Conversion Of N-octane Research Articles

Increased Light Olefin Production by Sequential Dehydrogenation and Cracking Reactions

In this study, a sequential reaction using selected metal oxides, followed by ZSM-5-based catalysts, was employed to demonstrate a promising route for enhancing light olefin production in the catalytic cracking of naphtha. The rationale for the reaction is based on the induction of alkenes into hydrocarbon feeds prior to cracking. The optimum olefin induction was achieved by carefully optimizing the dehydrogenation active sites Mo/Al2O3 catalyst. The formed alkenes have a lower activation energy for C-H/C-C bond breaking compared to alkanes. This could accelerate the formation of carbenium ions, thus promoting the conversion of n-octane to produce light olefins. Detailed product distribution and DFT calculation indicated a remarkable increase in ethylene and propylene production in the final product through a modified reaction pathway. Compared with the common metal-promoted zeolite catalysts, the new route could avoid the block of zeolite channels and corresponding decreased catalytic cracking activity. The feasibility of the proposed route was confirmed with different ratios of dehydrogenation catalyst to the reactant. The highest yields of ethylene and propylene reached 13.22% and 33.12% with ratios of Mo/Al2O3 and ZSM-5-based catalyst to n-octane both 10:1 at 600 °C. Stability tests showed that the catalytic activity of the double-bed system was stable over 10 cycles.

A highly efficient bi-functional zeolite catalyst for low temperature catalytic cracking of n-octane to produce propylene: Joint contribution of nanogold and dealumination

With respect to catalysis, the pursuit of low reaction temperatures has received continuous efforts for developing energy efficient and environmentally friendly processes. In this study, the significant promotion in the catalytic cracking performance of n-octane at low temperatures of 260–460 °C over Au/ZSM-5 catalysts was obtained via the joint contribution of dealumination and Au species. A 63.5% propylene selectivity and 100% n-octane conversion were obtained over the optimized catalyst at 410 °C. The higher propylene yield was attributed to an increase in the concentration of Brønsted acids and a decrease in that of Lewis acids, as well as synergy between acid sites and Au species. The positive effect of Au species during dehydrogenation at lower temperatures was verified, and electron transfer from Au to the zeolite framework was proposed.

Realumination of dealuminated HZSM-5 zeolites by acid treatment, the impact of AlF distribution and its catalytic cracking performance of alkanes

Realumination of dealuminated HZSM-5 zeolites by acid treatment has always been controversial and puzzling. Through characterizations of XRD, nitrogen adsorption, NH3-TPD, IR, XPS and 27Al MAS NMR, this work confirmed realumination of dealuminated HZSM-5 zeolites could indeed be achieved after treated with HCl solution. And it was found mainly a portion of the penta-coordinated extra-framework aluminia (EFAl) were reinserted into the framework during the process of realumination. Moreover, the characterizations of ICP-AES and UV–Vis-DRS of Co2+-exchanged zeolites indicated the realumination capacity was closely related to the distribution of framework Al (AlF). Realumination was more likely achieved when there was lower content of Al pairs and less AlF located in the channel intersections in HZSM-5. Finally, realuminated zeolites exhibited a higher conversion of n-octane due to its more Brønsted acid sites than dealuminated HZSM-5 in catalytic cracking reaction. The significantly lower content of Al pairs in realuminated zeolites compared to parent HZSM-5 inhibits the hydride transfer process to a certain extent, resulting in a higher selectivity of propylene.

Kinetics of dehydrogenation of n-octane on a promoted Pt-catalyst

In contrast to short as well as long chain paraffin dehydrogenation, the highly desirable reaction of intermediate chain length paraffins (C6 - C9) to the corresponding linear monoolefins receives only little attention in the literature. Consequently, the dehydrogenation of the model substance n-octane on promoted platinum catalysts was studied thoroughly. In the first instance, the effect of the addition of different promotors (Sn, K, Ce) on the catalytic performance with emphasis on activity and octene selectivity was tested by screening of 16 differently promoted Pt-catalysts. The optimized and non-deactivated catalyst was then used to investigate the kinetics of n-octane dehydrogenation including the unwanted consecutive formation of n-octadienes and C8-aromatics. The analysis revealed that the desired n-octenes are rapidly converted to n-octadienes, i.e. the thermodynamic equilibrium of this reversible reaction is quickly established. To a small extent, the n-octadienes are further converted to C8-aromatics. A kinetic model was developed, which also considers the inhibiting effect of n-octenes on the rate of n-octane conversion. The model accurately predicts the formation of mono- and diolefins as well as of aromatics in the initial reaction phase in the absence of deactivation.

