氟硅酸铵改性的HZSM-12分子筛催化合成2,6-二甲基萘

SHAPE-SELECTIVE SYNTHESIS OF 2,6-DIMETHYLNAPHTHALENE OVER (NH_4)_2SiF_6-MODIFIED HZSM-12 ZEOLITE

采用同晶置换方法制备了系列氟硅酸铵改性的HZSM-12分子筛。对改性前后的分子筛进行了XRD、NH3-TPD、Py-IR、N2物理吸附等表征,并在固定床微型反应实验装置上考察了它们对萘与甲醇烷基化反应合成2,6-二甲基萘的催化性能。结果表明,氟硅酸铵改性提高了HZSM-12分子筛的结晶度,在分子筛晶格中产生了二次介孔,增大了分子筛的介孔孔容和总孔容,有效地改变了分子筛的酸量及酸强度分布。经适宜浓度的氟硅酸铵水溶液改性后,HZSM-12分子筛对萘与甲醇烷基化反应的催化性能得到明显改善,在保持良好催化活性的基础上有效地提高了2,6-DMN的选择性及2,6-DMN/2,7-DMN摩尔比,反应6 h后2,6-DMN的选择性和2,6-DMN/2,7-DMN摩尔比分别为26%和1.93。

A series of （NH4）2SiF6-modified HZSM-12 catalysts were prepared by isomorphous substitution, and characterized by X-ray diffraction, temperature-programmed desorption of ammonia, FT-IR spectroscopy of adsorbed pyridine, N2-adsorption. Their catalytic performance for synthesis of 2,6-dimethylnaphthalene in a fixed-bed reactor by methylation of naphthalene with methanol was also investigated. The results showed that through （NH4）2SiF6-modified the crystallinity of HZSM-12 zeolite was increased, mesopore volume and total pore volume were enlarged due to the presence of secondary mesoporous, total acidity and distribution of acid strength were effectively altered. The catalytic performance of HZSM-12 for the methylation of naphthalene with methanol was improved by modification of （NH4）2SiF6 with optimum concentration. An obvious increase of selectivity to 2,6-DMN and 2,6-DMN/2,7-DMN molar ratio were observed on the premise that catalytic activity of （NH4）2SiF6-modified HZSM-12 was similar to that of HZSM-12. After 6 h methylation of naphthalene with methanol, 2,6-DMN selectivity of 26% and 2,6-DMN/2,7-DMN molar ratio of 1.93 were obtained.