Hydroisomerization Of N-octane Research Articles

Mesoporogen-free synthesis of hierarchical SAPO-11 from kaolin for hydroisomerization of n-alkanes

Hierarchical SAPO-11, featuring both micropore and mesopore channels, demonstrates an outstanding performance in high-octane gasoline production. In this work, we propose an economic and effective approach to directly fabricate hierarchical SAPO-11 molecular sieve from natural kaolin, eliminating the need for mesoporogens. The systematic characterization results show that the kaolin-derived SAPO-11 possesses abundant micro-mesoporous structure and more Brønsted (B) acid sites on the external surface in contrast with the conventional SAPO-11 prepared employing silica sol as silicon source as well as SAPO-11 synthesized with the assist with of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (F127). The analysis of the formation process reveals that the kaolin not only provides silicon source for the SAPO-11 crystal growth, but also offers confined environment for crystal growth along the preferential orientation, resulting in the generation of the microporous and mesoporous structure. Benefiting from these unique properties, the kaolin-derived Pt/SAPO-11 exhibits considerably improved selectivity for di-branched C8 isomers in n-octane hydroisomerization.

OSDA-free synthesis of FeZSM-22 zeolite from natural minerals for n-octane hydroisomerization

A seed-directed approach to synthesizing FeZSM-22 zeolite without organic structure directing agent (OSDA) was developed by using Fe-rich diatomite as all aluminum and iron sources. The FeZSM-22 zeolite with optimal crystallinity and purity can be obtained by systematically adjusting feed composition and synthesis conditions. Characterizations show that FeZSM-22 zeolite synthesized with OSDA-free owns high crystallinity, obvious thin needle-shaped morphology and high Bronsted/Lewis acid ratio. Significantly, when used for n-octane hydroisomerization reaction, its derived catalyst exhibits the best catalytic performance reflected by the highest selectivity to C8 isomers compared to the two reference catalysts prepared based on a Fe-containing and a Fe-free ZSM-22 synthesized through an OSDA-directed route from natural diatomite and conventional chemicals, respectively. This work provides an alternative route to sustainably synthesizing heteroatomic zeolites with high performance.

Al-functionalized mesoporous SBA-15 with enhanced acidity for hydroisomerization of n-octane

SBA-15, possessing uniform mesopore system and large specific surface area, shows a tremendous mass transfer advantage in the reactions involving reactant, intermediate or product whose dynamic diameter is larger than the pore size of microporous zeolites, but the low acidity greatly limits its application in acid-catalyzed reactions (e.g., hydroisomerization). Herein, we report an Al-functionalized SBA-15 molecular sieve (Al-SBA-15) with enhanced acidity obtained via a pH-adjusted prehydrolysis synthesis approach for hydroisomerization. Its physicochemical properties and catalytic performance were carefully characterized, evaluated in hydroisomerization of n-octane after loading active component Pt, and compared with a pure silica SBA-15 and two Al-containing samples (AlSBA-15 and Al/SBA-15) produced through direct synthesis and wetness impregnation, respectively. The results show that the acidity of three Al-functionalized samples is prominently improved, and thus the conversion of n-octane over them is greatly increased when compared with siliceous SBA-15. Moreover, among three Al-containing SBA-15 materials, Al-SBA-15 with the largest pore diameter and moderate acidity exhibits relatively high n-octane conversion and di-branched isomers selectivity but minimal cracking selectivity. These results demonstrate that pH-adjusted prehydrolysis is an effective route to preparing Al-functionalized SBA-15 with suitable acidity for the hydroisomerization of alkanes.

Zeolites in a good shape: Catalyst forming by extrusion modifies their performances

