Engineering redox-mediated electrochemical separations for sustainable process intensification in chemical manufacturing

Cotty, Stephen Richard

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https://hdl.handle.net/2142/121235 Copy

Description

Title

Engineering redox-mediated electrochemical separations for sustainable process intensification in chemical manufacturing

Author(s)

Cotty, Stephen Richard

Issue Date

2023-07-12

Director of Research (if dissertation) or Advisor (if thesis)

Su, Xiao

Doctoral Committee Chair(s)

Su, Xiao

Committee Member(s)

• Yang, Hong
• Jain, Prashant
• Flaherty, David W

Department of Study

Chemical & Biomolecular Engr

Discipline

Chemical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• separations
• process intensification
• electrification
• redox electrochemistry
• noble metal recovery
• homogeneous catalysts
• critical metal refinement

Abstract

Advanced redox-polymer materials provide a powerful platform for integrating electro-separations of value-added chemicals and process intensification, offering promising applications in water purification, environmental remediation, and metal recovery. Here, four distinct applications are presented that demonstrate the versatility and effectiveness of redox-mediated electrochemical approaches for process intensification. Chapter 1 introduces electrochemical separations platforms, their various modes of operation, and introduces many relevant separations challenges that are critical to building a more sustainable future. The following are brief outlines of the topics covered in this work: Chapter 2 focuses on addressing the challenge of selective capture and remediation of trivalent arsenic (As(III)) in water purification. As(III) is highly toxic and difficult to remove at ultra-dilute concentrations. Current methods suffer from low ion selectivity and require multistep processes to transform As(III) to the less harmful As(V) state. In this study, an asymmetric design utilizing two redox-active polymers, poly(vinyl)ferrocene (PVF) and poly-TEMPO-methacrylate (PTMA), enables the tandem selective capture and conversion of As(III) to As(V). PVF selectively captures As(III) with exceptional uptake (>100 mg As/g adsorbent), while PTMA catalyzes the efficient electrochemical oxidation of As(III) to As(V) (>90% efficiency). The system exhibits high removal efficiencies (>90%) with real wastewater, even at concentrations as low as 10 ppb. Moreover, the judicious design of asymmetric redox materials leads to an order-of-magnitude increase in energy efficiency compared to non-faradaic, carbon-based materials, demonstrating the effectiveness of redox-active polymers for integrated reactive separations and electrochemically-mediated process intensification. Chapter 3 addresses the reusability challenge of homogeneous catalysts in industrial catalysis. Although homogeneous catalysts possess rapid kinetics and reaction selectivity, their widespread use is limited by difficulties in recycling and reusing them. This study proposes a redox-mediated electrochemical approach for catalyst recycling using metallopolymer-functionalized electrodes. The redox-platform enables the efficient separation and recovery of key platinum and palladium homogeneous catalysts used in organic synthesis and chemical manufacturing. The redox-electrodes exhibit high sorption uptake for Pt-based catalysts (Qmax up to 200 mg Pt/g adsorbent) from product mixtures, with up to 99.5% recovery, while retaining full catalytic activity over multiple cycles. Mechanistic studies and electronic structure calculations reveal that selective interactions with anionic intermediates during the catalytic cycle play a crucial role in efficient separations. Additionally, continuous flow-cell studies support the scalability and favorable techno-economics of electrochemical catalyst recycling. Chapter 4 addresses the mounting demand for gold and the need for sustainable gold separation technologies in electronic waste recycling and mining. Selective gold separations from dilute streams, in the presence of various metallic species, pose significant challenges. The proposed modular electrochemical separation platform, utilizing metallopolymer-functionalized electrodes, enables the selective recovery and concentration of gold. The redox-electrodes, particularly polyvinylferrocene (PVF) redox-electrodes, exhibit superior performance, capturing cyano-gold with a 10-fold higher uptake (>200 mg/g) compared to conventional activated carbon. Importantly, the system achieves exceptional separation factors (>20) for gold versus competing metals found in mining and electronic waste, including silver, copper, nickel, and iron. The electrochemical process allows rapid gold uptake within 5 minutes and enables electrochemically mediated release and concentration, achieving a remarkable up-concentration ratio of 20:1. Recycling gold from real-world electronic waste demonstrates the system's potential as a drop-in replacement for activated carbon sorbents, with a recovery efficiency of 99% and superior techno-economics (94% cost reduction and a 90% increased final gold purity). Chapter 5 presents a novel electrified liquid-liquid extraction (e-LLE) system utilizing hydrophobic ferrocene as an electrochemically mediated extractant for the selective and efficient recovery of precious metals from dilute, contaminated metal leach solutions. The increasing demand for renewable energy technologies necessitates a sustainable supply of precious metals such as gold, platinum, palladium, and iridium. However, the traditional mining and recycling processes for these metals contribute to environmental damage and face challenges in terms of selectivity and energy consumption. The study demonstrates exceptional atomic efficiency of over 90% and over 20:1 selectivity, achieving fully continuous extraction and 16-fold up-concentration of gold and platinum group metals (PGMs). Technoeconomic analysis highlights the cost reductions of fully electrified workflow of precious metal recovery compared to conventional processes and showcases the potential for establishing a fully continuous circular economy for precious and critical metals, thereby addressing the material crisis associated with renewable energy technologies.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Stephen Cotty

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