Yingying Cheng,Yuanye Zhuang,Shiyang Bai,Meng Ge,Jihong Sun,Jingjing Sun,Xufeng Gong
The removal of CO2 from biogas is critically important for environmental protection and energy applications yet remains technically challenging in the chemical industry. In this work, novel composite adsorbents featuring ZIF-8 uniformly dispersed on randomly oriented clinoptilolite lamellae (LCP) were designed and fabricated through a straightforward composite method. The synthesis sequentially incorporated metal precursors into LCP via ion exchange and salt addition and then introduced organic ligands to generate ZIF-8. Comprehensive characterizations, including XRD, FT-IR, N2 adsorption–desorption isotherms, SEM, and TG analyses, confirmed the physicochemical properties and structural features of the composites. The synthesized Zn-LCP/ZIF-8 materials exhibited exceptional CO2/CH4 separation performance, demonstrating ultralow CH4 adsorption capacity (<0.1 mmol/g) coupled with superior CO2/CH4 selectivity (≈28). Complementary molecular simulations using Material Studio software provided mechanistic insights into the adsorption and separation behavior, which further confirmed the superiority of the composite structure in CO2/CH4 separation. These results establish an effective strategy for biogas purification, while offering new perspectives for enhancing the CO2/CH4 adsorption selectivity.
Membrane separation, a green and efficient gas purification method, has been underexplored for removing volatile methyl siloxanes (VMS) from biogas. This study investigates the feasibility of removing VMS from biogas through polydimethylsiloxane (PDMS) membranes. Permeation tests revealed that PDMS membranes exhibit exceptional permeability to D4 (octamethylcyclotetrasiloxane, a representative VMS compound), with a permeance of 1492.37 GPU, significantly higher than for CH 4 and CO 2 . The selectivity values for D4/CH 4 and CO 2 /CH 4 were 75.26 and 9.80, respectively, demonstrating the membrane’s dual potential for D4 removal and CH 4 recovery. The permeation mechanism of D4 in PDMS was elucidated using density functional theory (DFT) calculations and molecular dynamics (MD) simulations. The results revealed that D4 permeation in PDMS is driven by favorable solubility compatibility, with dissolution being the rate-limiting step. Furthermore, the 40-hour continuous permeation test demonstrated the long-term stability of the PDMS membrane. Process simulation using PRO II software evaluated the engineering application of PDMS membranes for biogas purification, identifying a trade-off between maximizing D4 removal and minimizing CH 4 loss. To address this challenge, an optimized strategy was proposed through PDMS layer thickening. By increasing the thickness of the PDMS layer from 3.32 μm to 15.27 μm, the selectivity of the PDMS membrane for D4/CH 4 was enhanced. PRO II simulation results demonstrated that the thickened membrane could reduce the D4 concentration in simulated biogas from 50 mg/m 3 to 0.79 mg/m 3 , with a CH 4 loss rate of only 3.39 %, meeting the requirements for engineering applications. This study provides a novel and sustainable approach for removing siloxane from biogas, highlighting its potential for practical applications and future research.
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