Abstract
In the paper, mesopores and macropores are introduced inside the crystals of micrometer microporous titanium silicate-1 (TS-1) to solve the problem of active site coverage and mass transfer during extrusion. Hierarchically porous titanium silicalite-1 (HPTS-1) was acquired by treating micrometer microporous TS-1 with TPABr and ethanolamine. Extruded HPTS-1 maintained greatly superior catalytic performance and possessed high mechanical strength. Characterization results showed that extruded HPTS-1 possessed macroporous, mesoporous structure inside the crystals. These abundant pores are not only beneficial for diffusion reactants, but also make Ti-peroxo species (η2), active oxidation sites in TS-1/H2O2 system become much more reactive. The formula of extruded HPTS-1 was optimized using an orthogonal experiment. The maximum strength of extruded HPTS-1 was up to 200 N/cm, the highest yield of propylene oxide was 92.5% and the specific rate was up to 41.9%. The research provides a scientific basis for producing extruded catalysts with excellent catalytic performance and high mechanical strength in industrial applications.
Highlights
Propylene oxide (PO) is a crucial intermediate of the chemical industry for producing polyurethane plastics, polyether polyols, unsaturated resins, surfactants and other products [1,2,3,4,5,6,7,8]
Hierarchically porous titanium silicalite-1 (HPTS-1) gave coffin morphology because the etching is carried out and the phenomenon Catalysts 2021, 11, x FOR PEER REVIEoWf dissolution and recrystallization occurs on its surface during the alkaline3 torfe1a0 tment of titanium silicate-1 (TS-1)
Compared with TS-1, the micropore area and volume of HPTS-1 obviously decreased, but the external area, total pore and mesopore volume increased markedly. This is due to the large amounts of mesopores and macropores inside the crystals produced in the modification of TS-1
Summary
Propylene oxide (PO) is a crucial intermediate of the chemical industry for producing polyurethane plastics, polyether polyols, unsaturated resins, surfactants and other products [1,2,3,4,5,6,7,8]. Large amounts of binder such as silica sol are often added into the extrusion process to make the catalysts possess excellent mechanical strength. Wu et al studied extrusion of hierarchically porous ZSM-5 and the influence of several process factors on the strength and textural properties [33] Zuo and his co-workers treated TS-1 extrudates using TPAOH to introduce the mesopore, and the final extrudates reached the strength of 150 N/cm and gained good catalytic performance in propylene epoxidation [34]. An orthogonal experiment was designed to examine the effect of some factors such as binder (silica sol), forming-pore agent (sesbania powder), water-retaining agent (polyvinyl alcohol, abbreviated as PVA) and lubricant (starch) on the strength of extruded HPTS-1 catalysts and the yield of PO
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