Nitrogen/oxygen doped hierarchical porous carbon with adjustable pore structure for efficient adsorption, separation, and enhancement mechanism of methanol and acetone azeotropes: Experimental and theoretical study

Abstract

The adsorption and separation of methanol and acetone are crucial for environmental protection and recycling. However, the separation of methanol and acetone azeotropes using carbon-based materials remains challenging, and the underlying mechanism is still unclear. Here, we propose the synthesis of porous carbon (NaOCs) using benzimidazole as a precursor and NaOH as an activator. With the increase of the proportion of NaOH and benzimidazole, the activation reaction was intensified, leading to the formation of numerous mesopores. NaOCs exhibit a maximum specific surface area (SBET) of 3084 m2/g, and has extremely high adsorption capacity of methanol (56.9 mmol/g at 13 kPa) and acetone (34.6 mmol/g at 18 kPa) at 25 °C. The results of experiments and molecular simulations indicate that the saturation adsorption capacity of methanol and acetone is determined by micropores and narrow mesopores at 25 °C, whereas the adsorption capacity at relatively low pressure is primary determined by ultramicropores and oxygen group. Furthermore, for methanol-acetone azeotropes separation, the acetone/methanol selectivity at low pressure depends on carbon surface polarity and ultramicropore, while methanol/acetone selectivity at high pressure depends on micropores of 1–2 nm. Our findings provide insights into the design and further development of adsorbents for VOCs adsorption and azeotrope separation applications.