Hexane Isomers Research Articles

A 3D Robust and Microporous B←N Framework with 8‐connected Sandwich Nodes for Efficient Separation of Hexane Isomers

Recently B←N organic frameworks (BNFs) have gained substantial attention owing to their unique dative bond energy, which imparts them with specialized functionalities across a broad spectrum of applications. Despite previous reports on BNFs with permanent porosity, research endeavors towards three‐dimensional (3D) BNFs with similar properties are scarce, with no report of robust 3D BNFs featuring permanent porosity to date. Herein, electrostatic complementarystrategy is proposed to construct the first example of 3D robust and microporous BNF, BNF‐100, featuring a reo topology with 8‐connected sandwich nodes assembled via dative B←N bonds. The activated form BNF‐100a exhibits excellent chemical stability and permanent porosity with Langmuir surface area of 645.9 m2 g−1 and pore volume of 0.23 cm3 g−1. BNF‐100a can efficiently separate hexane isomers through sieving mechanisms, as confirmed by vapor adsorption experiments and dynamic breakthrough tests, surpassing the performance of most MOF materials. Finally, we achieved the purification of different branched hexane isomers using a single breakthrough column in a combined breakthrough and purging experiment, which is the first reported instance in the literature on hexane isomer separation.

A 3D Robust and Microporous B←N Framework with 8-connected Sandwich Nodes for Efficient Separation of Hexane Isomers.

Recently B←N organic frameworks (BNFs) have gained substantial attention owing to their unique dative bond energy, which imparts them with specialized functionalities across a broad spectrum of applications. Despite previous reports on BNFs with permanent porosity, research endeavors towards three-dimensional (3D) BNFs with similar properties are scarce, with no report of robust 3D BNFs featuring permanent porosity to date.Herein,electrostatic complementarystrategyisproposedto constructthe first example of3Drobust and microporousBNF,BNF-100, featuring areotopology with 8-connected sandwich nodes assembled via dative B←N bonds. The activated formBNF-100aexhibits excellent chemical stability and permanent porosity with Langmuir surface area of 645.9 m2g-1and pore volume of 0.23 cm3 g-1.BNF-100acan efficiently separate hexane isomers through sieving mechanisms, as confirmed by vapor adsorption experiments and dynamic breakthrough tests, surpassing the performance of most MOF materials.Finally, we achieved the purification of different branched hexane isomers using a single breakthrough column in a combined breakthrough and purging experiment, which is the first reported instance in the literature on hexane isomer separation.

Recognition and order of multiple sidechains by metal–organic framework enhances the separation of hexane isomers

AbstractPorous materials perform molecular sorting, separation and transformation by interaction between their framework structures and the substrates. Proteins also interact with molecules to effect chemical transformations, but rely on the precise sequence of the amino acid building units along a common polypeptide backbone to maximise their performance. Design strategies that positionally order sidechains over a defined porous framework to diversify the internal surface chemistry would enhance control of substrate processing. Here we show that different sidechains can be ordered over a metal–organic framework through recognition of their distinct chemistries during synthesis. The sidechains are recognised because each one forces the common building unit that defines the backbone of the framework into a different conformation in order to form the extended structure. The resulting sidechain ordering affords hexane isomer separation performance superior to that of the same framework decorated only with sidechains of a single kind. The separated molecules adopt distinct arrangements within the resulting modified pore geometry, reflecting their strongly differentiated environments precisely created by the ordered sidechains. The development of frameworks that recognize and order multiple sidechain functionality by conformational control offers tailoring of the internal surfaces within families of porous materials to direct interactions at the molecular level.

Six-Membered Ring Directed Assembly of a Zirconium Zeolitic Metal-Organic Framework for Efficient Separation of Hexane Isomers.

