Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
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Initiatives to Develop CO2 Capture and Effective CO2Utilization Technology Systems
NORIAKI SENBA*1

TAKUYA HIRATA*1

MASAYUKI INUI*2

TAKAHITO YONEKAWA*3

YUJI NAKAGAWA*4

Reducing CO2 emissions is required to not only employ CO2 capture technology, but alsodecide where the captured CO2 will go and how it can be utilized effectively. At present, as theamount of CO2 utilized is quite small compared to that of CO2 emitted, underground storage(carbon capture and storage or CCS) is considered a realistic choice. However, because thelocations of storage sites are unequally distributed, some effective methods for CO2 utilization need
to be invented in areas away from these sites. Regarding the efforts of Mitsubishi Heavy Industries,
Ltd. (MHI) Group to address this issue, this report presents the applications in chemical products,fuels and direct use in this regard.

|1. Introduction
As part of the movement toward decarbonization against a backdrop of global warming, thedevelopment of fuel conversion technology for the use of renewable energy and hydrogen isaccelerating. However, it is not easy to provide all the energy by means other than fossil fuelcombustion. Mitsubishi Heavy Industries Engineering Ltd., which is part of MHI Group, has atechnology to capture CO2 from combustion exhaust gas. Having delivered the system to coal-fired
power stations and chemical plants, MHI Engineering boasts the world’s top market share. We will
expand the application of this technology to other industrial sectors in order to meet social needsfor decarbonization.
In the conventional CO2 capture system, on the other hand, the captured CO2 is used mainlyfor underground storage (CCS), enhanced oil recovery (EOR), and urea synthesis. However, if CO2
capture is to become more widely used in the years to come, other effective CO2 utilization
methods are required. This report presents MHI Group’s undertakings for technologicaldevelopment in this regard.

|2. CO2 as a source of carbon
Carbon is a chemical element widely used in chemical products (such as methanol,polyethylene, and carbon black). At present, these products are mainly manufactured from naturalgas (methane) or naphtha extracted from crude oil. Although it is technically possible to produce
carbon from CO2, CO2 is a stable substance from an energy point of view and using it for
production requires more energy than methane or naphtha. Figure 1 shows energy levels ofsubstances such as CO2, methane and methanol. The lower the energy level is, the more stable thesubstance is, which means that it is more unlikely to react with other substances. Although itdepends on the reaction pathway, the figure shows that more energy is required to produce
chemical products (such as methanol and ethylene) from CO2 (-394 kJ/mol), because it is at ahigher energy level than methane (-51 kJ/mol) or carbon monoxide (-137 kJ/mol). As this naturally
incurs extra costs, society needs to be willing to bear such costs.
*1

Chief Staff Researcher, Chemical Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*2

Chief Staff Manager, Business Development Department, Growth Strategy Office, Mitsubishi Heavy Industries, Ltd.

*3

Deputy Director, Decarbonization Business Department, Mitsubishi Heavy Industries Engineering, Ltd.

*4

Senior General Manager, Engineering Planning Department, Mitsubishi Heavy Industries Environmental & Chemical EngineeringCo., Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
2Figure 1

Properties of CO2 from viewpoint of reactivity|3. Currently available CO2 storage sites and utilization methods
It is estimated that the current human-related CO2 emissions are approximately 40 billion
tonnes per year. Figure 2 should be reduced to 4.3 to 13 billion tonnes if carbon neutrality is to beachieved(1). On the other hand, regarding the amount of CO2 that is required to be captured, thecurrent level of 0.04 billion tonnes should be increased to 4.3 to 13 billion tonnes. According to theInternational Energy Agency (IEA), the storage potential of CCS is said to be 8 trillion tonnes,
which is more than several hundred years’ worth of emissions based on the emissions projectionsfor 2050(2). Therefore, it can be said that there is a sufficient allocation for CO2 in total.
At present, the CO2 that is utilized as a refrigerant, for agricultural purposes, or as a welding
gas amounts to approximately 1.2 million tonnes per year. As the annual CO2 emissions in Japanare 1,000 to 1,200 million tonnes, the amount utilized is just about 0.1% of the total emissions(3).
Taking the above-mentioned cost issues into consideration as well, we think that CO2 storage andCCS are the most realistic choices.
However, the locations of currently available storage sites are concentrated in North America
or around the North Sea. In the remaining regions, therefore, CO2 needs to be transported tofaraway storage sites or some effective method for utilization should be invented in the neighboringareas of CO2 capturing sites.