Chemical interactions occurring between zeolites and alumina binders during the critical steps of catalyst forming are the focus of this study. Three widely used and commercially significant variants of FAU zeolite, covering a wide range of Si/Al ratios, micro-and mesoporosity and acidic properties (Y [LZY-64, Si/Al = 2.3] and USY [CBV 720 and CBV 760 with Si/Al = 16 and Si/Al = 28, respectively]) were shaped by extrusion with pseudoboehmite to produce bound extrudates. These extrudates were characterized by conventional techniques (XRD, 27 Al NMR and IR spectroscopy, N2 physisorption...) and compared to their parent powders activated under the same conditions. The catalytic performances of the zeolite powders, their derived alumina extrudates and physical zeolite/ γ-Al2O3 mixtures were also evaluated employing two different reactions: i) n-octane hydroisomerization, to probe all catalytic sites and ii) 1,3,5 tri-isopropyl benzene dealkylation to probe only the external/mesoporous surfaces. The bound zeolites systematically displayed catalytic performance superior to their parent powders or physical mixtures, especially in the dealkylation of 1,3,5 tri-isopropyl benzene. Infrared spectroscopy measurements of the number, nature and strength of the acid sites were consistent with these catalytic results demonstrating that new catalytic sites are created and located on the external or mesoporous surface of the zeolites, i.e. at the zeolite-binder interface. The work reported here clearly illustrates that binding and subsequent thermal treatment of zeolite powders to produce commercially representative forms can significantly alter the quality and quantity of active sites creating active centers not usually present in pure powders which are typically studied and reported in much of the open literature. Such a study is also a blueprint for other catalytic phases, other forming processes (spray-drying, oil-dropping, pelletizing…) and could also be applied to the shaping of adsorbents.

Effect of preparation method on the bimetallic NiCu/SAPO-11 catalysts for the hydroisomerization of n-octane

Abstract The bimetallic NiCu/SAPO-11 catalysts were prepared by co-impregnation, sequential impregnation, co-precipitation, and mechanical mixing methods. Powder X-ray diffraction, nitrogen adsorption-desorption, temperature-programmed desorption of ammonia, transmission electron microscopy, temperature-programmed reduction of hydrogen, and X-ray photoelectron spectroscopy were used to characterize the physicochemical properties of the catalysts. The catalytic performance of the catalysts was assessed by the hydroisomerization of n -octane. Results indicated that the conversion of n -octane and selectivity to n -octane isomers were related to the preparation methods of the catalysts. The catalysts with Ni-Cu alloy effectively restrained the hydrogenolysis reaction that decreases the selectivity of isomerization. The catalyst prepared by the mechanical mixing of NiO and CuO hardly formed Ni-Cu alloy, showing obvious hydrogenolysis and low selectivity to n -octane isomers. The unbalance between the metal and acid sites resulted in the low conversion of n -octane and selectivity to n -octane isomers. Among all the catalysts, the catalyst prepared by the co-impregnation method exhibited high catalytic activity and selectivity to n -octane isomers.

Hydroisomerization of n-octane over bimetallic Ni-Cu/SAPO-11 catalysts

Bimetallic Ni-Cu/SAPO-11 catalysts were prepared by co-impregnation method and assessed in the hydroisomerization of n-octane. Their physicochemical properties were characterized by means of powder X-ray diffraction, nitrogen adsorption-desorption, temperature-programmed desorption of ammonia, pyridine-adsorbed infrared spectroscopy, temperature-programmed reduction of hydrogen, transmission electron microscopy, energy dispersive X-ray, and X-ray photoelectron spectroscopy. The Ni-Cu alloy was formed after reduction in the H2 flow at 450°C. Copper changed the electronic interaction of nickel and diluted the nickel ensemble size in the Ni-Cu alloy. The hydrogenolysis reaction that decreases the selectivity of isomerization was effectively restrained over the bimetallic Ni-Cu/SAPO-11 catalysts. The selectivity to n-octane isomers over the bimetallic nickel (3%) and copper (1.5%) catalyst was 19% more than that over the monometallic nickel (3%) catalyst at the conversion of 70%. A possible reaction scheme was proposed to explain the catalytic properties in n-octane hydroisomerization.

Zinc-modified Pt/SAPO-11 for improving the isomerization selectivity to dibranched alkanes

Zinc-modified Pt/SAPO-11 catalysts were prepared by incipient wetness impregnation and assessed in the hydroisomerization of n-octane. Their physicochemical properties were investigated using powder X-ray diffraction, scanning electron microscopy, nitrogen adsorption-desorption, pyridine-adsorbed infrared spectroscopy, temperature-programmed desorption of NH3, temperature-programmed reduction of hydrogen, temperature-programmed desorption of hydrogen, transmission electron microscopy, and X-ray photoelectron spectroscopy. The addition of zinc resulted in high dispersion of platinum. Zinc acted as a competitive adsorbent, changed the location of platinum. The catalyst with a zinc loading of 0.5% gave the highest selectivity to dimethylhexanes, but the conversion was lower than those achieved with the other catalysts. Dimethylhexanes have large molecular diameters, and therefore their diffusion may be difficult. This weakens the catalytic activity of the zinc-modified catalysts and lowers the n-octane conversion.

