Revelation may decrease the ecological effect of chemical manufacturing

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• Source: University of Illinois at Urbana-Champaign


• Date: 07 Feb,2021

Chemical manufacturers frequently use toxic solvents such as alcohols and benzene to make products such as pharmaceuticals and plastics. Researchers are analyzing a previously overlooked and misunderstood phenomenon in the chemical reactions used to make these products.

Combining metal and ore nanoparticles hastens many chemical reactions and helps maximize yield and profit margins for the chemical industry. However, many solvents are toxic and difficult to safely dispose, the investigators said. Water works, too, but it is not anywhere near as efficient or reliable as organic solvents. The reason for the difference was thought to be the limited solubility of some reactants in water. However, multiple irregularities in experimental data have led the team to understand the reasons for these differences weren’t fully understood.

To better understand the process, the group conducted experiments to analyze the reduction of oxygen to hydrogen peroxide – one place using water, another with methanol, and others with water and methanol mixtures.

The team found that the residue, or surface redox mediator, holds oxygen-containing species, including a key component hydroxymethyl.

In experiments with methanol, we observed spontaneous decomposition of the solvent that leaves an organic residue, or scum, on the surface of the nanoparticles. In some cases, the scumlike residue clings to the nanoparticles and increases reaction rates and the amount of hydrogen peroxide formed instead of hampering the reaction. This observation made us wonder how it could be helping.”

David Flaherty, Professor of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign

“Once formed, the residue becomes a part of the cycle and is probably responsible for some of the various efficiencies among solvents reported over the past 40 years of work on this reaction,” Flaherty said. “Our work provides strong evidence that these surface redox mediators form in alcohol solvents and they might explain many previous mysteries for this chemistry.”

By working with multiple types of experiments and computational simulations, the group discovered that these redox mediators effectively transfer both protons and electrons to reactants, whereas reactions in pure water transport protons readily, but not electrons. These mediators also alter the nanoparticles’ surface in a manner that reduces the energy barrier to be overcome for proton and electron transfer, the analysis reports.

“We show that the alcohol solvents as well as organic additives can react to form metal-bound surface mediators that act much in the same way that the enzymatic cofactors in our own bodies perform in catalyzing oxidation and reduction reactions,” Neurock stated.

Additionally, this work may have implications for reducing the amounts of solvent used and waste generated in the chemical industry.

“Our research suggests that for some situations, chemical manufacturers could form the surface redox mediators by adding small amounts of an additive to pure water instead of pumping thousands of gallons of organic solvents through these reactors,” Flaherty said.

The Energy and Biosciences Institute throughout the EBI-Shell program and the National Science Foundation supported this research.