酸脱铝改性的HZSM-12分子筛催化合成2,6-二甲基萘的研究

Study on catalytic synthesis of 2,6-dimethylnaphthalene by acid dealuminated HZSM-12 zeolite

分别用盐酸和柠檬酸对HZSM-12分子筛进行脱铝改性。通过XRD、XRF、N2物理吸附、TP的方法对脱铝改性前后HZSM-12分子筛的结构及酸性进行表征,并研究了脱铝改性HZSM-12分子筛催化合成2,6-二甲基萘反应性能的影响规律。结果表明,盐酸脱铝的同时可以脱除分子筛的强酸中心和弱酸中心,10 mol/L的HCl脱铝还会伴有脱硅现象发生,导致微孔体积减少。而柠檬酸则优先脱出强酸中心,对于弱酸中心影响不显著。脱铝改性的HZSM-12分子筛强酸中心数量减少,对萘和甲醇烷基化反应的催化活性有所降低,但是烷基化产物中2,6-DMN/2,7-DMN比显著提高,而且改性后的HZSM-12分子筛表现出更强的抗失活能力。

In this paper,the dealumination of HZSM-12 zeolite was carried out using aqueous solutions of hydrochloric acid and critic acid.The structure and acid property of HZSM-12 before and after dealumination were characterized by XRD,XRF,N2 sorption and TPD of ammonia,and the influence of the catalytic performance of 2,6-dimethylnaphthalene dealuminated on the synthesis of 2,6-dimethylnaphthalene(2,6-DMN) was also studied.The results showed that the dealumination of HZSM-12 zeolite accompanied by the removal of its strong acid sites and weak acid sites by using hydrochloric acid.Dissolution of silica units from the framework was occured along with dealumination under 10 mol/L of hydrochloric acid,leading to the decrease of micropores volume.In contrast,the critic acid prefered to eliminate the strong acid sites compared with weak acid sites.The dealuminated HZSM-12 zeolite showed lower activity for methylation of naphthalene and methanol due to the lower amount of acid sites,however,the ratio of 2,6-DMN and 2,7-DMN was greatly enhanced.Simultaneously,its deactivation capability was higher.