Effect of silicon precursor on silicon incorporation in SAPO-11 and their catalytic performance for hydroisomerization of n-octane on Pt-based catalysts

SAPO-11 molecular sieves were synthesized using silica sol, hydrophilic fumed silica, and tetraethyl orthosilicate (TEOS) as silicon precursors. Their physicochemical properties were characterized using XRD, SEM, nitrogen adsorption-desorption, Py-IR, NH3-TPD, EDS, and 27Al, 31P, 29Si MAS NMR techniques. The catalytic performance was assessed in the hydroisomerization of n-octane. The results showed that the silicon precursors influenced the physicochemical properties and catalytic performance of SAPO-11. SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor showed higher silicon distribution and had more medium acid sites. SAPO-11 synthesized using TEOS as silicon precursor had more silicon content, but more silicon islands formed in its framework. The depolymerization of silicon precursors might affect the silicon content and distribution in SAPO-11. In the hydroisomerization of n-octane, the catalytic activity strongly depended on the number of medium acid sites instead of the number of total acid sites. SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor exhibited higher catalytic activity than the other samples because it has more medium acid sites.

N-octane catalytic isomerization with aluminium and aluminiumlanthanum pillared nontronite

Abstract Nontronite samples pillared with aluminium (Pt/Al-PilM) and aluminium-lanthanum (Pt/AlLa-PilM) were prepared from natural nontronite, characterized and tested as catalyst in n-octane hydroisomerization reaction. The results were compared with those obtained from the same reaction using commercial Y-zeolite impregnated with platinum (Pt-Y). Experiments with commercial zeolite show that platinum is essential to maintain the reactional selectivity of the products. The conversion capacities of (Pt/Al- PilM) and (Pt/AlLa-PilM) were 70% and 40%, respectively, surpassing the Pt-Y performance of 30%, but with the same selectivity. X-ray diffraction data show that organic matter oxidation followed by cationic homogenization is of paramount importance for pillared clay preparation.

Hydroisomerization of n-alkanes over Pt-modified micro/mesoporous materials obtained by mordenite recrystallization

Hydroisomerization of n-hexane, n-octane and n-hexadecane has been studied over Pt-containing micro/mesoporous materials obtained by mordenite (MOR) recrystallization in alkaline solution in the presence of cethyltrimethylammonium bromide. The degree of recrystallization was controlled by varying the concentration of NaOH. Micro/mesoporous nanocomposites MOR/MCM-41 with intermediate degree of recrystallization showed remarkably high activity and selectivity in hydroisomerization of n-octane and high selectivity in hydroisomerization of n-hexadecane. The effect is due to high accessibility of the active sites, improved transport of bulky molecules provided by mesopores and optimal size of Pt particles located in mesopores.

Synthesis, characterization and catalytic properties of Y-β zeolite composites

Y-β zeolite composites were hydrothermally synthesized by using high silica Y zeolite as the precursor and characterized by XRD, N2 adsorption, SEM and IR spectra of pyridine. The result showed that the N2 adsorption-desorption isotherm of the zeolite composites had a distinct hysteresis loop, and the SEM result showed that the zeolite composites had a different morphology from Y, β and the corresponding physical zeolite mixture. The acid catalytic performance of the zeolite composite catalysts was investigated in the hydrocracking and hydroisomerization of n-octane, and the results showed that the composite materials exhibited an excellent hydrocracking activity and good hydroisomerization performance. The yield of i-C4 over the zeolite composite catalyst was 4.45% higher than that on the corresponding zeolite mixture in the n-octane hydrocracking process at 553 K. The isomerization ability of n-octane over the composite catalyst was 3.6 fold that of the corresponding mixture at 503 K.

