Deactivation and regeneration of TS-1/SiO2 catalyst for epoxidation of propylene with hydrogen peroxide in a fixed-bed reactor

TS-1/SiO2 catalyst for the epoxidation of propylene with hydrogen peroxide in a fixed-bed reactor has been investigated. The catalyst activity decreases gradually with the online reaction time, but the selectivity of propylene epoxide is kept at about 93%. The fresh, deactivated and regenerated catalysts were characterized with X-ray diffraction, Fourier transform infrared spectro- scopy, ultra-violet-visible diffuse reflectance, Brunner- Emmett-TeUer method and thermogravimetric analysis, and the deactivated catalyst was regenerated with H2O2/ methanol solution. Compared with the fresh catalyst, both the framework structure and the content of titanium in the framework of the deactivated and regenerated TS-1/SiO2 catalysts were not changed. The major reason of the catalyst deactivation was the blockage of the channels of the catalyst by bulky organic by-products, which covered the active centers of titanium in TS-1. The deposited materials on the deactivated TS-1/SiO2 catalyst could be removed by treatment with hydrogen peroxide/methanol solution or pure methanol; the higher the treatment temperature and the higher the concentration of H2O2 in methanol, the higher the extent of the regeneration. The regeneration treatment did not influence the product selectivity in the propylene epoxidation.

Highly Effective Propylene Epoxidation over TS-1/SiO_(2) Hydrothermally Treated

The propylene epoxidation over TS-1/SiO2 catalyst hydrothermally treated was investigated. It was found by EPR characterization that two types of Ti (IV)-superoxide radicals, A (gz=2.0271; gy=2.0074; gx=2.0010) and B (gz=2.0247; gy= 2.0074; gx= 2.0010), were observed for TS-1/SiO2. The superoxo species A converted to B after TS-1/SiO2 catalyst was hydrothermally treated. The results show that over TS-1/SiO2 catalyst hydrothermally treated at 170℃, about 95% conversion of H2O2 with above 94% PO selectivity is obtained during continuous running for 300 h under the conditions of reaction temperature 45℃, 0.5 h-1WHSV of propylene.

Post-treatment of TS-1 with Mixtures of TPAOH and Ammonium Salts and the Catalytic Properties in Propylene Epoxidation

TS-1/SiO_2 extrudate was post-treated with mixed solution of tetrapropyl ammonium hydroxide(TPAOH)and various ammonium salts solution(NH_4F,(NH_4)_3PO_4,(NH_4)_2CO_3,(NH_4)_2SO_4,NH_4CH_3CO_2,NH_4NO_3,NH_4Cl and(NH_4)_2TiF_6).The obtained hierarchical TS-1 catalysts were characterized by many techniques and tested for propylene epoxidation using hydrogen peroxide as an oxidant in a fixed-bed reactor.It was shown that the physicochemical and catalytic properties of the treated TS-1/SiO_2 extrudate depended on the types of ammonium salts added.Compared to the treatment with TPAOH alone,the treatment with a mixed solution of TPAOH and some ammonium salts can greatly improve the catalytic properties of the treated TS-1/SiO_2 extrudate.Some of these ammonium salts were favorable for the incorporation of titanium in the framework,and the beneficial effect depended on the types of ammonium salt.TS-1/SiO_2 extrudate treated with a mixed solution of TPAOH and(NH_4)_3PO_4 exhibited the highest catalyst stability in propylene epoxidation.Such catalytic property can be correlated to high crystallinity,more framework titanium,large specific surface area and large external surface area.

Effects of the Water in Mixed Solvent on the Epoxidation Reaction of Propylene with TS-1 Catalyst

The epoxidation reaction of propylene and hydrogen peroxide with zeolite catalyst containing titaniumsilicalite (TS-1)has been studied, and the reaction in the mixed solvent of water/methanol has been discussed. It is shown that the selective of epoxidation propylene decreases while the selective of propylene glycol increases, when the water content increases in the mixed solvent of methanol/water.

钛硅沸石催化C_3H_6和H_2O_2合成丙二醇单甲醚反应条件的研究

在加压固定床反应器上 ,将钛硅沸石和 Si O2 混合制备的 TS-1 /Si O2 催化剂 ,用于 H2 O2 、 C3H6 及甲醇反应制备丙二醇单甲醚 (MME)。考察了反应温度、操作压力、原料中 H2 O2 浓度、H2 O2 与 C3H6 的摩尔比、进料总空速、空塔线速等反应参数对该催化剂催化性能的影响 ,找到了较佳的操作条件。实验结果表明 ,当反应温度 60℃ ,操作压力 3 .0 MPa,H2 O2 浓度 0 .85mol/l,H2 O2 与 C3H6 的摩尔比 1∶ 4 .1 7,液相进料总质量空速 3 .3 6h- 1 ,空塔线速 4 3 .74× 1 0 - 2 m/h时 ,MME的选择性达到 91 .3 5% ,H2 O2 有效利用率达 94 .3 7% ,H2 O2 转化率达 98.2 6% ,C3H6 实际转化率达 2 2 .2 4 % (此时 C3H6 理论转化率为 2 3 .98% )

钛硅催化剂的酸碱改性处理

在甲醇 -水体系中进行丙烯环氧化反应时 ,丙烯与双氧水在骨架钛上生成环氧丙烷 .TS-1中含有的微量酸中心能够导致环氧丙烷与溶剂反应生成丙二醇、1 -甲氧基 -2 -丙醇和 2 -甲氧基 -1 -丙醇 ;还能促进双氧水的分解 ,降低双氧水的有效利用率 .这种酸中心主要来自于TS-1中硅羟基、配位不饱和的 Ti4+产生的 L酸中心与微量铝产生的 B酸中心 .考察了 TS-1催化的丙烯与双氧水环氧化过程中的酸碱效应 ,以及微量添加物的作用 .结果表明 :添加微量钠盐 ( Na2 CO3 或 Na2 SO4)或 NH4OH可以明显提高环氧丙烷选择性 .采用氨水作为微量添加物能够明显提高催化剂的稳定性 .酸处理无法脱除催化剂中微量铝 ,反而引入了部分酸中心 。