Oil Recovery From Water By Hydrophobic/Oleophilic Fibers

Oil contamination of water is increasingly serious.Hydrophobic/oleophilic materials can selectively absorb oil from oil/water（O/W）mixture efficiently,and its application on oil removal and oil recovery is promising.In this study,three kinds of coated kapok fibers were prepared by modifying raw kapok fibers with hydrophobic Nano-SiO₂ particles and PDMS.The micro structure and hydrophobicity/oleophilicity of raw and coated fibers were investigated.Continuous oil recovery from water surface and O/W mixture were successfully achieved with fiber modules（FMs）fabricated with hydrophobic/oleophilic raw fibers.Both of the materials utilization and the oil/water separation efficiency were improved in this manner.The mechanism of hydrophobic/oleophilic FMs for continuous oil recovery was analyzed in detail,and the physical models for oil recovery were constructed.The influences of FMs characteristics and operation conditions on the performance of oil recovery system were investigated.This study might has some help for the development of new oil/water separation or oil recovery technologies.Study of raw kapok modification revealed that the hydrophobicity/oleophilicity of materials relied on its surface energy and micro structure.Hydrophobic Nano-SiO₂ coated fiber showed the best hydrophobicity,but its coated structure was the most fragile one.The hydrophobicity and oleophilicity of PDMS-SiO₂ coated fiber were better than raw fiber.Hydrophobicity of PDMS coated fiber was similar with raw fiber.As the packing density of fiber assemblies increased,the capillary force increased;however,the oil sorption rate would not increase necessarily due to the permeability drop of fiber assemblies.The oil adsorption equilibrium time of PDMS-SiO₂ coated fiber assembly for n-Hexane and hydraulic oil were about 30 s and 2000 s,respectively.In the study of floating oil recovery,only oil could penetrate the FMs and then be recovered continuously when the driving pressure（（35）P）was lower than breakthrough pressure（Pbreakthrough）.As（35）P increased,air and water would successively start to penetrate the FMs.The oil flux was 3.0ml×s^-1 at（35）P of 4.0kPa,and the effect of（35）P on oil flux followed Darcy’s law.Higher Pbreakthrough could successfully hinder the penetration of water by reducing the FMs porosity;however,the oil flux would decline due to the permeability drop of FMs.Increase of the oil thickness could improve the oil flux.Viscous oil would damage the FMs pore structures and then weaken the oil recovery performance significantly.Materials with excellent hydrophobicity/oleophilicity,small pore size and high porosity could provide remarkable oil recovery efficiency.In the study of dispersed oil recovery,the oil content of collected liquid（w1）has reached up to 98.5% when（35）P was slightly lower than Pbreakthrough.The process of continuous oil recovery from O/W mixture by FMs could be separately described as the oil adsorption by FMs and the liquid transportation through FMs.The oil enrichment of collected liquid was attributed not only to the difference of the capillary forces acting on oil and water but also to the oil droplets coalescence at the FMs bottom.Strong turbulent motion of O/W mixture was bad for the oil adsorption process.High oil recovery rate（ORR）was realized by the thin FMs with large porosity at high（35）P while oil enrichment rate（OER）had an opposite result.It was impossible that ORR and OER could achieve the maximums simultaneously.The top ORR was 81.8% with a OER of 706%,and the top OER was 3139% with a ORR of 28.0%.w1 was larger than 95.0% when the initial oil content of O/W mixture（w0）was above 6.0%,and an oil flux of 109.4 kg×m^-2×h^-1 was obtained at w0 of 8.0%.