Heptane Isomers Research Articles

Group contributions to the infinite dilution partial molar volumes of alkanes, alcohols, and glycols in polar organic solvents

Densities of binary mixtures of polar organic solvents with alcohols were measured at 25‡C. The solvents studied were N,N-dimethylformamide, dimethylsulfoxide, and formamide while alcohols were butanol, pentanol, hexanol, and 1,4-butanediol. Density measurements of hydrocarbons (from pentane to dodecane and some heptane isomers) + N,N-dimethylformamide were also performed. From these data the apparent molar volumes of alcohols and hydrocarbons as functions of concentration were calculated. The standard partial molar volumes were obtained by extrapolation to infinite dilution and are discussed in terms of group contributions.

Isomerization and Hydrocracking of Heptane over Bimetallic Bifunctional PtPd/H-Beta and PtPd/USY Zeolite Catalysts

Bifunctional catalysts are prepared by loading NH4-Beta zeolites with platinum, palladium, and platinum–palladium metal combinations via cation exchange and incipient wetness impregnation with Pt(NH3)4Cl2and Pd(NH3)4Cl2complexes, followed by calcination and reduction. In comparison to the Pt and Pd loaded acid zeolites, the bimetallic Pd–Pt zeolites are found to be more active and selective in the isomerization of heptane. The noble metal phases are characterized with temperature programmed reduction and hydrogen chemisorption. The dispersion of platinum is significantly improved in presence of as little as 20 mole% of palladium. The improved Pt dispersion leads to a better intimacy and balance of the acid and hydrogenation–dehydrogenation functions in these bifunctional catalysts and suppression of undesirable hydrogenolysis and dimerization-cracking activity. On Pt/USY zeolite, the addition of palladium has similar beneficial effects on the catalytic performances.

Isomerization of heptane on molybdenum oxides treated with hydrogen

Isomerization of heptane was carried out at 573 K under atmospheric pressure using molybdenum oxides as catalysts. MoO3 was inactive for this reaction. H2 reduction of MoO3 at 623 K, however, enhanced the isomerization activity and selectivity, which became almost constant after the reduction for 24 h. The reduced MoO3 exhibited a higher isomerization activity than a typical bifunctional catalyst, 0.5 wt%Pt/USY zeolite, while there was no appreciable difference in product distribution between these two catalysts. These results indicate that the reduced MoO3 catalyzed the isomerization of heptane via a conventional bifunctional mechanism.

Isomerization of heptane on molybdenum oxide catalysts with a small amount of nickel

T. Matsuda, H. Sakagami and N. Takahashi, J. Chem. Soc., Faraday Trans., 1997, 93, 2225 DOI: 10.1039/A701855J

Solid-State NMR Investigation ofn-Heptane Cracking over Zeolite Beta

n-Heptane cracking over zeolite H-Beta has been studied by solid-state NMR spectroscopy. It is shown that isomerisation and cracking are two related processes at the early stages of the reaction. Isomerisation is proposed to proceed faster than cracking via the intermediacy of protonated cyclopropane whereas cracking is suggested to progress through the classical β-scission route. Catalyst loading in the NMR experiments seems to be a very important factor for both initiation of the reaction and final product distribution. The initial source ofi-butane, which is observed as primary product, is the isomer 2,2-dimethylpentane, which cracks toi-butane and propene. Propene, which has never been observed, is suggested to be involved in polymerisation reactions producing long hydrocarbon chains which can rearrange and finally crack to a number of C5–C7isomers. At later stages, the reaction becomes very complex. More of the heptane isomers crack by β-scission to a number of C4and C3fractions. The carbenium ions desorb as paraffins by H-transfer while the olefinic fraction is involved in polymerisation reactions. At the final stages of the reaction, protolytic cracking starts contributing to this process, producing methane, ethane, and propane. Of great interest is the catalyst loading effect on this monomolecular reaction process which defines the final product distribution.

An algorithm for the computation of the hyper-Wiener index for the characterization and discrimination of branched acyclic molecules

An algorithm for the computation of the hyper-Wiener index ω of trees (i.e. branched acyclic molecules) is presented. The input for the algorithm is the list of connections. Multiple linear regression equation was derived between boiling points, ω and the flexibility index p in series of acyclic heptane, octane and nonane isomers. The multiple correlation coefficients obtained for the regression equations were equal to r = 0.992 (heptane), r = 0.975 (octane) and r = 0.960 (nonane).

Reaction Mechanisms of Isomerization and Cracking of Heptane on Pd/H-Beta Zeolite

The vapor-phase isomerization and cracking of heptane on H-Beta zeolites loaded with various amounts of Pd metal has been studied at a temperature of 505 K and at a total pressure of 0.3 MPa. The cracking of heptane is interpreted as a combination of classic bifunctional hydrocracking and dimerization cracking. The isomerization of heptane proceeds through the classic bifunctional mechanism and a second mechanism involving dimerization cracking. The contribution of the different mechanisms to the isomerization and cracking is derived from the formation of specific reaction products. The contribution of the different mechanisms is dependent on the Pd content of the zeolite.