The synthesis of zirconium MOFs with zeolite net is quite challenging due to the high connectivity of Zr6 clusters, which is far from tetrahedral connection, a requisite for zeolite net. In this work, we demonstrate a six-membered ring (6MR) strategy through mimicking of mineral zeolites with mixed ditopic and tritopic carboxylate linkers. With this strategy, the ditopic linker cross-links Zr6 clusters to form 4-connected zeolite-like nets, while the tritopic one is used to direct the formation of 6MR and simultaneously consumes extra coordination sites on the cluster. The feasibility of this strategy is shown by one zeolitic metal-organic framework (NNM-5) and this strategy has also led to the synthesis of the other dia-type zirconium MOF (NNM-6). Interestingly, as the tritopic linker not only directs the formation of 6MR but also partitions 6MR into small segments, NNM-5 with SOD topology shows a structural feature of small aperture and big cage, which has led to efficient separation of hexane isomers. With both exceptionally high n-hexane uptake (65.9 cm3 g-1) and size-exclusion selectivity, an exceptional separation capability is verified by breakthrough experiments. Calculation results demonstrate that the large difference of diffusion energy barrier due to the small aperture accounts for the underlying separation mechanism.

Engineering Trifluoromethyl Groups in Porous Coordination Polymers to Enhance Stability and Regulate Pore Window for Hexane Isomers Separation.

Effective separation of hexane (C6) isomers is critical for a variety of industrial applications but conventional distillation methods are energy-intensive. Adsorptive separations based on porous coordination polymers (PCPs) offer a promising alternative due to their exceptional porosity and tunable properties. However, there is still an urgent need to develop PCPs with high stability and separation performance. This study investigates how substituting a methyl (-CH3) group with a trifluoromethyl (-CF3) group can regulate pores and hydrophobicity in PCPs. This precise adjustment aims to enhance stability and improve the kinetic separation performance of hydrophobic C6 isomers by considering the size and hydrophobicity of the trifluoromethyl group. Two isostructural PCPs with pcu topology, PCP-CH3 and PCP-CF3, were synthesized to vary pore diameters and hydrophobicity based on the presence of -CH3 or -CF3 groups. PCP-CF3 showed greater stability in water compared to PCP-CH3. While PCP-CH3 had high adsorption capacities, it lacked selectivity, whereas PCP-CF3 demonstrated improved selectivity, particularly in excluding dibranched isomers. Dynamic column separation experiments revealed that PCP-CF3 could selectively adsorb linear and monobranched isomers over dibranched isomers at room temperature. These findings highlight the potential of fluorine-modified PCPs for efficient isomer separation and underscore the importance of stability improvement strategies.

Hydrodesulfurization and isomerization performance of model FCC naphtha over sulfided Co(Ni)–Mo/Y catalysts

The process of deep hydrodesulfurization (HDS) in gasoline typically results in the saturation of olefins, leading to significant reductions in octane number. In this work, Y-supported Co(Ni)–Mo catalysts that with different Ni–Co content were prepared by the incipient wetness impregnation method, the structure and properties were characterized and analyzed using HRTEM, XPS, H2-TPR, and NH3-TPD. The isomerization of 1-hexene and 1-octene as well as the HDS of thiophene were studied by using model FCC naphtha. The incorporation of Ni was found to enhance the number of MoS2 stacking layers, thereby improving the degree of sulfurization in Mo and subsequently increasing the desulfurization rate, with a maximum achieved desulfurization rate of 94.7%. When employing a Ni/Co ratio of 3:2, optimal synergy between Ni and Co is achieved, resulting in a greater presence of multi-layer stacked II-Co(Ni)MoS active phases. Additionally, appropriate Brønsted acidity levels are maintained to facilitate efficient olefin isomerization while preserving high HDS activity. As a result, the current isomerization yield stands at 58.2%(mass). These understandings shed light on the development of highly HDS and olefin isomerization catalysts.

Separation of C6 hydrocarbons on sodium dithionite reduced graphene oxide aerogels

The ability of reduced graphene oxide aerogels (rGOAs) for challenging gas-phase separation was investigated with hexane isomers and benzene (C6 hydrocarbons) using inverse gas chromatography (IGC). For the first, rGOAs were synthesized with sodium dithionite (DTN) as a reductant. Experiments revealed that the most optimal DTN to graphene oxide mass ratio was 2:1, resulting in the highest specific surface area of 432.3 m2 g−1 and the highest degree of graphitization among analyzed samples. C6 hydrocarbon adsorption tests demonstrated the dominant role of the kinetic effect for the adsorption of branched and cyclic hexane isomers - the partition coefficient decreased as the molecule kinetic diameter increased. The contribution of thermodynamic effects was distinguished for molecules with uneven charge distribution. A comparison of the partition coefficient ratios for different pairs of hydrocarbons demonstrated the potential of rGOAs in separating various C6 hydrocarbons. The selectivity, calculated from binary-component adsorption tests of benzene (Bz)/cC6 equimolar mixture, was 13.7, 8.5 and 2.8 for DTN4, DTN2, and DTN1. The research indicates that rGOAs may have potential as adsorbents for the selective separation of hydrocarbons, however, the competitive adsorption and performance at high surface coverages of adsorbates have to be accounted for in further research to assess the applicability of rGOAs reliably.

