Synthesis of azo-linked porous polymers as fillers to enhance the performance of mixed-matrix membranes for the separation of bioethanol fermentation tail gas

Bioethanol has received widespread attention as an alternative to conventional fossil fuels. However, bioethanol fermentation produces tail gas containing an ethanol/CO₂ gas mixture, which must be efficiently separated to recover ethanol and reduce the greenhouse effect. In this study, we propose using vapor permeation membrane technology to separate ethanol from CO₂. Four azo-linked polymers (ALPs) were successfully synthesized and characterized, which were mixed with polydimethylsiloxane (PDMS) to fabricate mixed-matrix membranes (MMMs). The performances of different ALP/PDMS MMMs were characterized and compared in the separation of 0.2 wt% ethanol/CO₂ modeling fermentation tail gas. ALP-1(synthesized by tetramethylbenzidine)/PDMS MMMs exhibited the highest selectivity and high ethanol permeability, and characterizations such as Raman spectroscopy, differential scanning calorimetry, and X-ray diffraction were thus conducted for ALP-1/PDMS MMMs with different ALP contents. Results showed that ALP-1/PDMS MMMs with 1 wt% ALP-1 content possessed selectivity and permeability of 15.8 and 30,074 Barrer, which are 98% and 40% higher than pure PDMS, respectively. The effects of operation parameters, such as feed concentration, temperature, permeate pressure, and stability, on the performance of ALP-1/PDMS MMMs were also studied. This study provides a new method for the efficient treatment of fermentation tail gas that has excellent industrial prospects.