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Chinese scientists have continuously made major breakthroughs in carbon dioxide conversion and are at the forefront of the world in this important field. With the advancement of new energy sources and catalysts, carbon dioxide conversion is expected to become a reality step by step, saving the earth and even saving foreign planets.
As we all know, carbon dioxide emissions are a major global problem. Can we turn waste into treasure and convert carbon dioxide into useful materials? The answer is yes, and the road is getting wider and wider.
For example, in September 2021, a sensation in the world was that Ma Yanhe, director of the Tianjin Institute of Industrial Biotechnology of the Chinese Academy of Sciences, and Associate Researcher Cai Tao and others realized carbon dioxide starch ("Carbon dioxide synthesis of starch and carbon monoxide synthesis of proteins, how about the | Technology Yuan Ren").
"Synthesis of Starch from Carbon Dioxide using cell-free chemical enzymes" (https://www.science.org/doi/10.1126/science.abh4049)
"Specific Carbon Dioxide to Formic Acid Catalyzed by Single Atom Alloying"
Nature Interview Photo: Zeng Jie and colleagues are studying ways to convert carbon dioxide into fuel that can be used for batteries
"Upgrading Carbon Dioxide into Energy-Rich Long-Chain Compounds through Electrochemical and Bio-Metabolic Engineering"
People's Daily made a long report on this (http://paper.people.com.cn/rmrb/html/2022-04/29/nw.D110000renmrb_20220429_1-11.htm). The main component of grain starch is the polymer of glucose, and the main component of edible oil is fatty acids, so jokingly, this time it is carbon dioxide into grain oil. Academician Li Can, director of the Catalysis Professional Committee of the Chinese Chemical Society, commented: "This work provides new technologies for artificial and semi-artificial synthesis of 'grain'. "So, how is this achieved?
"Carbon dioxide can synthesize glucose and fatty acids"
The basic answer is divided into three steps: first, carbon dioxide is energized and reduced to carbon monoxide; second, carbon monoxide and water catalytically synthesize acetic acid, which is the acetic acid in old vinegar; third, yeast bacteria "eat vinegar" fermentation to produce glucose.
Glucose process for carbon dioxide synthesis
But just looking at this description, it's like "three steps to put an elephant in the refrigerator", which is completely unconscionable. Let's take a closer look at it in a little more detail, and then you'll know where this series of operations is.
Loading the elephant into the refrigerator takes a total of three steps
First, acetic acid is relatively easy to understand as an intermediate product, because acetic acid can be converted into many other substances and is an excellent source of biosynthetic carbon. As a Shanxi native, I often consume acetic acid. But the question is, why turn carbon dioxide into carbon monoxide instead of directly into acetic acid?
Shanxi old aged vinegar
In fact, the technology of electrocatalytic production of acetic acid from carbon dioxide has long existed. But the problem is that the reaction rate is slow and the selectivity is low. What is particularly troublesome is that the acetic acid produced in this way is always mixed with other products and the salts of the electrolyte, and it takes a lot of cost to separate the acetic acid. What if it doesn't separate? If not separated, such a mixture is fed to microorganisms to ferment, and the microorganisms will soon be poisoned. Yeast shouts: We also have "bacterial rights"!
Therefore, the method of Zeng Jie and others is to break down one step into two steps. The first step is to change carbon dioxide to carbon monoxide. They invented a single-atom catalyst for Ni-N-C, which is very efficient at doing this. Efficient means that faradaic efficiency is close to 100%, which means that almost all the electrons in the current play the role they want them to play, that is, to reduce carbon dioxide to carbon monoxide. Of particular importance, this is achieved at considerable current densities. Many electrochemical reactions are efficient at small currents, not at large currents, and they can still maintain a Faraday efficiency of nearly 100% at a current density of 154 mA per square centimeter, which is a fairly high value.
Faraday (1791 - 1867)
The second step is the conversion of carbon monoxide to acetic acid. The core technology of this step is again an efficient catalyst: Cu with a large number of surface defects. Those who have studied chemistry can understand that surface defects often become centers of catalytic activity. They did a controlled experiment, and compared with the defect-free Cu, the Cu with a large number of surface defects increased the catalytic efficiency to 6.5 times. Although it has increased so much, because carbon monoxide can be turned into ethanol, propanol, ethylene and other products in addition to acetic acid, the Faraday efficiency of this step is not so high. At relatively low current densities, Faraday efficiency can reach 52%. What is really important, however, is the product of the current density and faraday efficiency, which determines the yield per unit time. In the end, they chose to increase the current density to 321 mA per square centimeter, at which point faraday efficiency remained at 46 percent, a good compromise.
Coo electrocatalytically reduced to pure acetic acid using a Cu catalyst with a large number of surface defects
There is also a problem. As mentioned earlier, the acetic acid produced by conventional electrocatalytic devices is mixed with many electrolyte salts, which will poison the fermented microorganisms. How to deal with this? They invented a solid electrolyte capable of conducting acetic and hydrogen ions, replacing electrolyte solutions. In this way, acetic acid comes out almost pure acetic acid, which greatly saves the cost of separation and purification.
