The RAPID Manufacturing Institute has focused on process intensification in the chemical process industries since the formation of the Institute in 2017. Chemical processes can be intensified in a variety of ways, including the use of novel energetics, such as microwave-driven processes (as discussed in a prior RAPID Success Story) and electrochemistry. In electrochemical systems, electricity is used to drive a chemical reaction (electrolytic cells), or a chemical reaction produces electricity (voltaic cells).
In the context of process intensification, electrical energy can be used to induce chemical reactions instead of thermal energy, as is often used in conventional reactions. Renewable energy can be used to power the process, enabling significant reductions in carbon emissions compared to conventional chemical processes.
Electrochemical systems
Electrochemical systems have two conductive electrodes and an electrolyte that allows charged ions to travel from one electrode to another as chemical reactions progress. In electrolytic cells, an external voltage source is applied across the two electrodes in the system, facilitating a chemical reaction. This type of cell can be used in a variety of applications, including refining metals, breaking water down into hydrogen and oxygen (electrolysis), and producing chemicals (electrosynthesis). Electrosynthesis is often considered to be a green alternative to traditional chemical production processes and can reduce or even prevent the generation of waste during chemical production.1 Membranes can be used in combination with electrochemistry to further intensify the process, enabling simultaneous reaction and separation.
Here, we explore two DOE-funded RAPID projects that use electrochemical systems to produce important chemicals and fuels.
RAPID’s work advancing electrochemical processes
As part of a RAPID project, researchers at the Idaho National Laboratory (INL) developed an electrochemical membrane reactor (EMR) that is capable of producing light olefins like ethylene. Olefins are useful in a variety of chemical processes as they can be used as building blocks in the production of chemical intermediates and polymers. Typically, olefins are produced from petroleum sources through a process known as steam cracking, which is energy intensive and emits carbon dioxide. Instead, the INL electrochemical process uses CO2 as a feedstock, significantly reducing the carbon intensity of the process.
The team developed specialized, iron-based catalysts to improve the selectivity of the reaction for hydrocarbon products. In their system, water is oxidized to hydrogen and oxygen on one side of the membrane, then the hydrogen passes through the membrane and then reacts with CO2 to form ethylene. Since these reactions occur in the same electrochemical cell, the whole system could be deployed in a modular format, which could help convert CO2 point sources to useful chemicals, even in remote locations.
Another team at Washington State University (WSU) investigated the production of hydrogen using an electrochemical process. In this case, the researchers used an electrochemical cell to oxidize ethanol and convert it into CO2 and hydrogen. Hydrogen is often produced through steam reforming processes, which requires a 330°C temperature, usually achieved through the combustion of fossil fuels. The WSU electrochemical process instead operates at about 80°C and at elevated pressure, so the produced hydrogen will not need to be compressed before use, as is required with other processes like steam reforming or water electrolysis.
Like the INL team, the WSU team examined different catalysts to improve the selectivity of the system to the desired reaction pathway. Since dilute ethanol is used as the feed, it is possible to avoid the energy-intensive distillation process to obtain pure ethanol and instead use the filtered fermentation product directly. A caustic electrolyte is used in this process, which has the added benefit of capturing the produced CO2 in the form of carbonate ions. The reaction of these carbonate ions with calcium hydroxide leads to the production of solid calcium carbonate, which can be separated from the liquid electrolyte.
The use of electrochemical systems can help reduce the carbon intensity of the chemical process industries. Additional work is needed to improve the economics and manufacturability of these systems, and RAPID is enabling progress in decarbonization through research projects in electrochemistry.
[1] Yuan, Y., Lei, A. Is electrosynthesis always green and advantageous compared to traditional methods?. Nat Commun 11, 802 (2020). https://doi.org/10.1038/s41467-020-14322-z (Accessed June 26, 2023).
Learn more RAPID projects and join the process intensification community today.