Study On Preparation And Performance Of Pebax/PES Thin-film Compostie Membrane For Air Dehumidification

Water vapor widely exists in air,flue and natural gas.Nevertheless,excessive humidity can cause many hazards to production and living activities.Therefore,it is essential to adopt appropriate technical methods for water vapor removal.Membrane dehumidification is a method using membranes,which preferentially permeate water vapor molecules while blocking the permeation of other gas molecules to achieve efficient and rapid water vapor removal.It gradually replaces conventional dehumidification methods such as condensation and adsorbent adsorption due to its low energy consumption,low noise level and ease of maintenance.As the key to membrane dehumidification,the preparation and modification of separation membranes are considerably crucial.An ideal dehumidification membrane is expected to have excellent permeability,high selectivity,good mechanical strength and pressure resistance.Therefore,thinfilm composite(TFC)membranes with ultra-thin selective layer and porous support layer have attracted more and more attention in membrane dehumidification.In this paper,a TFC membrane consisting of polyethersulfone(PES)substrate and polyether co-polyamide(Pebax)selective layer is fabricated,while the permeation and separation performance of the TFC membrane is optimized.The details are as follows:Based on the principle of phase separation,the mixture of N,N-dimethylacetamide and octane with the characteristics of mutual solubility at high temperature and phase separation at a certain temperature were selected as the solvents for the fabrication of porous PES membranes with good permeability.The structural properties of PES membranes were thermodynamically and kinetically regulated by changing PES solution concentration,pre-evaporation time and relative humidity.The Pebax/PES composite membrane was successfully prepared by surface coating,and the influence of the structure and pore size of the base membrane on the water vapor permeation separation performance of the prepared composite membrane was investigated.The permeability and selectivity of the composite membranes were optimized from the perspective of the preparation process of support layer.The effect of Pebax solution composition on the permeation and selectivity of the TFC membrane was investigated.The optimal membrane performance was achieved when the concentration of Pebax solution was 2wt%.The Pebax selective layer was then modified by blending polyethylene glycol(PEG200)and mesoporous silica(MSN),respectively to fabricate a TFC membrane with high permeability and high selectivity and overcome the "trade-off" effect of polymeric membranes.PEG with a large number of polar ether-oxygen groups has excellent affinity for water vapor and increases the free volume in the membrane,which improves the diffusion rate of water molecules in the membrane.Pebax-PEG200/PES TFC membrane achieves a water vapor permeance up to 2777 GPU and a selectivity of 1177 at 50wt% PEG200 addition.MSN improves the hydrophilicity of the membrane surface and its unique pore structure provides a fast passage for water vapor.The water vapor permeance of Pebax-MSN/PES TFC membrane is up to 2888 GPU,which is 46% higher than that of the unmodified TFC membrane,while the selectivity is 1360 at 6wt% MSN addition.It is able to reduce the relative humidity of air from 100% to 43.8%,which shows an excellent dehumidification performance and a potential application especially in extremely humid environments.