Showing papers on "Hexane published in 2021"

Effects of processing methods on the chemical composition and antioxidant capacity of walnut (Juglans regia L.) oil

Abstract: Various methods for the processing of walnut oil (cold pressing, roasting pressing, hexane extraction, subcritical butane extraction and supercritical carbon dioxide extraction) were compared, and hexane extraction was shown to provide for efficient lipid isolation. Among the investigated samples, roast-pressed and hexane-extracted oils exhibited the highest C18:1n-9 contents (18.74 and 18.52%, respectively), however featured the lowest C18:2n-6 (63.06 and 62.95%, respectively) and trilinolein (32.82 and 32.06%, respectively) contents. Moreover, the tocopherol (371.08 mg/kg) and the phytosterol (1206.30 mg/kg) content of subcritical butane-extracted walnut oil, the polyphenol content of hexane-extracted oil (45.43 mg/kg), and the squalene content of roast-pressed walnut oil (14.19 mg/kg) exceeded those of other samples. Multiple linear regression analysis was employed to evaluate the contributions of oil constituents to overall antioxidant capacity (oxidative stability and free radical scavenging capacity) and thus establish the corresponding numerical model. It was shown that C16:0, polyphenol, Δ5-avenasterol, SOS, γ-tocopherol, PLL, C18:3n-3, LLL, and C18:0 contributed to the antioxidant capacity of the walnut oil. Overall, the obtained results pave the way to the development of industrial-scale methods of high-quality and high-nutritional-value walnut oil production.

High‐Efficiency Separation of n‐Hexane by A Dynamic Metal‐Organic Framework with Reduced Energy Consumption

Abstract: The separation of n -alkanes from their branched isomers is vitally important to improve octane rating of gasoline. To facilitate mass transfer, adsorptive separation is usually operated under high temperatures in industry, which require considerable energy. Herein, we present a kind of dynamic pillar-layered MOF that exhibits self-adjustable structure and pore space, a behavior induced by guest molecules. A combination of the flexibility of the framework with the commensurate adsorption for n -Hexane results in exceptional performance in separating hexane isomers. More significantly, lower temperature prompts the guest molecules to open the dynamic pores, which may provide a new perspective for optimized separation performance at lower temperatures with less energy consumption.

Separation of hexane isomers by introducing “triangular-like and quadrilateral-like channels” in a bcu-type metal-organic framework

Abstract: The separation of hexane isomers is of vital importance to produce high quality gasoline in the petrochemical industry. However, the similar vapor pressure and boiling point of hexane isomers bring great difficulties and challenges in the separation process. Sieving effect, which allowing smaller molecules pass through and preventing others, should be a powerful strategy to solve this problem by making good use of porous materials. Therefore, physical separation by metal-organic framework (MOF) materials appears and becomes a burgeoning separation technique in industry. Due to the weak interaction between hexane isomers with absorbents, it puts forward higher requirements for the accurate design of MOF materials with optimal pore system. To address this issue, a novel MOF [Zn9(tba)9(dabco)3]·12DMA·6MeOH (abbreviation: Zn9(tba)9(dabco)3; H2tba = 4-(1H-tetrazol-5-yl)-benzoic acid; dabco = 1,4-diazabicyclo[2.2.2]octane; DMA = N, N-dimethylacetamide) with bcu network has been designed and synthesized by reticular chemistry strategy. Benefiting from the pre-designed topology and suitable linear ligand H2tba and dabco, the structure of Zn9(tba)9(dabco)3 exhibits two types of channels with triangular-like and quadrilateral-like geometry. Zn9(tba)9(dabco)3 with appropriate channel size and shape displays potential selective adsorption capacity of vapor-phase hexane isomers through sieving effect. Moreover, outstanding gas adsorptive separation properties of Zn9(tba)9(dabco)3 could also be speculated by theoretical ideal adsorbed solution theory (IAST), suggesting Zn9(tba)9(dabco)3 can be regarded as a potential adsorbent material for purification natural gas. Breakthrough experiments show that Zn9(tba)9(dabco)3 is capable of discriminating all four hexane isomers at 298 K, and the corresponding research octane number (RON) of the eluted mixture closes to 95, which is higher than the standard for industrially refined hexane blends (about 83). We speculate that sieving effect and diffusion are a synergetic contributory factor in their elution dynamics, which may be ascribed to temperature-dependent interaction between pore aperture and each isomer. This work presents a typical example for design of efficient MOF absorbents by reticular chemistry strategy.

