Design,Preparation And Structure Modification Of Gas Separation Membrane Derived From Poly(arylene Ether Ketone)

Membrane based gas separation technology,as a novel separation technology,is considered as the third generation technology with the most promising application prospect after "cryogenic separation" and "pressure swing adsorption separation" owing to its advantages of high efficiency,low energy consumption,less plant footprint,easy operation,environmental friendliness and easy integration with other technologies.Membrane is the core of the membrane base separation technology,and the current commercially available membrane are dominated by polymeric membranes.However,with the increasingly widespread application of the membrane based technology,the requirement from market for the membrane materials with high performance is growing.And the traditional polymeric membranes gradually fail to meet the market demand due to the common problems faced,such as low gas permeability,poor thermal and chemical stability,and easy plasticization under high feed pressure.Therefore,great efforts should be devoted to developing the novel membrane materials with high performance,which is of great importance for the development and large-scale application of the membrane based technology.In this work,the novel and commercially available poly（arylene ether ketone）（PEK-C）was selected as membrane material,and the thermal crosslinking membrane with high anti-plasticization property was prepared via low-temperature thermal treatment of the PEK-C polymeric membrane to induce interchain crosslinking;a method of the sulfonation/desulfonation was proposed to further enhance the gas permeability of the thermal crosslinking membranes;the carbon molecular sieve（CMS）membranes for gas separation with high permeability and ultrahigh selectivity were prepared via high-temperature carbonization of the polymeric membrane and controlling the aggregation state structure of the polymer and the ultra-microporous channel structure of the carbon matrix,respectively.The mechanism of thermal crosslinking reaction and the sulfonation and desulfonation,and the evolution of the polymer aggregation structure and the ultra-microporous channel structure of the carbon matrix were investigated by modern instrumental analysis.The relationships between the evolution of microstructure and the properties of membranes were also revealed.The main conclusions are as follows:（1）The thermal crosslinking membranes with high anti-plasticization properties were prepared from the PEK-C polymeric membrane via low-temperature thermal treatment.The cardo moieties suspended on the molecular chains decomposed and induced interchain crosslinking with the formation of the rigid and bulky biphenyl linkages during the thermal treatment（400～475℃）.This crosslinked structure reduced the packing density of polymeric chains,enlarged the interchain distance and formed a large number of free volume cavities,which enhanced significantly the gas permeability of membranes.Compared with the PEK-C polymeric membrane,the CO₂ permeability of the thermal crosslinking membrane was up to 392 barrer that was about 112 times higher,and the CO₂/CH₄ ideal selectivity was 30,which surpassed the 2008 Robeson upper bound.The CO₂ plasticization pressure of membrane was increased from 0.2 MPa to 3 MPa owing to the formation of the rigid biphenyl crosslinked structure that would effectively reduce the mobility of molecular chains.（2）A method of the sulfonation/desulfonation was proposed and enhanced greatly the gas permeability of the thermal crosslinking membrane.The bulky and strong polar-SO3H groups were introduced into the PEK-C molecular chains through the sulfonation reaction,which disrupted chain packing efficiency and reduced the mobility of polymeric chains owing to the enhancement of the rigidity and interchain interaction,thus preventing the polymeric membrane from melting during the heat treatment.The-SO3H groups decomposed and formed many microvoids during thermal treatment,which further enlarged the interchain distance and cavity size of the thermal crosslinking membrane.The higher the sulfonation degree of the polymer was,the larger the gas permeability of the derived thermal crosslinking membrane was.Compared with the thermal crosslinking membrane without treatment,the CO₂ permeability was up to 2.3 times without significantly sacrificing the CO₂/CH₄ selectivity,and the separation performance was positioned above the 2008 Robeson upper bound.（3）A method of constructing the ultra-microporous channel structure of CMS membrane via optimizing the pretreatment process to finely tuning the aggregation structure of precursor polymer was proposed,and the CMS membrane for gas separation with high CO₂ permeability was prepared.The relationship between the change of the aggregation structure and gas permeation property was revealed.It was found that when the polymer aggregation state was maintained in a state of high elasticity,the prepared CMS membrane had a larger interlayer distance,pore size and porosity,and exhibited the best gas permeability and selectivity.The CO₂ permeability of the CMS membrane obtained at the optimum condition was up to 8111 barrer with the CO₂/CH₄ and CO₂/N₂ selectivity of 43.8 and 40.8,respectively,which far exceeded the 2008 Robeson upper bound of polymeric membrane.The prepared CMS membrane exhibited a potential application prospect in CO₂ capture and separation.（4）CMS membranes with ultrahigh permselectivity for the H₂/CO,H₂/N₂ and H₂/CH₄ gas pairs were prepared via adjusting the carbonization temperature to control the ultra-microporous channel size of carbon matrix.The relationship between the carbonization temperature and the microstructure of CMS membrane was revealed.With an increase in carbonization temperature（700～900℃）,the average interlayer distance of the carbon crystallites of the prepared CMS membranes decreased,the packing density increased,and the ultra-micropore size decreased,resulting in a decrease in the gas permeability of CMS membrane and a substantial increase in the selectivity.The selectivities of the CMS membranes carbonized at 900℃ for the H₂/CO,H₂/N₂ and H₂/CH₄ gas pairs were 111,237 and 1859,respectively,with the H₂ permeability of 2919 barrer.The gas permeation in the ultra-microporous channels of CMS membrane was dominated by the diffusion selectivity.The obtained CMS membranes with ultrahigh permselectivity exhibited an attractive application prospect in hydrogen purification and recovery.