CO₂ topics at a glance

Difference between C, CO and CO₂

Carbon, C, is also known as the atom of life. It is in DNA and in half of our food – chemistry knows of 200,000 compounds in the world without carbon and 20 million with it. It is found in many compounds (including frequently as CO₂) and performs multiple functions: It is used to generate heat and power, as an aid in process technology (e.g. in steel production), and as a basic material in the manufacturing of products such as pharmaceuticals or plastics.

Carbon dioxide, CO₂, occurs naturally in the air at a rate of 0.038%. CO₂ absorbs part of the heat given off by the earth and radiates it back to the earth, which is why it is one of the greenhouse gases. It is a non-toxic, neither flammable nor explosive gas, and is a natural by-product of cellular respiration in many living organisms. CO₂ is also released as dead organisms decay or through natural CO₂ sources, such as volcanic gases. It is also produced, however, through combustion of wood, coal, oil or gas due to the carbon they contain (C), which combines with oxygen (O₂). 

Carbon monoxide, CO, is a flammable, toxic gas. Unlike CO₂, CO does not occur naturally in the atmosphere. It is formed by the incomplete combustion of coal, natural gas or oil. A low oxygen content and low temperatures lead to the formation of carbon monoxide during combustion, but it can be further burned to create CO₂ where there is a sufficient oxygen supply.

Unavoidable CO₂

Process-related CO₂ quantities result from the reaction itself and not through the use of the energy required for the process. In industry, these are considered unavoidable if their formation cannot be prevented despite optimisation of the production process or the product. This is the case when no alternative processes and no alternative products or resources are available to a sufficient extent for the same use case.

These currently include, for example, process-related CO₂ quantities from glass production, the chemical industry, lime and cement production, and electric arc furnaces in the steel industry.

Green or biogenic CO₂

Biogenes CO₂ wird aus der Verbrennung oder Vergärung von Bio­masse (biologischem Material, welches aus Kohlen­stoff, Wasser­stoff und Sauer­stoff besteht), wie z.B. Holz, gewonnen. Die Ver­brennung von Bio­masse führt zu Emissionen, die als CO₂-neutral angesehen werden, weil der Kohlen­stoff aus einem neutralen CO₂-Kreislauf entsteht. Bäume beispiels­weise binden beim Wachsen CO₂ aus der Luft, wird das Holz verbrannt, gelangt es wieder in die Luft. Die Gesamt­menge an CO₂ in der Atmo­sphäre bleibt in diesem Fall die gleiche. Die Nutzung von biogenem CO₂ ist unter den gleichen Umständen klima­neutral wie die Ver­wertung von Biomasse. 

Graues bzw. fossiles CO₂

Fossiles CO₂ entsteht bei der Nutzung fossiler Kohlen­stoffe (z.B. Kohle oder Kalk). Die Verwendung von fossilem CO₂ zur Herstellung von Produkten, in welchen der Kohlen­stoff nicht permanent chemisch gebunden ist (sog. langlebigen Produkten), ist somit nicht klima­neutral. Denn das CO₂ entweicht in die Atmo­sphäre und trägt zum Klima­wandel bei. Hier ist eine sinn­volle Kreis­lauf­wirt­schaft umso wichtiger, um den weiteren Einsatz konven­tioneller fossiler Kohlen­stoffe zu reduzieren.