Preparation Of Magnetic ZSM Zeolite As Adsorbent For Effective Adsorption Of Organics

A large amount of wastewater containing organic compounds and metal ions will be produced in the process of PTA production.It will lead to not only high economic losses,but also water,soil and atmosphere pollution if the wastewater is discharged directly into the environment.The extraction-ultrafiltration-reverse osmosis process is adopted to recover the majority of organic acids.While a small amount of PX will be retained in the wastewater after the extraction section,and the reverse osmosis membrane made of polyamide will be dissolved by PX,which affects the lifetime of the membrane.Hence an operation unit that realizes removal of PX by an adsorption method without affecting the concentration of the metal ions is added between the extraction operation unit and the ultrafiltratio-reverse osmosis operation unit.The selective adsorption of PX was carried out by means of shaped ZSM-5,while the adsorption performance was evidently decreased compared to the powder ZSM-5.Thus the powder magnetic ZSM-5 zeolite adsorbent is synthetized to get rid of PX,and the drawback of degradation of adsorption properties due to shaped process is overcome.TPA+was determined to the appropriate template for the synthesis of ZSM-5 by the molecular simulation method and related experiment researches.Firstly,the synthesis conditions of magnetic cores(Fe3O4/SiO2)were optimized.Secondly,hydrothermal method was adopted to prepare magnetic ZSM-5,then the crystallinity of ZSM-5 and its adsorption properties on PX were regarded as an indicator to ascertain the optimum conditions for ZSM-5 synthesis.The result showed that ZSM-5 with optimum crystallinity and adsorption performance were obtained when n(SiO2)/n(TPA+),synthesis temperature and synthesis time were 24:1,150 ? and 36 h respectively.Finally,it could be known that ZSM-5 with good magnetic and adsorption properties were successfully synthesized from the results of VSM,TEM,BET,XRD,TG,FT-IR and N2adsorption-desorption characterization.Furthermore,the effects of adsorbent dosage,adsorption time and adsorption temperature on the adsorption of PX on ZSM-5 were investigated.The suitable dosage of adsorbent was 1 g/L.The adsorption of PX was essentially in equilibrium in 10-30min.The removal percentage of PX decreased with the increase of adsorption temperature,while it was opposite for metal ions,which indicated that the adsorption process of PX and metal ions were exothermic and endothermic respectively.The adsorption thermodynamics of PX displayed that the adsorption behavior of PX on ZSM-5 was in accordance with the Langmuir adsorption model and belonged to monolayer adsorption and the saturated adsorption capacity reached 106.71mg/g at 25 °C.What's more,the process of adsorption was entropy subtractive process.It was showed that PX was adsorbed rapidly at the initial stage while adsorption rate began to slow with the adsorption process going on and the adsorption reached equilibrium state in 10-30min from the adsorption kinetics.In addition,the adsorption process of PX was consistent with the pseudo-second-order equation and controlled by the liquid film diffusion and the internal diffusion.Ammonium chloride was used as modifier to obtain the H-ZSM-5 adsorbent by modification.The adsorption effect of PX on H-ZSM-5 was basically unchanged compared to ZSM-5.However,the adsor:ption of Co2+ and Mrn21 was significantly decreased,which leads to the increase of adsorlption selectivity of PX to metal ions.When the dosage of modifier was 0.1 mol/L and the modification time was5 h,the selectivity coefficient of PX to Co2+ and Mn21 increased from 908.9 and 1079.4 to 6517.3and7887.6respectively.Finally,the saturated ZSM-5 was regenerated by roasting at 500 ?.The saturated adsorption capacity of PX was91.53mg/g after8times regeneration,and a good regeneration effect was obtained.