Adsorption Property of Starch-Based Microporous Carbon Materials with High Selectivity and Uptake for C1/C2/C3 Separation

Metal-organic frameworks with two different-sized aromatic ring-confined nanotraps for benchmark natural gas upgrade

Recovery of light alkanes from natural gas is of great significance in petrochemical production. Herein, a promising strategy utilizing two types of size-complementary aromatic ring-confined nanotraps (called bi-nanotraps here) is proposed to efficiently trap ethane (C2H6) and propane (C3H8) selectively at their respective sites. Two isostructural metal-organic frameworks (MOFs, SNNU-185/186), each containing bi-nanotraps decorated with six aromatic rings, are selected to demonstrate the feasibility of this method. The smaller nanotrap acts as adsorption sites tailored for C2H6 while the larger one is optimized in size for C3H8. The separation is further facilitated by the large channels, which serve as mass transfer pathways. These advanced features give rise to multiple C-H⋯π interactions and size/shape-selective interaction sites, enabling SNNU-185/186 to achieve high C2H6 adsorption enthalpy (43.5/48.8 kJ mol-1) and a very large thermodynamic interaction difference between C2H6 and CH4. Benefiting from the bi-nanotrap effect, SNNU-185/186 exhibits benchmark experimental natural gas upgrade performance with top-level CH4 productivity (6.85/6.10 mmol g-1), ultra-high purity and first-class capture capacity for C2H6 (1.23/0.90 mmol g-1) and C3H8 (2.33/2.15 mmol g-1).

pH-Regulated Refinement of Pore Size in Carbon Spheres for Size-Sieving of Gaseous C8 , C6 and C3 Hydrocarbon Pairs

Selective separation of industrial important C8 , C6 and C3 hydrocarbon pairs by physisorbents can greatly reduce the energy intensity related to the currently used cryogenic distillation techniques. The achievement of size-sieving based on carbonaceous materials is desirable, but commonly hindered by the random structure of carbons often with a broad pore size distribution. Herein, a pH-regulated pre-condensation strategy was introduced to control the carbon pore architecture by the sp2 /sp3 hybridization of precursor. The lower pH value during pre-condensation of glucose facilitates the growth of aromatic nanodomains, rearrangement of stacked layers and a concomitant transition from sp3 -C to sp2 -C. The subsequent pyrolysis endows the pore size manipulated from 6.8 to 4.8 Å and narrowly distributed over a range of 0.2 Å. The refined pores enable effective size-sieving of C8 , C6 and C3 hydrocarbon pairs with high separation factor of 1.9 and 4.9 for C8 xylene (X) isomers para-X/meta-X and para-X/ortho-X, respectively, 5.1 for C6 alkane isomers n-hexane/3-methylpentane, and 22.0 for C3 H6 /C3 H8 . The excellent separation performance based-on size exclusion effect is validated by static adsorption isotherms and dynamic breakthrough experiments. This synthesis strategy provides a means of exploring advanced carbonaceous materials with controlled hybridized structure and pore sizes for challenging separation needs.

Tunable Confined Aliphatic Pore Environment in Robust Metal-Organic Frameworks for Efficient Separation of Gases with a Similar Structure

The fine-tuning of the pore structure of metal-organic frameworks (MOFs) is of critical importance to developing energy-efficient processes for the challenging separation of structurally similar molecules. Herein, we demonstrate a strategy to realize a quasi-three-dimensional refinement of the pore structure that utilizes the tunability of ring size and number in polycycloalkane-dicarboxylate ligands. Two hydrolytically stable MOFs with a confined aliphatic pore environment, ZUL-C1 and ZUL-C2, were, for the first time, synthesized and applied in separating low-concentration C2-C3 hydrocarbons from natural gas and ultralow-concentration Xe from used nuclear fuel (UNF) off-gas. Validated by X-ray diffraction and modeling, an expansion of the polycycloalkane moiety enables sub-angstrom contraction in specific directions and forms a pore surface with more alkyl sites, which affords stronger trapping of guest molecules with relatively higher polarizability. The resultant material exhibits record C₂H₆/CH₄ and C₃H₈/CH₄ selectivities coupled with a benchmark low-pressure C₂H₆ capacity in alkane mixture separation and also a benchmark Xe capacity at extremely diluted feed concentration and record Kr productivity for the Xe/Kr (20:80, v/v) mixture in Xe/Kr separation.

Experimental Setup and Graphical User Interface for Zero-Length Column Chromatography

This work describes the design and implementation of a Zero-Length Column system to measure: diffusion coefficients, adsorption isotherm parameters of pure components and mixtures. In addition, a graphical user interface (GUI) was developed in LabVIEW for the semi-automatic operation of the system. The system is novel because it integrates all the aforementioned functionalities without using mass spectrometry. Two adsorbents, zeolite 5A and Basolite® C300 (Copper benzene-1,3,5-tricarboxylate) and two adsorbates methane and ethane were used to perform the validation of adsorption and diffusion experiments. The Henry constants and diffusion coefficients obtained reproduce those previously reported. The combination of the experimental setup and the GUI significantly reduce the amount of sample and measurement time needed in the characterization of the molecular sieves by conventional volumetric and gravimetric systems. The proposed system is relatively inexpensive, robust, easy to build, and capable of reproducing the results of other techniques.

Robust Nickel-Based Metal-Organic Framework for Highly Efficient Methane Purification and Capture

Developing energy-efficient alternatives for methane (CH₄) purification from natural gas and methane capture of coal-mine gas is of great significance and challenge in the chemical industry. Herein, we report a robust nickel-based metal-organic framework (MOF), Ni-BPZ, featuring one-dimensional (1D) rhombic channels decorated with abundant pyrazole rings. Ni-BPZ exhibits excellent separation performance toward both C₂H₆/CH₄ and CH₄/N₂ binary mixtures. The C₂H₆/CH₄ selectivity of Ni-BPZ is high, up to 50.2, exceeding those of most MOF adsorbents reported, and it simultaneously possesses a remarkable C₂H₆ uptake of 2.46 mmol/g at 298 K and 0.1 bar. The CH₄/N₂ selectivity of Ni-BPZ reaches 6.6, and its high CH₄ uptake is 1.56 mmol/g, which is also superior to most high-performance CH₄ adsorbents. The molecular simulation reveals that the uniform 1D rhombic channels with abundant pyrazole rings provide a high density of potential adsorption sites for efficient C₂H₆/CH₄ and CH₄/N₂ separations.