| Global climate change caused by carbon dioxide emission is accelerating at a faster rate.The capture and separation of CO2 is of strategic significance on reducing global warming.CO2 separation technology is one of the important processes in many industrial areas such as natural gas processing,biogas purification,enhanced oil recovery and flue gas treatment.While the use of biogas isconsidered as one of the most efficient wayto utilize therenewable energy and reduce greenhouse gas emission.The removal of CO2 frombiogas cannot only effectively increase the heat value,but also reduce the corrosion caused by acid gas and therefore extend the biogas application field.So far,the universally accepted traditional technologies such as the pressure swing adsorption,the amine absorption and membrane separation all need huge volume,serious energy consumption and high investment cost when employed in industrial scale production.Gas-liquid membrane contactor is a new type of separation and purification technology which combines membrane contactor with absorption liquid,to make membrane contactor have both large gas-liquid contact area and high selectivity with proper absorption liquid.Moreover,it also possesses the advantage of independence of two phases and flexible operation.Polyvinylidene fluoride(PVDF)with high gas permeability,hydrophobicity,acid and alkali resistance and strength was used as raw material,the hollow fiber membrane was prepared by wet and dry-wet spinning,and assembled into a membrane contactor for CO2 absorption experiment.Experiment studied the effect of operation condition on the CO2 absorption experiment,such as kinds of liquid absorbent,liquid velocity,CO2 content,gas pressure and packing density of membrane contactor.The feed gas of all the experiment was the mixture of CO2 and air and fed through the tube side of the membrane module,while the liquid absorbent was pumped into the shell side of the hollow fibers.The results showed that the CO2 removal efficiency,flux and overall mass transfer coefficient are increased with the increase of liquid velocity.Increasing CO2 removal performances for tested membrane contactor are observed in as the following order:0.1mol/L NaOH>0.1mol/L DEA>distilled water.In addition,the CO2 removal efficiency and overall mass transfer coefficient decreased while the CO2 flux increased with the increase of CO2 content.Besides,the gas pressure on the CO2 absorption property is positively correlated.Furthermore,the CO2 removal efficiency greatly improved while the overall mass transfer coefficient and CO2 absorption flux reduced with the increase of the packing density of membrane module.The influences of the concentration of LiCl,air gap and bore fluid composition to the morphology and performance were also studied.The PVDF membrane fabricated with addition of NMP as bore fluid induce delay phase-inversion and present an inner skinless surface with open microporous structure,removing the inner skin layer can improve the gas permeance and enhance CO2 flux.The thinner outer diameter and wall thickness of the spun fiber is made by the emergence of air gap,and defective goods also become more.The addition of 3 wt.%LiCl in the casting dope provide the membrane contactor with good CO2 separation performance,the best CO2 absorption flux can reach to 4.55×10-7kmol/(m2·s).Besides,the thesis conducted a preliminary exploration on the different additives and the modification of PVDF hollow fiber membrane.It was found that adding phosphoric acid(PA)in the casting solution made the N2 permeance reach 1.81×10-6mol/(m2·s-Pa)at 25?,100kPa,and the mean pore size of the hollow fiber is 32nm.At the same time,the CO2 removal efficiency and flux are attained 17.6%and 3.46x10"7kmol/(m2·s)respectively when used 0.1mol/L DEA as absorption liquid. |
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