Interplay of Metal-Acid Balance and Methylcyclohexane Admixture Effect on n-Octane Hydroconversion over Pt/HUSY

Hydroconversion feeds are mixtures comprising alkanes and cycloalkanes, for which the binary impact on the respective reaction pathways, is still not completely understood. Methylcyclohexane admixture on n-octane hydroconversion over Pt/HUSY catalysts has been investigated using the pure compounds and their equimolar mixtures in a wide range of operating conditions. The hydroconversion behavior on catalysts with various Pt loading was examined to investigate the role of the active sites. No impact of methylcyclohexane admixture to n-octane was observed over catalysts which ensured ideal hydrocracking (0.5 and 0.1 wt%Pt). In contrast, methylcyclohexane addition decreased the octane isomer yield at iso-conversion over 0.07 wt%Pt/HYUSY. A lower metal loading of 0.04 wt%Pt led to a pronounced decrease in n-octane conversion in the mixture. The methylcyclohexane conversion was not affected by n-octane addition regardless of the metal-acid balance. The negative admixture impact on the n-octane conversion and isomers yield, combined with the absence of any impact on the methylcyclohexane behavior, was attributed to preferred cycloalkane adsorption on metal sites, resulting in a reduced metal site availability for alkanes. A cycloalkane admixture to an alkane in hydrocracking can, hence, induce a regime shift from ideal to nonideal hydrocracking. Consequently, bifunctional catalysts developed purely for alkane hydroconversion may prove not to be optimal for realistic feeds, including cycloalkanes.

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.

The effects of metals and ligands on the oxidation of n-octane using iridium and rhodium “PNP” aminodiphosphine complexes

Ir and Rh “PNP” complexes with different ligands are utilized for the oxidation of n-octane. Based on the obtained conversion, selectivity, and the characterized recovered catalysts, it is found that the combination of Ir and the studied ligands does not promote the redox mechanism that is known to result in selective formation of oxo and peroxo compounds [desired species for C(1) activation]. Instead, they support a deeper oxidation mechanism, and thus higher selectivity for ketones and acids is obtained. In contrast, these ligands seem to tune the electron density around the Rh (in the Rh-PNP complexes), and thus result in a higher n-octane conversion and improved selectivity for the C(1) activated products, with minimized deeper oxidation, in comparison to Ir-PNP catalysts.

Effects of Framework Disruption of Ga and Ba Containing Zeolitic Materials by Thermal Treatment

The effect of the thermal treatment of some zeolitic materials was studied on oxidative dehydrogenation (ODH) of n-octane. Gallium containing faujasite catalysts were synthesized using isomorphic substitution, specifically, a galosilicalite (Ga-BaY(Sil)) and an aluminosilicalite substituted with gallium (Ga-BaY(IS)), with constant Si/M ratio. The catalysts were thermally treated at different temperatures (250, 550, and 750 °C) before catalytic testing. The quantification of total and strength of acid sites by FT-IR (O-H region), pyridine-IR, and NH3-temperature-programmed desorption (TPD) confirmed a decrease in the number of Brønsted acid sites and an increase in the number of Lewis acid sites upon increasing the calcination temperature. Isothermal n-octane conversion also decreased with the catalysts’ calcination temperature, whereas octene selectivity showed the opposite trend (also at iso-conversion). The COx selectivity showed a decrease over the catalysts calcined from 250 to 550 °C and then an increase over the 750 °C calcined catalysts, which was due to the strong adsorption of products to strong Lewis acid sites on the catalysts leading to the deep oxidation of the products. Only olefinic-cracked products were observed over the 750 °C calcined catalysts. This suggested that the thermal treatment increases Lewis acid sites, which activate n-octane using a bimolecular mechanism, instead of a monomolecular mechanism.

