Si、P、Mg改性HZSM-5提高甲苯/甲醇烷基化中对二甲苯的选择性

Si, P and Mg-modified HZSM-5 catalyst for enhancing the para-selectivity in toluene/methanol alkylation

采用浸渍法制备了Si(正硅酸乙酯)、P(磷酸、磷酸二氢铵)和Mg(六水合硝酸镁、四水合醋酸镁)复合改性的HZSM-5催化剂。采用XRD、XPS、Py-IR、NH3-TPD等方法对比研究了不同磷源、镁源改性对HZSM-5催化剂物化性质的影响,并在固定床上考察了甲苯/甲醇烷基化制对二甲苯(PX)的反应性能。结果表明,用正硅酸乙酯、磷酸二氢铵和四水合醋酸镁对HZSM-5复合改性,较好的调变了催化剂的酸性和孔结构,催化剂强酸量由0.15mmolNH3·g^-1降为0.06mmolNH3·g^-1,B/L值由1.33降为0.06,微孔分布变窄,最可几微孔孔径由0.88nm降为0.78nm,油相产物中对二甲苯的选择性从24.00%提高到87.20%。

The HZSM-5 catalysts modified by Si (Si(OC2H5)4),P (H3PO4,NH4H2PO4) and Mg (Mg(NO3)2·6H2O,Mg(CH3COO)2·4H2O) were prepared by impregnation method.Various characterizations including XRD,XPS,Py-IR and NH3-TPD were used,and the physicochemical properties of different P and Mg compounds-modified HZSM-5 catalysts were compared.The catalytic performances of the catalysts in the reaction of toluene/methanol alkylation to p-xylene were investigated in a fixed-bed reactor.The results showed that the HZSM-5 modified by Si(OC2H5)4,NH4H2PO4 and Mg(CH3COO)2·4H2O possessed appropriate acidity and pore structure.The amount of strong acid reduced from 0.15mmol NH3·g^-1 to 0.06mmol NH3·g^-1,and the B/L value decreased from 1.33 to 0.06.In addition,the micropore distribution became narrow with the most probable aperture reducing from 0.88 nm to 0.78 nm,and the selectivity of p-xylene in the oil phase increased from 24.00% to 87.20%.