Optimization And Dynamic Characteristics Of ACN-based Butadiene Extractive Distillation Towards Higher Energy Efficiency

The developing coal chemical and ethylene industries in China yields more and more by-product cracked C4 mixture,attracting more concerns on its deep processing technical improvement to add more product value and commercial benefits as well.About 20% of cracked C4 mixture is Butadiene,a major and important petrochemical basic material feedstock,high in industrial application value after being purified by extractive distillation.However,the traditional butadiene extraction process is disadvantageous for low thermodynamic efficiency,large equipment demand,and high investment cost,giving huge prespects to introduce energy-saving technologies.Differences between extractive agent/solvent characterize the Butadiene extraction distillation processes.Amongst the available extractive solvents,acetonitrile(ACN)are focused for rich in source and low in price.With the aid of advantageous deviding wall column(DWC)in energetic efficiency,this thesis proposes and optimizes a strongly coupled ACN-based butadiene production process.Starting from the spirit of ACN-based conventional extraction process,this study,in the first place,converts its extractive distillation and butadiene refining sections,on the basis of thermodynamic equivalence,into a double-wall extractive dividing wall column(EDWC)and a fully thermally coupled DWC,respectively.The models of conventional process and the strongly coupled process were built up in Aspen Plus,with missing binary interaction parameters obtained through regression of the vapor-liquid equilibrium data and ASPEN model estimation function.After process simulations,Techno-ecnomic evaluations of conventional and the strongly coupled DWC processes were conducted with total annual cost(TAC)the indicator.Results turn out that the strongly coupled DWC process lessens 17.73%energy and 15.84% TAC from the conventional process.In order to further minimize TAC of the strongly coupled DWC process,the equipment and operation parameters were optimized through response surface method(RSM)using Minitab,expanding the energy saving and TAC advantages of the strongly coupled process over the conventional process to 19.57% and 17.79%,respectively.Aspen Plus Dynamics was then used to test the dynamic characteristics of optimized DWC process,after temperature control structure developed according to the process characteristics of the optimal DWC process.At ± 5% disturbance of feed flow and composition,the system can maintain stability under quick response of the control system,with qualified butadiene product,or strong in flowsheet robustness.In summary,strongly coupled DWCs are used to improve the complex multi-component distillation process.This operation succed in implementing combined double-wall EDWC and fully thermally coupled DWC.In the next step,the complex DWC process parameters were optimizd through response surface method to overcome difficult-to-optimize problem caused by difficult-to-converge issue during simulation.Then the feasibility of the complex DWC process was further proved through research on its dynamic characteristics.The way of thinking and the methodology used herein is also applicable to indutrial butadiene units,as well as complicated extractive distillation processes.