Effect of carbon number on the production of propylene and ethylene by catalytic cracking of straight-chain alkanes over phosphorus-modified ZSM-5

Phosphorus-modified ZSM-5 (P-ZSM-5) shows catalytic activity for the cracking of alkanes to produce light olefins such as ethylene and propylene. Here, we investigated the effect of the carbon number (i.e., chain length) of straight-chain alkanes (n-pentane, n-hexane, n-heptane, and n-octane) on the production of ethylene and propylene by catalytic cracking over P-ZSM-5 at 923 K or 873 K. The percent of n-alkane converted and yields of light olefins increased with increasing carbon number of the reactant hydrocarbon. In the case of n-octane cracking at 923 K, 97.1% conversion of the alkane and 64.5% combined yield of ethylene and propylene were obtained. Up to a reaction time of 30 h, the P-ZSM-5 catalyst was stable and the n-octane conversion remained over 91.2%.

The Performance of Catalytic Conversion of ZSM-5 Comodified with Gold and Lanthanum for Increasing Propylene Production

Catalytic conversion of n-octane and light diesel oil was carried out over ZSM-5 comodified with gold and lanthanum by modified deposition-precipitation and wet impregnation methods. A series of ZS...

Flexible SNS pincer complexes of copper: Synthesis, structural characterisation and application in n-octane oxidation

Two new tridentate SNS ligands based on a flexible, straight chain amine backbone were prepared and in combination with three related but previously reported ligands were reacted with CuCl2 to yield new tridentate pincer-type copper(II) complexes. The molecular structures of the new ligands bis(cyclohexylthioethyl)methylamine (L1d), bis(t-butylthioethyl)methylamine (L1e), and all the complexes Cu[bis(Rthioethyl)methylamine]Cl2 (1) where R = methyl (a); ethyl (b); butyl (c); cyclohexyl (d) and t-butyl (e); were confirmed by a range of spectroscopic and analytical techniques. Single crystal X-ray diffraction analysis determined the solid-state structures of the salt of L1e and the complexes. Complexes 1a-e all exhibited five-coordinate ligand geometry around each Cu(II) centre defined by the tridentate SNS and two chlorido donors. The complexes were applied as catalysts in the oxidation of n-octane using t-butyl hydroperoxide and hydrogen peroxide (H2O2) as oxidants. The H2O2 based systems yielded up to 36% conversion of n-octane to C-8 oxygenates with very high alcohol selectivity of up to 78%.

The effect of varying the metal ratio in a chromium molybdate catalysts for the oxidative dehydrogenation of n-octane

Chromium molybdate catalysts with varying Cr/Mo ratios were synthesized by co-precipitation. The catalysts were characterized using XRD, Raman spectroscopy, TPR, BET surface area measurements, ICP-OES and HR-TEM. X-ray diffraction and Raman studies revealed that the dominant phase in the catalysts was Cr2(MoO4)3. Furthermore, Raman spectroscopy showed that excess Mo and Cr exist as MoO3 and Cr2O3 phases, respectively. The catalytic activation of n-octane was investigated from 350 to 550 °C, in a continuous flow fixed-bed reactor with the GHSV fixed at 4000 h−1. Catalytic testing revealed that the conversion of n-octane and product selectivity varied with Cr/Mo ratio. At 6% isoconversion (350 °C), the stoichiometric catalyst, i.e. the catalyst with a Cr/Mo ratio of 0.67, produced octenes and carbon oxides as the major products with a selectivity of 51% and 49%, respectively.

