6FDA-polyimide thin-film composite hollow fiber membranes for hydrofluorocarbons and CO2 separations
Sergio V. Gutiérrez-Hernández, Sandra Rico‐Martínez, Fernando Pardo, Cristina Álvarez, Jesús A. Miguel, Gabriel Zarca, Ane Urtiaga
Abstract
Herein, high molecular weight fluorinated aromatic polyimides were assessed for the first time to recover difluoromethane (R-32) from its blends with other hydrofluorocarbons and hydrofluoroolefins (R-134a: 1,1,1,2-tetrafluoroethane, R-125: pentafluoroethane, and R-1234yf: 2,3,3,3-tetrafluoropropene). First, a screening was performed with thick flat membranes made of the 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and three different amines: 2,2′-bis(4-aminophenyl)hexafluoropropane (6FpDA), 2,4,6-trimethyl-m-phenylenediamine (TMPD), and 2,3,5,6-tetramethyl-1,3-phenyldiamine (durene). As a result, 6FDA-TMPD was selected for the fabrication of defect-free hollow fiber-thin film composite membranes (HF-TFCM) due to its superior performance for the separation of R-32. These HF-TFCMs showed excellent separation performance to reclaim high-purity R-32 (permeate concentration >99 vol%) from the commercial binary blends R-410A and R-454B (a mixture of R-32 and R-1234yf). In addition, we report for the first time the membrane recovery of R-32 from the ternary blend R-407C (R-32/R-134a/R-125 38.2:43.8:18 vol%). Eventually, the separation of CO2 from synthetic gas mixtures of CO2/CH4 (50:50 vol%) and CO2/N2 (15:85 vol%) was performed for benchmarking, showing that the prepared HF-TFCM kept the separation performance of the 6FDA-TMPD thick membranes.