Research On Stability And Demulsification Of Unconventional Petroleum Oil-water Emulsions

Unconventional petroleum ores have been considered to be an important part of petroleum resources and an important alternative source of chemicals and energy supply.However,unlike the traditional crude oil production,unconventional petroleum ore is more difficult to separate due to its coexistence of oil and solid and high content of heavy components.In the process of separation of various unconventional oil ores,the participation of water is involved in different degrees.However,because of the existence of interfacial active components and nano mineral particles in heavy oil,the unconventional oil ore often forms stable oil-water emulsions during the separation process,affecting subsequent separation,purification,storage and transportation.Firstly,the interfacial active asphaltene component（IAA）in unconventional petroleum was extracted by the method of"solvent settling emulsification phase separation".The basic molecular weight of IAA（18259）was obtained by gel permeation chromatography（GPC）;the elemental composition（C,H,O,N,S,etc.）,chemical group structure and valence states of different elements of IAA were successively analyzed by means of element analysis（EA）,Fourier transform infrared spectrum（FTIR）,X-ray photoelectron spectroscopy（XPS）and nuclear magnetic resonance（NMR）;the molecular degree of polymerization（1.89）,monomer formula（C72H93NO3S4）of IAA were calculated by the improved Brown-Ladner（B-L）method The archipelagic structure model of IAA linked by fat chain was obtained.On this basis,the interfacial characteristics of IAA were analyzed by interfacial tension tester and rheometer,and the interfacial activity and viscoelasticity of IAA were obtained.The basic characteristics of IAA stabilized emulsion and the rule of droplet size distribution of oil-water emulsion were obtained by long period stability and microscopic imaging test.Through the method of all atom molecular dynamics simulation,it is found that IAA molecules can form aggregates throughπ-πstacking between aromatic rings and hydrogen bonds self polymerization between molecules,which can gather at the oil-water interface to form a membrane structure with certain strength;in addition,the heteroatoms（N,O,S）at the polar end of IAA molecules and hydrogen atoms in water molecules can form hydrogen bonds and gather the certain thickness of the interfacial film is formed at the oil-water interface.The interfacial film can prevent the aggregation of different droplets in the oil phase,resulting in the long-term existence of water droplets in the oil phase..In view of the above emulsion separation problem,through the molecular design,esterification reaction and polymerization reaction were used to introduce the ester group and carboxyl group in the structure of polyether molecule,the demulsifiers（JMNP and TJU-2）was obtained,which contains many kinds of oxygen-containing functional groups.The demulsifier is used in the demulsification separation process of different oil-water emulsion（asphaltene oil-water emulsion,asphalt oil-water emulsion,crude oil-water emulsion,diesel oil-water emulsion and IAA-stabilized emulsion）.The results showed that although the demulsification rate was different,the demulsifier had good demulsification capacity for the above emulsion.Taking the most stable IAA oil-water emulsion（IAA-W/O）as an example,the non-ionic polyether（JMNP）containing only ester groups can remove 50%of the water in the emulsion when the concentration is 400 ppm,60^oC and the demulsification time is 15 min.The non-ionic polyether（TJU-2）containing ester and carboxyl groups can remove 97.5%of the water in the emulsion at the same concentration and temperature,and prolong the demulsification time to 25min,the emulsion is completely demulsifiered.The distribution of JMNP and TJU-2demulsifiers in the oil phase and water phase after demulsification of IAA-W/O emulsion was studied by KI-I₂UV-Vis spectrophotometric method.The distribution coefficient of demulsifiers in oil-water two phase were 0.448 and 0.241 respectively.It showed that after breaking the emulsion,most of JMNP and TJU-2 molecules enters into the water phase,which indirectly indicated that JMNP and TJU-2 demulsifiers were highly hydrophilic.In order to explore the mechanism of demulsifier interaction at oil-water interface,the demulsification of TJU-2 demulsifier in IAA-W/O emulsion was studied by particle dissipation dynamics（DPD）simulation.The simulation results show that the oxygen of carboxyl group and ester group in TJU-2 molecule forms a strong hydrogen bond（35.038 k J/mol,32.357 k J/mol）with hydrogen in water molecule,which is stronger than the hydrogen bond（18.936 k J/mol,9.427 k J/mol,5.467 k J/mol）formed by heteroatom（O,N,S）in IAA molecule and hydrogen in water molecule.The hydrogen bonds formed between the molecules of the demulsifier and the water molecules on one hand replace the hydrogen bonds between IAA molecules and water molecules;on the other hand,they break theπbonds in the aggregates of IAA molecules,thus achieving the demulsification of IAA-W/O emulsions.