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

摘要

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Brønsted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；Brønsted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Brønsted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 Brønsted acid sites. The increase of intensity of Brønsted 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 Brønsted 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.