Synthesis of mesoporous titanosilicates from industrial by-product hexafluosilicic acid and application for catalytic cyclohexene epoxidation

doi:10.11949/j.issn.0438-1157.20160187

Abstract

Abstract:

The hexafluosilicic acid, a by-product in phosphate fertilizer industry, was used as the raw material for hydrothermal synthesis of mesoporous titanosilicates with cetyltrimethylammonium bromide (CTAB) as the cationic surfactant and ammonia as neutralization agent. The influence of synthesis conditions including hydrothermal time, the ratio of CTAB to silica, Si/Ti ratio, and surfactant removal methods on the structures and properties of mesoporous titanosilicates were investigated by characterization of the resulting product with techniques of X-ray diffraction (XRD), nitrogen adsorption/desorption, scanning electron microscopy (SEM), solid UV light scattering. At the optimized synthesis condition of the ratio of SiO₂:CTAB:Ti(OC₄H₉)4:NH₃:H₂O=1:1.50:0.03:10:150 and the hydrothermal time of 5 h, mesoporous titanosilicate had specific surface area of 1116 m²·g^-1 and porosity of 0.79 cm³·g^-1. When used as catalyst for cyclohexene epoxidation. this mesoporous titanosilicate showed good catalytic activities with cyclohexene conversion of 68.10%, cyclohexene epoxide selectivity of 96.60%, and turnover frequencies of Ti active sites of 99.5 h^-1. This new synthesis technique will greatly improve profit of phosphate fertilizer industry by utilizing the by-product hexafluosilicic acid for the production of value-added mesoporous titanosilicate.

Key words: hexafluosilicic acid, mesoporous, molecular sieves, hydrothermal, catalysis

摘要：

利用磷肥工业副产的氟硅酸为原料，在十六烷基三甲基溴化铵（CTAB）溶液中与氨水和钛酸四丁酯（TBOT）反应，水热陈化制取钛硅介孔分子筛，通过改变水热时间、CTAB的加入量、硅钛比和模板剂的脱除方法研究实验条件对钛硅介孔分子筛的结构和性能的影响，采用氮气吸脱附、扫描电镜、透射电镜和固体紫外漫反射对样品进行表征。结果表明，SiO₂:CTAB:TBOT:NH₃:H₂O的摩尔比为1:1.50:0.03:10:150，水浴时间为5 h时，所得样品的比表面积可达1116 m²·g^-1，介孔体积为0.79 cm³·g^-1。合成的钛硅介孔分子筛作为催化剂应用于环己烯环氧化反应，环己烯的转化率可达68.10%，环氧环己烷产物选择性为96.60%，Ti活性位的转化频率达到99.5 h^-1。该方法可以提高磷肥副产低浓度氟硅酸的附加值，降低钛硅介孔分子筛催化剂的生产成本。

关键词: 氟硅酸, 介孔, 分子筛, 水热, 催化

CLC Number:

TQ028.8

JIN Fang, LIU Tieliang, WANG Xianqiao, WU Yuanxin. Synthesis of mesoporous titanosilicates from industrial by-product hexafluosilicic acid and application for catalytic cyclohexene epoxidation[J]. CIESC Journal, 2016, 67(10): 4176-4186.

金放, 刘铁良, 王先桥, 吴元欣. 工业氟硅酸合成钛硅介孔分子筛催化环己烯环氧化[J]. 化工学报, 2016, 67(10): 4176-4186.

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