Preparation Of Carbon Dioxide Gsa Separation Membranes By A Molecule Self-assembly Method

CO2 is an important greenhouse gas responsible for global warming.In addition,CO2 in fuel gases like methane,natural gas can reduce their calorific value and cause the pipeline corrosion during transport.As a result,separation and recycling of CO2 are significantly important for the environment and energy.Among commercial CO2 separation technologies,membrane separation has received the most interest because this process is clean,simple,energy efficient,and low in cost.Although CO2 separation membranes can be prepared by many different methods,these membranes prepared by a green,simple,and efficient method have faced great challenges.In this work,a facilitated transport membrane with high CO2 permeance and CO2/N2 selectivity was prepared by an electrostatic self-assembly method using commercially available polyethylenimine(PEI)and reverse osmosis(RO)membranes as the assembled molecule and substrate,respectively.We investigated the effects of water molecules,self-assembly ways,different polyamide substrates,self-assembly layers,self-assembly time,varying the feed pressure and different self-assembly conditions on the structure and performance of the facilitated transport membranes to determine the applicable self-assembly rules and appropriate conditions for membrane preparation.The prepared membrane was also analyzed by scanning electron mocroscopy(SEM),fourier infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS)and contact angle measurements to analyze the structure,composition and property of membranes.(1)The prepared membranes achieved optimal permeance and selectivity at a PEI concentration of 50 mg/L,a pH value of 8.0,a way of dynamic self-assembly,a pump pressure of 0.6 MPa,an operating temperature of 25 °C and a self-assembly time of 1 h.The process of adsorption equilibrium between PEI molecules and membranes accomplished only needed a period of tens of seconds,and the monolayer self-assembly was better than that of multilayer self-assembly.(2)The increased free volume between polymer chains and facilitated transport by PEI(and H2O)are two important factors leading to the transport of CO2 through the membrane,while the transport of N2 was just the result of simple solution-diffusion.(3)The analysis results of SEM,XPS and contact angle measurements could prove that PEI molecules were self-assembled onto the membranes surface.But because the self-assembly layer was ultrathin and only a small number of PEI molecules were self-assembled,from cross section point of view and FT-IR measurement,we couldn't get some useful information.(4)The effective area of membranes prepared by electrostatic self-assembly was scaled up from 25 cm2 of membrane strips to 0.5 m2 and 1.3 m2 of spiral-wound membrane modules.The achieved self-assembly spiral-wound membrane modules also showed excellent gas separation performance.After the self-assembly membrane modules were dried and then immersed in deionized water,their separation performance could remain almost unchanged.This could illustrate that the performance of membranes was stable and wasn't to be damaged by the environment.The method of electrostatic self-assembly was easy to scale up and had use value.