Preparation And Dechlorination Performance Of Modified ZSM-5 Zeolites

In recent years,with the rapid development of society and the increasing demand for crude oil resources in many emerging economies,some artificial chlorine-containing oil production additives,such as viscosity reducing agent,corrosion inhibitor and paraffin removal agent,are added to improve the amount of oil recovery,resulting in the content of organic chloride in oil products seriously exceeding the standard.In the process of crude oil processing,organic chloride reacts with hydrogen to form hydrogen chloride,which intensifies the corrosion of the device and causes irreversible poisoning of the catalyst,the generated ammonium salt crystals will block the pipeline and seriously affect the normal operation of the process equipment.Therefore,it is of great significance to study the removal technology of organic chloride in oil for the safe and stable operation of oil refining enterprises.In this paper,the most promising direct adsorption dechlorination method was used to prepare a series of new adsorbent dechlorination agents by metal modification and alkali modification respectively.Combined with the series characterization and the evaluation results of static adsorption experiments,the structure-activity relationship was studied.The specific research contents are as follows:（1）A series of candidate adsorbents were screened on the basis of shape selection principle,and the optimal adsorbent ZSM-5 zeolite was selected as the research object,and its metal modification was carried out.The effects of different modification methods（equal volume impregnation method,ion exchange method）and different metals（silver,magnesium,cerium,iron）on the dechlorination performance of ZSM-5 zeolites were investigated.The experimental results show that the magnesium ion modified ZSM-5zeolite has the best dechlorination effect at an adsorption temperature of 60℃and an adsorption time of 6 h,with a dechlorination rate of 77.31%.The optimal modification conditions for the adsorbent are:impregnation temperature of 40℃,impregnation time of 4 h,metal loading capacity of 1 wt%,and silicon aluminum ratio of 27.The dechlorination agents before and after modification were characterized using XRD,SEM,TEM,low-temperature N₂ adsorption and desorption,NH₃-TPD,Py-IR,and other methods.（2）Taking Mg/ZSM-5 dechlorination agent with the best dechlorination effect as the object of investigation,the adsorption equilibrium and adsorption thermodynamics of its adsorption and removal of 1,2-dichloroethane from model oil were investigated.Firstly,the factors affecting the adsorption and dechlorination of the dechlorination agent（adsorption temperature,adsorption time,agent oil ratio,initial organic chlorine content）were investigated.The experimental results showed that at an adsorption temperature of 333.15 K,the adsorption equilibrium of 1,2-dichloroethane on Mg/ZSM-5 dechlorination agent could be achieved within 6 h,and the optimal agent oil ratio was1:40.Secondly,three adsorption isotherms,Langmuir,Freundlich,and Temkin,were selected to simulate the adsorption process of 1,2-dichloroethane by Mg/ZSM-5dechlorinating agent.It was found that Langmuir adsorption isotherms can better describe the adsorption process of 1,2-dichloroethane by Mg/ZSM-5.In the range of303.15 to 333.15 K,the determination coefficient R² is close to 1,with an ideal degree of fitting and high data reliability.Finally,the thermodynamic parameters of the adsorption process were calculated using Van’s Hoffs equation,It is calculated that the adsorption of 1,2-dichloroethane by Mg/ZSM-5 dechlorination agent,the average value ofΔH⁰ is 2.533 k J/mol,the average values ofΔS⁰ is 8.854 J/（mol·K）,the values ofΔG⁰are all negative,and the thermodynamic analysis shows that the process of removing 1,2-dichloroethane with Mg/ZSM-5 adsorbent is a spontaneous and endothermic physical adsorption reaction.（3）In order to provide HZSM-5 zeolites with better adsorption performance for removing macromolecular organic chlorides,subsequent alkali modification treatment was carried out to prepare an adsorbent with excellent dechlorination effect.The effects of different alkaline solutions（sodium carbonate,calcium carbonate,sodium carbonate）and different solution concentrations were investigated.It was found that when the concentration of sodium carbonate solution was 0.1 mol/L,and the ratio of ZSM-5zeolite mass（g）to sodium carbonate solution volume（m L）was 1:15,the HZSM-5/Na₂CO₃ adsorbent prepared had the best removal effect on 5-chloro-2-methylaniline,with a dechlorination rate of 72.85%.Then,XRD,SEM,low-temperature N₂ adsorption and desorption,and NH₃-TPD were used to characterize the prepared adsorbent,and the effects of changes in the pore structure and acid properties of the adsorbent before and after alkali modification on its dechlorination effect were analyzed.Finally,by fitting the adsorption process of HZSM-5/Na₂CO₃ adsorbent with a kinetic model,it was found that the pseudo second-order kinetic adsorption model could better describe the adsorption behavior of 5-chloro-2-methylaniline on the adsorbent,and the average adsorption activation energy was calculated to be 14.49 k J/mol,indicating that the adsorption process involves both physical adsorption and chemical adsorption.