Figure 2

Necessary CO2 reductions|4. Reuse of captured CO2When reusing CO2 after capture, it is hoped that such reuse leads to CO2 fixation or reduced
consumption of fossil fuels for decarbonization. In our group, several research projects on the reuseof CO2 are under way. Below are application examples for chemical products, fuels, and direct use.

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
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4.1

Dimethyl carbonate (DMC)

Dimethyl carbonate (DMC) is a chemical product used as an electrolyte in lithium batteries.
As such batteries will be used over a long time, they can be used as a means of carbon fixation. It isalso expected that the usage of lithium batteries will increase as their application becomes morecommon in the future. In other words, if CO2 fixation into DMC becomes practically andcommercially viable, this will make it possible to develop a new resource circulation model, forexample, by collecting CO2 from power station exhaust gas and distributing it to the market as anelectrolyte for lithium batteries. In this way, we can contribute to decarbonizing our society.
In the generally adopted DMC synthesis, CO is used as a raw material. We have successfully
established a process in which CO2 is used as a raw material(4). The synthesis method is shown
below. Optimization of the process is under way.
DMC is synthesized from CO2 and methanol, in which acetone dimethyl acetal (ADA) serves
as an intermediate. The reaction takes place in two stages. CO2 is first reacted with theabove-mentioned ADA in the presence of a catalyst, to produce DMC. This is followed by theacetone, a by-product in the first stage, being allowed to react with methanol for the ester exchange
reaction, through which ADA is reproduced. ADA is thus circulated for use within the process(Equations [1] and [2] and Figure 3).

Equation [1] Chemical reaction for DMC synthesis

Equation [2] Chemical reaction for ADA synthesis

Figure 3

Synthesis method of dimethyl carbonate (DMC)

When it comes to DMC demand, the average annual growth rate of the market will be 8% at
the maximum. The demand is expected to grow markedly, especially for on-board car battery

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
4applications. While the annual demand was about 700,000 tonnes in 2020, this amount may rise toaround 1.4 million tonnes in 2028 (Figure 4)(5). Especially high-demand regions are Europe, theUnited States, and Asia (China in particular). The 2020 forecast for the demand proportions is:
China (26%), Japan (11%), North America (12%) and Europe (15%) (Figure 5)(5). As a certain
level of demand is expected in East Asia, which is distant from the CO2 storage areas, DMC
synthesis can be expected to be of use for CO2 utilization.

Figure 4

DMC demand forecast

Figure 5

DMC demand by region

4.2

Methane (methanation)

Methane is used as the city gas. If produced from CO2, it will lead to reduced consumption ofnatural gas (a fossil fuel). Methanation is the production of methane by allowing CO2 to react withhydrogen under high-pressure and high-temperature conditions. It is represented by the following
chemical equation [3]:CO2＋4H2→CH4＋2H2O

Equation [3]Hydrogen is required in this reaction. Hydrogen itself can be used as a fuel and iscarbon-free. However, it has a lower heating value than methane. Therefore, blending with the citygas (i.e., existing methane) will result in a drop in the heating value of the blended gas. If hydrogenis reacted with captured CO2 to produce methane, such a drop in the blended gas can be prevented.
Moreover, the existing city gas infrastructure can be used for the blended gas without necessitating
modifications or causing problems.
Our group companies of Mitsubishi Heavy Industries Engineering, Ltd. and Mitsubishi
Heavy Industries Environmental & Chemical Engineering Co., Ltd. (MHIEC) are collaborating

