硼对HZSM-5分子筛酸性和择形性的影响

用不同含量的硼对HZSM-5分子筛进行改性,研究硼对HZSM-5酸性和对甲苯甲醇烷基化制对二甲苯反应的影响.通过XRD, SEM, N_2物理吸脱附, NH_3-TPD和Py-IR对催化剂进行表征,结果表明硼改性的催化剂仅有弱酸位,随着硼含量增加,弱酸位酸量和B/L增加,并且硼改性后在HZSM-5分子筛中产生新的弱B酸位.弱酸位有利于抑制二甲苯异构化反应和二甲苯进一步烷基化反应,提高对二甲苯选择性.实验结果表明随着弱酸酸量的增加,对二甲苯选择性增加,甲苯转化率减小.与HZSM-5相比, 1.7%B/HZSM-5催化剂弱酸酸量增加了226%,因此在1.7%B/HZSM-5催化剂上获得98.57%的对二甲苯选择性.

The Effect of Boron on HZSM-5 Zeolite Acidity and Shape Selectivity

The effect of boron on acidity of HZSM-5 and the alkylation of toluene with methanol into p-xylene was studied. The catalyst was characterized by XRD, SEM, N2 adsorption/desorption isotherms, NH3-TPD and Py-IR. The results of characterization indicate that boron-modified catalyst had almost no strong acid but more than weak acid amount of HZSM-5. As the increase of boron content, both weak acidity and B/L were increased, and new weak acidity were formed on HZSM-5. Xylene isomerization reaction and xylene further methylation were inhibited over weak acidity. Experimental data show that with the increase of weak acidity, the selective of p-xylene generally increase and toluene conversion decrease. As compared with HZSM-5, the amount of weak acidity for 1.7B%/HZSM-5 was increased 226%. Thus, 1.7%B/HZSM-5 catalyst showed the selectivity of p-xylene was 98.57%.