| In the process of chemical production,multi-component azeotrope containing low carbon alcohols will be produced,which makes it difficult to purify and recycle low carbon alcohols.Extractive distillation is one of the most common azeotrope separation techniques at present,but its high energy consumption is the main bottleneck restricting its further development.The use of highly efficient entrainer can significantly improve the separation efficiency and reduce the process energy consumption.It is of great significance to explore the influence of entrainer on extractive distillation process and the development of azeotrope separation process.In this paper,dichloromethane(DCM)-methanol(MeOH)-water and methyl tert-butyl ether(MTBE)-ethanol(EtOH)-water produced in the pharmaceutical and chemical industry were taken as examples,the effects of entrainer and process design on the economic and environmental benefits of extractive distillation were explored from three aspects: process optimization,mechanism analysis and economic correlation model.This paper aims to provide reference for the selection and process optimization of extractive distillation for the separation of ternary azeotrope containing low carbon alcohols.Firstly,the effects of more than ten entrainers(like glycerol(Gly),dimethyl sulfoxide(DMSO),1,3 propylene glycol(1,3-PDO)on the economic and environmental benefits of DCM-MeOH-water and MTBE-EtOH-water systems were investigated.The process parameters(stage number,entrainer flow rate,reflux ratio,etc.)of basic extractive distillation process were optimized by multi-objective optimization based on genetic algorithm.The results showed that 1,3-PDO as entrainer in DCM-MeOH-water system had the best economic and environmental benefits,with the total annual cost(TAC)of 786694.3 $/y and gas emission of 1555.1kg /y,and DMSO as entrainer in MTBE-EtOH-water system had the best economic and environmental benefits.The TAC was 568129.5 $/y and the gas emission was 982.5 kg/y.However,the Gly which had the greatest influence on relative volatility did not achieve the best economic and environmental benefits.The random forest algorithm was used to verify the contribution degree of thermodynamic factors to the economic and environmental benefits of extractive distillation.The contribution degree of specific heat was as high as 0.4,indicating that in addition to the relative volatility,specific heat and boiling point also have non-negligible effects on extractive distillation benefits.The energy saving scheme was further designed on the basis of the optimal basic extractive distillation separation process.For the DCM-MeOH-water system,the thermal integrated extractive distillation process using 1,3-PDO as entrainer has the best economic and environmental benefits,with TAC of 690977.9 $/y and gas emission of1103.1kg /y.For MTBE-EtOH-water system,the thermal integrated extractive distillation process using Gly as extractor has the best economic and environmental benefits,with TAC of 376621.9 $/y and gas emission of 404.3 kg/y.Different energy saving processes that can be designed with different entrainers may lead to different energy saving effects,and the entrainers that can obtain the optimal benefits may change.The optimal entrainer of MTBE-EtOH-water system changes from DMSO to Gly.Therefore,possible thermal integration schemes should also be considered in the screening process of entrainers.In order to explore the relationship between molecular interaction and extractive distillation effect,the separation mechanism of entrainer and azeotrope system was studied by molecular dynamics simulation and quantum chemistry calculation.The results showed that the difference of interaction energy between entrainer and azeotrope molecules was positively correlated with the relative volatility.The difference of the interaction between the molecules of entrainer on azeotrope system is the essential reason of the influence on relative volatility and extractive distillation process.Neural networks were used to construct the correlation models between the thermodynamic properties of entrainers in DCM-MeOH-water system and MTBEEtOH-water system and the economic performance of the process.The coefficients of determination of the models were 0.998 and 0.993,respectively,showing a strong correlation.Through the process design and optimization of tetrahydrofuran(THF)-EtOH-water system,the correlation model was verified,and DMSO was successfully selected as the economic optimal entrainer,which verified the feasibility of predicting the economy of extractive distillation process and the optimal entrainer screening through the model.The coupled extractive distillation pervaporation process was further designed on the basis of the economic optimal process,with TAC of 623381.5 $/y and gas emission of 1107.7kg /y.The model provides reference for extractive distillation entrainer screening and separation process design.In this paper,the influence of entrainer and process design on the separation of azeotrope containing low carbon alcohol by extractive distillation is studied systematically,and the energy saving scheme of extractive distillation for DCM-MeOHwater,MTBE-EtOH-water and THF-EtOH-water systems is developed.It is of great significance to the technology development and energy saving for separation of ternary azeotrope by ternary extractive distillation in practical industry. |
PDF Full Text Request