Preparation Of Amphiphilic Hemicellulose Derivatives And Research On Oil Removal Mechanism Of Oily Sludge

As global oil production increased,the amount of oily sludge generated during oil extraction,refining,storage and transportation also grows significantly.However,if these large quantities of oily sludge are not treated in time,it will have serious impact on the natural environment and human health.Then the treatment of oily sludge has become one of the most important problems to be solved in the oil industry.The surfactant thermal cleaning method has the advantages of low investment,low energy consumption and high efficiency,and is one of the important technologies for oily sludge treatment.However,most of the surfactants used in the existing thermal cleaning process are petrochemical-based surfactants,which are environmentally toxic and non-naturally degradable and easily cause secondary pollution to the ecological environment after use.Therefore,there is a need to develop environmentally friendly surfactants with good biocompatibility and degradability for green and harmless treatment of oil-bearing sludge.The molecular units of hemicellulose are rich in hydrophilic groups,which are important raw materials for the preparation of environmentally friendly biomass-based surfactants.The hemicellulose derivatives with amphiphilic properties,prepared by introducing lipophilic groups through esterification modification,can be applied to the treatment of oily sludge as biomass surfactants,which is of great practical significance for the resourceful/hazardous treatment of oil-bearing sludge.In this paper,hemicellulose derivatives with high surface activity and amphiphilicity were prepared from hemicellulose extracted from bamboo by homogeneous esterification with various succinic anhydrides and different hydrophobic side chains in the deep eutectic solvent(DES).Then these hemicellulose derivatives were used as environmentally friendly surfactants for the treatment of oily sludge,and the mechanism of oil removal was elaborated through studies at macroscopic and microscopic levels.The main research contents and results are as follows:(1)Succinic anhydride with different hydrophobic side chains was used as the esterifying agent for the homogeneous esterification of bamboo-derived xylan in a microwave-assisted DES system.Amphiphilic hemicellulose derivatives as succinic anhydride-modified hemicellulose(HC-SA),butyl succinic anhydride-modified hemicellulose(HC-BSA),octenyl succinic anhydride modified hemicellulose(HC-OSA),dodecenyl succinic anhydride modified hemicellulose(HC-DDSA),and octadecenyl succinic anhydride modified hemicellulose(HC-ODSA)with approximate degree of substitution(DS of 0.24)were prepared.The chemical structures of hemicellulose derivatives were analyzed with FT-IR,NMR and XRD.The results showed that the hemicellulose was efficiently esterified with anhydride reagent in the microwave-assisted DES system,and the modified hemicellulose derivatives were homogeneous in molecular weight and low in crystallinity.The surface/interfacial properties,foaming properties,emulsification properties and solubilization properties of the hemicellulose derivatives were further investigated,and it was found that the modified hemicellulose derivatives possessed certain amphiphilic properties,and the amphiphilic properties increased significantly with the increase of introduced hydrophobic side chain length,and the surface activity increased.(2)Based on the structural characteristics and physicochemical properties of oily sludge,three kinds of amphiphilic hemicellulose derivatives,HC-OSA,HC-DDSA and HC-ODSA,with good amphiphilicity and surface activity,were selected to study the oil removal effect of oily sludge,and the petrochemical-based sodium dodecyl sulfate(SDS)was used as a control sample.The results showed that the amphiphilic hemicellulose derivatives had certain oil removal effect on oily sludge,and the oil removal rate was 58.3%for HC-OSA,66.7% for HC-DDSA and the best effect was 79.9% for HC-ODSA under the optimal treatment process,which was significantly higher than the oil removal rate of SDS(69.9%).It can be concluded that amphiphilic hemicellulose derivatives modified with medium chain length succinic anhydride have the potential to be substitutable for fossil-based surfactants.The composition of oil in solids before and after treatment was analyzed and it was found that the light fraction was easily removed and the residual heavy fraction was one of the important factors affecting the removal efficiency of oiled sludge.(3)The desorption thermodynamics and kinetics experiments of the simulated oily sludge-1(OS-1)containing saturated hydrocarbons,aromatic hydrocarbons and colloidal light fractions and the simulated oily sludge-2(OS-2)containing heavy asphaltenes were conducted by using HC-OSA,HC-DDSA,HC-ODSA and SDS to investigate the desorption behavior and desorption mechanism of the oil fraction of Oily Sludge.The results showed that the Langmuir model could better describe the desorption of oil fractions in OS-1 and OS-2 in different indicated surfactants,and the desorption efficiency of HC-ODSA was the largest for light and heavy hydrocarbons,followed by HC-DDSA,HC-OSA was poor,and SDS was approximately the same as HC-DDSA;the thermodynamic parameters showed that the desorption of oil fractions in surfactant solution The desorption behavior of oil components in surfactant solution is spontaneous,and the desorption efficiency increases with the increase of temperature;the quasi-secondary kinetic model is more suitable to describe the desorption behavior of OS-1 and OS-2 in surfactant solution.(4)The effects of amphiphilic hemicellulose derivatives(HC-OSA,HC-DDSA and HC-ODSA)on the oil/water and solid/liquid interfacial behaviors of oily sludge during oil removal were investigated using QCM-D and surface tension meter.The results show that the amphiphilic hemicellulose derivative molecules decrease the oil/water interfacial tension by adsorbing at the oil/water interface,and the oil components on the surface of the oil-bearing sludge tend to disperse or solubilize into the aqueous phase,thus detaching from the solid surface;furthermore,the amphiphilic molecules adsorb on the solid surface of the oil-bearing sludge by hydrophobic interaction,which changes its wettability and thus promotes the desorption of the oil components.