Studies On Preparation Of Hydrotalcite-based Composite Membranes And Its Selective Permeability For Carbon Dioxide

Under the pressure from environmental pollution and energy shortage,CO2 membrane separation technology plays a crucial role in the recovery and utilization of CO2 and achieving socially sustainable development.Compared with other CO2 separate methods,membrane technology is one of the powerful solutions to global environmental problems due to its high energy efficiency,simple operation,and eco-friendliness.At present,there are many ways to prepare membranes,but some chanllenges still exist:1.Most polymer membranes or inorganic membranes exhibit a trade-off effect between permeability and selectivity.2.It is difficult to avoid the tiny defects in the membrane,which limits the improvement of membrane performance.3.It can not effectively utilize the differences of gas molecules in physical and chemical properties to achieve the efficient separation of gas from multiple channels.To solve these problems,layered double hydroxides(LDHs)were selected as the membrane building elements in this paper.Two kinds of LDH based composite membranes were obtained by vacuum filtration impregnation and spin coating,respectively.The specific research content is as follows:1.LDH-IL composite membranes were prepared by vacuum-assisted filtration.And the ionic liquid was introduced into the intercalation channels of LDH membranes by dip coating.The LDH-IL composite membranes had a high orientation and excellent CO2 selectivity.The hydrogen bond and electrostatic interaction improved the thermal stability and structural stability of the membrane,which enabled the membrane to run for a long time.The mechanism of membrane separation was explored.The orderly stacking of LDH nanoflakes blocked the transport of other gases to a certain extent.Compared with other gases,the interlaminar IL had a high solubility and diffusion of CO2,which made the membrane have high CO2 selectivity and permeability.The LDH80-IL,LDH100-IL and LDH150-IL membranes prepared in this work all break through the Robeson upper-bond and the LDH100-IL composite membrane has the best performance.The CO2 permeance is 105.61 GPU,the CO2/N2 and CO2/CH4 selectivity of the membrane still reach 128.82 and 221.75,respectively.The membrane has high-temperature resistance and long-term durability which is expected to be used in the actual purification of natural gas,flue gas separation,carbon dioxide capture,and concentration.2.(LDH/CMCS/PVAm)n composite membranes with compact structure were obtained by the way of rotating the coating membrane and compounding the exfoliated LDH nanoplates with carboxymethylcellulose(CMCS)and polyvinylamine(PVAm).(LDH/CMCS/PVAm)5,membrane with 0.45 m thickness shows CO2 permeance of 4226.94 GPU;and its CO2/N2,CO2/CH4 and CO2/H2 selectivities are 166.81,363.22 and 7.31,respectively.The selectivity of CO2/N2 and CO2/CH4 exceeded the Robeson upper bound.The gas separation performance is mainly based on the promotion transfer mechanism and the dissolution-diffusion mechanism.Besides,the salting-out effect of CMCS also plays an important role.The performance of the membrane in intake air humidity and mixture separation needs to be further explored.This work provides some theoretical guidance for the reasonable design and preparation of the CO2 separation membrane.