| Crude oil is an important kind of natural resources,which has improved the quality of human life greatly.It is estimated that the future demand of global energy may reach three times of 21st century.Unless there is a major change in global government politics,newly reported renewable energy sources or other alternative will not be able to affect the market share of fossil fuels in at least few decades.However,whether the occasional marine oil spill or the ship's regular sewage discharge caused a huge damage to the marine environment.Currently,traditional used materials and technologys to oil spill cleanup can be divided into four different types:1)chemical methods(dispersants,solifiders);2)burning;3)bioremediation and 4)mechanical methods(booms,skimmers,sorbents).Among them,sorbents can selectively absorb and recovery oil completely,so it is a good candidate to be used in oil spill cleanup.Sorbents with excellent performance should have following characteristic:hydrophobic and oleophilic,high sorption capacity and low cost.Last few decades,varies kinds of oil sorbents have been reported for oil-water separation,such as natural materials(plants,minerals,etc.),which are easy to get and have low cost.But they absorb oil and water simultaneously,then reduce the utilization rate of sorbents;then,membranes with selective wetting behavior were reported,which have high oil-water separation efficiency and separation speed.However,this separation process should collect oil-water mixture first,then pulled the mixture liquid into a container and separation,this separation process is labor and time consuming.While,oil sorbents can absorb and recover the oil floating on water surface completely,easy to operate and no secondary pollution to water.So it is efficient to cleanup oil spill by sorbents.While,these sorbents have a big shortcoming that it is only efficient to low viscousity oil(<500 mPa·s)and inefficient to high viscousity oil(103-105 mPa·s),such as crude oil,asphalt.To cope with the decreasing light weight crude oil reserves,the future demand to heavy oil will gradually increase.Due to its high viscousity and nonfluidity of heavy oil,there may have extra problem in exploit and transportation.Forcunately,crude oil is temperature sensitivity and heat effect(such as photothermal,magnetocaloric and joule heat)have been widely studied and utilized.Therefore,such thermal production matterials can be combined with ordinary sorbents to get a new kind of heating-sorbents,which could change the Rheological properties of crude oil and speed up the oil sorption rate.This dissertation focuses on the fabrication and characterization of new kind of sorbent which could recover the spilled oil on water surface quickly.To solve the low recovery rate of traditional 3D porous sorbents for high viscosity oil at room temperature,we fabricated self-heating sorbents,which could heat the heavy crude oil up and reduced its viscosity,then achieved a high oil recovery rate at room temperature.Combined with pump,this sorbent could realize continuous recovery with infinite oil sorption capacity.The main finding are summarized as follows:1.Fabricated a graphene wrapped sponge,endow hydrophobicity/oleophilicity and conductivity to melamine sponge.Once applied electricity power,this graphene wrapped sponge was heated up rapidly and made around oil warm,and the viscosity of crude-oil was decreased dramatically,so it could be absorbed into sorbent channels easily.By utilization the capillary pressure change at nozzle caused by pump,heated crude-oil could penetrated into channels and be transported to oil reservoir continuously.To obtained this graphene wrapped sponge,firstly,we fabricated graphene oxide(GO)nanosheets with 10-103 ?m width by modified hummer's method,and adjust its concentration to 3 mg/ml.Thanks to the abundant hydroxyl and carboxyl groups at GO surface,it could wrapped on the skeleton of sponge tightly through dip-coating.Then,GO was reduced to reduced graphene oxide(RGO)by HI in few seconds and dried at oven.Because this oil recovery method used electricity power,with the help of finite element method,combined with experimental test,we obtained an optimized coating structure:as for 5 mm thick oil layer and a 20 mm height sorbent,the structure of half RGO wrapped is the best.Besides,thinking of the practical application,scale up preparation is also important.Cause graphene and melamine sponge have realized commercial production,and the fabrication process was easy to operation,so it was simple to get a graphene wrapped sponge with its size of 30×10×5 cm3.2.In the first work,though melamine sponge flame retardant,the heat resistance of sponge is limited,so as the oil heating speed.If the heat resistance of substrate could be improved,the oil heating speed and sorption speed could be enhanced subsequently.In addition,the preparation process of graphene wrapped sponge produced strong acid wastewater,so finding an environment friendly preparation process is alsoconsiderable.In this work,we obtained a carbonized melamine sponge(CMS)by one step pyrolysis.This method produced no wastewater and the exhaust gas(ammonia)could dissolve in water.According to TGA curves,this CMS could endure high temperature of 500?,and kept stable in air above 250? for a long time.Besides,CMS is flame retardant,it showed no obvious change when put in alcohol lamp flame for 2 min.Compared with graphene wrapped sponge,CMS had a rapid oil heating rate and 14%improvement of oil sorption coeffi cient.And one joule-heated carbonized melamine sponge could continuously recover viscous oil spill 690 times its own weight in one hour from the water surface without pre-heating. |
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