Hydroisomerization Of N-hexadecane Research Articles

Single-Event Microkinetic Model for Long-Chain Paraffin Hydrocracking and Hydroisomerization on an Amorphous Pt/SiO2·Al2O3 Catalyst

Hydrocracking of a long-chain paraffin, n-hexadecane, was carried out on an amorphous Pt/SiO2·Al2O3 bifunctional catalyst. Through an isomerization selectivity analysis, it was found that the behavior of the system approaches the ideal hydrocracking conditions. The kinetic modeling of paraffin hydrocracking and hydroisomerization was realized by using the principles of the single-event microkinetic concept. The single-event microkinetic concept has been demonstrated to be efficient in the modeling of acid-catalyzed reactions. A lumped single-event microkinetic model was developed for heavy paraffin hydrocracking in the liquid phase, which considers a group of only nine rate constants for the reactions on the acid phase of the catalyst. The model’s lumping coefficients were calculated by the lateral-chain method, a computer-based approach that does not imply the generation of the whole reaction network. The rate constants were estimated at 340 °C from n-hexadecane hydroisomerization experiments in a plug-flow pilot reactor. The kinetic model was validated (upon extrapolation) by the simulation of two heavier paraffin feeds: a C20−C30 wax mixture and pure squalane. The agreement between the calculated and experimental data was satisfactory.

Hydroisomerization of <i>n</i>-Hexadecane over Pt/Beta and Pt/USY Zeolite Catalysts

Bifunctional platinum (0.8 wt%) catalysts containing beta and USY zeolites were tested for the hydroisomerization of n-hexadecane. The Pt/Beta(SiO2/Al2O3 = 40) catalyst with moderate acid strength showed better isomerization selectivity than the Pt/USY(SiO2/Al2O3 = 11) catalyst which showed higher n-hexadecane conversion but higher hydrocracking activity due to their strong acid sites. The Pt/Beta(SiO2/Al2O3 = 40) catalyst showed high isomerization selectivity and improvement in cold flow property even under more than 90% conversion of n-hexadecane.

Changing the hydroisomerization to hydrocracking ratio of long chain alkanes by varying the level of delamination in zeolitic (ITQ-6) materials

Several delaminated ITQ-6 acid samples have been synthesized and tested in the isomerization of n-hexadecane. It has been found that the swelling time is a decisive parameter to prepare ITQ-6 catalytic materials with different ratios of micro to mesoporous surface area. n-Hexadecane hydroisomerization results indicate that the appropriate control of the delamination conditions can drive to obtain optimized ITQ-6 materials highly active for the hydroisomerization/hydrocracking of long chain alkanes to produce lube oils, diesels or gasolines.

Modelling of n-hexadecane hydroisomerization and hydrocracking reactions on a Mo/Hβ-alumina Bi-functional catalyst, using the single event concept

Hydrocracking of a long chain paraffin, hexadecane, was carried out on a Mo/Hβ-alumina bi-functional catalyst with a weak dehydrogenating function. It was found through an isomerization selectivity analysis that the behavior of the system is away from ideal hydrocracking conditions. To implement for this system the single event concept, until now applied only to systems for which the ideal hydrocracking assumption was valid, a hybrid model that includes the more general case in which reactions on the acid sites are not rate determining was developed. This model was called the single-event-lumped-parameter hybrid (SELPH) model, for it considers fundamental rate constants for the reactions that take place on the acid sites using the single event concept, and lumped rate constants for the reactions on the metal sites. The kinetic coefficients at 533 K were estimated and the agreement between the calculated and experimental data was satisfactory.

