pH法制备的催化剂, 恒pH法制备的催化剂具有较高的比表面积和Pt分散度, 在H 2 气氛中产生更多的B酸位, 从而表现出更高的催化正庚烷临氢异构化反应活性; 在200 °C和质量空速0.9 h −1 的反应条件下, 正庚烷转化率达70.0%, 明显高于非恒pH法制备的催化剂(43.5%). An Al 2 O 3 -doped Pt/WO 3 /ZrO 2 catalyst prepared using a constant pH method exhibited significantly higher activity in n -heptane hydroisomerization than did the corresponding catalyst prepared using a variable pH method. This was because more Brnsted acid sites were generated on the former catalyst in the presence of H 2 .

Characterization of sulfated zirconia prepared using reference catalysts and application to several model reactions

The sulfated zirconia project was carried out in order to obtain a broad understanding of the preparation, characterization, and application of the solid superacids of sulfated zirconia. The sulfated zirconia catalysts were prepared by the equilibrium adsorption method and the ammonium sulfate kneading method using the reference catalysts JRC-ZRO-2, -3, -4, and -5, supplied by the Reference Catalyst Division of the Catalysis Society of Japan. The catalysts were characterized by elemental analysis, NH 3-TPD, XRD, TG-DTA, CO 2-TPD, Raman spectroscopy, and measurements of the surface area, pore size distribution, coverage (by the BAT method), and heat of Ar adsorption. In order to compare the catalytic activities, we used the prepared catalysts in the isomerizations of butane and n-heptane, hydroisomerization of heptane, aldol condensation, acylation, esterification, and cracking of cumene. The sulfated zirconia prepared using JRC-ZRO-2 by the equilibrium adsorption method showed the highest activity and larger surface area. On the other hand, the kneading method provided catalysts with high reproducibility.

Characterization and catalytic properties of montmorillonite pillared with aluminum/lanthanum

Abstract This work describes the synthesis, characterization and catalytic properties of montmorillonite pillared with mixed aluminum/lanthanum pillars. This material presents characteristics that are very different from montmorillonite pillared only with aluminum. It shows a bimodal micropore structure, through generation of pores at the limit between microporosity and mesoporosity. The textural parameters show higher values and it is thermally more stable, maintaining high values of specific surface area and micropore volume up to 700 °C. The acidity of aluminum/lanthanum pillared material reveals that its surface shows more acid centers, mainly Lewis-type. The increase of the conversion in dehydration of 1-butanol as in hydroisomerization of heptane shows its better behavior as an acid catalyst. The study of 1-butanol dehydration shows that there is an increase in the acidity and the thermal stability and a smaller deactivation by carbonaceous deposits in the aluminum/lanthanum pillared material.

Charge Reduction in a Vermiculite by Acid and Hydrothermal Methods: A Comparative Study

A comparative study on acid and hydrothermal methods as ways to reduce interlamellar charge has been carried out on a vermiculite. This study showed that the application of the hydrothermal treatment as a previous step to pillaring the vermiculites, reported here for the first time, is a new route to obtain the porous material with a particular interest as heterogeneous catalysts, starting from mineral clays with a high density of charge. Modified clays have been characterized by atomic absorption, emission spectrograph, X-ray diffraction, cation-exchange capacity, total acidity, infrared spectroscopy (DRIFT), and nitrogen adsorption. The results have shown that all solids have been structurally modified. However, acid and hydrothermal methods showed different behavior. For the vermiculite, the hydrothermal treatment did not produce major differences in terms of the crystalline structure, whereas the acid method caused severe structural damage. The catalytic properties have been tested over Pt-impregnated samples (1%) using the hydroisomerization of heptane. Important catalytic activity was established for all solids with high selectivity regarding the isomer products.

Technical and economical evaluation of a zeolite membrane based heptane hydroisomerization process

Abstract An industrial scale heptane hydroisomerization process was simulated based on a concept of two reactors and a zeolite membrane. A product stream containing tribranched, and part of the dibranched C 7 isomers with octane number up to 92 is predicted. The economics of the process shows an investment cost of 40 million euros, with the membrane unit as the main cost driver. The technical and economical feasibility of this industrial scale heptane hydroisomerization process depends mainly on further development and performance of zeolite membranes.