Adsorption performance of ZSM-5 and MCM-41 molecular sieves for light hydrocarbons and liquefied petroleum gas

Abstract

Minor hydrocarbon emissions during crude oil storage and transportation lead to resource loss and environmental risks. However, conventional adsorbents exhibit low selectivity and limited adsorption capacity for light hydrocarbons (C₂–C₄). In this study, dynamic adsorption experiments combined with molecular simulations were employed to elucidate the adsorption mechanisms of light hydrocarbon molecules on microporous ZSM-5 and mesoporous MCM-41. Experimentally, ZSM-5 exhibits a higher adsorption capacity for lighter alkanes, with an ethane adsorption capacity of 76.96 mg g⁻¹, which is approximately 2.5 times that of isobutane. In contrast, MCM-41 achieves superior adsorption of larger alkanes (isobutane: 177.58 mg g⁻¹) owing to its exceptional surface area (969.9 m² g⁻¹), representing a 5.7-fold increase compared to ZSM-5. The simulations revealed distinct mechanisms: the diffusion coefficients in ZSM-5 are governed by size-pore matching, while the adsorption behavior of MCM-41 is predominantly influenced by intermolecular interactions. This work establishes a pore engineering strategy that synergistically integrates size exclusion (in micropores) and surface-mediated molecular stacking (in mesopores), providing theoretical guidance for designing hierarchical adsorbents to mitigate light hydrocarbon emissions from crude oils of various origins.