Anion-modified zirconia: effect of metal promotion and hydrogen reduction on hydroisomerization of n-hexadecane and Fischer–Tropsch waxes

The effect of metal promoters on the activity and selectivity of tungstated zirconia (8 wt.% W) for n-hexadecane isomerization in a trickle bed continuous reactor is studied by using different metals (Pt, Ni, and Pd) and, in one case, by varying metal loading. Platinum is found to be the best promoter. The effect of hydrogen reduction is investigated using platinum-promoted tungstated zirconia catalysts (Pt/WO 3/ZrO 2, 0.5 wt.% Pt and 6.5 wt.% W). Pretreatment at temperatures between 300 and 400°C for 3 h in hydrogen is found to be slightly beneficial for achieving high yields of isohexadecane. A platinum promoted sulfated zirconia (Pt/SO 4/ZrO 2) is compared with a Pt/WO 3/ZrO 2 catalyst for the hydroisomerization of n-hexadecane in the same reactor at the same n-hexadecane conversion. The former is a good cracking catalyst and the latter is suitable for use as a hydroisomerization catalyst. In a 27-ml microautoclave reactor, studies of the hydroisomerization and hydrocracking of two Fischer–Tropsch (F–T) wax samples are carried out. Severe cracking can be effectively suppressed using a Pt/WO 3/ZrO 2 catalyst so as to obtain branched isomers in the diesel fuel or lube-base oil range.

Comparison of Pt/zeolite catalysts for n-hexadecane hydroisomerization

Bifunctional platinum (0.5 wt.%) catalysts containing ZSM-5, ZSM-22, SAPO-11, Al-MCM-41, H-Y and H-β were tested for the hydroisomerization of n-hexadecane and their catalytic activities were compared. The Pt/ZSM-5, Pt/ZSM-22 and Pt/H-β catalysts showed higher hydrocracking activity due to their strong acid sites, while the Pt/SAPO-11, Pt/Al-MCM-41 and Pt/H-Y catalysts with moderate acid strength showed better isomerization selectivity. Especially the Pt/Al-MCM-41 catalyst, where Al-MCM-41 was prepared by post-synthetic metal implantation method from siliceous MCM-41, showed the highest isomerization selectivity as well as the highest yield of multibranched isohexadecanes, presumably not only due to its moderately weak acidity and mesoscale pores but also due to higher metal dispersion. This result indicates that the Pt/Al-MCM-41 catalyst can be a promising candidate for good dewaxing catalysts.

Hydroisomerization of normal hexadecane with platinum-promoted tungstate-modified zirconia catalysts

The present work examines the activity, selectivity and long-term stability of platinum-promoted tungstate-modified zirconia (Pt/WO 3/ZrO 2) catalysts for the hydroisomerization of long-chain linear alkanes under relatively mild conditions, using n-hexadecane as a model compound. The preparation of catalysts is described. A trickle-bed reactor is used to compare the activities and selectivities of three Pt/WO 3/ZrO 2 catalysts prepared by different methods and to investigate the effects of tungsten loading and of reaction conditions for hydroisomerization of n-hexadecane. A run of 93.5 h was conducted using the most highly active Pt/WO 3/ZrO 2 catalyst which contains 0.5 wt.% well-dispersed Pt and 6.5 wt.% W. Reaction conditions were manipulated and five shutdown (feed stopped, reactor temperature lowered but H 2 flow rate maintained) and restart operations were carried out. This catalyst showed high activity and stability. Considerable success has also been achieved in converting n-hexadecane to isohexadecanes for 100 h at temperatures of about 220°C and under H 2 pressure as low as 160 psig (1 psig = 6.895 kPa). Our best results (highest i-C 16 yield) are a 79.1 wt.% n-C 16 conversion, 89.9 wt.% i-C 16 selectivity and 71.1 wt.% i-C 16 yield at 218°C, 160 psig H 2, H 2/ n-C 16 mole ratio = 2 and weight hour space velocity (WHSV) = 1 h −1. The Pt/WO 3/ZrO 2 catalyst is rugged and has properties which allow one to propose that it may attain commercial use after further study.

