Captured carbon dioxide can be used either directly or it may undergo various biological or chemical processes prior to being used as a raw material or ingredient in the manufacture of various products (Carbon Capture and Utilization, CCU). Currently, according to the International Energy Agency (IEA), about 230 million tonnes of carbon dioxide are directly utilized worldwide every year. Almost 130 million tonnes are used to make synthetic urea for fertilizers. Oil companies inject an estimated 80 million tonnes into the subsurface in order to extract oil reserves more quickly and as completely as possible (Enhanced Oil Recovery, EOR). The remaining carbon dioxide is utilized in the food and beverage industries or is pumped into greenhouses to enhance plant growth. Carbon dioxide can also be used as an extinguishing agent or refrigerant.
There are some relatively new proposals to use captured carbon dioxide as a carbon source in the production of synthetic fuels for ships and aircraft, for carbon-based feedstocks in chemical industry, or for plastics and construction materials. If these prove to be feasible on a large scale, products containing carbon from captured carbon dioxide could replace materials formerly made from fossil-sourced carbon. The ultimate goal of these ideas would be to establish an added-value chain and circular economy for carbon, in which carbon from coal, oil or natural gas is no longer needed. For the production of chemicals and fuels from carbon dioxide, the gas must be synthesized with hydrogen. In this way, methanol and other hydrocarbons can be produced that will ultimately be useful in chemical industry or as synthetic fuels. A pilot project for this purpose is being planned at a refinery in Schleswig-Holstein, for example. If chemical industry implements the CCU projects it has already announced, the sector could see an estimated five million tonnes of captured carbon dioxide being used worldwide for fuel production in 2030. However, almost half of the proposed projects are still in the early development stage, and in many locations the pipelines and other infrastructures for transporting hydrogen and carbon dioxide are not yet in place.

Emissions balance – the devil is in the details

The emissions balances for the various carbon dioxide processing methods are highly complex. The products that are made can only be considered climate neutral if the carbon dioxide used originates from the atmosphere, if green hydrogen is used, and all of the production processes are powered by energy from renewable sources. But even under these conditions, the reprocessing of carbon dioxide can only be designated as permanent removal in a few exceptional cases.
This status requires that the manufactured products be used or recycled over a climate-relevant time period (longer than 100 years), and they must also retain the carbon they contain for that long. However, these two conditions are very rarely met.
As a rule, CCU products only last for a few weeks or months, and during their use or disposal the carbon they contain is released again in the form of carbon dioxide. This is the case, for example, when the synthetic fuel product is burned in ship motors or airplane turbines. The climate balance of the fuel is only neutral if an equivalent amount of carbon dioxide was removed from the atmosphere to make the fuel as was emitted during its production and combustion.
If the carbon dioxide used in CCU products originates from oil, natural gas or coal, there will even be new emissions created in the long run. This means that only a few of the yet known and applied CCU technologies actually do result in the removal of carbon dioxide. In its development scenario for achieving carbon dioxide neutrality by 2050, the IEA assumes that only about five per cent of the captured carbon dioxide will actually be reprocessed in 2030. The greatest share of the greenhouse gas must therefore be stored underground.

fig. 8.11 > Captured carbon dioxide, and particularly the carbon it contains, can be used in a large variety of applications. However, to achieve a positive climate effect, the gas or carbon must be processed in such a way that it can no longer escape into the atmosphere.