Recognition and order of multiple sidechains by metal-organic framework enhances the separation of hexane isomers.

Porous materials perform molecular sorting, separation and transformation by interaction between their framework structures and the substrates. Proteins also interact with molecules to effect chemical transformations, but rely on the precise sequence of the amino acid building units along a common polypeptide backbone to maximise their performance. Design strategies that positionally order sidechains over a defined porous framework to diversify the internal surface chemistry would enhance control of substrate processing. Here we show that different sidechains can be ordered over a metal-organic framework through recognition of their distinct chemistries during synthesis. The sidechains are recognised because each one forces the common building unit that defines the backbone of the framework into a different conformation in order to form the extended structure. The resulting sidechain ordering affords hexane isomer separation performance superior to that of the same framework decorated only with sidechains of a single kind. The separated molecules adopt distinct arrangements within the resulting modified pore geometry, reflecting their strongly differentiated environments precisely created by the ordered sidechains. The development of frameworks that recognise andorder multiple sidechain functionality by conformational control offers tailoring of the internal surfaces within families of porous materials to direct interactions at the molecular level.

Six‐Membered Ring Directed Assembly of a Zirconium Zeolitic Metal‐Organic Framework for Efficient Separation of Hexane Isomers

The synthesis of zirconium MOFs with zeolite net is quite challenging due to the high connectivity of Zr6 clusters, which is far from tetrahedral connection, a requisite for zeolite net. In this work, we demonstrate a six‐membered ring (6MR) strategy through mimicking of mineral zeolites with mixed ditopic and tritopic carboxylate linkers. With this strategy, the ditopic linker cross‐links Zr6 clusters to form 4‐connected zeolite‐like nets, while the tritopic one is used to direct the formation of 6MR and simultaneously consumes extra coordination sites on the cluster. The feasibility of this strategy is shown by one zeolitic metal‐organic framework (NNM‐5) and this strategy has also led to the synthesis of the other dia‐type zirconium MOF (NNM‐6). Interestingly, as the tritopic linker not only directs the formation of 6‐MR but also partitions 6‐MR into small segments, NNM‐5 with SOD topology shows a structural feature of small aperture and big cage, which has led to efficient separation of hexane isomers. With both exceptionally high n‐hexane uptake (65.9 cm3·g‐1) and size‐exclusion selectivity, an exceptional separation capability is verified by breakthrough experiments. Calculation results demonstrate that the large difference of diffusion energy barrier due to the small aperture accounts for the underlying separation mechanism.

Efficient separation of linear and mono-branched hexane isomers using large-area silicalite-1 membranes

Membrane-based hydrocarbon isomer separation is a promising and energy-saving alternative to distillation. For the first time, tubular silicalite-1 membranes with large areas of 180 cm2 were employed in this study to separate linear and mono-branched hexane isomers. The membrane had a thickness of around 8 μm and showed highly (h0h) orientation. In binary and ternary mixtures of n-hexane (n-C6), 2-methylpentane (2MP), and 3-methylpentane (3MP), the effects of temperature and partial pressure on the separation performance of silicalite-1 membrane were examined. Moreover, the long-term stability of the membrane in binary and ternary mixture separation was also investigated. The large-area membrane showed a n-C6 permeance of 2.4 × 10-8 mol/(m2 s Pa) and n-C6/2MP and n-C6/3MP separation factors of 36 and 74 in the ternary n-C6/2MP/3MP (2.8 kPa/2.9 kPa/2.8 kPa) mixture with N2 as the balanced gas at 100 kPa absolute and 303 K, respectively. The scaling-up membranes demonstrated good and stable separation performance during the long-term test, highlighting the effectiveness and potential application of using large-area silicalite-1 membranes for the separation of hexane isomer mixtures.