Hydroisomerization and hydrocracking of long chain n-alkanes on Pt/amorphous SiO 2–Al 2O 3 catalyst

The hydroisomerization and hydrocracking of n-hexadecane, n-octacosane and n-hexatriacontane on a 0.3% platinum/amorphous silica–alumina (MSA/E) catalyst was investigated in a stirred microautoclave at 345, 360 and 380°C and between 2 and 13.1 MPa hydrogen pressure. For each n-paraffin, the reaction pathway and the kinetic parameters were determined. The results were used to elucidate the effect of chain length and operating conditions on isomerization and cracking selectivity. The conversion of the n-paraffins lead to the formation of a mixture of the respective isomers, as the main product, together with cracking products. At every temperature, the iso-alkane/ n-alkane ratio of cracking products increased considerably with increasing conversion degree. At the same conversion level, higher reaction temperatures lead to cracking products characterized by a lower iso-alkane/ n-alkane ratio. The conversion rate constants showed a considerable increase between n-C 16 and n-C 28, whereas a slight decrease between n-C 28 and n-C 36 was observed. The hydroisomerization selectivities showed a decrease as a function of chain length and with increasing conversion levels. The increase in reaction temperature leads to a small decrease in the isomerization selectivities only at low-medium conversion degrees and at the highest temperature investigated, while the effect of this parameter on the maximum yields achievable in iso-C16, iso-C28 and iso-C36 was negligible. The results indicate that the conversion of the n-paraffins follows a first-order kinetic in hydrocarbon while the order in hydrogen pressure was −1.1 ± 0.21 for n-C 16 and −0.66 ± 0.15 for n-C 28. Furthermore, an increase in hydroisomerization selectivity at higher hydrogen pressure for n-C 28 conversion was observed.

Computer-assisted mechanistic modeling of n-hexadecane hydroisomerization over various bifunctional catalysts

Graph theoretic concepts were exploited to construct candidate computer models describing the hydroisomerization of n-hexadecane over bifunctional catalysts at a mechanistic level. The molecules and carbenium ions were represented as atomic connectivity matrices and the reactions as matrix operations. The computer-generated models were then automatically converted to a set of ordinary differential equations representing the reactions in a plug flow reactor. Typical diagnostics for the model building process indicate that models containing about 1000 species (molecules and ions) and 3000 reactions could be generated in around 1000 CPU seconds. Thus, some 25 candidate hydroisomerization models were built and evaluated through qualitative and quantitative comparisons with experimental data. The resulting best model was further pruned by removing extraneous reactions which did not result in observable products. This model was tuned against experimental data on three different catalysts at different temperatures. Good agreement between model predictions and experimental data was obtained. Trends in the fundamental mechanistic rate constants obtained from the model fitting process were in harmony with the trends in the acid and metal loadings of the catalysts. Thus, fundamental mechanistic modeling can provide valuable insight into the nature of the catalytic action.

The effect of Pt concentration on the activity and selectivity of SO 42−ZrO 2 catalysts for the hydrocracking and hydroisomerization of n-hexadecane

The addition of Pt to promote the long-term activity of SO 4 2−ZrO 2 catalysts is showm to have a strong influence on the conversion of n-hexadecane. The maximum conversion occurs at the 0.6–1.0 wt.% Pt concentration range; increasing further the Pt concentration up to 5.0 wt.% does not increase the conversion of n-hexadecane. At a constant conversion, the selectivity for isomerization and cracking is the same for different levels of Pt. However, the carbon number distribution of the cracked products shows a small shift to higher carbon numbers with increasing Pt loadings.

Impact of Catalyst Metal−Acid Balance in n-Hexadecane Hydroisomerization and Hydrocracking

The reaction pathways and kinetics of n-hexadecane hydroisomerization and hydrocracking were determined in the presence of each of three platinum-containing dual-function catalysts: (a) Pt on a proprietary zeolite (Pt/Ζ), (b) Pt on silica−alumina (Pt/Si−Al), and (c) Pt on MCM-41 (Pt/MCM-41). The reaction networks were used to interpret differences in isomerization selectivity. The low isomerization selectivity observed in the presence of Pt/Si−Al was shown to be a consequence of changes in both relative isomerization/cracking rates and reaction pathways. Using the classical bifunctional reaction scheme, the changes in pathway were hypothesized to be consistent with changes in the relative concentrations of metal and acid sites (i.e., the metal−acid balance). On the basis of a recently proposed model of dual-function catalysis, the different observed pathways were subsequently shown to be those expected in two limiting case of the metal−acid balance. The simplified quantitative picture given here provides a preliminary basis for relating catalyst preparation variables to catalyst performance for dual-function catalysts.

