DOI：https://doi.org/10.1016/j.cjche.2019.04.005
Molecular dynamics simulation of supercritical CO2 microemulsion with ionic liquid domains: structures and properties
Zhu Hongyue, Li Ying, Ren Hongrui, Zhou Dan, Yin Jianzhong
(Dalian University of Technology)
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In this paper, the ls-36 / CO2 / H2O / [bmim] [PF6] quaternary system was constructed, and the molecular dynamics of the system was simulated. All the molecules were randomly placed in the box. After a short time of energy minimization, the unreasonable conformation with large energy was removed, and then the system was operated for 200 ns. At 1 ns, the system is relatively dispersed; at 8 ns, there are four small agglomerates, each of which is composed of water molecules, surfactant molecules and ILS; at 27 ns, the small agglomerates gradually gather into two larger agglomerates, two of the 12 surfactants are free in the continuous phase of CO2, the rest are concentrated in the water mass; at 74 At 123 ns, the agglomerate was spherical, and all the surfactants were concentrated in the water group, and the ILS and water molecules were wrapped in the agglomerate, and the tail of the surfactant extended to SCCO2; 123 NS-200 During the operation time of NS, most of the water molecules remain in the agglomerate, and a surfactant molecule presents a dynamic process of aggregation dissociation, and the system basically reaches a dynamic equilibrium state. The formation process, aggregation morphology and structural information of Ls-36/H2O/[bmim][PF6]/CO2 microemulsion were analyzed by molecular dynamics simulation.
(1) gradually adding 1-3 [bmim][PF6] in the three component system which had been pre assembled and stabilized microemulsion. By analyzing the operating track of the system, it is observed that ILs can be dissolved in the water core wrapped by surfactant in a relatively short time. In the initial stage, a certain amount of ILs was added at one time to simulate the time of 150 NS-200 ns, so as to ensure that the system has enough running time, and the formation of microemulsion agglomerates containing ILS can also be observed.
(2) the results of molecular dynamics simulation directly show the formation process of Ls-36/H2O/[bmim][PF6]/CO2 microemulsion: the system initially formed a number of (3-6) small clusters, and the small clusters were composed of water molecules, ILs and surfactants, and the sizes varied. With the extension of simulation time, the 2-3 small clusters were fused into larger clusters, and finally, at a certain time, all the clusters were fused. It is a large agglomerate and remains stable for the following simulation time.
(3) the analysis of the radial distribution function, density distribution function and radius of gyration results that the Ls-36/H2O/[bmim][PF6]/CO2 microemulsion cluster radius is 10 nm, and the structure is divided into three layers: [bmim][PF6] and water are gathered in the water core of the microemulsion, the Ls-36 header and partially bound water form an interlayer, and the tail base extends in scCO2.
(4) compared with the three yuan microemulsion system without ILs, the addition of a small amount of ILs enhanced the dissolution of water molecules in the microemulsion group, and also accelerated the aggregation of surfactant molecules, and ultimately improved the aggregation efficiency of surfactant.
(5) By analyzing the density distribution of water and CO2 in different parts of surfactant molecule, it is found that there are three kinds of conformations in the system, most of which are "d" conformations, while "L" and "C" conformations occupy a small proportion. The self-assembly process of LS Mn accords with the principle of entropy increase.
(6) ILS can be stably dissolved in the water core, so the geometric center of ILs represents the polar core, and the distance between the center and the last carbon atom of the surfactant long carbon chain is the radius; because the carbon chain is not easy to bend, the vector composed of two carbon atoms C00 ﹣ C10 represents the surfactant long tail chain. It is observed that the opening angle of surfactant tail chain is about 78 ° - 125 °. The opening of the tail chain increases the solubility of surfactant in SCCO2, which is conducive to the stability of the agglomerate.
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Introduction to the author and the team
Yinjianzhong: doctor, Professor, doctoral supervisor. In July 1986, Inner Mongolia University of technology obtained bachelor's degree in chemical equipment and machinery; in July 1992, Dalian University of technology obtained master's degree in chemical process machinery; in March 2002, Dalian University of technology obtained doctor's degree in chemical process machinery. 2004.1-2005.7 postdoctoral of Chemical Engineering Department of Tsinghua University in Taiwan; 2007.12-2008.3 visiting professor of Chemical Engineering Department of Tsinghua University in Taiwan. Member of American Chemical Society (ACS), member of British chemical industry society (SCI), member of supercritical fluid Professional Committee of Chinese chemical society, vice chairman of editorial board of Applied Science and technology and editorial board of contemporary chemical industry. Green Chem.；Bioresource Technology；Chemical Engineering J；Energy Conversion and Management；J of Physical Chemistry；Fuel；Energy & Reviewers of fuels; J of supercritical fuels; chemical engineering communication; Chinese Journal of chemical engineering; Journal of inorganic materials; chemical progress; Journal of chemical engineering; Journal of college chemical engineering; Journal of high pressure physics; Journal of fuel chemistry, etc. It won one second prize of national teaching achievement, one first prize of Liaoning teaching achievement and one third prize of Liaoning natural science. He presided over 4 NSFC projects, 2 subprojects of 863 program, 1 Doctoral Program Fund of the Ministry of education, and 3 NSFC projects of Liaoning Province. It has applied for 35 national invention patents and authorized 20. He has published more than 160 academic papers, 70 SCI papers and 80 EI papers.
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