Dissipative Particle Dynamics Simulation Of Pickering Interfacial Catalysis

Green catalysis is an important component of green chemical industry.It is the demand of modern chemical industry and important way to realize sustainable development to develop new catalytic processes with high efficiency,ecconmy and environmental protection.Pickering interfacial catalysis(PIC)system,as a new type of solvation-free reaction,greatly increases the contact area and interfacial diffusion rate of immiscible two phases,and shows a good economy and broad application prospect.It is also expected to develop into a new environment-friendly green catalysis process.At present,the research on Pickering interfacial catalysis system mainly focus on process realization,reaction efficiency measurement and macro-control.The stability of solid particles at the reaction interface,the microstructure of the oil and water on the particle surface and its regulation effect on the reaction are not well understood.In response to this challenge,this dissertation uses dissipative particle dynamcis(DPD)simulation and other methods to systematically study the micro-mixing of oil and water components on the surface of solid particle in the Pickering interfacial catalysis system.And the effect of liquid-liquid interface properties on the three-phase contact angle were quantitatively evaluated,and a simple prediction model was constructed.This dissertation is mainly composed of the following parts:(1)By using the alkyl chain and sulfonic acid group-modified silica particles as solid stabilizers,glycerol as water phase,and the dodecanol as oil phase.The meso-and microsacle properties of Pickering interfcial catalysis system were studied by DPD simulation and emulsification experiments.The optimal surface properties was determined according to the effect of length and surface density of the alkyl chain.The local density distribution of glycerol and dodecanol on the solid surface shows that the nanimxing of liquid components near the acids centers was effectively enhanced,so that the system exhibits efficient interfacial catalysis performance.(2)Sulfonated polystyrene-modified silica particles can effectively emulsify and catalyze the etherification of glycerol-dodecanol emulsion.Through meso-and microscale joint research,found that glycerol-dodecanol emulsification performance of the system is related to the length of polystyrene chain,the surface density,the sulfonation rate and the distribution of sulfonic acid groups on the polystryrene chain.And the reactants show efficient nanomixing near the sulfonic acid center,which was verifying the solid-liquid interface area is the potential reactivity area of the interfacial catalysis system.(3)The stability of nanoparticles at the liquid-liquid interface is the prerequisite for the stability of Pickering emulsions.Herein,in view of the lack of theoretical prediction of its stability,based on DPD calculation,a quantitative prediction model is proposed for predicting the three-phase contact angle of nanoparticle at the liquid-liquid immiseible interface.The model simpley depends on the Flory-Huggins parameters and solid particles size,and shows good consistency in comparsion with experimental results.This study provides an intuitive,concise and effective method for the stability study of Pickering interfacial catalysis.(4)Further expand the above model system to a system where the two-phase interface is partially miscible.Combining binary phase equilibrium and DPD theory,the solid-liquid interfacial tension and the three-phase contact angle were quantitatively evaluated.It is revealed that the stability of nanoparticle at the liquid-liquid interface is mainly composed of two factors:the balance of interfacial tension and the properties of liquid film.The basic physical properties of each component determine the inherent stability of nanoparticle,and the properties of liquid film determines the apparent stability of nanoparticle.Through the meso-and microscopic multi-scale research of various properties of Pickering interfacial catalysis,the microscopic mixing of various components on the solid surface and the stability criterion of the emulsion are comprehensively analyzed.The physical and chemical laws of Pickering interfacial catalysis are summarized from the aspects of interface properties and microstructure,which provides theoretical support for the directional control and expansion of the interfacial catalysis system.