Ultraselective carbon molecular sieve membrane for hydrogen purification

Hydrogen is a green clean fuel and chemical feedstock. Its separation and purification from hydrogencontaining mixtures is the key step in the production of hydrogen with high purity(>99.99%). In this work, carbon molecular sieve(CMS) membranes with ultrahigh permselectivity for hydrogen purification were fabricated by high-temperature(700–900 ℃) pyrolysis of polymeric precursor of phenolphthaleinbased cardo poly(arylene ether ketone)(PEK-C). The evolution of the microstructural texture and ultramicroporous structure and gas separation performance of the CMS membrane were characterized via TG-MS, FT-IR, XRD, TEM, CO2 sorption analysis and gas permeation measurements. CMS membranes prepared at 700 ℃ exhibited amorphous turbostratic carbon structures and high H2 permeability of 5260 Barrer with H2/CH4, H2/N2 and H2/CO selectivities of 311, 142, 75, respectively. When carbonized at900 ℃, the CMS membrane with ultrahigh H2/CH4 selectivity of 1859 was derived owing to the formation of the dense and ordered carbon structure. CMS membranes with ultrahigh permselectivity exhibit an attractive application prospect in hydrogen purification.

Preparation and characterization of novel carbon molecular sieve membrane/PSSF composite by pyrolysis method for toluene adsorption

Carbon molecular sieve membrane(CMSM)/paper-like stainless steel fibers(PSSF)has been manufactured by pyrolyzing poly(fiirfuryl alcohol)(PFA)coated on the metal fibers.PFA was synthesized using oxalic acid dihydrate as a catalyst and coated on microfibers by dip coating method.For the purpose of investigating the effects of final carbonization temperature,the composites were carbonized between 400℃ and 800℃ under flowing nitrogen.The morphology and microstructure were examined by X-ray diffraction,Fourier transforms infrared spectroscopy,scanning electron microscopy,thermogravimetric analysis,N2 adsorption and desorption,Raman spectra and X-ray photoelectron spectra.The consequences of characterization showed that the CMSM containing mesopores o f 3.9 nm were manufactured.The specific surface area of the CMSM/PSSF fabricated in different pyrolysis temperature varies from 26.5 to 169.1 m^2·g^-1 and pore volume varies from 0.06 to 0.23 cm^3·g^-1.When pyrolysis temperature exceeds 600℃,the specific surface,pore diameter and pore volume decreased as carbonization temperature increased.Besides,the degree of graphitization in carbon matrix increased with rising pyrolysis temperature.Toluene adsorption experiments on different structured fixed bed that was padded by CMSM/PSSF and granular activated carbon(GAC)were conducted.For the sake of comparison,adsorption test was also performed on fixed bed packed with GAC.The experimental results indicated that the rate constant κ′ was dramatically increased as the proportion of CMCM/PSSF composites increased on the basis of Yoon-Nelson model,which suggested that structured fixed bed padded with CMSM/PSSF composite offered higher adsorption rate and mass transfer efficiency.

Microstructure Manipulation of Covalent Organic Frameworks(COFs)-based Membrane for Efficient Separations

Covalent organic framework(COF) membranes have exhibited great potential to become the next-generation membranes for efficient separations due to the diverse structures, ordered framework pores, tunable functionality and excellent stability. This review presents the microstructure manipulation strategies for separation performance enhancement of COF membranes in recent years. Based on the three mechanisms of molecular sieving, surface diffusion, and facilitated transport, the structural modulation methods to enhance the selectivity of COF membranes are analyzed in detail. Next, strategies of realizing ultrashort mass transfer pathways and ultralow mass transfer resistance for the permeability enhancement are elaborated. Furthermore, the framework stability in COFs, interlayer stability between COF nanosheets and interfacial stability between COF layer and substrate are discussed. Finally, we discuss the existing challenges and perspectives on the future development of COF membranes, targeting at identifying the most promising strategies and directions for the engineering of COF membranes.