An investigation of iron modified hydroxyapatites used in the activation of n-octane

Iron (9wt.%) modified hydroxyapatites were synthesised using two chemical techniques, namely wet impregnation and co-precipitation. SEM-EDX showed that the material prepared using a wet impregnation technique (9-WET) contained iron distributed on the surface of hydroxyapatite, identified as small particles of Fe2O3, using PXRD and Mössbauer spectroscopy. In contrast, PXRD, Mössbauer spectroscopy and SEM-EDX of the material prepared using a co-precipitation technique (9-COP) revealed that both iron and calcium had been incorporated into the hydroxyapatite structure. The formation of an iron pyrophosphate phase upon reduction of 9-COP was identified using in situ XRD. The material was then oxidised back to form a single phase hydroxyapatite-like material. NH3-TPD showed that the surface of the material prepared by co-precipitation was dominated by both weak acidic and basic sites. The material prepared using the wet impregnation technique, showed a greater degree of reduction. Hydroxyapatite and the iron modified hydroxyapatite materials were tested in the activation of n-octane, using a continuous flow, fixed-bed reactor operated in a down flow mode, and gave a range of octene isomers, aromatic compounds, cracked products and carbon oxides. The product distribution was in agreement with the acid-base properties of the materials. The material prepared using the co-precipitation technique favoured the formation of octene isomers. The conversion of n-octane was in accordance with the reducible nature of the materials. The selectivity toward octene isomers was relatively high over the material prepared using the co-precipitation technique (49 mol% at 550°C), and may have been due to the formation of the iron pyrophosphate phase formed at higher temperatures. The material prepared using the wet impregnation technique showed a maximum selectivity of 27mol% towards octene isomers at 350°C. Selectivity towards carbon oxides was lower over the material prepared using the co-precipitation technique compared to the material prepared using the wet impregnation technique over the entire temperature range tested.

Oxidative dehydrogenation of n-octane over Mg-containing SBA-15 material

In this study, it is proposed the incorporation of MgO into of SBA-15 via the direct synthesis different atomic ratios of Si/Mg (20, 40 and 80). Although the incorporation of Mg did not affect the mesoporous character of SBA-based materials, it was found dramatic changes in the SBA-15 characteristic honeycomb structure even after the incorporation of small amount of Mg. The creation of more basic sites in SBA-15, because of the addition of Mg, improved ODH conversion of n-octane with respect to SBA-15, used as reference. Sample with a Si/Mg molar ratio of 20 showed the best catalytic performance in the oxidative dehydrogenation of n-octane, while the sample with a Si/Mg molar ratio of 40 achieve the highest productions of olefins.

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.

Influence of pressure (100 Pa–100 Mpa) on the pyrolysis of an alkane at moderate temperature (603 K–723 K): Experiments and kinetic modeling

Confined pyrolysis of n-octane was performed in a closed, constant-pressure gold reactor at pressure ranging 1 MPa–70MPa, temperature between 603K and 723K and residence times from 1h to 1 month. The main products of reaction are n-alkanes of molecular weight lower than n-octane and branched alkanes of molecular weight higher than n-octane. Alkenes are minor products. At moderate temperature (603K–623K) the conversion of n-octane increases with pressure up to a maximum and then decreases (at constant duration of pyrolysis). For higher temperature (723K) the conversion increases continuously with increasing pressure. A mechanism consisting of 182 free-radical reactions is set up and used to model these experimental results (1–70MPa) as well as those obtained in a previous study at very low concentration (100Pa diluted in inert gas, total pressure 0.15MPa). The agreement between the experimental data and simulation results is satisfactory in terms of product distribution and conversion of n-octane in a wide range of pressure (100Pa to 70MPa). Some mechanistic explanations concerning the effect of pressure are proposed.

Catalytic Influence of Bimetallic Bifunctional Ni-Pd/H-β and H-Mordenite Nanoporous Catalysts for Hydroisomerisation of n-Octane

Zeolite-β and mordenite were impregnated with 0.1 wt% Pd and varying the amount (0.1–0.5 wt%) of Ni. The prepared nanoporous catalyst were characterized by various physico-chemical techniques such as XRD, nitrogen adsorption–desorption isotherm (BET), NH3-TPD and TPR, XPS and TEM. Hydroisomerisation of n-octane was carried out in the temperature range from 200 to 450 °C in the presence of flowing H2 gas under 1 atm. Finally we found that Ni addition up to 0.3 and 0.2 wt% over 0.1 wt% Pd/H-β and H-mordenite enhances the n-octane conversion and isomerisation selectivity. As the Ni amount exceeds the threshold values, the conversion decreases with increase in cracked products, and also, the selectivity of mono and dibranched isomers were improved suggestion operation of PCP intermediate mechanism. The bimetallic catalysts were more selective to the formation of dibranched isomers with higher octane number, when compared with monometallic catalysts. Ni-Pd loaded zeolite-β supports always show higher activity and selectivity than mordenite supports. Moreover, we achieved higher conversion (74.9 %) and isomerisation selectivity (92.5 %) at low Ni loading (0.3 Ni wt% over 0.1 Pd wt%/Hβ) for the first time.