Synthesis and Modification of Polyurethane Foam Doped with Multi-walled Carbon Nanotubes for Cleaning up Spilled Oil from Water

Abstract: Marine oil spills have raised widespread environmental concerns. Adsorbents with high oil absorption efficiency and reusability are highly desirable. This paper demonstrates a technical route for the manufacture of polyurethane-based adsorbents, aiming at developing robust and efficient materials for treating oil-contaminated water or remedying emergency oil spill accidents. The investigation includes the synthesis of polyurethanes modified with multi-walled carbon nanotubes, the characterizations of their properties, and the analysis of the capacity and feasibility of their applications in oil–water separation. The compositions of the products were characterized by FTIR, XPS, and Raman spectroscopy; the morphologies were analyzed by SEM; the hydrophobicities were tested by the water contact angle, and the thermal properties by TGA; the mechanical properties were depicted by Young’s modulus and the tensile-strain response performance; and the measurements of the absorption capacities and their performance in applications for oils-water separation were conducted in a self-designed apparatus and determined by gravimetric analysis. The results indicate that the developed adsorbents are superhydrophobic and highly robust with a water contact angle of 159°, tensile strain 27% higher and compressive strain 35% lower than regular polyurethanes, absorption capacity up to 60 g g−1, and reusability of 900 absorption–desorption cycles. The high oil absorption efficiency, capacity, and reusability of the adsorbents were confirmed by various oil/organics-water systems, such as engine oil-, silicone oil-, chloroform-, hexane-, toluene-, and kerosene-water system. It is concluded that the adsorbents are efficient not only for floating oils/organics-water but also for well dispersed or mixed oils/organics-water systems; and they can be operated in not only a batch mode for high absorption–desorption cycles but also in a continuous mode for a long operational period, which exhibits great potential and is of particular interest for the adsorbents to be used in large scale oil/organics spill cleanups.

Dry and Aqueous 2-Methyloxolane as Green Solvents for Simultaneous Production of Soybean Oil and Defatted Meal

Abstract: Edible oils are currently largely obtained by solvent extraction using hexane. Despite the fact that this petroleum solvent is known to be neurotoxic, hexane extraction remains the accepted standard process for seed oil extraction and particularly, but not exclusively, for soybean oil extraction. This study evaluates an alternative replacement of hexane with a bio-based and safe solvent, 2-methyloxolane (2-MeOx), either in its dry or in its water-saturated (4.5%w) aqueous form, referred to as 2-MeOx 95.5% in this paper. The analyses focused on extraction yields, composition, and quality of the extraction products. This study also evaluates the feasibility to substitute hexane in industrial extraction processes. Therefore, a kinetic study and multistage cross-current extractions were performed. The work concluded that both 2-MeOx and 2-MeOx 95.5% are good candidates to replace hexane in industrial processes for the extraction of soybean oil, as they gave similar compositions for oil and defatted meal. Hexane and 2-MeOx also gave similar results in terms of extraction rate and performances. 2-MeOx 95.5% exhibited a slightly different behavior during extraction, which was attributed to water diffusion from the solvent to the solid matrix due to its high water activity.

Diffusivities in Binary Mixtures of n-Hexane or 1-Hexanol with Dissolved CH4, Ne, Kr, R143a, SF6, or R236fa Close to Infinite Dilution

Abstract: This work is a continuation of previous studies focusing on the influence of intermolecular interactions on the diffusive mass transport in mixtures consisting of liquids with dissolved gases by de...

A Series of Crystallographically Characterized Linear and Branched σ-Alkane Complexes of Rhodium: From Propane to 3-Methylpentane.

Abstract: Using solid-state molecular organometallic (SMOM) techniques, in particular solid/gas single-crystal to single-crystal reactivity, a series of σ-alkane complexes of the general formula [Rh(Cy2PCH2CH2PCy2)(ηn:ηm-alkane)][BArF4] have been prepared (alkane = propane, 2-methylbutane, hexane, 3-methylpentane; ArF = 3,5-(CF3)2C6H3). These new complexes have been characterized using single crystal X-ray diffraction, solid-state NMR spectroscopy and DFT computational techniques and present a variety of Rh(I)···H-C binding motifs at the metal coordination site: 1,2-η2:η2 (2-methylbutane), 1,3-η2:η2 (propane), 2,4-η2:η2 (hexane), and 1,4-η1:η2 (3-methylpentane). For the linear alkanes propane and hexane, some additional Rh(I)···H-C interactions with the geminal C-H bonds are also evident. The stability of these complexes with respect to alkane loss in the solid state varies with the identity of the alkane: from propane that decomposes rapidly at 295 K to 2-methylbutane that is stable and instead undergoes an acceptorless dehydrogenation to form a bound alkene complex. In each case the alkane sits in a binding pocket defined by the {Rh(Cy2PCH2CH2PCy2)}+ fragment and the surrounding array of [BArF4]- anions. For the propane complex, a small alkane binding energy, driven in part by a lack of stabilizing short contacts with the surrounding anions, correlates with the fleeting stability of this species. 2-Methylbutane forms more short contacts within the binding pocket, and as a result the complex is considerably more stable. However, the complex of the larger 3-methylpentane ligand shows lower stability. Empirically, there therefore appears to be an optimal fit between the size and shape of the alkane and overall stability. Such observations are related to guest/host interactions in solution supramolecular chemistry and the holistic role of 1°, 2°, and 3° environments in metalloenzymes.

