Correlation of adsorbent cavity structure with adsorption behavior and interaction of long-chain α-olefin/paraffin on microporous adsorbents

Long-chain alpha-olefins have a high added value as important raw materials for many highly marketable products. Fishcher-Tropsch synthesis products contain ultrahigh-content alpha-olefins, which are of great value if the challenging separation of alpha-olefin/paraffin is achieved through energy-saving ways, for which adsorption separation is an attractive technology. One of the most significant differences between the adsorption separation of long-chain and light hydrocarbons is the steric hindrance of the molecular chain. Herein, we propose a combination of window size, metal node spacing, and bending degree to quantitatively describe the adsorption cavity structure for the separation of long-chain alpha-olefin/paraffin. The general cavity structural characteristics of microporous materials with good separation performance for long-chain alpha-olefin/paraffin are revealed. The selective adsorption of liquid C-6 and C-8 alpha-olefin/paraffin mixtures on CuBTC (BTC = benzene-1,3,5-tricarboxylate) was studied in detail to reveal the influence of the cavity structure on the adsorption and interaction using a combination of batch adsorption experiments and molecular simulation techniques. CuBTC exhibited 360 and 366 mg/g olefin adsorption capacities for C-6 and C-8 linear alpha-olefins, respectively. The adsorption energies were -0.540 and -0.338 eV for C-8 linear alpha-olefin and paraffin, respectively. The contributions of different types of interactions to the overall adsorption energy were quantified to illustrate the adsorption energy difference between alpha-olefin/paraffin and CuBTC. This work provides a new understanding of the long-chain hydrocarbon adsorption behavior different from ethylene/ethane and propylene/propane, which guides the design of adsorbents for alpha-olefin/paraffin separation.

Automated summary

This study proposes a quantitative description of the adsorption cavity structure for the separation of long-chain alpha-olefin/paraffin and reveals the general cavity structural characteristics of microporous materials with good separation performance. The selective adsorption of C-6 and C-8 linear alpha-olefins on CuBTC was studied in detail, and the influence of the cavity structure on the adsorption and interaction was revealed. The research provides a new understanding of the long-chain hydrocarbon adsorption behavior and guides the design of adsorbents for alpha-olefin/paraffin separation.