An investigation on structural and gas transport properties of modified cross-linked PEG-PU membranes for CO2 separation

A thermodynamic study on relationship between gas separation properties and microstructure of polyurethane membranes

The lattice fluid (LF) thermodynamic model and extended Vrentas' free-volume (E-VSD) theory were coupled to study the gas separation properties of the linear thermoplastic polyurethane (TPU) membranes with different chemical structures by analyzing their microstructures. A set of characteristic parameters were extracted using the repeating unit of the TPU samples and led to prediction of reliable polymer densities (AARD < 6%) and gas solubilities. The viscoelastic parameters, which were obtained from the DMTA analysis, were also estimated the gas diffusion vs. temperature, precisely. The degree of microphase mixing based on the DSC analysis was in order: TPU-1 (4.84 wt%) < TPU-2 (14.16 wt%) < TPU-3 (19.92 wt%). It was found that the TPU-1 membrane had the highest degree of crystallinity, but showed higher gas solubilities and permeabilities because this membrane has the least degree of microphase mixing. These values, in combination with the gas permeation results, showed that the content of the hard segment along with the degree of microphase mixing and other microstructural parameters like crystallinity were the determinative parameters.

Improved CO2/N2 separation performance of Pebax-1074 blend membranes containing poly(ethylene glycol)

Developing blend membrane material is one feasible and effective route for improving the gas separation efficiency and commercial attractiveness of membrane technologies. Here, free-standing membranes were prepared by casting method using Pebax-1074 as continuous polymer matrix and poly(ethylene glycol) (PEG) as dispersive organic fillers. The morphology, surface functional groups, microstructure and thermal stability of the membranes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry, respectively. The effects of preparation variables including average molecular weight and dosage of PEG on the microstructure, morphology and properties of the blend membranes were investigated. In addition, the effects of operation conditions including permeation temperature and permeation pressure on the gas separation performance of the blend membranes were also examined. The results showed that the addition of PEG can obviously modify the structure-properties and significantly improve the separation performance of resultant membranes. Under the conditions of 30°C and 0.25 MPa, the optimal CO2 permeability and CO2/N2 selectivity respectively reached to 124.3Barrer and 115.8 for the blend membranes made by PEG600 with a content of 20% in Pebax-1074 matrix. In brief, the as-prepared blend membranes are proved to be promising for CO2/N2 separation application.