Design And Control Of Extractive Distillation Process For The Separation Of Benzene/Tert-butyl Alcohol Azeotropic Systerm

Both benzene and tert-butyl alcohol are widely used as common basic chemical materials.Tert-butylbenzene is generated under the catalysis of anhydrous aluminum chloride by the reaction of benzene and tert-butanol,the production process will generate mixture of benzene and tert-butanol.It is difficult to separate them effectively by conventional distillation methods because of the formation of minimum azeotrope at the atmospheric pressure,there will be some industrial application value in developing special distillation separation process.In this paper,the extractive distillation process was studied to separate the benzene/tert-butanol.Economy and dynamic robustness were explored in this process based on different feed composition with different solvent.The confirmation of suitable solvent for extractive distillation.Three substances,namely,MEA,DMSO and MMEA,were preselected as solvent by drawing residue curve map and vapor-liquid equilibrium phase diagram.MEA and MMEA were selected as the suitable solvents for extractive distillation of benzene/tert-butanol finally.The economy of extractive distillation separating benzene/tert-butyl alcohol was carried out using Aspen Plus.Based on the model of cost,which is total annual cost(TAC),the effect of the number of tray,feed stage,reflux ratio and solvent/feed flow ratio were investigated in different feed composition under different solvents.The results show that the minimum TAC of MEA as solvent is smaller than that of MMEA in the same feed composition.The control scheme of this extractive distillation was studied by Aspen Plus Dynamics.When MEA was selected as the solvent,the basic control structure with fixed reflux ratio cannot achieve the robust control in three feed compositions,respectively.R/F proportional control structure can get perfect results for ±20 % feed flow rate and feed composition disturbances for the mixture with 20 mol% benzene.For the mixture with 50 mol% benzene,QR/F proportional control structure has a strong anti-disturbance ability.As for the mixture with 80 mol% benzene,R/F proportional control structure was adopted for ±10 % feed flow rate and feed composition disturbances.When MMEA was selected as the solvent,the basic control structure with fixed reflux ratio cannot also reach the requirements.QR/F proportional control structure was added to solve the ±20 % feed flow rate and feed composition disturbance problems for the mixture with 20 mol% benzene.When the mole fraction of benzene was 50 %,QR/F proportional control structure was useful for ±20 % feed flow rate disturbances and ±10 % feed composition disturbances.R/F proportional control structure can achieve robust control for the mixture with 80 mol% benzene in dealing with ±20 % feed flow rate and feed composition disturbances.