In this work, a highly efficient synthetic route for TS-1 zeolites has been developed in a flow system, a greener preparation method is further proposed by recycling the mother liquid. The prepared TS-1 by recycling the mother liquid contained no extraframework Ti species with uniform size and high crystallization as well as excellent catalytic performance for cyclohexanone ammoximation in the flow system containing a tubular reactor and an autoclave. As the fast heating rate of flow chemical process, the crystallization time was shortened to 20 min at 175 °C. Due to the short crystallization, hardly TPAOH participated in the Hofmann elimination reaction except for the structure-directing usage. The full recycle of remained TPAOH in the mother liquid was reused after being concentrated via vacuum distillation, and this novel recycling technology could have 98.5% TPAOH utilization as well as 98.3% TS-1 yield. These results indicate that the flow chemical process plays a key role in the new greener approach for the TS-1 synthesis.
Researches on zeolite silicalite-1 have focused mainly on improving its performance, with little attention paid on green and economic synthesis. Herein, a novel route for green synthesis of pure silicalite-1 from the recycled mother liquor has been developed. This route starts from the hydrothermal reaction of natural quartz with NaOH to form a sodium silicate solution, which is then transformed into a silicic acid (H 2 SiO 3 ) gel by hydrochloric acid titration. Then the solid silicic acid (H 2 SiO 3 ) gel and fumed silica (SiO 2 ) are mixed with water under stirring to form a highly active slurry, which can be hydrothermally “dissolved” in a dilute NaOH aqueous solution. Using this slurry with a high SiO 2 /Na 2 O molar ratio of 5 : 1 as the silica source as well as tetrapropylammonium bromide (TPABr) as the organic template, MFI-type pure silicalite-1 has been successfully synthesized. After each synthesis, the mother liquor of centrifuged supernatant was recovered and recycled. The silica source and organic template were added to the recycled mother liquors for the synthesis of pure silicalite-1. The minimum TPABr/SiO 2 molar ratio needed to synthesize pure silicalite-1 in the initial run is 0.04 : 1. In comparison, only half the amount of the organic template is needed in subsequent runs with the recovered mother liquors. Through recycling, all reactants in the mother liquors were ultimately utilized without any waste, leading to not only effectively reducing the cost of silicalite-1 synthesis but also minimizing its environmental impact.
危险品化学品经营许可证（带存储）