Plastic has become an element of Environmental pollution. And its manufacture increases the climatic problems. Ethylene and Carbon monoxide are the precursors for common plastics. The preparation of these precursors consumes fossil fuels and liberates large quantities of Carbon dioxide. Chemists designed electrochemical cells in recent years. These devices use water and waste CO2 from the industrial process. And uses renewable electricity for turning them into feedstocks for plastics. But a problem for the greener way is that these cells consume alkaline additives which themselves take energy to make.
Solving Alkalinity Problem in Electrochemical cells:
Peidong Yang, an American chemist at the University of California Berkeley, commented that it is a very challenging scientific problem. Yang’s team and the second group increased their speed to solve the alkalinity problem. In one method, two electrochemical cells were placed one after the other to avoid the problem altogether. Whereas in another method it changes to an enzyme-like catalyst for generating the desired chemical without the consumption of alkaline additives.
According to Feng Jiao, an electrochemist at the University of Delaware, the plastic industry is using steam instead of fossil fuels for renewable electricity and carbon dioxide. Currently, Ethylene is prepared by using superheated steam under pressure for cracking the larger hydrocarbons in oil. Even though the process is efficient, it generates about 200 million tons of carbon dioxide yearly (0.6 % of the world’s emissions).
The electrochemical cell feeds electricity to a catalyst which produces chemicals. These convert CO2 to valuable chemicals. Then the dissolved gas and water react at the cathode to form Ethylene and other hydrocarbons. Potassium hydroxide (KOH) spiked with the electrolyte and the chemical conversions occur at lower voltages. Thereby the overall energy efficiency got boosted through the phenomena. Also, most of the added electricity is directed towards preparing hydrocarbons instead of hydrogen gas.
Arrival of Partial Solution:
According to Matthew Kanan, an electrochemist at Stanford University, the hydroxide ions react with carbon dioxide. Carbonate formed and precipitated as solid out of solution. Due to this reaction, hydroxide ions should be continuously replenished. Kanan and his colleagues reported a partial solution in 2019. They fed their cell with carbon monoxide instead of carbon dioxide and it did not react with hydroxide ions. This made the cell more efficient. 75% of the electrons that they fed their catalyst (Faradaic Efficiency FE- efficiency with which electrons transferred in a system facilitating a reaction) made Acetate. This acetate can be later used as a feedstock for industrial microbes. But the main issue is that the preparation of CO requires fossil fuels.
Solid Oxide Electrochemical Cells:
Edward Sargent, a chemist at the University of Toronto, and his team started with a commercially available device called Solid Oxide Electrochemical cell. It converts CO2 to CO under high temperatures and is powered by renewable electricity. The prepared carbon monoxide flows into another electrochemical cell. And its catalysts are designed to favor ethylene production (a widely used commodity than acetate). As per last week’s report in Joule, the reactor will not consume hydroxide. And also has a FE of 65% for energy stored in ethylene produced by the device. This is recorded as a significant advance.
Redesigned Catalyst:
In Nature Energy (December 2020 issue) reported redesigned catalyst by Yang and his colleagues. This catalyst works at neutral pH without the addition of OH ions. Moreover, the gas is converted into Carbon monoxide with the generation of only a minimal quantity of carbonate. But Yang notes that this cell does not convert that CO and H2 from water into other hydrocarbons, Ethylene.
Electrochemical cells are not the only force pushing the research forward. Expansion in solar and wind energy generation thereby reduces the prizes of renewable energy. These low energy prices indicate that the doubling of the overall energy efficiency of tandem electrochemical cells can make them cost-competitive with the standard fossil-fuel approach for Ethylene manufacture.
Let’s aim and work together for an eco friendly production, use of plastics.
Source: https://www.sciencemag.org/news/2021/02/chemists-close-greener-way-make-plastics
Also Read: https://shasthrasnehi.com/why-is-the-impact-of-microplastics-on-plants-a-concern/
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