离子改性Y分子筛吸附分离1,1,1,2-四氟乙烷/1,1-二氟-2-氯乙烯

Adsorptive separation of 1,1,1,2-tetrafluoroethane/1,1-difluoro-2-chloroethylene over ion-exchanged Y zeolites

用CaCl2、La(NO3)3和Ce(NO3)3溶液对NaY分子筛进行离子改性制备出CaY、LaY和CeY分子筛。将其及NaY为吸附剂,利用动态吸附法评价其吸附分离1,1,1,2-四氟乙烷(HFC-134a)产品中微量1,1-二氟-2-氯乙烯(HCFC-1122)的性能。同时采用X射线衍射(XRD)、吡啶红外(FTIR)和氨-程序升温脱附(NH3-TPD)等手段对新鲜及再生后的吸附剂进行结构和表面性质表征。结果表明:CaY、LaY与CeY分子筛上的Brφnsted酸中心可与HCFC-1122形成π-吸附配合物,从而将吸附流出气中HCFC-1122的残余率降低至1.0%以下;Brφnsted酸强度越高,π-吸附配合物越容易形成,最低吸附温度越低(CeY<LaY<CaY)。220℃下穿透吸附容量随CaY<LaY<CeY增加,归因于较少的强Brφnsted酸和弱Lewis酸数量有利于HCFC-1122的π-吸附配合物引发程度较低的聚合反应。吸附剂的热脱附再生性能不佳与其表面酸中心覆盖物难以脱除有关。

Using CaCl2, La（NO3）3 and Ce（NO3） 3 solutions, NaY was ion-exchanged to prepare CaY, LaY and CeY zeolites. Adsorptive removal of trace amount of 1,1-difluoro-2-chloroethylene （HCFC-1122） from 1,1,1,2-tetrafluoroethane product over NaY, CaY, LaY, and CeY zeolites were investigated. The structure and surface properties of fresh and regenerated adsorbents were characterized by X-ray diffraction, pyridine infrared spectra techniques and temperature programmed desorption of ammonia. Results show that the residual ratio of HCFC-1122 impurity in the eluate can be decreased to 1.0% over CaY,LaY and CeY zeolitesvia the formation ofπ-adsorption complexes between HCFC-1122 and Br？nsted acid sites. The increase of intensity of Br？nsted acid favors the formation ofπ-adsorption complexes, consequently decreasing adsorption temperature for complete removal of HCFC-1122 （CeY 〈 LaY 〈 CaY）. Breakthrough adsorption capacity of HCFC-1122 at 220℃ increases in the order of CaY 〈 LaY 〈 CeY, since lower density of strong Br nsted and weak Lewis acid sites are favorable to lower degree polymerization initiated byπ-adsorption complexes. The thermal regeneration of adsorbents is unsatisfactory, attributed to hardly removal of contaminant on the acid sites of saturated adsorbents during the thermal regeneration process.