Carbon dioxide is a very special substance! It is both a curse and a blessing. In excessively high concentrations it is a climate-damaging gas, but at the same time it can be one of the raw materials to lead us out of the current climate crisis. Many people will only become aware of its real significance for the synthesis of storable energy sources in the next decade!


How important is CO2 for our work at KR&P?

Carbon dioxide (CO₂) is the essential raw material we need to produce synthetic fuels. Recycling CO₂ can be a first step on the way to becoming a CO₂-neutral society. Synthetically produced fuels can help us in the short term to “freeze” the carbon emissions which are partly responsible for climate change, and to reduce them in the long term. It is very important in this context that we talk about defossilized but not yet decarbonized liquid energy carriers!

For us, the fuels synthetically produced with “recycled” CO₂ are therefore an indispensable part of the goals of the CO₂-neutral energy generation required by the German government by 2050. Providing synthetic fuels can also help to more broadly distribute the enormous efforts associated with transforming the energy sector.

The move towards a defossilized energy sector will make CO₂ increasingly important as a raw material, which is needed in particular for the production of fuels with a high energy density.


What is important to us at KR&P:

Providing CO₂-neutral energy does not necessarily mean that we have to do without energy sources such as gasoline or diesel! To understand that we will continue to rely on carbon-based energy sources in many areas, we need to gain a deeper understanding of the energy cycles in our economy. In this context, as an engineering group, we also deal extensively with the concept of sector coupling.


At KR&P we have come to the following important conclusion:

In the long term, a net zero in CO₂ emissions can only be implemented through an established carbon capturing infrastructure. CO₂ as a raw material in a defossilized energy sector will make the extraction of CO₂ from exhaust gases with a high CO₂ concentration and at a later stage from less productive sources even more appealing.


CO2 climate protection targets

Within the framework of the Sustainable Development Goals (SDGs) defined for 2015 to 2030, the United Nations has included Climate Action in its program for the first time.


The goals defined by the UN in this regard are as follows:

The value defined in  2015 Paris Agreement confirms that the maximum responsible temperature increase of the Earth’s atmosphere may be 1.5°C, referencing the value from pre-industrial times.


The climate protection targets derived by the EU from this are as follows:

The EU Commission is calling for Europe to become climate neutral by 2050!

This means that our energy sector must be  defossilized  by 2050! In implementing these EU targets, reference is made to the concentration of CO2 in the year 1990.

If progress is made in the following steps A to D, then this goal can be achieved by 2050.

  • A: 2020 Reduction of CO2 emissions by 20% compared to 1990
  • B: 2030 Reduction of CO2 emissions by 55% compared to 1990
  • C: 2040 Reduction of CO2 emissions by 70% compared to 1990
  • D: 2050 Reduction of CO2 emissions by 100% compared to 1990

See the following comments and references:


The German government’s stated CO2 targets (as of 2019) are as follows:

The German government supports the EU’s 2050 targets, subject to a target range for CO2 reduction of 80% to 90%!

This means that the targets set by the UN and the EU for 2050 cannot be achieved.

This inevitably means that we will have to continue to remove CO2 from the atmosphere well beyond 2050. We will achieve this either through exhaust technologies that we will make available to emerging markets, or through technology that captures CO2 directly from the air in Europe after 2050.


When is carbon dioxide produced?

The CO2 content of the atmosphere can be considered as being virtually constant up to pre-industrial times.  In the period between the last ice age and the industrial revolution there was a balance between the input and output of CO2 in the atmosphere.

Since the industrial revolution, this balance has been disturbed by the anthropogenic burning of fossil fuels.

Carbon dioxide is produced, among other things, during the combustion of hydrocarbons.  The stochiometric combustion of one litre of fuel produces the following amounts of liquid  carbon dioxide:


The concentration of CO2 in fossil fuel exhaust is as follows:

  • Power industry (gas turbines 3-4 vol.%), (IGCC (very high purity); integrated gasification 14 vol.%)
  • Cement production between 14 and 33 vol.%
  • Steel production between 15 and 27 vol.%
  • Refineries between 3 and 13 vol.%
  • Chemical industry (very high purity)
  • Transport (diesel 1 vol.%, gasoline 21 vol.%)
  • Oxygen combustion (approx. 80 vol.%, compared to 4-14% for combustion with air)
  • Lignite (12.3 – 14.8 vol.%)
  • Lignite in oxyfuel processes (54.4 – 75.8 vol.%)
  • Heating oil (13 – 13.5 vol.%)
  • Natural gas (8.7 – 9.0 vol.%)


Share of CO2 in the production of:

  • Global ammonia synthesis production (2006): 124Mt, where 970kg CO2/t ammonia (120Mt/a)
  • Ethylene oxide synthesis: 5.1Mt/a
  • Natural gas purification


Carbon dioxide currently (as of 2020) accounts for 0.0407 vol.% of the gas mixture in the air, i.e. in our Earth’s atmosphere.


Changes in the concentration of carbon dioxide in our atmosphere!

In the middle of the 18th century (pre-industrial age), the carbon dioxide content in the air was 0.019 vol.%.

By 1958, the carbon dioxide content in the air had risen to 0.031 vol.%.

In 2015, it reached 0.040 vol.%!

Atmospheric CO2 levels varied from 0.019 vol.% at the peak of the ice ages to 0.026 vol.% during warm periods.

