Hexane isomers, separation

Fig. 12. Isomer separation. Gradient elution of 50 pg polystyrene 800 on a tandem of two silica column (2x250x4.6 mm dD = 6 nm dP = 5 pm). Gradient n-hexane/dichloro-methane, 11-21% B in 100 min flow rate 1 ml/min UV detection at 265 nm, 0.05 AUFS. (From Ref.46) with permission)...

Separation of organic/organic mixtures Extraction of water from an aqueous solution of ethanol Extraction of water from solutions of ethanol, acetic acid Separation of benzene/ -hexane mixtures Separation of xylene isomers... 

In solvent extraction crude vegetable oil and other useful materials are dissolved in a solvent to separate them from the insoluble meal. Many solvents have been evaluated for commereial extraction. Commercial hexane has been the main solvent for the oilseed processing industry since the 1940s because of its availability at reasonable eost and its suitable fiinetional characteristics for oil extraction. However, the interest in alternative solvents to hexane has continued and is motivated by one of a eombination of faetors desire for a nonflammable solvent, more efficient solvent, more energy efficient solvent, less hazardous and environmentally friendly solvent, solvent with improved produet quality, and solvents for niche/specialty markets. Today eommereial isohexane (hexane isomers) is replacing commercial hexane in a few oilseed extraction operations and other solvents (e.g., isopropanol, ethanol, acetone, etc.) are also being used for various extraction processes or have been evaluated for use as extracting solvents. ... 

Hexane isomers and benzene-p-xylene mixtures have been separated by PV through an MFl-type zeolite membrane by Matsufuji et al. (2000). The PV tests for n-hexane, 2-methylpentane (2-MP), and 2,3-dimethylbutane (2,3-DMB) were performed using an MFl-type zeolite membrane at 303 K. -Hexane preferentially permeated through the MFI membrane in the PV tests for binary mixtures of n-hexane-2-MP and n-hexane-2,3-DMB. The separation factors (a( -hexane-2-MP) and a(n-hexane-2,3-DMB)) were always greater than their ideal selectivi-ties. The ideal selectivities of n-hexane-2-MP and -hexane-2,3-DMB were 37 and 50, respectively. It was observed that separation factor a( -hexane/2,3-DMB) was as high as 270 when the feed concentration of n-hexane was 10 mol%. Matsufuji et al. (2000) claimed that the MFI membranes have promising potential to separate n-hexane and branched hexane-isomer mixtures. 

When one has an interest in the separation of different types of compound, silica or alumina, with the appropriate mobile phase, can readily accomplish this. Also, isomer separation frequently can easily be accomplished with adsorption chromatography for example, 5,6-benzoquinoline can be separated from 7,8-benzoquinoline with silica as the stationary phase and 2-propanol hexane (1 99). This separation is difficult with reversed-phase liquid chromatography. "... 

Huddersman, K., and Klimczyk, M., Separation of branched hexane isomers using zeolite molecular sieves, AlChE J., 42(2), 405-408 (1996). 

Further isomer separation was achieved on a second plate developed with a hexane-ether (4 1) mixture after three developments in the same direction. 

The residual activity of the racemic mixture and the most insecticidally active stereoisomers [S,S] were investigated on soil samples. Before application the isomer separation of the C-fenvaler-ate was carried out by six consecutive developments in hexane-ether (20 1). The [S,S] and [R,R] isomers were located at R/0.46 and the [R,S] and [S,R] stereoisomers at R/0.49 (Table 9). The isonter pairs were finally resolved in HPLC using a chiral stationary phase. Soil extracts were analyzed in order to investigate the degradation processes and persistence of C-fenvalerate (Table 9) (115). The parent compound and its degradation products were separated by two-dimensional TLC (Table 9)... 

Deng, Z., Pera-Titus, M., Guo, Y., and Giroir-Fendler, A. (2010) Molecular sieving separation of hexane isomers within nanocomposite (B)-MFI-alumina hollow fiber membranes a modeling study. Ind. Eng. Chem. Res., 49,... 

Long s group recently reported a MOF, Fe2(BDP)3 (BDP = 1,4-benzenedipyrazolate), a highly stable framework with triangular channels that can separate the hexane isomers based on the degree of branching, as shown in Figure 10. The adsorption isotherms... 

The reverse shape selectivity of MOFs was also observed when introducing University of Oslo (UIO)-66 into the GC separation of hydrocarbons. The pore window of the octahedral cavities of UIO-66 is 7 A, which is accessible to all of the hexane and heptane isomers. However, the elution sequence of hexane isomers is quite different from ZIF-8, MOF-5, and other commercial GC capillary columns. The linear alkanes, hexane, and heptane, eluted first from UIO-66 colimm, with other branched isomers retained more on UIO-66 coIimm, which performs as reverse shape selectivity. The moderate pore size of UIO-66 (11 A) makes the adsorbed branched alkanes have a closer distance and stronger Van der Waals interaction with the inside walls, leading to the reverse shape selectivity. 

Although many attempts have been made to separate or exclusively synthesize one isomer of an unsymmetrically substituted phthalocyanine,72-89-296,297 the product mixture has been separated in only two cases.96 103,104 Besides the chromatographic separation of the statistical product mixture it is also possible to prepare exclusively the D4h isomer by use of steric hindrance of bulky substituents, e.g. 7-ferr-butylnaphthalene-l,2-dicarbonitrile only forms the respective An isomer of the tetra(to -butyl)-substituted 1,2-NcFe by heating in hexan-l-ol.73 Recently, some 1,8,1 5,22-substituted pure isomers have also been synthesized by the use of bulky substituents in 3-substituted phthalonitriles298,299 at low temperature (see Section 2.1.4.).94... 

TLC Analysis. Samples were examined by TLC using standard procedures. Rf values were determined and compared with those of authentic reference materials. Radioactive components were located by scanning (Vanguard Instrument Corp., North Haven, Conn., Model 885) or by autoradiography (Eastman Kodak, Rochester, N. Y., type AA film). The relative Rf value of DCDD on silica gel plates (Brinkmann Instruments, Inc., Westbury, N. Y., type For,4) when developed with n-hexane dioxane acetic acid, 90 10 4, V/V/V, was 0.90. The observed impurity had a relative Rf value of 0.40. On Brinkmann alumina plates, developed with n-hexane, DCDD had a relative Rf of 0.32. Neither system separated the chlorinated dibenzodioxin isomers. 

Molecular sieving effect of the membrane has been evidenced using a mixture of two isomers (i.e. no Knudsen separation can be anticipated), n-hexane and 2-2 dimethylbutane (respective kinetic diameters 0.43 and 0.62 nm). Figure 10 shows the permeate contains almost only the linear species, due to the sieving effect of the zeolite membrane (pore size ca 0.55 nm). This last result also underlines that the present zeolite membrane is almost defect-fi ee. 

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