A thiophene-rich microporous metal–organic framework for CH4 purification and C3H8 enrichment from simulated natural gas

Abstract

Efficient separation of CH₄, C₂H₆ and C₃H₈ from natural gas is crucial for natural gas purification and the recovery of high-value chemical raw materials. However, traditional cryogenic distillation technology has high energy consumption and harsh equipment requirements. Adsorption separation technology based on metal–organic framework (MOF) adsorbents is an ideal alternative. This work systematically investigates the separation ability of thiophene-rich zirconium-based microporous metal–organic framework Zr-DMTDC for CH₄, C₂H₆ and C₃H₈. Single-component adsorption tests confirm that the equilibrium adsorption capacities of this material for C₂H₆ and C₃H₈ reach 69.7 cm³ g⁻¹ and 86.9 cm³ g⁻¹, respectively, while the adsorption capacity for CH₄ is very low at 298 K and 1 bar. Ideal Adsorbed Solution Theory (IAST) calculations show that the selectivity of C₃H₈/CH₄ (5/85) reaches up to 133 and the selectivity of C₂H₆/CH₄ (10/85) is approximately 15.8. The relatively low heats of adsorption of the three gases further reduce energy consumption for desorption and regeneration. DFT simulations show that the abundant S atoms and π electrons in the microporous channels of Zr-DMTDC provide adsorption sites for alkanes through C–H⋯S and C–H⋯π interactions. Dynamic breakthrough experiments on CH₄/C₂H₆/C₃H₈ (85/10/5) mixed gas demonstrate that the material can efficiently separate the mixed gas, producing CH₄ with a purity of >99.8% (yield: 183.6 L kg⁻¹). Meanwhile, high purity of C₃H₈ can be enriched by a heat treatment process. More importantly, after being treated with argon gas containing saturated water vapor for 12 h, Zr-DMTDC can still retain excellent separation performance, which underscores its potential for industrial applications.