Study Of Spontaneous Wetting Of Alkanolamine Solution Into Hydrophobic Porous Membrane And Its Prevention

Membrane contactor is a strong candidate for C02 capture.However,in this processes,the liquid absorbent(such as ethanolamine,MEA;diethanolamine,DEA)could wet the hydrophobic membrane,resulting in a sharp decrease of mass transfer coefficient.Membrane wetting is generally divided into two cases:one is forced wetting;the other is spontaneous wetting.Forced wetting is caused by the pressure difference of gas-liquid phase,while the causes of spontaneous wetting are not yet clear.Based on the mechanism of spontaneouse wetting of surfactants into hydrophobic porous substrates,an adsorption-wetting mechanism for membrane wetting was proposed.On this basis,the total flow equation of spontaneous wetting was proposed by using the creeping flow analysis.The overall wetting process of the membrane was simulated by using the extended Starov's equations.Finally,a method for preventing spontaneous wetting was proposed.The main research contents and conclusions of this paper are as follows:1.Fitting method of the van der Waals surface tension according to van Oss,molecular simulation by HyperChem75,Fitting method of critical property,Hamaker calculation and some other methods were used to calculate the interfacial interference energy of DEA molecules on PVDF and PET membrane,and the spontaneous wetting mechanism of alkanolamine absorbent was proposed:The main cause of spontaneous wetting is due to the adsorption of the alkanolamine solution on the S-L interface of the PVDF/PET membrane.2.Based on the adsorption-wetting mechanism,the total flow equation is deduced by the creeping flow equations.This equation is very effective to predict the spontaneous membrane wetting of high-concentration and low-temperature liquids in the case of partial wetting.3.Based on the adsorption-wetting mechanism,the extended Starov's equations and the image processing method of Matlab are used to calculate the average contact angle of membrane pores.It is found that the advancing contact angles of spontaneous wetting are very close to 90°.Matlab algorithm simulation was used to quantitatively predict the wetting ratio of the whole wetting process with time.Compared with the mass transfer experiment of membrane contactors,it was estimated that spontaneous wetting contributes to membrane-phase wetting by about 20%.4.A method for preventing spontaneous wetting by adding salts or alkalis in alkanolamine absorbent was proposed.The best choice is that the added anions and cations can both increase the interfacial tension of the liquid-vapor(L-V)and solid-liquid(S-L)interface,such as adding NaCl,KCl,NaHCO3.