Study On The Membrane Wetting In The Process Of Co₂ Absorption By PVDF Membrane Contactor

Using membrane contactors to absorb C02 by membrane absorption technology has a good industrial application prospect.The technology absorbs has the advantages of high separation selectivity,compact equipment,easy modularization,and easy amplification.However,the membrane in the membrane contactor is easily wetted,so that the membrane resistance gradually increases and becomes the main resistance to the mass transfer process,which greatly limits the practical application of the membrane absorption technology in the industry.In this paper,diethanolamine aqueous solution was used as absorbent,and CO2 was absorbed in a polyvinylidene fluoride(PVDF)hollow fiber membrane contactor.An effective method for retarding membrane wetting during membrane absorption was studied.The research work mainly includes two aspects:on the one hand,the forced wetting in the process,and the improvement of the inhibitory effect of gas phase(shell side)pressure on membrane wetting;on the other hand,based on the spontaneous wetting,improve the properties of the absorbent to inhibit membrane wetting.The main research contents and conclusions of this thesis are as follows:(1)Through the membrane absorption experiment,it is found that the degree of membrane wetting comes from two contributions,one is spontaneous wetting,and the other is forced wetting.In the absorption experiment,if the transmembrane pressure difference is greater than the penetrating pressure,the forced wetting will occur at the beginning of the experiment;if the transmembrane pressure difference is less than the penetrating pressure,spontaneous wetting will occur first,which will change the membrane.The hydrophobicity of the surface causes the penetration pressure to drop sharply,and the forced wetting thus begins.(2)Based on the mechanism of membrane wetting,this paper proposes to increase the gas phase pressure to inhibit the membrane wetting process.Experimental studies have found that as the pressure value of the intermittent pressure in the gas phase increases,the percentage of membrane wetting gradually decreases,and the intermittent pressurization of the gas phase has an optimum pressurization time and a reasonable pressurization procedure to maximize the retardation effect of the wetting process.Keeping the gas phase pressure in a high pressure state does not effectively delay the membrane wetting.On the one hand,the intermittent pressurization of the gas phase destroys the quasi-steady state of spontaneous wetting,and on the other hand,it can blow out part of the wetting liquid,so that the membrane wetting can be well delayed.(3)Based on the understanding of the mechanism of spontaneous wetting of membranes,this paper inhibits the spontaneous wetting process of membranes by adding different kinds of inorganic salt components to the absorbent.Experimental studies have found that by adding inorganic salts to the absorbent,not only can increase the surface tension of the absorbent but also the adsorption of DEA molecules on the surface of the membrane can be disturbed,thereby reducing the spontaneous wetting.At the same time,using the above two techniques of inhibiting membrane wetting,under the optimal operating conditions,the membrane phase mass transfer resistance is significantly reduced,the membrane wetting percentage is decreased by 41.6%,and the absorption efficiency can be increased by more than 48.3%.