液相硅沉积改性HZSM-5分子筛的择形吸附分离性能研究

Effect of silica modification on the shape selective adsorption performance of HZSM-5

以聚硅氧烷作为改性剂,通过液相硅沉积表面修饰对HZSM-5分子筛吸附剂进行了择形功能化改性,采用X射线衍射(XRD)、NH3-TPD、比表面积与孔径分析和热重分析(TGA)等手段对改性前后的吸附剂进行了表征。分别采用液相吸附法和气相吸附法研究了ZSM-5择形分子筛对于对二甲苯(pX)和间二甲苯(mX)混合物的择形吸附分离效果,考察了硅沉积改性程度、液相吸附及气相吸附工艺条件对硅沉积修饰分子筛Si/ZSM-5择形吸附分离性能的影响。研究结果表明,分子筛吸附剂中介孔体积随着硅沉积改性次数增加而减少,而微孔体积改变较小,但4次硅改性后的分子筛吸附剂的晶体结构未发生明显变化。同时,随着硅沉积改性次数的增加,分子筛吸附剂的吸附量减小,而吸附剂的择形吸附分离系数βpX/mX增大;另一方面,气相热解吸得到的pX/mX选择性高于液相解吸法,并且二氯甲烷作为液相解析剂的pX/mX择形选择性高于甲苯和环己烷解析剂。吸附重量动态分析测试结果表明,Si/ZSM-5(0)、Si/ZSM-5(2)和Si/ZSM-5(4)的平均吸附容量分别为102.1,82.12和71.84mg/g,pX&mX二甲苯混合物的扩散速率随着硅沉积改性程度的增加而明显减小。

The HZSM-5molecular sieve adsorbent was modified using polysiloxane as modifier and were characterized by means of X-ray diffraction(XRD),NH3-TPD,Surface Area and pore size analysis and thermogravimetric analysis(TGA).The effects of silicon deposition degree,liquid phase adsorption and gas phase adsorption process conditions on the shape-selective adsorption performance were investigated using liquid phase adsorption and gas phase adsorption.It was concluded that with the increase of deposited silica,the mesopore volune reduced,the micropore volume hardly changed and the crystal structure of adsorbents have not changed after the fourth deposition.Meanwhile the average adsorption capacities decrease while the selectivy of p-xylene increased;on the other hand,the p-xylene selectivity of the gas phase thermal desorption was higher than that of liquid phase desorption,and the shape selectivity of dichloromethane as desorption solution is higher than that of tolune and cyclohexane.Adsorption gravimetric test results show that the average adsorption capacity of Si/ZSM-5(0),Si/ZSM-5(2)and Si/ZSM-5(4)were 102.1,82.12 and 71.84mg/g and the diffusion rate of xylene mixture decreases with the increase of deposited silica.