Process Optimization And Control For The Separation Of Binary And Ternary Azeotropic System By Double-column Batch Distillation

With the sustained-steady growth of the national economy and the continuous adjustment and upgrading of industrial structure,the state attaches great importance to the development of fine and pharmaceutical industry,and the industry will usher in good development opportunities and broad markets in the future.Complex azeotropes are often produced in the fine and pharmaceutical industries.Batch distillation is the most commonly used separation method,it is of great scientific and practical significance to develop novel batch distillation process for the separation of complex azeotropic systems.In this paper,the double-column batch distillation process was developed based on the inherent characteristics of the system with the goal of efficient separation of complex azeotropic system.The feasibility of the process was demonstrated by exploring the phase behavior of the system,and the control strategy to ensure the high purity of the product was proposed.The process was comprehensively analyzed from the aspects of economy,environment and energy consumption.The energy saving and consumption reduction of the process were realized through heat integration.Taking advantage of the characteristic of n-heptane-isobutanol system that is the minimum boiling point azeotrope at low pressure and the maximum boiling point azeotrope at high pressure,the double-column pressure swing batch stripper-rectifier process was designed.The exergy loss of the distillation column was reduced by the feed precooling.The proposed composition-flow cascade control structure realized the effective control of the process.The multi-objective optimization of the process was carried out with the equipment cost and CO₂ emissions as the objectives.The optimal TAC and CO₂ emissions were 2.26×10~5$/Y and 4.92×10~5 kg/Y respectively.The treatment time was 6.67 h.Total annual cost（TAC）and CO₂emissions of process were reduced by 7.1%and 22.76%via considering the heat integration of the process respectively.Based on the heterogeneous and minimum boiling point characteristics of cyclohexane-acetonitrile-toluene system,the double-column batch stripper process with a decanter was proposed.The vessels automatic switching control strategy was developed.The process was comprehensively evaluated from the aspects of TAC,environmental performance,product recovery ratio and treatment time,the optimal process operating parameters were obtained.The minimum TAC was 4.60×10~5$/Y,the recovery ratio was94.5%,the CO₂ emission was 3.45×10~6 kg/Y,the treatment time was 24.5 h.For n-hexane-ethanol-butanone ternary system with three binary azeotropes,the double-stripper parallel connection batch process,the double-stripper parallel-series connection sequence switching batch process and the single-double stripper sequence switching batch process were designed and optimized.The processes were comprehensively evaluated from the aspects of economy,environment,treatment time and recovery ratio.The double-stripper parallel-series connection sequence switching batch process had the best economic and environmental performance,and recovery ratio and treatment time were also best.The minimum TAC was 1.99×10~5$/Y,the recovery ratio was96%,the CO₂ emission was 2.88×10~6 kg/Y,the treatment time was 7.24 h.The proposed feed preheating and steam waste heat recovery scheme reduced the operating cost of the butanone separation process by 28.87%,the TAC by 3.03%,and the n-hexane-ethanol separation process operating cost by 30%.