UiO-66/PIM-1 Mixed-Matrix Membrane for Hexane Isomer Separation.

The separation of high-octane dibranched alkanes from naphtha is critical in the refining of gasoline. To date, research on the membrane-based separation of alkane isomers has been limited, with a particular paucity of investigations into mixed-matrix membranes. Herein, the continuous and dense UiO-66/PIM-1 mixed-matrix membrane, which was prepared through precise control of the interfacial structure, was first applied to the differentiation of C6 alkane isomers. Due to the synergistic combination of UiO-66 with differential adsorption capabilities for alkanes and PIM-1 that possesses a cross-linkable structure, the resulting UiO-66/PIM-1-(20) membrane demonstrated remarkable separation performance and high stability. Pervaporation measurements showed that the mass fraction of 2,2-dimethylbutane in the feed side was increased from 50.0 to 75.8 wt % while an excellent flux of 1700 g m-2 h-1 was maintained over a continuous 40 h period. The UiO-66/PIM-1-(20) membrane, characterized by its facile replication and processing, shows potential for large-scale fabrication. This study offers a new approach to the membrane separation of alkane isomers.

Stable CAAC-Triazenes: A New Nitrogen Ligand System With Donor and Conformational Flexibility, and With Application in Olefin Activation Catalysis.

N-heterocyclic imines such as pyridylidene amines impart high catalytic activity when coordinated to a transition metal, largely imposed by their electronic flexibility. Here, this donor flexibility has been applied for the first time to CAAC-based systems through the synthesis of CAAC-triazenes. These new ligands offer a larger π-conjugation that extends from the N-heterocyclic carbene through three nitrogens rather than just one, as observed in N-heterocyclic imines. We demonstrate the straightforward synthesis of three new CAAC-triazenes containing different substituents on the terminal triazene nitrogen. These compounds are remarkably stable up to 120 °C without loss of N2 as typically observed with similar triazenes. E-to-Z isomerization within the triazene is instigated by UV light and is partially reversible dependent on the triazene substituent. The quinoline-substituted CAAC-triazene 1-Q has been applied as an L,L'-type ligand in the synthesis of [PdCl2(1-Q)], [PdCl(Me)(1-Q)] and [Pd(Me)(H2O(1-Q)]+. E-to-Z ligand isomerization also occurs when coordinated to PdCl2, providing access to on-metal manipulation. The cationic complex [PdMe(H2O)(1-Q)]+ is a precatalyst for oligomerization of ethylene to form initially 2-butene and subsequently linear and branched C8-C12 products from butene activation. Moreover, isomerization of 1-hexene takes place efficiently with exceptionally low catalyst loading (10 ppm) and up to 74,000 turnover numbers.

Exploring affinity between organic probes and Prussian Blue Analogues via inverse gas chromatography

Prussian Blue Analogues (PBAs), which are characterized by their open structure, high stability, and non-toxic properties, have recently been the subject of research for various applications, including their use as electrode precursors for capacitive deionization, gas storage, and environmental purification. These materials can be readily tailored to enhance their affinity towards gases for integration with sensing devices. An improved understanding of PBA-gas interactions is expected to enhance material development and existing sensor deposition schemes greatly. The use of inverse gas chromatography (IGC) is a robust approach for examining the relationship between porous materials and gases. In this study, the adsorption properties of (functionalized) hydrocarbons, i.e., probe molecules, on the copper hexacyanoferrate (CuHCF) lattice were studied via IGC, demonstrating that alkylbenzenes have a higher affinity for this material than n-alkanes. This difference was rationalized by steric hindrance, π–π interactions, and vapour pressure effects. Along the same line, the five isomers of hexane showed decreasing selectivity upon increased steric hindrance. Enthalpy values for n-pentane, n-hexane and n-heptane were lower than that of toluene. The introduction of increased probe masses resulted in a surface coverage of 46% for toluene. For all n-alkane probe molecules this percentage was lower. However, the isotherms of these probes did not show saturation points and the observed linear regime proves beneficial for gas sensing. Our work demonstrates the versatility of CuHCF for gas sensing purposes and the potential of IGC to characterize the adsorption characteristics of such a porous nanomaterial.

