Issue 6, 2017

Epoxidation of 1-octene under harsh tail-end conditions in a flow reactor I: a comparative study of crystalline vs. amorphous catalysts

Abstract

Amorphous silica versus crystalline delaminated-zeolite catalysts consisting of grafted Ti(IV) Lewis-acid active sites were investigated from the perspective of 1-octene olefin epoxidation with ethylbenzene hydroperoxide (EBHP) as oxidant. Reactions were performed at conditions of temperature and concentrations of organic hydroperoxide and inhibitors (epoxide product and alcohol co-product) that mimic the harsh conditions found at the tail-end of the flow reactor for industrial propylene-oxide (PO) synthesis, where there is a current need to improve activity and selectivity, because of deactivation. Catalyst synthesis was performed by grafting a Ti-alkoxide precursor onto framework vacancies (“silanol nests”) of the delaminated zeolite UCB-4, as well as onto amorphous SiO2. Both catalysts were characterized by powder X-ray diffraction (PXRD), nitrogen physisorption at 77 K, and UV-visible spectroscopy before and after catalysis. Experiments at different conversions were performed, and show that crystalline Ti-UCB-4 exhibits a ∼9% higher average selectivity (73% versus 64%) and greater conversion, stability, and robustness upon increasing time on stream relative to amorphous Ti–SiO2. UV-vis spectra are discussed for fresh, spent, and spent/calcined materials and demonstrate that Ti sites in Ti-UCB-4 exist as isolated grafted complexes with four-fold coordination to the zeolite framework, whereas Ti–SiO2 consists of grafted Ti-sites on the silica surface, some of which are isolated but a dominant proportion of which are TiO2 oligomers. The observed increased stability of the crystalline catalyst under tail-end reactor conditions is attributed to the surface pockets of the crystalline material, in which Ti is grafted.

Graphical abstract: Epoxidation of 1-octene under harsh tail-end conditions in a flow reactor I: a comparative study of crystalline vs. amorphous catalysts

Supplementary files

Article information

Article type
Paper
Submitted
31 May 2017
Accepted
26 Jul 2017
First published
26 Jul 2017

React. Chem. Eng., 2017,2, 842-851

Epoxidation of 1-octene under harsh tail-end conditions in a flow reactor I: a comparative study of crystalline vs. amorphous catalysts

M. Aigner, N. A. Grosso-Giordano, A. Okrut, S. Zones and A. Katz, React. Chem. Eng., 2017, 2, 842 DOI: 10.1039/C7RE00076F

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements