| Aqueous foam is a dispersion system of gas in liquid phase,which has been widely applicated in daily life and social production.Since foam is a thermodynamically unstable system,exploring the foam stability mechanism and novel ways to improve foam stability has always been a concern in related fields.Studies have shown that the foam stability can be improved by surfactant composited with surfactants,polymers,or nanoparticles.However,maintaining the stability of foam under severe conditions is still a bottleneck restricting the practical applications of foam.For instance,in the field of enhanced oil recovery(EOR),where foam flooding has been proven to be a promising EOR technology,especially in improving the efficiency of thermal recovery of viscous oil,while CO2 foam flooding has been proved having high technical potential and advantages in improving the recovery efficiency of oil and gas in unconventional reservoirs.However,as these technologies usually need to face harsh conditions such as high temperatures,oil and shear disturbance or CO2 being used as the foaming gas,achieving foam stabilization is extremely difficult and challenging,and the traditional systems couldn’t meet the performance requirements well,which severely limit the application of foam flooding.Therefore,it is necessary and important to investigate the stability mechanism of foam,explore the technical approach to improve the stability of aqueous foam under harsh conditions,and develop new aqueous foam systems with high-temperature foam stability and CO2 foam stability,for the purpose of promoting the application development of foam flooding.Meanwhile,based on rising of the global attention to environmental protection,enhancing foam performance using green biomaterials is of great significance for promoting the construction of green foam functional system and the sustainable development of related technical fields.In view of the above problems,in this thesis bio-based lignin nanoparticles(LNPs)were selected to form complex system with surfactants,of which the foam properties was investigated.It was found that the LNPs greatly enhanced the foam stability,especially under harsh conditions such as high temperature,mechanical shear disturbing,and CO2 being used as the foaming gas.Several experimental methods was used to explore the mechanism of foam stabilization in the composite system,and the interactions mechanism between LNPs and surfactants based on hydrogen bonding or electrostatic interactions was reveal,which is the key point improving the properties of the foaming system.What we learned may enriches the theoretical understanding of the synergistic effect between nanoparticles and surfactants in foam stabilization,and provide ideas and guidance for the construction of green foam composite systems using green bio-based materials and surfactants,and expanding the functionalized utilization of lignin.The research content of this thesis mainly includes the following two parts:(1)The properties of N2 foam stabilised by LNPs and anionic surfactant α-olefin sulfonates(AOS)were investigated.The differences in static/dynamic foam stability,liquid carrying capacity,the rate of coalescence and bubble size of AOS foams and AOS/LNPs composite foams were determined byusing the vibration shaking method,Foamscan and optical microscopy,and it was found that the stability of AOS/LNPs composite foams was significantly improved.The interactions between LNPs and surfactants were explored in combination with IR spectroscopy,dynamic light scattering,surface tension and SEM,and the mechanism for LNPs help to stabilize foams was revealed.Research results show that there exist interactions between LNPs and AOS,so LNPs are carried by surfactants into the foam film,which not only promotes the adsorption of surfactant molecules at the gas/liquid interface,but also enhances the liquid-holding capacity of the foam film to maintain a large film thickness,thus effectively inhibiting the diffusion of gas through the film,reducing the rate of bubble aggregation and significantly,and improving the stability of the foam to the extent.The system exhibit excellent stability at 150℃ and under mechanical shear disturbance.The influence of high temperature treating processes on the properties of LNPs was investigated,for the purposse to further clarify the structural characteristics of LNPs that are conducive to the performance in co-stablizing foam,and provide guidance for the development of future application systems.LNPs are natural in origin,environmental friendliness,structural stability,and have excellent performance as a compound foam system with surfactants,and have good prospects for application in tertiary oil recovery and related fields such as environment and daily chemical.(2)Based on the aforementioned research,the compounding of anionic/cationic/nonionic surfactants was used to further enhance the denseness of surfactant gas/liquid interfacial layer in the foam film,and the compounding of LNPs with xanthan gum(XG)was used to further improve the liquid-holding capacity of the foam film,thereby a synergistic compounding system of natural polymers containing LNPs and surfactants was constructed to achieve the stabilization of CO2 foam.In this part of the research,anionic surfactants sodium dodecyl sulfate(SDS),cationic surfactants cetyl trimethyl ammonium bromide(CTAB),and nonionic surfactants alkyl glycosides(APG)were used.The stability,apparent viscosity,liquid-holding capacity,rheology and coarsening rate of SDS foam,SDS/CTAB/APG(SCA)foam and SCA/XG/LNPs composite foam were investigated by various experimental methods,and the interactions between SCA and LNPs/XG were studied by infrared spectroscopy and SEM,for the purpose to reveal the microscopic mechanism of the synergistic effect achieved by the multiple compounding of surfactants and polymers on stabilization of CO2 foam.This research not only provides a solution to effectively solve the difficult problem of stabilizing CO2 foam,but also provides a new view for the research of multivariate complex,which is of reference for further exploration of the functionalization of aqueous foam systems.In summary,the LNPs-enhanced surfactant aqueous foam system studied in this thesis has excellent performance to achieve the stability of aqueous foam under harsh conditions such as high temperature,mechanical shear,and carbon dioxide foaming,and lays the foundation for the application of related technologies.The study reveals the foam stabilizing mechanism of bio-based lignin nanoparticles synergistically with surfactants,and the theoretical learning can provide meaningful guidance for the future development and application of green aqueous foam systems.Meanwhile,LNPs are naturally sourced,structurally stable,and green.The composite system of LNPs and surfactants constructed in this thesis has good prospects for application in the fields of enhanced oil recovery and daily chemical. |
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