Isomerization of n-Heptane over Pd-Loaded Silico-Alumino-Phosphate Molecular Sieves

Isomerization of n-heptane was studied on a series of bifunctional SAPO-based catalysts with contents of 0.1 wt% Pd. From results on temperature programmed desorption of NH 3 it is deduced that the different molecular sieve structures contain nearly identical amounts of silicon substituting for phosphorus in the framework (0.3 to 0.5 silicon atoms per unit cell). Best activities and selectivities for branched heptane isomers are achieved with SAPO-11 and SAPO-31. SAPO-17 and SAPO-5 show substantially lower activities. With SAPO-5, there is a high cracking selectivity which is assumed to be caused by the reduced accessibility of parts of the bridged hydroxyl groups within the molecular sieve framework. Different locations of these acid sites are evidenced by infrared OH vibration spectra recorded after adsorption of n-heptane.

Application of Computer-Assisted13C NMR Spectrometry for Separation and Determination of Heptane Isomers in the Feed Stocks of Cyclohexane Used in Purification Process

Abstract A computer-assisted 13C NMR spectrometric method for separation, identification and quantitative determination of C7 hydrocarbons in cyclohexane has been developed. A simulated library containing chemical shift and multiplicity data of 131 compounds of C7 hydrocarbons has been prepared. The method incorporates the unique features of quantitative and edited 13C NMR spectra for separation and identification of mixture of hydrocarbons. It serves as an alternative method to GC-MS for monitoring the composition of feed stocks used for cyclohexane purification process.

ChemInform Abstract: Skeletal Reactions of Heptane Isomers over EUROPT‐1: A Comparison with Pt Black.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Novel molecular descriptor for structure—property studies

We report on a novel molecular descriptor for the study of structure—property relationships which appears to complement existing molecular descriptors. The descriptor is derived from a matrix associated with molecular graph, the entries of which are related to the Wiener number. Use of the novel descriptor is illustrated in a correlation with the molecular surface areas in heptane isomers.

Skeletal Reactions of Heptane Isomers over EUROPT-1: A Comparison with Pt Black

The reactions of five heptane isomers (n-heptane, 3-methylhexane, 3-ethylpentane, 2,4-dimethyl-pentane, and 3,3-dimethylpentane) are compared over a 6.3% Pt/SiO2 catalyst (EUROPT-1) as a function of the hydrogen pressure between 6 and 60 kPa. Preferred reactions are isomerization and C5-cyclization; substituted pentanes exhibit higher reactivity and higher C5-cyclization ability. Increasing H2 pressures enhance the reactivities in most cases, except for aromatization and C5-cyclization, where maxima are observed. The observed product compositions (including fragments involving more than one CC bond rupture) do not change within a rather wide conversion range. This is explained in terms of the metal catalyst being covered mainly by hydrocarbons: their reactivity, in turn, is determined first of all, by the amount of hydrogen available. Differences between EUROPT-l and Pt black may be due to their different surface structure and purity.

Search for nondegenerate real vertex invariants and derived topological indexes

AbstractTwo new types of real (i.e., noninteger) local vertex invariants (LOVIs), denoted by ci and c′i and called distance‐enhanced exponential connectivities, are defined via eqs. (1)–(3) and (1′)–(3′), respectively. Only the case when the exponent z equals 1 in eqs. (3) and (3′) is discussed in detail. Both these LOVIs span the range from 0–1, but their dependence upon topology is fairly different, as seen from Table II, where ci and c′i values for all heptane and octane isomers are displayed. From these LOVIs, by simple summation over all graph vertices two new topological indexes (TIs), denoted by XC and XC′, respectively, are obtained. Their intermolecular ordering of all alkanes with four to nine carbon atoms is discussed. On their basis, correlations with boiling points and critical pressures of alkanes are presented. © 1993 John Wiley & Sons, Inc.

Hydroconversion of Heptane Catalyzed by Sulfided NiMo/HY Zeolites

A series of catalysts made of Ni, Mo and NiMo sulfide encaged in HY zeolites (Si/Al = 3 to 17) were tested for the hydroconversion of heptane. The reaction was carried out at P(H2) = 8 MPa and with a constant supply of H2S. Propane and isobutane were the main products, but bimolecular cracking processes occurred to some extent. The yield of heptane isomers was low, showing a deficient hydrogenation function. The influence of the Si/Al ratio upon catalytic activity and selectivity was examined.

