Products from Electrochemical CO? Reduction: Ethylene

In this post, we explore ethylene, one of the main products that can be obtained through Electrochemical CO? Reduction (ECR).

Ethylene (C?H?) is a fundamental building block in the chemical industry. It is primarily produced through cracking processes in oil refineries, where hydrocarbons are broken down into lighter molecules at high temperatures (e.g. C?H? → C?H? + H?)

The global ethylene market is large, approximately 150 million tonnes annually. Ethylene is essential for the production of polymers such as polyethylene - the most widely used plastic, polyvinyl chloride, polystyrene, and chemicals such as ethylene oxide, ethylene glycol, and acrylonitrile, among others.?

The carbon footprint for ethylene is estimated as 1.56 tonnes of CO? equivalent per tonne of ethylene, resulting in 230 million tonnes of CO? equivalent just for producing ethylene.

Electrochemical CO? Reduction to Ethylene

ECR to ethylene has been the focus of research studies in the last two decades. C?H? is a 12-electron product from CO?:

2CO? + 8H?O + 12e? → C?H? + 12OH?

Copper (Cu) metal catalysts are the only materials capable of producing C?+ products via ECR due to their ability to facilitate C–C coupling. However, because of the low selectivity of Cu, various other products are also formed alongside ethylene, including hydrogen, methane, and carbon monoxide in the gas phase, as well as ethanol, acetate, propanol, and formate in the liquid phase. This diversity of products makes the separation process extremely challenging.??

Several startups are developing ECR technology to produce ethylene; however, most are still operating at relatively small scales.

Challenges

The technology for ECR to produce ethylene is less developed than that for syngas, primarily due to the low selectivity and limited stability of Cu catalysts under ECR conditions. Another significant challenge is the production cost. Since the process consumes 12 electrons per molecule of ethylene, the energy consumption is at least six times higher than that of 2-electron products like carbon monoxide and formic acid/formate salts. Additionally, the current market value of ethylene is low, making it difficult for ECR to ethylene to be cost-competitive. Given the present price of renewable electricity and the market value of ethylene, ECR faces challenges in competing with established industrial processes. However, the future potential of this technology remains promising, especially as renewable energy becomes more accessible and affordable.

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