Hydroisomerization of n-octane on molybdenum based catalyst

Balanced metal–acid bifunctional MoO 2− x (OH) y catalytic system has been prepared. 2–3 monolayers of this phase on the sample surface were obtained following controlled reduction by hydrogen of equivalent 5 monolayers of MoO 3 deposited on TiO 2. Hydroisomerization reaction of n-octane on this Mo bifunctional phase, at similar experimental conditions to those employed in the case of nC5–nC7 hydrocarbons, produce branched species of relatively high octane numbers as compared to parent molecule, in contrary to Pt based catalysts in which hydrocracking reactions were observed. Bench scale catalytic experiments were carried out using 15 g catalyst under 5 bar hydrogen pressure, 25 SLPH, 0.4 h −1 LHSV and 623 K reaction temperature. Time on stream (TOS) experiments for several days did not show any changes in neither the conversion nor the isomerization selectivity. The stability and the resistance of the catalytic system towards poisoning by hydrocarbon species as well as its high performances towards n-octane hydroisomerization are attributed to its specific spatial geometry in which Mo atoms are present in alignment positions placed along the C-axis of the deformed rutile structure of MoO 2 phase, as well as the moderate (metal–acid) functions strength of the surface MoO 2− x (OH) y phase.

Catalytic performance of Pt/HY-β in n-octane hydroisomerization

A bifunctional catalyst Pt/HY-β was prepared from a bimicroporous composite zeolite Y-β. Characterization results showed that the specific surface area, pore volume, and acid amount of the catalyst Pt/HY-β all decreased compared to the original zeolite. The catalytic performance of this catalyst in n-octane hydroisomerization was investigated in a fixed bed stainless steel tubular reactor. The results showed that at a hydrogen/n-octane volume ratio of 1000, pressure of 0.6 MPa, temperature of 230 °C and LHSV of 3 h−1, the conversion of n-octane, yield of liquid, hydrocracking rate and yield of iso-octane were 52.32%, 88.66%, 12.60%, 39.51%, respectively.

Hydroisomerization of n-Octane over Bifunctional Ni−Pd/HY Zeolite Catalysts

Bifunctional catalysts containing 0.1−0.5 wt % nickel and 0.1 wt % palladium supported on HY zeolite were prepared through incipient wetness impregnation (IWI) and characterized by X-ray diffraction (XRD), Brunauer−Emmett−Teller (BET) surface area, temperature-programmed desorption of ammonia (NH3-TPD), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Hydroisomerization of n-octane was carried out between 200 and 450 °C under 1 atm of pressure, and it was found that Ni addition up to 0.3 wt % over 0.1 wt % Pd/HY zeolite enhanced the n-octane conversion and isomerization selectivity with a low percentage of cracked products. As the Ni amount exceeds the threshold values, the conversion decreases with an increase in cracked products, and also, the selectivity of mono- and dibranched isomers was improved, suggesting the operation of a protonated cyclopropane (PCP) intermediate mechanism. As a conclusion, the bimetallic catalysts were ...

Influence of the Addition of a Second Metal on the Catalytic Performance of Pt-Beta Agglomerated Catalyst in the Hydroisomerization of n-Octane

In this work, the hydroisomerization of n-octane on mono and bimetallic beta agglomerated zeolite based catalysts was investigated. As the metal function, platinum and combinations with nickel and tin were studied. Test reactions were carried out at 10 bar and 290–410 °C. The bimetallic catalyst with the lowest amount of Ni yielded the greatest multibranched selectivity.

Effect of the binder content on the catalytic performance of beta-based catalysts

The influence of the amount of a clay binder (sodium bentonite) on the properties and performance of beta zeolite based catalysts for the hydroisomerization of n-octane was studied. The contribution of the bentonite to the total acidity of agglomerated catalysts was very low, although its presence could affect to the acidic properties. Experimental acidity values for the agglomerated catalysts did not match with those theoretically expected due to a solid-state ion exchange between protons of the zeolite and sodium of the clay during the calcination following the ion-exchange step. Metal dispersion values were in agreement with the specific surface area of the zeolite in the agglomerated catalysts, suggesting that the metal were mainly located into the zeolite. Catalysts were tested in the hydroisomerization of n-octane. Concerning the agglomerated catalysts, the higher the strong acid site density per gram of zeolite was, the higher the n-octane conversion was observed. Non-agglomerated catalysts, even showing a higher strong acid site density per gram of zeolite, exhibited the lowest n-octane conversion. EFAL species were present on the agglomerated catalysts enhancing their acid strength through a synergetic effect that allowed them to be much more active for the hydroisomerization of n-octane.

