Properties Of Octanes Research Articles

The minimal chemical tree for the difference between geometric–arithmetic and Randić indices

AbstractTopological indices are numerical parameters derived from the structural information of chemical compounds. By providing a quantitative description of molecular structures, topological indices enable researchers to predict various properties and behaviors of molecules. The Randić index () and the geometric–arithmetic index () are widely recognized topological indices. It is observed that, for any given graph . We aim to investigate the gap between and for chemical tree. The complete characterization of minimal chemical tree for is carried out here. This article offers an interesting finding that, whereas and provide same minimal chemical trees, yields minimal tree structures that are totally different from and . Moreover is observed to correlate well with physico‐chemical properties of octanes.

Physicochemical Properties of Octane Isomers in View of the Structural Numbers

The structural features of octane isomers were quantified with help of the Structural Numbers. A Mutually Optimized Contribution of the Structural Numbers (MOCSN) was used to calculate which parts of information regarding branching contribute the tested Structural Numbers. Besides the known Structural Numbers, two Asymmetry Numbers were developed in order to quantify the asymmetry of the octane isomers, one regarding the asymmetry along the main chain of the molecule and the other one regarding the asymmetry perpendicular to the main chain of the molecule. Their correlation to the values of 29 tested physicochemical properties of octanes was low, |R| < 0.6. After optimization of the Mutually Optimized Contribution of the Structural Numbers, the Information Content of the Mutually Optimized Contribution of the Structural Numbers ranged from 34.3% to 89.0% of the information contained in the physicochemical properties. The Structural Numbers enable the first step of the structural interpretation of physicochemical properties of octane isomers. In 17 out of 29 cases the most of information contained in the physicochemical properties is presented among the Structural Numbers by the Number of Branches, in 8 cases by the Peripheral Number, in 3 cases by an Asymmetry Number and in 1 case by the Distance Number.

Molecular dynamics simulations of oil transport through inorganic nanopores in shale

Understanding the transport of liquid hydrocarbon through nanopores of inorganic minerals is crucial not only to develop liquid-rich shale reservoirs, but also to grasp oil migration from deeply buried extremely low permeability source rocks. We report a molecular study of liquid hydrocarbon (octane) flow through inorganic (quartz) nanopores ranging in size from 1.7 to 11.2nm. Through equilibrium molecular dynamics (EMD), we observe the layering structure of confined octane and conclude that in the center of slits having apertures greater than 3.6nm, the octane properties, e.g., density, self-diffusion coefficient, and viscosity, tend to be bulk-liquid-like. Near the solid–liquid interface, octane molecules diffuse more slowly. Then we use nonequilibrium molecular dynamics (NEMD) to study the pressure-driven flow of octane in quartz slits and present two methods to characterize the behavior: (1) slip length coupled with effective viscosity and (2) apparent viscosity. The Navier–Stokes equation can reasonably describe the flow in quartz nanopores larger than 1.7nm; however, a slip boundary condition or viscosity correction is essential. Although the slip length (∼0.9nm) is small, significant error can be caused in the estimation of overall flux if it is neglected. The variations in slip length and apparent viscosity with driving force, pore size, and temperature can be described by empirical exponential functions. These results can be readily incorporated into existing techniques to estimate apparent liquid permeability of shale—the most fundamental property required for shale exploitation.

Elements of an Universal Matrix as Topological Indices for Physicochemical Properties of Octanes.

Some of the elements of the Universal matrix and their combinations are useful topological indices of physicochemical properties of octanes. Whereas single elements of the Universal matrix give rise to 0.70 < R < 0.99, mutually optimized combinations of only four to six out of 56 of them in the Universal matrix of octanes give rise to R > 0.99 and in the worst cases to R > 0.98. Also a new measure of goodnes of correlation, the Amount of information in the topological index, Ainfo (%), is introduced. Structural interpretation of some of the physicochemical properties of octanes is demonstrated as well as of the contribution by the most useful elements of the Universal matrix.

Topological indices are not necessarily invariant to graph labeling.

Each element of the Universal matrix U (vertex-degree vertex-distance weighted matrix) represents the mutual contribution of two vertices weighted for the vertex degrees and the distance between them. Regarding different labeling ways of graph vertices, particular matrix elements are not invariant to molecular labeling. Regarding the structural features they are invariants since there are only particular vertex combinations representing particular structural features. Some of the matrix elements are the best descriptors of a physicochemical property in question. Some combinations of matrix elements are very good descriptors of physicochemical properties of octanes regardless how we enumerate their vertices.

A Method for Determining Optimum Second Stage Pressure in Three Stage Separation

Introduction This investigation was prompted by the absence of a simple, accurate method to predict optimum second stage separation pressure in three stage separation operations. Three stage separation as used here includes two separators plus the stock tank. The first stage pressure is usually fixed by gas sales conditions and the third stage is at atmospheric pressure. Thus, the second stage pressure is the only one that may be varied indiscriminate during production operations. No variations in temperature were considered in this study, even though it will vary among systems, for a change in temperature has little effect on the optimum pressure. Optimum pressures may be determined from flash calculations, but these are tedious unless a computer is available. An early attempt to develop a simpler method yielded an equation which gave the optimum pressure only as a function of initial and final pressure. Experience, however, confirms theoretical relationships which show that composition as well as pressure and temperature must be a factor. Development of New Correlation Wellstreams having 17 different analyses, ranging from low gravity crude to condensate, were used to determine the effect of composition. Each wellstream was flashed through three stages to determine the optimum second stage pressure for each first stage pressure. Equilibrium vaporization ratios proposed by Latham and Campbell were used throughout. The heptane plus fraction, for simplicity, was assumed to have the properties of octane.