Oxygenation cascade analysis in conversion of n-octane catalyzed by cytochrome P450 CYP102A3 mutants at the P331 site.

To improve the hydroxylation efficiency of cytochrome P450 CYP102A3 to substrate n-octane, a previously reported triple-mutant F88V/S188Q/A330V with altered regioselectivity was selected and site-saturation mutagenesis was performed at its P331 site, which is adjacent to one of the active sites A330. Using whole-cell biotransformations to analyze the created mutants, four better mutants P331A, P331T, P331S, and P331V were achieved and exhibited significantly improved conversion rates toward n-octane, which are 33%, 33%, 22% and 28%, respectively, whereas the activity of P331R was greatly reduced and P331K gave almost zero conversion of n-octane. Besides the main product octanols, different octanones and 1,7-octanediol were also detected for some of the mutants. The above results demonstrated that the P331 site of CYP102A3 also plays an important role in the n-octane oxidation and CYP102A3 is a functionally flexible biocatalyst that can be optimized for a variety of industrial applications.

Influence of tin content on the texture properties and catalytic performance of bi-metallic Pt–Re and tri-metallic Pt–Re–Sn catalyst for n-octane reforming

The effect of a relatively inactive metal on the texture properties and catalytic performance of bi-metallic platinum–rhenium (Pt–Re)–S/Al2O3–Cl catalyst was investigated. The concentration of introduced tin (Sn) varied between 0.06 and 0.32 % (weight basis). The parent and modified catalysts were characterized using the following techniques; BET, X-ray diffraction, SEM–EDX, and atomic absorption spectroscopy/inductively coupled plasma spectroscopy. The bi-metallic and tri-metallic catalysts were also screened for their activity and selectivity in the reforming of n-octane under the following conditions: T = 480 °C, p = 10 bar, WHSV = 3.3 h−1 and H2:HC = 4.5. Results showed that, on n-octane conversion, selectivity have changed favorably i.e., low selectivity to aromatics but high selectivity to iso-paraffins and olefins. In addition, less cracking products were detected and high liquid yields (LYs) were obtained. However, there is a strong and closely linear correlation between aromatics and octane number. The results of this work showed that catalyst with Sn >0.14 and <0.32 performed the best catalyst i.e., no major effect on research octane number, LY and selectivity with the addition of more Sn.

Coordination chemistry of Co complexes containing tridentate SNS ligands and their application as catalysts for the oxidation of n-octane.

The selective oxidation of saturated hydrocarbons to terminal oxygenates under mild catalytic conditions has remained a centuries long challenge in chemical catalysis. In an attempt to address this challenge, two series of tridentate donor ligands {2,6-bis(RSCH2)pyridine and bis(RSCH2CH2)amine [R = alkyl, aryl]} and their respective cobalt complexes {Co[2,6-bis(RSCH2)pyridine]Cl2 and Co[bis(RSCH2CH2)amine]Cl2} were synthesized and characterized. Crystal structures of Co[2,6-bis(RSCH2)pyridine]Cl2 [R = -CH3 (), -CH2CH3 (), -CH2CH2CH2CH3 () and -C6H5 ()] are reported in which crystallized as a homo-bimetallic dimer that incorporated two bridging chloride atoms in an octahedral geometry around each cobalt center, while , and crystallized as mono-metallic species characterized by trigonal bipyramidal arrangement of ligands around each cobalt center. As catalysts for the homogeneous selective oxidation of n-octane, the catalysts yielded ketones as the dominant products with a selectivity of ca. 90% for the most active catalyst Co[bis(CH2CH2SCH2CH2)amine]Cl2 () at a total n-octane conversion of 23%. Using tert-butyl hydroperoxide (TBHP) as an oxidant, optimization of reaction conditions is also reported.