Hexane

About: Hexane is a research topic. Over the lifetime, 3759 publications have been published within this topic receiving 57996 citations. The topic is also known as: CH3-[CH2]4-CH3 & hexyl hydride.

Microporous Metal-Organic Frameworks for Adsorptive Separation of C5-C6 Alkane Isomers

Abstract: The separation of alkane isomers, particularly C5-C6 alkanes, is of paramount importance in the petrochemical industry to achieve high quality gasoline. Upon catalytic isomerization reactions, less branched alkanes (with lower octane number) need to be separated from their more branched isomers (with higher octane number) in order to improve the octane rating of gasoline. To reduce the high energy input associated with distillations, the primary separation technique currently used in industry, adsorptive separation by porous solids has been proposed. For example, zeolite 5A has been used as the adsorbent material for adsorptive separation of linear alkanes from their branched isomers, as a supplement technology to distillations. However, due to the limited number of zeolite structures and the lack of porosity tenability in these compounds, the task has not been fully fulfilled by using zeolites. Metal-organic frameworks (MOFs), in light of their structural diversity and high tunability in terms of surface area, pore size, and pore shape, offer new opportunities for resolving industrially relevant separation of alkanes through selective adsorption. This Account summarizes recent development of microporous MOFs for the separation of alkanes, with an emphasis on C5-C6 alkane isomers, including early examples of alkane separation by MOFs, as well as the latest advancement on tailor-made microporous MOFs for size sieving of C5-C6 alkane isomers. The limitation of zeolite 5A as a sorbent material for the separation of C5-C6 alkane isomers lies in its relatively low adsorption capacity. In addition, it is not capable of separating branched alkanes, which is a crucial step for further improving the octane rating of gasoline. The high porosity and tunable pore size and pore shape of MOFs may afford them higher adsorption capacity and selectivity when used for alkane separation. MOFs with pore size slightly larger than the kinetic diameter of branched alkanes can effectively separate alkane isomers through thermodynamically controlled separation, as seen in the case of Fe2(bdp)3 (bdp2- = 1,4-benzenedipyrazolate). This MOF is capable of separating a mixture of hexane isomers by the degrees of branching, with higher adsorption capacity than zeolites under similar conditions but with relatively low selectivity. One effective strategy for obtaining MOFs with optimal pore size and pore shape for highly selective adsorption is to make use of reticular chemistry and precise ligand design. By applying topologically directed design strategy and precisely controlling the pore structure or ligand functionality, we have successfully synthesized a series of highly robust MOFs built on tetratopic carboxylate linkers that demonstrate high performance for the separation of C5-C6 alkane isomers. Zr-bptc (bptc4-= 3,3',5,5'-biphenyltetracarboxylate) adsorbs linear alkanes only and excludes all branched isomers. This size-exclusion mechanism is very similar to that of zeolite 5A. Yet, Zr-bptc has a significantly enhanced adsorption capacity for n-hexane, 70% higher than that of zeolite 5A under identical conditions. Zr-abtc (abtc4- = 3,3',5,5'-azobenzenetetracarboxylate) is capable of discriminating all three C6 alkane isomers via a thermodynamically controlled process, yielding a high separation factor for monobranched over dibranched isomers. MOFs with flexible framework may exhibit unexpected but desired adsorption properties. Ca(H2tcpb) (tcpb4- = 1,2,4,5-tetrakis(4-carboxyphenyl)-benzene) can fully separate binary or ternary mixtures of C5-C6 alkane isomers into pure form through selective molecular sieving as a result of its temperature- and adsorbate-dependent framework flexibility. The intriguing structural properties and exceptional tunability of these MOFs make them promising candidates for industrial implementation of adsorptive separation of alkane isomers.

Alkane effect in the Arizona liquid systems used in countercurrent chromatography

Abstract: Countercurrent chromatography (CCC) is a separation technique that uses a biphasic liquid system; one liquid phase is the mobile phase, the other liquid phase is the stationary phase. Selection of the appropriate liquid system can be a problem in CCC, since it is necessary to select both the “column” and the mobile phase at the same time as the first is completely dependent on the second. A range of systems with various proportions of solvents were developed to ease this choice; 23 variations of the heptane/ethyl acetate/methanol/water biphasic liquid system were labeled A to Z. This range proved to be extremely useful and became the popular Arizona (AZ) liquid system. However, authors often replace the heptane with hexane. In this work, the chemical compositions of the upper phases and the lower phases of 55 Arizona systems made with various alkanes (pentane, hexane, heptane, isooctane and cyclohexane) were determined by gas chromatography and Karl Fischer titration. The test mixture separated consisted of five steroid compounds. The lower phases were found to have similar compositions when different alkanes were used, but the upper phases were found to change. Exchanging heptane for hexane or isooctane produced minimal changes in the CCC chromatogram, while changing the proportions of the solvents resulted in an exponential change in the retention volumes. The high density of cyclohexane made liquid stationary phase retention difficult. All Arizona systems equilibrated within 30 min, but were not stable: water slowly hydrolyzed the ethyl acetate (as shown by a continuous decrease in the pH of the lower aqueous phase), especially in the water-rich systems (early alphabet letters).

Surface Tensions, Refractive Indexes and Excess Molar Volumes of Hexane + 1-Alkanol Mixtures at 298.15 K

Abstract: Surface tensions and refractive indexes for binary mixtures of {hexane + ethanol, + 1-propanol, + 1-butanol, + 1-pentanol, + 1-hexanol, + 1-heptanol, and + 1-octanol} have been measured at 298.15 K. Surface tension deviations and changes of refractive index have been also calculated. Excess molar volumes of {hexane + ethanol, + 1-pentanol, and + 1-hexanol} mixtures have been determined at 298.15 K from density data and compared with literature.