Preparation And Gas Permeability Of PEBA/Surfactant Gel Membranes By Solvent Evaporation Method

The threat to human life of greenhouse effect has received extensive attention on a globlescale with the development of modern industry. The efficient separation of greenhouse gasCO2from the air is an important research subject at present. Membrane separation technologyhas attracted people’s attention for its advantages of simple equipment, easy to operate andenergy-efficient in the field of gas separation. At present, to find a gas separation membranethat can meet the requirements of industrialization is still the focus of further research.Gel membrane is a new type of membrane material, which is composed of polymermolecules with liquid functional carrier to form a spatial network structure by crystallizationor hydrogen bond and other effects. It possesses a good permeability and selectivity since theliquid functional carrier has a high CO2adsorption and permeability. People found that thePolyoxyethylene surfactant (such as Tween, TX, etc.) with low price has a strong ability todissolve CO2and also has advantages of low volatility and good thermal stability. Thepolyoxyethylene surfactant is a kind of attractive functional carrier to build gel membranes.In this paper, polyether block amide (PEBA) was selected as the polymer to prepare aseries of gel membranes by solvent evaporation method, and they were used for the separationof CO2and N2. The following conclusions are obtained:(1) In order ro research the impact of different ration of hard and soft segments in PEBAon the compatibility, thermal performance, mechanical properties and gas permeation,PEBA2533-Tween20, PEBA3533-Tween20and PEBA4033-Tween20gel membranes wereprepared. The results showed that PEBA4033had the best compatibility with Tween20inthree types of PEBA. The crystalline phase increased with the increasing PA content in PEBA,and then decreased after adding Tween20. The tensile strength, Young’s modulus andmaximum deformation of PEBAxx33-Tween20gel membranes were reduced due to theplasticizing effect of Tween20on the polymer. The diffusion, solubility and permeability ofCO2and N2enhanced with the increase of amorphous poly(tetramethylene ether)(PTMO) inPEBA, exhibiting the excellent permeability of CO2in PEBA2533and the high CO2/N2selectivity in PEBA4033. The use of Tween20strongly increased the CO2diffusivity andsolubility in all polymers, inducing the skyrocketing permeability of CO2. The permeability ofN2was almost constant, because the diffusion increased and solubility decreased. Therefore,CO2/N2selectivity greatly improved.(2) In order ro research the impact of different hydrophilic and hydrophobic chains of thenon-surfactant (Tween) on the compatibility, density, thermal performance, mechanicalproperties and gas permeation, a series of Tween for the reaearch object were and PEBA2533-Tween20, PEBA2533-Tween21and PEBA2533-Tween80gel membranes were prepared. Theresults showed that PEBA2533had the best compatible with Tween21compared to Tween20and Tween80. The crystallization of PA segment disappeared when Tween was added in thepolymer substrate, and the activity of polymer chains enhanced. The tensile strength andYoung’s modulus of PEBA2533-Tween gel membranes were reduced due to the plasticizingeffect of Tween20on the polymer, but they still have excellent mechanical properties as gas separation membranes. With the content of Tween increased, gas diffusion coefficientselevated in different magnitude. The permeability of CO2increased and N2almost unchanged,causing αCO2/N2greatly improved. In addition, comparing three kinds of PEBA2533-Tweengel membranes, PEBA2533-Tween80had the better diffusion, solubility, permeability andαCO2/N2than PEBA2533-Tween20and PEBA2533-Tween21membranes.(3) Based on the above research, PEBA2533-TX100gel membranes were prepared inthis chapter and we researched the impact of different TX100content on the compatibility,density, thermal performance, mechanical properties and gas permeation. The results showedthat PEBA2533had a brilliant compatibility with TX100. The crystallization of PA segmentcompletely disappeared when Tween was added in the polymer substrate, and the amorphousphase increased. The tensile strength, Young’s modulus and maximum deformation ofPEBA2533-TX100gel membranes were reduced due to the plasticizing effect of TX100onthe polymer. With the increase of TX100content, the permeability codfficient of CO2andCO2/N2selectivity were simultaneously improved. When the mass fraction of TX100is65%,the separation performance surpassed the Robeson upper bound in2008. However,PEBA2533-TX100(65) gel membrane also had the problems of lower adding quantity andpoorer mechanical strength due to the plasticizing effect of TX100on the polymer. Thus, themechanical properties of gel membranes were improved by adding multi-walled carbonnanotubes (MWCNTs), and PEBA2533-TX100(65)-CNTs hybrid gel membranes wereprepared. It could be seen the MWCNTs was uniformly dispersed in the film by SEM analysis,and it had better tensile strength and Young’s modulus than PEBA2533-TX100(65) gelmembranes. However, the permeability of two gases and CO2/N2selectivity deceased. Futherimproved the permeability and separation properties, PEBA2533-TX100(80)-CNTs hybridgel membranes (the TX100content is80%) were prepared. We discovered it had the excellentfilm-forming and higher PCO2and αCO2/N2than PEBA2533-TX100(65).