Solid-state electrolyte reactor (courtesy of Zeng Jie)
In fact, the basic principle of Zeng Jie et al.'s 2021 carbon dioxide to formic acid is also to directly produce an aqueous solution of formic acid with a solid electrolyte reactor, eliminating the separation step that accounts for up to 70% of the total cost. In this way, the aqueous solution of formic acid can be used immediately, for example as battery fuel. That's why Nature's interview with Zeng jie is titled "Turning Industrial CO2into Battery Fuel." Now, you see why this achievement is worth interviewing with Nature, right? （http://news.ustc.edu.cn/info/1055/78782.htm）
Turning Industrial Carbon Dioxide into Battery Fuel
Back to the recent carbon dioxide production of glucose. Dilute the pure acetic acid with water and feed it to Saccharomyces cerevisiae bacteria. This is the third and final step, the conversion of acetate to glucose. This is a credit to Saccharomyces cerevisiae, but not ordinary Saccharomyces cerevisiae, but gene-edited Saccharomyces cerevisiae.
Why Gene Editing? Because Saccharomyces cerevisiae can convert acetic acid into glucose, but it also metabolizes a part of the glucose, the yield is not high. Yu Tao's team, a researcher at the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences, knocked out five genes related to glucose metabolism in Saccharomyces cerevisiae, so that they can only produce glucose, but not consume it. They also inserted glucose phosphatase elements from U.S. and E. coli, which convert phosphate molecules from other pathways in yeast into glucose, further enhancing yeast's ability to accumulate glucose. After these modifications, yeast became a tool bacterium specialized in the efficient production of glucose, with a yield of 2.2 grams per liter. How the programmers of 996 were made...
Engineering of Saccharomyces cerevisiae bacteria
Acetic acid can also be turned into fatty acids through fermentation. Similarly, they also enhanced yeast's ability to produce fatty acids through gene editing techniques, reaching a yield of 448.5 milligrams per liter.
Glucose and fatty acids are produced through microbial fermentation
To sum up, this work is divided into three steps, and each step has some kind of core technology that greatly improves efficiency. The core technology of the first step of carbon dioxide to carbon monoxide is the single atom catalyst of Ni-N-C, the core technology of the second step of carbon monoxide to acetic acid is a Cu catalyst and a solid electrolyte device with a large number of surface defects, and the core technology of the third step of acetate to glucose or fatty acid is gene editing of yeast. By superimposing these innovations, revolutionary results can be achieved.
You may ask, can this approach replace agriculture? Won't we have to farm in the future? In fact, the cost is certainly higher now than growing plants directly, and it is impossible to replace agriculture so quickly. However, the following points are worth noting.
First, compared with agriculture, this method does not require the process of cultivation, harvesting, extraction, etc., the production cycle is short, the footprint is small, it is not affected by the region, climate, etc., and can be used immediately. This approach is therefore more valuable when it is not available for cultivation,—— such as space exploration.
Second, the source of energy for this method is electricity. If fossil energy is used to generate electricity, it doesn't make much sense, because the original purpose is not to reduce carbon dioxide emissions! But now that new energy is developing vigorously, it is valuable to convert carbon dioxide into chemicals with wind power, photovoltaics, hydropower, etc. If controlled nuclear fusion is successful in the future, it is even more unlimited.
Third, the value of this approach lies not only in itself, but also in proposing a universal idea of a combination of electrocatalysis and synthetic biology. For example, in the future, to synthesize starch, pigments, drugs, etc., electrocatalytic facilities do not need to change, only need to change the fermented microorganisms. This opens up endless space for imagination.
Fourth, there is much room for improvement in this approach. For example, increasing the tolerance of yeast to acetic acid concentration can increase yield. After a variety of improvements, it is possible to become economically advantageous.
Finally, you may want to ask, what is the difference and connection between this work and co2 starch production in 2021?
The answer is that the carbon dioxide starch production of the Tianjin Institute of Industrial Biotechnology of the Chinese Academy of Sciences does not use biological cell systems. It was an unprecedented breakthrough, the most remarkable place, so it caused a sensation in the world. They synthesized new enzyme catalysts, but these enzymes work directly outside of the organism. If no microorganisms can be used, such as on Mars, then starch can be created in this way,—— as long as there is energy input. In fact, one of the raw materials of this method is hydrogen, which is the energy input, because hydrogen is a high-energy substance, which is generally produced from electrolyzed water.
Design and module assembly of artificial starch synthesis pathways
The method of Zeng Jie et al. is chemical and biological, and if there are microorganisms that can be used, it is more convenient to achieve. Its raw materials are only carbon dioxide and water, excluding high-energy substances such as hydrogen. In addition, its three-step process is carried out under mild conditions at room temperature and pressure, while the first step of carbon dioxide to starch is methanol, which requires high temperature and high pressure. Therefore, the two approaches and ideas have their own strengths and can be used in the future to complement each other and even cooperate to produce greater results.
From the larger picture, Chinese scientists continue to make major breakthroughs in carbon dioxide conversion and are at the forefront of the world in this important field. With the advancement of new energy sources and catalysts, carbon dioxide conversion is expected to become a reality step by step, saving the earth and even saving alien planets.
Sea of stars