Synthesis of Low Cost Titanium Silicalite-1 Zeolite for Highly Efficient Propylene Epoxidation

Abstract

Developing an effective and low-cost system to synthesize titanium silicalite-1 (TS-1) zeolite is desirable for a range of industrial applications. To date, the poor catalytic activity of the synthesized zeolite due to the low amount of framework titanium and large crystal size is the main obstacle limiting the widespread application of this material. Moreover, a large amount of wastewater is often produced by the existing synthesis process. Herein, a green and sustainable route for synthesizing small-crystal TS-1 with a high fraction of framework Ti was demonstrated via a seed-assisted method using a tetrapropylammonium bromide (TPABr)-ethanolamine hydrothermal system. The influence of the synthesis conditions on the physicochemical properties and catalytic activities of TS-1 was investigated. With the assistance of nanosized S-1 seeds, the incorporation of Ti into the framework of TS-1 was promoted, and the crystallization rate was effectively accelerated. After alkaline etching, the obtained hierarchical TS-1 had higher catalytic activity towards propylene epoxidation with an extremely high turnover frequency of 1,650 h−1. Furthermore, the mother liquid during the hydrothermal reaction could be reused for the next synthesis procedure. Consequently, utilization ratios of both ethanolamine and TPABr exceeding 95% were achieved by recycling the mother liquid. This low-cost approach for reducing wastewater could be easily scaled up to provide a promising synthesis method for the industrial production of TS-1 and other topological zeolites.

Review and perspectives on TS-1 catalyzed propylene epoxidation

“… 228 Some recent studies showed that the graded TS-1 obtained after alkali etching has higher catalytic activity for propylene epoxidation, and the turnover frequency is as high as 1650h −1 . 256 …”

Constructing Highly Efficient Ti Sites of TS-1 for Alkene Epoxidation

“…Liu et al synthesized TS-1 using TiCl 3 , TBOT, and Ti(SO 4 ) 2 as titanium sources, TPABr as the template agent, ethanolamine as the alkaline source, and vapor-phase silica as the silicon source. 70 The mixed sol gel prepared with TBOT as the titanium source, had the relative crystallinity and framework titanium content of the TS-1 due to its higher alkalinity. The TS-1 synthesized with TBOT as the titanium source showed the highest epoxidation selectivity for propylene epoxidation.…”

“…Therefore, in this system, using Ti­(SO 4 ) 2 as the titanium source can restrain the formation of nonframework titanium species, thus increasing the content of framework titanium species and further exhibiting the highest epoxidation yield (99.04%) in chloropropene epoxidation. Liu et al synthesized TS-1 using TiCl 3 , TBOT, and Ti­(SO 4 ) 2 as titanium sources, TPABr as the template agent, ethanolamine as the alkaline source, and vapor-phase silica as the silicon source . The mixed sol gel prepared with TBOT as the titanium source, had the relative crystallinity and framework titanium content of the TS-1 due to its higher alkalinity.…”