Ethane removal from ethylene-rich mixtures at room temperature by ethane-selective reduced graphene oxide adsorbents

Energy-efficient removal of alkanes from light alkenes is considered as one of the most important separations of the chemical industry. Here, reduced graphene oxide (rGO) adsorbents were developed via controlled hydrothermal reduction of GO resulting, after optimizing the synthesis conditions with respect to the type of reducing agent and reduction reaction duration, in reversed selectivity for the removal of ethane from ethylene-rich mixtures. The optimum adsorbent, prepared by using hydrazine hydrate as reducing agent and a 4-h reduction treatment time (rGO-4-H), exhibited a high ethane capacity of 3.45 mmol/g at 273 K and 1 bar and a kinetic selectivity of 2.4, with low heat of adsorption (24 kJ/mol for C 2 H 6 ) ensuring facile regeneration. Atomic force microscopy was used to measure the weak van der Waals interactions of ethane and ethylene with the rGO surface, while molecular dynamics simulations indicated that both ethane and ethylene exhibit heats of adsorption in the range of 10–40 kJ/mol that tend to increase with the oxygen content of the adsorbent, with ethane under certain conditions showing stronger adsorption than ethylene thus explaining the experimentally observed reverse selectivity. Packed bed breakthrough experiments at room temperature revealed a significant difference in elution time between the two adsorbate species indicating dynamic separation capability that yielded a breakthrough selecti v ity of 2 and production of ethylene of polymer-grade with purity of >99.99 % and productivity of 0.92 mmol/g for an ethane/ethylene (1/9 v/v ) mixture at 1 bar. This work demonstrates that rGO adsorbents are promising to extract ethane traces from ethylene-rich streams at room temperature. • Ethane-selective rGO adsorbents for ethane/ethylene separation at room temperature. • Selectivity reversed from ethylene-selective for GO to ethane-selective for the optimal rGO adsorbents. • High ethane capacity of 3.45 mmol/g at 273 K and 1 bar. • Breakthrough ethane/ethylene selectivity of 2.02 at ambient conditions. • Stable performance for multiple adsorption-desorption cycles.