The Application Of Reaction Engineering Theory In Some New Technology Fields

The preparation of nano-TiO2 powder materials with high-frequency plasma chemical vapor deposition (HF-PCVD) reactor, the oxidative stabilization of polyacrylonitrile (PAN) fiber during the preparation of PAN-based carbon fibers, the photocatalytic water treatment process and non-aqueous rechargeable lithium-oxygen battery all belong to materials, environment and energy-related high-tech fields, and have great value and broad development prospects. Currently, these technologies all exist theoretical issues in the reaction process to be solved, such as:the reaction in the preparation of nanopowder materials and the controlment of particle size; the elimination of the skin-core structure during the oxidative stabilization of PAN fiber; the effect of light intensity distribution on the degradation rate of pollutant during photocatalytic water treatment process; the effect of mass transfer, charge transfer in rechargeable lithium-oxygen battery porous oxygen cathode on the capacity and cycle performance. Based on the reaction engineering theory, this paper does the modeling theoretical analysis on the four important reaction processes, gets their universal laws, and provides a theoretical basis for these high-tech research and development.1. The preparation of nano-TiO2 powder materials with HF-PCVD reactorIn the view of the reaction engineering, the nano-TiO2 powder preparation process with high-frequency plasma is a thermochemical reaction conversion process first, and then splice a gas-phase condensation physical process. The two processes are together called HF-PCVD process. HF-PCVD reactor is a flow reaction system, and the temperature difference between the inside surface temperature of the plasma torch and the water wall temperature is approximately 5000 K, and great unevenness of the reaction rate is formed in the reactor. For the existing measurement methods can not effectively determine operating state under the high temperature inside the reactor, and in order to analyze and predict basic law of inputs, outputs about the HF-PCVD reactor, the generalizing two-dimensional mathematical model of HF-PCVD reactor used to prepare nano-TiO2 powder is founded by the author.The model makes reasonable simplification about momentum transfer in the process, and it considers the effect of axial convection, radial back mixing and heat radiation on the TiO2 generation rate through the vapor phase oxidation of TiCl4, and can theoretically describe the distribution of temperature and TiO2 product concentration within the reactor.Three types of nano-TiO2 were prepared with the experimental reactor using three different experimental conditions, and the average particle diameters were 25,60,45nm. We verifyied the model using experimental conditions, and then further calculated the saturation distribution of TiO2 in the reaction zone, the results could clarify the nanocrystalline TiO2 average particle size and the law of particle size distribution changes, i.e., a shorter residence time and lower TiCl4 concentration were conducive to generate nano-TiO2 with smaller particle size, and more uniform distribution, but the conversion rate of TiCl4 was low, and vice versa. Figure 1 is the result that obtained using the optimized experimental operating conditions:the outlet conversion rate was about 40%, and the average particle diameter of product was 45nm.The generalizing mathematical model can provide a theoretical basis for the design and operation of the reactor optimization, and also prepare the conditions for further quantitative analysis of the nucleation, condensation, growth process of TiO2 nanoparticles with HF-PCVD.2. The evolution of the skin-core structure during the oxidative stabilization of PAN fiberThe oxidative stabilization of PAN fiber is an important step of the preparation of PAN-based carbon fiber, and it affects the quality and yield of the final carbon fiber. Owing to the uneven reaction degree resulted from the oxygen diffusion, the skin-core structure is formed in the fiber, and seriously affects the quality of the pre-oxidized fibers.Oxidative stabilization PAN fiber is a non-catalytic gas-solid phase reaction process, the authors first reasonably simplified the complex chemical reactions in the process to the cyclization, dehydrogenation and oxidation, containing both the effect of oxygen diffusion on the reaction process, and the relationship between the reaction conversion and material structure.Following this, the authors established a reaction engineering model of oxidative stabilization of PAN fiber to quantitatively investigate the effect of form of fibers, the preparation conditions and other factors during the reaction process, and to study the relationship between the reaction and skin-core structure evolution: Figure 2 is the distribution of the oxidation product concentration and the evolution law of core-sheath interface with time calculated by the model when fiber radius is 4μm