Studies On The Reaction And Purification Of Methyl Esterification Of Alkali Weight-reduction Wastewater Residue

Alkali weight-reduction process is a critical step to improve the quality of polyester.During this process,a great deal of alkaline organic waste water named alkali weight-reduction wastewater would be produced,which would severely pollute the soil and water resources if it is discharged without indispensable further treatment.Acid eduction is a common method to recover the main ingredient of alkali weight-reduction wastewater-terephthalic acid(TA)to avoid excessive resource waste.The product from acid eduction is called alkali weight-reduction wastewater residue,which is always used to supply heat as a kind of fuel or be the raw material of low-end polyester.In this paper,alkali weight-reduction wastewater residue was taken as the raw material to react with methanol to produce dimethyl terephthalate(DMT)and the reaction conditions,kinetic,production purification methods and integrated process simulation were investigated.The research results showed TA accounted for 87.79%of the residue and the other were water,inorganic salt and soluble organics.The reaction was sensitive to temperature.The second order kinetics model was reliable and could predict the reaction properly.In addition,the distillation condition for DMT was studied and the difficulties and solutions were also taken into consideration.The designed vacuum distillation tower was applied to detect the effect of vacuum degree and reflux ratio to distillation results.The experiment data showed the best vacuum degree was 8-lOkPa and the optimal reflux ratio was 2.Under the distillation condition above,the purity of DMT achieved more than 99.3%.Beyond that,the binary solid-liquid equilibrium of DMT,Dimethyl Isophthalate(DMI)and Dimethyl Phthalate(DMP)was investigated by experiments and differential scanning calorimetry(DSC).The results illustrated DMT/DMI and DMT/DMP systems were eutectic while DMI/DMP was a solid-solution system.The eutectic temperature of DMT/DMI and DMT/DMP system was 63.5? and-2?,respectively.The eutectic composition of DMT/DMI system was 12.8%wt%for DMT and 87.2 wt%for DMI and that of DMT/DMP system was 7 wt%for DMT and 93 wt%for DMP.Furthermore,a classical solid-liquid phase equilibrium model was used to fit the experimental data of eutectic systems and the theoretical model could describe the eutectic solid-liquid phase diagrams properly.Based on above,three binary solid-liquid phase diagrams were drawn and the mixed crystallization technology,including fall film crystallization and solution crystallization,was designed.Finally,the software named Aspen Plus was applied to design and simulate the integrated technology of methyl esterification reaction,which included esterification reaction,reactive distillation,methanol recycling,DMT purification and heat utilization.The material and energy balance were also provided and the new concept of alkali weight-reduction wastewater residue utilization was proposed.