Study On The Transport And Transformation Characteristics Of Reactants Based On The Photocatalytic Reduction Process Of CO₂ In Microreactor

At present,photocatalytic reduction of carbon dioxide is one of the effective ways to solve the greenhouse effect and alleviate the energy crisis at the same time.Because the microreactor has the advantages of simpler structure,higher specific surface area,uniform light distribution and precise controllable reaction time than conventional reactors,the application of optofluidics to photocatalytic reduction of carbon dioxide has broad prospects.However,it is difficult to track and observe the flow,mass transfer,and reaction process of microreactos in real-time to reveal the general laws.Therefore,in this thesis,the numerical simulation of the photocatalytic reduction of carbon dioxide in the flat microreactor was firstly performed by using the Computational Fluid Dynamics technique and the FLUENT software to define the component transport equations and photocatalytic chemical reaction rates.Then combined with the inverted convex microreactor which can enhance mass transfer,the effect of reactor structural changes on the photocatalytic mass transfer process and chemical reaction rate was also studied by using numerical simulation method.Finally,because the existence of two phase flow can enhance the transport of material in the microreactor,a microreactor with a substrate loaded micronano catalytic layer was fabricated,and the effects of different two phase flow states on the photocatalytic conversion in the microreactor were investigated by experiments.The main research contents and results are as follows.(1)The Langmuir-Hinshelwood model and User-Defined dynamic mass transfer model were used to simulate the photocatalytic reduction of gaseous carbon dioxide in a flat microreactor respectively.It was found that the dynamic mass transfer model is more consistent with the experimental results,which indicating that in the process of photocatalytic reduction of carbon dioxide in the microreactor,the transfer of reactive substances plays a leading role in the reaction rate.And with the increase of the reactant inlet flow rate,the corresponding product yield increase first and then decrease,when the inlet flow rate of carbon dioxide was 2 mL/min,the yields of methanol and ethanol reached the maximum,which were 25.66 μmol/g-cat?h and 40.49 μmol/g-cat?h respectively,the conversion of carbon dioxide reached the highest at this time.A correlation of the mass transfer characteristics related to the Reynolds number was established.(2)The process of photocatalytic reduction of carbon dioxide in an inverted convex microreactor was simulated by using dynamic mass transfer model.It was found that the existence of the convex plate enhanced the transfer of the reaction substance,thereby improving the reaction rate effectively.With the reactant inlet flow rate increase,the product yield increase first and then decrease,when the carbon dioxide inlet flow rate was 3.5 mL/min,the yield of ethanol reached the maximum,which was 100.34 μmol/g-cat?h,and the conversion of carbon dioxide reached the highest at this time.A correlation was established.(3)Two phase photocatalytic reduction of carbon dioxide was carried out on a microreactor with substrate loaded micronano catalytic layer.Compared with the pure liquid phase,the photocatalytic reaction efficiency is higher when the reactants are gas-liquid phase state.When the liquid inlet flow rate is fixed,the yields of methanol increase with the increase of gas inlet flow rate.When the gas inlet flow rate is fixed,the yields of methanol increase first and then decrease with the increase of liquid inlet flow rate.When the gas flow rate was 70 μL/min and the liquid flow rate was 1 mL/min,the yield of methanol reached the maximum,which was 262.22 μmol/g-cat?h.