Research Results

Successful Direct Synthesis of Plastics from Carbon Dioxide at Atmospheric Pressure for the First Time in the World

This research has been featured in the following media outlets:
* denotes Web edition

• July 28: The Japan Steel Journal, Nikkei Business Daily, Teleto BIZ*
• July 29: The Nikkan Kogyo Shimbun
• July 30: @DIME*
• August 4: The Chemical Daily
• September 7: Nikkei Business Daily
• September 25: Monthly Scientific Magazine "Newton" (November Issue)
• November 23: The Mainichi Newspapers

Summary

A research group including Masazumi Tamura (Associate Professor, Research Center for Artificial Photosynthesis, Osaka City University), Keiichi Tomishige (Professor, Department of Applied Chemistry, Graduate School of Engineering, Tohoku University), and Kenji Nakao (Manager, Advanced Technology Research Laboratories, Nippon Steel Corporation) has successfully developed the world's first catalytic process for the direct synthesis of aliphatic polycarbonate diols from carbon dioxide at atmospheric pressure and diols^*1 without using any dehydrating agents. They announced in the academic journal Green Chemistry that aliphatic polycarbonate diols can be synthesized with high yield and high selectivity by combining a cerium oxide catalyst.

Polycarbonate diols are crucial intermediates in the synthesis of polyurethanes, represented by plastics. Currently, they are synthesized using phosgene^*2 or carbon monoxide as raw materials. However, because these raw materials are highly toxic, there is a strong demand from the perspective of green chemistry^*3 to develop technologies to replace them. The method of synthesizing polycarbonate diols by reacting diols using carbon dioxide as an alternative raw material has attracted attention as a green reaction system that produces only water as a byproduct. However, to obtain a high yield, it was previously necessary to use high-pressure carbon dioxide or dehydrating agents. The method discovered in this research overcomes these issues. By using a cerium oxide catalyst and bubbling carbon dioxide at atmospheric pressure into the diol, it has become possible to remove the generated water from the reaction system, successfully obtaining the target polycarbonate diol with high selectivity and high yield.

This research result was published online in Green Chemistry (IF=10.18) on Monday, July 26, 2021.

Comments from the Researcher

Background

Climate change and natural disasters associated with global warming have become more prominent, and there is a global demand for the reduction of carbon dioxide, which is one of the major greenhouse gases (Paris Agreement, reduction targets, and action plans). In recent years, methods that treat carbon dioxide as a C1 chemical raw material^*4 and convert it into useful chemical products have attracted attention, and they are highly anticipated as technologies that contribute to carbon dioxide fixation.

However, carbon dioxide is an extremely stable molecule, and sophisticated catalyst design and process design are key to its activation. As a conversion technology for carbon dioxide, there is a non-reductive method that converts carbon dioxide without changing the oxidation state of its carbon atom. If carbon dioxide can be successfully reacted with alcohols or diols, organic carbonates^*5 and aliphatic polycarbonates, which are useful chemical products, can be synthesized.

These carbonate compounds are currently synthesized mainly using highly toxic chemical raw materials such as phosgene or carbon monoxide, and there is a strong demand for the development of technologies to replace these processes. For the long-term fixation of carbon dioxide, converting it into polymers is considered advantageous. However, the synthesis of polycarbonates from carbon dioxide and diols hardly proceeds under ordinary conditions, posing a significant challenge where the target polycarbonate is scarcely obtained (less than 1%) unless the co-produced water is removed. As an example of direct polymerization from carbon dioxide and diols, a catalytic reaction system using nitrile as an organic dehydrating agent and cerium oxide as a catalyst has been reported. However, this system requires high-pressure carbon dioxide, and the recovery and regeneration of the dehydrating agent remain issues.

Furthermore, it faces problems such as the reaction of the nitrile dehydrating agent with the raw material diol or the product, which results in the contamination of the generated byproducts. Therefore, a catalytic process that does not require any dehydrating agents has been strongly desired.

Research Content

In the synthesis of polycarbonate diols from carbon dioxide and diols, water is produced as a byproduct, making the removal of water essential to improve the yield. As a water-removal method that does not rely on dehydrating agents, we focused on the difference in boiling points between water and the products or diols. We expected that the target carbonate synthesis would proceed by bubbling carbon dioxide at atmospheric pressure to evaporate and remove the water. As a result, among various metal oxide catalysts, only the cerium oxide catalyst demonstrated high activity, and we successfully developed an extremely simple catalytic reaction system that does not require dehydrating agents or high-pressure carbon dioxide.

Expected effects

This technology provides a novel catalytic process capable of chemically converting carbon dioxide at atmospheric pressure without using any additives. Furthermore, this technology is considered applicable to any substrate with a boiling point sufficiently higher than that of water. We believe it can also be extended to the synthesis of organic carbonates, carbamates^*6, and ureas, which are useful as additives for lithium-ion batteries and raw materials for polymer synthesis. By establishing various routes for synthesizing chemical products from carbon dioxide, this catalytic process is highly expected to contribute significantly to carbon dioxide fixation.

4. Future Developments

We plan to further advance our research and development by improving the solid catalyst toward practical application, while simultaneously conducting process studies that include scale-up evaluation.

Research Projects

The results of this research were obtained through a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) under the "NEDO Leading Research Program / Unexplored Challenge 2050."

Osaka City University and Tohoku University have been continuously conducting research and development on solid catalysts for carbon dioxide conversion, and they found that metal oxide catalysts based on cerium oxide are effective for activating carbon dioxide. In this project, with the goal of reacting carbon dioxide at atmospheric pressure emitted from blast furnaces and other sources as a raw material, they developed a solid catalyst system that achieves polymer synthesis from carbon dioxide without requiring any dehydrating agents, which would otherwise need recovery and recycling.

Nippon Steel Corporation published the "Nippon Steel Carbon Neutral Vision 2050 - A Challenge to Zero-Carbon Steel" in March 2021 as its unique initiative toward climate change issues, and has positioned the achievement of carbon neutrality by 2050 as the most important management priority. The results of this research demonstrate that carbon dioxide emitted from steelworks can be separated and captured, and then converted into useful substances such as functional chemicals with low energy consumption. Therefore, it is considered highly significant as it can contribute to carbon dioxide fixation and reduction.

Terminology

*1: Diol

A general term for compounds in which two hydroxyl groups (-OH groups) are bonded to two different carbon atoms.

*2: Phosgene

Also known as carbonyl chloride. While it is widely used as a raw material for various products due to its extremely high reactivity, it is also highly toxic to the human body, causing severe eye irritation and choking (asphyxiating) toxicity.

*3: Green Chemistry

A general term for the concept and technologies aimed at reducing the burden on the human body and the environment throughout the design, synthesis, application, and disposal of chemical compounds and products.

*4: C1 chemical raw materials

Chemical raw materials containing a single carbon atom, such as carbon dioxide, carbon monoxide, and methane.

*5: Carbonate

Compounds having an -O-CO-O- structure are generally referred to as carbonate compounds or carbonic acid esters.

*6: Carbamate

A general term for carbamic acid ester compounds having a >N-CO-O- structure.

Publication Information

All Press Release (PDF:1069KB)

Article source: Osaka City University website