Is ethylene a petrochemical?

Paths to post-petrochemicals - Electroreduction of carbon monoxide for the highly selective production of ethylene

Research results, scientific publications

Ethylene is one of the most important basic chemicals in the chemical industry, for example as a starting point for the manufacture of a wide variety of plastics. In the journal Angewandte Chemie, scientists are now presenting a new electrocatalytic approach for a selective, energy-efficient and ecological route for the production of ethylene from carbon monoxide, which could be obtained from renewable raw materials and waste.

From both an economic and an ecological point of view, the conversion of carbon monoxide (CO) into ethylene (ethene, C2H4) through energy-efficient strategies is seen as one of the key processes for the chemical use of non-petrochemical raw materials. Today, ethylene is commonly produced by steam cracking naphtha from petroleum refineries. Long-chain hydrocarbons are split into shorter chains at 800 to 900 ° C. An alternative is the production from synthesis gas, a mixture of CO and hydrogen from coal gasification - but which can also be obtained from biogas, wood and waste as a carbon source. A mixture of different hydrocarbons, including ethylene, can be obtained from synthesis gas in a Fischer-Tropsch synthesis. Disadvantages are the energy-intensive conditions of 200 to 450 ° C and 5 to 50 bar as well as the consumption of valuable hydrogen. In addition, a maximum of 30% of the products are usually the preferred C2 hydrocarbons (ethylene and ethane), higher chain lengths cannot be avoided, ethylene has to be separated in a laborious manner and around 30 to 50% CO2 is generated, which leads to undesirable emissions and a loss of carbon means.

The researchers from Xiamen University and the Dalian Institute of Chemical Physics at the Chinese Academy of Sciences headed by Dehui Deng are now presenting a new approach for a direct electrocatalytic process for the highly selective production of ethylene. In this process, CO is reduced with water at room temperature and ambient pressure over a copper catalyst with the aid of electric current.

By optimizing the structure of the gas diffusion electrode used, the researchers were now able to achieve a Faraday efficiency (transfer efficiency of the charge for this reaction) of unprecedented 52.7% and crack the “magic” 30% limit for C2 selectivity. There are no CO2 emissions. The way to success was a microporous layer of carbon fibers with optimally adjusted hydrophobicity as a carrier for catalytically active copper particles and an optimized potassium hydroxide concentration in the aqueous phase. This increases the CO concentration at the electrode and strengthens the coupling between the carbon atoms. The by-products that occur, ethanol, n-propanol and acetic acid, are liquid, so that the gaseous ethylene can easily be separated off.

Applied chemistry: Press release 32/2019

Author: Dehui Deng, Dalian Institute of Chemical Physics, Chinese Academy of Sciences (China),

Angewandte Chemie, Postfach 101161, 69451 Weinheim, Germany

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