Effect of membrane-casting parameters on the microstructure and gas permeation of carbon membranes

Abstract

In this work, membrane-casting parameters including solvents and drying methods were investigated to adjust the microstructure and gas permeation of poly(phthalazinone ether sulfone ketone) (PPESK) based carbon membranes. The structure and properties of the membrane samples were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, transmittance electron microscopy, single gas and mixed gas permeation. Results have shown that the membrane-casting parameters greatly influence the physico-chemical properties of the polymeric membranes, so as to affect the structure and gas permeation of their derived carbon membranes. Under the same drying conditions, the selection of a solvent with a high boiling point is beneficial to the thermal degradation of the polymeric membrane during pyrolysis. In addition, the adoption of a solvent with a close solubility parameter to PPESK is favorable to improving the permeability of carbon membranes. Compared to common warm air drying, cold drying is more favorable for the improvement of the thermal stability of the precursor membranes. With variation of the pyrolysis temperature from 650 °C to 850 °C, the best selectivities of carbon membranes are obtained at 850 °C for refrigerate-drying and at 750 °C for freeze-drying, respectively. All the gas separation data of the present carbon membranes made by cold drying surpass the Robeson's upper bound.