Date of Award

Fall 2021

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

John R. Regalbuto

Second Advisor

John R. Monnier

Abstract

First synthesized in 1859 by French chemist Charles-Adolphe Wurtz, ethylene oxide (EO) is produced from the direct epoxidation of ethylene and molecular oxygen over a low surface area α-Al₂O₃ supported silver (Ag) catalyst [1-6]. With a production capacity over 35 Mt/year, EO is the largest chemical by volume synthesized from a heterogeneously catalyzed process and is used in the production of ethylene glycol, ethoxylates, and ethanolamines [6, 7]. State-of-the-art catalyst formulations contain high loadings of Ag, typically 12-30wt%, required to recover activity in the presence of promoter elements which increase EO selectivity from ~75% for unsupported Ag to 80% for Cs-Ag/α-Al₂O₃ and 82% for Cs-Re-Ag/α-Al₂O₃ but reduce the number Ag-O sites available for olefin epoxidation. In addition to Cs and Re, current generation high selectivity catalysts also contain co-promoter high valent transition metal oxy anions and Group I light elements such as Li and K [8, 9] that when combined with ppm levels of a halide moderator, typically chloroethane (EtCl) or vinyl chloride (VCL), added during operation, EO initial selectivity can reach 92% at 1.5 – 2.5 mole% EO in the product [10].

In Chapter 1 the structure sensitivity of Ag for EO formation is studied using a novel synthesis technique, electroless deposition (ED), to vary particle size distributions for a series of Ag catalysts supported on an α-Al₂O₃ used for industrial epoxidation reactions. In this work, catalytic evaluation is combined with ex-situ microcopy and hydrogen titration collected before and after reaction to show that particlesFurthermore, prescreening of the alumina indicates the absence of acid catalyzed isomerization of EO suggesting that the observed structure sensitive performance is intrinsic to direct epoxidation on the Ag surface and not dependent on background combustion from the support. In Chapter 2, the hydrogen titration of unpromoted Ag is expanded to include combinations of Cs, Re, Mo, S, and W which complicate the quantification of Ag active sites [11] but are critical for state-of-the-art material compositions [2, 10, 12]. In this section the question is proposed, can one extract meaningful information from the pulsed titration of promoted Ag/α-Al₂O₃ samples? Finally, in Chapter 3, the exothermicity of selective and nonselective epoxidation is studied though the application of a microfibrous mesh comprised of Ni, Cu, or stainless steel (SS), and packed with Cs promoted Ag/α-Al₂O₃ in a configuration known as a microfiborous entrapped catalyst (MFEC). In this section it is shown that heat transfer rates can be controlled using MFEC technology providing an isothermal intrabed temperature profile that is resistant to process upset. Consequently, improvements to several key performance indicators (KPI) are discussed.

Available for download on Thursday, December 15, 2022

Share

COinS