Study On Application Of The Superhydrophobic Coating And Its Mechanicsm For Enhancing Foam Drainage

There are two essential processes in foam fractionation: interfacial adsorption and foam drainage and a lot of literature have reported their mechanisms and strategies for their enhancement.Foam drainage has a significant effect on the concentration characteristics of foam fractionation compared with interfacial adsorption.Lu et al.designed a cross internal which was structurally simple and significantly increased the wall contact area with the foam.Their result indicated that the more exterior channels were created,the faster foam drainage rate should get.However,the drainage efficiency of the cross internal dramatically decreased with increasing the concentration of the target material in the bulk liquid phase.In order to overcome this defect,the surface of the cross internal was covered by a superhydrophobic coating(SHC)in this work.In this work,the mechanism of SHC in the enhancement of foam drainage was investigated.And then a novel foam fractionation with the cross internal coating SHC was designed and was assessed for recovering whey soy proteins(WSP)from its waste water and recovering alfalfa leaf protein(ALP)from the leaching solution of Medicago sativa L.The theoretical analysis showed that the cross internal with SHC not only increased the wall contact area in the foam phase significantly and then provide more exterior channels,but also facilitated the flow rate of interstitial fluid between foam phases.Thus,the cross internal with SHC could decreased the liquid holdup of the foam out of the column effectively and then increased the target material concentration in the foamate.The experimental results indicated that SHC could strengthen foam drainage significantly through decreasing the flow resistance of the interstitial liquid in the exterior channels at room temperature.The suitable length of the cross internal with SHC was 600 mm and the drainage velocity was dramatically accelerated when it was installed at 50 mm from the top of the column.Under the suitable operation conditions,enrichment ratio and recovery percentage of WSP reached 10.5 and 82.3%,respectively.In order to simultaneously obtain a high recovery percentage of ALP,a two-stage foam fractionation technology was developed.Inside,the physiochemical properties of the recovered ALP were characterized for estimating the effects of interfacial adsorption on the structural stability of ALP.ALP were first concentrated using the novel foam fractionation with a cross internal component,which was covered with SHC,under the suitable operating conditions of pH 6.0,temperature 25°C,volumetric air flow rate 75 mL/min,loading liquid volume 450 mL and the pore diameter of the gas distributor of 0.180 mm,respectively.The residual solution would be used as the feeding solution for further recycling ALP at second stage foam fractionation under condition volumetric air flow rate of 150 mL/min,which was only investigated.The two-stage batch foam fractionation for recovering ALP from its leaching solution had a high enrichment ratio of 4.33 and the total recovery percentage could reach as high as 89.0%.Meanwhile,the result shows that the effect of foam fractionation on the physiochemical properties of ALP was insignificant.In short,it was effective for the cross internal covered with SHC to enhance the foam drainage and improve the separation characteristics of foam fractionation.This work provides a new light for strengthening foam drainage at room temperature and facilitates the industrialization of foam fractionation.