Research On The Preparation,Performance And Mechanism Of Carbon-Based Materials Based On Oil-Water Emulsion Treatment

Crude oil as an important energy and basic chemical raw material is an important strategic resource.With the rapid development of our social economy,the demand for petrochemical products is also growing rapidly.Most crude oil is produced as water-in-oil emulsions or oil-in-water emulsions.Emulsified water contained in crude oil has many adverse effects such as corrosion of equipment and pipelines,increase transportation costs,and seriously affect the subsequent refining process.Meanwhile,oily wastewater also exists widely in the petroleum and petrochemical industry,and its direct discharge inevitably causes problems such as waste of resources,environment and ecology,and even threatens human health.The separation of oil-water emulsions is still one of the serious challenges faced by petroleum industry.Chemical demulsification is the most widely used technology in petroleum industry,i.e.adding a small amount of demulsifier to the oil-water emulsion to achieve the purpose of oil-water separation.Traditional chemical demulsifiers have many problems such as dangerous and complicated production process,high cost and non-environmental friendly,and poor adaptability to complex environments,which are increasingly difficult to meet the needs of field.Carbon-based materials are environmentally friendly and have unique physicochemical properties,which have received a lot of attention in the petroleum industry.Based on the sources of carbon-based materials,three types of environmentally friendly demulsifiers of carbon-based materials were prepared in this paper,mainly including composites of traditional carbon materials（carbon black,graphene,carbon nanotubes,etc.）with functional organic molecules or inorganic nanoparticles,modified materials of natural products with special surface and chemical composition（lotus leaves,rice husks,etc.）,and modified materials of cellulose-based solid wastes（waste paper,etc.）.The demulsification performance of these demulsifiers in oil-water emulsions was comprehensively evaluated,while their demulsification mechanism was discussed in detail.The main contents are as follows:（1）The Ox-CB@SiO₂ demulsifier was prepared by grafting nano-SiO₂onto the surface of oxidized carbon black（Ox-CB）using sol-gel method.The structure,morphology and composition of Ox-CB@SiO₂ demulsifier were analyzed by FT-IR,SEM,EDS and XRD,and the effects of demulsification temperature,demulsification time and demulsification dosage on the demulsification performance of water-in-oil emulsion were investigated in detail.The possible demulsification mechanism of the demulsifier was analyzed by wettability,oil-water interfacial tension and interfacial activity of Ox-CB@SiO₂ demulsifier.The results showed that the demulsification performance of the water-in-oil emulsion was more than 90%when the dosage of Ox-CB@SiO₂ demulsifier was 500 mg/L and the demulsification temperature was 75℃.Ox-CB@SiO₂ demulsifier could demulsify water-in-oil emulsion by bridging,flocculation and coalescence,while the high interfacial activity was the main factor affecting the demulsification performance of Ox-CB@SiO₂ demulsifier.（2）A reduced graphene oxide/titanium dioxide（RGO@TiO₂）demulsifier with good demulsification performance was prepared by sol-gel method.The structure,morphology and composition of RGO@TiO₂ was characterized by FT-IR,UV-Vis,XRD,SEM and EDS.The results of bottle test showed that the light transmittance of the separated aqueous phase was up to 79.1%when the dosage of RGO@TiO₂was 500mg/L and settling for 30 min at ambient temperature.Meanwhile,RGO@TiO₂ had good demulsification performance under acidic,neutral and high salt conditions.The possible demulsification mechanism was further studied by wettability,interfacial activity,dynamic interfacial tension,zeta potential,self-assemble of the interfacial film and microscopic analysis of the demulsification process of RGO@TiO₂.The results showed that RGO@TiO₂could rapidly migrate to the oil-water interface and then to destroy the stability of oil droplets by adsorbing or replacing asphaltenes throughπ-πinteraction.