Kinetics of Formation of Molecular Hydrogen during the Radiolysis of Hexane and a Mixture of C 6 H 14 -H 2 O on a Surface of ZrO 2 Nanoparticles

Abstract: The kinetics of the accumulation of molecular hydrogen during the radiolysis of hexane and a hexane–water mixture is studied at different concentrations of the components in the presence of ZrO2 nanoparticles (n-ZrO2) at T = 300 K. It is found that n-ZrO2 displays radiation catalytic activity in the decomposition of hexane and a hexane–water mixture, as a result of which the rate of accumulation of molecular hydrogen increases. It is established that the radiation chemical yield of molecular hydrogen G(H2) grows sharply along with temperature.

Cotton fabrics modified with tannic acid/long-chain alkylamine grafting for oil/water separation

Abstract: Backgrounds Cotton fabrics were modified on surface wettability for efficient oil/water separation. The modification adopted in previous literature are commonly complicated in steps, expensive in chemicals applied, and not environmentally begien in solvents used. Experiments This article applied a novel one-step modification protocol to modified cotton fabrics using tannic acid (TA) grafted via Michael addition/Schiff base reactions with long-chain alkylamines, including 1-tetradecylamine (TDA), 1-hexadecylamine (HDA), and 1-octadecylamine (ODA) with 14, 16 and 18 methyl groups, respectively, were applied in this study for cotton fabrics modification. The TA, an inexpensive natural polyphenol, was adopted for providing excess catechol groups for linking the cotton surface and the alkylamines. The grafting reactions via Michael addition/Schiff base reaction were performed at room temperature and pH 8.5 with catalysts CuSO4/H2O2 for significantly reducing the reaction time needed. Results The chemical analysis confirmed the modification of the cotton fabrics to possess hydrophobic surface, with contact angles for water droplets on the modified surface as 133.3o, 136.0o and 142.9° for TA-TDA, TA-HDA, and TA-ODA cotton fabrics, respectively; and diiodinemethane droplets on the modified surface being 56.0o, 58.8o and 59.3o, respectively. The modified cotton surface has intermediate dispersive component of surface energy (29.0–31.2 mJ/m2) and low polar component (4.2–6.2 mJ/m2), yielding high affinity to oil but low affinity to water. Parametric study revealed that the pH value and reaction time are the most important parameters for the alkylamine grafting reactions, while the reduction of catalyst amount used but still with sufficient modification on cotton fabrics can be achieved. The oil absorption tests with cotton fabrics contacting hexane (top)-water (bottom) layers revealed high hexane adsorption capacity: 0.96, 1.22, 1.25 g hexane/g cotton for TA-TDA, TA-HAD and TA-ODA cotton fabrics, respectively. The absorption tests with cotton fabrics contacting water first for 30 s then hexane for another 30 s had much lower absorption capability of hexane: 0.52, 0.85, 0.87 g hexane/g cotton for TA-TDA, TA-HAD and TA-ODA cotton fabrics, respectively, since water would penetrate the major pores for inhibiting further oil absorption.

Evaluation of the work of adhesion at the interface between a surface-modified metal oxide and an organic solvent using molecular dynamics simulations

Abstract: Advancing the practical applications of surface-modified nanoparticles requires that their dispersion in solvents can be controlled. The degree of dispersion depends on the affinity between surface-modified nanoparticles and solvents, which can be quantified using the work of adhesion at the interface. Herein, the affinity between a surface-modified inorganic solid and an organic solvent was evaluated by calculating the work of adhesion at the interface. The phantom-wall method, which is a thermodynamic route for evaluating the work of adhesion at an interface using molecular dynamics simulations, was applied to the decanoic acid-modified Al2O3/hexane interface. Molecular dynamics simulations were performed for flat interface systems to focus on the interactions between substances that affect the affinity on the surface. As a result, the surface coverage of decanoic acid was found to affect the work of adhesion, with a maximum value of 45.66 ± 0.75 mJ/m2 at a surface coverage of 75%. An analysis of the mass density profiles of Al2O3, decanoic acid, and hexane in the vicinity of the interface showed that the increase in the work of adhesion with the surface coverage was due to the penetration of hexane molecules into the decanoic acid layer on the Al2O3 surface. At a surface coverage of 75%, some hexane molecules were trapped in the layer of oriented decanoic acid molecules. These results suggested that the interfacial affinity can be enhanced by controlling the surface modification so that the solvent can penetrate the layer of the modifier.