CONVERSİON OF n-HEXANE OVER CATALYSTS BASED ON SULFATED ZIRCONIUM DIOXIDE

The isomerization process is becoming increasingly important in the modern petroleum refining context due to the limitations on the content of benzene, aromatic compounds, and olefins in gasoline. Isomerization is an effective and profitable process for octane enhancement of gasoline unlike other octane increasing processes. Due to the low sulfur and benzene content, the isomerate can be used as an ideal blending gasoline component. Therefore, the isomerization process has a great importance in petroleum refineries to increase the fuel octane number. This article aimed to study the conversion process of normal hexane over palladium and platinum containing catalysts on the base of sulfated zirconium dioxide. It has been determined that due to their high-performance characteristics, catalytic systems based on sulfated zirconium dioxide can be considered the most promising for isomerization of normal alkanes. Moreover, comparison of palladium-containing catalysts based on sulfated zirconium dioxide with platinum-containing catalysts based on sulfated zirconium dioxide showed that palladium sulfated zirconia catalysts have high catalytic performance in the isomerization of normal hexane. Keywords: alkanes, catalyst, platinum, palladium, isomerization, temperature, sulfated zirconium dioxide. .

Dehydration‐Induced Cluster Consolidation in a Metal‐Organic Framework for Sieving Hexane Isomers

AbstractMetal‐organic frameworks (MOFs) that exhibit dynamic phase‐transition behavior under external stimuli could have great potential in adsorptive separations. Here we report on a zinc‐based microporous MOF (JNU‐80) and its reversible transformation between two crystalline phases: large pore (JNU‐80‐LP) and narrow pore (JNU‐80‐NP). Specifically, JNU‐80‐LP can undergo a dehydration‐induced cluster consolidation under heat treatment, resulting in JNU‐80‐NP with a reduced channel that allows exclusion of di‐branched hexane isomers while high adsorption of linear and mono‐branched hexane isomers. We further demonstrate the fabrication of MOF‐polymer composite (JNU‐80‐NP‐block) and its application in the purification of di‐branched isomers from liquid‐phase hexane mixtures (98 % di‐branched) at room temperature, affording the di‐branched hexane isomers with 99.5 % purity and close to 90 % recovery rate over ten cycles. This work illustrates an interesting dehydration‐induced cluster consolidation in MOF structure and the ensuing channel shrinkage for sieving di‐branched hexane isomers, which may have important implications for the development of MOFs with dynamic behavior and their potential applications in non‐thermal driven separation technologies.

Dehydration-Induced Cluster Consolidation in a Metal-Organic Framework for Sieving Hexane Isomers.

Metal-organic frameworks (MOFs) that exhibit dynamic phase-transition behavior under external stimuli could have great potential in adsorptive separations. Here we report on a zinc-based microporous MOF (JNU-80) and its reversible transformation between two crystalline phases: large pore (JNU-80-LP) and narrow pore (JNU-80-NP). Specifically, JNU-80-LP can undergo a dehydration-induced cluster consolidation under heat treatment, resulting in JNU-80-NP with a reduced channel that allows exclusion of di-branched hexane isomers while high adsorption of linear and mono-branched hexane isomers. We further demonstrate the fabrication of MOF-polymer composite (JNU-80-NP-block) and its application in the purification of di-branched isomers from liquid-phase hexane mixtures (98 % di-branched) at room temperature, affording the di-branched hexane isomers with 99.5 % purity and close to 90 % recovery rate over ten cycles. This work illustrates an interesting dehydration-induced cluster consolidation in MOF structure and the ensuing channel shrinkage for sieving di-branched hexane isomers, which may have important implications for the development of MOFs with dynamic behavior and their potential applications in non-thermal driven separation technologies.

In situ conversion of ZnO anchored on porous carbon foams to antiflexible ZIF-8-X (X = Co or NH2) for sieving linear and mono-branched hexane isomers