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)5with the City of Yokohama and Tokyo Gas Co., Ltd. on a pilot test for CO2 capture andmethanation (Figure 6; publicly announced in January 2022). Specifically, a small CO2 capturesystem will be installed at an incineration plant in Yokohama City to collect CO2 from combustion
exhaust gas of a city waste incinerator. Meanwhile, water will be electrolyzed to produce hydrogenusing solar power generation or surplus electricity. Methanation converts these two substances intomethane. We are currently moving ahead with the pilot test project, in which we will conductrecovery testing.
The biggest advantage of methanation in the reuse of CO2 lies in enabling the existing city
gas infrastructure to continue to be used in the way it is now. However, from where hydrogen canbe obtained and how much it costs are the challenges to deal with.

Figure 6

4.3

CO2 capture/methanation from city waste incinerator

Agricultural use

In protected horticulture, attempts are under way to improve the quality of crops and theiryields by controlling the environment in the greenhouses. One of the methods is CO2 application(CO2 fertilization). Plants take in CO2 through stomata on the leaf surface, and light energy is used
to produce oxygen and sugar from CO2 and water in the plants (photosynthesis). Generally
speaking, high CO2 concentrations speed up the rate of photosynthesis. This often results in theclosing of stomata and reduces water evaporation (transpiration) through the stomata, whichenables plants to lose less water. It is assumed that the CO2 concentration in the greenhouse ismaintained roughly in the range of 400 ppm to several thousand ppm, which is equivalent to theCO2 levels in the air. Therefore, high-purity CO2 such as a raw material for chemical synthesis is
not necessarily required. The generally practiced CO2 application methods are the combustion(kerosene and LPG) and the use of the product (liquefied carbon dioxide). The issues to address
include: the prevention of formation of harmful substances through complete combustion, highcosts of fuels/liquefied carbon dioxide, and stabilization of carbon dioxide procurement (smallquantities and supply chain diversity).
In June 2022, our group company Mitsubishi Heavy Industries Engineering, Ltd. delivered
the first unit of a compact CO2 capture system to Taihei Dengyo Kaisha Ltd. in Hiroshima, Japan.
With this system, CO2 is captured from the exhaust gas of a biomass-fired boiler. This CO2 is sent
to a newly built plastic greenhouse on the premises of the power plant and is used for agriculturalpurposes. Thus, depending on the surrounding environment, the agricultural application can be oneof the solutions.

|5. Conclusion
For the reduction of CO2 emissions, not only CO2 capture but also fixation/storage are
critical challenges. From a quantitative point of view, CCS is the most realistic choice. However,the locations of the storage sites are concentrated in North America and around the North Sea. In
the areas away from these sites, effective utilization of captured CO2 and fixation technology arerequired.
MHI Group is trialing various applications in this regard, for example, in chemical products,
fuels and direct use, thus dedicating itself to establishing a carbon cycle from CO2 capture to reuseand fixation. However, as CO2 is a chemically stable substance, its use as a raw material of a

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
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chemical product or fuel has many problems from an economic point of view. To tackle thesechallenges, we continue to work on technological development to contribute to CO2 reduction,
while cooperating not only among our group companies but also with any related organizations
such as companies and municipalities.

References
(1)
(2)
(3)
(4)
(5)

McKinsey 1.5℃ Scenario, IEA Net Zero by 2050，IEA SDS，IPCC, etc.
Global CCS Institute, 2020, The Global Status of CCS : 2020, Australia“Development of technology using CO2 separation type Chemical Looping Combustion of Coal Domestic CO2 Market Research Data”, 2015 to 2017, NEDO Project, (JCOAL and IAE in charge)
CO2 Emission Free Synthetic Fuel Production Plant and LMG Plant, Mitsubishi Heavy Industries
Technical Review Vol. 41 No. 4 p204-207 (2004)
Dimethyl Carbonate Market – Global Forecast to 2025 (Market and Market TM)