In 2017, the 10-year average increase was a good 0.0002 vol.% per year! Anthropogenic carbon dioxide emissions amounting to approximately 36.3 gigatons per year are responsible for this increase.

In comparison, the Earth’s carbon dioxide emissions, which come primarily from natural sources, amount to approximately 550  gigatons annually.


What are the effects of changing the concentration of carbon dioxide in the atmosphere?

Carbon dioxide absorbs electromagnetic radiation mainly in the spectral range of infrared radiation and is thereby excited to higher energetic vibrational modes. Its effect as a greenhouse gas is based on this property.


What can be made from carbon dioxide?

Synthetic fuels can be produced from carbon dioxide and hydrogen.
Renewable energy from wind turbines and solar panels can be used to produce green hydrogen via electrolysis. This hydrogen can be converted into methane using carbon dioxide in power-to-gas plants (Sabatier process).

Furthermore, synthesis gases can be used to produce fuels (power-to-fuel) and chemical raw materials (power-to-chemicals). This can be done, for example, via a  Fischer-Tropsch synthesis.

With synthetic fuels, technical realization is closely linked to a future hydrogen economy in which hydrogen production must of course be based only on regenerative processes.


How can carbon dioxide be captured or separated from exhaust gases?

Nature shows us how it is done. Plants and photosynthetic bacteria absorb carbon dioxide from the atmosphere. Carbohydrates are formed under the influence of light and the absorption of water. 30% of anthropogenic carbon emissions can be captured this way.  A tree can thus store about 12kg of CO2 in one year.

However, it should be noted that plants also react sensitively to an increasing CO2 concentration and may be damaged. So this carbon sink is not inexhaustible!

The ocean also acts as a major carbon sink, absorbing about 25% of the carbon dioxide released by human activity. The associated increase in CO2 concentration above the natural level has been proven to lead to long-term acidification of our oceans!

The remainder of anthropogenic CO2 emissions, amounting to 45%, is absorbed by the Earth’s atmosphere.


Technical processes for separating CO2 from exhaust gases:

  • Post-combustion: Flue gas scrubbing by means of suitable absorbers (amines; the best known is monoethanolamine)
  • Pre-combustion: Separation before combustion by means of integrated gasification

Separation may be carried out using the following methods:


Technical processes for enriching CO2 in exhaust gases:

  • Oxyfuel process: Combustion with oxygen

Oxyfuel, or oxygen combustion, is a process that produces an exhaust gas mixture with a very high CO2 content.

Separation may then be carried out using the above-mentioned methods which are then more effective.


How can carbon dioxide be stored?

The colour coding of CO2 cylinders:

Carbon dioxide is stored in grey steel cylinders or white cylinders (for medical purposes) with a grey neck.


  • As a gas: Under standard conditions, the density of carbon dioxide is 98 kg·m−3 (0 °C and 1013 hPa)
  • As a liquid: Below the critical temperature of0°C, carbon dioxide can be compressed to a colourless liquid by increasing the pressure. At room temperature, this requires a pressure of approximately 60 bar
  • As a solid: Carbon dioxide exists as a solid at normal pressure below −78.5°C and is colloquially known as dry ice
  • As a material: As regeneratively produced fuel (e.g. methane; short-term), by developing products based on CO2 (polymers; medium-term), in earth deposits as crude oil (long-term)


CO2 storage:

  • Cryogenic tanks
  • Pressure tanks
  • Hybrid tanks
  • Storage in reservoirs (gas-impermeable reservoirs such as: already exploited gas caverns, salt mines, oil and gas reservoirs, etc.; see Statoil, Sleipner field)
  • Pipelines


The mere cost of transporting CO2, excluding investment costs

  • Pipelines (cost: 1-3€/t 250km)
  • By ship in pressure, cryogenic, hybrid tanks (cost: 1€/t 250km)
  • By truck or rail in pressure tanks (cost: >25€/t 250km)


Investment costs for the transport of CO2

  • Pipelines (330km, 350mm in diameter, 1,8Mt/a throughput, 152bar pressure, 330000$/km; for example the Weyburn pipeline)
  • Ship (34-82M$ for 10-50kt capacity)
  • Truck, rail


What is the price of CO2?

  • Market price
  • Production price (direct air capturing)
  • CO2 stock exchange price (certificate) of 25 euros from January 2021. After that, the price will gradually increase to 55 euros in 2025. After that, a price range of at least 55 and at most 65 euros is to apply


Who has to pay CO2 tax?

  • In Germany, only companies in the energy sector, industrial corporations and airlines
  • From 2021, manufacturers and suppliers of goods and services are to pay a fixed price per ton of carbon dioxide


What are the properties of carbon dioxide?


  • Liquid CO2 exists only at temperatures between -56.6 and 31°C and pressures above 5.18 bar
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Effect on animals and humans:

  • Breath stimulus: Carbon dioxide dissolved in the blood activates the respiratory centre of the brain
  • Toxicity: A carbon dioxide concentration of eight percent leads to death within 30 to 60 minutes

Ventilation guidelines state that for an optimal indoor climate the carbon dioxide level should not exceed 1030 ppm.


Technical applications:

  • Carbon dioxide can be used to extinguish fires because of its oxygen displacing properties
  • Carbon dioxide is used as a refrigerant under the designation R744
  • Carbon dioxide is used as a shielding gas in welding technology
  • Cryogenic cooling and freezing (e.g. of food)
  • Carbonization (e.g. of beverages)