Hydroisomerization and Hydrocracking of n-Hexadecane over a Platinum-Promoted Sulfated Zirconia Catalyst

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHydroisomerization and Hydrocracking of n-Hexadecane over a Platinum-Promoted Sulfated Zirconia CatalystRobert A. Keogh, Dennis Sparks, Jianli Hu, Irving Wender, John W. Tierney, Wei Wang, and Burtron H. DavisCite this: Energy Fuels 1994, 8, 3, 755–762Publication Date (Print):May 1, 1994Publication History Published online1 May 2002Published inissue 1 May 1994https://doi.org/10.1021/ef00045a032RIGHTS & PERMISSIONSArticle Views357Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (830 KB) Get e-Alerts Get e-Alerts

Hydroisomerization and hydrocracking of n-heptane and n-hexadecane on solid superacids

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHydroisomerization and hydrocracking of n-heptane and n-hexadecane on solid superacidsMichael Y. Wen, Irving Wender, and John W. TierneyCite this: Energy Fuels 1990, 4, 4, 372–379Publication Date (Print):July 1, 1990Publication History Published online1 May 2002Published inissue 1 July 1990https://doi.org/10.1021/ef00022a007RIGHTS & PERMISSIONSArticle Views588Altmetric-Citations73LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (906 KB) Get e-Alerts Get e-Alerts

Kinetics of n-hexadecane hydrocracking on nickelmolybdenum/alumina catalysts

Composition of the products of n-hexadecane hydrocracking on Ni−Mb−Al catalysts has been determined. It is shown that the data of a single experiment can be used to obtain four rate constants for hydroisomerization and hydrocracking of n-hexadecane and its isomers.

Hydrocracking product distributions from n-alkanes and iso-alkanes

Crystalline phase pure ZSM-22 framework (bulk molar ratio ~45) has been synthesized and employed to investigate the effect of tailored Brønsted acidity on hydroisomerization of n-hexadecane. Typically, ZSM-22 framework Brønsted acidity is tailored with Group-II cations viz. Mg2+, Ba2+ and Ca2+, by means of ion-exchange method. The physico-chemical characterization of the various samples have been performed using powder X-ray diffraction, nitrogen adsorption–desorption isotherm measurement at 77 K, inductively coupled plasma (ICP) and scanning electron microscopy (SEM) techniques. The framework acidity w.r.t. Brønsted level has been characterized and estimated using ammonia temperature programmed desorption (NH3-TPD) and Fourier transform infrared spectroscopy of Pyridine (Py-FTIR) as a function of temperature, respectively. Hydroisomerization of n-hexadecane is performed over Pt (~0.45 wt%)/M-H-ZSM-22 samples (in extrudate form) in an up-flow fixed bed reactor and the effect of process parameters namely temperature and WHSV have been investigated. Based on the obtained results, Pt/Ca-H-ZSM-22 framework with calcium exchange level of about 10% showed the optimum performance among all the prepared samples with maximum isomer selectivity, yield (85.8 and 77.8%, respectively) vis-à-vis Pt/H-ZSM-22 sample (79.3 and 70.5%, respectively) and more importantly branching index of 4 in favor of mono-branched isomers, at a conversion level of about 90% at 585 K.Among Group II cations, calcium exchange over ZSM-22 framework is found to be effective in enhancing selectivity in favor of mono-branched isomers. In view of this, the role of tailored acidity through Group II cation exchange for optimization of degree of branching during hydroisomerization of long chain n-paraffin is discussed. Furthermore, the relative maximization of mono-branched isomers using calcium exchange is expected to offer platform for development of hydroisomerization catalyst with minimum cetane loss.