Efficient separation of linear hexane from their isomers is a vital petrochemical process to produce high-quality gasoline. Zeolitic imidazolate frameworks-8 (ZIF-8), one of the most famous metal-organic frameworks (MOFs), is a promising separation material due to its special pore size (3.4 Å), whereas the flexible framework limited its separation ability, showing unsatisfied trade-off between adsorption capacity and separation selectivity. Here, we propose a novel strategy of post metal-oxide modification (PMOM) to suppress ZIF-8 flexibility by in situ growth on rigid layer of porous carbon foam (PCF) based the intermediation of anchored ZnO nanoparticles directly obtained from the pyrolysis of sucrose and zinc nitrate mixture. Afterwards, synergistic flexible suppression technology (SFST) was adopted to design antiflexible PCF/ZIFs with mixed-metal and mixed-ligand, including bi-metal PCF/ZIF-8-Co and di-ligand PCF/ZIF-8-NH2. Therein, the tight interfaces generated with benzene-ring inhabited the swinging of linkers and hindered 3-MP entry into the pore channels, showing both remarkable nHex adsorption capacity (q = 2.26 mmol·g−1) and nHex/3-MP selectivity (Su = 9.42). Moreover, bi-component adsorption experiments confirm the practical separation performance and cycling stability, showing promising application in adsorptive separation processes.

Engineering pore limiting diameter of metal–organic frameworks for benchmark separation of mono- and di-branched hexane isomers

The separation of mono- and di-branched hexane isomers remains an important and challenging industrial process for the production of high-octane gasoline. Suitable adsorbents with high adsorption selectivity and capacity are urgently required. Herein, we demonstrate a strategy to realize highly efficient kinetically controlled hexane isomers adsorption separation that utilizes the tunability of the pore limiting diameter in M2TTFTB (M=Zn, Mn, Cd) by metal substitution. The appropriate refinement of the partially contracted pore not only improved the kinetic selectivities, but also enhanced the host–guest interaction and increased the adsorption capacity of 3MP and nHEX. The resulting Mn2TTFTB brought about both the record capacity of 3MP and the record kinetic selectivities of 3MP/22DMB and nHEX/22DMB, exhibiting the largest productivity of high-purity 22DMB in the breakthrough experiments, which sets a new benchmark for the hexane isomers separation via a rarely reported kinetically controlled mechanism.

Selective sorting of hexane isomers by anion-functionalized metal-organic frameworks with optimal energy regulation

Extensive efforts have been made to improve the separation selectivity of hydrocarbon isomers with nearly distinguishable boiling points; however, how to balance the high regeneration energy consumption remains a daunting challenge. Here we describe the efficient separation of hexane isomers by constructing and exploiting the rotational freedom of organic linkers and inorganic SnF62− anions within adaptive frameworks, and reveal the nature of flexible host-guest interactions to maximize the gas-framework interactions while achieving potential energy storage. This approach enables the discrimination of hexane isomers according to the degree of branching along with high capacity and record mono-/di-branched selectivity (6.97), di-branched isomers selectivity (22.16), and upgrades the gasoline to a maximum RON (Research Octane Number) of 105. Benefitting from the energy regulation of the flexible pore space, the material can be easily regenerated only through a simple vacuum treatment for 15 minutes at 25 °C with no temperature fluctuation, saving almost 45% energy compared to the commercialized zeolite 5 A. This approach could potentially revolutionize the whole scenario of alkane isomer separation processes.

A Microporous Multi-Cage Metal-Organic Framework for an Effective One-Step Separation of Branched Alkanes Feeds.

The improvement of the Total Isomerization Process (TIP) for the production of high-quality gasoline with the ultimate goal of reaching a Research Octane Number (RON) higher than 92 requires the use of specific sorbents to separate pentane and hexane isomers into classes of linear, mono- and di-branched isomers. Herein we report the design of a new multi-cage microporous Fe(III)-MOF (referred to as MIP-214, MIP stands for materials of the Institute of Porous Materials of Paris) with a flu-e topology, incorporating an asymmetric heterofunctional ditopic ligand, 4-pyrazolecarboxylic acid, that exhibits an appropriate microporous structure for a thermodynamic-controlled separation of hydrocarbon isomers. This MOF produced via a direct, scalable, and mild synthesis route was proven to encompass a unique separation of C5/C6 isomers by classes of low RON over high RON alkanes with a sorption hierarchy: (n-hexane≫n-pentane≈2-methylpentane>3-methylpentane)low RON≫(2,3-dimethylbutane≈i-pentane≈2,2-dimethylbutane)high RON following the adsorption enthalpy sequence. We reveal for the first time that a single sorbent can efficiently separate such a complex mixture of high RON di-branched hexane and mono-branched pentane isomers from their low RON counterparts, which is a major achievement reported so far.