Epoxidation Of1-butene Over Titanium Silicalite-1and Catalyst Deactivation

A nano-sized titanium silicalite-1(TS-1), with a crystal size of200run, and a small-crystal TS-1, with a crystal size of600nm, were synthesized intetrapropyl ammonium hydroxide and a tetrapropyl ammonium bromide hydrothermal systems, respectively. The orthogonal experiment of1-butene epoxidation in a batch reactor was introduced to investigate the influences of temperature, catalyst loading and reaction time on the catalytic performance of nano-sized TS-1. The two different sized TS-1were extruded, and the obtained extrudates were added to a fixed-bed reactor to evaluate their catalytic performance in1-butene epoxidation. The main conclusions were as follows:1. The orthogonal experiment demonstrated that the H2O2concentration has the most significant effect on the conversion of H2O2, reaction time has a minimal effect on H2O2conversion, and the reaction temperature strongly influences the selectivity of BO.2. Treatment with TPAOH can improve the catalytic activity and stability of TS-1significantly. The mechanism of improvement differs between the two samples. For the small-crystal TS-1, the primary impact of TPAOH treatment was to generate mesopores inside the crystals that improved the diffusion rate of reactants and products. For the nano-sized TS-1, the crystallization of amorphous SiO2on the external surface unblocked the channels as well as its smaller crystal size. By comparing the catalytic performances over the two TS-1samples with different crystal sizes, we found that both samples showed a high activity at a low weight hourly space velocity (WHSV) of hydrogen peroxide. However, the nano-sized TS-1exhibited a higher activity and a longer lifetime than the small-crystal TS-1at high H2O2WHSV.3. The catalytic performance of TS-1in mixed solvents increased with the increase of permittivity of aprotic solvents. When a mixture of acetonitrile/methanol (3/1, v/v) was adopted as the solvent, the conversion of H2O2remained above80%after253h of reaction. The blocking of channels by oligomers was considered as the reason for the deactivation of nano-sized TS-1during1-butene epoxidation.