Study On The Modified Preparation Of Chitosan-based Flocculant And Its Flocculation Performance Of Emulsified Oil Removal

Oily wastewater widely produced from oil processing and utilization industries,such as food,textile,leather,steel and oil industries,has been considered as a globally common pollutant.Due to its strong toxicity,hazardous component,organic volatility and highly carcinogenic,oily wastewater is undoubtedly regarded as a serious threat to aquatic ecosystem and human health if it is directly discharged into water bodies without any proper disposal.Flocculation is considered as an effective treatment for emulsified oil because of its high efficiency,easy operation,low cost and environmental friendliness.Flocculant is the critical factor in flocculation process,and chitosan was used in the paper,because of its excellent properties,including richness in natural resources,non-toxicity,biocompatibility,biodegradability.Therefore,in this study,cationic monomer and hydrophobic monomer were grafted onto the CS to solve the problems of narrow p H range and high dosage in oily water flocculation.On this basis,to reduce flocculants consumption and oily sludge production,and realize the recovery of flocculants,silane coupling agent was used to covalently bond magnetic nanoparticles and MCS polymers,and finally the oil removal with high-efficiency and low-consumption was realized under external magnetic field.The contents of the paper mainly include two parts,as follows:（1）Study on structure-activity relationship between functional chitosan-based flocculant and emulsified oily water.In this paper,three cationic monomers（DMC,DMD and DBC）and four hydrophobic monomers（DPL,ST,BA and VT）with different functional group structures were selected and grafted onto the chitosan（CS）chain together with acrylamide（AM）by low pressure UV initiation to synthesize seven different chitosan-based modified flocculants（MCS）.Scanning electron microscopy（SEM）,Fourier infrared spectrum（FT-IR）,X-ray diffraction（XRD）,Nuclear magnetic resonance(¹H NMR,¹³C NMR),X-ray photoelectron spectroscopy（XPS）and Differential thermal-thermogravimetric（TG-DTA）were used to analyze the appearance shape,functional structure and thermal stability properties,further confirmed that the monomers were successfully grafted onto the chain of CS.The influence of different functional groups on the oil removal efficiency of MCS was explored by controlling the dosage and p H factor.Results showed that the optimal oil removal rates of MC1～MC7 were 91.75%,79.05%,87.93%,89.71%,86.54%,66.25%,81.46%,respectively.Mechanism of oil removal was attained by analysis of Zeta potential,FT-IR,UV,three-dimensional fluorescence（EEM）,Gel permeation chromatograph（GPC）,and Gas chromatography-mass spectrometry（GC-MS）techniques,and results showed that raw water contained alkane,cyclanes and aromatics,MC4,MC6,and MC7exhibited favorable removal efficiency（96.60%～98.73%）on cycloalkanes,whereas MC5 had better flocculation efficiency on alkane.The successful modification of MCS flocculant widened the range of flocculation p H and improved the hydrophobic demulsification ability.（2）Study on magnetic covalently bonded chitosan based flocculant preparation and its performance in emulsified oily water flocculation.On the basis of the above experiments,to achieve the recovery of flocculants,promote the separation of oil-water,reduce flocculants consumption and oily sludge production,magnetic Fe₃O₄nanoparticles was introduced,and Si O₂ shell was coated through St?ber method to protect its superparamagnetism,improve the dispersion and provide binding site.And then silane coupling agent was used to covalently bond magnetic nanoparticles and MCS polymers.The results can be confirmed by Transmission electron microscopy（TEM）,XRD,Vibration sample magnetometer（VSM）,FT-IR and TG analysis.Additionally,some technologies were conducted to prove the excellent oil removal efficiency and recycling performance of FS-MC,including the single factor flocculation experiment and Zeta potential,FT-IR,UV,EEM,GPC and GC-MS analysis of water samples,it is concluded that the FS-MC1,FS-MC2 and FS-MC3 had optimal oil removal efficiencies of 94.47%,93.95%and 92.9%.Recycling experiments showed that the magnetic FS-MC flocculants could be reused up to five cycles without showing remarkable decline in separation efficiency.Specially,FS-MC exhibited an excellent behavior on removal of organic compounds with molecular weight>10 k Da,including long chain alkane,cycloalkanes,and aromatic hydrocarbon compounds.Accordingly,these findings also provided a new perspective to develop high efficient and recyclable magnetic flocculants with excellent performance for emulsified oil removal under external magnetic field.