Preparation Of Chitosan Quaternary Ammonium Modified Clay Demulsifier And Their Demulsification Performance

With the exploitation of major oilfield entering the middle and late stage,the produced crude oil is mostly O/W type crude oil emulsion,which not only brings transportation costs and corrosion of transportation pipelines,but also increases subsequent refining difficulties.In addition,with the development of petrochemical industry,machinery processing and nonferrous metallurgy industry,the discharge of emulsified oily wastewater is increasing day by day,which poses a serious threat to the ecological environment.Compared with traditional demulsifier,nanoparticle（NP）demulsifier has attracted extensive attention due to its unique demulsification performance.It has been founded that the surface modification of clay nanoparticles can achieve good NP demulsifiers.In this paper,kaolin and montmorillonite,two most representative layered clay minerals,were chemically modified by chitosan quaternary ammonium salt to obtain efficient NP demulsifiers with low cost and environmental friendliness.The demulsification performance of modified kaolin and montmorillonite for O/W emulsion was investigated,and the demulsification mechanism was analyzed and revealed.The main research results are as follows:（1）KAO-NH₂ and KAO-QC NP demulsifiers were synthesized by surface amination and graft of chitosan quaternary ammonium salt（QC）of the kaolin with different particle sizes（KAO₁ and KAO₂）.Bottle test was used to evaluate the demulsification performance of the prepared materials.It was found that the original kaolin also had a certain demulsification performance,but the demulsification efficiency was relatively low（85.27%）.After modification,the demulsification performance is greatly improved and can work in a wide p H range.Moreover,the modified kaolin with smaller particle size has better demulsification performance and can achieve rapid and efficient demulsification at room temperature（25℃）.The demulsification efficiency of KAO₂-NH₂ and KAO₂-QC reached 98.29%and 99.05%,respectively,at room temperature with the dosage of demulsifier 800 mg/L and p H=8,respectively.It was further shown that the demulsification efficiency could be improved by increasing temperature and the salinity of emulsion.By comparing the demulsification properties of kaolin before and after modification,it can be concluded that good interfacial activity,proper surface charged characteristics and functional groups are essential for constructing clay mineral demulsifier with excellent demulsification performance.（2）Using montmorillonite（MMT）as raw material,Fe₃O₄ nanoparticles were loaded on the surface of MMT by solvothermal method to obtain the magnetic montmorillonite（M-MMT）,which was further modified by（3-Aminopropyl）triethoxysilane（APTES）and QC to prepare various NP demulsifiers of MMT-NH₂,MMT-QC,M-MMT-NH₂ and M-MMT-QC.SEM and FT-IR analysis showed that the Fe₃O₄ nanoparticles were successfully loaded on MMT surface.EDS and TGA analysis further confirmed that APTES and QC has been successfully grafted on MMT surface.VSM magnetic property analysis showed that M-MMT-QC possessed good superparamagnetism and could be easily recovered after demulsification under the external magnetic field.Zeta potential measurement showed that the positivity charge of MMT-QC and M-MMT-QC was greatly improved due to the graft surface of QC,which is favorable to enhance the interaction between demulsifier and negatively emulsified oil droplets.Oil-water distribution analysis and wettability characterization of the prepared NP demulsifies showed that the MMT-QC and M-MMT-QC had good interfacial activity and amphiphilicity.The demulsification performance of each material was evaluated.It was found that the demulsification efficiency of MMT-NH₂ and M-MMT-NH₂ was relatively low,while it was significantly improved due to the introduction of QC and reached 98.00%and 98.82%for MMT-QC and M-MMT-QC,respectively,at room temperature（25℃）,demulsifier dosage of 1000 mg/L and p H=6.In addition,the M-MMT-QC has a good recycling performance.（3）Both KAO and MMT are layered clay minerals with different structures,while the demulsification performance is different after modification.KAO has a certain demulsification ability under acidic conditions.After modified with APTES（KAO-NH₂）,the demulsification performance become much better.In contrast,MMT itself basically has no demulsification performance.After modification with APTES（MMT-NH₂）,the demulsification performance is also poor.Only with further modification by QC（MMT-QC）,rapid and excellent demulsification efficiency was obtained.This is because there is abundant-OH on the surface of kaolin,and more-NH₂ can be introduced after APTES modification.However,there is less-OH on the surface of montmorillonite,and mainly distributed on the side of the material.After APTES is grafted,the amount of-NH₂ is also less,so the demulsification performance is poor.When larger molecules of QC are grafted,a large number of functional groups are introduced,and then obtain an excellent demulsification performance.There results indicates that the composition and structure of clay minerals play an important role in the demulsification performance.The modification methods and characteristics of clay minerals should be considered comprehensively in the construction of NP demulsifiers with high demulsification performance.