Hydroconversion of n-heptane on catalysts containing platinum, rhenium and platinum-rhenium on sodium mordenite

On catalysts containing Pt, Re and Pt-Re on sodium mordenite (NaM), the hydroconversion of n-heptane was 61, 22 and 25 wt.-%, respectively, at 400°C, 3.0 MPa, F/W = 1.2 (vol. n-heptane (vol. catalyst) −1h −1) and a hydrogen-to-n-heptane molar ratio of 10:1. The production of heptane isomers was 38 wt.-% on Pt/NaM but < 1% on the others under these conditions. The total acidity and strength of acid sites were lowest for Pt/NaM and highest for Re/NaM, whereas the metal dispersion in NaM was highest for Pt/NaM and lowest for Pt-Re/NaM. The weaker acidic character, assisted by the presence of Na+ ions, combined with the higher dispersion of Pt in NaM appear to enhance the isomerization activity of the Pt/NaM catalyst and decrease the cracking activity. Diffusion limitation in the catalysts studied is significant. Linear compensation effect relationships for the overall reaction and hydrocracking on the catalysts studied were obtained.

Partial-least-squares models for the octane number of alkanes based on subgraph descriptors

A new multivariate topological descriptor, the subgraph count set (SCS) is described. Chemically, the SCS is a count of all (or some of) the radicals obtained by breaking one bond in a molecule. The SCS is applied in modelling the octane number of heptane and octane isomers by using the multivariate partial-least-squares method. Results are discussed with reference to the meaning of the subgraphs (radicals) found to be relevant in establishing the predictive ability of the models. Most of the important radicals are simple and the algebraic signs of their regression coefficients in the final PLS (validated) models are consistent with their contribution to the degree of branching of the molecules.

Sintering of platinum-black in hydrogen: Morphology and catalytic activity

Pt-black (Pt-473 and Pt-633) reduced in aqueous solution with HCHO was sintered at 473 and 633 K in hydrogen. Electron micrographs show a considerable sintering, especially at 633 K. High-resolution EM indicates the presence of agglomerates of rounded crystals; lattice fringes are also seen. Samples sintered at different temperatures show identical catalytic activity in ring opening and aromatization of alkylcyclopentanes; their activity was also similar in bond-shift isomerization of heptane isomers. On the other hand, aromatization, hydrogenolysis, and C 5-cyclic isomerization were more rapid on Pt-473, while C 5-cyclization was more rapid on Pt-633. These effects are discussed in terms of various active sites for these skeletal reactions and their abundance on two samples which have different morphology, hence different hydrogen retention ability; also the chemical state of their carbon impurity may be different.

Heptane isomerization over a platinum-loaded mordenite catalyst. Effect of heptane isomer cofeeding.

A monobranched (3-methylhexane, 3MH), a dibranched (2, 3-dimethylpentane, 23DMP), and a multibranched (2, 2, 3-trimethylbutane, 223TMB) heptane isomer were separately added to heptane feed, and the reaction mixture was converted on a platinum-loaded hydrogen-mordenite catalyst. The cofeeders were chosen so as to represent typical isomerized products, at concentrations close to those obtained in the conversion of a pure feed. The reaction of heptane occurs free of any diffusion limitations. The presence of 3MH or 223TMB did not affect the reaction, whereas a multiple effect was obtained by 23DMP addition. In the latter case, the reaction was found to proceed autocatalytically. The results were interpreted in view of a mass-transport mechanism and the ease of cofeeder for carbocation formation. In the light of these considerations, the effect of contact time on heptane conversion is discussed, and potential practical applications are delineated.

Chemical ordering of molecules: A graph theoretical approach to structure‐property studies

AbstractThe problem of ordering of chemical structures and subsequent comparison of their relative properties is initiated here by an approach which uses chemical points of view as well as graph theoretical considerations. Briefly, a collection of structurally related compounds (such as isomers, but even more broadly, compounds of similar chemical architecture even if involving different atoms) is examined pairwise and the degree of structural similarity is deduced from a comparison matching of their skeletons. Depending on the nature of the similarity found, some compounds qualify as related and are depicted as vertices of a graph with the corresponding connection. The derived “comparison graph” represents the framework for subsequent comparison of selected molecular properties. “Comparison graph” can also be viewed as depicting a hierarchy of dominance for the compounds and can be drawn with arcs (directed edges), or alternatively as a poset (partially ordered set). Usefulness of such viewing on a collection of structures is illustrated on hexane and heptane isomers and their properties. The results are discussed, particularly with respect to alternative ordering schemes. It was found that the present approach complements and does not duplicate other results, thus offering some novel structural insights.

Topological Index and Thermodynamic Properties. III. Classification of Various Topological Aspects of Properties of Acyclic Saturated Hydrocarbons

Abstract To elucidate the physical meaning of the structure-activity relationship of alkanes, correlation coefficients between 24 thermodynamic properties of hexane, heptane, octane, and nonane isomers and four different topological indices were calculated. These properties were classified into five different types depending on the signs and magnitudes of their correlation coefficients with the two indices, Z and p3. It is interpreted that Z and p3, respectively, represent the dynamical and static features of the topological properties of molecules. The merit of correlation pattern recognition is demonstrated.