Crystalline microporous transition metal oxides are generally composed of metal-oxygen octahedra, and therefore they are also called zeolitic octahedral metal oxides (ZOMOs). The frameworks of ZOMOs consist of polyoxometalates (POMs) as building units and metal ions as linkers. Owing to the unique compositions and structures, ZOMOs show both advantages of transition metal oxides and zeolitic materials. Hydrocarbons are important raw chemicals and energy sources. Hydrocarbons with the same carbon number are difficult to be separated because of their similar physical and chemical properties, and hydrocarbons separation and purification causes huge energy consumption. Therefore, it is a challenging and difficult topic in not only fundamental sciences but also practical applications. Compared with traditional distillation separation, adsorption separation method stands out for its advantages of energy saving, environmental protection, and strong sustainability. Microporous materials are critical in adsorption separation. Here, we report two zeolitic vanadotungstates with cubic symmetry (VT-1) and triangular symmetry vanadotungstate (VT-5), for adsorption and separation of C2, C3 and C4 hydrocarbons. The composition and structure of the materials have a significant impact on the gas separation performance. Cation affects the separation performance of the material. Incorporating Cu2+ in VT-1 by ion-exchange enhances the interaction between the framework and olefins, which enables effective separating C2H4/C2H6 and C3H6/C3H8 not only at low temperatures and humidities but also at high temperatures and humidities. From the perspective of structure, pore size is a major factor affecting the separation performance. The specific pore size of VT-1 is between n-butane and isobutane, resulting in a size-sieving effect for n-butane and isobutane separation by VT-1. Moreover, VT-5 as a isomeric material of VT-1 shows a high performance for separating 1,3-butene from other C4 hydrocarbons.

Zeolitic octahedral metal oxides based on vanadotungstate for gas separation

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