磷水热改性HZSM-5分子筛对二甲醚转化合成异构烷烃的催化性能

采用磷水热法和磷浸渍法对HZSM-5分子筛进行改性,以X射线衍射、N_2吸附-脱附、扫描电子显微镜、吡啶吸附傅里叶变换红外光谱、热重分析和原子光谱等表征技术,研究了不同磷改性方法对HZSM-5分子筛晶型结构和酸性的影响;并在固定床反应器中评价了磷改性HZSM-5分子筛对二甲醚合成异构烷烃的催化性能。实验结果表明,在水热气氛下磷与HZSM-5分子筛骨架结构中的B酸中心生成H_2PO_4~-,且不会影响分子筛的孔道尺寸,明显不同于磷浸渍改性的HZSM-5分子筛。以磷水热改性的HZSM-5分子筛为催化剂合成汽油烃类,汽油中异构烷烃选择性达到50%左右。

Catalytic Performance of Steam-Phosphorus Modified HZSM-5 Zeolites in Conversion of Dimethyl Ether to iso-Paraffins

A series of HZSM-5 zeolites modified by steam-phosphorus process or by impregnation in phosphorus acid solution were prepared. The effects of phosphorus on structure and acidity of the modifed zeolites were studied by XRD, N_2 adsorption-desorption, SEM, TG, FTIR spectrum of adsorbed pyridine and atomic spectrum. The catalytic performance of the modified zeolite catalysts in conversion of dimethyl ether to iso-paraffins was evaluated in a continuous flow fixed-bed reactor. The results showed that in steam-heat atmosphere the presence of phosphorus rendered B acid sites on HZSM-5 zeolite framework transforming into H_2PO_4~- without changing the pore size of the zeolites. The situation was obviously different from the HZSM-5 zeolite modified by phosphorus acid impregnation. In the former case selectivity to iso-paraffins in gasoline reached to about 50%.