Nonlinear Analysis And Control Of The Rate Variation Of Catalytic CO Oxidation On Platinum Group Metals

The catalytic oxidation of carbon monoxide(CO)is an important reaction process involved in the field of chemistry and energy industries,and it is also involved in military,environmental protection and safety fields.It is one of the hot spots of basic research in recent decades,among which the catalytic oxidation with platinum group metals is more common.During the process of online hydrogen production for fuel cell,the content of CO should be controlled within 100 ppm for Ru/Pt alloy electrode with high CO resistance,and even within 10 ppm for Pt based electrode.However,the amount of CO generated in the actual online hydrogen production process is usually thousands of ppm,which requires regulating the reaction rate of catalytic CO oxidation to remove as much CO and as little H2 as possible.The specific way is to change the parameter values of reaction components and temperature through the feedback control,so as to ensure the efficient chemical reaction.The stability control problem caused by the intrinsic nonlinear properties of catalytic CO oxidation process,such as bistability,catastrophe and hysteresis,needs to be solved urgently and has important engineering significance.In this thesis,the macroscopic geometric properties of the catastrophe boundary of CO oxidation catalyzed by platinum group metals are studied from the perspective of topology.Based on the topological rule,the catastrophe and hysteresis phenomena that cause the great change of the rate of catalytic CO oxidation are preliminarily analyzed,and these phenomena are classified from the perspective of function classification.On the basis of this analysis framework,further research on control strategy is carried out.In addition,the reasons for the catastrophic change and hysteresis in the catalytic CO oxidation were analyzed from the physical and chemical mechanism.The main research contents are as follows:According to the characteristic that the cusp geometry distribution of phase transition points of catalytic CO oxidation,the elemental topology model is determined to be the cusp model.Using the experimental data,the model is built based on the classical stochastic catastrophe theory,but the error is large.By improving the modeling strategy and using the method of geometric symmetry to construct the topological transformation relationship,an empirical model with higher accuracy is established,which is consistent with the theoretical analysis.According to the Langmuir-Hinshelwood mechanism of bimolecular adsorption and the average field model of catalytic CO oxidation,the analytical results of the critical criterion for the reaction rate catastrophe of catalytic CO oxidation are obtained,so as to expand the analysis of the catastrophe boundary of catalytic CO oxidation from the local to the whole.In this process,the method of variable substitution is innovatively put forward,the low order polynomial equation of catalytic CO oxidation is derived,and the analytical solution of the catastrophe boundary of reaction rate is realized.According to the geometric properties of the catastrophe boundary of catalytic CO oxidation,various possible changes in the process of catalytic CO oxidation are predicted.When the input variables such as reaction temperature and CO component change along different paths,the reaction process will have different hysteresis behaviors.Based on the analysis of the geometric properties of the hysteretic function,the finite state automata model of discrete mathematics is used to describe the geometric properties of the hysteresis function.The concepts of discrete state and discrete event are defined in the process of catalytic CO oxidation.According to the logic operation method,a finite class of finite state automata model is constructed to describe the topological structure of the function,and on this basis,the phenomenon of hysteresis in catalytic CO oxidation is classified.Five kinds of hysteresis phenomena of catalytic CO oxidation are predicted,and the predicted phenomena are verified by simulation results.Then,according to the result of mathematical classification of the critical criterion of catalytic CO oxidation,the physical and chemical mechanism is used to explain those phenomena,and the integrity of logical analysis is combined with the physical concept.Based on the above research,the stability mechanism of various nonlinear phenomena in the process of catalytic CO oxidation is analyzed from the first-order dynamic phase transition caused by the interaction of chemical adsorption and surface oxidation.From the viewpoint of control theory,the nonlinear properties of catalytic CO oxidation,such as sudden change of reaction rate,bistability and hysteresis,are considered.The design scheme based on the switch strategy is proposed,but the simulation results of the conventional switch strategy show that the reaction rate of catalytic CO oxidation changes too much at the switch time.In order to solve this problem,a smooth switching control method based on the reset of integral initial value is applied.By tracking the real-time output of each controller,the continuity of control output in the switching process is ensured,so as to prevent the sudden change of chemical reaction rate in the control process.The simulation results show that the proposed method can realize the continuous change of catalytic CO oxidation reaction rate at the switching time in principle,so as to improve the dynamic performance of the system.