and 6μm. It can be seen that interface of fiber that has smaller radius completely disappears in about 7500s, and achieves structural stabilization.The results of model calculations show that the effect of the rate of the cyclization reaction on the interface location of the final fiber is weak; Improving oxygen diffusion coefficient, appropriately increasing the oxygen concentration, reducing fiber radius are conducive to shorten the time of the-oxidative stabilization, and to promote the elimination of skin-core structure. In the early stage of oxidative stabilization, lower temperature should be used to avoid the formation of skin-core structure; and in the late stage, we can raise the temperature to eliminate the skin-core structure as soon as possible, shortening the oxidative stabilization time.3. Photocatalytic water treatment flat plate falling film reactorSolar photocatalytic oxidation treatment of wastewater is one of the focus in the field of environment and energy. Most laboratory studies use a linear light source, but few to study the optical radiation field of linear light source. In this paper, we use the low irradiance linear light source with the similar intensity of UV light in sunlight, a homemade flat plate falling film reactor, and P25 TiO2 photocatalyst to study the photocatalytic degradation of low concentrations of methyl orange solution; and examine the effect of light source distance, the concentration of catalyst (catalyst loading), the reaction liquid flow rate on the reaction conversion. We also esablish the light irradiance distribution expression of the flat plat reactor using linear light source radiation model; Based on the surface light irradiance distribution, mass balance, photon amount balance and kinetic equation, we establish flat plate falling film slurry bed and flat falling film fixed-bed photocatalytic reactor reaction engineering model, focus on the analysis of the effect of light intensity distribution in the surface of the reactor and the liquid film on the degradation rate, and regress the slurry and immobilized film catalyst reaction rate constant based on the experimental data. The results proved that the correct description of the light radiation field is important. The experimental and theoretical analyses in paper provide a reliable data basis for the practical flat plate falling film reactor using in the sun light.(1) Obtain the light irradiance expression at any point on the line light source tablet falling film reactor surface The figure 3 shows the light irradiance distribution of the reactor surface based on formula(2) The established mathematical models of flat plate falling film slurry bed and fixed bed reactor are shown in Table 1.(3) The theoretical model calculation results show that, within the scope of certain experimental conditions, increasing the amount of photocatalyst and reducing the light distance can improve the flat falling film reactor outlet conversion rate; the increasing of the flow will reduce the outlet conversion rate; But for the system as a whole, the total degradation rate is still increasing with the flow rate increasing; we also investigated the effect of the width changes of plate reactor when length keeping constant on the outlet conversion rate, and the results showed that the higher conversion rate could be found when the length and width were similar.(4) Experiment studies have shown that slurry bed has better methyl orange degradation effects, but fixed bed is more suitable for industrial applications, so need to study how to increase the active surface area of the immobilized film. 4. The establishment of Non-aqueous rechargeable lithium-oxygen battery positive electrode discharge process reaction engineering modelNon-aqueous rechargeable lithium-oxygenbattery (NRLOB), the highest theoretical energy density rechargeable battery in the current research and development, has broad application prospects. The primary task is to make the battery porous oxygen cathode electrochemical reaction ongoing in a relatively high reaction rate, the deposition of insoluble discharge products Li2O2 in the electrode pores is the key factor.Currently there are just a few lithium-oxygen battery models, and only analysis the macro electrode scale of oxygen cathode, lacking accuracy. As the deposition of insoluble discharge products mainly occurs in electrode clusters, the author established the theoretical model from the clusters micro and electrode macro two scales which could accurately describe the oxygen electrode electrochemical reaction process at the same time, the detailed models are shown in Table 2.The model considered the coupling of pore diffusion and the electrochemical reaction process in inner surface in the cluster scale, the effect of the deposition of insoluble discharge products on the pore diffusion and reaction, and coupled the cluster efficiency factor and electrode macro scale model together. The next step will be the combination of theoretical models and battery kinetic experiments.