Process Design,optimization And Control Of Distillation System For Separating The Multi-componnet Multi-azeotrope Systems

The multi-azeotrope mixtures containing organic components are always generated in the production of petroleum,pharmaceutical and chemical industries.However,the direct emission of the above-mentioned mixtures will lead to environmental pollution and waste of available resources.Therefore,it is necessary to develop a separation and purification process with energy-saving,robust operability and high thermodynamic efficiency.Special separation processes with multiple columns(e.g.,extractive distillation,pressure-swing distillation and reactive distillation)are required to the complex multi-component and azeotropic systems.So far,the investigation of conceptual design is limited.How to ensure the optimal feed flow rate of solvent? How to determine the feasible operation conditions to break the separation limit caused by multi-azeotrope? How to get the suitable operating pressure of multiple columns? How to design the distillation sequence? How to obtain the composition and flow rate of recycle stream? It is a great challenge and has a practical significance to the azeotrope separation of petrochemical and pharmaceutical enterprises.On the other hand,the extraction mechanism for the breaking azeotrope is explained according to the formation mechanism of azeotrope.A feasibility and energy-efficient separation strategy is then developed,which has important guiding significance for process optimization design.It can provide important theoretical foundation for subsequent small-scale,pilot scale and industrialization of multi-component and multi azeotropic complex system separation.Thereby,a systematic approach is proposed for the effective separation of multi-componnet and multi-azeotrope mixtures.Firstly,the ternary system with two azeotropes(i.e.,Serafimov 2.0-2b)and ternary system with four azeotropes(i.e.,Serafimov 3.1-2)as two cases are used to solve unclear issue of the extraction mechanism for changing or breaking azeotropic equilibrium using solvent.Based on quantum chemistry calculation,the strength of hydrogen bond energy between solvent and azeotropic system is explained and the mechanism of solvent breaking the phase equilibrium of complex azeotropic system in extractive distillation process is revealed.Furthermore,the energy-efficient extractive distillation with optimal operation conditions such as pressure and separation sequence are determined based on the thermodynamic topological theory.For the ternary system with three azeotropes(i.e.,Serafimov 3.0-2),the feasibility of different regions in the ternary phase diagram,which is divided via the thermodynamic topological theory such as residual curve,equal relative volatility curve,component equilibrium line and distillation boundary,are analyzed.A novel framework of process synthesis and design is established,and then a feasibility and energy-efficient separation process with pressure range,separation sequence and optimal process conditions is determined for seaparating that complex system.An improved genetic algorithm program is developed by introducing the repeated solution elimination mechanism and weak mutation mechanism realizing the global optimization of chemical process.A robust dual temperature feed-forward control strategy is developed to deal with the large dynamic response based on the open-loop sensitivity analysis/singularity value decomposition;the intensified energy saving and emission reduction configurations are developed to solve the high energy consumption issue in the distillation process and achieve sustainable production of petrochemical and pharmaceutical industries.The details are listed as below:(1)A computer aided molecular design(i.e.,CAMD)program based on UNIFAC group contribution method is developed to quickly and intelligently screen entrainer,which is adopted to the separation of Serafimov 2.0-2b classification.Three candidates entrainers are obtained via the calculation of CAMD.The obtained entrainers are compared with the N-methyl pyrrolidone(obtained from the experimental data in the literature)based on the thermodynamic insights(i.e.,relative volatility lines)and the result indicated that the dimethyl sulfoxide have the best separation performances than N-methyl pyrrolidone and other candidate solvents.In addition,the establised apporach could also be extended to screen entrainer of the Serafimov 3.1-2 classification.Furthermore,the charge density distribution of separated components and entrainer are calculated via the Material Studio to explain the strength of hydrogen bond energy between solvent and azeotropic system,and the mechanism of solvent breaking the phase equilibrium of complex azeotropic system in extractive distillation process is revealed.(2)Thermodynamic insights of the extractive distillation such as distillation boundary,relative volatility line and residue curve are extended to explore the conceptual design of pressure-swing distillation for the effective separation of pressure-sensitive system.Firstly,the possible separation sequence in each feasible operational(or distillation)region through the thermodynamic insight.The following questions are tackled as crucial issues in the conceptual design: Is the separation of targeted mixtures feasible using the pressure-swing distillation? Which separation sequences are most suitable? What are the limits on operating pressures to achieve the minimum total annual cost? Finally,the separation of Serafimov 3.0-2 classification is taken as an example to verify the proposed method.(3)Reactive distillation assisted extractive and pressure-swing distillation processes are developed to overcome the high energy consumption,low thermodynamic efficiency and environmental pollution issues in the above-mentioed extractive and pressure-swing distillation processes.The third component,ethylene oxide,is introduced to remove the water component in the ternary azeotropic mixture and then the remaining components are separated via the extractive distillation or pressure-swing distillation.The energy consumption and energy utilization efficiency could be reduced and improved via the proposed reactive distillation process because the heat released by the reaction can be used in the separation process.In addition,the complexity and difficulty of the separated system can be reduced by removing the component water.(4)The NSGA-II intelligent algorithm is developed to to solve the problems of difficult and time-consuming in the process optimization for the chemical process with highly nonlinear,strong coupling and many operating conditions.The improved NSGA-II algorithm with a repeated solution elimination mechanism and a weak mutation mechanism can effectively solve the MINLP problem of special distillation process and quickly obtain the optimal process operation variables.(5)To explore the feasibility of the establised process in the actual operation,the control strtucture of the special distillation process is designed by using proportional integral control strategies such as single-end temperature,dual-temperature and temperature difference control strategies.The robust control of the special distillation process can be achieved via the above-mentioned control structures.In addition,it could provide further guidance for its application in industry.