Ethylene production from C2 hydrocarbon mixtures through one separation step is desirable but challenging because of the similar size and physical properties of acetylene, ethylene, and ethane. Herein, we report three new isostructural porous coordination networks (NPU-1, NPU-2, NPU-3; NPU represents Northwestern Polytechnical University) that are sustained by 9-connected nodes based upon a hexanuclear metal cluster of composition [Mn6(μ3-O)2­(CH3COO)3]6+. NPU-1/2/3 exhibit a dual cage structure that was systematically fine-tuned in terms of cage size to realize selective adsorption of C2H2 and C2H6 over C2H4. Dynamic breakthrough experiments demonstrated that NPU-1 produces ethylene in >99.9% purity from a three-component gas mixture (1:1:1 C2H2/C2H4/C2H6). Molecular modeling studies revealed that the dual adsorption preference for C2H2 and C2H6 over C2H4 originates from (a) strong hydrogen-bonding interactions between electronegative carboxylate O atoms and C2H2 molecules in one cage and (b) multiple non-covalent interactions between the organic linkers of the host network and C2H6 molecules in the second cage.

Peroxotungsten and peroxomolybdenum complexes such as [WO(O2)2·Phen·H2O] and [MoO(O2)2·Phen] (Phen:  1,10-phenanthroline) have been synthesized and characterized and were immobilized in 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-n-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF4), 1-butyl-3-methyl-imidazolium hexafluorophosphate ([Bmim]PF6), and 1-n-octyl-3-methylimidazolium hexafluorophosphate ([Omim]PF6) for extraction and catalytic oxidation of dibenzothiophene (DBT) remaining in n-octane. The results demonstrated that ionic liquid (IL) was only used as an extractant for DBT-containing model oil and the removal of sulfur was only about 12.2−22.0%. After addition of 30 wt % H2O2 in IL, model oil with 30.0−63.0% sulfur removal was given via chemical oxidation. While H2O2 and catalyst were introduced together, the removal of sulfur increased sharply. In the case of the system containing H2O2, WO(O2)2·Phen·H2O and [Bmim]BF4, extraction and catalytic oxidation increased the sulfur removal to 98.6%. However, the oxidative desulfurization systems containing WO(O2)2·Phen·H2O and H2O2 only led to 50.3% sulfur removal in the absence of IL. This experiment demonstrated that a combination of catalytic oxidation and extraction in IL can deeply remove DBT from model oil. This result also indicated the remarkable advantage of this process over the desulfurization by mere solvent extraction with IL or catalytic oxidation without IL.

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A combination of catalytic oxidation and extraction in ionic liquid (IL) was used for the removal of benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) from the model oil. Three peroxophosphomolybdates+ and [C 16 H 33 NC 5 H 5 ] + ) were synthesized and characterized. In the catalytic oxidation desulfurization (CODS) system containing the peroxophosphomolybdate with short alkyl chain ([(C 4 H 9 ) 4 N] 3 {PO 4 [MoO(O 2 ) 2 ] 4 }) and H 2 O 2 , the process exhibited low sulfur removal (16.8%). However, with addition of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF 4 ), the extraction and catalytic oxidative desulfurization (ECODS) system remarkably increased the removal of sulfur to 97.3% (with stoichiometric amounts of H 2 O 2 ). The process was superior to the simple extraction with IL (16.3%). The results demonstrated that the ECODS system could deeply remove DBT from the model oil, and this desulfurization system could be recycled 4 times with slight decrease in activity. We also found that the catalysts with short alkyl chains exhibited higher catalytic activity than that with long alkyl chain in the ECODS system. Moreover, the reactivity of sulfur compounds decreased in the order of DBT > 4,6-DMDBT > BT.

A simplified extraction and catalytic oxidative desulfurization (ECODS) system composed of phosphotungstic acid (H3PW12O40·14H2O), 30% H2O2, and [bmim]BF4 was found suitable for the deep removal of sulfur in model oil. By this desulfurization system dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT), and benzothiophene (BT) could be effectively removed. Removal of DBT could reach 98.2% at room temperature (30 °C) for 1 h, which was remarkably superior to mere solvent extraction with IL (14.2%) or catalytic oxidation without IL (15.9%). When the reaction temperature increased to 70 °C, treatment of BT, DBT, and 4,6-DMDBT with our ECODS system showed 100% removal of sulfur compounds in 3 h. This desulfurization system could be recycled five times with slight decrease in activity.

One-step adsorptive purification of ethylene (C2H4) from four-component gas mixtures comprising acetylene (C2H2), ethylene (C2H4), ethane (C2H6) and carbon dioxide (CO2) is an unmet challenge in the area of commodity purification. Herein, we report that the ultramicroporous sorbent Zn-atz-oba (H2oba = 4,4-dicarboxyl diphenyl ether; Hatz = 3-amino-1,2,4-triazole) enables selective adsorption of C2H2, C2H6 and CO2 over C2H4 thanks to the binding sites that lie in its undulating pores. Molecular simulations provide insight into the binding sites in Zn-atz-oba that are responsible for coadsorption of C2H2, C2H6 and CO2 over C2H4. Dynamic breakthrough experiments demonstrate that the selective binding exhibited by Zn-atz-oba can produce polymer-grade purity (>99.95%) C2H4 from binary (1:1 for C2H4/C2H6), ternary (1:1:1 for C2H2/C2H4/C2H6) and quaternary (1:1:1:1 for C2H2/C2H4/C2H6/CO2) gas mixtures in a single step.

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Three decatungstates with short carbon chains as the cations, such as tetrabutylammonium decatungstate ([(C4H9)4N]4W10O32), tetramethylammonium decatungstate ([(CH3)4N]4W10O32), and benzyltriethylammonium decatungstate ([(C2H5)3NC7H7]4W10O32), were synthesized and then used as a catalyst in the extractive catalytic oxidative desulfurization (ECODS) system in the ionic liquid (IL) of [Bmim]PF6, and hydrogen dioxide (H2O2) was used as an oxidant. During the optimized process, the sulfur level in the model oil (1000 ppm S) can be reduced to 8 ppm, which is consistent with the standards of deep desulfurization. The temperature, the reaction time, and the amount of H2O2 and catalyst, as well as the type of the cations of decatungstates, all played vital roles in desulfurization efficiency, which were studied in detail to optimize the reaction conditions. The system could be recycled five times before the sulfur removal decreased sharply.