Tuning the hexane isomer separation performances of Zeolitic Imidazole Framework-8 using mechanical pressure.

Abstract: Hybrid osmotic Monte Carlo simulations were performed to anticipate the tunability of the separation performance of the flexible Zeolitic Imidazole Framework-8 (ZIF-8) via the application of an external mechanical pressure. This synergistic combination of mechanical control of the pore aperture/cage dimension and guest adsorption was applied to the challenging hexane isomers separation processes of vital importance in the field of petrochemical industry. The application of a mechanical pressure above 1 GPa was predicted to boost the linear hexane/2-methylpentane and 2-methylpentane/2,3-dimethylbutane selectivity by 40% and 17%, respectively, as compared to the pristine ZIF-8. We further unraveled the microscopic origin of this optimized performance with an in-depth analysis of the critical interplay between the structural changes of the ZIF-8 framework and the conformational rearrangements of C6 isomers under mechanical pressure.

From biomass to diesel additives: hydrogenation of cyclopentanone-furfural aldol condensation adducts

Abstract: The hydrogenation of furfural-cyclopentanone (C15) condensation adduct is studied in this work. Three different metals (Pt, Pd, Ni) supported on two materials (Al2O3 and Nb2O5) were compared, highlighting the good results obtained with Pd/Al2O3. The kinetic analysis of the reaction results suggests a parallel route in which the hydrogenation of cyclic unsaturation can occur simultaneously with the hydrogenation of aliphatic C˭C. A key role of metal dispersion is discarded, concluding that this reaction is selective to the presence of Pd nanoparticles with a synergetic effect with the Al2O3 support, mainly due to the presence of strong acidic sites. Different organic solvents have been tested, including protic, polar and apolar ones. The best results are obtained with hexane and butanol, combining the absence of competitive adsorption and reactant solvation. At optimum conditions, more than 75% of yield to the fully hydrogenated molecules were obtained in less than two hours, obtaining a mixture with good properties as a fuel additive.

Efficient hexane isomers separation in isoreticular bipyrazolate metal-organic frameworks: The role of pore functionalization

Abstract: Hydrocarbons separation in petrochemical industries is a key, energy-consuming stage in the manufacture of high-quality added-value products—hence the need for more efficient materials and environmentally friendly methodologies to improve this process. In this context, we have studied the effect of metal-organic frameworks (MOFs) pore functionalization in hexane isomers separation, isolating the robust isoreticular zinc(II) bipyrazolates Zn(BPZ), showing no pore decoration, Zn(Me2BPZ), the pores of which are decorated with apolar methyl groups, and Zn(BPZ(NH2)2), the spacers of which possess polar Lewis-basic functions (H2BPZ = 1H,1′H-4,4′-bipyrazole; H2Me2BPZ = 3,3′-dimethyl-1H,1′H-4,4′-bipyrazole; H2BPZ(NH2)2 = 3,5-diamino-1′H,1′H-4,4′-bipyrazole; DMF = dimethylformamide). After characterizing Zn(BPZ(NH2)2) as per its crystal structure and thermal behaviour, and all the three MOFs as per their textural properties, we investigated, from the experimental and computational points of view, the impact of the square one-dimensional channels decoration on the separation of the hexane isomers, demonstrating the relevance of pore constrictions in the resolution of the title alkanes mixture.

Liquid–Liquid Separation of an Azeotropic Mixture (Hexane/Ethyl Acetate) with Imidazolium-Based Ionic Liquids

Abstract: This work comprises the separation of an azeotropic mixture (hexane/ethyl acetate) with two different ionic liquids, viz, (1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM][BF4], and 1-ethyl-3-...

Shape-Selective Ultramicroporous Carbon Membranes for Sub-0.1 nm Organic Liquid Separation.

Abstract: Liquid-phase chemical separations from complex mixtures of hydrocarbon molecules into singular components are large-scale and energy-intensive processes. Membranes with molecular specificity that efficiently separate molecules of similar size and shape can avoid phase changes, thereby reducing the energy intensity of the process. Here, forward osmosis molecular differentiation of hexane isomers through a combination of size- and shape-based separation of molecules is demonstrated. An ultramicroporous carbon membrane produced with 6FDA-polyimides realized the separation of isomers for different shapes of di-branched, mono-branched, and linear molecules. The draw solvents provide the driving force for fractionation of hexane isomers with a sub-0.1 nm size difference at room temperature without liquid-phase pressurization. Such membranes could perform bulk chemical separations of organic liquids to achieve major reductions in the energy intensity of the separation processes.