Hydroisomerization of n-Octane over Nickel−Tungsten Supported on Silica−Alumina Catalysts

The hydroisomerization of n-octane over Ni-WO x /silica-alumina based catalysts has been investigated in a down flow fixed-bed quartz reactor by changing operating conditions such as time on stream, reaction temperature, SiO 2 /Al 2 O 3 and H 2 /n-octane ratio, andspace velocity. This study aims to understand the activity and selectivity properties of the prepared catalysts and to analyze the relationship between the metal content, the acidity (nature and strength) of the samples, and the main reaction paths. It was found that all catalysts deactivate with time on stream, with the conversion remaining steady after 100 min. On increasing the nickel loading, conversion increases as does selectivity to isomerization, which reaches a maximum and then decreases. Moreover, the obtained results showed that the H 2 partial pressure and SiO 2 /Al 2 O 3 ratio positively affect isomerization selectivity while the opposite effect was observed for activity (conversion). In addition, the main reaction pathways in n-octane hydroconversion over the prepared solids were found to be isomerization, cracking, and hydrogenolysis. At steady-state conditions (after 100 min TOS), the catalyst with 15% of nickel and 10% of tungsten (WT(15,10)) showed the best results (69% of selectivity at 32.5% conversion).

Liquid-Phase Hydroisomerization of n-Octane over Platinum-Containing Zeolite-Based Catalysts with and without Binder

Liquid-phase hydroisomerization of n-octane with three different framework zeolites catalysts with similar Si/Al ratios, USY, mordenite, and beta, was performed in a stirred batch autoclave microcatalytic reactor. As the hydrogenating−dehydrogenating function, platinum supported by impregnation (1 wt %) was used. Additionally, these zeolites were agglomerated with bentonite, the catalytic performance being compared with that obtained for the nonagglomerated samples. To characterize the catalysts, surface area measurements, temperature-programmed desorption of ammonia, atomic absorption spectroscopy, inductively coupled plasma emission spectrophotometry, hydrogen chemisorption, and solid-state 27Al NMR were used. In all cases, a decrease in the catalytic activity of agglomerated samples, because of the modification of the acidity and the porosity of the zeolites by the binder was observed. The decrease in the acidity after the agglomeration could be attributed to solid-state ion exchange between zeolite pr...

Influence of clay binder on the liquid phase hydroisomerization of n-octane over palladium-containing zeolite catalysts

The influence of the clay binder on the properties and performance of palladium-containing zeolite catalysts in the liquid phase hydroisomerization of n-octane was studied. Three different framework zeolites with similar Si/Al ratio were used as catalysts: USY, mordenite and beta with or without binder. In all cases, a decrease in the catalytic activity of agglomerated samples, because of the modification of the acidity and the porosity of the zeolites by the binder, was observed. The decrease in the acidity after the agglomeration could be attributed to solid-state ion exchange between zeolite protons and clay sodium during the calcination of the catalyst. Moreover, the aluminium extraframework species (EFAL) created during the agglomeration process could cause a partial blocking of the micro-pore mouths, which would lead to an increase in the length of the effective diffusional pathway. After the agglomeration process, the monobranched isomers selectivity increased for all the samples while the multibranched isomers selectivity decreased. Due to the high pressure in the liquid phase, a significantly higher isomers selectivity was obtained as compared to vapour-phase conditions, and cracking became important only at relatively high average conversions.

Kinetic Model of the n-Octane Hydroisomerization on PtBeta Agglomerated Catalyst: Influence of the Reaction Conditions

The aim of this work was to study the influence of the reaction conditions in the hydroisomerization of n-octane over beta agglomerated zeolite, using platinum as the hydrogenating/dehydrogenating function. From the obtained data, a kinetic model was constructed to obtain the fundamental rate coefficients of the hydroisomerization reaction. The influence of the temperature was studied first, observing higher n-octane conversions with increasing temperature. The opposite effect was observed for the isomer selectivity. Next, it was observed that n-octane conversion decreased with the total pressure of the reaction, with the opposite effect being observed for the isomer selectivity. The effect of the reaction pressure in suppressing cracking and simultaneously promoting isomerization was attributed to the increase in the partial pressure of hydrogen. A similar effect was observed when the molar hydrogen/n-octane ratio was studied due to a better removal of alkenes species. When the influence of the contact t...