Effect of particle size on the thermodynamic properties of benzene adsorbed by magnesium oxide nanoparticles

The pollution caused by the emission of sulfur dioxide and nitrogen oxides in China is becoming more and more serious, and the national efforts to control air pollution are gradually increasing. It is necessary and urgent to research and develop economic, efficient and simple flue gas desulfurization and denitrification technology.

The chemically prepared magnesium oxide nanoparticles have excellent properties such as high purity, small particle size, large specific surface area, high hardness, high reactivity, strong adsorption and good low temperature sintering, which can be used as adsorbent for environmental pollution control.

In this thesis, the preparation of magnesium oxide nanopowder and adsorbent were systematically studied and applied to the simultaneous flue gas desulfurization and denitrification test, and good treatment effect was obtained.

The paper introduces the properties, applications and preparation methods of magnesium oxide nanoparticles, and presents an in-depth study on the preparation of its powder and adsorbent. MgSO4-7H2O and Na2C03 were used as raw materials, and the surfactant polyethylene glycol 1000 was added to prepare the nano-magnesium oxide powder with good crystallization and large specific surface area by a combination of direct precipitation method and microwave water bath heating method. The effects of reaction temperature and time of precursors, baking temperature and time and the amount of polymer polyethylene glycol on the specific surface area of the powders were discussed. The structure and morphology of the magnesium oxide nanopowders and the thermal decomposition temperature of the precursors were analyzed by thermogravimetric analyzer, X-ray diffractometer, scanning electron microscope and Fourier infrared spectrometer.

The results showed that the precursors were roasted at 500℃ for 1.5h to produce magnesium oxide nanopowder with the specific surface area of 183.35m2/g and the average particle size of 7.2nm. The magnesium oxide nanopowder adsorbent was prepared by the co-blending method (magnesium oxide nanopowder: MgSO4-7H2O: sweetening powder=75:32:1, mass ratio), and the adsorbent was characterized before and after the simultaneous desulfurization and denitrification. In the self-designed and installed flue gas desulfurization and denitrification device, the magnesium oxide nanosorbent was used.

The effect of the particle size of magnesium oxide nanoparticles on the thermodynamic properties of adsorption was investigated using magnesium oxide nanoparticles and benzene in aqueous solution as the adsorption system. The experimental results showed that the particle size of magnesium oxide had a great influence on the standard equilibrium constant of adsorption, standard molar Gibbs free energy, standard molar enthalpy of adsorption and standard molar entropy of adsorption; and the standard equilibrium constant of adsorption increased, standard molar Gibbs free energy, standard molar enthalpy of adsorption and standard molar entropy of adsorption decreased as the particle size of magnesium oxide decreased.