| The membrane contactor absorption is considered as an effective way to capture the carbon dioxide generated from industry production.This technology is a coupling of the traditional absorption technology and the membrane separation technology.However,the existence of the membrane introduces a new resistance-membrane resistance,and the membrane is easy to be infiltrated by absorbent during the use of membrane contactor,therefore,it further increases the membrane mass transfer resistance,resulting in a greatly reduce of mass transfer rate and a serious decline of membrane absorption efficiency.This work probed into the evolution processes of membrane wetting caused by CO2 absorbent.It adopts the direct weighing method,and the weight of membrane was recorded through a data collection program in real time.Consequently,the curve of increased membrane weight per unit area or membrane wetting percentage with time was obtained.The experimental or characterization results indicate:1.During the bilateral wetting between the membrane and the absorbent,the percentage of membrane wetting of all the experiments shown a trend of slow growth after rapid growth,and it's less than 50%within the 24h;During the bilateral wetting between the membrane and the absorbent,the increased membrane weight per unit area of all the experiments shown the tendency to rise after the first decline,and that the duration of the descent stage is about 20-120min.2.X-ray photoelectron spectroscopy analysis(XPS),Fourier transform infrared spectroscopy(FT-IR),Thermogravimetric analysis(TG),SEM,determination of the membrane pore size distribution and contact angle measurement methods analyzed the wetted membrane samples.Characterization results mean that the solute molecule diffuse into the membrane phase,causing the membrane to be swelling,and it results in an increase of the average pore size and a decline of the porosity.Besides,the adsorption of the solute molecule on the membrane causes a significant reduction in the hydrophobic properties of the membrane.3.Energy dispersive X-ray spectroscopy(EDX)analysis shows that the adsorption quantity of the target element within the membrane pores decreased from the contact side to the other side.In addition,the adsorption quantity and adsorption distance of the target element increased gradually as the increase of contact time between the membrane and the absorbent.In combined with the experimental results of unilateral and bilateral wetting,it further deduced the evolution processes of membrane wetting in absorbent solution;the results were described as:(i)the gas-liquid interface at the inlet of membrane pores changed from the convex to concave liquid level,meaning the transition of hydrophobic membrane from non-wetting to wetting;(ii)the membrane pore wall gradually became hydrophilic with the diffusion of solute molecules in front of the moving meniscus,and liquid went forward driven by the concentration gradient within the membrane pores.In addition,this work also investigated the influence of different factors on membrane wetting.Three kinds of membrane material(polyvinylidene;polypropylene and polytetrefluoroethylene)and three organic absorbents(diethanolamine;propylene carbonate and potassium glycine)were adopted.The experimental results shown that the higher of solution temperature or the greater of pressure difference both sides of the membrane,the rate of membrane wetting is faster.The influence of absorbent types on membrane wetting is closely related to the surface tension of the absorbent.For a given membrane material and absorbent solution,surface tension and viscosity properties of the solutions are the key factors to affect membrane wetting under the different concentration.Besides,factors such as pore size and porosity also affect the rate of membrane wetting. |
PDF Full Text Request