| CO2/N2-switchable compounds become the hotpots of researches in recent years.As the chemical properties of these CO2/N2-switchable compounds can be changed reversibly by bubbling CO2 or N2,the CO2/N2-switchable compounds have great economic benefits and environmental value in oil recovery and other fileds.At present,the researches on CO2/N2-switchable emulsifiers are the most widly studied by the scienctists.The emulsions stabilized by these CO2/N2-switchable emulsifiers can be demulsified and re-emulsified by bubbling CO2 or N2,so that the recycling of these emulsifiers can be realized.However,there are many practical problems in the application and popularization of these CO2/N2-switchable emulsifiers:the synthesis of CO2/N2-switchable emulsifiers usually requires expensive raw materials and a long synthesis route;most of the CO2/N2-switchable emulsifiers can only be worked by strong shear stress;some CO2/N2-switchable emulsifiers have poor emulsifying property,or the emulsions cannot be completely demulsified by bubbling CO2.These problems greatly limit the practical application of this CO2/N2-switchable emulsifier.Therefore,a CO2/N2-switchable emulsifier with low price and excellent CO2/N2-switchable emulsifying/demulsifying property will promote it to play a greater role in industrial productionBased on the above background,we chose natural chitosan as the object of this research:first,the CO2/N2-switchable property of chitosan was confirmed,as well as the CO2/N2-switchable emulsifying/demulsifying property and the CO2/N2-switching mechanism;second,the effect of molecular weight on the CO2/N2-switchable property of chitosan was studied,as well as the CO2/N2-switchable emulsifying/demulsifying property and the CO2/N2-switching mechanism;third,on the above two basises,chitosan was chemically modified.Magnetic nanoparticles-modified high molecular weight chitosan and small organic compounds-grafted low molecular weight chitosan were all synthesized;both of the two kinds of chitosan-based compounds were with good CO2/N2-switchable emulsifying/demulsifying property.The main contents and the conclusions of this research are as follows:First,the experiments of transmittance,conductivity and pH under the condition of bubbling CO2 or N2 confirmed that natural chitosan can be switched by CO2/N2;CO2/N2-switched emulsification/demulsification experiments confirmed that natural chitosan can be used as a kind of CO2/N2-switchable emulsifier;CO2/N2-switched experiments of IFT,rheology and microscopic observation of emulsion droplets illustrated that this CO2/N2-switchable emulsification/demulsification of the emulsions stabilized by chitosan was the dissolution of chitosan under the condition of bubbling CO2 and the re-aggregation of chitosan under the condition of bubbling N2:in initial state,the deprotonated chitosan aggregates were adsorbed on the oil-water interface and formed a three-dimensional network between the droplets to stabilize emulsion;after CO2 was bubbling,chitosan aggregates became protonated,the hydrophilicity of chitosan increased and finally the chitosan aggregates dissolved in water.The three-dimensional network,which was constructed by chitosan aggregates and existed between the emulsion droplets before,was disappeared.As a result,the droplets coalesced and finally demulsification occurred.After N2 was bubbling and heated to 65?,chitosan became deprotonated,the hydrophilicity of the chitosan decreased and finally they re-aggregated from water and adsorbed on the oil-water interface again under the action of mechanical force.The three-dimensional network was rebuilt;as a result,the emulsion could be stabilized again.Second,the different of CO2/N2-switched emulsification/demulsification performance of chitosan with different molecular weight was studied.It was found that the emulsifying property of chitosan was increased with the increase of molecular weight,while the switching demulsifying property was decreased.The CO2/N2-switched expriments of conductivity,interfacial rheological properties,macroscopic rheological properties,viscosity,emulsification and demulsification of four kinds of chitosan samples with different molecular weight illustrated that the influence on the CO2/N2-switched emulsification/demulsification performance of chitosan was caused by the increase of viscosity,which was due to the high molecular weight:Before bubbling CO2,comparing with chitosan with low molecular weight,chitosan with high molecular weight formed a more stable three dimensional network structure in continuous phase because of the more serious physical cross-linking caused by the long molecular chain,which leaded to the formation of a closer cross-linked system and hence a more stable emulsion;after bubbling CO2,the high molecular weight caused high viscosity of the protonated chitosan in continuous phase,which the droplets were difficult to coalesce from it,so that the incomplete demulsification happened finally.Third,a kind of high molecular weight chitosan-based emulsifier was synthesized by Fe3O4 nanoparticles grafting.On the basis of the above conclusions,the chitosan sample with high molecular weight,which was good at emulsification and bad at CO2-switching demulsification,was grafted with magnetic Fe3O4 nanoparticles;the product CTS-g-VT-MNPs with excellent CO2/N2-switched emulsifying/demulsifying property was obtained.The FT-IR,1HNMR and SEM tests confirmed that the magnetic Fe3O4 nanoparticles were grafted in the chitosan structure successfully,and the product aggregate in water with a shape of chitosan coat magnetic Fe3O4 nanoparticles.The conductivity and IFT experiments confirmed that the grafting of Fe3O4 nanoparticles does not affect the CO2/N2-switchable capability of chitosan,while the emulsification experiments confirmed that the grafting does not affect the emulsifing capability of chitosan.The CO2-magnetic demulsification experiments illustrated that the emulsion stabilized by the Fe3O4 nanoparticles-grafted chitosan can be demulsified completely in the synergistic reaction of CO2 and magnetic,so that,the grafting of Fe3O4 nanoparticles improved the demulsification performance of chitosan.Fourth,a series of low molecular weight chitosan-based emulsifier was synthesized by small organic compounds grafting.The chitosan sample with low molecular weight,which was good at CO2-switchable demulsification and bad at emulsification,was grafted with small organic compound dimethylaminoethyl acrylate(DMAEA),dimethylaminoethyl methacrylate(DMAEMA)and N,N-dimethylacrylamide(DMAA).The product CTS-g-DMAEA,CTS-g-DMAEMA and CTS-g-DMAA were obtained,which were all with excellent CO2/N2-switchable emulsifying/demulsifying property.The FT-IR and1 HNMR tests confirmed that the organic compounds were grafted onto the molecular structure of chitosan by chemical reactions.The appearance and conductivity tests of the grafted products confirmed that the grafting does not affect the CO2/N2-switchable capability of chitosan,while the emulsification experiments confirmed that the grafting improved the emulsification capability of chitosan.The CO2/N2-switched emulsification/demulsification of these products illustrated that the emulsions can be demulsified completely by bubbling CO2 and re-emulsified by bubbling N2,so that,the grafting of organic compounds improved the emulsification performance of chitosan. |
PDF Full Text Request