（3）Carbon nanotubes grafted withβ-cyclodextrin（MCNT@β-CD）was prepared by an ultrasonic method for the treatment of oily wastewater.The structure,morphology,composition and thermal stability of MCNT@β-CD were characterized by FTIR,UV-Vis,SEM and TGA.The demulsification performance of MCNT@β-CD in oily wastewater was comprehensively evaluated.The possible demulsification mechanism of MCNT@β-CD was investigated by interfacial activity,wettability,self-assembly at oil-water interface,dynamic interfacial tensions,zeta potential and photomicrograph of demulsification process.The results showed that the light transmittance of the separated aqueous phase was up to 94.5%and the corresponding oil remove rate was about 99.76%at a low concentration of 50 mg/L within a few minutes at room temperature.At the same time,MCNT@β-CD had good acid and salt resistance.The study of demulsification mechanism showed that the surface wettability of carbon nanotubes could be turned withβ-CD,so that MCNT@β-CD could rapidly migrate to the oil-water interface and replace asphaltenes throughπ-πinteractions.In addition,charge neutralization could reduce the electrostatic repulsion between droplets and promoted the demulsification of the emulsion.（4）CNTs-NH₂demulsifier was prepared by grafting ethylenediamine on the surface of carbon nanotubes for the treatment of oily wastewater.The structure,composition,morphology and interfacial properties of CNTs-NH₂ were characterized and analyzed.The demulsification performance of CNTs-NH₂ in oily wastewater was comprehensively evaluated,and its possible demulsification mechanism was explored.The results showed that CNTs-NH₂ had an eminent amphipathicity and high interfacial activity,which allows it to sharply migrates to the oil-water interface under the synergistic effect ofπ-πinteraction and electrostatic attraction,and interact with the interfacial film to reduce the stability of the interfacial film.The demulsification tests exhibited that CNTs-NH₂could effectively remove emulsified oil from the oily wastewater.CNTs-NH₂ could also be used at acidic,neutral,and high salinity conditions.The light transmittance of the separated aqueous phase was up to 88.1%and the corresponding oil removal rate was 99.2%with 100 mg/L of CNTs-NH₂ for 30min at room temperature.Moreover,CNTs-NH₂ could be recycled for reuse and still maintained better interfacial activity,thusly the oil removal rate of CNTs-NH₂remained above 97.8%after 6 cycles.（5）Natural lotus leaf was used as raw material to prepare a HLLF demulsifier by a simple hydrothermal method without the addition of any chemical reagent.The HLLF demulsifier was utilized to demulsify the water-in-crude oil emulsions.Effect of the demulsifier dosage,demulsification time,demulsification temperature and treatment method of HLLF on the demulsification efficiency of water-in-crude oil emulsions was evaluated.The possible demulsification mechanism was systematically investigated by SEM,three-phase contact angle,dynamic interfacial tensions,self-assembly of interfacial film and microscopic analysis.The results showed that the demulsification of HLLF in the water-in-crude oil emulsions could occur quickly,and the optimal demulsification efficiency was up to 88.17%with 1000 mg/L of dosage and 90 min of settling time at 70℃.The three-phase contact angle value of HLLF was81.53°and its interfacial tensions was 25.65 m N/m with the dosage of 500 mg/L at room temperature.The prominent demulsification ability of HLLF was attributed to the micro-nano structure on its surface,which may soften or destroy the rigid interfacial film to enhance the film drainage.（6）An environmentally friendly and amphipathic rice husk carbon（RHC）demulsifier was prepared by a simple carbonization process using agricultural by-product rice husks as starting materials.The structure,composition,morphology and surface charge of RHC were characterized and analyzed by SEM,EDS,FTIR,UV-Vis,XRD,TGA and zeta potential.The factors such as dosage,demulsification temperature,demulsification time,p H value and salinity on the demulsification efficiency of water-in-oil emulsions were systematically investigated,and the possible demulsification mechanism was explored.The results indicated that the dehydration efficiency reached as high as 96.99%with 600 mg/L of RHC for 80 min at 70℃.RHC exhibited an optimal dehydration efficiency under neutral condition,as well as RHC had a good acid,alkali and salt resistance.The results showed that the oxygen-containing groups and high content of silica in RHC were the main reasons for its high interfacial activity to achieve effective demulsification.（7）An amine-functionalized recycling wastepaper demulsifier（AWP）was prepared for the treatment of oily wastewater.The morphology,composition,wettability,and interfacial property of AWP were investigated.The demulsification performance of AWP in oily wastewater was comprehensively evaluated,and its possible demulsification mechanism was explored.The results showed that AWP had appropriate amphipathy and excellent interfacial activity,which could adsorb and displace asphaltene at the oil-water interface,thus destroying or softening the interfacial film.AWP exhibited an excellent demulsification performance,the light transmittance of the separated aqueous phase and the oil removal rate exceeded 89.6%and 99.16%,respectively.Meanwhile,AWP had a good acid,alkali and salt resistance.